High-toughness, low yield-to-tensile ratio, and low longitudinal-to-transverse strength anisotropy yp460mpa grade weathering steel sheet and method of making

Abstract

High-toughness, low yield ratio and low longitudinal-transverse strength anisotropy YP460MPa grade weathering steel plate and its manufacturing method, the component weight percentage is: C 0.04~0.08%, Si≤0.20%, Mn1.10~1.50%, P≤0.018%, S≤0.003%, Cu 0.25~0.40%, Ni 0.15~0.45%, Cr0.35~0.65%, Nb 0.015~0.040%, Ti 0.008~0.016%, Als 0.040~0.070%, N≤0.0050%, Mg 0.0010~0.0040%, the balance includes Fe and other inevitable inclusions.The application obtains high strength, excellent low temperature toughness, low yield ratio, high weather resistance and low longitudinal-transverse strength anisotropy of the base material weathering steel plate, and the low temperature toughness of HAZ is also excellent when large heat input welding, that is, the base material weathering steel plate-40℃ impact toughness KV2≥120J, the welding heat affected zone-40℃ Akv≥60J, and it is particularly suitable for the steel structure of ocean platform, cross-sea bridge, water and electricity metal structure component, port machinery and engineering machinery in cold regions.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of weathering steel plate, and particularly relates to a high-toughness, low-yield-strength-ratio and low longitudinal-transverse-strength anisotropy YP460MPa-grade weathering steel plate and a manufacturing method thereof. BACKGROUND

[0002] It is well known that low-carbon (high-strength) low-alloy steel is one of the most important engineering structural materials, which is widely used in oil and gas pipelines, offshore platforms, shipbuilding, hydropower engineering, bridge structures, boiler vessels, building structures, automobile industry, railway transportation and mechanical manufacturing; the performance of low-carbon (high-strength) low-alloy steel depends on its chemical composition and manufacturing process, in which the strength, toughness, plasticity, weldability and the matching therebetween are the most important performances of low-carbon (high-strength) low-alloy steel, which are ultimately determined by the microstructure and dislocation substructure of the finished steel; with the continuous development of metallurgical technology, people have put forward higher requirements for the toughness, plasticity and especially weldability and low anisotropy of high-strength steel, that is, the steel plate has the ability of resisting brittle fracture and plastic instability fracture at low temperature (under the condition of-40℃), and at the same time, the fracture elongation and uniform elongation reach the level of 500MPa-grade steel plate, and the steel plate has excellent weldability, low anisotropy of performance and can withstand large heat input welding (can withstand welding heat input of ≥100kJ / cm); and under the conditions of relatively low alloy content, especially the content of precious metals, and low manufacturing cost, the comprehensive mechanical properties and use performance of the steel plate are greatly improved, so as to reduce the alloy content of the steel and save the cost, the high-strength light weight reduces the self weight, stability and safety of the steel member, and more importantly, further improves the cold / heat workability of the steel member and the safety and reliability in the service process.

[0003] At present, a research climax of developing a new generation of high-performance steel materials has been started in Japan, South Korea, the European Union and North America, and it is tried to obtain better microstructure matching through optimization of alloy combination, control of fine structure of submicrostructure and innovative manufacturing process technology, and to make the high-strength steel obtain better matching of strength and plasticity and plasticity and toughness, weldability and low anisotropy by means of superfine metallographic microstructure and fine structure of substructure (dislocation substructure configuration, packet, block, etc.).

[0004] The prior art in manufacturing thick steel plates with yield strength ≥ 420 MPa and low temperature impact toughness at -60°C ≥ 34 J, generally adds a certain amount of Ni or Cu + Ni elements (≥ 0.30%) in the steel (The Firth (1986) international Symposium and Exhibit on Offshore Mechanics and Arctic Engineering, 1986, Tokyo, Japan, 354; "DEVELOPMENTS IN MATERIALS FOR ARCTIC OFFSHORE STRUCTURES"; "Structural Steel Plates for Arctic Use Produced by Multipurpose Accelerated Cooling System" (Japanese), Kawasaki Steel Technical Report, 1985, No. 1 68-72; "Application of Accelerated Cooling For Producing 360 MPa Yield Strength Steel plates of up to 150 mm in Thickness with Low Carbon Equivalent", Accelerated Cooling Rolled Steel, 1986, 209-219; "High Strength Steel Plates For Ice-Breaking Vessels Produced by Thermo-Mechanical Control Process", Accelerated Cooling Rolled Steel, 1986, 249-260; "420 MPa Yield Strength Steel Plate with Superior Fracture Toughness for Arctic Offshore Structures", Kawasaki Steel Technical Report, 1999, No. 40, 56; "420 MPa and 500 MPa Yield Strength Steel Plate with High HAZ toughness Produced by TMCP for Offshore Structure", Kawasaki Steel Technical Report, 1993, No.29, 54; "Toughness Improvement in Bainite Structure by Thermo-Mechanical Control Process" (Japanese) Sumitomo Metal, Vol. 50, No. 1 (1998), 26; "Steel Plate for Offshore Platform Structure Used in Ice Sea Area" (Japanese), Steel Research, 1984, No. 314, 19-43), to ensure that the base steel plate has excellent low-temperature toughness, the toughness of the heat-affected zone HAZ can also reach Akv≥34 J at -60°C when welding with a heat input of <50 KJ / cm. However, when welding with a super-large heat input (≥100 KJ / cm), it is generally difficult to achieve low-temperature toughness of the heat-affected zone (HAZ), and the low-temperature toughness of the heat-affected zone (HAZ) deteriorates severely.

[0005] A large number of patent documents only describe how to achieve low-temperature toughness of the base steel plate, and there are few descriptions of how to achieve excellent low-temperature toughness of the heat-affected zone (HAZ) under welding conditions, especially how to ensure the low-temperature toughness of the heat-affected zone (HAZ) when welding with a super-large heat input, and in order to ensure the low-temperature toughness of the steel plate, a certain amount of Ni or Cu+Ni elements are generally added to the steel, and the low-temperature toughness of the heat-affected zone (HAZ) of the steel plate when welding with a super-large heat input is also rarely able to reach -60°C (Japanese Patent Sho 63-93845, Sho 63-79921, Sho 60-258410, Tokihei 4-285119, Tokihei 4-308035, Hei 3-264614, Hei 2-250917, Hei 4-143246, US Patent 4855106, US Patent 5183198, US Patent 4137104).

[0006] At present, the only way to improve the low-temperature toughness of the heat-affected zone (HAZ) of the steel plate when welding with a super-large heat input is to use the oxide metallurgy technology of Nippon Steel Corporation (US Patent 4629505, WO 01 / 59167A1), that is, during the large heat input welding process, due to the long time high temperature effect, TiN particles dissolve and lose their effect, and Ti2O3 is more stable than TiN, and even if it reaches the melting point of the steel, it will not dissolve. Ti2O3 particles can become the nucleation site of intragranular acicular ferrite, promote the nucleation of intragranular acicular ferrite (acicular ferrite-AF), effectively divide the austenite grain size, refine the HAZ structure, and form a high-strength and high-toughness acicular ferrite structure.

[0007] Chinese patent application numbers 201410300713.X, 201310244712.3, 201310244706.8, 201310124065.2, 201310244713.8, ZL201210209637.2, 201410815614.5, 201710183350.X, 201910149978.7 disclose a series of large heat input welding various low temperature steel plates, in order to ensure the low temperature toughness of the heat affected zone of large heat input welding, a certain amount of valuable alloying elements Cu, Ni are added in the steel plate (especially super-thick steel plate), when the yield strength YP reaches 460 MPa, a small amount of Mo needs to be added appropriately, the steel plate has good large heat input welding process performance, but the toughness of the welding heat affected zone, especially the low temperature toughness of the welding heat affected zone of thick steel plate is not very stable (Mo promotes the formation of coarse upper bainite under large heat input welding conditions, which deteriorates the toughness of the welding coarse grain heat affected zone), which cannot stably reach the requirement of-40℃ impact toughness, and the manufacturing cost of thick steel plate is also high;

[0008] Secondly, Chinese patent application number 202110734971.9 discloses a steel plate with excellent strength, toughness, low yield strength ratio (≤0.86), transverse and longitudinal anisotropy (≤30 MPa) and welding property.

[0009] However, the above-mentioned developed TMCP steel plates do not involve the atmospheric corrosion resistance of the steel plate, and the steel structure made of the steel plate not only needs to be coated for corrosion prevention, but also seriously pollutes the environment during the coating process, and more importantly, the steel structure must be recoated every interval (generally 3-5 years), which leads to environmental pollution and high maintenance cost, and cannot meet the design requirements of special large heavy steel structures (such as large-span highway and railway bridge structures, marine engineering structures and giant floating cranes for ships, etc.) without coating and corrosion resistance, and is not in line with the low-carbon, green and environmentally friendly requirements of engineering construction. SUMMARY

[0010] The purpose of the present application is to provide a high-toughness, low-yield-strength-ratio and low-longitudinal-transverse-strength-anisotropy YP460MPa-grade weathering steel plate and a manufacturing method thereof, which can obtain high strength, excellent low temperature toughness, low yield strength ratio, high weather resistance and low longitudinal / transverse strength anisotropy of the base material weathering steel plate, and the low temperature toughness of the HAZ during large heat input welding is also excellent, i.e. the-40℃ impact toughness KV2 of the base material weathering steel plate is ≥120J, the-40℃ Akv of the welding heat affected zone (HAZ) is ≥70J, which is particularly suitable for marine platforms, large-span bridges, water and electricity metal structural components, port machinery and engineering machinery in cold regions, and can realize low-cost stable batch industrial production.

[0011] To achieve the above-mentioned purpose, the technical scheme of the present application is:

[0012] Corrosion resistance, high toughness, low yield ratio and low anisotropy TMCP weathering steel plate is one of the most difficult varieties in thick plate products, the reason is that the plate not only requires low C, low carbon equivalent CEV, high strength, excellent low temperature toughness, fatigue resistance, weather resistance and low yield ratio and low anisotropy, but also can withstand super large heat input welding (welding heat input ≥ 100 KJ / cm), and the low temperature impact toughness of the heat affected zone is excellent, but these performance requirements are difficult to meet simultaneously: A) low C, low Pcm and high strength, low yield ratio; B) high strength, high toughness, weather resistance and low yield ratio, low anisotropy of longitudinal and transverse strength; C) high strength, weather resistance (high Cu, Cr content, especially high Cr content for large heat input welding) and excellent weldability, especially large heat input weldability, the above-mentioned properties are in conflict with each other in composition design and TMCP process design, and it is difficult to reconcile: when the C content and Pcm are reduced, it is difficult to realize high strength and low yield ratio of the plate; while improving the strength, low temperature toughness and weather resistance, it is difficult to realize low yield ratio and low longitudinal and transverse strength anisotropy of the plate; when the plate has high strength and excellent weather resistance, the weldability of the plate, especially the super large heat input plate, is difficult to guarantee.

[0013] How to balance low Pcm, high strength, high toughness, excellent weather resistance, low yield ratio, low longitudinal and transverse strength anisotropy and large heat input weldability is one of the most difficult points of the product, and is also a key core technology; therefore, the present application comprehensively considers the key factors affecting the high strength, high toughness, low yield ratio, low longitudinal and transverse strength anisotropy and large heat input weldability of the plate in the key technology route, composition and process design, and successfully avoids the technical blockade (titanium oxide metallurgy and HITFF technology) of the patents of European, American, Japanese and Korean steel companies.

[0014] The present application starts from alloy design, adopts low carbon C-low Si-low Mn low alloy steel as the basis, Pcm ≤ 0.22%, low N content and Al / N ≥ 10, (Cu+Ni+Cr+Mo) alloying and weather resistance index I ≥ 6.15, Ti+Nb micro-alloying, Mg treatment and Mg / S ratio controlled between 0.75-2.75 and 2.5×10 -3 ≤(%Mg)×(%S)×2.5×10 -2 , etc. Optimize the TMCP process: [(%Nb)×ξ] / [ζ×H×(T 终轧 )]≤5.18×10 -5 , [ξ×(T 开冷 -T 停冷 )×(Pcm)×(V c )] / [T 终轧 ×H]≥0.30, so that the finished weathering steel plate has uniform and fine ferrite + low carbon bainite microstructure, and the average crystal grain size is below 20 μm.

[0015] Specifically, the high-toughness, low yield ratio and low longitudinal-transverse strength anisotropy YP460MPa-grade weather-resistant steel plate provided by the present application has the following component weight percentages:

[0016] C: 0.04%~0.08%

[0017] Si: ≤0.20%

[0018] Mn: 1.10%~1.50%

[0019] P: ≤0.018%

[0020] S: ≤0.003%

[0021] Cu: 0.25%~0.40%

[0022] Ni: 0.15%~0.45%

[0023] Cr: 0.35%~0.65%

[0024] Nb: 0.015%~0.040%

[0025] Ti: 0.008%~0.016%

[0026] Als: 0.040%~0.070%

[0027] N: ≤0.0050%

[0028] Mg: 0.0010%~0.0040%

[0029] The balance contains Fe and other unavoidable inclusions; and the above element contents must simultaneously satisfy the following relationships:

[0030] Pcm ≤0.22%, and Als / N ≥10; wherein, the welding cold crack sensitivity index Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B, unit: %;

[0031] The weather resistance index I ≥6.00;

[0032] I = 26.01Cu + 3.88Ni + 1.2Cr + 1.49Si + 17.28P - 7.29Cu×Ni - 9.10Ni×P - 33.39Cu 2 ;

[0033] [(%Nb)×ξ] / [ζ×H×(T 终轧 )]≤5.18×10 -5 ,

[0034] wherein,

[0035] ξ is the cumulative reduction ratio of non-recrystallization controlled rolling, unit %;

[0036] ζ is the spread ratio, i.e. the width of the finished steel plate / the width of the slab;

[0037] H is the thickness of the finished steel plate, unit mm;

[0038] T 终轧 is the finish rolling temperature of non-recrystallization controlled rolling, unit ℃;

[0039] [ξ×(T 开冷 -T 停冷 )×(Pcm)×(V c )] / [T 终轧 ×H]≥0.30;

[0040] wherein, ξ is the cumulative reduction ratio of non-recrystallization controlled rolling, unit %;

[0041] T 开冷 is the starting temperature of accelerated cooling, unit ℃;

[0042] T 停冷 is the stopping temperature of accelerated cooling, unit ℃;

[0043] V c is the accelerated cooling speed of the steel plate, unit ℃ / s;

[0044] T 终轧 is the finish rolling temperature of non-recrystallization controlled rolling, unit ℃;

[0045] H is the thickness of the finished steel plate, unit mm;

[0046] The ratio of Mg / S is controlled in 0.75-2.75, and, 2.5×10 -3 ≤(%Mg)×(%S)×2.5×10 -2 .

[0047] Further, the balance is Fe and other inevitable impurities.

[0048] The microstructure of the weathering steel plate described in the present application is uniform and fine ferrite + low-carbon bainite, and the average crystal grain size of the microstructure is below 20 μm.

[0049] The yield strength of the weathering steel plate is equal to or greater than 460 MPa, the tensile strength is equal to or greater than 570 MPa, the impact energy KV2 (single value) at -40 DEG C is equal to or greater than 120 J, the yield strength ratio is equal to or less than 0.85, the low longitudinal and transverse strength anisotropy, i.e. the longitudinal / transverse strength difference, is equal to or less than 30 MPa, the weldability is excellent, no preheating is needed before welding, the welding heat input can be equal to or greater than 100 J / cm, and the impact energy KV2 (single value) at -40 DEG C in the heat affected zone is equal to or greater than 60 J.

[0050] In the component design of the high-toughness, low-yield-strength-ratio and low-longitudinal-and-transverse-strength-anisotropy YP460MPa-grade weathering steel plate according to the present application:

[0051] C has a great influence on the strength, low-temperature toughness, elongation and weldability of the TMCP weathering steel plate, and it is desirable to control the C content in the steel relatively low from the perspective of improving the low-temperature toughness and high-heat-input weldability of the weathering steel plate; however, the C content should not be controlled too low from the perspective of controlling the strength, low-temperature toughness, low-yield-strength-ratio and low-longitudinal-and-transverse-strength-anisotropy of the weathering steel plate, and controlling the microstructure and manufacturing cost in the production process; too low C content can result in a high yield strength ratio, and high grain boundary migration rate, and can cause coarse grains and mixed grains in the microstructure of the base steel plate and the welding HAZ, and can also cause grain boundary weakening and seriously deteriorate the low-temperature toughness of the base steel plate and the welding HAZ; therefore, the reasonable range of the C content is 0.04% to 0.08%.

[0052] Si promotes the deoxidization of molten steel and can improve the strength of the weathering steel plate; however, the deoxidization effect of Si is not great when Al is used for deoxidization, and Si can improve the strength of the weathering steel plate, but seriously deteriorates the low-temperature toughness, elongation and weldability of the weathering steel plate, especially for high-strength weathering steel with high alloy content, when high-heat-input welding is performed, Si not only promotes the formation of M-A islands, but also causes the M-A islands to be coarse and unevenly distributed, which seriously deteriorates the low-temperature toughness of the welding heat affected zone (HAZ); therefore, the Si content in the steel should be controlled as low as possible, and the Si content is controlled to be less than 0.20% considering the weather resistance of Si and the economy and operability of the steelmaking process.

[0053] Mn is the most important alloying element in steel. In addition to improving the strength of weathering steel plate, it also has the effects of expanding the austenite phase region, reducing the Ar3 point temperature, refining the TMCP weathering steel plate grains to improve the strength of the weathering steel plate (fine-grain strengthening effect), improving the low-temperature toughness of the weathering steel plate (fine-grain toughening), improving the fatigue resistance of the weathering steel plate, promoting the formation of low-temperature phase change structure (phase change strength effect) to improve the strength of the weathering steel plate; however, Mn is prone to segregation during the solidification of molten steel, especially when the Mn content is high and the content of weathering elements (Cu, Cr, etc.) is high, not only will it cause casting operation difficulties, but it is also prone to conjugate segregation with C, P, S and other elements, especially when the C content in the steel is high, the segregation and porosity in the center of the casting blank is aggravated, and severe center area segregation of the casting blank is prone to form abnormal structure during subsequent TMCP and welding, resulting in low-temperature toughness and low-temperature toughness of the weathering steel plate and cracks in the welded joint. In addition, for high-strength TMCP weathering steel plate, excessive Mn content not only causes the low-temperature toughness, elongation and weldability of the steel plate to deteriorate rapidly, but also causes the yield ratio, longitudinal and transverse strength anisotropy of the steel plate to increase sharply, and the weather resistance and super-large heat input weldability to deteriorate seriously; therefore, the suitable Mn content is 1.10% to 1.50%.

[0054] P is a harmful inclusion in steel that has a huge damaging effect on the mechanical properties of weathering steel, especially low-temperature impact toughness, elongation and weldability. In theory, the lower the better; but considering the excellent weather resistance, steelmaking operability and steelmaking cost, for TMCP weathering steel plate that requires large heat input welding, -40°C toughness, high strength and super-large heat input welding, the P content needs to be controlled at ≤0.018%.

[0055] S is a harmful inclusion in steel that has a great damaging effect on the low-temperature toughness, weldability, fatigue resistance and weather resistance of weathering steel. More importantly, S combines with Mn in steel to form MnS inclusions. In the hot rolling process, the plasticity of MnS causes the MnS to extend along the rolling direction, forming MnS inclusion bands along the rolling direction, which not only severely damages the low-temperature impact toughness, elongation, Z-direction performance, fatigue resistance and weldability (especially large heat input weldability) of the weathering steel plate, but also causes serious anisotropy of longitudinal and transverse strength and toughness. At the same time, S is also the main element that causes hot brittleness during hot rolling. In theory, the lower the better; but considering the steelmaking operability, steelmaking cost and smooth logistics principles, for TMCP weathering steel plate that requires large heat input welding, -40°C toughness, high strength, low longitudinal and transverse strength anisotropy and super-large heat input welding, the S content needs to be controlled at ≤0.003%.

[0056] Cu is the main weathering element and also the austenite stabilizing element. Adding Cu can also reduce the Ar1 and Ar3 point temperature, improve the atmospheric corrosion resistance of the steel plate, refine the microstructure of the TMCP weathering steel plate, and improve the low temperature toughness of the TMCP weathering steel plate. However, if the Cu content is too high, higher than 0.45%, it will not only cause copper brittleness, surface cracking of the casting blank, reduction of the weather resistance, internal cracking problem, and especially the low temperature toughness of the impact load fracture characteristics (i.e. plastic toughness) of the welded joint of the thick weathering steel plate, but also cause the high yield ratio, high anisotropy of the longitudinal and transverse strength of the weathering steel plate. At the same time, considering that Cu is a relatively valuable alloying element, from the cost-effectiveness point of view, the upper limit of Cu should be controlled at 0.40%. If the Cu content is too low, lower than 0.25%, the weathering effect is small. Therefore, the Cu content should be controlled between 0.25% and 0.40%.

[0057] Adding Ni can not only reduce the BCC crystal structure dislocation lattice friction force (i.e. P-N force), improve the low temperature dislocation mobility of the ferrite phase, promote the dislocation cross-slip, and improve the intrinsic plasticity and toughness of the ferrite; in addition, as a strong austenite stabilizing element, Ni can greatly reduce the Ar1 and Ar3 point temperature, improve the driving force of the austenite to ferrite phase transformation, cause the austenite to transform at a lower temperature, greatly refine the microstructure of the TMCP weathering steel plate, improve the expansion resistance of the crack through the ferrite grain, and greatly improve the low temperature toughness of the TMCP weathering steel plate. Therefore, Ni has the effect of improving the strength and low temperature toughness of the TMCP weathering steel plate without reducing the elongation (i.e. plastic toughness); adding Ni in the steel can also reduce the copper brittleness of the copper-containing steel, reduce the intergranular cracking during hot rolling, and improve the atmospheric corrosion resistance of the steel plate. Therefore, theoretically speaking, the higher the Ni content in the steel within a certain range, the better. However, too high Ni content will not only harden the welding heat affected zone, which is not conducive to the weldability of the weathering steel plate and the low temperature toughness of the super-large heat input welded joint, but also greatly increase the yield ratio, anisotropy of the longitudinal and transverse strength of the weathering steel plate, and the alloy cost of the weathering steel plate (Ni is a valuable alloying element). Therefore, the Ni content should be controlled between 0.15% and 0.45%.

[0058] For weathering steel, Cr element promotes the role of dense amorphous oxide layer, and it is essential to add a certain amount of Cr in weathering steel; adding a certain amount of Cr (≤0.65%) can improve the weather resistance of the steel plate without compromising the low-temperature toughness, bending cold working and super large input welding of the steel plate; but if the Cr content is too low (<0.35%), the contribution of Cr to the weather resistance of the steel plate is small, which cannot meet the requirement of high weather resistance; if the Cr content is too high (>0.65%), the low-temperature toughness, bending cold workability of the weathering steel plate are damaged, especially the weldability of the weathering steel plate, especially the super large heat input weldability, and the low-temperature toughness of the welding heat affected zone is seriously deteriorated (coarse feather-like upper bainite structure is formed in the welding heat affected zone); therefore, the Cr content is controlled between 0.35% and 0.65%.

[0059] The purpose of adding a small amount of Nb element in the steel is to control the unrecrystallization rolling, refine the grain size of the weathering steel plate, and improve the strength and toughness of the TMCP weathering steel plate; when the C content in the steel is low (≤0.08%), when the Nb addition is less than 0.015%, not only the effect of controlled rolling is not effective, but also the strength and toughness of the TMCP weathering steel plate are insufficient; when the Nb addition is more than 0.040%, not only the yield ratio, the anisotropy of longitudinal / transverse strength of the weathering steel plate and the alloy cost of the steel plate (Nb is also a valuable alloy element) are high, but also the formation of upper bainite (Bu) and the Nb(C, N) secondary precipitation embrittlement are induced under the condition of super large heat input welding, which seriously damages the low-temperature toughness of the super large heat input welding heat affected zone (HAZ); therefore, the Nb content is controlled between 0.015% and 0.040% to obtain the best effect of controlled rolling, realize the matching of strength and toughness / plasticity of the TMCP weathering steel plate, low yield ratio, low longitudinal / transverse strength, and not damage the super large heat input weldability of the weathering steel plate.

[0060] The purpose of adding a small amount of Ti in the steel is to combine with N in the steel to form TiN particles with high stability, and to inhibit the grain growth of the weathering steel plate and the welding HAZ; the Ti content added in the steel should match the N content in the steel, and the matching principle is that TiN cannot be precipitated in liquid steel but must be precipitated in solid phase; therefore, the precipitation temperature of TiN must be ensured to be lower than 1400℃; when the Ti addition in the steel is too low (<0.008%), the number of TiN particles formed is insufficient, which is not enough to inhibit the austenite grain growth during TMCP and welding thermal cycle and to improve the low-temperature toughness and weldability of the weathering steel plate; when the Ti content is too high (>0.016%), the precipitation temperature of TiN exceeds 1400℃, and part of the TiN particles are precipitated in the form of large size TiN particles during the solidification of the steel liquid, which not only cannot inhibit the grain growth, but also becomes the starting point of crack initiation; therefore, the optimal control range of Ti content is 0.008% to 0.016%.

[0061] Als in the steel plate can fix free [N] in the steel, reduce free [N] in the welding heat affected zone (HAZ), and improve the low temperature impact toughness of the HAZ of large heat input welding; however, excessive Als in the steel will form a large number of dispersed needle-like Al2O3 inclusions in the steel, which will damage the low temperature impact toughness and weldability of the weathering steel plate; according to the analysis of the composition system of the weathering steel plate, the optimal content of Als is controlled within 0.040% to 0.070%.

[0062] The control range of N corresponds to the control range of Ti, and N is used to control the grain of the weathering steel plate and improve the low temperature toughness and weldability of the weathering steel plate; if the content of N is too low, the number of TiN particles is small and the size is large, which cannot play a role in controlling the grain of the steel plate and improving the low temperature toughness and weldability of the steel plate, and instead is harmful to the low temperature toughness and weldability of the steel plate; however, if the content of N is too high, the free [N] in the steel increases, especially the free [N] content in the heat affected zone (HAZ) under the condition of large heat input welding increases sharply, which seriously damages the low temperature toughness and bend cold workability of the HAZ, and deteriorates the processing and use characteristics of the steel. Therefore, the content of N is controlled within ≤0.0050%.

[0063] Mg treatment is performed on the steel, which can further purify the molten steel and modify the sulfides in the steel into non-deformable and stable fine spherical sulfides, inhibit the hot brittleness of S, improve the low temperature toughness, elongation and Z-direction performance of the weathering steel plate, and improve the anisotropy of the longitudinal and transverse strength and toughness and weldability of the weathering steel plate. In addition, the Mg treatment improves the castability of the high acid-soluble aluminum molten steel. More importantly, the Mg(O, S) particles are not easy to agglomerate and grow in the liquid molten steel and the solid steel, and are distributed in the steel in a fine and dispersed state. The high melting point Mg(O, S) particles can pin the growth of the austenite grains in the heat affected zone during the ultra-large heat input welding, refine the grains in the heat affected zone, and greatly improve the low temperature plasticity and toughness of the heat affected zone under the condition of ultra-large heat input. The amount of Mg added depends on the content of S in the steel. If the amount of Mg added is too low, the treatment effect is not good; if the amount of Mg added is too high, the size of the Mg(O, S) formed is too large, the brittleness is also increased, and the Mg(O, S) can become the starting point of the fracture crack, which reduces the low temperature toughness and elongation of the steel and the ultra-large heat input weldability of the steel plate, and also reduces the purity of the steel and contaminates the molten steel. Generally, the content of Mg is controlled according to ESSP=(%Mg)[1-1.24(%O)] / 1.25(%S), wherein ESSP is the shape control index of sulfide inclusions, and the value range of ESSP is preferably 0.75 to 2.75. Therefore, the suitable range of the content of Ca is 0.0010% to 0.0040%.

[0064] In particular, the component design of the present application emphasizes:

[0065] Pcm≤0.22% and Als / N≥10; wherein, Pcm is the welding cold crack sensitive index, Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B, unit is %.

[0066] The purpose is: A) to improve the weldability of weathering steel plate, to ensure that the weathering steel plate has ultra-large heat input weldability; B) to eliminate the free [N] content in the heat-affected zone of large heat input welding, to improve the microstructure (to form high-density fine AlN particles, to pin the austenite grain growth, to refine the microstructure of HAZ), low-temperature toughness and crack arrest characteristics (to eliminate the free [N] in HAZ, to eliminate the serious embrittlement effect of free [N]) of the heat-affected zone.

[0067] The weather resistance index I≥6.00; to ensure that the steel plate has excellent weather resistance, wherein I=26.01Cu+3.88Ni+1.2Cr+1.49Si+17.28P-7.29Cu×Ni-9.10Ni×P-33.39Cu 2 .

[0068] [(%Nb)×ξ] / [ζ×H×(T 终轧 )]≤5.18×10 -5 , to ensure that the weathering steel plate has low yield ratio, low longitudinal and transverse strength anisotropy while obtaining high toughness; wherein, ξ is the cumulative reduction rate of unrecrystallized controlled rolling, unit %; ζ is the spread ratio, i.e. the width of the finished steel plate / the width of the slab; H is the thickness of the finished steel plate, unit mm; T 终轧 is the finish rolling temperature of unrecrystallized controlled rolling, unit ℃; this is one of the key core technologies of the present application.

[0069] [ξ×(T 开冷 -T 停冷 )×(Pcm)×(V c )] / [T 终轧 ×H]≥0.30; wherein, ξ is the cumulative reduction rate of unrecrystallized controlled rolling, unit %; T 开冷 is the starting temperature of accelerated cooling, unit ℃; T 停冷 is the stopping temperature of accelerated cooling, unit ℃; V c is the accelerated cooling speed of the steel plate, unit ℃ / s; T 终轧 is the finish rolling temperature of unrecrystallized controlled rolling, unit ℃; H is the thickness of the finished steel plate, unit mm;

[0070] Ensure that under the condition of low C, low Pcm, the steel plate has high strength, high toughness, low yield ratio, at the same time, the steel plate has excellent super large heat input weldability and weather resistance, and successfully eliminates the mutual contradiction between low C, low Pcm and high strength, high toughness, low yield ratio, low longitudinal and transverse strength anisotropy of the weather resistant steel plate, which is difficult to be compatible. This is one of the key core technologies of the application.

[0071] Mg treatment, the ratio of Mg / S is controlled between 0.75 and 2.75, 2.5*10 -3 ≤(%Mg)×(%S)×2.5*10 -2 : Ensure that the sulfidation spheroidization and Mg(O, S) particles reduce the low temperature toughness to the minimum, at the same time, the Mg(O, S) particles are uniformly and finely distributed in the steel, the austenite grain growth in the super large heat input welding heat affected zone is inhibited, and the low temperature toughness of the super large heat input welding heat affected zone of the steel plate is improved; This is one of the key core technologies of the application.

[0072] The component data in the above relationship is calculated in percentage, for example, if the carbon content is 0.10%, when calculating the relationship, 0.10 is used to calculate.

[0073] The manufacturing method of the high toughness, low yield ratio and low longitudinal and transverse strength anisotropy YP460MPa grade weather resistant steel plate provided by the application comprises the following steps:

[0074] 1) Smelting and casting

[0075] Smelting according to the above components, and continuously casting into a slab;

[0076] 2) Slab heating

[0077] The heating temperature is controlled at 1050-1150℃;

[0078] 3) Rolling, rolling spread ratio≥1.3

[0079] The first stage is ordinary rolling, and the maximum rolling capacity of the rolling mill is used for continuous rolling;

[0080] The second stage adopts non-recrystallization controlled rolling, the opening rolling temperature is controlled at 780-880℃, the rolling pass reduction rate is≥7%, the cumulative reduction rate is≥50%, and the finish rolling temperature is 770-830℃; and,

[0081] [(%Nb)×ξ] / [ζ×H×(T 终轧 )]≤5.18*10 -5 ,

[0082] Among them,

[0083] ξ is the cumulative reduction rate of non-recrystallization controlled rolling, unit: %;

[0084] ζ is the spread ratio, i.e. the width of the finished steel plate / the width of the slab;

[0085] H is the thickness of the finished steel plate, in mm;

[0086] T 终轧 is the finish rolling temperature of the non-recrystallization controlled rolling, in ℃;

[0087] 4) cooling

[0088] After the controlled rolling, the steel plate is immediately sent to an accelerated cooling device to accelerate the cooling of the steel plate;

[0089] The open cooling temperature of the steel plate is 750-800 ℃, the cooling speed is ≥5 ℃ / s, and the stop cooling temperature is 330-450 ℃;

[0090] Then the steel plate is naturally air-cooled to room temperature; and,

[0091] [ξ×(T 开冷 -T 停冷 )×(Pcm)×(V c )] / [T 终轧 ×H]≥0.30;

[0092] Wherein, ζ is the cumulative reduction rate of the non-recrystallization controlled rolling, in %;

[0093] T 开冷 is the start temperature of the accelerated cooling, in ℃;

[0094] T 停冷 is the stop temperature of the accelerated cooling, in ℃;

[0095] V c is the accelerated cooling speed of the steel plate, in ℃ / s;

[0096] T 终轧 is the finish rolling temperature of the non-recrystallization controlled rolling, in ℃;

[0097] H is the thickness of the finished steel plate, in mm.

[0098] Preferably, in step 1), the tundish pouring superheat is controlled at 7-30 ℃, the drawing speed is controlled at 0.6-1.0 m / min, and the crystallizer liquid surface fluctuation is controlled at ≤5 mm.

[0099] Preferably, in step 4), when the thickness of the steel plate is ≥50 mm, the steel plate is subjected to slow cooling, and the slow cooling process is to keep the temperature at not less than 300 ℃ for more than 24 hours, and then the steel plate is naturally air-cooled to room temperature.

[0100] In the manufacturing method described in the present application:

[0101] According to the component system of the steel, the strength, plasticity and low temperature toughness of the steel plate, the steel is cast by continuous casting, the overheat degree of the tundish casting is controlled at 7-30°C, the drawing speed is controlled at 0.6-1.0 m / min, and the liquid level fluctuation of the crystallizer is controlled at ≤5 mm.

[0102] According to the content ranges of C, Mn, Nb and Ti, the slab heating temperature is controlled at 1050-1150°C, so that the Nb in the steel is completely solid-solved into the austenite during the slab heating process, and the slab austenite grains do not abnormally grow.

[0103] In order to ensure that the steel plate has low longitudinal and transverse strength anisotropy, the rolling spread ratio is ≥1.3.

[0104] The first stage is normal rolling, the maximum rolling capacity of the rolling mill is adopted for continuous rolling, the rolling line capacity is maximized, and the deformed slab is recrystallized to refine the austenite grains. The second stage adopts non-recrystallization controlled rolling, according to the content range of the Nb element in the steel, in order to ensure the non-recrystallization controlled rolling effect, the controlled rolling opening rolling temperature is controlled at 780-880°C, the rolling pass reduction is ≥7%, the cumulative reduction is ≥50%, and the finish rolling temperature is 770-830°C.

[0105] And, it is particularly emphasized that:

[0106] [(%Nb) x ξ] / [ζ x H x (T 终轧 )]≤5.18 x 10 -5 ,

[0107] Among them,

[0108] ξ is the cumulative reduction of the non-recrystallization controlled rolling, unit: %;

[0109] ζ is the spread ratio, i.e. the width of the finished steel plate / the width of the slab;

[0110] H is the thickness of the finished steel plate, unit: mm;

[0111] T 终轧 is the finish rolling temperature of the non-recrystallization controlled rolling, unit: °C;

[0112] With increasing Nb content and cumulative reduction in non-recrystallized controlled rolling, the number of crystal defects (dislocations and deformation bands, etc.) within the austenite body increases significantly, as does the deformation texture. These crystal defects are nucleation sites for ferrite and bainite. The abundance of nucleation sites leads to a substantial reduction in the grain size of ferrite and bainite. This significant reduction in grain size contributes to the high toughness of the steel plate, but also increases the yield strength ratio. The deformation texture results in a significant increase in the anisotropy of the longitudinal and transverse strength of the steel plate. As the width-to-width ratio increases, the anisotropy of the longitudinal and transverse strength of the steel plate decreases. As the final rolling temperature and steel plate thickness increase, the yield strength ratio of the steel plate decreases. This invention, by controlling the matching relationship between Nb content, width-to-width ratio, final rolling temperature in non-recrystallized controlled rolling, and thickness, ensures that the steel plate possesses high toughness while also maintaining a low yield strength ratio and low longitudinal and transverse strength anisotropy.

[0113] After controlled rolling, the steel plate is immediately transported to the accelerated cooling equipment for accelerated cooling. The initial cooling temperature of the steel plate is 750-800℃, the cooling rate is ≥5℃ / s, and the cooling stop temperature is 330-450℃. When the thickness of the steel plate is ≥50mm, the steel plate is subjected to slow cooling. The slow cooling process involves holding the plate at a temperature of not less than 300℃ for at least 24 hours, after which the steel plate is naturally air-cooled to room temperature.

[0114] This invention also particularly emphasizes:

[0115] [ξ×(T 开冷 -T 停冷 )×(Pcm)×(V c )] / [T 终轧 [×H]≥0.30;

[0116] Wherein, ξ represents the cumulative reduction rate of non-recrystallized controlled rolling, in percentage (%).

[0117] T 开冷 The starting temperature for accelerated cooling, measured in °C;

[0118] T 停冷 The stopping temperature for accelerated cooling, in °C;

[0119] V c The unit for accelerating the cooling rate of the steel plate is ℃ / s;

[0120] T 终轧 The final rolling temperature for controlled rolling without recrystallization is expressed in °C.

[0121] H represents the thickness of the finished steel plate, in mm.

[0122] Ensure that under the condition of low C, low Pcm, the steel plate has high strength, high toughness, low yield ratio, at the same time, the steel plate has excellent super large heat input weldability and weather resistance, and successfully eliminates the contradiction between low C, low Pcm and high strength, high toughness, low yield ratio, low longitudinal and transverse strength anisotropy of the weather resistant steel plate.

[0123] The beneficial effects of the present application are:

[0124] The steel plate of the present application is produced at low cost by reducing the content of valuable alloying elements, matching and designing the main alloying elements, micro-alloying elements and inclusion elements, i.e. low C-medium Mn-low (Cu+Ni+Mo) alloying-Nb micro-alloying-ultra-fine Ti treatment composition system, and combining with TMCP manufacturing process, to produce TMCP type weather resistant steel plate with excellent comprehensive performance.

[0125] The high performance and high value-added of the steel plate are concentrated in the perfect match of high strength, high toughness and excellent weather resistance with low yield ratio, low longitudinal and transverse strength anisotropy and super large heat input weldability, which successfully solves the contradictions between: ① low C, low Pcm and high strength, low yield ratio, ② high strength, high toughness and excellent weather resistance and low yield ratio, low anisotropy of longitudinal and transverse strength, and ③ high strength, excellent weather resistance and excellent weldability, especially super large heat input welding, in composition design and TMCP process design, which greatly improves the safety, stability and durability of large heavy steel structures; good weldability (especially large heat input welding) saves the cost and time of steel structure manufacturing for user enterprises, and excellent weather resistance eliminates the surface rust-proof coating of steel structure, which not only creates great value for users, but more importantly, reduces carbon emissions (no preheating before welding, no need for heat treatment after welding, super large heat input high efficiency welding), reduces the pollution and toxicity of surface coating to the environment, so such steel plate is not only a high value-added, full life green and environmentally friendly product. BRIEF DESCRIPTION OF DRAWINGS

[0126] Figure 1 The microstructure (1 / 4 thickness) photo of the steel of Example 6 of the present application. DETAILED DESCRIPTION

[0127] The present application will be further described below in combination with examples and drawings.

[0128] The composition of the steel of the present application is shown in Table 1, and the remaining amount contains Fe and other unavoidable impurities, Table 2 and Table 3 are the manufacturing process parameters of the present application, and Table 4 is the performance parameters of the steel of the present application.

[0129] By Figure 1It can be seen that the finished steel plate has a microstructure of uniform fine ferrite + low-carbon bainite, and the average grain size of the microstructure is below 20 microns; the steel plate has high strength, high toughness, low yield strength ratio, low longitudinal and transverse strength anisotropy, and has excellent weather resistance and weldability, especially can be welded with super-large heat input.

[0130] The steel plate is mainly used for ship structures, ocean engineering structures, bridge engineering structures, energy development engineering, wind power engineering, engineering machinery, mining machinery and heavy vehicle manufacturing, and can realize low-cost stable batch industrial production.

[0131]

[0132]

[0133]

[0134]

Claims

1. YP460MPa grade weathering steel plate with high toughness, low yield strength ratio, and low longitudinal and transverse strength anisotropy, its composition by weight percentage is: C：0.04%~0.08% Si: ≤0.20% Mn: 1.10%~1.50% P：≤0.018% S：≤0.003% Cu: 0.25%~0.40% Ni: 0.15%~0.45% Cr：0.35%~0.65% Nb: 0.015%~0.040% Ti: 0.008%~0.016% Als: 0.040%~0.070% N：≤0.0050% Mg: 0.0010%~0.0040% The balance includes Fe and other unavoidable inclusions; and the contents of the above elements must simultaneously satisfy the following relationship: Pcm≤0.22%, and Als / N≥10; where, Welding cold cracking susceptibility index Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B, in percentage terms. Weather resistance index I ≥ 6.00; I=26.01Cu+3.88Ni+1.2Cr+1.49Si+17.28P-7.29Cu×Ni-9.10Ni×P-33.39Cu 2 ; [(%Nb)× ] / [ζ×H×(T 终轧 )]≤5.18×10 -5 , in, The cumulative reduction rate of controlled rolling without recrystallization is expressed in % (%). ζ is the width-to-width ratio, which is the width of the finished steel plate / the width of the slab. H represents the thickness of the finished steel plate, in mm; T 终轧 The final rolling temperature for controlled rolling without recrystallization is expressed in °C. [ ×(T 开冷 -T 停冷 )×(Pcm)×(V c )] / [T 终轧 ×H]≥0.30; in, The cumulative reduction rate of controlled rolling without recrystallization is expressed in % (%). T 开冷 The starting temperature for accelerated cooling, measured in °C; T 停冷 The stopping temperature for accelerated cooling, in °C; V c The unit for accelerating the cooling rate of the steel plate is ℃ / s; T 终轧 The final rolling temperature for controlled rolling without recrystallization is expressed in °C. H represents the thickness of the finished steel plate, in mm; The Mg / S ratio should be controlled between 0.75 and 2.

75. 2.5×10 -3 ≤(%Mg)×(%S)×2.5×10 -2 。 2. The high-toughness, low-yield-strength ratio, and low longitudinal and transverse strength anisotropy YP460MPa grade weathering steel plate as described in claim 1, characterized in that, The balance consists of Fe and other unavoidable impurities.

3. The high-toughness, low-yield-strength ratio, and low longitudinal and transverse strength anisotropy YP460MPa grade weathering steel plate as described in claim 1 or 2, characterized in that, The microstructure of the finished weathering steel plate is uniform and fine ferrite + low carbon bainite, with an average grain size of less than 20 mm.

4. The high-toughness, low-yield-strength ratio, and low longitudinal and transverse strength anisotropy YP460MPa grade weathering steel plate as described in claim 1 or 2, characterized in that, The weathering steel plate has a yield strength ≥460MPa, tensile strength ≥570MPa, impact energy KV2 at -40℃ with a single value ≥120J, yield strength ratio ≤0.85, low longitudinal and transverse strength anisotropy (i.e., longitudinal / transverse strength difference ≤30MPa), excellent weldability, no preheating required before welding, can withstand welding heat input ≥100kJ / cm, and impact energy KV2 at -40℃ in the weld heat-affected zone with a single value ≥60J.

5. The high-toughness, low-yield-strength ratio, and low longitudinal and transverse strength anisotropy YP460MPa grade weathering steel plate as described in claim 3, characterized in that, The weathering steel plate has a yield strength ≥460MPa, tensile strength ≥570MPa, impact energy KV2 at -40℃ with a single value ≥120J, yield strength ratio ≤0.85, low longitudinal and transverse strength anisotropy (i.e., longitudinal / transverse strength difference ≤30MPa), excellent weldability, no preheating required before welding, can withstand welding heat input ≥100kJ / cm, and impact energy KV2 at -40℃ in the weld heat-affected zone with a single value ≥60J.

6. The method for manufacturing high-toughness, low-yield-strength ratio, and low longitudinal and transverse strength anisotropy YP460MPa grade weathering steel plate as described in any one of claims 1 to 5, characterized in that, Includes the following steps: 1) Smelting and casting Smelting according to the composition described in claim 1 or 2, and continuously casting into slabs; 2) Slab heating The heating temperature is controlled at 1050~1150℃; 3) Rolling, with a rolling width ratio ≥ 1.3 The first stage is ordinary rolling, which is continuous rolling using the maximum rolling capacity of the rolling mill; The second stage employs controlled rolling without recrystallization, with the initial rolling temperature controlled at 780~880℃, a reduction rate per rolling pass ≥7%, a cumulative reduction rate ≥50%, and a final rolling temperature of 770~830℃; and... [(%Nb)× ] / [ζ×H×(T 终轧 )]≤5.18×10 -5 , in, The cumulative reduction rate of controlled rolling without recrystallization is expressed in % (%). ζ is the width-to-width ratio, which is the width of the finished steel plate / the width of the slab. H represents the thickness of the finished steel plate, in mm; T 终轧 The final rolling temperature for controlled rolling without recrystallization is expressed in °C. 4) Cooling After controlled rolling, the steel plate is immediately sent to an accelerated cooling device for rapid cooling; the initial cooling temperature is 750~800℃, the cooling rate is ≥5℃ / s, and the final cooling temperature is 330~450℃; subsequently, the steel plate is allowed to air cool to room temperature. [ ×(T 开冷 -T 停冷 )×(Pcm)×(V c )] / [T 终轧 ×H]≥0.30; in, The cumulative reduction rate of controlled rolling without recrystallization is expressed in % (%). T 开冷 The starting temperature for accelerated cooling, measured in °C; T 停冷 The stopping temperature for accelerated cooling, in °C; V c The unit for accelerating the cooling rate of the steel plate is ℃ / s; T 终轧 The final rolling temperature for controlled rolling without recrystallization is expressed in °C. H represents the thickness of the finished steel plate, in mm.

7. The manufacturing method of YP460MPa grade weathering steel plate with high toughness, low yield strength ratio and low longitudinal and transverse strength anisotropy as described in claim 6, characterized in that, In step 1), the superheat of the tundish casting is controlled at 7~30℃, the casting speed is controlled at 0.6~1.0m / min, and the liquid level fluctuation in the crystallizer is controlled at ≤5mm.

8. The method for manufacturing YP460MPa grade weathering steel plate with high toughness, low yield strength ratio, and low longitudinal and transverse strength anisotropy as described in claim 6, characterized in that, In step 4), when the steel plate thickness is ≥50mm, the steel plate is slowly cooled. The slow cooling process involves holding the plate at a temperature of no less than 300℃ for at least 24 hours, and then the steel plate is naturally air-cooled to room temperature.

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