TW201226582A - High-strength steel plate and producing method thereof - Google Patents

Abstract

A high-strength steel plate includes the following chemical composition: by mass%, C: 0.05% to less than 0.10%, Si: 0.20% to 0.50%, Mn: 0.20% to less than 1.20%, Cr: 0.20% to 1.20%, Mo: 0.20% to 0.60%, Nb: 0.010% to 0.050%, Ti: 0.005% to 0.030%, Al: 0.01% to 0.10%, B: 0.0003% to 0.0030%, V: 0% to 0.10%, Cu: 0% to 0.50%, Ca: 0% to 0.0030%, and the balance consisting of Fe and inevitable impurities. In the high-strength steel plate, the amounts of Ni, P, S, and N are limited to 0.1% or less, 0.012% or less, 0.005% or less, and 0.0080% or less, respectively. In addition, in the high-strength steel plate, Pcm is 0.22% or less, A is 2.0 or less, the sum of the ratio of lower bainite and the ratio of martensite is 90% or more, the ratio of lower bainite is 70% or more, the aspect ratio of prior-austenite grains is 2 or more, the yield strength is 885 MPa or higher, and the tensile strength is from 950 MPa to 1130 MPa.

Description

201226582 VI. Description of the Invention: [Technical Field] The present invention relates to a high-strength thick steel plate excellent in weldability and a method for producing the same. In particular, the present invention relates to a structural member used for constructing a machine or an industrial machine, and has a tensile strength of 885 MPa or more and a tensile strength of 950 MPa or more and 1130 MPa or less. Most of the high-strength steel plates having a thickness of 6 mm or more and 25 mm or less Production method. The present application claims priority from Japanese Patent Application No. 2010-248032, filed on Jan. [Prior Art 3] A construction machine such as a crane or a concrete system tends to increase in size as the building is highly stratified in recent years. In order to control the increase in weight with the increase in the size of the construction machinery, the lightweighting requirements for structural members are further enhanced, that is, high strength for 100 kg steel grade (for example, a relief strength of 885 MPa or more and a tensile strength of 950 MPa or more). The need for steel is increasing. On the other hand, in such a high-strength steel, since the amount of the alloy element to be added is increased, preheating is generally performed in order to avoid welding cracks during welding. However, in order to carry out the welding construction more efficiently, it is pursuing steel that does not require preheating. Since the sensitivity of the fusion crack is very susceptible to the diffusion of hydrogen, it is preferable to suppress the amount of diffusion hydrogen of the metal to be welded. However, for example, in the construction of carbon dioxide electricity 201226582, which is widely used in the welding of structural members of machinery or industrial machinery, it is particularly necessary to reduce the amount of diffused hydrogen, not only the selection or management of the welding material, but also the welding construction. Various managements such as the management of the lubricating oil of the welded metal wire which does not mix hydrogen or the cleaning of the grooved surface, and the burden on the construction become large. Therefore, in the case of carbon dioxide arc welding, in the case where the steel contains diffused hydrogen in an amount of about 3.0 to 5.0 ml/100 g which is considered to be mixed when the welding construction management is slightly insufficient, the steel may be welded without preheating. A steel having a crack with a sufficiently low crack sensitivity is preferred. The general strength specification of a 100 kg steel grade steel plate is usually 885 MPa or more. Although there is no upper limit for the strength of the fall, the tensile strength is, for example, a range of 950 MPa or more and 1130 MPa or less, and the tensile strength is limited. Although many steel sheets are bent for mechanical use, the load required for bending processing becomes large when the tensile strength of the steel sheet is larger than the upper limit of the specification. Therefore, it is also necessary to consider the case where the processing is limited by the ability of the equipment, and the tensile strength of the steel sheet is not excessively high. Regarding a high-strength steel sheet having a relief strength of 885 MPa, for example, Patent Document 1 and Patent Document 2 disclose a high-tensile steel sheet having a tensile strength of 95 〇 Mpa. However, these steel plates are used for thick steel plates such as pressure steel pipes. Therefore, these steel sheets, in particular, have not considered the bending workability, and a large amount of ruthenium is added as an essential element for securing toughness, and it is economically disadvantageous in the use of construction equipment. Patent Document 3 discloses a technique for high-tensile steel excellent in weldability and economy. This technique suppresses the weld crack sensitivity index pcm below 〇 29 to ensure weldability. However, in the Type 7 weld crack test, the crack stops pre-201226582. The minimum heat temperature is 100 °C, and it is considered that the weldability cannot be ensured under the welding without preheating. Patent Document 4 discloses a technique for high-tensile steel excellent in weldability and cessation property. In order to ensure toughness, this technology requires the addition of Ni, which is economical in the use of construction equipment. Further, in the 丫-type weld crack test, no crack was generated even if it was not preheated, but the condition of the test was that the amount of diffused hydrogen was 1.2 ml/l 〇〇g. Therefore, it is expected that the load at the time of the welding construction for managing the amount of diffusion hydrogen of the welded metal becomes high. Patent Document 5 discloses a technique for high-tensile steel excellent in weldability and HIC resistance. This technology needs to be added to ensure the toughness of Ni, and 〇 6% or more of Mo, which is not economical in the use of construction equipment. Moreover, in the type J joint crack test, no crack occurred even if it was not preheated, but the condition of the test was to limit the amount of diffused hydrogen to 1.5 ml/l〇〇g, so it is expected to manage the amount of diffused hydrogen of the molten metal. The load during welding is increased. Patent Document 6 discloses a method of producing a steel sheet having a tensile strength of more than 980 MPa without heat treatment. This method is intended to be in (4). The following extremely low C amount ensures a tensile strength of more than _MPa, and it is necessary to add a large amount of alloying elements such as Μη or more in the steel to the steel. In particular, when the amount is large, there is a concern that the crack sensitivity of the segregation portion is lowered. However, there is no evaluation of Na's connectivity. 'Excellent weldability cannot be expected. Patent Document 7 discloses a hot-rolled steel sheet having a tensile strength of 95 GMPam in consideration of bending workability and refining property. This hot-rolled steel sheet is known to have a large amount of Tl', so that the wetness is lowered. Further, in order to solve the problem that the addition of Ni is caused by the addition of a large amount of Ti, it is economical. 201226582 Patent Document 8 discloses a method for producing a steel sheet having a tensile strength of 950 MPa or more which is mainly used for pipelines and excellent in toughness and weldability. Since the amount of Μη needs to be 1.8% or more, there is a concern that the crack sensitivity of the segregation portion is lowered, and the productivity is low because of the low-temperature rolling under the 2-phase region of the ferrite-iron-Worstian iron. 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 Japanese Laid-Open Patent Publication No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. No. Hei. OBJECTS OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION The object of the present invention is to economically provide a structural member for use in a machine or an industrial machine, which is excellent in weldability, has a lodging strength of 885 MPa or more, and is resistant to tensile stress. The strength is 950 MPa or more and 1130 MPa or less, and is a high-strength thick steel plate having a thickness of 6 mm or more and 25 mm or less and a method for producing the same. Means for Solving the Problems The gist of the present invention is as follows. (1) A high-strength steel sheet according to one aspect of the present invention has a chemical composition of: 201226582% by mass: C: 0.05% or more and less than 0.10%, Si: 0.20% or more and 0.50% or less, Μη: 0.20% The above is less than 1.20%, Cr: 0.20% or more and 1.20% or less, Mo: 0.20% or more and 0.60% or less, Nb: 0.010% or more and 0.050% or less, Ti: 0.005% or more, and 〇.〇3〇〇/0 Hereinafter, A1: 0.01% or more and 0.10% or less, B: 0.0003% or more and 0.0030% or less, V: 0% or more and 0.10% or less, Cu: 0% or more and 0.50% or less, and C a : 0% The above is 0.0030% or less, and is limited to: Ni: 0.1% or less, P: 0.012% or less, S: 0.005% or less, and N: 0.0080% or less, and the remainder is composed of Fe and unavoidable impurities. The Pcm defined by the following (Formula 1) is 0.22% or less, and the A-system 2.0 or less defined by the following (Formula 2) is the sum of the tissue fraction of the lower toughened iron and the tissue fraction of the granulated iron. % or more, the structural fraction of the lower toughened iron is more than 2 in the aspect ratio of the former Wostian iron particles, the undulation strength is 885 MPa or more, and the tensile strength is above 90 50 MPa and 1130 MPa. .

Pcm=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/20+ [Mo]/15+[V]/10+5x[ B]·.. (Formula 1) A=([Mn]+1.5x[Ni])/([Mo]+1.2x[V])· · (Expression 2) Here, [C], [Si ], [Μη], [Cu], [Ni], [Cr], [Mo], [V], [B] are respectively C, Si, Mn, Cu, Ni, Cr, Mo ' V in the above chemical composition And the mass% of B. (2) The high-strength steel sheet according to the above (1), wherein the number density of the stellite carbon iron of 5 〇 nm or more may be 20 / μπι 3 or less. (3) The high-strength steel sheet according to the above (1) or (2), wherein the sheet thickness may be 6 mm or more and 25 mm or less. 201226582 (4) A method for producing a high-strength steel sheet according to one aspect of the present invention, which is characterized in that a steel having a chemical composition having a chemical composition of 1100 ° C or higher is contained, and the chemical composition contains, by mass %: C: 0.05% or more Less than 0.10%, Si: 0.20% or more and 0.50% or less, Μη: 0.20% or more and less than 1.20%, Cr: 0.20% or more and 1.20% or less, Mo: 0.20% or more and 0.60% or less, and Nb: 0· 010% The above is 0.050% or less, Ti: 0.005% or more and 0.030% or less, A1: 0.01% or more and 0.10% or less, b: 0,0003% or more and 0.0030% or less, and V: 0% or more and 0.10% or less, Cu: 0% or more and 0.50% or less, and Ca: 0% or more and 0.0030% or less, and are limited to: Ni: 0.1% or less, P: 0.012% or less, S: 0.005% or less, and N: 0.0080% or less, and remaining The part is composed of Fe and unavoidable impurities, and the Pcm system defined by the following (Formula 3) is 0.22% or less, and the A system is 2.0 or less as defined by the following (Formula 4); The cumulative reduction ratio of the non-recrystallization temperature region is 60% or more; and the on-line is 1 Torr. The cooling rate of (:/s or more) is accelerated by the temperature of Ar3 or higher to a temperature of 450 ° C or lower and 300 ° C or higher, and is allowed to cool after the accelerated cooling is stopped.

Pcm=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/20+ [Mo]/15+[V]/10+5x[ B] . · (Expression 3) A = ([Mn] + 1.5x [Ni]) / ([Mo] + 1.2x [V]) · · · (Expression 4) Here '[C], [Si ], [Μη], [Cu], [Ni], [Cr], [Mo], [V], [B] are respectively C, Si, Mn, Cu, Ni, Cr, M in the above chemical composition. , V, B mass%. Advantageous Effects of Invention According to the present invention, it is possible to economically provide a structural member for use in a construction machine or a 201226582 industrial machine, and has a high-strength steel plate having a high-strength welding strength of 885 MPa or more and a thickness of 6 mm or more and 25 mm or less. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a graph showing the relationship between the crack stop preheating temperature in the Pcm and y-type weld crack test. Figure 2 is a graph showing the relationship between the tissue fraction of the lower toughened iron and the ratio of the drop. Figure 3 is a graph showing the relationship between the A value and the tissue fraction of the lower toughened iron. Fig. 4 is a flow chart showing the outline of a method for producing a high-strength steel sheet according to an embodiment of the present invention. C Embodiment 3 Mode for Carrying Out the Invention It is well known that in order to reduce the sensitivity of welding cracks, it is effective to reduce the welding crack sensitivity index Pcm. The inventors have reviewed that, in the case of carbon dioxide arc welding, diffusion of hydrogen in an amount of about 3_0 to 5.0 ml/100 g which is considered to be insufficient when the welding construction management is insufficient may be contained in the steel, so that no weld crack occurs in the case of not preheating. How much pcm needs to be reduced. The y-type fusion crack test (1 7 kJ/mm of heat of dissolution) specified in JIS z 3158 (1993) was carried out to adjust the temperature and humidity with respect to the steel having various chemical compositions. The test piece has a plate thickness of 25 mm, and it is necessary to test two test materials under the same conditions. Among them, one was used as a test material for hydrogen analysis, and the test material was immediately sampled after the test, and the amount of diffused hydrogen was measured by a gas chromatograph. As a result of the analysis, only when the amount of diffused hydrogen is greater than 5 〇1111/1〇〇§, the remaining test piece 9 201226582 is used for the test to evaluate the presence or absence of cracks. From the results obtained, the relationship between the Pcm of the steel material shown in Fig. 1 and the preheating temperature for preventing cracks can be obtained. In other words, Fig. 1 shows the influence of the Pcm of the steel material and the preheating temperature on the presence or absence of cracks. As is apparent from the first drawing, if the Pcm is reduced to 〇22% or less, it is in the range of 5.1 to 6.0 ml/100 g in the diffused hydrogen, and cracks are not generated under the conditions of no preheating (test temperature: 25 Å). However, the previous 100 kg steel grade thick steel plate was manufactured by multiple tempering processes, generally containing tempered granita iron as the main organization. However, in order to satisfy the composition (chemical composition) of a low pcm of 0.22% or less, when the main structure is tempered granulated iron, it is not easy to obtain the strength of 1 〇〇 kg of steel. In order to obtain a high strength with such a low P c m , it is not necessary to temper the granulated iron structure, that is, to directly use the quenched granulated iron structure. However, the quenched granulated loose iron structure has many characteristics of low displacement ratio (lowering strength/tensile strength) due to the difference in movable displacement, and the tensile strength must be improved in order to ensure the fall strength of the specified specification. The strength specification value of 1 kg steel in the JIS specification is 885 MPa or more, and the tensile strength is 95 MPa or more and 1130 MPa or less. When the above-mentioned specification value is considered to be uneven in the quality (strength) of the manufacturing, the lower limit target value of the drop strength is 915 MPa, and the upper limit target value of the tensile strength is set to llOO MPa, and the fall ratio (falling strength/tensile strength) is known. ) is a necessary condition of 830 / 〇 or more. This ratio is not easily obtained in the quenched granulated iron structure. The inventors reviewed the relationship between various organizations and strengths, and as a result, 'make a high-ratio ratio in the bonfire state, control the quenching structure to the structure of the lower tough iron body, and reduce the rate of the granulated iron structure in the field. Effective conclusions. In addition, the inventors of the present invention investigated in detail the relationship between the composition ratio of the steel material having various component compositions, the strength, and the ratio of the drop ratio, in which the amount of c is 5% or more and less than 0.10% Å Pcm is 0.22% or less. As a result, it has been found that, in order to ensure the declination strength of 5 MPa or more, the sum of the tissue fraction of the lower iron (the lower fraction of diligent iron) and the tissue fraction of the granulated iron (the balance of the granules of the granules) must be taken. Above (the tissue fraction of upper toughened iron and fertilized iron is less than 1%). In addition, in order to meet the drop ratio of 83/〇 or more, the structure of the steel plate must be the following as the main structure (the mixed structure of the lower or the lower and the lower and the mixed structure of the granulated iron) The knowledge of the microstructure of the steel sheet is 7 G% or more (Fig. 2). In addition, in Fig. 2 and Fig. 3 which will be described later, 'the steel plate having a thickness of 6 to a claw, a lower tensile iron fraction, and a balance of the granulated iron is 90% or more, and the steel plate is 3 〇〇. ~45〇<t Stop water cooling and control the organization. Then, the inventors reviewed the method of stably controlling the steel sheet structure in the structure of the lower tough iron body. For example, although the cooling rate during quenching is controlled to a certain range, the toughened iron can be obtained, but the cooling rate of the lower toughening iron is generally small, so the control of the cooling rate is not a good strategy in the industry. . The manufacturing process for obtaining the structure of the lower toughened iron body stably and simply is not accelerated cooling to room temperature during quenching, but is stopped at a suitable temperature during cooling, and then the cooling rate is slowed down by cooling. To be effective. When the temperature at which the water cooling is stopped (the temperature of the steel sheet which is switched from water cooling to cooling) is lower than 3 °C, the distribution of the iron in the field becomes too high. Conversely, the water cooling temperature is above 450. (: When it is easy to generate the upper toughening iron. Therefore, stop the water cooling temperature to 300. (: Above and 450 °C or less is preferred. 11 201226582 The inventor specializes in the amount of C is 0.05% or more and less than 〇. 1 〇 %, steel with a composition of 0.22% or less, having a plate thickness of 6 to 25 mm, stopping the water-cooling temperature of 300 ° C or more and 450 ° C or less, and forming a steel sheet for the lower toughened iron The relationship between the strength and the tissue fraction was investigated in detail with the steel with a mass fraction of more than 90% of the tissue of the granulated iron. The result 'is known that Μη and Ni have the effect of suppressing the deformation of the lower iron, so it is especially stopped halfway. In the water-cooling process, the microstructure of the lower toughened iron is decreased. 'When the water cooling temperature is low, the tissue fraction of the granulated iron is increased. When the water cooling temperature is high, the tissue fraction of the upper ferrous iron is increased. The tendency of the rate is high. It is also confirmed that Mo and V inhibit the formation of ferrite iron or up-regulated iron, and the tendency to increase the tissue fraction of the lower iron is high. Therefore, it can be known that in the process of stopping the water cooling in the middle Easy to stably obtain the lower iron body Weaving, suppressing the amount of Μη and Ni, and increasing the amount of Mo and V is very effective. Specifically, it is understood that the amount of C is 0.05% or more and less than 〇·1〇%, which is defined by the following (Formula 5). In addition to the component composition conditions of the Pcm of 0.22% or less, when the A (A value) defined by the following (Formula 6) is adjusted to 2.0 or less, the tissue fraction of the granulated iron and the microstructure fraction of the lower toughened iron are determined. When the sum is 90% or more, the structure of the lower tough iron fraction of 70% or more can be surely obtained (Fig. 3). By obtaining the structure of the lower tough iron body, the drop ratio is 83% or more. Considering the unevenness of the strength to a certain extent, the lower limit of the drop strength (885 MPa) and the upper limit of the tensile strength (1130 MPa) can be stably satisfied.

Pcm=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/20+ [Mo]/15+[V]/10+5x[ B] · · · (Expression 5) A=([Mn]+1.5x[Ni])/([Mo]+1.2x[V])· · ·(Formula 6) 12 201226582 Here, [c], [Si], [Μη], [Cu], [Ni], [Cr], [Mo], [V], [B] are respectively C, Si, Mn, Cu, Ni, Cr, Mo, V, B mass%. Hereinafter, a high-strength steel sheet according to an embodiment of the present invention will be described in detail. First, the reason for limiting the steel component of the present embodiment will be described. In addition, "%" means "% by mass". The C system greatly affects the important element of the strength of the steel of the present embodiment having the following toughened iron as the main structure. In order to obtain a drop strength of 885 MPa or more, the amount of C needs to be 〇.〇5°/. The above is preferably 0.055% or more or 0.060% or more. However, the tensile strength will become too high when the amount of C is 0.10% or more. Therefore, the amount of C is preferably less than 0.10%, preferably less than 0.095% or less than 〇_〇9〇%.

In the process of stopping the water cooling in the middle of the process described later, the Si system suppresses the coarsening of the swarf carbon in the slow cooling after the water cooling is stopped. Therefore, it is preferable to increase the amount of Si in order to increase the amount of Si. Therefore, the amount of Si is 〇.2〇°/. The above is preferably 0.25% or more or 〇3% or more. However, when Si is excessively added to the steel, there is a concern that the fineness is impeded, so the upper limit of the amount of Si is 0.50%, which is 〇45. /. Or 0.40% is preferred. The Μη system contributes to the improvement of the hardenability and the strength of the element. Therefore, the amount of Μη is 0.20% or more, preferably 0.30% or more or 0-50% or more. However, Μη has the effect of suppressing the transformation of the toughened iron, especially in the process of stopping the water cooling in the middle, reducing the tissue fraction of the lower toughened iron, and the organization rate of the iron to the granulated iron when the water cooling temperature is low. When the water cooling temperature is stopped, the tendency to increase the upper tough iron fraction is high. In particular, the amount of Μη is 1.2〇. /. In the above case, it is difficult to obtain a fall ratio of 83% or more. Therefore, the amount of Μη is less than 12〇%, preferably l.OO/o or 〇.9〇% or less. 13 201226582

Since Cr contributes to the improvement of the hardenability and the strength, the amount of the & is more than 0.25 Ο / Ο or more than 0 の 30%. ‘However, when adding Cr to the steel and adding excess Cr, the weldability will be lowered. Therefore, the amount of Cr is 丨2〇% or less, and 1.10% or less or 1.00% or less is preferable.

Mo suppresses the formation of ferrite iron, and contributes to the stable formation of the toughened iron in the process of stopping the water cooling in the middle of the following. Therefore, the amount of M〇 needs to be 〇 or more, preferably 0_25〇/〇 or more. 30.30% or more. However, when adding too much Mo to the steel, there is a case where the weldability is impaired, and M〇 is also a high-priced element. Therefore, the Mo amount is 0.60 〇/〇 or less, and 〇.58% or less or 〇55% or less. It is better.

Ni also has the effect of suppressing the transformation of the lower toughening iron in the same manner as the Μη. In the process of stopping the water cooling in the middle, the structure of the lowering of the lower axis is made to increase the tissue fraction of the granulated iron in the case of stopping the water cooling temperature. ^ When the water-cooling temperature is high, the tendency to increase the fraction of the upper toughening iron is high. Κ LJ, when Ni is added to steel, it is not easy to obtain a drop strength of 83% or more. Thus, Ni is added to the steel, and the amount of Ni is controlled to be inevitably in the steel = square. Specifically, the upper limit of the amount of Ni is 〇.1%. 〇 5% or two is better. The lower limit of the amount of Ni is not particularly limited, and is 〇%. '' 乃, added to the steel as a selection element (10)' can also be - the amount of lion is suppressed below the amount of the front side, while Adding 0.5 times or more of Cu to steel

Nb forms fine carbides during rolling, increases the area of the non-recrystallization temperature, improves the control rolling effect, and improves the secret by refining the crystal grains. Therefore, the amount of Nb is 0% or more, preferably 15% or more. 'However' because of the excessive addition of _ in the steel, there is a hindrance to the splicing. ^ - itNbf ^0.050〇/〇ατ « α〇.045〇/〇,χτ^〇〇4〇%^τ^ 14 201226582 good. In the present palladium form, B is used to ensure proper hardenability of the toughened iron structure. In order to obtain the appropriate hardenability, it is necessary to ensure that the free BM during the direct quenching generates BN and reduces the free b. Therefore, an appropriate amount of Ti is added to the steel, and BN is not formed, and TiN is fixed.

Ti is used to fix N as TiN and is contained in steel. In other words, in steel, 'Τι董系0.005% or more' is preferably 0〇1〇% or 〇〇12% or more. However, since the addition of Ti excessively causes the weldability to decrease, the upper limit of the amount of Ti is 0.030%, preferably 0.025% or 0.020%. B has an effect of improving the hardenability of steel, and in order to exert this effect, the amount of B needs to be 0.0003% or more, preferably 0.0005% or more or 〇1% or more. However, when more than 0.0030% iB is added to the steel, the weldability or toughness is lowered. Therefore, the amount of B is 0.0030% or less, preferably 5% or less or 0.0020% or less. When N is excessively contained in the steel ten, as described above, 81^ is formed, which hinders the effect of improving the hardenability of B and lowers the toughness. Therefore, the amount of 1 is suppressed to 0.0080% or less, preferably 0.0060% or less or 0.0050% or less. Further, since the N system is inevitably contained in the steel, the lower limit of the amount of n is not particularly limited and is 0%. A1 is added to steel as a deoxidizing material, and in this steel, the amount of niobium is usually 0.01% or more. However, since the excess of A1 is added to reduce the toughness, the upper limit of the amount of A1 is 0.10%, preferably 0.08% or 0.05%. P is a harmful element that reduces toughness. Therefore, the amount of P is suppressed to 〇〇12% or less, preferably 0.010% or less or 0.008% or less. Also, because? It is unavoidable that the lower limit of the amount of p is not particularly limited, and is 〇%. S forms MnS and reduces the harmful elements of the bending processability, so it is preferable to reduce the amount of s as much as possible. Therefore, it is preferable to suppress the amount of s to 5% or less and 〇〇〇4% or less or 0.003% or less. Further, since s is an unavoidable impurity, the lower limit of the s amount is not particularly limited, and is 〇%. The above elements are the basic components of the present embodiment, the basic components (basic elements) of the steel include the basic elements, and the remaining part is composed of & and the chemical composition which is unavoidable, which is the basic composition of this embodiment. However, in addition to the basic composition (instead of a part of the remaining portion F e ), in the present embodiment, the following elements (selective elements) may be contained as needed. Further, even if these selective elements are inevitably mixed into the steel, the effects of the present embodiment are not impaired. In other words, in addition to the above-described basic components, one or more of V, Cu, and Ca may be added to the steel. V can improve the hardenability, and there is also the tempering of the granulated iron structure or tempering. The precipitation strengthening effect in the iron structure is known. Since it helps to increase the strength, it is also possible to add V as needed. However, the addition of a large amount of v has a hindrance to the fusion, and because of the element of the price, the quantity is 〇.1〇. /. Hereinafter, it is preferably 〇〇9〇% or less or 0_080% or less. X ′ is to reduce the cost of the alloy, and it is not necessary to intentionally add V to the steel. The lower limit of the amount of V is 〇〇/0.

Cu is an element that enhances strength by solid solution strengthening, and Cu may be added as needed. For example, €:11 can be added to the steel so that the amount of 〇1 is 〇 5% or more. However, when Cu is added in a large amount, the effect of strengthening the strength by solid solution strengthening will reach the limit. Therefore, the amount of Cu is 〇.5〇. /. Below, take 〇4〇. /((The following or 〇3〇% 201226582 means good and 'Cu is a high-priced element, in order to reduce the cost of the alloy, it is not necessary to add Cu to the steel, Clidan + . u Ujh: the lower limit system 〇〇 / 〇 * ^ has the effect of spheroidizing the spheroidal material of Kawasaki, and the workability of the remaining MnS is reduced. It is also possible to add Ca to the steel as needed. In addition, in order to add Ca to steel for the purpose of hai, it is also possible to steel. It contains 0.0001% or more of Ca. However, 'the addition of a large amount of Ca reduces the weldability, so the upper limit of the amount of Ca is 0.,0030% or less, and 〇〇〇2〇% or less or 〇〇〇1〇% or less. Further, in order to reduce the alloy cost, it is not necessary to intentionally add Ca to the steel, and the lower limit of the amount of Ca is 0°/〇. As described above, the high-strength steel sheet of the present embodiment has the aforementioned basic elements, and the remaining portion is a chemical composition composed of Fe and unavoidable impurities, or a chemical composition comprising the above-mentioned basic element and at least one selected from the above-mentioned selected elements, and the remainder being composed of Fe and unavoidable impurities. In addition to the range of conditions, as mentioned above, Sufficient weldability 'adjusts the composition of the component so that the Pcm defined by the above formula (5) is 0.22% or less. As described above, under the condition that the Pcm is 0.22% or less, the plate is satisfied to have an embedding ratio of 83% or more. The sum of the distribution of the granulated iron and the lower toughening iron in the organization is more than 90%. The fraction of the lower tempering iron needs to be above. In order to stably obtain the structure of the lower tough iron body, the composition is adjusted. The composition is such that the enthalpy (Α value) defined by the above (Formula 6) is 2. 〇 or less. When the steel does not contain v&Cu as a selective element, Pcm and A respectively are as follows (Formula 7) And (Expression 8). These (Formula 7) and (Formula 8) respectively correspond to (Formula 5) and (Formula 6) above.

Pcm=[C]+[Si]/30+[Mn]/20+[Ni]/60+[Cr]/20+[Mo]/15+5 x[B] · · · (Expression 7) A= ([Mn]+1.5x[Ni])/[Mo] · (Expression 8) In the above (Formula 5) to (Formula 8), the element corresponding to each variable in the formula is not contained in the steel ( For example, in the case of V, Cu, and Ni), 〇 is substituted into the variable. The component composition satisfying the range of the amounts of the above respective elements and the conditions of Pcm and A is the component composition in the present embodiment. Next, the structure of the steel of this embodiment will be described. As described above, the weldability required for the usual welding construction management meets the fall ratio of 83% or more, and the sum of the balance of the granulated iron and the lower toughened iron is more than 90%, of which the lower toughening iron is The rate must be above 7〇%. Here, a large amount of fine swarf carbon iron in the lower toughening iron exists in the interface of ferrite lath or ferrite iron thin crystal. The fine snow-capped carbon iron is considered to increase the strength of the fall, especially the diameter of the snow (equivalent diameter) is about 1~l〇mn, and the effect of the lifting strength of the snow-capped carbon iron is large, so that the fine snow-minding carbon iron More is better. However, it is difficult to accurately measure a few nm of smectite carbon iron. On the other hand, considering the production conditions corresponding to the amount of C and the like, when the amount of swarf carbon iron is generated in the steel, the more the fine swarf carbon iron is, the smaller the (four) carbon iron is. Therefore, the inventors of the present invention investigated in detail the magnitude of the fall strength and the number and density of the ferritic carbon iron. As a result, it was found that the diameter of the steel sheet structure (circle equivalent diameter) of the coarser snow carbon of 50 nm or more was found. The number density of iron is less than 20 W, which is a preferable condition for containing a large number of fine Xueming carbon irons to significantly increase the strength of the fall. Thanks to the steel plate structure 201226582, there are many such fine snow-minding carbon irons, which can achieve a drop-over ratio of 83% or more. In addition, the lower limit of the number density of the Xueming carbon iron is 〇/3. / Outside, preparing a base material of a steel plate of a predetermined volume by electrolytic dissolution and extracting a sample of (tetra) carbon iron by an extraction impression method, and observing the sample by a transmission electron microscope (TEM), which has 5 ( ) The number of units per unit volume (number density) of stellite carbon iron (snow carbon iron of 50 legs or more) of a circle equivalent to a diameter of nm or more. In addition, as will be described later, the aspect ratio of the former Wostian Iron (formerly Vostian Iron) is 2 or more. The ratio of the length of the long axis of the former Woostian Iron (4) to the short axis length of the former Voss (the axial ratio) is the average of the axial ratios of the former Worthfield iron particles. Therefore, the lower limit of the aspect ratio is 1. Further, a high-strength steel sheet according to the embodiment of the present invention will be described in detail. (4) A high-strength steel sheet is produced by using the following method to form a flat steel preform (steel) which is composed of components in a hard steel such as the addition to satisfy the composition of the above embodiment. Further, Fig. 4 is a view showing the outline of a method for producing a high-strength steel sheet according to the present embodiment. Heating the above-mentioned flat steel at a temperature (heating temperature) (8)) to sufficiently improve the effect of controlling the rolling effect or the carbide or the carbide of the alloying element such as m to be hardenable. The upper limit of the temperature is not made, but the productivity is reduced, or the particle size of the Worthite iron is changed when the time is increased. c is better. The heated flat steel is heat-deferred to a target thickness (S2) so that the cumulative rolling reduction ratio in the non-recrystallization temperature region is 嶋 or more. In the flat steel slab which is reduced, that is, the steel plate (steel), the plate thickness is usually 6 to 25 coffee, but it is not limited to 19 2 〇 12265582. Here, when the cumulative rolling reduction ratio in the non-recrystallization temperature region is 60% or more, sufficient processing strain can be introduced into the steel, and the strength characteristics of the steel sheet can be appropriately controlled. Further, the non-recrystallization temperature region is a temperature region of Ar3 or more and 960 °C or lower, and in this temperature region, recrystallization after rolling (reduction in processing strain) can be prevented. Further, when Ar3 (Ar3 metamorphic point) is cooled, the temperature at which the ferrite iron starts to be metamorphosed can be measured by a thermal processing simulation tester (THE RME CMA STOR-Z) of Fuji Electric Wave mechanism. This Ar3 was measured by heating steel (sample) to 1200. (: After holding for 1 minute, then 2.5. (: / minute cooling 'measures the volume change during cooling, and determines Ar3 according to the volume change. In addition, the cumulative rolling reduction rate under the non-recrystallization temperature region is less than 10 〇〇 /钢板. For the steel sheet (steel) obtained by hot rolling, the hot rolling is followed by accelerated cooling (water cooling) from the temperature above Ar3 (starting water cooling temperature) on the line. Accelerated cooling on the line improves the hardenability. In order to lower the pcm, the accelerated cooling temperature is set to a temperature equal to or higher than Ar3, and when accelerated cooling is started from a temperature lower than Ar3, ferrite iron or upper toughening iron is formed, and the strength of the steel sheet is greatly reduced. After the accelerated cooling, the accelerated cooling is stopped at 3 〇〇 above and below 45 ° C (the water cooling temperature is stopped), and then the cooling is performed (S3). When the water cooling temperature is stopped above 45 (rc, it is easy to generate) The upper toughened iron has a high tendency to decrease the tensile strength and the tensile strength. Moreover, when the water cooling temperature is less than 300 C, the tissue fraction of the granulated iron is higher and the drop ratio is decreased, so it is difficult to balance the strength of the fall. The upper limit of the tensile strength is limited. Here, the accelerated cooling (water cooling) is in the p degree region above the cooling stop temperature and below Ar3, and the average cooling rate of the l/4t portion of the steel sheet is 忉 々 or more 2 cooling. The upper limit of the average cooling rate of the accelerated cooling is particularly limited.

20 201226582 In addition, in the temperature range where the cooling (maintained in the atmosphere) is at room temperature or more and less than the cooling stop temperature, the average cooling rate of the 1/41 portion of the steel sheet is /s or less, and the average cooling of the occupational cooling The lower limit of the speed is not limited. In addition, the l/4t portion of the steel plate is a portion from the surface of the steel plate toward the center of the plate thickness (depth) at a distance of 1/4 of the thickness of the plate, and the cooling degree of the portion is the temperature obtained by performing temperature analysis. Change is sought. Further, by arranging the cooling after the accelerated cooling, it is obtained by _% or more (four) iron, and indeed: sufficient fine swarf carbon iron. At this time, in most of the obtained steel sheets, the number density of the coarser stellites of 50 n m or more is 2 or less and 3 or less. In the steel sheet manufactured by the present embodiment, the aspect ratio of the former Worth iron is 2 or more, and the sum of the lower fluctuation iron fraction and the methadrite fraction is 90% or more, and the lower _ iron fraction is more than or equal to And the structural characteristics of the steel plate produced by the accelerated cooling on the line. X. In the present embodiment, the undulation strength of 885 or more and the tensile strength of 9130 ip (10) and 1130 MPa or less are achieved without tempering. On the other hand, when the steel sheet is accelerated and cooled on the line, and the reheating and quenching are performed after the end of the cooling, the longitudinal rod ratio of the steel sheet before the steel sheet is less than 2 〇. At this time, in order to ensure the ratio of undulation, it is necessary to temper, so the number of projects and the time required for the project are increased, and the cost of the industry is increased. Further, after the steel sheet is taken up after the accelerated cooling, and the steel sheet is placed in the state of the coil, the cooling rate at the time of cooling is small (4) (four), and the number density of the coarser stellite carbon on the heart is larger than 2_哗2. Therefore, it is preferable that the cooling system after the accelerated cooling of the steel sheet in the coil state is not preferable, and it is preferable to leave the steel sheet 21 201226582 one by one until the temperature of the steel sheet is 250 ° C or less. In other words, it is preferable that the steel sheet is not overlapped with the stacking steel sheet (for example, the surface of the steel sheet can be brought into contact with air) until the temperature of the steel sheet is 25 〇 ° C or lower. Alternatively, after the temperature of the steel sheet reaches 250 ° C or lower, the steel sheets may be placed in an overlapping manner. In addition, the steel plate obtained by the accelerated cooling by the hot tempering at the local temperature tempering, and the snow-stained steel, is not easy to sufficiently ensure the fine carbon-carbon. EXAMPLES A steel sheet obtained by refining steel having the composition of the components shown in Tables 1 and 2 and having a steel composition No. A to AP was produced by the manufacturing conditions shown in Tables 3 and 4 to a thickness of 6 to 25 mm. Steel plate No. 1 to 55. In Tables 1 and 2, when Cu, Ni, and V ' Ca were not added to the steel, the amount of these chemical components was added to the brackets. Further, in Tables 3 and 4, after the accelerated cooling (water cooling) was stopped, the steel sheet was cooled one by one without winding the steel sheet until the temperature of the steel sheet was 25 Torr. According to the method shown below, the steel plate N〇.Bu 55, the microstructure fraction of the lower toughening iron and the granulated iron, and the number of stellite carbons (number density) of 5〇11〇1 or more were measured. )] The aspect ratio of the front lining, the amount of diffused hydrogen of the fused metal under the y-type secret test, and the evaluation of the drop strength, tensile strength, weldability, and toughness. The compositions and characteristics of the steel sheets obtained by these measurements and evaluations are shown in Tables 5 and 6. twenty two

ON as r** (N 5 oo oo (N 卜 m oo (N 卜 o JO ON (N o (一) 9 CN VO 〇〇o <N v〇S vq 〇〇〇s CN (N cn 00 (NV AV£> (N 〇(N (N * N®' •ϋ· ε μ 0.204 | 0.207 | I 0.196 | I 0.198 | | 0.187 | | 0.210 | 1 0.196 | 0.192 [0.206 | 0.206 I 0.185 | | 0.203 I 0.196 0.184 :0.202 1 0.193 0.189 | 0.188 ,0.209 | I 0.193 1 ! 0.192 | *裒| 0.446 | | 0.477 | | 0.442 1 1 0.473 | 1 0.481 | I 0.468 | | 0.457 | 0.463 | 0.428 1 0.468 1 0.474 1 0.464 | 0.455 | 0.538 1 | 0.366 | | 0.470 1 | 0.369 1 0.415 | 0.527 | | 0.429 | I 0.432 1 Component (% by mass) ca U 1 (0.0001) | o N 〇oso 0 oo 0 r? oo 0.0012 | os /—*N 〇0 ooso | 0.0009 1 o 0 ooo, 〇oo, S"' 〇/—N ooo /•""N 〇ooso 0 〇〇> I (o.ooi) 1 Oo, | 0.031 | (0.001) 1 gs o I 0.092 | o I 0.047 | ss 〇o, oo, soo, ! 0.062 I (0.003) o (0.002) 1 so ! (0.003) | (0.000) , (0.001) 1 (o.oon 1 | 0.0041 I | 0.0031 | | 0.0037 | | 0.0031 | | 0.0051 | | 0.00 34 | 1 0.0044 I | 0.0052 | I 0.0042 II 0.0036 | I 0.0044 | | 0.0048 | 0.0041 0.0036 | 0.0034 | I 0.0048 | | 0.0035 1 I 0.0033 | 0.0046 [0.0031 | | 0.0034 1 κη | 0.002 1 | 0.003 | | 0.001 | 0.001 | | 0.001 | I 0.002 | I 0.001 I | 0.003 | I 0.001 I | 0.001 | | 0.001 | | 0.002 | 0.003 0.001 | 0.002 | | 0.002 | | 0.001 | | 0.001 | | 0.002 | | 0.001 1 1 0.009 1 α -1 0.003 II 0.003 II 0.004 II 0.004 II 0.003 I | 0.003 I 1 0.002 II 0.004 II 0.008 II 0.003 II 0.004 II 0.002 ! | 0.001 | | 0.003 II 0.005 I | 0.004 | I 0.004 I | 0.003 | | 0.004 | 0.018 I 0.004 CQ 1 0.0009 II 0.0012 II 0.0012 II 0.0010 II 0.0012 I | 0.0011 I | 0.0009 II 0.0009 II 0.0011 II 0.0015 II 0.0010 II 0.0022 I [0.0019 | 0.0012 I 0.0011 I | 0.0012 | I 0.0011 II 0.0014 I 0.0009 I 0.0021 I 0.0015 < 1 sososogosoisoso 1 soi SOS 〇1 so SO sdisoso 1 0.015 II 0.014 I | 0.021 I | 0.011 I | 0.012 I | 0.012 I 1 0.015 II 0.009 I | 0.018 I 0.012 I 0.010 1 | 0.012 I | 0.01 | | 0.012 II 0.015 I ! 0.015 I 1 0.012 I 0.011 , 0.012 | 0.020 I 0.011 I 0.034 I 0.021 0.017 | 0.022 I 0.044 0.015] 0.035 0.016 0.028 0.027 0.021 0.021 0.035" 0.021 | 0.016 0.012 0.015 I 0.014 ,0.020 | 0.024 II 0.022 | (0.02) (0.03) /—*s SO, (0.01) (0.02) 〇g S sgo (0.01) (0.02) (0.03) (0.01) so, Q o, 〇Q g· o. s 〇 , 3 υ (0.01) (0.02) /-s (0.03) (0.02) 〇S' ss % CN o 〇, (0.03) (0.02) (0.01) (0.02) o, 0 gs o g" 0 /—V Se color ο s 〇v〇o ON ro 〇o 00 (N oogo guide o' 00 oo O »no ON (N d (N i〇o P; oo 〇a; o wear o (N cn d 00 o in ( NO (N 00 o & oo 00 VO do CN o oo 00 o O 00 o 〇\ o S ov〇〇On <N 〇On 〇ooc % 00 oo o OS (N d JO o 00 o δ o 00 o ON v〇dsm ό O ON VO dd CN ON d 5 〇VO oo 〇P o (N 00 o yn cn d inch o 00 m O ON CN c> oo oo 穸 o o CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN CN o 〇5; O om 〇沄od U 0.094 0.088 0.076 0.081 0.059 0.090 0.079 0.068 0.087 0.081 0.0 61 0.072 0.077 0.034 1 0.124 0.077 0.085 0.087 0.065 I 0.078 0.080 Steel composition No. < CQ U Q ω (X a X O CL 〇 C/3 H D (>] X(N. I+0S))/([! κ]X ΓI+CS】)=V * * * [ars+ol/>]+sl/ow】+o<N/[J3]+09/[! N]+o(N/3u)+o(N/cs]+oi:/[!s]+u]=E3d** inch 1>]+inch/ow】+s/[Ju]+0w [!N]+9/[uw]+inch Z7[!s]+u]=b3u* 23 201226582 [<N<] 00 pi r- P Bu m Bu P; Bu Os P Os P Bu ο ΓΛ (Ν cn ιη ΓΛ 卜 (Ν as Ρ * * P P N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N N 〇lo — — — — — 一 — — — (Ν! (ν| <νΙ * Co1 〇, B Os 2 1 0.230 1 0.193 m (N 00 冃2 00 o rs 0.191 1 0.193 1 1 0.207 I 00 inch) m (Ν 00 m (Ν Ν ο § 00 (Ν Ν Ν Ν Ν t t t t t t t t t * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * \ m VO JO r- (N m 0.428 ON CN inch o 00 00 ϊ mm mm mm mm mm «—s /<—N rs N oo 〇〇N s 豸g' 运/-Ν/-Ν UU o 〇oooooo Ο ο ο ο ό ο ο ο ο Ο ο 〇 oo oo ο ο ο ο ο ο ο > o /*—ssoo, /<—N o /«—sss /«—Ν SS /-"-ν /<-Ν S o, o, o ο, ο, ο, ο ό, ο , somso | 0.0043 | mmmmo 00 1 0.0050 1 5 00 m S 00 ΓΛ (Ν ? 5 苕 oooooooo Ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο ο Soo ΓΛ ooso ο 1 0.003 1 1 0.002 ι 1 0.002 ι 1 0.003 ι ο ο ο ο ο ο ooooooooo ο ο ο ο ο ο ο ο CU so | 0.005 | | 0.003 | o S | 0.003 | go I 0.005 II 0.003 | 0.003 1 so 1 0.003 1 1 0.005 ι 1 0.005 ι 1 0.004 1 1 0.003 ι 1 0.005 1 1 0.003 ι 1 0.005 ι 1 0.005 ι 1 0.005 1 1 0.005 ι ddoo Laughter (N oo 2 2 o 2 00 1 0.0045 1 1 0.0011 1 1 0.0011 1 (Ν as 1 0.0011 1 2 CQ o 〇O osooooo ο ο Ο ο ο ο ο oooooooooo ο ο ο ο ο ο ο ο ο s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s ο ο ο ο ο ο ο ο ο ο Φ p 0.016 0.012 0.013 0.015 0.021 0.013 0.013 0.015 0.014 0.001 0.055 0.011 0.014 0.013 0.015 0.014 0.012 0.014 0.014 0.014 0.014 0.027 0.015 | 0.021 0.015 I 0.015 | 0.030 0.024 I 0.001 | 0.080 0.015 0.013 1 0.012 0.018 Ι 0.022 0.032 0.024 1 0.022 1 0.029 0.023 1 0.023 0.021 2 ;l /—NS /—N rn s rn /—SS /-'ν g 8 /—Ν ΓΠ ol 0 oo 0 o ο, 0 ο 0 0 ο, S ο 0 3 /—N o g" N gv /«—sg' /—Ν /«—S g1 /—S g' /—S q S /—Ν /«—Ν U o, 0 o. o, o, Ο, 0 ο, έ ο, ο, 色Ο, 〇00 v〇m irj m Os\ 00 *T) (N *〇m 吞艺Os ΓΛ 妄«η α; 寸卜(Ν Ο ΓΛ cn 容 o O d ol oooooo Ο Ο ο ο ο ο ο ο ο ο ύ j CjJ SI fN On m (N (N <N »n jn VjJ α α α 〇 茬 茬 ΐ ΐ ri ri O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O ο cs 00 m Os sv〇v〇ON Os (N ON 00 os S ΓΛ 00 s 5; 00 ΟΝ Ον 00 α\ ΟΝ SS SS Os oodd 〇oodo ο ο Ο d ο ο Ο ο ο ο Ο π oo (N 荛mm On <N CO (N ΓΛ ΓΛ wm rn m 沄 ΟΝ oo oooo 〇o 〇ο ο ο ο Ο ο ο ο ο Ο 1 u 1 0.080 I | 0.084 II 0.079 II 0.086 II 0.071 II 0.069 II 0.089 I | 0.079 II 0.084 I | 0.088 II 0.080 1 1 0.090 1 1 0.078 Ι 1 0.091 II 0.092 Ι Ι 0Ό72 Ι 1 0.086 I 1 0.085 II 0.061 II 0.094 Ι 1 0.088 ι Steel composition d > X >- N < ϊ ([>X(N. I+0S))/([! Zl x S. 1+ns])=v * * * [ars+0l/[>+sl/ow]i(N/[Ju]+09/[!N]+0(N/[nu]+ 0<N/[uw]+0i:/[!s]+u]=E3d** H/[>+inch/ow]+s/[Ju]+0w[!z]+9/[uw] +々(N/[!s]+u]=b3u* 24 201226582 [Table 3] Steel plate No. Steel composition No. Hot rolling and accelerated cooling rolling heating temperature (°C) Thickness (mm) The rolling shrinkage Φ (%) in the crystallization temperature region starts the water cooling temperature cycle CC) Stops the water cooling temperature (°C) The cooling rate at the accelerated cooling (°C/s) Example 1 A 1180 25 64 804 325 42 2 A 1170 6 70 761 420 105 3 B 1150 25 66 819 360 40 4 B 1175 9 62 750 425 71 5 C 1200 25 64 794 330 38 6 D 1165 25 63 820 370 40 7 D 1130 12 61 767 410 66 8 E 1150 25 64 809 335 41 9 E 1135 12 66 764 395 67 10 F 1160 25 66 798 405 40 11 G 1155 25 64 802 375 44 12 H 1135 25 70 799 360 37 13 I 1125 25 64 779 375 38 14 J 1180 25 65 794 410 37 15 K 1150 25 67 804 350 38 16 L 1160 25 66 787 320 41 17 M 1180 25 66 784 335 37 18 M 1145 16 69 765 365 58 Comparative example 19 N 1170 25 67 820 350 43 20 0 1175 25 68 782 360 40 21 P 1150 25 64 820 380 40 22 Q 1150 25 66 816 370 37 23 R 1150 25 66 810 375 42 24 S 1165 25 65 789 315 38 25 s 1165 25 68 792 435 43 26 T 1160 25 67 804 345 39 27 u 1160 25 62 798 330 40 28 V 1150 25 65 802 430 40 25 201226582 [Table 4] Comparative Example Steel Plate No. Steel Composition No. Hot Rolling and Accelerated Cooling Delay Heating Temperature ( °C) Plate thickness (mm) Rolling rate in the region of non-recrystallization temperature (%) Start water cooling temperature CC) Stop water cooling temperature CC) Cooling rate CC/s during accelerated cooling 29 V 1150 25 66 797 320 43 30 W 1150 25 66 785 410 41 31 X 1140 25 67 799 375 37 32 Y 1155 25 66 805 370 42 33 Z 1180 25 65 801 375 38 34 AA 1175 25 66 798 350 40 35 AB 1160 25 64 788 370 35 36 AC 1165 25 66 813 380 43 37 AD 1160 25 66 778 340 39 38 AE 1160 25 68 800 375 41 39 AF 1165 25 65 779 350 43 40 AG 1160 25 67 804 360 41 41 AH 1175 25 66 799 345 37 42 AI 1165 25 64 802 350 39 43 AJ 1145 25 66 789 355 40 44 AK 1155 25 66 800 405 40 45 AL 1125 25 65 785 380 3 7 46 AM 1160 25 67 805 440 39 47 AN 1160 25 66 799 325 38 48 AO 1130 25 66 784 435 40 49 AP 1130 25 67 769 330 38 50 D 1050 25 65 799 355 35 51 B 1170 25 63 680 360 30 52 A 1150 25 68 801 495 13 53 A 1140 25 64 798 150 41 54 A 1150 25 62 氺 ** ** 55 A 1170 25 64 802 333 7 ** After rolling and cooling, reheat to 930 ° C, It was further cooled to 810 ° C to 350 ° C at a cooling rate of 40 ° C / s. 26 201226582 Sο'ωΛ 3 inch lsl1 f! 95 one inch 99 '"' 0rl I inch 0 inch 1 —Ml 86 zq sg ZL s 98 36 38 H 36 96 Bu 8 *6e 16 MA inch 6 sft $ ^—i Hpl— $ f I 竣Kpl 浚Kpl Hard KDI Over Kpl s I f— s €"w^瑕(00..) 峒 铋 铋 衔 衔 ( (SW) -3⁄4 ^*2 (-) -*绥W 恝田绽-ΕΠ/学) Fu·S Li Chu驭S WTV^ios (%) -1° L- s1- 9- 9.g 1^, HM MM ΤΓ 9.11°MMMH inch 1-1ΥΓ " 7Γs.g 11° inch 01 '-'01 1 to ϋΠΐ L66 £TISI S6 ^TT/,86 3901 osl Z601 6C01 3901 8901 I" Bub 01 0901 0601 igo1-1 lool£or 3lsll 6801 ZZQl Bu inch 2 §1 E60-' βε6 I inch 6 s LZ6 g£6 Yuan Bu inch 60 inch Z6 eg 961001 i lr~'e66Ϊ6 S6 '-'6 IS6 916 og 0£6 9£6 '-'ό" 8Z6 '-'6 Inch s 6.1 MM LZ MM 8.3 IT 3'" FT FT 7T 1^,re HM HM ''3 t-£ L'Z WM inch·ε 0'-' ~§τ TT- Lz 1·1 inch Tr1 inch -1 ° inch - inch π ~91001 u^ H 1^1 ~ZL ul8~ —Ml u6T6A ~LS "91001 yn is 6<u6Τ6ΛΙ 10011001ul6 Mrlun "6<T6<i6< lsl 1^1

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28 201226582 After the cross section of the steel plate was mirror-polished, the surface of the steel plate was observed by scanning electron microscopy (SEM) with a nitrite solution. The 4-port rate is 3〇00 times, and the field of view is in the range of 25μΓηχ2〇μιη. The area of (4) iron and hemp iron was measured by the image obtained by the observation, and the respective tissue fractions (area ratio) were determined. Further, an image obtained by observing a cross section parallel to the rolling direction (longitudinal direction) of the steel sheet in the vicinity of the l/4t portion in the same manner as the image is obtained (the cross section perpendicular to the center of the sheet thickness direction). Before measuring the length and short axis length of the Worth w iron, the aspect ratio is obtained by dividing the long axis length by the short axis length. Further, a base material of a steel sheet of a predetermined volume of electrolytically eluted steel sheets No. 1 to 55 was produced, and a sample of Xueming carbon iron was extracted by an extraction stamping method, and the sample was observed by a transmission electron microscope (TEM). The number of stellites having a circle equivalent diameter of 50 nm or more was determined. When the number of the samples was measured, the precipitates other than the smectite carbon were distinguished by EDX. However, in the steel sheets No. 1 to 55, precipitates of 5 〇 nm or more other than the ferritic carbon iron were not present. Further, 'Ar3 (Ar3 metamorphic point) was measured using a thermal processing simulation tester (THE RME CMA STOR-Z) of Fuji Electric Wave Mechanism. In the measurement of Ar3, steel (sample) was heated to 1200 ° C and kept 10 Minutes, then cooling at 2.5 ° C / min 'measures the volume change during cooling, and determines Α γ 3 according to the volume change. Further, the tensile test pieces of ία specified in JIS Ζ 2201 (1998) were taken out from the steel sheets No. 1 to 55, and the tensile strength and the tensile strength were measured by a tensile test prescribed in JIS Z 2241 (1998). As a result of the tensile test, when the tensile strength is 885 MPa or more and the tensile strength is 950 MPa or more and 1130 MPa or less, the tensile strength and the tensile strength of the steel sheet are respectively evaluated as "合袼29 201226582, as defined in JIS Z 3158 (1993). The y-type weld crack test was used to evaluate the weldability of the steel sheets No. 1 to 55. In the y-type weld crack test, the temperature and humidity were adjusted, and carbon dioxide arc welding was performed at a heat of 15 kJ/cm, and the steel plate for evaluation was used. The thickness was 25 mm. As a result of the test, when the root crack rate was 〇 without preheating (room temperature 25 C), the weldability of the steel sheet was evaluated as "acceptable". Further, steel sheets N〇2, 4, 7, 9, and 18 having a thickness of 6 mm to 16 mm can be regarded as having the same weldability as steel sheets No. 3, 6, 8, and 17 having similar compositions. The steel plate No. 2, 4, 7, 9, and 18 were omitted from the y-type weld crack test. Further, in the y-type weld crack test, the two test materials were respectively subjected to welding under the conditions of temperature, humidity, or heat, and the latter was used as a sample immediately after welding, by JIS Z 3118 (2007). The gas chromatograph method is prescribed to measure the amount of diffused hydrogen of the molten metal. As a result of the analysis, only when the amount of diffused hydrogen was more than 5.0 ml/100 g, the remaining test materials were used for the evaluation test of the aforementioned weldability (with or without cracks). The No. 4 satay test piece specified in JIS z 2201 (1998) was taken out from the center of the plate thickness in the direction perpendicular to the rolling direction, and the absorption energy of the impact test in _4〇»c was measured and absorbed by the three test pieces. The average value of energy (vE_4〇) is evaluated as toughness' 5 and the turbulent target value is 27J. On the other hand, for a steel plate having a thickness of (10)!^ and 9 mm, a sandpaper test piece of 5 mm order size was taken out, and the target value of the toughness was set to be 27 J or more per lcm2. Further, the amounts of the chemical components indicated in Tables 1 and 2, the values of pcm, and A did not satisfy the composition conditions of the steel sheets of the present invention. Similarly, the values marked with the bottom line in Tables 3 and 4 do not satisfy the manufacturing conditions of the present invention. Tables 5 and 30 201226582 Table 6 shows that H has a numerical value of the structure of the steel sheet of the present invention or the steel sheet is insufficient. In Table 2, the steel sheets N〇1~1 8 and β 18 ' are both the ratio of the lower tough iron fraction and the Ma Tian iron fraction (lower domain fraction + Ma Tian iron fraction) of 90% or more, and The lower _ iron fraction is above 鸠, the lodging strength, the tensile strength, the drop ratio, and the refining splicing knife I·sheng meet the target values. Here, in the y-type fusion crack test performed to evaluate the meltability, the amount of diffusible hydrogen in the refined metal is in the range of 5" to 6. 〇ml/1 〇〇g, and it is confirmed that the range does not occur in the range. Refining cracks. Therefore, it is considered to be a carbon dioxide (10) towel, which may be mixed when the refining construction management is slightly insufficient. (IV) The amount of hydrogen is about 3.0~5.Gml/1〇〇g. The amount of diffused hydrogen is low, and it is known that no cracks in the refining process occur. Here, the steel plate N is used. "~18 is more important." When c is tempered, the number density of coarser stellites above 5 〇 nm increases, and the undulation strength is lower than that in the case where tempering is not performed. Further, for example, in the condition k of the steel sheet n〇7, the cumulative rolling reduction ratio in the non-recrystallization temperature region is changed to J at 60/. In the case where sufficient processing strain cannot be introduced into the steel, any of the strength characteristics (for example, toughness) is lower than that of the steel sheet No. 7. On the other hand, in the steel sheets N〇19 to 42 which do not satisfy the conditions of the present invention in the amounts of the respective chemical components shown by the bottom line in Tables 1 and 2, although the manufacturing conditions of the present invention are satisfied, the lodging strength and the tensile strength are satisfied. One of the weldability and toughness has not yet reached the target value. In the steel sheets Νο·43 to 49, the amount of each chemical component satisfies the conditions of the present invention. However, in the steel sheet ν〇.43-45 in which the value of Pcm does not satisfy the conditions of the present invention, the weldability is unacceptable. Similarly, in the steel sheets No. 46 to 47 in which the value of the crucible did not satisfy the condition 31 201226582 of the present invention, the fall strength was unacceptable. Further, in the steel sheets No. 48 to 49 in which the pcm value and the A value did not satisfy the conditions of the present invention, the weldability and the fall strength were unacceptable. In the steel sheets Νο·50 to 55, the amounts of the respective chemical components, the values of pcm and A satisfy the conditions of the present invention. However, at least one of the manufacturing conditions in the steel sheets Νο. 50 to 55 does not satisfy the conditions of the present invention. Therefore, in the steel sheet Ν〇.50~55, in addition to the structural conditions of the steel sheet (one or more of the lower toughening iron + the maitian iron fraction and the lower toughening iron fraction), the conditions of the present invention are not satisfied, and the lodging strength, At least one of the tensile strength 'toughness is unacceptable. In addition, in the steel plate Νο·54, the steel sheet is produced on the rolled steel sheet, and after cooling, the steel sheet is further heated to 930 ° C, and then cooled to 810 C to 3 50 C at a cooling rate of 40 ° C / s. Temperature zone. Therefore, for example, compared with the steel plate 1^〇.52, the steel plate.54 increases the manufacturing cost. Industrial Applicability It is economically possible to provide a high-strength thick steel plate having a tensile strength of 885 MPa or more, a tensile strength of 950 MPa or more, and a U3 〇 MPa or less, and excellent weldability, and a method for producing the same. [Simple description of the drawing] Fig. 1 is a graph showing the relationship between the crack stop preheating temperature in the PCm and y-type weld crack test. Figure 2 is a graph showing the relationship between the tissue fraction of the lower toughened iron and the ratio of the drop. Figure 3 is a graph showing the relationship between the A value and the tissue fraction of the lower toughened iron. 32 201226582 Fig. 4 is a flow chart showing an outline of a method for producing a high-strength steel sheet according to an embodiment of the present invention. [Main component symbol description] S1~S3...Step 33

Claims (1)

201226582 VII. Patent application scope: 1. A high-strength steel sheet characterized in that its chemical composition is contained in mass%: C: 0.05% or more and less than (U0%, Si: 0.20% or more and 0.50% or less, Μη: 0.20% or more and less than 1.20%, Cr: 0·20°/. or more and 1.20% or less, Mo: 0.20% or more and 0.60% or less, Nb: 0.010% or more and 0.050% or less, Ti: 0.005% or more and 0.030% Hereinafter, A1: 0.01% or more and 0.10% or less, B: 0.0003% or more and 0.0030% or less, V: 0% or more and 0.10% or less, Cu: 0% or more and 0. 50% or less, and Ca: 0% or more And 0.0030% or less, and is limited to: Ni: 0.1% or less, P: 0.012% or less, S: 0.005% or less, and N: 0.0080% or less, and the remainder is composed of Fe and unavoidable impurities. The Pcm defined by (Formula 1) is 0.22% or less, and the sum of the microstructure fraction of the lower toughened iron and the tissue fraction of the granulated iron is defined by the following A (2) of the formula (2). More than 90%, the above-mentioned lower toughening iron has a tissue fraction of 70% to 34 201226582, and the aspect ratio of the former Vostian iron particles is more than 2, The drop strength is 885 MPa or more, and the tensile strength is 950 MPa or more and 1130 MPa or less; Pcm=[C]+[Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/ 2 0+[Mo]/15+[V]/10+5x[B]· · · (Formula 1) A=([Mn]+1.5x[Ni])/([Mo]+1.2x[V] ) · · · (Formula 2) Here, [C], [Si], [Μη], [Cu], [Ni], [Cr], [Mo], [V], [B] are the aforementioned chemistry The mass 〇/〇 of c, Si, Mn, Cu, Ni, Cr, Mo, V, B in the composition. 2. The high-strength steel plate of the first application of the patent scope 'the sulphur carbon iron of 5 〇 nm or more The number density is 20/μπι3 or less. 3. The high-strength steel sheet according to claim 1 or 2 wherein the thickness is 6 mm or more and 25 mm or less. 4. A method for producing a high-strength steel sheet, characterized in that: The steel having the chemical composition described below is heated to ll 〇 0 ° C or more, and the chemical composition is contained in mass %: C: 0.05% or more and less than 〇〇.1 〇〇 /0, Si : 0.20% or more and 0.50% or less Μη : 0.20% or more and less than 1.20%, Cr: 0.20% or more and 1.20% or less, Mo: 0.20% or more and 0.60% or less, Nb: 0.010% or more and 0.050% or less, Ti: 0.005% or less And 0.030% or less, A1: 0.01% or more and 〇.i〇Q /. Hereinafter, B: 0.0003% or more and 0.0030% or less, 35 201226582 V: 0% or more and 0.10% or less, Cu: 0% or more and 0.50% or less, and Ca: 0% or more and 0.0030% or less, and are limited to: Ni : 0.1% or less, P: 0.012% or less, S: 0.005% or less, and N: 0.0080% or less, and the remainder is composed of Fe and unavoidable impurities, and the Pcm system defined by the following (Formula 3) 0.22. /. Hereinafter, the following is the following: (A is 2.0 or less as defined in the formula; hot rolling is performed on the steel, and the cumulative reduction ratio in the non-recrystallization temperature region is 60% or more; and on-line The steel is accelerated to a temperature of 45 C or more at a cooling rate of 10 ° C/s or more, and is cooled to a temperature of 300 ° C or more, and is cooled after stopping the accelerated cooling; Pcm = [C] + [Si]/30+[Mn]/20+[Cu]/20+[Ni]/60+[Cr]/2 0+[Mo]/15+[V]/10+5x[B] · . (Formula 3) A = ([Mn]+1.5x[Ni])/([Mo]+1.2x[V]) · · (Expression 4) Here, [C], [Si], [Μη] [Cu], [Ni], [Cr], [Mo], [V], [B] are the mass % of c, Si, Mn, Cu, Ni, Cr, Mo, V, B in the above chemical composition, respectively. 36