CN102251175B

CN102251175B - Thick steel plate

Info

Publication number: CN102251175B
Application number: CN2011101357898A
Authority: CN
Inventors: 伊庭野朗; 冈崎喜臣; 名古秀德; 出浦哲史; 杉谷崇; 畑野等; 岛本正树
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 2010-05-20
Filing date: 2011-05-20
Publication date: 2013-07-10
Anticipated expiration: 2031-05-20
Also published as: KR101320220B1; CN102251175A; KR20110128154A

Abstract

The invention provides a thick steel plate, which is excellent in HAZ toughness during the large energy welding process. The characteristics of the thick steel plate satisfy the following chemical composition by mass% except oxygen constituent elements: Ti> 10%, A1<20%, 5 % <ca<40 % and 5 % <REM<50 %, 5 %<zr<40 % of at least any one of oxide, which satisfies the following formula (1) and (2). (1) Measured by an equivalent circle diameter gauge, the number of the oxide below 2 mu m is 200/mm < 2 > or more. (2) Measured by an equivalent circle diameter, the number of the oxide over 2 mu m is 100/mm < 2 > or less.

Description

Plate Steel

Technical field

The present invention relates to the employed Plate Steels of welded structure such as bridge, high-rise and boats and ships, in more detail, relate to when carrying out the large-line energy welding, welding heat affected zone is (hereinafter referred to as " HAZ ".) the Plate Steel of tenacity excellent.

Background technology

In recent years, be used to the desired characteristic of steel of welded structures such as bridge, high-rise and boats and ships, the tendency of increasingly stringent is arranged along with the maximization of these welded structures.Particularly among these many characteristics that are required, for the requirement of relevant toughness stricter tendency is arranged.

Employed steel such as welded structure are subjected to heat affecting when existing in welded joint and the such problem of the easy deterioration of toughness of the HAZ that forms.It is more big and present to such an extent that more be remarkable such tendency that the deterioration of this HAZ toughness has a heat input in when welding, therefore in order to improve HAZ toughness, thinks that the heat input when doing one's utmost to suppress to weld gets final product.But, from improving this viewpoint of operating efficiency of welding, for employed steel such as works for building, the tendency of requirement large-line energy welding is arranged on the contrary then, such as heat input is the above such large-line energy welding of 100kJ/mm.

Typical example as carrying out improving when large-line energy welds the technology of HAZ toughness has high Ni steel plate, for example discloses a kind of steel plate in patent documentation 1, by the Ni that adds about 2% intensity and toughness is improved.But Ni is the unusual high price element that is difficult to start with, does not therefore preferably improve the Ni amount of adding, industrial would rather be preferably as far as possible the addition of Ni be suppressed very low method.

Also be under such background, unlike patent documentation 1 is described, become high Ni, but do one's utmost to reduce the addition of Ni that the addition that for example makes Ni is that the technology that improves HAZ toughness on the basis below 1.5% has also obtained various researchs.HAZ during the large-line energy welding, be to remain on the back, austenite (γ) zone of high temperature for a long time owing to heat input by Xu Leng, γ grain growing when therefore the high temperature maintenance under the above-mentioned heat input takes place and the growth of thick ferrite (α) crystal grain in the Xu Leng process, cause thickization of tissue easily, the reason that HAZ toughness reduced when this became the large-line energy welding.Therefore, thickization of the tissue when need suppressing the large-line energy welding, the technology stable and that remain on high level of the HAZ toughness when exploitation makes the large-line energy welding problem that necessitates.

Organize thickization when be used for suppressing the large-line energy welding, guarantee the main means of HAZ toughness, proposition has the technology that relates to following content: the γ grain growing pinning by inclusion particles such as oxide compound, nitride, sulfide carry out generates the miniaturization of the tissue that carries out etc. by the intracrystalline α that with the inclusion particle is starting point.As the proposition example of such technology, patent documentation 2～4 described technology are arranged.Open in this patent documentation 2～4, make in the steel and to disperse to separate out the fine Ti nitride that contains, make it to play a role as γ grain growing pinning particle, thereby be suppressed at thickization of the austenite crystal that the HAZ in large-line energy when welding produces, suppress the deterioration of HAZ toughness.But if weld with desired this large-line energy in recent years, it is many then to contain the quantitative change that the Ti nitride disappears, and can not fully guarantee number density, can not obtain stable HAZ toughness.

With respect to this, as patent documentation 5～7, the technology that proposition utilizes the oxide based inclusion of high temperatures to be used as γ grain growing pinning particle.But oxide based inclusion is compared with containing the Ti nitride, and number density is few, is difficult to obtain sufficient pinning effect, therefore, is that welding under large-line energy such more than the 100kJ/mm can't fully be tackled for heat input, also needs further improvement.

Namely, in patent documentation 5,6, record and narrate, contain the oxide compound existence that Ti-REM-Ca-Al is oxide compound and REM and Zr by making, can access good HAZ characteristic, it is low-level that but the heat input of setting also rests on, and still can not obtain good HAZ characteristic under large-line energy such more than the 100kJ/mm.In addition in patent documentation 7, record has a kind of and the patent documentation 6 the same technology of utilizing the oxide compound that contains REM and Zr, but with above-mentioned the same, the heat input that sets also rests on low-level, still can not obtain good HAZ characteristic under large-line energy such more than the 100kJ/mm.

In addition, in patent documentation 8, record and narrate have a kind of by utilizing oxide based inclusion and contain Ti inclusion both sides as γ grain growing pinning particle, thereby obtain the technology of high HAZ toughness.But if consider the increase tendency of existing energy in recent years, then there is limitation in the utilization based on the γ grain growing pinning that contains the Ti inclusion, needs to establish as early as possible the HAZ toughness raising means under the large-line energy that utilizes oxide based inclusion.

In addition, the starting point that generates as the intracrystalline α that with oxide based inclusion particle is starting point and the technology that makes it to play a role, the technology that contains the composite oxides of Ti and REM and MnS except the utilization described in the patent documentation 9 is suggested to, present inventors also take the lead in proposing in patent documentation 10, promote the technology that intracrystalline α generates by control inclusion shape.These technology are to generate at intracrystalline α, construct under (intracrystalline α/inclusion) effective prerequisite of inclusion that interfacial energy is low.But in patent documentation 9 described technology, the initial heat input of setting is little, can't fully ensure large-line energy HAZ toughness.

In addition, employed steel such as works for building except requiring excellent HAZ toughness, also require intensity, low yield strength ratio and the base metal tenacity etc. of mother metal.In recent years, along with high stratification, the maximization of buildings, as the steel that buildings is used, use the trend of high tensile steel to improve.

For example, the technology that proposes as patent documentation 11 is, fine carbonitride is disperseed, and guarantees ferrite more than a certain amount of, realizes the low yield strength ratio of the steel plate of tensile strength more than 590MPa thus.But the technology that this patent documentation 11 relates to not is the technology of the HAZ toughness when being conceived to implement heat input and being the above such large-line energy welding of 100kJ/mm.In addition, also propose to have a kind of technology in patent documentation 12, it disperses by making oxide based inclusion, and guarantees ferrite more than a certain amount of, realizes the low yield strength ratio of the steel plate of tensile strength more than 590MPa thus, but little as the heat input of object.

As described above, about guaranteeing the HAZ toughness when to implement heat input be large-line energy welding such more than the 100kJ/mm, the technology that other characteristics (intensity of mother metal and the raising of toughness or further low yield strength ratio) are increased is in and does not obtain the present situation developed as yet.

[patent documentation]

[patent documentation 1] TOHKEMY 2006-118007 communique

[patent documentation 2] TOHKEMY 2001-98340 communique

[patent documentation 3] TOHKEMY 2004-218010 communique

[patent documentation 4] Japanese kokai publication sho 61-253344 communique

[patent documentation 5] TOHKEMY 2001-20031 communique

[patent documentation 6] TOHKEMY 2007-100213 communique

[patent documentation 7] TOHKEMY 2007-247005 communique

[patent documentation 8] TOHKEMY 2008-223062 communique

[patent documentation 9] Japanese kokai publication hei 7-252586 communique

[patent documentation 10] TOHKEMY 2008-223081 communique

No. 2901890 communique of [patent documentation 11] Japanese Patent

[patent documentation 12] TOHKEMY 2007-247004 communique

Summary of the invention

The present invention does in view of above-mentioned existing practical situation, and its basic purpose is, even provide a kind of when large-line energy welds, has still given play to the Plate Steel of excellent HAZ toughness.

In more detail, one object of the present invention is, a kind of Plate Steel (hereinafter referred to as " Plate Steel of this case first mode ") of tenacity excellent of welding heat affected zone is provided, HAZ tenacity excellent when it is estimated as mean value, and be that high intensity region more than the 490MPa can realize low yield strength ratio in tensile strength, can guarantee good base metal tenacity in addition.

Another object of the present invention is to, a kind of Plate Steel (hereinafter referred to as " Plate Steel of this case second mode ") is provided, the mean value excellence of its described large-line energy HAZ toughness, and be that high intensity region more than the 590MPa also demonstrates low yield strength ratio in tensile strength, and demonstrate good base metal tenacity.

Another purpose of the present invention is, a kind of Plate Steel (hereinafter referred to as " Plate Steel of this case Third Way ") is provided, and the mean value of its described large-line energy HAZ toughness is excellent certainly, can also improve the minimum value of the HAZ toughness in the zone of being estimated.

Another other purposes of the present invention are, a kind of Plate Steel (hereinafter referred to as " Plate Steel of the cubic formula of this case ") is provided, even it is in the high intensity region of tensile strength 780MPa level, also can improve the mean value of the HAZ toughness when carrying out the large-line energy welding and the minimum value of HAZ toughness.

Can reach the Plate Steel of the present invention of aforementioned problems, have following such composition of steel and tissue as basic comprising.That is, be following Plate Steel, it contains C:0.02～0.15 quality %; Si:0～0.50 quality %; Mn:1.0～3.0 quality %; P: bigger than 0 quality %, below 0.03 quality %; S: bigger than 0 quality %, below 0.015 quality %; Al:0～0.07 quality %; Ti:0.010～0.080 quality %; Ca:0.0005～0.010 quality %; N:0.002～0.020 quality %; In addition, also contain more than one that select among REM:0.0001～0.02 quality %, Zr:0.0001～0.02 quality %, surplus is iron and unavoidable impurities, wherein, except the formation element of deoxidation, in quality %, satisfy 10%＜Ti, Al＜20%, 5%＜Ca＜40%, and satisfy the oxide compound of at least any one party of 5%＜REM＜50%, 5%＜Zr＜40%, exist in the mode of the condition that satisfies following formula (1) and (2).

(1) in diameter of equivalent circle, the described oxide compound that is lower than 2 μ m is 200/mm ²More than,

(2) diameter of equivalent circle is that the above described oxide compound of 2 μ m is 100/mm ²Below.

Also have, the so-called diameter of equivalent circle that illustrates among the present invention is the size that is conceived to oxide compound etc., tries to achieve and is assumed to the circular diameter that equates with its area, can observe with transmission electron microscope (TEM) or scanning electron microscope (SEM), try to achieve by image analysis.

Then, the Plate Steel of so-called described this case first mode of inventing based on such basic comprising, be constructed as follows: Si content is 0～0.46 quality %, Mn content is 1.0～2.0 quality %, among the described oxide compound, diameter of equivalent circle is among the above oxide compound of 2 μ m, and diameter of equivalent circle is that 2 μ m oxide compound above, that be lower than 5 μ m exists 30～70/mm ², and diameter of equivalent circle is that the existence of the above oxide compound of 5 μ m is lower than 30/mm ², and contain the Ti nitride, and described containing among the Ti nitride, diameter of equivalent circle is that the following Ti nitride that contains of 100nm exists 5 * 10 ⁶Individual/mm ²More than.

In addition, the Plate Steel of so-called described this case second mode of inventing based on such basic comprising, be constructed as follows: Si content is 0.01～0.35 quality %, Mn content is 1.0～2.0 quality %, described oxide compound is the oxide compound that also satisfies the relation of Al/ (REM+Zr)＜0.7, and diameter of equivalent circle is lower than the every 1mm of oxide compound of 2 μ m ²In have more than 300, and contain the Ti nitride, and described containing among the Ti nitride, diameter of equivalent circle is that the following Ti nitride that contains of 100nm exists 5 * 10 ⁶Individual/mm ²More than.

In addition, the Plate Steel of so-called described this case Third Way of inventing based on such basic comprising, be constructed as follows: Si content is 0～0.25 quality %, Mn content is 1.0～2.0 quality %, and the scope at REM:0.0003～0.02 quality %, Zr:0.0003～0.02 quality % contains REM and Zr both sides, the A value of being tried to achieve by following formula satisfies 0.4≤A≤2.4

A＝10 ⁴×{[Ti]-0.7×([O]-0.09×[Al]-0.16×[Ca]-0.07×[REM]-0.04×[Zr])}×[N]

And described oxide compound is the oxide compound that also satisfies 3%＜N, 2＜Ti/N, and diameter of equivalent circle is lower than the every 1mm of oxide compound of 2 μ m ²In have more than 300.Also have, in described A formula, [] represents the content (quality %) of each element at this.

In addition, the Plate Steel of the so-called cubic formula of described this case of inventing based on such basic comprising, be constructed as follows: Si content is 0.02～0.50 quality %, Mn content is 1.4～3.0 quality %, and, contain REM and Zr both sides in the scope of REM:0.0003～0.02 quality %, Zr:0.0003～0.02 quality %, contain Cr:0.5～2.0 quality % in addition, the D value of being tried to achieve by following formula satisfies 238＜D＜388

D＝62×[Mn]+27×[Ni]+111×[Cr]

And among the described oxide compound, diameter of equivalent circle is lower than the every 1mm of oxide compound of 2 μ m ²In have more than 300, and at diameter of equivalent circle among the oxide compound more than the 2 μ m, diameter of equivalent circle more than 2 μ m, there is 30～70/mm in the oxide compound that is lower than 5 μ m ², and the existence of the oxide compound of diameter of equivalent circle more than 5 μ m is lower than 30/mm ²Also have, in described D formula, [] represents the content (quality %) of each element at this.

The Plate Steel of the cubic formula of this case among the described oxide compound, also have to satisfy 10%＜REM+Zr＜70%, and the mass ratio Ti/Ca of Ti and Ca satisfies and surpass 1, be lower than 1.4 oxide compound, and there is 300/mm in the oxide compound that preferred diameter of equivalent circle is lower than 2 μ m ²More than.

The Plate Steel of described this case first～Third Way preferably also contains at least one group who selects from following (a)～(c).

(a) more than one that select the group who constitutes below Ni:1.50 quality %, below the Cu:1.50 quality %, below the Cr:1.50 quality %, below the Mo:1.50 quality %;

(b) more than one that select the group who constitutes below Nb:0.10 quality %, below the V:0.10 quality %;

(c) below the B:0.005 quality %.

In addition, the Plate Steel of the cubic formula of aforementioned this case as other elements, preferably also contains at least one group who selects from following (a ')～(c ').

More than one that select the group that (a ') constitutes below Ni:1.50 quality %, below the Cu:1.50 quality %, below the Mo:1.50 quality %;

More than one that select the group that (b ') constitutes below Nb:0.10 quality %, below the V:0.10 quality %;

(c ') below the B:0.005 quality %.

Plate Steel of the present invention, basic comprising as the aforementioned, chemical constitution is appropriately controlled, its every kind size of oxide compound with chemical constitution of regulation is all disperseed with appropriate amount, in the Plate Steel of this case first mode, in addition, therefore the fine Ti nitride that contains is secured at more than the specified amount, even so when to implement heat input be large-line energy welding such more than the 100kJ/mm, also can guarantee good HAZ toughness.In addition, be that low yield strength ratio can be realized in high strength territory more than the 490MPa in tensile strength, can guarantee good base metal tenacity in addition.

In the Plate Steel of this case second mode, except basic comprising, on the basis that further the control oxide chemistry is formed, guaranteed that also the fine Ti nitride that contains is secured at more than the specified amount, therefore, even when to implement heat input be large-line energy welding such more than the 100kJ/mm, also can guarantee good HAZ toughness, and, can suppress the deviation of HAZ toughness, can realize demonstrating the high-strength steel plate of low yield strength ratio and good base metal tenacity in addition.

In the Plate Steel of this case Third Way, except basic comprising, the chemical constitution of chemical composition of steel and oxide compound is further controlled, even when carrying out the large-line energy welding, also can guarantee the mean value of HAZ toughness, can improve its minimum value in addition.

In the Plate Steel of the cubic formula of this case, except basic comprising, chemical composition of steel is further controlled, therefore in the high tensile steel plate of tensile strength 80 feather weight (キロ Network ラス), even when carrying out the large-line energy welding, also can guarantee the mean value of HAZ toughness, can improve its minimum value in addition.

Embodiment

Below, at first describe for basic comprising of the present invention.

Exploitation is about the employed Plate Steel of welded structure of bridge, high-rise and boats and ships etc., particularly develop when to carry out heat input be welding under large-line energy such more than the 100kJ/mm, during the Plate Steel of welding heat affected zone tenacity excellent, at first, inventors are conceived to, and can utilize oxide based inclusion (the following oxide compound that all only is expressed as.) guarantee high HAZ toughness this point, study from various angles.

Utilize the HAZ toughness of the Plate Steel of this oxide compound to have merits and demerits in developing skill.Advantage is, oxide compound becomes intracrystalline α and generates starting point, makes HAZ organize miniaturization, and HAZ toughness is improved, otherwise its shortcoming is that oxide compound becomes the starting point of destruction from body, brings HAZ toughness disadvantageous effect.

In the past from such viewpoint, when the starting point that generates as intracrystalline α with oxide compound is used, at the oxide compound that is lower than 2 μ m based on diameter of equivalent circle, under this technological thought that larger sized oxide compound then reduces as far as possible, carry out the exploitation of Plate Steel.

But, if based on research and development in recent years, then confirm in theory and report, from this viewpoint of starting point that intracrystalline α generates, import to the big side of size of the oxide compound in the Plate Steel, the generative capacity height of intracrystalline α, in addition, also confirm in theory and report that the toughness evaluation temperature is more high, be used for guaranteeing that the upper limit of size of the oxide compound (thick second phase) of toughness more obtains relaxing.

According to such research and development result, present inventors think, under the situation of toughness evaluation temperature than the higher employed Plate Steel of welded structure, HAZ toughness is caused on the basis that the upper limit of size of the oxide compound of disadvantageous effect relaxes, follow existing technological thought, namely, be dispersed in Plate Steel interior oxidation thing, with the same on the basis of the oxide compound that is lower than 2 μ m based on diameter of equivalent circle in the past, intracrystalline α generative capacity is high, the oxide compound that size is bigger imports to inside, thereby can make HAZ organize miniaturization, can improve HAZ toughness, present inventors study at this point.

Secondly, inventors further study from this viewpoint of low yield strength ratio of mother metal.As described above, oxide compound becomes the starting point that intracrystalline α generates, and can help the raising of HAZ toughness.In addition, owing to oxide compound imports the karyogenesis point is increased, compare with the situation that does not import oxide compound, bainitic transformation takes place in mother metal under than higher temperature, therefore we can say the yield tensile ratio that can reach lower.On the other hand, oxide compound self becomes the starting point of destruction, also has to make base metal tenacity reduce such defective.In addition, known this defective increases along with the intensity of mother metal and becomes big, when importing oxide compound to high-strength steel, we can say that base metal tenacity is reduced is most important.

As the means that improve base metal tenacity, it is generally acknowledged the thermal treatment of effectively trying every possible means to carry out steel, to realize the miniaturization of steel tissue.But, because thermal treatment makes operation numerous and diverse, so industrially do not think preferred means.Therefore, inventors think, and are the same with the raising of HAZ toughness in the raising of base metal tenacity, by to the inner oxide compound that imports of steel, can promote the generation of intracrystalline α effectively.

But mother metal tissue and HAZ tissue compare, and old γ particle diameter is little.The size of tissue is usually by generating from the α of intracrystalline and determine from the balance that the α of old γ crystal boundary generates, so little this situation of old γ particle diameter of mother metal tissue, can regard as from this side of force of the α generation of crystal boundary relatively big.Therefore, generate the micronized effect of organizing that brings by intracrystalline α, in mother metal, if compare with HAZ, then be difficult to obtain performance.Therefore, for the intracrystalline α that promotes to be brought by oxide based Control and Inclusion Removal generates, make mother metal organize miniaturization, need more suitably composition and the size of the oxide compound of control importing.

Inventors guarantee such viewpoint based on the technological thought that has carried out research from above various angles from the raising of HAZ toughness and the characteristic of mother metal, attempt the control of oxide compound.It found that, formation element except oxygen, in quality %, make and satisfy 10%＜Ti, Al＜20%, 5%＜Ca＜40%, and the oxide compound that satisfies at least any one party of 5%＜REM＜50%, 5%＜Zr＜40% imports, and among these oxide compounds, there is 200/mm in the oxide compound that makes diameter of equivalent circle be lower than 2 μ m ²More than, making diameter of equivalent circle is that the above oxide compound of 2 μ m exists 100/mm ²Below, generate the HAZ that brings by grain boundary and organize micronized effect significantly to be embodied, confirm and can obtain more excellent HAZ toughness.

Also have, among the described oxide compound, the oxide compound that diameter of equivalent circle is lower than 2 μ m only exists and is lower than 200/mm ²The time, generate the micronized effect of organizing that brings by intracrystalline α and can not get demonstrating fully.Be lower than the oxide compound of 2 μ m about diameter of equivalent circle, recommend the preferred 220/mm of existence ²More than, more preferably there is 250/mm ²More than.Its number upper limit is not particularly limited, but in fact at 1000/mm ²Following degree.

Among the described oxide compound, diameter of equivalent circle is that 2 μ m are above, because encourage brittle rupture, makes HAZ toughness deterioration, so the least possible being advisable is 100/mm ²Below.

In addition, described oxide compound, the quality of Ti in the oxide compound, Al, Ca, REM, Zr, with respect to the total quality of the formation element that removes deoxidation, the scope that is in 10%＜Ti, Al＜20%, 5%＜Ca＜40%, 5%＜REM＜50% and/or 5%＜Zr＜40% gets final product.In the formation element except oxygen, except Ti, Al, Ca, REM, Zr element, also allow to contain elements such as Si, Mn.In addition, this oxide compound exists in the mode of the composite oxides that contain the element beyond the aforesaid oxygen usually.

＜chemical ingredients is formed 〉

Next, the chemical ingredients composition for Plate Steel of the present invention describes.Plate Steel of the present invention, can HAZ toughness and base metal tenacity be improved by aforesaid oxide compound, in addition, suitably adjust the content of each chemical ingredients (element), the present invention can be reached as HAZ toughness and the base metal tenacity of the height of target, other characteristics (low yield strength ratio etc.) can be realized in addition.Therefore, in Plate Steel of the present invention, it also is important document that the content of each chemical ingredients is in the scope of following explanation.Among these chemical ingredientss, the content of Ti, the Al of formation oxide compound, Ca, REM, Zr shows as its action effect is mandatory, for containing the amount that constitutes oxide compound.

C:0.02～0.15 quality %

C is be used to the necessary element of the intensity of guaranteeing steel plate.When the content of C is lower than 0.02 quality %, can not guarantee the intensity that needs.The preferred lower limit of C content is 0.03 quality %, is limited to 0.04 quality % under preferred.On the other hand, if the content surplus of C, then the island martensite body (MA) of hard is a large amount of generates, and causes the toughness deterioration of mother metal.Therefore, the content of C need be below 0.15 quality %.The preferred upper limit of the content of C is 0.12 quality %, is limited to 0.10 quality % on preferred.

Si:0.50 quality % following (containing 0%)

Si is guaranteeing element useful on the intensity by solution strengthening, and also is useful element being used for guaranteeing containing on the individual number density of Ti nitride.According to the intensity rank of steel plate, be used for guaranteeing that it also is useful element that α goes up mutually in addition.If but the content surplus of Si, then α is imported superfluously, can not guarantee the tensile strength (TS) that needs.Therefore, the content of Si on be limited to 0.5 quality %.In addition, be limited to 0.46 quality % on preferred, be limited to 0.42 quality % on preferred, be limited to 0.35 quality % on further preferred, be limited to 0.25 quality % on particularly preferred.Also have, specially the lower limit of the content of Si do not stipulated especially in the present invention, but according to the thickness of slab as the Plate Steel of object, have Si be must element situation.Therefore that is, when the ingot casting size was big, speed of cooling was slow, even do not add Si, also can guarantee to contain individual number density of Ti nitride, but ingot casting size hour, speed of cooling is fast, so adds Si and improve the Ti activity, thereby guarantees the individual number density of Ti nitride.The content of Si in this case preferably is limited to 0.01 quality % down.In addition, be limited to 0.02 quality % under the content of Si preferred, be limited to 0.05 quality % under further preferred, be limited to 0.08 quality % under particularly preferred.

Mn:1.0～3.0 quality %

Mn is useful element in the intensity of guaranteeing steel plate, in order to bring into play this effect effectively, need make it to contain more than the 1.0 quality %.The content of Mn preferably is limited to 1.3 quality % down, is limited to 1.4 quality % under preferred.On the other hand, contained if make above 3.0 quality %, then the intensity of HAZ excessively rises superfluously, the situation of flexible deterioration, and therefore, the content of Mn is below the 3.0 quality %.The content of Mn is limited to 2.5 quality % on preferably, is limited to 2.0 quality % on preferred, is limited to 1.8 quality % on further preferred, is limited to 1.6 quality % on particularly preferred.

P:0.03 quality % following (not containing 0%)

P causes intercrystalline failure and toughness is caused the element of disadvantageous effect that therefore preferred its content is the least possible easily.From this viewpoint of toughness of guaranteeing mother metal and HAZ, the content of P need be suppressed at below the 0.03 quality %, is preferably below the 0.02 quality %, more preferably below the 0.01 quality %.About the lower limit Chinese of the content of P regulation especially, but industrially be difficult to make P to reach 0%.

S:0.015 quality % following (not containing 0%)

S and Mn form sulfide, are the elements that makes the toughness deterioration of mother metal, and therefore preferred its content is few as much as possible.From guaranteeing this viewpoint of base metal tenacity, S content need be suppressed at below the 0.015 quality %, preferably below 0.010 quality %, more preferably below the 0.008 quality %.About the lower limit Chinese of the content of S regulation especially, but industrially be difficult to make S to reach 0%.

Al:0.07 quality % following (containing 0%)

Al is useful element by adding before Ti or Ca and REM or Zr forming the effective oxide compound of the generation of intracrystalline α.In order to bring into play this effect effectively, preferably make it to contain more than the 0.003 quality %, more preferably more than the 0.010 quality %.But if its content surplus, then thick oxide compound generates, and therefore the toughness deterioration of mother metal and HAZ need be suppressed at below the 0.07 quality %.The preferred upper limit of the content of Al is 0.05 quality %, is limited to 0.04 quality % on more preferably, and further preferred upper limit is 0.03 quality %.

Ti:0.010～0.080 quality %

Ti added before Ca and REM or Zr by after the interpolation of Al, thereby formed the effective oxide compound of the generation of intracrystalline α, was the element that helps the raising of HAZ.In order to bring into play such effect effectively, need make it to contain more than the 0.010 quality %.The content of Ti preferably is limited to 0.012 quality % down, is limited to 0.015 quality % under preferred.On the other hand, if the content surplus of Ti, then thick oxide compound generates in a large number, makes HAZ toughness deterioration, therefore need be suppressed at below the 0.08 quality %.The preferred upper limit of the content of Ti is 0.060 quality %, is limited to 0.040 quality % on more preferably.

Ca:0.0005～0.010 quality %

Ca is by interpolation behind 3～20 minutes after the interpolation of Ti, thereby formation is the element that helps the raising of HAZ to the effective oxide compound of the generation of intracrystalline α.In order to bring into play such effect effectively, need make it to contain more than the 0.0005 quality %.The content of Ca preferably is limited to 0.0008 quality % down, is limited to 0.0010 quality % under preferred.On the other hand, if the content surplus of Ca, then thick oxide compound generates, and makes the toughness deterioration of mother metal and HAZ, therefore need be suppressed at below the 0.010 quality %.The content of Ca is limited to 0.008 quality % on preferably, is limited to 0.007 quality % on more preferably.

N:0.002～0.020 quality %

N by at high temperature form fusing residual contain the Ti nitride, be useful element in the toughness of guaranteeing mother metal and HAZ.In order to bring into play such effect effectively, need make it to contain more than the 0.002 quality %.The content preferred lower limit of N is 0.003 quality %, is limited to 0.004 quality % under preferred.Other direction, if the content surplus of N, then solid solution N amount increases, because strain aging causes the toughness deterioration of mother metal and HAZ, therefore need be suppressed at below the 0.020 quality %.The content preferred upper limit of N is 0.018 quality %, is limited to 0.013 quality % on preferred.

More than one that select among REM:0.0001～0.02 quality %, Zr:0.0001～0.02 quality %

REM (rare earth element) and Zr add the back at Ti, Ca adds before adding, thereby form the effective oxide compound of the generation of intracrystalline α, are the elements that helps the raising of HAZ.This effect increases and increases along with its content, but in order to bring into play such effect effectively, all needs to make it to contain more than the 0.0001 quality %.The preferred lower limit of the content of REM and Zr is 0.0003 quality %, is limited to 0.0005 quality % under preferred, is limited to 0.0010 quality % under further preferred.On the other hand, if these elements are contained superfluously, then oxide compound becomes thick, makes the toughness deterioration of mother metal and HAZ, therefore all needs to be suppressed at below the 0.02 quality %.The preferred upper limit of these content is 0.015 quality %, is limited to 0.01 quality % on preferred.Also have, so-called REM (rare earth element) represents lanthanon (15 kinds of elements in the periodic table of elements from La to Ln), Sc and Y.Also have, REM also can be the mode of norium (for example contain Ce and be about 50%, La be about 25%).

It more than is the necessary element that contains that the present invention stipulates.In addition, also can also contain element described later, surplus is iron and unavoidable impurities.As unavoidable impurities, the sneaking into of elements such as Sn, the As that allows to mix because of the situation of raw material, goods and materials, producing apparatus etc., Pb.

More than Shuo Ming basic comprising of the present invention is as the basis, is specifically described for the Plate Steel of this case first mode.Also have, about then omitting explanation with the common content of aforementioned basic comprising.

In the one-tenth of the Plate Steel of this case first mode was grouped into, making Si content was 0.46 quality % following (containing 0), and Mn content is the method for 1.0～2.0 quality %, and the effect that Si, Mn are contained that illustrates in described basic comprising is significantly brought into play.

The Plate Steel of this case first mode, it is constructed as follows: becoming on the basis that such one-tenth is grouped into, among the oxide compound, diameter of equivalent circle is among the above oxide compound of 2 μ m, diameter of equivalent circle is that 2 μ m oxide compound above, that be lower than 5 μ m exists 30～70/mm ², and diameter of equivalent circle is that the existence of the above oxide compound of 5 μ m is lower than 30/mm ², and contain the Ti nitride, and described containing among the Ti nitride, diameter of equivalent circle is that the following Ti nitride that contains of 100nm exists 5 * 10 ⁶Individual/mm ²More than.

Making diameter of equivalent circle is that 2 μ m oxide compound above, that be lower than 5 μ m exists 30～70/mm ², making diameter of equivalent circle is that the existence of the above oxide compound of 5 μ m is lower than 30/mm ², intracrystalline α generates the HAZ that brings and organizes micronized effect significantly to be embodied.

Diameter of equivalent circle is that 2 μ m oxide compound existence above, that be lower than 5 μ m is lower than 30/mm ²The time, with 30/mm of existence ²Above situation is compared, and intracrystalline α generates the HAZ that brings and organizes micronized effect to be difficult to embody.Be more than the 2 μ m, be lower than the oxide compound of 5 μ m about diameter of equivalent circle, recommend the preferred 50/mm of existence ²More than, more preferably there is 60/mm ²More than.

Also have, among these oxide compounds, the mass ratio of Ti and Ca (Ti/Ca) satisfy to surpass 1, is lower than 1.4 oxide compound, also can be in the heat of HAZ a part of liquid phaseization, and in process of cooling thereafter crystallization takes place and has for intracrystalline α and generate favourable crystalline texture, therefore, except (the reduction of the interfacial energy of intracrystalline α/γ), can also realize lower (intracrystalline α/inclusion) interfacial energy, the generation of intracrystalline α is promoted extremely actively, therefore we can say effective especially.

Except controlling described oxide compound, make and contain the above fine Ti nitride that contains of suitable number (individual number density) in the Plate Steel, the Plate Steel that also is this case first mode needs, and utilizes such Ti nitride, pinning that can carry out the old γ grain growing of HAZ of containing.

Also have, first mode is defined to be contained in the Ti nitride, comprises TiN certainly, but also comprises a part of replacing the Ti of TiN with other nitride forming elements (Nb, Zr, V etc.), specifically, be that unit below 50% usually substitutes Ti in order to atomic ratio measuring exactly.

If this contains the Ti nitride and described oxide compound compares then very fine, can fine dispersion very in large quantities in steel before the heat input of welding, therefore, even process is large-line energy welding like this more than the 100kJ/mm at heat input for example, contain the Ti nitride and disappear in a large number, still can make quantity sufficient to contain the Ti nitride residual.So, after large-line energy welding, have can make quantity sufficient to contain the Ti nitride residual, therefore can bring into play the pinning of the old γ grain growing of HAZ effectively.

In the Plate Steel of this case first mode, in order to ensure HAZ toughness, making the diameter of equivalent circle that imports in the steel is that the following fine individual number density that contains the Ti nitride of 100nm is 5 * 10 ⁶Individual/mm ²More than.This be because, if be lower than 5 * 10 ⁶Individual/mm ², then a little less than the pinning effect of old γ grain growing.

Also have, the diameter of equivalent circle that imports in the steel is that the following fine preferred number density of Ti nitride that contains of 100nm is 5.4 * 10 ⁶Individual/mm ²More than, preferred number density is 6 * 10 ⁶Individual/mm ²More than.The upper limit of its number is not particularly limited, but in fact 15 * 10 ⁶Individual/mm ²Following degree.In first mode, there is not special stipulation about the lower limit that imports the fine diameter of equivalent circle that contains the Ti nitride in the steel, but according to the measurement boundary of the transmission electron microscope of measuring (TEM), we can say about the following 10nm of being limited to of actual diameter of equivalent circle.

＜manufacturing important document 〉

In order to make the Plate Steel of this case first mode that satisfies above-mentioned important document, during preferred suitably control melting and the manufacturing important document during casting, make Plate Steel.Below, being divided into one by one, project explains its manufacturing important document

(soluble oxygen content in the molten steel during melting)

During melting, using Mn to carry out deoxidation, also can use Si to carry out deoxidation under the situation of needs, make the soluble oxygen content that melts in the steel in quality % thus, is 0.002～0.01% scope.Soluble oxygen content in the molten steel is lower than at 0.002% o'clock, and the oxide compound that then can not guarantee to constitute the suitable composition that has of the starting point that intracrystalline α generates reaches requirement.On the other hand, surpass at 0.01% o'clock at soluble oxygen content, then diameter of equivalent circle is that the above thick oxide compound of 2 μ m exceedingly forms, and brings disadvantageous effect for HAZ toughness.The preferred lower limit of soluble oxygen content is 0.0025%, and preferred upper limit is 0.008%.

(addition of Ti, REM, Zr)

In order to ensure diameter of equivalent circle be more than the 2 μ m, the oxide compound that is lower than 5 μ m more than specified amount, preferred Ti more rambunctious, REM among the oxide compound forming element, the addition of Zr and the balance of addition thereof suitably adjusted.The total addition that surpasses 160ppm, REM and Zr at the addition of Ti surpasses on the basis of 55ppm, adjusts the addition balance, makes according to the value that [Ti]/[REM]+[Zr] this formula is tried to achieve to be more than 0.8, to be lower than 11.8 and to get final product.

Wherein, [] is the value of representing the addition of each element etc. with quality % in the formula.Also have, [Ti], [REM], [Zr] may not be necessarily with the steel that finally obtain in Ti amount, REM measure, Zr measures consistent.This be because, these elements evaporate in manufacturing processed, or are included in the slag and are removed.

(the interpolation order of oxide compound forming element)

The oxide compound forming element of Al, Ti, REM, Zr, Ca, need add according to the order of Al → Ti → (REM, Zr →) Ca, if add each element with the order beyond this interpolation order, the oxide compound with suitable composition that then can not guarantee to constitute the starting point that intracrystalline α generates reaches requirement.Particularly Ca has the extremely strong such characteristic of deoxidation power, if added before Ti and Al, then the oxygen of being combined with Ti and Al all disappears, and can not form the oxide compound that the one-tenth stipulated in first mode is grouped into.Also have, when REM and Zr add, its interpolation order which before can, also can add simultaneously.

Also have, in the interpolation of Al, Ti, REM, Zr, Ca, as described later, get final product within the limits prescribed from interpolation Ti to the time of adding Ca, the interval outside it then is not particularly limited.

(from adding Ti to the time t1 that adds Ca)

Ti is 3～20 minutes to the time t1 (branch) that adds Ca from interpolation.If from add Ti to the time t1 (branchs) that adds Ca than 3 minutes weak points, then fully do not carry out adding the oxide compound generation that the element that adds before the Ca carries out, the oxide compound with suitable composition that can not guarantee to constitute the starting point of intracrystalline α generation reaches requirement.In addition, if this time t1 (branch) is longer than 20 minutes, then to adding Ca, the generation of oxide compound is carried out superfluously, and the composition of oxide compound does not reach expectation, and the oxide compound that can not guarantee to have the suitable composition of the starting point that constitutes intracrystalline α generation reaches requirement.Also have, the preferred lower limit from interpolation Ti to the time t1 (branch) that adds Ca is 5 minutes, and preferred upper limit is 15 minutes.

(from adding Ca to the time t2 of casting beginning)

Time t2 (branch) from interpolation Ca to the casting beginning is to satisfy between the ta and tb that is tried to achieve by following formula (1), (2), i.e. the time of ta (branch)＜t2 (branch)＜tb (branch).

Ta=4-10 * [Ca]/([Ti]+2 * [Al]+5 * [REM]+2 * [Zr]+0.01 ... formula (1)

Tb=25-40 * [Ca]/([Ti]+2 * [Al]+5 * [REM]+2 * [Zr]+0.01 ... formula (2)

Wherein, [] is the value of representing the addition of each element etc. with quality % in aforesaid formula (1), (2).

Also have, [Ca], [Ti], [Al], [REM], [Zr] may not be consistent with Ca amount, Ti amount, Al amount, REM amount, the Zr amount in the steel that finally obtain.This is because these elements evaporate in manufacturing processed, or is included in the slag and is removed.

From adding Ca to the time t2 (branch) of casting beginning, be that Ca is in the needed time of oxide compound that forms expectation from adding other oxide compounds that generate before the Ca to seize oxygen, if this time t2 (branch) is in below the ta (branch), the formation reaction that contains the Ca oxide compound after then Ca adds is not fully carried out, and the oxide compound with suitable composition that can not guarantee to constitute the starting point that intracrystalline α generates reaches requirement.In addition, if this time t2 (branch) is in more than the tb (branch), the formation reaction that contains the Ca oxide compound after then Ca adds is carried out superfluously, and the oxide compound that can not guarantee to have the suitable composition of the starting point that constitutes intracrystalline α generation reaches requirement.T2 (branch) so need satisfy ta (branch)＜t2 (branch)＜tb (branch), but from the viewpoint of productivity, preferably short as far as possible time in this scope.Also having, try to achieve formula (1), (2) of ta and tb, is that the oxide compound of considering each element forms ability, the formula of trying to achieve through a large amount of repeatedly experiments.

More than be used to the oxide compound of guaranteeing requirement from adding Ca to the condition of the time t2 (branch) of casting beginning, but in the Plate Steel of this case first mode, also needing diameter of equivalent circle is that the Ti nitride that contains below the 100nm is guaranteed 5 * 10 ⁶Individual/mm ²More than.For this reason, the relation of the tx (branch) that is tried to achieve by following formula (3) and t2 (branch), ta (branch), tb (branch) need satisfy ta (branch)＜tx (branch)＜t2 (branch)＜tb (branch).

Tx=6-{[Si]/([Ti]+2 * [Al]+5 * [Ca]+5 * [REM]+2 * [Zr]+0.01) } ... formula (3)

Wherein, [] is the value of representing the addition of each element etc. with quality % in aforesaid formula (3).

Adding the situation of Si, is to add before deoxidation, oxidized state to the deoxidation.In order to ensure solid solution Si more than specified amount, need be by the strong deoxidant element bigger than Si with the avidity of oxygen, the Si of oxidation is carried out adequate time reduction, tx (branch)＜t2 (branch) for this reason.On the other hand, the oxide compound that has suitably carried out the composition adjustment because need guarantee to constitute intracrystalline α starting point also reaches specified amount, thus need make the needed time ratio specified time of the reduction of Si oxide compound short, so t2 (branch)＜tb (branch).

(t3 cooling time during casting)

T3 cooling time (second) under 1500～1450 ℃ during casting is below 300 seconds.If this cooling time of t3 (second) surpasses 300 seconds, then diameter of equivalent circle is the growing amount increase of the above thick oxide compound of 5 μ m, HAZ toughness deterioration.Also have, t3 cooling time (second) during casting was preferably below 280 seconds.The lower limit of t3 (second) is not particularly limited, and can be preferably about 190 seconds.

(addition of oxide compound forming element)

The addition of Ca (quality %) among the oxide compound forming element, namely [Ca] satisfies between the A1 value and B1 value of being tried to achieve by following formula (4), (5), i.e. the addition (quality %) of A1≤[Ca]≤B1.Also having, try to achieve following formula (4), (5) of A1 value and B1 value, is the formula of trying to achieve through a large amount of repeatedly experiments.

A1=2.25 * [Of] ... formula (4)

B1=[Of] * [Ti]/(0.25 * [REM]+0.12 * [Zr]) ... formula (5)

Wherein, in aforesaid formula (4), (5), [Of] is the soluble oxygen content (quality %) before Ca adds, and [Ti], [REM], [Zr] are that each element is respectively to the addition (quality %) that melts in the steel.

If the Ca addition is littler than the A1 value, then the major part of the Ca of Tian Jiaing is consumed as the oxide alone of Ca, therefore can not guarantee the oxide compound with suitable composition for the starting point that constitutes intracrystalline α generation.On the other hand, if the Ca addition surpasses the B1 value, then the ratio of the Ti in the oxide compound (quality %) diminishes, and at this moment can not guarantee the oxide compound with suitable composition for the starting point that constitutes intracrystalline α generation.

(adjustment of the total addition of the element that Si addition and deoxidizing capacity are higher than Si)

In first mode, need guarantee that diameter of equivalent circle is that the following Ti nitride that contains of 100nm exists 5 * 10 ⁶Individual/mm ²More than, for this reason, the solid solution Si amount of preferably in steel, fully guaranteeing to make the activity of Ti to improve.As previously described, when adding Si, before the deoxidation of being undertaken by Ca, Ti, Al, REM, Zr, add, in steel making working procedure, have a certain amount of oxidized, therefore measure for the solid solution Si that in steel, guarantees to expect, need make the deoxidizing capacity element higher than Si, i.e. the total of the addition of Al, Ti, Ca, REM, Zr, % counts more than 0.020% with quality.

Preferred addition when adding Si is counted more than 0.02% with quality %, and preferred addition is more than 0.10%.On the other hand, the preferred total addition of Al, Ti, Ca, REM, Zr is more than 0.025%, and preferred total addition is more than 0.030%.

When making the Plate Steel of this case first mode, during the melting of the above explanation of preferred suitably control and the manufacturing important document during casting, make Plate Steel, but after melting and casting, after recommending the resulting casting sheet of heating to carry out hot rolling, implement to quench, after austenite, the heating of ferrite two phase regions, carry out Q-tempering and handle again.

Quenching after the described hot rolling except the direct quenching of quenching immediately after the hot rolling (DQ), also can be used hot rolling material off-line quench (RQ).Also have, because the situation that DQ handles can not be done over again, so compare with the situation that RQ handles, require the beginning temperature of quenching is carried out stricter temperature treatment.

In addition, be heated to austenite, ferrite two phase regions and after the quenching of carrying out that RQ handles etc., if needs are arranged, preferably begin the following temperature of temperature (Ac1) with ferrite transformation and carry out tempering, with the intensity of adjustment steel.

Next, the Plate Steel for this case second mode is specifically described.Also have, about the content common with aforementioned basic comprising, omit explanation.

In the one-tenth of the Plate Steel of this case second mode was grouped into, making Si content was 0.01～0.35 quality %, and Mn content is 1.0～2.0 quality %, and this mode is significantly brought into play the effect that contains Si, Mn that illustrates in the aforementioned basic comprising.

The Plate Steel of this case second mode, it constitutes, and is grouped on the basis at such one-tenth, and described oxide compound still satisfies the oxide compound of the relation of Al/ (REM+Zr)＜0.7, and diameter of equivalent circle is lower than the every 1mm of oxide compound of 2 μ m ²In have more than 300, and contain the Ti oxide compound, and described containing among the Ti oxide compound, diameter of equivalent circle is that the following Ti nitride that contains of 100nm exists 5 * 10 ⁶Individual/mm ²More than.

In the described oxide compound, owing to still satisfy the oxide compound of the relation of Al/ (REM+Zr)＜0.7, thereby easy fluidization under the heat of HAZ, in process of cooling thereafter, crystallization taking place and has for intracrystalline α generates favourable crystalline texture, therefore, except (the reduction of the interfacial energy of intracrystalline α/γ), can also realize lower (intracrystalline α/inclusion) interfacial energy, consequently the generation of intracrystalline α is promoted that row is more active.Consequently, in the Plate Steel of this case second mode, owing to generating, the intracrystalline α of mother metal promotes to make mother metal organize miniaturization, can guarantee base metal tenacity, and can realize low yield strength ratio, also can guarantee any one characteristic of HAZ toughness, yield tensile ratio and base metal tenacity evenly.

In addition, the number about the oxide compound that satisfies above-mentioned compositing range is lower than the every 1mm of oxide compound of 2 μ m by making diameter of equivalent circle ²The middle existence more than 300, can further promote intracrystalline α to generate.

Among the above-mentioned oxide compound, diameter of equivalent circle is lower than the every 1mm of oxide compound of 2 μ m ²Number, be preferably more than 350, more preferably more than 400.Its number upper limit is not particularly limited, but in fact at 1000/mm ²Following degree.

In addition, the described oxide compound of diameter of equivalent circle more than 2 μ m is at every 1mm ²In number, in the Plate Steel of this case second mode, be preferably below 85, more preferably below 70.

Also have, when the calculating of the value of the above-mentioned Al/ (REM+Zr) of the oxide compound of second mode, when oxide compound did not contain REM or Zr, its content calculated by 0 and gets final product.

In the Plate Steel of this case second mode, except controlling above-mentioned oxide compound, the feature that has also is following this point: utilize the fine Ti nitride that contains complementaryly, carry out the pinning of the old γ crystal grain of HAZ.Contain the Ti nitride in second mode, its aim is, comprises TiN certainly, but also comprise with other nitride forming elements (for example Nb, Zr, V etc.) replace the Ti of TiN a part (with atomic ratio measuring be below 50% about).If before the welding heat input, compare, then owing to contain the fine dispersion of Ti nitride, its number density is compared with oxide based inclusion and can be guaranteed manyly in the extreme, therefore, even through the large-line energy welding, the major part that contains the Ti nitride disappears, and still can contain that the Ti nitride is remaining guarantees number density by making, by this remaining fine pinning effect that the Ti nitride is brought into play old γ crystal grain effectively that contains.In order to reduce the deviation of HAZ toughness, namely not only the mean value of HAZ is remained on high level, and its minimum value is also remained on high level, contain Ti nitride equivalent diameter below 100nm at every 1mm ²In have 5 * 10 ⁶More than individual.This be because, if every 1mm ²Be lower than 5 * 10 ⁶Individual, then can not bring into play pinning effect effectively.The number that contain Ti nitride of diameter of equivalent circle below 100nm is at every 1mm ²In, be preferably 5.4 * 10 ⁶More than individual, more preferably 6.5 * 10 ⁶More than individual.Its number upper limit is not particularly limited, but is actually 15 * 10 ⁶Individual following degree.Lower limit as the diameter of equivalent circle that contains the Ti nitride of object in the Plate Steel of this case second mode is not particularly limited, but according to the measuring limit of the TEM that uses in embodiment described later, the following of diameter of equivalent circle is limited to about 10nm.

In order to make the oxide compound of second mode that chemical constitution suitably controlled, its every kind size is all adjusted in the above described manner, during preferred suitably control melting and the condition during casting.That is the soluble oxygen content in the molten steel during (i) melting effectively; The (ii) interpolation of oxide compound forming element (Ti, Al, Ca, REM, Zr) order and (iii) among the described oxide compound forming element, from adding Ti to the time of adding Ca; (iv) add last oxide compound forming element (Ca) afterwards to the time of casting and beginning; Also has (the cooling time under the temperature range of the regulation when v) suitably control is cast.In addition, among the oxide compound of second mode, be lower than the oxide compound of 2 μ m in order to ensure diameter of equivalent circle more than regulation, except above-mentioned (i)～(v), (addition of vi) reciprocally controlling oxide based forming element is also very important.Below, for (i)～(vi) describe.

Soluble oxygen content in the molten steel during (i) about melting

At first, the preferably deoxidation by using Mn and Si to carry out when melting, making soluble oxygen content is 0.002～0.01%.If soluble oxygen content is lower than 0.002%, then can not guarantee the oxide compound of second mode of requirement, on the other hand, if surpass 0.01%, then thick oxide compound forms, and toughness is caused disadvantageous effect.Soluble oxygen content more preferably more than 0.0025%, below 0.008%.

(ii) about the interpolation of oxide compound forming element order

According to the order of Al → Ti → (REM, Zr) → Ca add Al, Ti, REM, Zr, Ca is advisable, if outside order add, can not guarantee that then the oxide compound that has suitable composition as constituting the starting point that intracrystalline α generates reaches requirement.Particularly Ca deoxidation power is extremely strong, if added before Ti and Al, then the oxygen of being combined with Ti and Al all disappears, and can not form the oxide compound of the composition with above-mentioned expectation.Also have, when REM and Zr add, the interpolation of REM and Zr order which before can, also can add simultaneously.

Also have, in the interpolation of Al, Ti, REM, Zr, Ca, as described later, get final product within the limits prescribed to the time of adding Ca from adding Ti, other interval then is not particularly limited.

(iii) about among the described oxide compound forming element, from adding Ti to the time of adding Ca

Among the described oxide compound forming element, be 3～20 minutes from adding Ti to the time t1 (branch) that adds Ca.If t1 is than 3 minutes weak points, then generate and fully do not carry out adding oxide compound that the element that adds before the Ca carries out, can not obtain the oxide compound of suitable composition of starting point of the formation intracrystalline α generation of requirement.In addition, if t1 surpasses 20 minutes, then to adding Ca, the generation of oxide compound is carried out superfluously, and the composition of oxide compound does not reach expectation, can't obtain the oxide compound of the suitable composition of the starting point that the formation intracrystalline α of requirement generates.T1 (branch) is more preferably more than 5 minutes, below 15 minutes.

(iv) add last oxide compound forming element (Ca) afterwards to the time of casting and beginning

From adding Ca to the time t2 (branch) of casting beginning, preferably be controlled to be, the pass that makes it with the ta, the tb that represent respectively according to following formula (1), (2) is ta＜t2＜tb.

Ta=4-10 * [Ca]/([Ti]+2 * [Al]+5 * [REM]+2 * [Zr]+0.01) ... formula (1)

Tb=25-40 * [Ca]/([Ti]+2 * [Al]+5 * [REM]+2 * [Zr]+0.01) ... formula (2)

In following formula (1), (2), [Ca], [Ti], [Al], [REM] and [Zr] represent that respectively Ca, Ti, Al, REM and Zr are to the addition (quality %) that melts in the steel.Also have, above-mentioned [Ca], [Ti], [Al], [REM] may not be consistent with Ca amount, Ti amount, Al amount, REM amount and the Zr amount in the steel that obtain with [Zr].This is owing to there are these elements vaporizations, or is included in the slag and situation about being removed.

From adding Ca to the time t2 (branch) of casting beginning, be that Ca is seizing oxygen and forming the needed time of oxide compound from adding other oxide compounds that generate before the Ca, if this time is in below the ta, the formation reaction that contains the Ca oxide compound after then Ca adds is not fully carried out, and can not guarantee to constitute the oxide compound with suitable composition of the starting point that intracrystalline α generates.In addition, if this time t2 is in more than the tb, the formation reaction that contains the Ca oxide compound after then Ca adds is carried out superfluously, still can not guarantee the oxide compound with suitable composition for the starting point that constitutes intracrystalline α generation.From the viewpoint of productivity, preferred in fact t2 satisfies above-mentioned scope and is the short as far as possible time.Also have, following formula (1), (2) are that the oxide compound of considering above-mentioned element forms ability, the formula of trying to achieve through a large amount of repeatedly experiments.

(v) about the cooling time under the temperature range of the regulation in when casting

T3 cooling time (second) under 1500～1450 ℃ during casting was preferably below 300 seconds.If t3 surpasses 300 seconds, thick oxide compound then, namely the growing amount of the above oxide compound of diameter of equivalent circle 2 μ m increases, and makes HAZ toughness deterioration.T3 is more preferably below 280 seconds.The lower limit of t3 is not particularly limited, but is generally about 190 seconds.

(vi) about the addition of the oxide based forming element of mutual control

The Ca addition with the relation that has of the A1 value of trying to achieve by following formula (4), (5) and B1 value, preferably is adjusted into the scope of A1≤[Ca]≤B1.The A1 value of following formula (4), (5) defined and B1 value are the formulas of trying to achieve according to a large amount of experiments.

A1=2.25 * [Of] ... formula (4)

B1=[Of] * [Ti]/(0.25 * [REM]+0.12 * [Zr]) ... formula (5)

In following formula (4), (5), [Of] is the soluble oxygen content (quality %) before Ca adds, and [Ti], [REM] and [Zr] are that Ti, REM and Zr are respectively to the addition (quality %) that melts in the steel.

If the Ca addition is lower than the A1 value, then the major part of the Ca of Tian Jiaing is consumed as the oxide alone of Ca, therefore can not guarantee the oxide compound with suitable composition for the starting point that constitutes intracrystalline α generation.On the other hand, if the Ca addition surpasses the B1 value, then the ratio of the Ti in the oxide compound diminishes, and can not guarantee the oxide compound with suitable composition for the starting point that constitutes intracrystalline α generation.

In addition, Al addition, REM addition and Zr addition are controlled to be [Al]/([REM]+[Zr])＜1.0 and get final product.If the value of [Al]/([REM]+[Zr]) is more than 1.0, then the ratio of the Al in the oxide compound uprises, and the inclusion that consequently (intracrystalline α/inclusion) interfacial energy is high increases, and intracrystalline α generative capacity reduces.The value of [Al]/([REM]+[Zr]) is more preferably below 0.9.

In addition, except being used for obtaining the optimum condition of above-mentioned oxide compound, contain the Ti nitride for what more than regulation, guarantee second mode, preferably (vii) adjust the total addition of interpolation Si amount and the deoxidizing capacity element higher than Si, and (viii) except above-mentioned important document (iv), more strictly control from adding Ca to the time of casting beginning.

(vii) about the adjustment of the total addition of Si addition and the deoxidizing capacity element higher than Si

The Ti nitride that contains in order to ensure second mode reaches specified amount, the solid solution Si amount of effectively guaranteeing to make the activity of Ti to improve in steel.Si amount before deoxidation (deoxidation of being undertaken by Ca, Ti, Al, REM and Zr) is added, in steel making working procedure, have a certain amount of oxidized, therefore guarantee aforesaid solid solution Si amount, effectively the Si addition is more than 0.01%, and in order to reduce the Si of oxidized state, make the deoxidizing capacity element higher than Si, namely the addition of Al, Ti, Ca, REM, Zr adds up to more than 0.020%.The Si addition is more preferably more than 0.02%, more preferably more than 0.10%.The total of the addition of Ca, Ti, Al, REM, Zr is more preferably more than 0.025%, more preferably more than 0.030%.

(viii) about the time from interpolation Ca to the casting beginning

Oxide compound in order to ensure second mode of requirement, from adding Ca to the time t2 (branch) of casting beginning, be preferably ta＜t2＜tb, its aim is illustrated in (iv) above-mentioned, but from guaranteeing to stipulate the above viewpoint that contains the Ti nitride, effectively further control, with the relation of the represented tx of following formula (3) in, satisfy the relation of ta＜tx＜t2＜tb.

Tx=6-{[Si]/([Ti]+2 * [Al]+5 * [Ca]+5 * [REM]+2 * [Zr]+0.01) } ... formula (3)

Si adds before deoxidation, is in oxidized state to deoxidation.More than specified amount, need carry out the adequate time reduction by the strong deoxidant element bigger than Si with the avidity of oxygen to oxidized Si, therefore preferred t2＞tx in order to ensure solid solution Si.On the other hand, in order to realize and the existing side by side of the oxide compound of second mode (suitably having carried out the oxide compound that composition is adjusted in the mode that constitutes intracrystalline α starting point) that the needed time of the reduction of Si oxide compound need be below regulation, t2＜tb.

Next, the Plate Steel for this case Third Way describes particularly.Also have, for the content omission explanation common with described basic comprising.

The Plate Steel of this case Third Way, it is constructed as follows: in the one-tenth of the Plate Steel of this case Third Way is grouped into, Si content is 0.25 quality % following (containing 0%), Mn content is 1.0～2.0 quality %, and the scope at REM:0.0003～0.02 quality %, Zr:0.0003～0.02 quality % contains REM and Zr both sides, and this mode makes containing to produce effect and being brought into play significantly of these elements of illustrating in the aforementioned basic comprising.And the A value of being tried to achieve by following formula satisfies 0.4≤A≤2.4,

A＝10 ⁴×{[Ti]-0.7×([O]-0.09×[Al]-0.16×[Ca]-0.07×[REM]-0.04×[Zr])}×[N]

At first, the Plate Steel of this case Third Way, the A value of being tried to achieve by aforementioned A formula needs to satisfy 0.4≤A≤2.4, this be because, if this A value is lower than 0.4, then can not obtain sufficient TiN, HAZ toughness reduces, on the other hand, the A value is bigger than 2.4, then thick TiN crystallization and HAZ toughness is caused disadvantageous effect in the molten steel.

In addition, present inventors find, make the surface recombination of the oxide compound that illustrates in the basic comprising separate out TiN, can make the TiN stabilization, and the intracrystalline α promoter action of being brought by described oxide compound and on this oxide compound the intracrystalline α promoter action of the compound TiN that separates out worked in coordination with promotion, intracrystalline α generates and is further promoted, until the Plate Steel that obtains this case Third Way.

Then, in these complex inclusions, the oxide compound that makes diameter of equivalent circle be lower than 2 μ m disperses 300/mm ²More than, thereby can access excellent HAZ toughness.

(oxide compound that diameter of equivalent circle is lower than 2 μ m is 300/mm ²More than)

Make the diameter of equivalent circle of oxide compound be lower than 2 μ m, promote to promote HAZ toughness by intracrystalline α.If the diameter of equivalent circle of oxide compound is more than the 2 μ m, then become whole state of TiN capping oxide particle, oxide compound is unfavorable for that intracrystalline α generates, so intracrystalline α growing amount reduces.In addition, the composition of oxide compound, in quality %, if break away from 3%＜N, 5%＜Ca＜40%, 5%＜REM＜50%, 5%＜Zr＜40%, this scope of 2＜Ti/N, the sufficient intracrystalline α that then can not get expecting in the Plate Steel of this case Third Way generates.In addition, if diameter of equivalent circle is lower than the oxide compound of 2 μ m than 300/mm ²Few, the then starting point deficiency that generates of intracrystalline α, so the growing amount of intracrystalline α still can't be increased to the degree that the Plate Steel of this case Third Way is expected, can not get sufficient HAZ toughness.The upper limit of its number is not particularly limited, but is actually 1000/mm ²Following degree.

(manufacture method)

In order to make the Plate Steel of this case Third Way that satisfies above-mentioned important document, needs satisfy following manufacturing important document and make Plate Steel.

Its create conditions into, when melting, by using Mn, the deoxidation that Si carries out, make the soluble oxygen content in the molten steel count 0.002～0.01% with quality %, afterwards according to (Al →) Ti → (REM, Zr) → order of Ca, on one side be controlled to be 3～20 minutes with adding Ti to the time t1 that adds Ca, add each element on one side, the time t2 that begins extremely casting from interpolation Ca remains on 40～90 minutes scope, t3 cooling time under 1500～1450 ℃ the temperature range when making casting again is in 300 seconds, and when rolling resulting ingot casting, making rolling preceding Heating temperature Th is 1050～1200 ℃, heat-up time, t4 was 2～5 hours, and to make the not crystallized domains draft when rolling be to get final product more than 40%.Then, be elaborated for these regulation reasons of making important document.

(Al) soluble oxygen content in the molten steel before Ti adds: 0.002～0.01%

When the soluble oxygen content in the molten steel before (Al) Ti adds was lower than 0.002%, the oxide compound with suitable composition that can not guarantee to constitute the starting point of intracrystalline α generation reached requirement.In addition, when soluble oxygen content was higher than 0.01%, diameter of equivalent circle was that the above thick oxide compound of 2 μ m increases, and makes HAZ toughness deterioration.

When melting, add according to the order of (Al →) Ti → (REM, Zr) → Ca

If add each element with the order beyond this interpolation order, the oxide compound with suitable composition that then can not guarantee to constitute the starting point that intracrystalline α generates reaches and needs quantity.Particularly the deoxidation power of Ca is extremely strong, and therefore if added before Ti and Al, then the oxygen of being combined with Ti and Al all disappears.

Also have, in the interpolation of Al, Ti, REM, Zr, Ca, as described later, get final product within the limits prescribed to the time of adding Ca from adding Ti, for outside the interval then be not particularly limited.

Ti is 3～20 minutes to the time t1 that adds Ca from interpolation

If from add Ti to the time t1 that adds Ca than 3 minutes weak points, then the reaction of oxide compound is not fully carried out before adding Ca, the oxide compound with suitable composition that can not guarantee to constitute the starting point of intracrystalline α generation reaches and needs quantity.In addition, if this time t1 is long than 20 minutes, then the reaction of oxide compound is carried out superfluously before adding Ca, and the oxide compound with suitable composition that can not guarantee to constitute the starting point of intracrystalline α generation reaches and needs quantity.

Time t2 from interpolation Ca to the casting beginning is 40～90 minutes

In order to obtain the compound TiN that separates out in oxide compound, retailoring stage oxide type Ti need make solid solution Ti increase.If t2 than 40 minutes weak points, then can not fully guarantee the compound TiN of separating out thereafter.On the other hand, if t2 is long than 90 minutes, then the reaction surplus of the oxide compound after the Ca interpolation carries out that (REM, Zr are reduced by surplus.), can not get the oxide compound with suitable composition of the starting point that the formation intracrystalline α of desired number generates.

T3 cooling time under 1500～1450 ℃ during casting is in 300 seconds

If 1500～1450 ℃ of t3 cooling time down in when casting surpass 300 seconds, then the component segregation owing to solidifying causes toughness is caused the thick TiN crystallization of disadvantageous effect, makes HAZ toughness deterioration.The lower limit of t3 is not particularly limited, but is generally about 190 seconds.

Heating temperature Th before rolling is 1050～1200 ℃, and heat-up time, t4 was 2～5 hours

The stage of heating can access TiN and separate out to the compound of oxide surface before rolling.Heating temperature Th is lower than 1050 ℃ or when heat-up time, t4 was lower than 2 hours before rolling, and it is insufficient that TiN compound separated out.On the other hand, if Heating temperature Th is higher than 1200 ℃ before rolling, then TiN compound separated out insufficiently, needing to can not get the oxide compound of the regulation of quantity.In addition, if heat-up time t4 than 5 little durations, then the compound amount of separating out of TiN is saturated, on the other hand, mother metal is organized thickization, causes disadvantageous effect for the toughness of mother metal.

The crystallized domains draft is not more than 40%

Depress by applying in crystallized domains not, strain be directed to oxide compound around, this strain becomes drive source, can access the compound TiN of separating out in addition.If this not the crystallized domains draft be lower than 40%, then do not import sufficient strain, the compound TiN deficiency of separating out.

Next, the Plate Steel for the cubic formula of this case specifically describes.Also have, for the content common with described basic comprising, omit explanation.

The Plate Steel of the cubic formula of this case, it constitutes, in the one-tenth of the Plate Steel of the cubic formula of this case is grouped into, Si content is 0.02～0.50 quality %, Mn content is 1.4～3.0 quality %, and, containing REM and Zr both sides in the scope of REM:0.0003～0.02 quality %, Zr:0.0003～0.02 quality %, this mode makes containing to produce effect and being brought into play significantly of these elements of illustrating in the aforementioned basic comprising.And, also contain Cr:0.5～2.0 quality %.The D value of being tried to achieve by following formula satisfies 238＜D＜388,

D＝62×[Mn]+27×[Ni]+111×[Cr]

And among the described oxide compound, diameter of equivalent circle is lower than the every 1mm of oxide compound of 2 μ m ²In have more than 300, and diameter of equivalent circle is among the oxide compound more than the 2 μ m, diameter of equivalent circle more than 2 μ m, there is 30～70/mm in the oxide compound that is lower than 5 μ m ², and the existence of the oxide compound of diameter of equivalent circle more than 5 μ m is lower than 30/mm ²Also have, in described D formula, [] represents the content (quality %) of each element at this.

In the Plate Steel of the cubic formula of this case, containing Cr is 0.5～2.0 quality %, and it is to guarantee that tensile strength is effective elements on the high strength of 780MPa level, therefore needs to add more than the 0.5 quality %.But, if add superfluously, then cause the excessive rising of HAZ intensity, HAZ toughness is caused disadvantageous effect, therefore need be suppressed at below the 2.0 quality %.The preferred lower limit of the content of Cr is 0.6 quality %, is limited to 0.7 quality % under preferred.The preferred upper limit of the content of Cr is 1.8 quality %, is limited to 1.6 quality % on preferred.

In addition, the Plate Steel of the cubic formula of this case, the D value of being tried to achieve by aforementioned D formula needs to satisfy 238＜D＜388, this be because, if this D value is lower than 238, the intracrystalline α that then can't fully obtain the oxide compound starting point generates, the desired HAZ toughness of Plate Steel that can not get the cubic formula of this case improves effect, on the other hand, if the D value is bigger than 388, the then excessive rising of the intensity of HAZ can not be guaranteed HAZ toughness.

The Plate Steel of the cubic formula of this case, as more than, except the control of oxide compound composition and size, by implementing the average control of alloying element, in the high tensile steel plate of tensile strength 780MPa level, the minimum value of the HAZ toughness when carrying out the large-line energy welding is improved, and the high tensile steel plate of so-called tensile strength 780MPa level represents that specifically tensile strength surpasses the high tensile steel plate of 780MPa level.

Why the oxide compound that diameter of equivalent circle is lower than 2 μ m is 300/mm ²More than, be the growing amount that obtains intracrystalline α for the degree of the HAZ toughness in the Plate Steel of having given play to the cubic formula of this case, expected.The upper limit of its number is not particularly limited, but is actually 1000/mm ²Following degree.

Diameter of equivalent circle more than 2 μ m, be lower than the oxide compound of 5 μ m, compare with the oxide compound that is lower than 2 μ m of the composition with aforementioned regulation, the generative capacity height of intracrystalline α is therefore by making it to disperse 30/mm ²More than, even in the high tensile steel plate of tensile strength 780MPa level, the miniaturization of organizing for HAZ also has significant effect.On the other hand, if a number density surpasses 70/mm ², then significantly change as the disadvantageous effect of brittle rupture starting point, therefore need control at 70/mm ²Below.

Therefore diameter of equivalent circle causes huge disadvantageous effect as the brittle rupture starting point for HAZ toughness at the oxide compound of 5 μ m, need control to such an extent that be lower than 30/mm ²

Also have, the Plate Steel of the cubic formula of this case among the described oxide compound, also has the 10%＜REM+Zr of satisfying＜70%, and the mass ratio of Ti and Ca (Ti/Ca) satisfy to surpass 1, is lower than 1.4 oxide compound, and more preferably there is 300/mm in the diameter of equivalent circle oxide compound that is lower than 2 μ m ²More than.

(manufacture method)

In order to make the Plate Steel of the cubic formula of this case that satisfies above-mentioned important document, needs satisfy following manufacturing important document and make Plate Steel.

Its create conditions into, when melting, by the deoxidation of using Mn, Si to carry out, make the soluble oxygen content in the molten steel count 0.002～0.01% with quality %, afterwards according to the order of Al → Ti → (REM, Zr) → Ca, on one side be controlled to be 3～20 minutes with adding Ti to the time t1 that adds Ca, add each element on one side, the scope that time t2 (branch) from interpolation Ca to the casting beginning is kept satisfying ta (branch)＜t2 (branch)＜tb (branch), and t3 cooling time under 1500～1450 ℃ the temperature range when making casting is in 300 seconds.In addition, at this moment the addition of Ti, REM, Zr must make the value by [Ti]/([REM]+[Zr]) tries to achieve be more than 0.8, be lower than 11.8.Also have, [expression] each element is to the addition (quality %) that melts in the steel in preceding formula.Below, be elaborated for these regulation reasons of creating conditions.

Also have, before shown in ta (branch) and tb (branch) can try to achieve according to following formula.

ta＝4-10×[Ca]/([Ti]+2×[Al]+5×[REM]+2×[Zr]+0.01)

tb＝25-40×[Ca]/([Ti]+2×[Al]+5×[REM]+2×[Zr]+0.01)

Wherein, [Ca], [Ti], [Al], [REM] and [Zr] represent that respectively Ca, Ti, Al, REM and Zr are to the addition (quality %) that melts in the steel.

Also have, above-mentioned [Ca], [Ti], [Al], [REM] may not be consistent with Ca amount, Ti amount, Al amount, REM amount and the Zr amount in the steel that obtain with [Zr].This be because, these elements vaporizations are arranged, or are included in the slag and situation about being removed.

In addition, formation element except deoxidation, in quality %, satisfy 10%＜Ti, Al＜20%, 5%＜Ca＜40%, 5%＜REM＜50%, 5%＜Zr＜40%, and 10%＜REM+Zr＜70%, the mass ratio of Ti and Ca (Ti/Ca) surpasses 1, is lower than among 1.4 the oxide compound in addition, and there is 300/mm in the oxide compound that diameter of equivalent circle is lower than 2 μ m ²More than, in order to ensure such condition, the control of the addition [Ca] of Ca is got final product in the scope of the A1 that tries to achieve based on following formula≤[Ca]≤B1.Also have, the A1 that tries to achieve based on following formula and the value of B1 are tried to achieve according to experiment.

A1＝2.25×[Of]

B1＝[Of]×[Ti]/(0.25×[REM]+0.12×[Zr])

Wherein, [Of] is the soluble oxygen content (quality %) before Ca adds, and [Ti], [REM] and [Zr] expression Ti, REM and Zr are respectively to the addition (quality %) that melts in the steel.

That is, if Ca addition [Ca] is littler than A1 value, then the major part of the Ca of Tian Jiaing is consumed as the oxide compound of the monomer of Ca, therefore can not fully obtain to constitute the oxide compound (the formation element is the oxide compound that satisfies above-mentioned important document) of the starting point of intracrystalline α generation.In addition, if Ca addition [Ca] surpasses B1 value, then make the Ti/Ca ratio in the oxide compound be lower than 1, therefore can not guarantee to constitute intracrystalline α generation starting point oxide compound need quantity.

Soluble oxygen content in the molten steel before A1 adds: 0.002～0.01%

When the soluble oxygen content in the molten steel before Al adds was lower than 0.002%, the oxide compound with suitable composition that can not guarantee to constitute the starting point of intracrystalline α generation reached requirement.In addition, when soluble oxygen content was higher than 0.01%, diameter of equivalent circle was that the above thick oxide compound of 2 μ m increases, and makes HAZ toughness deterioration.

When melting, add according to the order of Al → Ti → (REM, Zr) → Ca

Ti is 3～20 minutes to the time t1 that adds Ca from interpolation

If from add Ti to the time t1 that adds Ca than 3 minutes weak points, then the reaction of oxide compound is not fully carried out before adding Ca, the oxide compound with suitable composition that can not guarantee to constitute the starting point of intracrystalline α generation reaches and needs quantity.In addition, if this time t1 is long than 20 minutes, then the reaction of oxide compound is carried out superfluously before adding Ca, and the oxide compound with suitable composition that can not guarantee to constitute the starting point of IGB generation reaches and needs quantity.

From adding Ca to the time of time t2 (branch) for satisfying ta (branch)＜t2 (branch)＜tb (branch) of casting beginning

From add Ca to the time t2 of casting beginning be the important document that exerts an influence of the generating state to oxide compound (Ca captures oxygen and forms time of oxide compound from other oxide compounds), if this time t2 is in below the ta (branch), then can not fully carry out the oxide compound reaction after Ca adds, the oxide compound with suitable composition that can not guarantee to constitute the starting point that intracrystalline α generates reaches and needs quantity.In addition, if this time t2 is in more than the tb (branchs), the reaction surplus of the oxide compound after then Ca adds is carried out, can not guarantee to constitute intracrystalline α generation starting point the oxide compound with suitable composition need quantity.Also have, the formula of trying to achieve ta and tb is to consider that each element to the corresponding difficulty of oxide compound, tries to achieve by experiment.

T3 cooling time under 1500～1450 ℃ during casting is in 300 seconds

If t3 cooling time under 1500～1450 ℃ during casting surpasses 300 seconds, then the growing amount of the thick oxide compound more than the diameter of equivalent circle 5 μ m increases, and makes HAZ toughness deterioration.The lower limit of t3 is not particularly limited, but is generally about 190 seconds.

The addition of Ti, REM, Zr: be more than 0.8, be lower than 11.8 by the value that [Ti]/([REM]+[Zr]) tries to achieve

If be lower than 0.8 by the value that [Ti]/([REM]+[Zr]) tries to achieve, then compare with Ti as weak deoxidant element, many as the addition of REM, the Zr of strong deoxidant element.If such addition, then the free oxygen concentration in the molten steel reduces, and the oxide growth rate of adding Ca then and being reduces, can not guarantee therefore that diameter of equivalent circle is that 2 μ m are above, the oxide compound that is lower than 5 μ m 30/more than the mm2.On the other hand, if by value that [Ti]/([REM]+[Zr]) tries to achieve more than 11.8, otherwise then diameter of equivalent circle is that 2 μ m oxide compound above, that be lower than 5 μ m surpasses 70/mm ²

Also have, when making the Plate Steel of the cubic formula of this case, be not particularly limited about the manufacture method beyond the important document of melting～manufacturing stage of above explanation, but recommend is to carry out hot rolling after the resulting casting sheet of heating, after implementing to quench, reheat carries out Q-tempering and handles to austenite, ferrite two phase regions.

The Plate Steel of aforesaid this case first～Third Way as other elements, preferably also contains at least one group who selects from following (a)～(c).

(c) below the B:0.005 quality %.

Below, describe for the reason of adding these elements.

More than one that select the group who constitutes below Ni:1.50 quality %, below the Cu:1.50 quality %, below the Cr:1.50 quality %, below the Mo:1.50 quality %

Ni, Cu, Cr and Mo all are that the intensity-tough sexual balance for steel plate improves effective elements, and this effect increases and increases along with its content.In order to bring into play such effect effectively, all preferably make it to contain more than 0.05%, more preferably make it to contain more than 0.10%.But Ni is expensive element, from the viewpoint of cost, preferably is suppressed at below 1.50%, more preferably below 1.20%.In addition, Cu, Cr and Mo then cause the excessive rising of intensity if make it to contain superfluously, might make the toughness deterioration of mother metal and HAZ, therefore all preferably are suppressed at below 1.50%, more preferably below 1.20%.

More than one that select the group who constitutes below Nb:0.10 quality %, below the V:0.10 quality %

Nb and V separate out as carbonitride, suppress thickization of γ crystal grain, have improving the base metal tenacity effective elements.This effect increases and increases along with its content.In order to bring into play such effect effectively, all preferably make it to contain more than 0.002%, more preferably make it to contain more than 0.005%.But, if it contains superfluously, then cause thickization of HAZ tissue, might make HAZ toughness deterioration, therefore all preferably be suppressed at below 0.10%, more preferably below 0.08%, further preferably below 0.05%.

Below the B:0.005 quality %,

The generation of the grain boundary that the B inhibition is thick is effective elements for the toughness that improves mother metal and HAZ.This effect increases and increases along with its content.In order to bring into play such effect effectively, B is contained more than 0.0010%, more preferably make it to contain more than 0.0015%.But, if the content surplus of B, then cause the separating out of BN of austenite grain boundary, might make the toughness deterioration of mother metal and HAZ, therefore preferably be suppressed at below 0.005%.Be limited to 0.004% on the content of B is preferred, be limited to 0.003% on further preferred.

In addition, the Plate Steel of the cubic formula of aforesaid this case as other elements, preferably also contains at least one group who selects from following (a ')～(c ').

(c ') below the B:0.005 quality %.

Below, describe for the reason of adding these elements

More than one that select the group who constitutes below Ni:1.50 quality %, below the Cu:1.50 quality %, below the Mo:1.50 quality %

Ni, Cu and Mo all are that the intensity-tough sexual balance for steel plate improves effective elements, and this effect increases and increases along with its content.In order to bring into play such effect effectively, all preferably make it to contain more than 0.05%, more preferably make it to contain more than 0.10%.But Ni is expensive element, from the viewpoint of cost, preferably is suppressed at below 1.50%, more preferably below 1.20%.In addition, Cu and Mo then cause the excessive rising of intensity if make it to contain superfluously, might make the toughness deterioration of mother metal and HAZ, therefore all preferably are suppressed at below 1.50%, more preferably below 1.20%.

Below the B:0.005 quality %,

Though be the Plate Steel of this case the first～the cubic formula, general so-called Plate Steel, defined as JIS2402, expression be that thickness of slab is the above steel plate of 3.0mm.The Plate Steel of this case the first～the cubic formula can give play to excellent characteristic in the Plate Steel of special thickness of slab more than 50mm, but these only only is preferred mode, does not get rid of to apply the present invention to the Plate Steel that 3mm is above, be lower than the thickness of slab of 50mm.

[embodiment]

Below, enumerate embodiment and be described more specifically the present invention, but the present invention is not limited by following embodiment certainly, can also can suit to be changed in the scope of aim according to the invention, these all are included in the technical scope of the present invention.

[about the embodiment of the Plate Steel of this case first mode]

In an embodiment, at first, by vacuum melting stove (No.1～54:50kgVIF, behind the steel that No.55～57:150kgVIF) each shown in melting table 1～table 3 becomes to be grouped into, use and molten steel casting to cast sheet, re-use this casting sheet and carry out hot rolling, if No.1～54 item obtain the hot-rolled sheet of thickness of slab 50mm, if No.55～57 item obtain the hot-rolled sheet of thickness of slab 80mm.This hot-rolled sheet is heated to austenite, ferrite two phase regions, after quenching, carries out tempering at 50 ℃, become the Plate Steel of test usefulness.

When making the Plate Steel of this test usefulness, each condition of control is presented in table 4～table 6.Its condition has, soluble oxygen content [Of] in the molten steel before Al adds, the interpolation order of Al, Ti, (REM, Zr), Ca, from adding Ti to the time t1 that adds Ca, from adding Ca to the time t2 of casting beginning, t3 cooling time under 1500～1450 ℃ during casting, each addition of Al, Ti, REM, Zr, Ca.

Also have, also show in the lump, whether satisfy A1 value and B1 value for the addition of trying to achieve suitable Ca, the total addition of the Al that Plate Steel contains, Ti, REM, Zr, Ca is used for guaranteeing that diameter of equivalent circle is the preferred condition ([Ti]＞160ppm, ([REM]+[Zr])＞55ppm, (0.8≤[Ti]/[REM]+[Zr]≤11.8)) of oxide compound more than specified amount that 2 μ m are above, be lower than 5 μ m.

Also have, in table 1～table 3, REM is in quality %, is about 50% and to contain La be that the form of about 25% norium is added to contain Ce.In table 1～table 3, this element is not added in "-" expression in addition.

In addition, in table 4～table 6, the interpolation of Al, Ti, (REM, zr), Ca order by " zero " expression, is represented with " * " when adding with the order beyond it when adding with the order of Al → Ti → (REM, Zr) → Ca.Also have, because No.33 does not add Ca, so the interpolation order is represented by "-".

In addition, about from adding Ca to the time t2 of casting beginning, satisfy being represented by " zero " of aforesaid ta (branchs)＜tx (branch)＜t2 (branch)＜tb (branch), ungratifiedly represented by " * ".In addition, about Ca addition [Ca], satisfy Al≤[Ca]≤B1 relation by " zero " expression, ungratifiedly represented by " * ".

[table 1]

[table 2]

[table 3]

No	C	Si	Mn	P	S	Al	Ti	Ca	N	REM	Zr	Ni	Cu	Cr	Mo	Nb	V	B
																			47	0.14	0.10	1.90	0.005	0.003	0.003	0.025	0.0010	0.0060	0.0028	0.0025	-	-	-	-	-	-	-
48	0.11	0.15	1.98	0.005	0.003	0.003	0.025	0.0010	0.0060	0.0028	0.0025	-	-	-	-	-	-	-
																			49	0.08	0.15	1.55	0.005	0.003	0.003	0.025	0.0010	0.0060	0.0028	0.0025	1.00	-	-	-	-	-	-
50	0.08	0.15	1.55	0.005	0.003	0.003	0.025	0.0010	0.0060	0.0028	0.0025	-	1.00	-	-	-	-	-
																			51	0.08	0.10	1.55	0.005	0.003	0.003	0.025	0.0010	0.0060	0.0028	0.0025	-	-	1.00	-	-	-	-
52	0.04	0.10	1.50	0.007	0.001	0.003	0.025	0.0010	0.0060	0.0028	0.0025	1.00	0.80	0.70	-	-	-	-
																			53	0.03	0.15	1.65	0.005	0.003	0.003	0.025	0.0010	0.0060	0.0028	0.0025	0.50	1.00	0.70	-	0.010	-	-
54	0.03	0.15	1.55	0.005	0.003	0.003	0.025	0.0010	0.0060	0.0028	0.0025	0.50	1.00	0.00	0.30	0.010	-	0.0025
																			55	0.03	＜0.01	1.54	0.004	0.002	0.008	0.020	0.0007	0.0058	0.0024	0.0020	0.75	0.78	0.71	-	0.010	-	0.0031
56	0.03	＜0.01	1.54	0.004	0.002	0.008	0.020	0.0007	0.0058	0.0024	0.0020	0.75	0.78	0.71	-	0.010	0.030	0.0031
																			57	0.03	＜0.01	1.54	0.004	0.002	0.008	0.020	0.0007	0.0058	0.0024	0.0020	0.75	0.78	0.71	0.20	0.010	-	0.0031

[table 4]

[table 5]

[table 6]

Use each Plate Steel of making by above important document, by measurement try to achieve the oxide compound (oxide based inclusion) of all size individual number density, contain the individual number density of Ti nitride, production rate, tensile strength TS, yield tensile ratio YR, base metal tenacity and the HAZ toughness of intracrystalline α in the mother metal.These measuring results are presented in table 7～table 9.

(diameter of equivalent circle is lower than the measurement of individual number density of the oxide compound of 2 μ m)

From (t: test film (extract by the mode of the position of t/4 in the axle center with test film) is downcut in position thickness of slab) apart from each dark t/4 in Plate Steel surface, use the electric field radioactive scanning electronic microscope " SUPRA35 (trade(brand)name) " (hereinafter referred to as FE-SEM) of Carl Zeiss society system, the cross section that observation is parallel with the thickness of slab direction with rolling direction.Its observation condition is multiplying power: 5000 times, and field of view: 0.0024 μ m ², observe the place: 20 places.By image analysis, measure the area of each oxide compound in this field of view, calculated the diameter of equivalent circle of each oxide compound by its area.Also have, each oxide compound satisfies that above-mentioned one-tenth is grouped into, and is confirmed by EDX (energy dispersion type x-ray fluorescence analyzer).Then, above-mentioned satisfies among the oxide compound that is grouped into, and the number (N1) that diameter of equivalent circle is lower than the oxide compound of 2 μ m is converted into and is equivalent to 1mm ²In individual number density and try to achieve.But for the oxide compound of diameter of equivalent circle below 0.2 μ m, the reliability of EDX is insufficient, therefore gets rid of from analyze.

(diameter of equivalent circle more than 2 μ m, be lower than the measurement of individual number density of the oxide compound of 5 μ m)

From (t: test film (extract by the mode of the position of t/4 in the axle center with test film) is downcut in position thickness of slab), uses the FE-SEM observation cross section parallel with the thickness of slab direction with rolling direction apart from each dark t/4 in Plate Steel surface.Its observation condition is multiplying power: 1000 times, and field of view: 0.06 μ m ², observe the place: 20 places.By image analysis, measure the area of each oxide compound in this field of view, calculated the diameter of equivalent circle of each oxide compound by its area.Also have, each oxide compound satisfies that above-mentioned one-tenth is grouped into, and is confirmed by EDX.Then, above-mentioned satisfies among the oxide compound that is grouped into, with diameter of equivalent circle more than 2 μ m, the number (N2) that is lower than the oxide compound of 5 μ m is converted into and is equivalent to the individual number density among the 1mm2 and tries to achieve.

(diameter of equivalent circle is the measurement of the individual number density of the above oxide compound of 5 μ m)

From (t: test film (extract by the mode of the position of t/4 in the axle center with test film) is downcut in position thickness of slab), uses the FE-SEM observation cross section parallel with the thickness of slab direction with rolling direction apart from each dark t/4 in Plate Steel surface.Its observation condition is multiplying power: 1000 times, and field of view: 0.06 μ m ², observe the place: 20 places.By image analysis, measure the area of each oxide compound in this field of view, calculated the diameter of equivalent circle of each oxide compound by its area.Also have, each oxide compound satisfies that above-mentioned one-tenth is grouped into, and is confirmed by EDX.Then, above-mentioned satisfies among the oxide compound that is grouped into, and the number (N3) of the oxide compound of diameter of equivalent circle more than 5 μ m is converted into be equivalent to 1mm ²In individual number density and try to achieve.

(containing the measurement of the individual number density of Ti nitride)

Use transmission electron microscope (TEM), observe apart from the dark t/4 (t: the position of position thickness of slab) in the surface of each Plate Steel.Its observation condition is multiplying power: 60000 times, and field of view: 2 μ m * 2 μ m, observe the place: 5 places.By image analysis, measure the area that respectively contains the Ti nitride in this field of view, calculated the diameter of equivalent circle that respectively contains the Ti nitride by its area.Also have, contain the Ti nitride when being analyzed by EDX, detect Ti and N peak value for containing the Ti nitride.Then, be that the number that contains the Ti nitride (N4) below the 100nm is converted into and is equivalent to 1mm with diameter of equivalent circle ²In individual number density and try to achieve.

(measurement of the intracrystalline α production rate of mother metal)

From (t: test film (extract by the mode of the position of t/4 in the axle center with test film) is downcut in position thickness of slab), uses the observation by light microscope cross section parallel with the thickness of slab direction with rolling direction apart from each dark t/4 in Plate Steel surface.Its observation condition is multiplying power: 400 times, and field of view: 0.04mm ², observe the place: 20 places.In the oxide compound more than 2 μ m, be starting point with this oxide compound, when the central shaft of at least one central shaft that is the lath-shaped α that radiation dress prolongs more than the direction and oxide compound lath-shaped α group on every side on average has poor more than 15 °, judge that this oxide compound is the starting point of intracrystalline α, with the intracrystalline α production rate of (constituting the oxide compound number of the starting point of intracrystalline α)/(all oxide compound numbers) as mother metal.

(evaluation of tensile strength and yield tensile ratio)

From (t: position thickness of slab), with respect to the rectangular direction of rolling direction, No. 4 test films of extraction JIS Z 2201 are pressed JIS Z 2241 described main points and implemented tension tests, measure tensile strength TS, yield strength YS respectively apart from each dark t/4 in Plate Steel surface.Yield tensile ratio YR calculates by the such calculating of YS/TS.In the present embodiment, the TS that tries to achieve is more than the 490MPa.YR is lower than 80% the excellent that is evaluated as machinery.

(evaluation of base metal tenacity)

From apart from the dark t/4 (t: position thickness of slab) in each Plate Steel surface, extract pendulum impact test sheet (No. 4 test films of JISZ 2201) each 3 (extract by the mode of the position of t/4 in the axle center with test film), carry out pendulum impact test at 0 ℃, measuring absorption can (vE ₀) and ask its mean value, with the base metal tenacity of this mean value as each Plate Steel.In the present embodiment, the vE that tries to achieve ₀Mean value be that 200J is above, be evaluated as the base metal tenacity excellence.

(evaluation of HAZ toughness)

From apart from the dark t/4 (t: position thickness of slab) in each Plate Steel surface, extract pendulum impact test sheet (No. 4 test films of JISZ 2201) each 3 (extract by the mode of the position of t/4 in the axle center with test film), reproduce the pendulum impact test of HAZ thermal cycling V otch.Reproducing the HAZ thermal cycle conditions is the thermal process of the fusion portion of simulation electro-gas welding, and namely the hold-time under 1400 ℃ is 45 seconds, and be 800 seconds 800～500 ℃ cooling time, heat input: 100kJ/mm.For each test film that has applied this thermal cycling, the absorption under measuring 0 ℃ can (vE0), tries to achieve the mean value of 3 test films.In the present embodiment, the vE that tries to achieve ₀Mean value reach steel for building desired standards, namely 70J is above, is evaluated as the HAZ tenacity excellent.

[table 7]

[table 8]

[table 9]

No.1～23,47～57th, the example of the important document of satisfied second mode, chemical ingredients composition, oxide compound and to contain the dispersion of Ti nitride proper, tensile strength TS, yield tensile ratio YR, base metal tenacity, the HAZ toughness when heat input is 100kJ/mm all satisfy the judgement criteria of present embodiment.Namely, No.1～23,47～57 can be called the Plate Steel of the tenacity excellent of welding heat affected zone, its HAZ tenacity excellent when to implement heat input be large-line energy welding such more than the 100kJ/mm, and be that low yield strength ratio can be realized in high strength territory more than the 490MPa in tensile strength, also can guarantee good base metal tenacity in addition.

With respect to this, the comparative example of a certain important document among the important document of second party formula is not satisfied in No.24～46th, and a certain item of tensile strength TS, yield tensile ratio YR, base metal tenacity, the HAZ toughness when heat input is 100kJ/mm does not satisfy judgement criteria as can be known.

Also have, in table 4～table 6 as can be known, satisfy for whether and to be used for guaranteeing that diameter of equivalent circle is more than the 2 μ m, is lower than the preferred condition ([Ti]＞160ppm, ([REM]+[Zr])＞55ppm, (0.8≤[Ti]/[REM]+[Zr]≤11.8)) of oxide compound more than specified amount of 5 μ m, by zero * expression, but do not satisfy No.31 and the No.36 of this condition, diameter of equivalent circle is the number that 2 μ m are above, be lower than the oxide compound of 5 μ m, and the No.33 that does not then add Ca is lower.

[about the embodiment of the Plate Steel of this case second mode]

With vacuum melting stove (VIF:50kg), with table 12, condition shown in the 13 (soluble oxygen content in the molten steel, Al, Ti, REM, Zr, the interpolation order of Ca, from adding Ti to the time t1 that adds Ca, from adding Ca to the time t2 of casting beginning, and Si, Al, Ti, REM, Zr, the addition of Ca) melting table 10, various one-tenth shown in 11 are grouped into (Si, Al, Ti, REM, Zr, except the Ca) steel, become table 10, the molten steel that chemical ingredients shown in 11 is formed, t3 cooling time under 1500～1450 ℃ when making casting is table 12, condition shown in 13, so casting should molten steel and become casting sheet (cross-sectional shape: 120mm * 120mm).Heat this casting sheet and carry out hot rolling, become the hot-rolled sheet of thickness of slab 50mm.

Also have, in the table 10,11, "-" expression element does not add.In table 12,13, [REM] is about 50% and to contain La be that the form of about 25% norium is added to contain Ce." interpolation order " in the table 12,13 be the order of Al → Ti → (REM, Zr) → Ca when adding by " zero " expression, represent with " * " during with the interpolation of the order beyond it.From adding Ca to the time t2 of casting beginning, by " zero " expression, do not satisfy and represented by " * " when satisfying ta＜tx＜t2＜tb.In addition, in table 12,13, when the Ca addition satisfies A1≤[Ca]≤B1, in Ca addition one hurdle, represented by " zero ".Also have, No.32 is the example that does not add Ca, so the order of the interpolation in the table 13, t1, t2 one hurdle are represented by "-".

In addition, above-mentioned hot-rolled sheet is heated to after austenite, ferrite two phase regions quench, carries out tempering at 500 ℃.

[table 10]

[table 11]

[table 12]

The addition of ※ element, unit are quality %

[table 13]

※ element addition, unit are quality %

For each steel plate that obtains in the above described manner, to measure the individual number density of oxide compound, the individual number density that contains the Ti nitride, tensile strength, yield tensile ratio, base metal tenacity and HAZ toughness by following main points.

(1) measurement of the individual number density of oxide compound

Diameter of equivalent circle is lower than the oxide compound of 2 μ m

From (t: test film (extract by the mode of the position of t/4 in the axle center with test film) is downcut in position thickness of slab) apart from each dark t/4 in Plate Steel surface, use the electric field radioactive scanning electronic microscope " SUPRA35 (trade(brand)name) " of Carl Zeiss society system, the cross section that observation is parallel with the thickness of slab direction with rolling direction, observe multiplying power: 5000 times, field of view: 0.0024 μ m ², observe the place: 20 places.Then, by image analysis, measure the area of each oxide compound in this field of view, calculate the diameter of equivalent circle of each oxide compound according to its area.Also have, the one-tenth whether each oxide compound satisfies the oxide compound of above-mentioned second mode is grouped into, and is differentiated by EDX (energy dispersion type x-ray fluorescence analyzer).Then, will satisfy the composition of the oxide compound of second mode, the number (N1) that diameter of equivalent circle is lower than the oxide compound of 2 μ m is converted into every 1mm ²And try to achieve.

The oxide compound that diameter of equivalent circle 2 μ m are above

Making and observing multiplying power is 1000 times, and field of view is 0.06mm ², all to be lower than the measurement of individual number density of oxide compound of 2 μ m identical with diameter of equivalent circle in addition, will satisfy the composition of the oxide compound of second mode, and diameter of equivalent circle is the number (N2) of the above oxide compound of 2 μ m, is converted into every 1mm ²And try to achieve.

(2) contain the measurement of the individual number density of Ti nitride

Use transmission electron microscope (TEM), to observe multiplying power: 60,000 times, field of view: 2 μ m * 2 μ m, the condition of observing 5 places, place is observed the t/4 position (t: thickness of slab) of each steel plate.Then, by image analysis, measure the area that respectively contains the Ti nitride in this visual field, calculated the diameter of equivalent circle that respectively contains the Ti nitride by its area.Also have, when being analyzed by EDX, detect Ti and N peak value for containing the Ti nitride.Then, be that the number that contains the Ti nitride (N3) below the 100nm is converted into every 1mm with diameter of equivalent circle ²And try to achieve.

(3) measurement of the intracrystalline α production rate of mother metal

From (t: test film (extract by the mode of the position of t/4 in the axle center with test film) is downcut in position thickness of slab) apart from each dark t/4 in Plate Steel surface, use the observation by light microscope cross section parallel with the thickness of slab direction with rolling direction, observe multiplying power: 400 times, field of view: 0.04mm ², observe the place: 20 places.In the inclusion more than 2 μ m, be that the central shaft of the lath-shaped α of an end is when becoming angle more than 15 ° with the central shaft of α around the inclusion with inclusion, this inclusion is judged as the starting point of intracrystalline α, incites somebody to action (the oxide compound number of the starting point of formation intracrystalline α)/(all oxide compound numbers) as intracrystalline α production rate.

(4) tensile strength and yield tensile ratio

T/4 position (t: thickness of slab) from each steel plate, with respect to the rectangular direction of rolling direction, extract No. 4 test films of JIS Z 2201, follow JIS Z 2241 and carry out tension test, measure tensile strength TS, yield strength YS respectively, calculate yield tensile ratio YR=YS/TS.Then, TS is more than the 590MPa, and YR is lower than 80% the excellent that is evaluated as machinery.

(5) measurement of base metal tenacity

T/4 position (t: thickness of slab) extract pendulum impact test sheet (No. 4 test films of JIS Z 2201) (extract by the mode of the position of rolling direction t/4 in the axle center with test film), carry out pendulum impact test at 0 ℃, measure absorption energy (vE from each steel plate ₀).Metering needle carries out 3 test films, with the base metal tenacity of its mean value as each steel plate.VE ₀For more than the 200J, be evaluated as the base metal tenacity excellence.

(6) measurement of HAZ toughness

T/4 position (t: thickness of slab) extract pendulum impact test sheet (No. 4 test films of JIS Z 2201) (extract by the mode of the position of rolling direction t/4 in the axle center with test film), reproduce the pendulum impact test of HAZ thermal cycling V otch from each steel plate.Reproducing the HAZ thermal cycle conditions is the thermal process of the fusion portion of simulation electro-gas welding, i.e. the hold-time under 1400 ℃: 45 seconds, 800～500 ℃ cooling time: 800 seconds, heat input was 100kJ/mm.For each test film that has applied this thermal cycling, the absorption under measuring 0 ℃ can (vE0), and metering needle carries out 3 test films, tries to achieve its mean value and minimum value.VE then ₀Mean value be that 100J is above, minimum value be 70J above be evaluated as the HAZ tenacity excellent.

The result is presented in the table 14,15.

[table 14]

※ N1 is the number that diameter of equivalent circle is lower than 2 μ m in the oxide compound of second mode

N2 is that diameter of equivalent circle is the above numbers of 2 μ m in the oxide compound of second mode

N3 is the number that contains the Ti nitride of second mode

[table 15]

N3 is the number that contains the Ti nitride of second mode

No.1～22,46～53rd, the example of the important document of the satisfied second mode defined, chemical ingredients composition, oxide compound and contain the Ti nitride and suitably controlled, therefore HAZ tenacity excellent, and base metal tenacity is also excellent, and mechanical characteristics is excellent (high strength and low yield strength ratio) also.

On the other hand, No.23～45 are not satisfied and are preferably created conditions, and therefore are the examples that base metal tenacity and HAZ toughness reduce.

Therefore No.23 is that C is many, generates base metal tenacity and HAZ toughness deterioration so the island martensite body (MA) of hard is a large amount of.In addition, because the C amount causes hardenability to uprise more, becoming main body than the bainite structure that forms under the lower temperature, so YR uprises.No.24, contains the Ti nitride and reduces base metal tenacity and HAZ toughness deterioration so cause the active of Ti excessively to rise because the Si amount is few.No.25 generates base metal tenacity and HAZ toughness deterioration because the Si amount is many so the island martensite body (MA) of hard is a large amount of.No.26 is because the Mn amount is many, so intensity excessively rises base metal tenacity and HAZ toughness deterioration.In addition, because the Mn amount causes hardenability to uprise more, becoming main body than the bainite structure that forms under the lower temperature, so YR uprises.No.27,28 is respectively because P measures, the S amount is many, so base metal tenacity and HAZ toughness deterioration.No.29 is because the Al amount is many, so thick oxide compound forms base metal tenacity and HAZ toughness deterioration.No.30 is because Ti amount is few, is lower than the number of 2 μ m and contains number, base metal tenacity and the HAZ toughness deterioration of Ti nitride so can not guarantee diameter of equivalent circle among the oxide compound.No.31 is the many examples of Ti amount, and the above number of diameter of equivalent circle 2 μ m becomes many, base metal tenacity and HAZ toughness deterioration among the oxide compound.No.32 is because Ca amount is few, is lower than number, base metal tenacity and the HAZ toughness deterioration of 2 μ m so can not guarantee diameter of equivalent circle among the oxide compound.No.32 is because the Ca amount is many, so diameter of equivalent circle is lower than 2 μ m and the following oxide compound of 2 μ m all can not be adjusted to suitable number, base metal tenacity and HAZ toughness deterioration.No.34 is because the N amount is many, so because strain aging causes base metal tenacity and HAZ toughness deterioration.No.35,36 is respectively because REM measures, the Zr amount is many, so the above number of diameter of equivalent circle 2 μ m becomes many, base metal tenacity and HAZ toughness deterioration among the oxide compound.No.37,38 is respectively because Cu measures, the Cr amount is many, so intensity excessively improves base metal tenacity and HAZ toughness deterioration.In addition, owing to for Cu measures, the Cr amount is many, cause hardenability to uprise, becoming main body than the bainite structure that forms under the lower temperature, so YR uprises.

No.39 is not because the interpolation order of Al, Ti, REM, Zr, Ca is preferred, No.41,42 incorrect to the time t1 that adds Ca from adding Ti, No.42,43 incorrect to the time t2 of casting beginning from adding Ca, be lower than the number of the oxide compound of 2 μ m so can not guarantee diameter of equivalent circle, base metal tenacity and HAZ toughness deterioration.No.44 is because 1500～1450 ℃ of t3 cooling time down in when casting are long, so the number change of the above oxide compound of diameter of equivalent circle 2 μ m is many, and base metal tenacity and HAZ toughness deterioration.The time t2 that No.45 begins because of extremely casting from interpolation Ca is below tx, so can not guarantee to contain the number of Ti nitride, base metal tenacity and HAZ toughness deterioration.

[about the embodiment of the Plate Steel of this case Third Way]

At first, with vacuum melting stove (VIF:150kg), behind melting table 16 and the steel that each shown in the table 17 becomes to be grouped into, use and should molten steel casting cast sheet (cross-sectional shape: 150mm * 250mm), re-use this casting sheet and carry out hot rolling obtains the hot-rolled sheet of thickness of slab 80mm.Also have, change in order to make the non-recrystallization draft P shown in table 18 and the table 19, adjust by slab thickness is changed.

When making this hot-rolled sheet (Plate Steel), each condition of control is presented in table 18 and the table 19.Its condition has, soluble oxygen content [Of] in the molten steel before Al (Ti) adds, the interpolation order of Al, Ti, REM, Zr, Ca, from adding Ti to the time t1 that adds Ca, from adding Ca to the time t2 of casting beginning, Heating temperature Th before rolling, rolling preceding t4 heat-up time, non-recrystallization draft P.

Also have, in table 16 and table 17, [REM] in quality %, contains Ce and be about 50% and to contain La be that the form of about 25% norium is added.In table 16 and table 17, this element is not added in "-" expression in addition.

In addition in table 16 and table 17, when being the order of (Al →) Ti → (REM, zr) → Ca in proper order, the interpolation of Al, Ti, REM, Zr, Ca by " zero " expression, represented by " * " during order beyond it.

[table 16]

[table 17]

[table 18]

No.	[O R measures %)	The interpolation order	t1(m in)	t2(m in)	t3(t)	Th(℃)	t4(hr)	P(％)
									1	0.0083	○	10	45	276	1100	3.1	47
2	0.0055	○	10	55	265	1140	2.5	47
									3	0.0045	○	8	45	277	1100	2.8	47
4	0.0071	○	10	45	274	1100	2.8	47
									5	0.0036	○	10	45	289	1060	3.0	58
6	0.0050	○	10	80	256	1100	2.8	58
									7	0.0048	○	10	45	270	1100	3.0	47
8	0.0053	○	5	45	265	1100	3.2	47
									9	0.0066	○	8	45	271	1110	4.7	47
10	0.0040	○	10	80	272	1100	3.5	54
									11	0.0069	○	10	45	270	1100	3.0	47
12	0.0053	○	10	45	261	1150	2.3	47
									13	0.0041	○	5	45	279	1100	3.0	54
14	0.0055	○	10	45	257	1090	3.1	54
									15	0.0036	○	15	45	264	1120	3.0	47
16	0.0046	○	10	60	244	1100	3.0	58
									17	0.0063	○	5	45	183	1100	3.8	54
18	0.0028	○	10	60	255	1100	2.8	58
									19	0.0033	○	10	45	250	1100	3.0	51
20	0.0068	○	18	45	276	1100	3.1	54
									21	0.0055	○	10	65	273	1080	2.7	47
22	0.0030	○	10	45	273	1080	3.2	47
									23	0.0044	○	10	45	268	1100	2.8	50
24	0.0077	○	10	45	271	1100	3.0	47
									25	0.0061	○	5	45	266	1060	2.6	47
26	0.0072	○	8	70	280	1100	3.2	54
									27	0.0053	○	10	70	277	1100	3.0	47
28	0.0046	○	10	70	274	1180	3.5	47
									29	0.0050	○	10	45	274	1170	3.4	47
30	0.0038	○	10	50	274	1100	4.3	47

[table 19]

No.	[O R quality %	The interpolation order	t1(m in)	t2(m in)	t3(s)	Th(℃)	t4(hr)	P(％)
									31	0.0118	○	10	45	255	1100	3.5	47
32	0.0018	○	5	50	271	1150	3.4	47
									33	0.0061	×	8	70	268	1100	3.5	54
34	0.0051	○	2	50	270	1080	3.5	58
									35	0.0042	○	25	50	241	1080	3.2	54
36	0.0058	○	10	30	266	1160	2.8	54
									37	0.0060	○	10	100	276	1100	2.4	47
38	0.0070	○	5	45	310	1100	2.5	47
									39	0.0061	○	5	80	266	1020	4.8	47
40	0.0038	○	18	80	271	1240	2.4	50
									41	0.0082	○	10	45	270	1100	1.8	47
42	0.0038	○	10	50	270	1100	3.1	36
									43	0.0061	○	10	45	281	1060	2.8	47
44	0.0045	○	15	50	263	1100	3.0	58
									45	0.0035	○	10	45	278	1100	3.0	58
46	0.0028	○	10	45	272	1140	2.4	50
									47	0.0081	○	15	45	272	1100	2.8	54
48	0.0053	○	10	50	266	1150	3.0	47
									49	0.0024	○	10	45	281	1180	3.2	47
50	0.0043	○	10	45	284	1100	2.8	47

Use each hot-rolled sheet (Plate Steel) of making by above important document, by following measurement, obtain the individual number density N1 that diameter of equivalent circle is lower than the inclusion of 2 μ m, individual number density N2 and the HAZ toughness of the inclusion of diameter of equivalent circle more than 2 μ m.These measuring results be presented at 20 and table 21 in.

From (t: test film (extract by the mode of the position of t/4 in the axle center with test film) is downcut in position thickness of slab) apart from each dark t/4 in Plate Steel surface, use the electric field radioactive scanning electronic microscope " SUPRA35 (trade(brand)name) " (hereinafter referred to as FE-SEM) of Carl Zeiss society system, the cross section that observation is parallel with the thickness of slab direction with rolling direction.Its observation condition is multiplying power: 5000 times, and field of view: 0.0024 μ m ², observe the place: 20 places.By image analysis, measure the area of each oxide compound in this field of view, calculated the diameter of equivalent circle of each inclusion by its area.Also have, each inclusion satisfies that above-mentioned one-tenth is grouped into, and is confirmed by EDX (energy dispersion type x-ray fluorescence analyzer).The acceleration voltage that the one-tenth that EDX carries out is grouped into when measuring is 15kV, and Measuring Time is 100 seconds.Then, the number (N1) that diameter of equivalent circle is lower than the inclusion of 2 μ m is converted into and is equivalent to 1mm ²In individual number density and try to achieve.But for the oxide compound of diameter of equivalent circle below 0.2 μ m, the reliability of EDX is insufficient, therefore gets rid of from analyze.

(measurement of the individual number density of the oxide compound of diameter of equivalent circle more than 2 μ m)

From (t: test film (extract by the mode of the position of t/4 in the axle center with test film) is downcut in position thickness of slab), uses the FE-SEM observation cross section parallel with the thickness of slab direction with rolling direction apart from each dark t/4 in Plate Steel surface.Its observation condition is multiplying power: 1000 times, and field of view: 0.06 μ m ², observe the place: 20 places.By image analysis, measure the area of each inclusion in this field of view, calculated the diameter of equivalent circle of each inclusion by its area.Also have, each inclusion satisfies that above-mentioned one-tenth is grouped into, and is confirmed by EDX (energy dispersion type x-ray fluorescence analyzer).The acceleration voltage that the one-tenth that EDX carries out is grouped into when measuring is 15kV, and Measuring Time is 100 seconds.Then, above-mentioned satisfies among the oxide compound that is grouped into, and the number (N2) of the inclusion of diameter of equivalent circle more than 2 μ m is converted into be equivalent to 1mm ²In individual number density and try to achieve.

(evaluation of base metal tenacity)

Extract the welding joint test film from each Plate Steel, after the processing of V groove, implement electro-gas welding with heat input 50kJ/mm.From these test films, extract each 3 of pendulum impact test sheets (the V nick-break test sheet of JIS Z 2202), (t: the welding line of position thickness of slab) (welded bonds) neighborhood HAZ is processed with otch to this test film at the surperficial dark t/4 apart from each Plate Steel, carry out pendulum impact test under-40 ℃, measuring absorption can (vE _-40), ask its mean value and minimum value.According to this measuring result, vE _-40Mean value surpass 180J, minimum value surpasses 120J, is evaluated as the HAZ tenacity excellent.

In addition, except implement electro-gas welding with 60kJ/mm, all carry out pendulum impact test with the condition identical with above-mentioned condition, the absorption of measuring 3 test films can (vE _-40), ask its mean value.According to its measuring result, vE _-40Mean value surpass 120J be evaluated as the HAZ tenacity excellent.

[table 20]

[table 21]

The example of the important document of Third Way is satisfied in No.1～30th, the dispersions of chemical ingredients composition, inclusion etc. suitably, HAZ toughness (mean value) excellence when the HAZ toughness when heat input is 50kJ/mm (mean value and minimum value), and heat input as can be known is 60kJ/mm.That is, No.1～30 can be called the Plate Steel of the tenacity excellent of welding heat affected zone.

With respect to this, the comparative example of a certain important document in the important document of Third Way is not satisfied in No.31～50th, each of HAZ toughness (mean value) when the HAZ toughness when heat input is 50kJ/mm (mean value and minimum value), and heat input as can be known is 60kJ/mm do not satisfy judgement criteria.

[about the embodiment of the Plate Steel of the cubic formula of this case]

At first, with vacuum melting stove (VIF:150kg), melting table 22 becomes to be grouped into each shown in the table 23 (to be also had, records and narrates the quality % after adding about Al, Ti, REM, Zr, Ca.) steel after, use should molten steel casting casting sheet (cross-sectional shape: 150mm * 250mm), re-use this casting sheet and carry out hot rolling obtains the hot-rolled sheet of thickness of slab 50mm.

When making this hot-rolled sheet (Plate Steel), each condition of control is presented in table 24 and the table 25.Its condition has, soluble oxygen content [O] in the molten steel before Al adds, the interpolation order of Al, Ti, REM, Zr, Ca, [Ti]/([REM]+[Zr]), from adding Ti to the time t1 that adds Ca, from adding Ca to the time t2 of casting beginning, t3 cooling time under 1500～1450 ℃ during casting, Ca addition [Ca].

Also have, in table 22 and table 23, REM is in quality %, contains Ce and be about 50% and to contain La be that the form of about 25% norium is added.In table 22 and table 23, this element is not added in "-" expression in addition.

Also have, in table 22 and the table 23, the interpolation of Al, Ti, REM, Zr, Ca be in proper order the order of Al → Ti → (REM, Zr) → Ca when adding by " zero " expression, represent with " * " during for its in addition order.In addition, about from adding Ca to the time t2 of casting beginning, satisfy being represented by " zero " of ta (branch)＜t2 (branch)＜tb (branch), do not satisfy and represented by " * ".

In addition, about Ca addition [Ca], by " zero " expression, do not satisfy and represented by " * " when satisfying aforesaid A1≤[Ca]≤B1.

Use each hot-rolled sheet (Plate Steel) of making by above important document, obtain individual number density, HAZ toughness, the tensile strength of the oxide compound (oxide based inclusion) of all size by measurement.These measuring results be presented at 24 and table 25 in.

[table 22]

[table 23]

[table 24]

[table 25]

In addition, among the oxide compound of measuring, formation element except deoxidation, in quality %, satisfy 10%＜Ti, Al＜20%, 8%＜Ca＜40%, 5%＜REM＜50%, 5%＜Zr＜40%, and satisfy 10%＜REM+Zr＜70%, the mass ratio of Ti and Ca surpasses 1, is lower than among 1.4 the oxide compound in addition, and the number (NA) that diameter of equivalent circle is lower than the oxide compound of 2 μ m is converted into and is equivalent to 1mm ²In individual number density and try to achieve.

From (t: test film (extract by the mode of the position of t/4 in the axle center with test film) is downcut in position thickness of slab), uses the FE-SEM observation cross section parallel with the thickness of slab direction with rolling direction apart from each dark t/4 in Plate Steel surface.Its observation condition is multiplying power: 1000 times, and field of view: 0.06 μ m ², observe the place: 20 places.By image analysis, measure the area of each oxide compound in this field of view, calculated the diameter of equivalent circle of each oxide compound by its area.Also have, each oxide compound satisfies that above-mentioned one-tenth is grouped into, and is confirmed by EDX (energy dispersion type x-ray fluorescence analyzer).Then, with diameter of equivalent circle more than 2 μ m, the number (N2) that is lower than the oxide compound of 5 μ m is converted into and is equivalent to 1mm ²In individual number density and try to achieve.

From (t: test film (extract by the mode of the position of t/4 in the axle center with test film) is downcut in position thickness of slab), uses the FE-SEM observation cross section parallel with the thickness of slab direction with rolling direction apart from each dark t/4 in Plate Steel surface.Its observation condition is multiplying power: 1000 times, and field of view: 0.06 μ m ², observe the place: 20 places.By image analysis, measure the area of each oxide compound in this field of view, calculated the diameter of equivalent circle of each oxide compound by its area.Also have, each oxide compound satisfies that above-mentioned one-tenth is grouped into, and is confirmed by EDX (energy dispersion type x-ray fluorescence analyzer).Then, the number (N3) of the oxide compound of diameter of equivalent circle more than 5 μ m is converted into is equivalent to 1mm ²In individual number density and try to achieve.

(evaluation of HAZ toughness)

From apart from the dark t/4 in surface of each Plate Steel (t: position thickness of slab), extract the test film of 12.5 * 32 * 55mm, 1400 ℃ keep 5 seconds down after, be 200 seconds and control speed cools off cooling times that makes 800～500 ℃.This is simulation corner joint union-melt weld (heat input: thermal cycling 50kJ/mm).Extract each 3 of pendulum impact test sheets (JIS Z 2202V nick-break test sheet) from these test films, carry out pendulum impact test under 0 ℃, measuring absorption can vE0.According to these 3 capable pendulum impact test measuring results, minimum absorption can vE0 (min) surpasses 70J, is evaluated as the HAZ tenacity excellent.

(evaluation of tensile strength and yield tensile ratio)

From (t: position thickness of slab), with respect to the rectangular direction of rolling direction, No. 4 test films of extraction JIS Z 2201 are implemented the tension test of JIS Z 2241, try to achieve tensile strength TS apart from each dark t/4 in Plate Steel surface.Satisfy the excellent strength that is evaluated as of TS＞780MPa.

No.1～32nd, the example of the important document of satisfied cubic formula, the dispersions of chemical ingredients composition, oxide compound etc. are suitable, as can be known HAZ toughness and excellent strength.That is, No.1～32 can be called big line can after the intensity of HAZ and the Plate Steel of tenacity excellent.

Also have, in general, the tensile strength of HAZ toughness has the tendency that shows negative correlation.In the example of the important document that satisfies cubic formula, if relatively tensile strength is the No.26,32 of 810～820MPa, then an oxide compound number NA does not satisfy its E of No.6 of the described important document of second invention ₀(min) be lower than 110kJ.

With respect to this, the comparative example of a certain important document among the important document of cubic formula is not satisfied in No.33～64th, and at least one side of HAZ toughness, intensity does not satisfy judgement criteria as can be known.

In detail and with reference to specific embodiment the application has been described, but can be under the premise without departing from the spirit and scope of the present invention in addition various changes and modification, this area practitioner should be clear.

The application is based on the Japanese patent application (2011-044075) of the Japanese patent application (the special 2010-218205 of hope) of the Japanese patent application (the special 2010-116485 of hope) of the Japanese patent application (the special 2010-088347 of hope) of on April 7th, 2010 application, application on May 20th, 2010, application on September 29th, 2010, the Japanese patent application of application on September 29th, 2010 (special be willing to 2010-219511), application on March 1st, 2011, its content this to some extent with reference to and quote.

Claims

1. a Plate Steel is characterized in that, contains C:0.02～0.15 quality %; Si:0～0.46 quality %; Mn:1.0～2.0 quality %; P: bigger than 0 quality %, below 0.03 quality %; S: bigger than 0 quality %, below 0.015 quality %; Al:0～0.07 quality %; Ti:0.010～0.080 quality %; Ca:0.0005～0.010 quality %; N:0.002～0.020 quality %;

And, also containing more than one that from REM:0.0001～0.02 quality %, Zr:0.0001～0.02 quality %, select, surplus is iron and unavoidable impurities, wherein,

The formation element that removes deoxidation satisfies 10%＜Ti, Al＜20%, 5%＜Ca＜40% in quality %, and any one the oxide compound at least that satisfies in 5%＜REM＜50%, 5%＜Zr＜40% exists in the mode of the condition that satisfies following formula (1) and (2)

(1) the described oxide compound that is lower than 2 μ m in diameter of equivalent circle is 200/mm ²More than,

(2) diameter of equivalent circle is that the above described oxide compound of 2 μ m is 100/mm ²Below,

And, in described oxide compound, among diameter of equivalent circle is oxide compound more than the 2 μ m,

Diameter of equivalent circle is that 2 μ m oxide compound above, that be lower than 5 μ m exists 30～70/mm ²,

And diameter of equivalent circle is that the existence of the above oxide compound of 5 μ m is lower than 30/mm ²,

And, contain the Ti nitride, and described containing among the Ti nitride, diameter of equivalent circle is that the following Ti nitride that contains of 100nm exists 5 * 10 ⁶Individual/mm ²More than.

2. a Plate Steel is characterized in that, contains C:0.02～0.15 quality %; Si:0.01～0.35 quality %; Mn:1.0～2.0 quality %; P: bigger than 0 quality %, below 0.03 quality %; S: bigger than 0 quality %, below 0.015 quality %; Al:0～0.07 quality %; Ti:0.010～0.080 quality %; Ca:0.0005～0.010 quality %; N:0.002～0.020 quality %;

(1) the described oxide compound that is lower than 2 μ m in diameter of equivalent circle is 300/mm ²More than,

Described oxide compound is the oxide compound that also satisfies the relation of Al/ (REM+Zr)＜0.7,

3. a Plate Steel is characterized in that, contains C:0.02～0.15 quality %; Si:0～0.25 quality %; Mn:1.0～2.0 quality %; P: bigger than 0 quality %, below 0.03 quality %; S: bigger than 0 quality %, below 0.015 quality %; Al:0～0.07 quality %; Ti:0.010～0.080 quality %; Ca:0.0005～0.010 quality %; N:0.002～0.020 quality %;

And, containing REM and Zr both sides in the scope of REM:0.0003～0.02 quality %, Zr:0.0003～0.02 quality %, surplus is iron and unavoidable impurities, wherein, the A value of being tried to achieve by following formula satisfies 0.4≤A≤2.4,

A＝10 ⁴×{[Ti]-0.7×([O]-0.09×[Al]-0.16×[Ca]-0.07×[REM]-0.04×[Zr])}×[N]

Wherein, [] represents the mass percentage content of each element in the following formula,

And, the formation element that removes deoxidation satisfies 10%＜Ti, Al＜20%, 5%＜Ca＜40% in quality %, and any one the oxide compound at least that satisfies in 5%＜REM＜50%, 5%＜Zr＜40% exists in the mode of the condition that satisfies following formula (1) and (2)

And described oxide compound is the oxide compound that also satisfies 3%＜N, 2＜Ti/N.

4. a Plate Steel is characterized in that, contains C:0.02～0.15 quality %; Si:0.02～0.50 quality %; Mn:1.4～3.0 quality %; P: bigger than 0 quality %, below 0.03 quality %; S: bigger than 0 quality %, below 0.015 quality %; Al:0～0.07 quality %; Ti:0.010～0.080 quality %; Ca:0.0005～0.010 quality %; N:0.002～0.020 quality %;

And, contain REM and Zr both sides in the scope of REM:0.0003～0.02 quality %, Zr:0.0003～0.02 quality %, and contain Cr:0.5～2.0 quality %, surplus is iron and unavoidable impurities, wherein, the D value of being tried to achieve by following formula satisfies 238＜D＜388

D＝62×[Mn]+27×[Ni]+111×[Cr]

And, at diameter of equivalent circle among the oxide compound more than the 2 μ m, diameter of equivalent circle more than 2 μ m, there is 30～70/mm in the oxide compound that is lower than 5 μ m ², and the existence of the oxide compound of diameter of equivalent circle more than 5 μ m is lower than 30/mm ²

5. Plate Steel according to claim 4 is characterized in that, among described oxide compound, is also to satisfy 10%＜REM+Zr＜70%, and the mass ratio Ti/Ca of Ti and Ca satisfy to surpass 1, is lower than 1.4 oxide compound.

6. according to each described Plate Steel in the claim 1～3, it is characterized in that, also contain at least one group who from following (a)～(c), selects,

(c) below the B:0.005 quality %.

7. according to claim 4 or 5 described Plate Steels, it is characterized in that described Plate Steel also contains at least one group who selects as other elements from following (a ')～(c '),

(c ') below the B:0.005 quality %.