CN101787488B - Steel material of a welding heat effect part with excellent toughness - Google Patents

Steel material of a welding heat effect part with excellent toughness Download PDF

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CN101787488B
CN101787488B CN2010101049977A CN201010104997A CN101787488B CN 101787488 B CN101787488 B CN 101787488B CN 2010101049977 A CN2010101049977 A CN 2010101049977A CN 201010104997 A CN201010104997 A CN 201010104997A CN 101787488 B CN101787488 B CN 101787488B
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inclusion
steel
cas
cao
haz
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CN101787488A (en
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加藤拓
太田裕己
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Kobe Steel Ltd
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Kobe Steel Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium

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  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

The invention relates to a steel material which satisfies the specified chemical composition. The following impurities are dispersed: when the length at maximum width is set as the size of the impurity along the maximum projection length direction of the impurity when observing the impurity perpendicular to a microscope, the size is more than 2Mum and the impurities satisfy the following formulas (1) (2). The generation of massive TiN is prevented and the HAZ toughness is excellent. 0.01<=[Ca]/[Al]<=0.50...(1), 0.08<=([CaO]+[CaS])/([A]2O3])<=1.80...(2), wherein [Ca], [Al], [CaO], [CaS] and [Al2O3} respectively represent the content (mass%) of the Ca, Al, CaO, CaS and Al2O3 in the impurity.

Description

The steel of the tenacity excellent of welding heat affected zone
Technical field
The present invention relates to the steel that welded structure was suitable for of bridge, high-rise and boats and ships etc., particularly the tenacity excellent of the heat affected zone (following only be called " HAZ ") after the large-line energy welding steel.
Background technology
In recent years, along with the maximization of above-mentioned various welded structures, the heavy wall of steel are urged into, from the viewpoint of the reduction of manufacturing cost, the high efficiency of operation etc., weld heat input surpasses the such large-line energy welding of 400kJ/cm and is applied.
But; If carry out the large-line energy welding; Then HAZ is kept back Xu Leng for a long time in pyritous austenite (γ) zone; γ when therefore heating grows up, and causes this thickization of organizing that is generated as representative with thick ferritic (α) crystal grain in the process of cooling easily, has the problem of the easy deterioration of toughness of this part.From the viewpoint of security,, also can stablize and keep the technology of the toughness (below be called " HAZ " toughness) of HAZ high-levelly even then require a kind ofly in large-line energy welding.
As the method that is used to guarantee that the HAZ flexible is main; Proposition has the γ crystal grain-growth pinning (being designated hereinafter simply as " γ pinning ") by the inclusion particle that comes autoxidisable substance, nitride, sulfide etc., generates the miniaturization of carrying out of organizing by the intracrystalline α that with the inclusion particle is starting point.As such technology; Shown in for example Japanese special public clear 55-26164 number; Proposition has following this technology: it is through making the fine TiN of dispersion in the steel as γ pinning particle; Thereby be suppressed at thickization of carrying out the austenite crystal that large-line energy when welding produce in HAZ, to suppress HAZ flexible deterioration.But in this technology, except carrying out the reheat with suitable temperature after the casting, also not considering the inclusion morphology in the steel, be that the thick TiN of nuclear generates with the inclusion, so practical situation is that HAZ toughness may not be good.
On the other hand, in TOHKEMY 2001-98340 number, also proposing has a technology, and it is suitably changed through the addition that makes Ti and N, and the dispersion state of TiN is suitably changed, and with thickization of inhibition austenite crystal, thereby suppresses HAZ flexible deterioration.But, only control the addition of Ti and N, in the process of molten steel solidification, the density unevenness one of Ti and N is being difficult to obtain the such problem of sufficient dispersion effect.Particularly finally solidifying portion etc., Ti and N multiviscosisty, thick TiN separates out in molten steel, so HAZ toughness deterioration on the contrary.
Summary of the invention
The present invention is in view of doing under this situation, and its purpose is, a kind of generation that suppresses thick TiN is provided, the steel of HAZ tenacity excellent.
Can solve the steel of the present invention of above-mentioned problem, contain the C:0.02～0.15% (meaning of " quality % " respectively.Relate under the chemical ingredients with), Si:0.03～1.0%, Mn:1.0～2.0%, below the P:0.02%, S:0.0002～0.01%, Al:0.005～0.08%, Ti:0.003～0.03%, Ca:0.0003～0.005%, N:0.001～0.01% and below the O:0.004%; Surplus is made up of iron and inevitable impurity; And disperse following inclusion: when the maximum length of width is made as inclusion big or small on the direction of the maximal projection length of the inclusion in the time of will be perpendicular to microscopic examination; Its size is more than the 2 μ m, and this inclusion satisfies following formula (1) and formula (2).
0.01≤[Ca]/[Al]≤0.50 …(1)
0.08≤([CaO]+[CaS])/([Al 2O 3])≤1.80 …(2)
Wherein, [Ca], [Al], [CaO], [CaS] and [Al 2O 3], represent Ca, Al, CaO, CaS and Al in the inclusion respectively 2O 3Content (quality %).
Also have, the size of above-mentioned so-called inclusion, the meaning be with the vertical direction of maximal projection length of inclusion on, the length of the maximum part of width, its size can be measured through the picture processing of SEM and EPMA etc. at an easy rate.In addition, [Ca], [Al], [CaO], [CaS] and [Al in following formula (1) and the formula (2) 2O 3], the meaning is that contained aforementioned size is the composition of the above whole inclusiones of 2 μ m in the mensuration steel, the content when converting as independent inclusion.In addition, the so-called dispersion, the meaning is that size is the above inclusiones of 2 μ m, in mother metal, roughly disperses such state equably independently.
In steel of the present invention, as the form of inclusion, preferred said size is that the above Ti that contains of 2 μ m is the number that contains the Ti inclusion more than 10%, is below 7% of number of the whole inclusiones more than the 2 μ m for said size.
In steel of the present invention, also contain like inferior element also useful as required: (a) below the B:0.005%, below the Nb:0.06%, below the V:0.1%, below the Cu:1.5%, below the Ni:3.5%, below the Cr:1.5% and at least a kind of element among below the Mo:1.5%; (b) below the Zr:0.05%, below the REM:0.005% and at least a kind of element among below the Mg:0.005%, through containing these elements, according to its kind, the characteristic of steel will be further improved.
According to the present invention; Through being formed, chemical composition of steel includes in the suitable scope; And making the size with specified chemical composition composition is that the above inclusion of 2 μ m suitably disperses; The generation of the TiN that can either realize both having suppressed thick has realized the steel of the tough property improvement of welding heat affected zone (HAZ) again, and such steel are extremely useful as the steel that are applied to welded structures such as bridge, high-rise and boats and ships.
Description of drawings
Fig. 1 is expression ([CaO]+[CaS])/([Al 2O 3]) with the graphic representation of the relation of fracture transition temperature vTrs.
Fig. 2 is the graphic representation of the relation of the expression ratio and the fracture transition temperature vTrs that contain the Ti oxide compound.
Fig. 3 is the explanatory view of form of the inclusion in the steel plate of expression No.25.
Fig. 4 is the explanatory view of form of the inclusion in the steel plate of expression No.27.
Fig. 5 is the explanatory view of form of the inclusion in the steel plate of expression No.35.
Fig. 6 is the explanatory view of form of the inclusion in the steel plate of expression No.37.
Embodiment
Present inventors influence HAZ toughness essential factor when welding for large-line energy, study from various angles.Its result distinguishes that the major cause of HAZ toughness deterioration is the thick existence that contains the Ti inclusion, and such Ti inclusion that contains mainly is TiN or TiO in molten steel solidification stage crystallization 2
For the essential factor that above-mentioned such thick generative process that contains the Ti inclusion and this inclusion make HAZ toughness deterioration, can consider as follows.At first, carry out deoxidation through in molten steel, adding Al, the result is the Al that in molten steel, is dispersed with the shape that is flattening (flat) 2O 3Solid, produce solid δ mutually or the γ phase at liquidus temperature (for example below 1535 ℃) by the part of molten steel, Ti, N, S multiviscosisty in remaining liquid phase.Then, if surpass the solubility product of Ti and N, then with solid Al 2O 3For nuclear, TiN is separated out, and do not solidifying the S of portion multiviscosisty, thereby solidus temperature is reduced.Consider finally to grow up at the temperature province between liquidus line and the solidus curve (for example about 1535～1490 ℃) TiN.
Consider such formation mechanism, present inventors just are used for can either suppressing to contain the generation of Ti inclusion, can access the further research repeatedly of good HAZ flexible important document again.Its result finds; If suitably adjusting the chemical ingredients of steel (mother metal) forms; And satisfy the relation of following formula (1) and formula (2), and the size that is dispersed with aforementioned manner definition is the inclusion more than the 2 μ m, then can either suppresses to contain the generation of Ti inclusion; Can access good HAZ toughness again, thus the present invention fully.
0.01≤[Ca]/[Al]≤0.50 …(1)
0.08≤([CaO]+[CaS])/([Al 2O 3])≤1.80 …(2)
Wherein, [Ca], [Al], [CaO], [CaS] and [Al 2O 3], represent Ca, Al, CaO, CaS and Al in the inclusion respectively 2O 3Content (quality %).
In steel of the present invention, the dispersive inclusion need satisfy following formula (1) and formula (2), stipulates the reasons are as follows of these conditions.
[[Ca]/[Al]: 0.01～0.50, the relation of following formula (1)]
The promotion of revealing for the eutectic that suppresses inclusion and the eutectic of molten steel are revealed, in addition for the crystallization of the TiN that suppresses to cause because of CaS, and in order to obtain best (CaO) and (Al 2O 3) ratio, need control the interpolation ratio of Ca and Al.In order to obtain these effects, need [Ca]/[Al] is controlled in 0.01～0.50 the scope.If the value of [Ca]/[Al] is lower than 0.01, the inclusion eutectic is revealed, thick TiN crystallization makes HAZ toughness deterioration.On the other hand, if the value of [Ca]/[Al] surpasses 0.50, then except the cleanliness factor that makes steel reduces, be accompanied by the minimizing of the addition of Al, TiO 2Separate out, therefore make HAZ toughness deterioration.Also have, be limited to 0.40 on the value of [Ca]/[Al] preferred.
[([CaO]+[CaS])/([Al 2O 3]): 0.08～1.80, (relation of following formula (2))]
Through being become, inclusion contained in the steel (being oxide based inclusion basically) contains CaO, CaS and Al 2O 3Complex inclusion, the inclusion eutectic is revealed, on the other hand because suppress the reduction of the fusing point of molten steel, so also can suppress the crystallization of thick TiN.And, because the separating out of CaS can be reduced the generative capacity from the TiN of the complex inclusion that contains Ca and Al, so can suppress the crystallization of thicker TiN.In order to bring into play these effects, need with size contained in the steel ([CaO]+[CaS])/([Al of the inclusion more than the 2 μ m 2O 3]) value be controlled in 0.08～1.80 the scope.(if [CaO]+[CaS])/([Al 2O 3]) value be lower than 0.08, then inclusion fully eutectic reveal, in addition because the amount of separating out of CaS also is suppressed, so thick TiN crystallization makes HAZ toughness deterioration.On the other hand, if ([CaO]+[CaS])/([Al 2O 3]) value surpass 1.80, the cleanliness factor of steel is reduced, and must reduce Al addition, TiO 2The amount of separating out increase, therefore make HAZ toughness deterioration.Also has ([CaO]+[CaS])/([Al 2O 3]) value preferably be limited to 0.10 down, be limited to 1.1 on preferred.
In steel of the present invention, satisfy the inclusion (complex inclusion) of above-mentioned important document through suitable dispersion, can make HAZ toughness good, but as above-mentioned aim showed, corresponding with it, (for example except that TiN, also comprise TiO at the Ti inclusion that contains of TiN representative 2) among, preferably reducing its size as far as possible is the above thick inclusiones of 2 μ m.From this viewpoint, in steel of the present invention, as the form of inclusion, the size that preferably contains Ti and be more than 10% is the above numbers that contain the Ti inclusion of 2 μ m, is that size is below 7% of number of the above whole inclusion of 2 μ m.Also have,,, can not cause what influence HAZ toughness regardless of its number in fine like this containing in the Ti inclusion (particularly below the 0.5 μ m) of big or small less than 2 μ m.
About through making the inclusion that satisfies above-mentioned such important document disperse to make the good mechanism of HAZ toughness of steel; Can be to its explanation of all illustrating; If but also considering the formation mechanism of above-mentioned thick TiN, then can consider as follows.
If in molten steel, add Al, then aluminum oxide (Al 2O 3) form, but, then becoming complex inclusion at this moment if contain Ca simultaneously, fusing point reduces, and becomes liquid state.This state still can continue in the initial stage of solidifying of iron.If be in this state, even the nuclear that then during TiN separates out, does not also have to separate out exists, separating out of TiN is suppressed.Thereafter, even TiN separates out, because iron is the state that solidifies, TiN can't thickization.
In addition, Al 2O 3Become solid with CaO and separate out (separating out), make the liquid phase multiviscosisty of S at iron from liquid phase.At this moment, as if the liquid phase multiviscosisty of S at iron, then iron becomes the state that is difficult to solidify.This state promotes thickization of TiN, but because there be (S becomes CaS) in CaS, so think that S does not have multiviscosisty, TiN is difficult to thickization.
Can know in addition; CaS lattice match property with respect to TiN poor (for example " tissue that steel inclusion forms with the present situation of material control and the research of control mechanism " (society) Japanese iron and steel institute fundamental research meeting is put down in September, 7 and issued); Think that CaS is difficult to become the crystallization point of TiN; Also be because the existence of CaS, thereby become the reason that thickization of TiN is suppressed.
Want to realize the dispersion state of above-mentioned such inclusion, follow following step and make steel and get final product.At first, make Al concentration in the molten steel become 0.005～0.08% and after adding Al and carrying out deoxidation, with device for deoxidizing (for example RH device) enforcement deoxidation more than 10 minutes.Thereafter, add Ti before finish to deoxidation 5 minutes, circulation is more than 1 minute thereafter.Finish to add Ca after the deoxidation, in each inclusion more than said size is 2 μ m, make Al 2O 3, MnS, MnO, CaO, CaS the quality (100%) of total in shared Al 2O 3, CaO and CaS the standard deviation of quality %, be respectively σ (Al 2O 3Cast behind)≤30 quality %, σ (CaO)≤15 quality % and σ (CaS)≤20 quality % and get final product.At this, said σ (Al 2O 3) looking like is, when investigating the inclusion of the majority in the steel, about the Al in each inclusion 2O 3Contain ratio (with respect to the Al in the inclusion 2O 3, MnS, MnO, CaO, CaS the quality % of total quality) the standard deviation of distribution.σ (CaO), σ (CaS) also are the same meanings.The composition of each inclusion can be investigated with this method that [composition measuring of inclusion] in the explanation of embodiment at the back set forth.Inclusion for majority carries out such mensuration, tries to achieve standard deviation by the data that obtain and gets final product.
Initial Al deoxidation power of adding is strong, combines formation Al with oxygen in the molten steel 2O 3Then utilize de-gassing vessel to make thick Al 2O 3Float separation Deng impurity.To finishing before 5 minutes of the degassing extraction rate of Ti to be improved, circulation more than 1 minute thereafter, thus Ti is evenly dispersed in the molten steel.
After finishing the degassing, add Ca, make generate CaO and CaS in the molten steel after, owing to Al 2O 3, CaO and CaS the standard deviation of quality % be respectively σ (Al 2O 3)≤30 quality %, σ (CaO)≤15 quality % and σ (CaS)≤20 quality %, CaO and CaS and Al 2O 3Combine above-mentioned such (CaO+CaS) and Al equably 2O 3Have good equilibrated [relation of following formula (2)], contain Al 2O 3, CaO and Ca complex inclusion be formed.
Also have, when making steel of the present invention, though make with above-mentioned such condition in the stage of molten steel useful, in hot-rolled process, also preferred this condition of suitably control.That is, during the former material of HRS (slab), its Heating temperature is preferably about 1000～1250 ℃.When this temperature is lower than 1000 ℃, in hot rolling, causes temperature and reduce, be difficult under suitable temperature, finish rolling, and be difficult to make the casting flaw pressing in the slab.On the other hand, if this Heating temperature surpasses 1250 ℃, then thickization of austenite, and TiN be thickization also, so HAZ toughness deterioration.
Be heated to the slab of said temperature scope, then from Ar 3Transformation temperature is to (Ar 3Transformation temperature+100 ℃) temperature province, making the accumulation draft is to implement hot rolling more than 30% to get final product.Carry out hot rolling with above-mentioned such condition,, guarantee on the good base metal tenacity useful making the crystal grain diameter granular of steel.After above-mentioned condition end hot rolling, the speed of cooling of counting more than 3 ℃/second with the surface temperature of steel (steel plate) is cooled to below 500 ℃.The upper limit of rolling end temp is in the scope of above-mentioned Heating temperature.Also has above-mentioned so-called Ar 3Transformation temperature is the value of trying to achieve through following formula (3).
Ar 3Transformation temperature (℃)=868-369 [C]+24.6 [Si]-68.1 [Mn]-36.1 [Ni]-20.7 [Cu]-24.8 [Cr] ... (3)
Wherein, [C], [Si], [Mn], [Ni], [Cu] and [Cr] represent respectively the content (quality %) of C, Si, Mn, Ni, Cu and Cr when not adding alloying element, then not calculate this.
Next, describe with regard to the composition of the chemical ingredients in the Plate Steel of the present invention (mother metal).Steel of the present invention, even the dispersion state of inclusion is suitable, and if chemical composition of steel is formed not in proper range, then can not make the characteristic of mother metal and HAZ good.Therefore, in steel of the present invention, the amount of each chemical ingredients is in the proper range that is described below.Also have, among these compositions, form the content of the element (for example Al, Ca, Ti etc.) of inclusion, contain and constitute the amount that is mingled with so that its action effect is obvious.
(C：0.02～0.15％)
C is the element that is used to guarantee that the intensity of steel plate (mother metal) and weld part (welding base metal) can not be short of.In order to bring into play such effect, the content of C need be for more than 0.02%.Be preferably more than 0.03%.But if C content is superfluous, then make HAZ toughness and weldableness deterioration, therefore need be suppressed at (preferably below 0.13%) below 0.15%.
(Si：0.03～1.0％)
Si has desoxydatoin, and on the intensity of mother metal and weld part improves, is effective elements.In order to bring into play such effect, Si is contained more than 0.03%, be preferably more than 0.05%.But if Si contained superfluously, the toughness deterioration of weldableness and mother metal then, so need be below 1.0%.Preferably below 0.7%.
(Mn：1.0～2.0％)
Mn is an effective elements on the intensity of mother metal and weld part improves, and in order to bring into play this effect effectively, need make it to contain more than 1.0%.Preferably contain more than 1.2%.Yet if Mn content is superfluous, HAZ toughness and weldableness deterioration therefore need be for below 2.0%.Preferably below 1.8%.
(below the P:0.02%)
P is the impurity element that in steel, is unavoidably contained, if its content surpasses 0.02%, then HAZ flexible deterioration is remarkable, therefore need be suppressed at below 0.02%, preferably below 0.0015%.But, be difficult to make the P in the steel to reach 0% industrial.
(S：0.0002～0.01％)
S forms CaS and is bringing into play the effect of the generation that suppresses thick TiN.In order to bring into play this effect, need S content to contain more than 0.0002%.But if S content is superfluous, then a large amount of MnS that extend that generate, HAZ flexible deterioration is remarkable, therefore need be suppressed at below 0.01%, preferably below 0.008%.
(Al：0.005～0.08％)
Al is strong deoxidant element, and is few as if Al content, then TiO 2The a large amount of generation, so its content need be for more than 0.005%, but if Al content is superfluous then can not be guaranteed and (CaO+CaS) corresponding form [preceding formula (2)], therefore need be suppressed at below 0.08%.The preferred upper limit of Al content is 0.06%.
(Ti：0.003～0.03％)
Ti separates out as TiN in steel, thereby thickization that Austria of the HAZ that prevents in when welding owes body crystal grain promotes ferrite transformation, therefore is to improve the needed element of HAZ toughness.In order to bring into play such effect effectively, Ti need contain more than 0.003%, is preferably more than 0.005%.But if Ti is contained superfluously, then solid solution Ti amount increases, and separating out of TiC taken place, and make the toughness deterioration of mother metal and HAZ, so its content should be suppressed at below 0.03%.Preferably below 0.02%.
Ca：0.0003～0.005％
Ca is the element that accounts for center-stage in steel of the present invention, as CaOCaS and Al 2O 3Form complex inclusion together,, solid solution S reduced except making the inclusion eutectic reveals, thus the eutectic that suppresses steel reveal, therefore have the approaching effect of fusing point that makes inclusion and steel, can suppress the crystallization of thick TiN.In addition, because the separating out of CaS can be reduced the generative capacity from the TiN of the complex inclusion that contains Ca and Al, so can suppress the crystallization of thick TiN.In order to bring into play this this effect, Ca is contained more than 0.0003%.Be preferably more than 0.0005%.But, if Ca content is superfluous, the cleanliness factor of steel is reduced, and when casting, produce the melting loss of casting nozzle, therefore need be for below 0.005%.Be preferably below 0.004%.
N：0.001～0.01％
N separates out as TiN in the steel tissue, suppresses thickization of the austenite crystal of HAZ, promotes ferrite transformation in addition, therefore is the element that makes the toughness raising of HAZ.In order to bring into play such effect, need N to contain more than 0.001%.Be preferably more than 0.003%.But if N content is superfluous, then solid solution N amount increases, and the toughness of HAZ is deterioration on the contrary.Thus, N content need be suppressed at below 0.01%, is preferably below 0.008%.
(below the O:0.004%)
O is the element that constitutes inclusion in the present invention, need manage.Surpass 0.004% superfluous like this O the cleanliness factor of steel is reduced, the thick inclusion that constitutes the destructive starting point is generated in a large number, base metal tenacity, HAZ toughness are reduced.Therefore be below 0.004%.Preferred below 0.003%.On the other hand, O content lacks and more is preferred, therefore need not set its lower limit, but there is the limit in the reduction of O in industry, can contain more than 0.0005% usually.
The present invention regulation contain element as stated, surplus is iron and unavoidable impurities, as this unavoidable impurities, element (for example Co, Zn, the Pb etc.) that can allow to mix because of the situation of raw material, goods and materials, producing apparatus etc. sneak into.In addition, it is also effective further to contain following element energetically, and according to the kind of the composition that is contained, the characteristic of steel plate is further improved.
(below the B:0.005%, below the Nb:0.06%, below the V:0.1%, below the Cu:1.5%, below the Ni:3.5%, below the Cr:1.5% and the element more than at least a kind among below the Mo:1.5%)
B, Nb, V, Cu, Ni, Cr and Mo all are useful elements on the intensity that makes steel improves, and can make it to contain a kind or 2 kinds as required.Wherein, B improves the hardenability of steel, improves the intensity of mother metal and weld part, and when welding in the heated HAZ refrigerative process, combines with N and separates out BN, in austenite crystal, promote ferrite transformation, so it is high that HAZ toughness is got.Such effect increases and increases along with its content, but in order to bring into play such effect effectively, preferably makes it to contain (more preferably more than 0.0005%) more than 0.0002%.But if B content is superfluous, then therefore the toughness of mother metal and HAZ and weldableness deterioration are preferably below 0.005%.More preferably below 0.004%.
Nb is useful element improving on intensity and the base metal tenacity, and its effect increases and increases along with its content, but in order to bring into play such effect effectively, preferably makes it to contain more than 0.005%.But if Nb content is superfluous, then therefore the toughness deterioration of mother metal and HAZ preferably is suppressed at below 0.06%.
V is useful element improving on the intensity, and its effect increases and increases along with its content, but in order to bring into play such effect effectively, preferably makes it to contain more than 0.005%.But if V content is superfluous, then therefore HAZ toughness and weldableness deterioration preferably are suppressed at below 0.1%.
Cu is in the hardenability that improves steel, and improving on the intensity is effective elements.This effect increases and increases along with its content, but in order to bring into play such effect effectively, preferably makes it to contain more than 0.05%.But if Cu content is superfluous, then therefore the toughness deterioration of mother metal and HAZ is estimated and is elected as below 1.5%.
Ni is useful element on intensity that improves steel and weld part and toughness, and its effect increases and increases along with its content, but in order to bring into play such effect effectively, preferably makes it to contain more than 0.05%.But if Ni content is superfluous, then will become extremely expensive, therefore, preferably be suppressed at below 3.5% from the viewpoint of economy as structural steel.
Cr is an effective elements on the intensity that improves steel.This effect increases and increases along with its content, but in order to bring into play such effect effectively, preferably makes it to contain more than 0.01%.But if Cr content is superfluous, then therefore HAZ toughness deterioration is preferably below 1.5%.
Mo is an effective elements on intensity that improves steel and toughness.This effect increases and increases along with its content, but in order to bring into play such effect effectively, preferably makes it to contain more than 0.01%.But if Mo content is superfluous, then therefore HAZ toughness and weldableness deterioration are preferably below 1.5%.
(below the Zr:0.05%, below the REM:0.005% and at least a kind of element among below the Mg:0.005%)
Zr, REM (rare earth element) and Mg are effective elements on the HAZ flexible improves, and can make it as required to contain more than a kind or 2 kinds.Wherein, Zr and REM form oxide compound to be disperseed imperceptibly, thereby HAZ toughness is improved.Such effect increases and increases along with its content, but in order to bring into play such effect effectively, preferably all makes it to contain more than 0.001%.But,, then can not keep (CaO+CaS)/(Al if its content is superfluous 2O 3) optimum balance, HAZ toughness deterioration.Thus, preferred Zr is below 0.05%, and REM is below 0.005%.Also have, in the present invention, so-called REM (rare earth element) is the meaning that contains lanthanon (15 elements from La to Ln) and Sc (scandium) and Y (yttrium).
Mg improves HAZ toughness through the miniaturization of crystal grain.Such effect increases and increases along with its content, but in order to bring into play such effect effectively, preferably makes it to contain more than 0.001%.But even contain Mg superfluously, its effect also is saturated, therefore is preferably below 0.005%.
Steel of the present invention be set at the former material of Plate Steel basically, but so-called Plate Steel are defined like JIS, and referring generally to thickness of slab is that 3.0mm is above.Steel of the present invention; Even for thickness of slab is that Plate Steel such more than the 30mm carries out the heat input large-line energy welding such above 400kJ/cm; Still demonstrate good HAZ toughness; Therefore the steel plate that is applied to this thickness is preferred mode, but the thickness that is not limited to steel plate is more than the 30mm, does not also get rid of the steel plate that is applied to be lower than this thickness.
The Plate Steel that so obtains can use as the material of the for example works of bridge, high-rise and boats and ships etc., and certainly much less little～middle heat input welds, even in the large-line energy welding, also can prevent the toughness deterioration of welding heat affected zone.
[embodiment]
Below, illustrate in greater detail the present invention through embodiment, but following embodiment not limiting character of the present invention, the scope of the aim of before and after can meeting, stating also can suitably change enforcement, and these all are included in the scope of technology of the present invention.
After the molten steel that below table 1, the chemical ingredients shown in 2 is formed with continuous casting machine becomes slab, this slab is heated to 1000～1250 ℃, at Ar 3Transformation temperature～(Ar 3Transformation temperature+100 ℃) temperature province, making the accumulation draft is to implement hot rolling more than 30%, obtains the steel plate of thickness of slab 50mm.Also have, in table 1,2, REM is about 30% to be that the form of about 50% norium is added with containing Ce to contain La.Element is not added in "-" expression in the table 1 in addition.
Figure GSA00000009979900121
Figure GSA00000009979900131
[composition measuring of inclusion]
For each steel plate that obtains in the above described manner, observe its cross section (in the cross section of rolling direction and Surface Vertical) with Shimadzu Seisakusho Ltd.'s system " EPMA-8705 ", be the inclusion more than the 2 μ m for size like aforementioned definitions, quantitative analysis becomes to be grouped into.At this moment viewpoint condition is to observe multiplying power: 100～400 times, and field of view: 10～70mm 2, the one-tenth of the wavelength dispersion quantitative spectrometric analysis inclusion central part of through characteristic X ray is grouped into.
At this moment analytic target element is Al, Mn, Si, Mg, Ca, Ti, Zr, Ni, Cu, V, S, Cr, REM; Use known substance; Try to achieve the X ray intensity of each element and the relation of concentration of element in advance and measure line, the X ray intensity that then quantitatively obtains by said inclusion and according to the concentration of element of quantitative each inclusion of said inspection amount line as inspection.Based on these measured values, follow following standard, measure CaS, CaO and Al 2O 3Content, and try to achieve [Ca]/[Al], ([CaO]+[CaS])/([Al 2O 3]) value (measuring method such as aforementioned).In addition, will contain Ti and be inclusion more than 10% and be defined as and contain the Ti inclusion, with its size be inclusion more than the 2 μ m as object, calculate this and contain Ti inclusion (measuring) shared ratio (%) in whole inclusion numbers by EPMA.
(1) calculating of CaS content: detected S preferentially combines with Mn, forms MnS, and the S superfluous with respect to Mn forms CaS.
(2) calculating of CaO content: among the detected Ca, the Ca beyond the CaS exists as CaO.
(3) Al 2O 3The calculating of content: detected Al is all as Al 2O 3Exist.
[evaluation of HAZ flexible]
In order to estimate the toughness that the time receives the HAZ of heat affecting in welding, be the large-line energy welding of 1000kJ/cm or 600kJ/cm for each steel plate simulation weld heat input, carry out the welding shown in following and reproduce test.
(1) weld heat input is 1000kJ/cm: heating keeps cooling off in 30 seconds after making the sample integral body of downcutting from slab become 1400 ℃.At this moment speed of cooling be adjusted into from 800～500 ℃ cooling time be 730 seconds.
(2) weld heat input is 600kJ/cm: heating keeps cooling off in 60 seconds after making the test portion integral body of downcutting from slab become 1400 ℃.At this moment speed of cooling be adjusted into from 800～500 ℃ cooling time be 500 seconds.
From cooled sample, the V nick-break test sheet of JIS Z 2202 that there is the otch of vertical incision on the plate surface that is extracted in the position of HAZ carries out pendulum impact test by the main points of JIS Z 2242, measures the disconnected alternating temperature degree vTrs (1 measured value) of fracture.Then, the disconnected alternating temperature degree vTrs of fracture be 0 ℃ to be evaluated as HAZ toughness good.
These results are presented in the below table 3,4 in the lump.In addition based on these results, ([CaO]+[CaS])/([Al 2O 3]) with being presented among Fig. 1 of the relation of fracture transition temperature vTrs, contain the ratio of Ti oxide compound and the relation of fracture transition temperature vTrs and be presented among Fig. 2.
[table 3]
Figure GSA00000009979900161
[table 4]
Figure GSA00000009979900171
Can investigate (also have, following No. representes the steel No. of table 1～4) as follows by these results.The example of the important document of the present invention regulation is satisfied in No.1～34th, and chemical ingredients is formed, the dispersion of inclusion is suitable, can know to access good HAZ toughness.With respect to this, No.35～50th, the example of the important document of disengaging the present invention regulation can be known HAZ toughness deterioration.
For accessing the good HAZ flexible steel plate (No.2,3,26) and the steel plate (No.47) of HAZ toughness deterioration, each the composition (Al before just casting in the inclusion 2O 3, MnS, MnO, CaS, CaO) standard deviation investigate.Its result is presented in the below table 5, demonstrates good HAZ flexible, and each composition before can confirming to cast in the inclusion is in the interior [σ (Al of scope of regulation 2O 3)≤30 quality %, σ (CaO)≤15 quality % and σ (CaS)≤20 quality %], CaO and CaS and Al 2O 3Combine equably.With respect to this, the scope that the disengaging known of HAZ deterioration is above-mentioned.
[table 5]
For accessing the good HAZ flexible steel plate (No.2,3,11,13) and the steel plate (No.35,36) of HAZ toughness deterioration, be that the individual number density of the TiN below the 0.5 μ m is investigated with regard to size.Its result is presented in the below table 6, can know that the individual number density of fine TiN has no impact to HAZ toughness.
[table 6]
Steel No. TiN number density (individual * 10 7)
2 0.36
3 1.30
11 0.93
13 1.12
35 0.58
36 0.52
Among each above-mentioned steel plate, the form of getting its representational demonstration inclusion.Fig. 3 representes the form [Fig. 3 (a) is for drawing substitutes microphotograph, and Fig. 3 (b) is the explanatory view that medelling ground shows the form of inclusion] of the inclusion in the steel plate of No.25.The part of representing with the reference marks 1 of Fig. 3 (a) is CaO:36%, CaS:29%, Al 2O 3: SiO 63%, 2: 1% part, the part of representing with reference marks 2 is CaO:24%, CaS:6%, MgO:2%, Al 2O 3: 68% part.
Fig. 4 representes the form [Fig. 4 (a) is for drawing substitutes microphotograph, and Fig. 4 (b) is the explanatory view that medelling ground shows the form of inclusion] of the inclusion in the steel plate of No.27.The part of representing with the reference marks 1 of Fig. 4 (a) is MnO:2%, CaS:76%, CaO:19%, Al 2O 3: 3% part, the part of representing with reference marks 2 is CaO:38%, CaS:4%, Al 2O 3: 57% part, the part of representing with reference marks 3 is MnO:1%, CaO:23%, CaS:18%, Al 2O 3: TiO 20%, 2: 38% part.
Fig. 5 representes the form [Fig. 5 (a) is for drawing substitutes microphotograph, and Fig. 5 (b) is the explanatory view that medelling ground shows the form of inclusion] of the inclusion in the steel plate of No.35.The part of representing with the reference marks 1 of Fig. 5 (a) is the part of TiN:100%, and the part of representing with reference marks 2 is MgO:13%, Al 2O 3: the part of TiN:1% 85%.
Fig. 6 representes the form [Fig. 6 (a) is for drawing substitutes microphotograph, and Fig. 6 (b) is the explanatory view that medelling ground shows the form of inclusion] of the inclusion in the steel plate of No.37.The part of representing with the reference marks 1 of Fig. 6 (a) is MnO:10%, CaO:46%, CaS:2%, MgO:2%, Al 2O 3: SiO 26%, 2: TiO 11%, 2: 2% part, the part of representing with reference marks 2 is MnO:4%, CaO:13%, MgO:1%, Al 2O 3: SiO 7%, 2: TiO 4%, 2: 71% part.

Claims (3)

1. steel; It is characterized in that; In quality % contain C:0.02～0.15%, Si:0.03～1.0%, Mn:1.0～2.0%, below the P:0.02%, S:0.0002～0.01%, Al:0.005～0.08%, Ti:0.003～0.03%, Ca:0.0003～0.005%, N:0.001～0.01% and below the O:0.004%; Surplus is iron and inevitable impurity
And disperse following inclusion: when the maximum length of width was made as inclusion big or small on the direction of the maximal projection length of the inclusion in the time of will be perpendicular to microscopic examination, its size was more than the 2 μ m, and this inclusion satisfies following formula (1) and formula (2),
0.01≤[Ca]/[Al]≤0.50…(1)
0.08≤([CaO]+[CaS])/([Al 2O 3])≤1.80…(2)
Wherein, [Ca], [Al], [CaO], [CaS] and [Al 2O 3], represent Ca, Al, CaO, CaS and Al in the inclusion respectively 2O 3Mass percentage content,
And, be containing in the Ti inclusion more than 10% contain Ti in quality %, size is that the above number that contains the Ti inclusion of 2 μ m accounts for below 7% of number that size is the above whole inclusiones of 2 μ m.
2. steel according to claim 1; It is characterized in that at least a kind of element that also contains below B:0.005%, below the Nb:0.06%, below the V:0.1%, below the Cu:1.5%, below the Ni:3.5%, below the Cr:1.5% and select below the Mo:1.5% in quality %.
3. steel according to claim 1 is characterized in that, also contain at least a kind of element below the Zr:0.05%, below the REM:0.005% and in below the Mg:0.005% in quality %.
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