High ductility high crack arrest steel and method of making same

Abstract

The application provides a high-ductility high-rupture-resistance steel plate and a manufacturing method thereof. The steel plate comprises the following components in percentage by weight: C: 0.08%-0.12%, Si: 0.10%-0.25%, Mn: 0.60%-1.20%, P: 0.005%-0.013%, S: ≤0.008%, Al: 0.02%-0.05%, Nb: 0.01%-0.035%, Ti: 0.007%-0.016%, Ni: 0.40%-0.70%, Cu: 0.15%-0.35%, N: 0.001%-0.004%, and the balance of Fe and inevitable impurities. The manufacturing method comprises smelting, continuous casting, heating, controlled rolling and controlled cooling, and heat treatment. The application can obtain a high-ductility high-rupture-resistance steel plate with super-high strength grade, which meets the requirements of super-large container ships for steel strength grade and fracture toughness improvement. Furthermore, the steel plate can improve the resistance to flexural deformation failure under the working conditions such as long-distance operation of ships at sea and surges, and significantly improve the safety of the ship structure.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metal materials, and particularly relates to a 51kg ultra-high-strength high-ductility high-crack-arrest steel and a manufacturing method thereof, BACKGROUND

[0002] With the rapid development of economy, the volume of shipping industry has rapidly increased. As the first of the three major ship types, container ships have developed rapidly in the past decade, from 7-8 thousand containers in 2000 to more than 20,000 standard containers at present. However, the large-scale of ships puts forward higher requirements on the comprehensive performance of steel plates for construction. Especially for the key parts such as the side plate and the upper deck of the ship, since they need to bear the repeated alternating loads such as surge and container collision during the operation of the ship, the materials not only need to have excellent strength, toughness, crack arrest and good weldability, but also need to have excellent plasticity to resist the deflection deformation of the steel plate caused by surge and container compression, or the plastic deformation caused by the collision of the hatch coaming, so as to reduce the risk of material fracture. The fracture of metal materials is caused by deformation exceeding the plastic limit, and the formation of cracks is the result of plastic deformation. Therefore, the plasticity of the material indicates its ability to suppress cracks. The material with high ductility has stronger anti-fracture ability. Especially when the material is subjected to impact load, the material with high strength and high ductility (i.e. high strength and plastic product) has higher resistance to fracture caused by impact.

[0003] At present, advanced steel companies at home and abroad have taken ship crack arrest steel as a strategic product. The manufacturers who have successfully developed and commercially produced such products include JFE, Nippon Steel, Kobe Steel, POSCO, Hyundai Steel and Ansteel. Since then, Baosteel and Nansteel and other domestic enterprises have also begun to research and develop such products.

[0004] The patent document "355MPa grade low temperature anti-collision steel plate and manufacturing method" (publication number: CN112746222B) provides a high-strength steel with a 36kg level, which is mainly used for the load-bearing structure of the key parts of the offshore platform. The invention steel is mainly composed of ferrite, with a ferrite content of ≥80% and a bainite content of ≤10%. The main characteristic indexes can only meet the strength, F-class toughness grade and other requirements of the 36kg steel grade in the ship classification society standard, with a yield strength of ≤400MPa, a tensile strength of ≤510MPa, a maximum thickness of 60mm, and only the low-temperature impact toughness is evaluated, and the brittleness fracture, crack suppression and other characteristic evaluations are not carried out. The strength and thickness indexes are not suitable for the key parts such as the hatch coaming of the ultra-large container ship.

[0005] Patent document "High-strength steel material with excellent ductility and low-temperature toughness and manufacturing method thereof" (publication number CN113166885A) provides a high-strength steel of 32kg and 36kg grade, which adopts a low-carbon + micro-alloying composition system, and has a microstructure composed of refined ferrite + pearlite. The strength grade is only 32kg and 36kg, the steel plate thickness is ≤60mm, and there is no crack arrest index. It is mainly used to meet the requirements of ship hull plating, and is not suitable for key parts of large container ships.

[0006] Patent document "YP500MPa grade steel plate with low yield ratio, high toughness and high weldability and manufacturing method thereof" (publication number CN112746219A) proposes a steel plate for offshore wind power, low-temperature pressure vessel and other structures, which adopts billet light pressing, control of casting temperature and two-stage controlled rolling, obtains a steel plate with a small amount of fine ferrite + dispersedly distributed lower bainite microstructure, and the average grain size is about 15μm. In the aspect of brittle crack arrest toughness, it reaches 6000-7000N / mm 3 / 2 , and the elongation is only 21%, and the evaluation index of crack toughness CTOD is not given, which does not meet the design and application requirements of high crack arrest toughness materials for upper deck, side plate and other structural parts of super-large container ships.

[0007] Patent document "Method for improving impact toughness of TMCP steel for ships by using texture control" (publication number CN112126759B) proposes a method for improving toughness by controlling intermediate billet deformation distribution and improving texture configuration based on EH47 steel plate. However, the rolling process adopts four-stage cooling mode of air cooling + water cooling + air cooling + water cooling, which obviously prolongs the steel plate online production time, greatly reduces the rolling efficiency, and the requirements for cooling system and rolling line layout are extremely complex, which cannot meet the actual mass production. Moreover, its strength grade is low, and there is no crack arrest toughness evaluation, which cannot meet the technical requirements of crack arrest steel for container ships.

[0008] Patent document "Low-cost tensile strength 520MPa grade welding structural steel and manufacturing method thereof" proposes a production technology for obtaining a tensile strength 520MPa grade steel by adding low-cost Ti, Si elements and micro-alloying elements Nb for a steel plate with a maximum thickness of 50mm. The thickness is ≤50mm, and it does not have the technical characteristics of crack arrest toughness and high ductility, and cannot be used for design and material selection of key parts of container ships and construction. SUMMARY

[0009] The present application aims at overcoming the above problems and deficiencies and providing a 51kg steel plate suitable for key parts such as deck of ultra-large container ships, high-ductility high-crack-arrest steel with excellent strength-toughness, high ductility, plastic instability resistance, brittle fracture prevention, good weldability and manufacturing method thereof, realizing matching between strength-plasticity-toughness, high fracture arrest toughness and weldability, and meeting the demand of upgrading of key materials for ultra-large container ships.

[0010] The present application is achieved as follows:

[0011] A high-ductility high-crack-arrest steel, the composition of the steel plate is as follows in terms of percentage by weight: C: 0.08%-0.12%, Si: 0.10%-0.25%, Mn: 0.60%-1.20%, P: 0.005%-0.013%, S≤0.008%, Al: 0.02%-0.05%, Nb: 0.01%-0.035%, Ti: 0.007%-0.016%, Ni: 0.40%-0.70%, Cu: 0.15%-0.35%, N: 0.001%-0.004%; the balance is Fe and inevitable impurities.

[0012] The steel further comprises one or more of Cr: 0.2%-0.35%, Mo: 0.15%-0.35%, V: 0.02%-0.05%.

[0013] The microstructure of the steel is fine lath bainite + a small amount of granular bainite and residual austenite, wherein the percentage by volume is as follows: fine lath bainite 60%-80%, granular bainite 20%-30%, and residual austenite 5%-10%; the average grain size of the microstructure of the steel plate is 8-15μm, and the percentage of grains with large-angle grain boundaries is more than 35%, wherein the large-angle grain boundary refers to a grain boundary with an orientation difference of more than 15° between adjacent grains.

[0014] The mechanical properties of the steel are as follows: yield strength 510-615MPa, tensile strength 618-716MPa, elongation after fracture 24.5%-27%, low-temperature impact energy at-60℃≥200J, CTOD of base material and welded joint is more than 0.65mm and 0.22mm respectively, and Kca at-10℃≥6200N / mm 3 / 2 After 5% deformation and 1-hour holding at 250℃, the low-temperature impact energy of the steel plate at-40℃ is more than 100J.

[0015] The reasons for the component design are as follows:

[0016] C: is the necessary element to ensure the strength of steel, in order to ensure 51 kg super high strength, and based on the delivery state of heat treatment, the content is above 0.06%, but when the content exceeds a certain amount, the effect of the low temperature toughness, crack arrest toughness and weldability of the material deteriorates significantly. In addition, the increase of C content also increases the tendency of residual austenite formed by cooling in the steel, which deteriorates the weldability and low temperature toughness, so the upper limit is 0.12%. Preferably, the C content is controlled in the range of 0.08% to 0.12%.

[0017] Si: is the main deoxidizing component in the steelmaking process, and must be above 0.10% in order to obtain sufficient deoxidizing effect. However, if it exceeds the upper limit, the toughness of the base material and the welded part will be reduced. Si existing in the form of solid solution can increase the strength and the ductile-brittle transition temperature at the same time, so the content of Si is 0.10% to 0.25%.

[0018] Mn: is the necessary element to ensure the strength and toughness of steel, (FeMn)S formed by combining Mn and Fe exists in the form of solid solution, which avoids the formation of low melting point FeS at the grain boundary, which reduces the plasticity during subsequent steel plate processing and causes hot crack defects, thereby greatly improving the harmful effect of S; at the same time, Mn is also a good deoxidizer. As a low-cost strength and toughness element, if the content of Mn is too low, the strength of the material cannot be guaranteed, but when the content of Mn is higher than 1.30%, the segregation of the casting blank will be increased and the low temperature toughness of the coarse grain heat affected zone (CGHAZ) will be deteriorated, so the preferred content of Mn should be controlled in the range of 0.60% to 1.20%.

[0019] P: is an unavoidable impurity element in steel, which can deteriorate the toughness and weldability of steel. Studies have shown that when the content of P is too high, its brittleness performance increases significantly, so P: 0.005% to 0.013%.

[0020] S: if the content exceeds 0.01%, a large amount of MnS inclusions will be formed in the steel, and the formation of MnS inclusions and the anisotropy they produce will seriously reduce the toughness and plasticity of the steel plate, and the weldability; at the same time, the increase of S content will increase the tendency of hot cracking of hot-rolled steel plate, therefore, measures will be taken during smelting to reduce the S content in the steel as much as possible. In the present invention, S≤0.008% is determined.

[0021] Al: as a deoxidizing and grain refining element, the content is generally above 0.01%, but when it exceeds 0.05%, hot cracks of the casting blank are prone to occur, a large amount of inclusions are formed, and the toughness of the steel is reduced, so the upper limit of Al content is 0.05%, and the preferred content range is 0.02% to 0.05%.

[0022] Ni: as an austenite stabilizing element, can greatly reduce the Ar1, Ar3 phase transition temperature, reduce the critical cooling rate, improve the driving force of austenite to ferrite phase transition, delay the pearlite transformation, make the austenite phase transition at lower temperature, significantly refine the microstructure of TMCP steel plate, At the same time, increase the angle between bainite lath, improve the crack propagation resistance in bainite grain, obtain the function of anti-crack and crack resistance; It is beneficial to the organization control, grain refinement and homogenization of the high ductility crack resistant steel plate of the application. But too high Ni content will significantly increase the cost and easily cause the deterioration of the toughness of the welding heat affected zone, so it is appropriate to control the content between 0.40% and 0.70%.

[0023] Cu: can significantly improve the hardenability and corrosion resistance of the steel plate, and is also an austenite stabilizing element. Appropriate addition can refine the microstructure of TMCP steel plate and improve low temperature toughness; but too much addition will cause "copper brittleness" tendency, cracks on the surface and inside of the casting blank, reduce the mechanical properties of the rolled steel plate, and reduce the toughness, causing the steel plate to be brittle, therefore, the Cu content of the application is controlled between 0.15% and 0.35%.

[0024] Cr: chromium is a weak carbide forming element. A certain amount of Cr can improve the hardenability of the steel plate and promote the formation of bainite as the representative of the strengthening organization. It can replace part of the C, Mn and other strengthening elements, reduce the toughness deterioration caused by the increase of the former strength, but higher Cr addition will also lead to the deterioration of the welding performance, therefore, under the TMCP process, the preferred Cr content range is between 0.20% and 0.35%.

[0025] Mo: as an element that significantly improves hardenability and bainite tendency, especially for materials using heat treatment process, appropriate addition of Mo in steel can inhibit the formation of pearlite, which improves the strengthening effect of steel similar to Cr, and improves the strength of steel through carbide formation, but too much addition will also cause the deterioration of weldability and low temperature toughness, therefore, the preferred Mo content range is between 0.15% and 0.35%.

[0026] Nb: one of the key elements for fine-grain strengthening, the refining effect is reflected in two aspects: first, it significantly delays the recrystallization of austenite, increases the recrystallization temperature, and prevents the growth of recrystallized austenite; The second is that with the decrease of rolling temperature, NbC, N compound in austenite diffuses and precipitates before the transformation of austenite to ferrite, becomes the ferrite nucleation site, makes the ferrite form at small supercooling degree, and is not easy to grow, and the ferrite grain size is refined. As the Nb element that expands the non-recrystallization temperature interval, the average grain size of 10-15 μm can be obtained by delaying the recrystallization of austenite, and the proportion of grains with large angle grain boundaries is increased to more than 35%, thereby improving the crack resistance and toughness, and the content is controlled between 0.01% and 0.035%.

[0027] Ti: trace titanium combines with C, N in steel to form fine and stable C, N compound particles, which can effectively prevent austenite grain coarsening during slab heating, and can inhibit welding heat affected zone grain coarsening during welding, thereby improving the low-temperature toughness of the base structure and the weld heat affected zone, and the content is controlled to be Ti: 0.007% to 0.016%.

[0028] N can form fine precipitates with Nb and Ti to play a strengthening and fine-grain effect to improve strength and toughness, but excessive content can deteriorate weldability and easily produce strain aging, thereby deteriorating low-temperature toughness, and the content is controlled to be 0.001% to 0.004%.

[0029] The second technical solution of the present application provides a manufacturing method of high-ductility high-crack-arrest steel, including smelting, continuous casting, heating, controlled rolling and controlled cooling, and heat treatment.

[0030] (1) Smelting:

[0031] Deep desulfurized molten iron with a sulfur content of ≤0.003% is used, and after the molten iron enters the converter, a process combining "double slag" dephosphorization and "slag scraping" of the molten steel after the converter is used, the converter slag basicity is controlled to be R=2.8 to 3.2, and through effective slag blocking operation, a large amount of slag is prevented from being discharged, and the steel tapping time is not less than 5 min.

[0032] The smelting process is produced by high carbon extraction one-point blowing. The main elements of the steel are adjusted in the converter to be within the range of the present application, and other alloying elements are added according to requirements for smelting.

[0033] The molten steel taken out from the converter is subjected to secondary refining to further reduce the content of harmful impurities such as O, S, non-metallic inclusions, etc. Aluminum particles, silicon carbide, and calcium carbide are used for slag adjustment during LF refining, and the final slag basicity is controlled to be above 2.2.

[0034] (2) Continuous casting:

[0035] During continuous casting, the superheat is ≤25℃, heavy pressing down and electromagnetic stirring at the solidification end of the cast slab are used, the pressing down amount of the heavy pressing down is 5 to 15 mm, the secondary cooling of the continuous cast slab uses a segmented type, the continuous cast slab casting speed is 0.7 to 1.2 m / min, and the cast slab thickness is 250 to 360 mm.

[0036] (3) Heating:

[0037] The above-mentioned steel slab is heated to a temperature not lower than 1050℃ but not higher than 1150℃. This is because a temperature lower than 1050℃ is not enough to make the alloying elements completely dissolve into austenite, which cannot guarantee the finish rolling temperature required for hot rolling. And higher than 1150℃, the original austenite grain coarsening is significant, which will reduce the low-temperature toughness of the steel plate.

[0038] (4) Controlled rolling and controlled cooling:

[0039] Two-stage controlled rolling is adopted, including austenite recrystallization zone rolling and non-recrystallization zone rolling, wherein: the rolling temperature of the austenite recrystallization zone is 950-1100℃, and the cumulative rolling reduction is not less than 40%; preferably, due to the different progress of recrystallization in different thickness sections, at least 2 passes are ensured in the recrystallization rolling stage to realize the homogenization of the recrystallization degree in the thickness direction, with the single pass reduction rate being more than 10%.

[0040] The rolling temperature of the non-recrystallization zone is 760-830℃, and the final rolling temperature is 740-780℃, so that the cumulative rolling reduction in this stage is not less than 40% to ensure sufficient phase change driving force.

[0041] The cooling mode after rolling is laminar cooling, and the cooling rate is controlled at 1-5℃ / s to cool the steel plate to below 600℃; then the steel plate is subjected to slow cooling by stacking, and the slow cooling temperature is 300-500℃, and the stacking time is not less than 48 hours.

[0042] (5) Heat treatment:

[0043] The rolled steel plate is subjected to quenching and tempering heat treatment, the quenching temperature is 850-890℃, the holding time is 1.2-1.4mm / min, the tempering temperature is 550-580℃, the holding time is 2-4mm / min, and the air cooling is performed after discharging to room temperature.

[0044] The beneficial effects of the present application are:

[0045] (1) The steel plate of the present application is based on the chemical composition system of the traditional 51kg steel grade of the ship classification society, and has super high strength grade and high ductility crack arrest toughness, which meets the requirements of improving the strength grade and fracture toughness of the steel material of the super large container ship, and improves the ability of the steel plate to resist flexural deformation failure under the working conditions such as wave surge during long-distance operation of the ship at sea, and significantly improves the safety of the ship structure.

[0046] (2) The present application adds appropriate amounts of C, Mn and other solid solution strengthening elements to obtain super high strength; appropriate amounts of Ni and Cu elements are added to enhance the solid solution strengthening effect, and the Ni element is used to improve the low temperature toughness; Nb and Ti elements are used to inhibit the growth of austenite grains and promote nucleation during the transformation of austenite to refine the grains, control the thickness core structure and improve the uniformity of the structure.

[0047] (3) The steel plate is subjected to quenching and tempering heat treatment in the two-phase zone, and has not less than 5% of residual austenite structure, and in the subsequent cold working deformation process, the metastable residual austenite has TRIP effect, which improves the plasticity of the matrix and obtains a high elongation after fracture of more than 24.5%.

[0048] (4) The crack arrest steel obtained by using the component design and production method of the present application has a multi-phase structure of fine platelet B+M+ a small amount of residual austenite, and the effective control of the grain size of the original austenite and the phase transformation structure is realized mainly by low-temperature heating and stage high-deformation pass-down, which lays a foundation for the subsequent heat treatment structure refinement, thereby ensuring the high strength-toughness-plasticity of the finished steel plate. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 The microstructure metallographic chart of Example 1 of the present application. DETAILED DESCRIPTION

[0050] The present application is further described below by examples.

[0051] The Example of the present application is smelted, continuously cast, heated, controlled-rolled and controlled-cooled, and heat treated according to the component proportion of the technical scheme.

[0052] Heating:

[0053] The slab heating temperature is 1050-1150℃;

[0054] Controlled-rolling and controlled-cooling: two-stage controlled-rolling of austenite recrystallization zone rolling and non-recrystallization zone rolling is adopted,

[0055] In which: the austenite recrystallization zone rolling temperature is 950-1100℃, and the rolling cumulative reduction is not less than 40%; the non-recrystallization zone rolling open rolling temperature is 760-830℃, the finish rolling temperature is 740-780℃, and the non-recrystallization zone rolling cumulative reduction is not less than 40%;

[0056] The post-rolling cooling mode is laminar flow cooling, and the cooling rate is controlled at 1-5℃ / s to cool the steel plate to below 600℃; then the steel plate is subjected to stacking slow cooling, the slow cooling temperature is between 300-500℃, and the stacking time is not less than 48 hours;

[0057] Heat treatment:

[0058] The rolled steel plate is subjected to quenching and tempering heat treatment, the quenching temperature is 850-890℃, the holding time is 1.2-1.4mm / min, the tempering temperature is 550-580℃, the holding time is 2-4mm / min, and the air cooling is performed to room temperature after discharging.

[0059] Further; there are at least 2 passes in the recrystallization rolling stage to ensure that the single pass reduction is more than 10%.

[0060] Further; smelting:

[0061] Deep desulphurized hot metal with sulfur content of 0.003% or less is used, and after the hot metal is transferred to the converter, a process combining double-slag dephosphorization and post-converter molten steel slag skimming is used, the converter slag basicity is controlled at R=2.8-3.2, and the tapping time is not less than 5 minutes; the high carbon extraction one-point blowing mode is used in the smelting process, and the molten steel taken out from the converter is subjected to secondary refining, and the LF refining final slag basicity is controlled at 2.2 or more.

[0062] Further, the superheat during continuous casting is 25 DEG C or less, heavy press-down and electromagnetic stirring at the solidification end of the cast blank are used, the two-cooling is of the sectional type, the continuous casting blank drawing speed is 0.7-1.2 m / min, and the cast slab thickness is 250-360 mm.

[0063] Further, the press-down amount of the heavy press-down is 5-15 mm.

[0064] The composition of the steel of the embodiment of the present application is shown in Table 1.

[0065] Table 1 Composition of the steel of the embodiment of the present application (wt%)

[0066]

[0067] Table 2 Main smelting and continuous casting process of the steel of the embodiment of the present application

[0068]

[0069] Table 3 Main process parameters of the steel of the embodiment of the present application

[0070]

[0071] Table 4 Performance of the steel of the embodiment of the present application

[0072]

[0073] Table 5 Microstructure of the steel of the embodiment of the present application

[0074]

[0075] The 51kg steel plate provided by the present application is suitable for key positions such as deck of super-large container ships, and has excellent technical features such as strength and toughness, high ductility, plastic instability resistance, brittle fracture prevention, good weldability, etc., the yield strength of the steel plate is 510-615MPa, the tensile strength is 618-716MPa, the elongation after fracture is 24.5%-27%, the low temperature impact energy at -60 DEG C is ≥200J, and the Kca at -10 DEG C is ≥6200N / mm 3 / 2The -10 DEG C CTOD of the base material and the welding joint is more than 0.65 mm and 0.22 mm respectively; after 5% deformation and 1 hour of heat preservation at 250 DEG C, the low-temperature impact energy of the steel plate at -40 DEG C is greater than or equal to 100 J. As can be seen from the above, the present application aims at upgrading the manufacturing of super-large container ships, solves the material instability and fracture problem caused by the deformation load of large-thickness material, and meets the comprehensive performance requirement of having multiple key characteristics for guaranteeing the high safety of the material based on the mandatory specification.

[0076] In order to describe the present application, the above-mentioned embodiments are appropriately and sufficiently described by the examples of the present application, the above embodiments are only used to illustrate the present application, and are not limited to the present application. Any modification, equivalent replacement, improvement and the like made by those skilled in the art without departing from the spirit and scope of the present application should be included in the protection scope of the present application, and the patent protection scope of the present application should be defined by the claims.

Claims

1. A high ductility high crack arrest steel, characterized by, The composition of the steel plate is as follows in terms of percentage by weight: C: 0.08%~0.12%, Si: 0.10%~0.25%, Mn: 0.60%~1.20%, P: 0.005%~0.013%, S≤0.008%, Al: 0.02%~0.05%, Nb: 0.01%~0.035%, Ti: 0.007%~0.016%, Ni: 0.40%~0.50%, Cu: 0.15%~0.35%, N: 0.001%~0.004%; the balance being Fe and inevitable impurities; the steel further comprises one or more of Cr: 0.2%~0.35%, Mo: 0.15%~0.35%, V: 0.02%~0.05%; the mechanical properties of the steel are as follows: yield strength 544~615 MPa, tensile strength 641~716 MPa, elongation after fracture 24.5%~27%, low-temperature impact energy at -60℃≥200 J, CTOD of the base material and the welded joint being above 0.84 mm and 0.3 mm respectively, Kca at -10℃≥7200 N / mm 3 / 2 ; After strain aging with 5% deformation and 1 hour holding at 250℃, the low temperature impact energy of the steel plate at -40℃ is ≥100J.

2. A high ductility high crack arrest steel according to claim 1, characterized in that, The microstructure of the steel is fine lath bainite + a small amount of granular bainite and residual austenite, wherein the percentages by volume are as follows: fine lath bainite 60%-80%, granular bainite 20%-30%, and residual austenite 5%-10%; the average grain size of the microstructure of the steel plate is 8-15μm, and the percentage of grains with large-angle grain boundaries is more than 35%.

3. A method for preparing the high-ductility high-crack-arrest steel according to claim 1 or 2, comprising smelting, continuous casting, heating, controlled rolling and controlled cooling, and heat treatment; characterized in that: heating: the slab heating temperature is 1050-1150℃; controlled rolling and controlled cooling: two-stage controlled rolling in the austenite recrystallization zone and the non-recrystallization zone, wherein the rolling temperature in the austenite recrystallization zone is 950-1100℃, and the cumulative rolling reduction is not less than 40%; the rolling temperature in the non-recrystallization zone is 760-830℃, the finish rolling temperature is 740-780℃, and the cumulative rolling reduction in the non-recrystallization zone is not less than 40%; the rolling cooling mode is laminar cooling, the cooling rate is controlled at 1-5℃ / s, and the steel plate is cooled to below 600℃; then the steel plate is subjected to stack slow cooling, the slow cooling temperature is 300-500℃, and the stack time is not less than 48 hours; heat treatment: the rolled steel plate is subjected to quenching and tempering heat treatment, the quenching temperature is 850-890℃, the holding time is 1.2-1.4mm / min, the tempering temperature is 550-580℃, the holding time is 2-4mm / min, and the steel plate is air-cooled to room temperature after being discharged.

4. A method of producing a high ductility high crack arrest steel according to claim 3, characterized in that: There are at least 2 passes in the recrystallization rolling stage to ensure that the single-pass reduction is more than 10%.

5. The method according to claim 3, characterized in that, smelting: deep desulfurization molten iron is used, the sulfur content is ≤0.003%, after the molten iron is transferred to the converter, a "double-slag" dephosphorization process is combined with "slag skimming" of the molten steel after the converter, the converter slag basicity is controlled at R=2.8-3.2, and the tapping time is not less than 5min; high carbon extraction one-point blowing is used in the smelting process, and the molten steel discharged from the converter is subjected to secondary refining, and the LF refining final slag basicity is controlled at more than 2.

2.

6. The method according to claim 3, characterized in that, during continuous casting, the superheat is ≤25℃, heavy reduction and electromagnetic stirring at the solidification end of the cast slab are used, the secondary cooling adopts a segmented cooling mode, the continuous casting speed is 0.7-1.2m / min, and the cast slab thickness is 250-360mm.

7. The method of claim 6, wherein the high ductility high crack arrest steel is prepared by the steps of: preparing a molten steel by adding a predetermined amount of each of the components to a molten iron, and then stirring the molten iron; and pouring the molten steel into a mold. The heavy reduction amount is 5-15mm.

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