High-rupture-resistance and easy-to-weld super-thick yp460 grade steel plate and method for manufacturing the same

Abstract

High-rupture-resistance and easy-to-weld super-thick YP460 grade steel plate and manufacturing method thereof, the component weight percentage of which is: C 0.030-0.060%, Si≤0.15%, Mn 1.55-1.90%, P≤0.015%, S≤0.003%, Cu 0.15-0.40%, Ni 0.15-0.50%, Cr 0.05-0.30%, Nb 0.025-0.050%, Ti 0.008-0.016%, Als 0.025-0.060%, N≤0.0050%, Ca 0.0010-0.0040%, the rest containing Fe and inevitable inclusions, and must simultaneously satisfy: welding cold crack sensitivity index Pcm≤0.20%; Als / (N-0.292Ti)≥32; BCC crystal structure dislocation low-temperature mobility index θ≥0.51, Ca / S ratio controlled at 1-3, (%Ca)×(%S)≤1.5×10 ‑3 The present application is suitable for large-power offshore wind pile legs, offshore platforms, cross-sea bridge steel tower structures and engineering machinery, etc.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-strength steel, and particularly relates to a high-crack-arrest and easy-to-weld ultra-thick YP460-grade 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, and is widely used in oil and gas pipelines, offshore platforms, shipbuilding, hydropower engineering, bridge structures, boiler vessels, building structures, automobile industry, railway transportation and machinery manufacturing; the performance of low-carbon (high-strength) low-alloy steel depends on its chemical composition and manufacturing process, and the strength, toughness, plasticity, weldability and 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 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 precious metal content and low manufacturing cost, the comprehensive mechanical properties and use performance of the steel plate are greatly improved to reduce the alloy content of the steel and save the cost, the high-strength lightweight 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; at present, a research climax of developing a new generation of high-performance steel materials has been started in Japan, 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 super-fining the metallographic microstructure and fine structure (dislocation substructure configuration, packet, block, etc.).

[0003] The prior art in the manufacture of thick steel plates with a yield strength of > 420 MPa and a low temperature impact toughness of > 34 J at -60°C generally requires the addition of a certain amount of Ni or Cu+Ni elements (> 0.30%) to 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" (in 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" (in Japanese) Sumitomo Metal, Vol. 50, No. 1 (1998), 26; "Steel Plate for Offshore Platform Structure Used in Ice Sea Area" (in Japanese), Chitetsu Kenkyu, 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 reach Akv≥34 J at -60 °C when welding with a heat input of <50 KJ / cm; but when welding with a super-large heat input (≥100 KJ / cm), the low-temperature toughness of the heat-affected zone HAZ is generally difficult to achieve, and the low-temperature toughness of the heat-affected zone HAZ deteriorates severely. A large number of patent documents only explain how to achieve the low-temperature toughness of the base steel plate, and there are few explanations on how to obtain 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 there are few explanations on how to ensure the low-temperature toughness of the steel plate. 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 welded with a super-large heat input is also difficult to reach -60 °C. (See Japanese Patent Nos. 63-93845, 63-79921, 60-258410, 4-285119, 4-308035, 3-264614, 2-250917, 4-143246, US Patent Nos. 4855106, 5183198, 4137104).

[0004] Currently, only Nippon Steel Corporation of Japan uses oxide metallurgy technology (see US Patent No. 4629505, WO 01 / 59167A1) to improve the low-temperature toughness of the heat-affected zone HAZ of steel plates welded with a super-large heat input, that is, during the large heat input welding process, TiN particles lose their effect due to dissolution under the action of high temperature for a long time, 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 high-strength and high-toughness acicular ferrite structure.

[0005] In order to ensure the low-temperature toughness of the heat-affected zone of the large heat input welding, the steel plate (especially the ultra-thick steel plate) is added with a certain amount of precious alloy elements Cu and Ni, and a small amount of Mo is particularly needed to be added when the yield strength YP reaches 460 MPa. 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 the thick steel plate, is not very stable (under the condition of large heat input welding, Mo promotes the formation of coarse upper bainite, which deteriorates the toughness of the welding coarse grain heat-affected zone), and the requirement of-40℃ impact toughness cannot be stably met. The manufacturing cost of the thick steel plate is also high.

[0006] The steel plate applied for by Baosteel (such as Chinese patent application number 202110734971.9, 202211365790.4) has excellent strength, toughness, low yield ratio (≤0.86), transverse and longitudinal anisotropy (≤30 MPa), atmospheric corrosion resistance and weldability, and is practically batch-engineered for application (Changtai Bridge, Chaoma Bridge, etc.). The weldability and weather resistance are excellent, but the crack arrest characteristic Kca is not involved, the plastic crack instability propagation resistance of the steel plate is insufficient, and the thickness of the steel plate for bridge engineering application is less than 80 mm. SUMMARY

[0007] The purpose of the present application is to provide a high-crack-arresting and easy-to-weld ultra-thick YP460-grade steel plate and a manufacturing method thereof. The steel plate has high strength, excellent low-temperature toughness and high crack arrest characteristic, and the low-temperature toughness of the fusion line and HAZ is also excellent when large heat input welding is performed. The yield strength of the steel plate is ≥460 MPa, the tensile strength is ≥590 MPa, the impact energy KV2 at-40℃ (single value) is ≥100 J, and the Kca at-10℃ is ≥6000 N / mm 3 / 2 . The weldability is excellent, no preheating is required before welding, the steel plate can withstand a welding heat input of ≥50kJ / cm, the impact energy KV2 of the heat-affected zone at-40℃ (single value) is ≥60 J, and the steel plate is particularly suitable for large-power offshore wind pile legs, offshore platforms, steel tower structures of cross-sea bridges, metal structural components of hydropower, port machinery and engineering machinery, etc., and can realize low-cost stable batch industrial production.

[0008] High toughness, high crack arrest super-thick steel plate is one of the most difficult varieties in thick plate products, the reason is that the steel plate not only requires ultra-low C, low carbon equivalent CEV, high strength, excellent low temperature toughness and high crack arrest characteristics, and the steel plate can also withstand a larger heat input welding (welding heat input ≥ 50 KJ / cm), the steel plate welding fusion line, heat affected zone has high strength, excellent low temperature impact toughness and high crack arrest characteristics, but these performance requirements are difficult to meet at the same time:

[0009] A) ultra-low C, low Pcm and large thickness, high strength;

[0010] B) low temperature toughness, high crack arrest and large thickness, low manufacturing cost (low Ni content);

[0011] C) high strength, high crack arrest characteristics and excellent weldability, especially larger heat input weldability.

[0012] The above characteristics are in conflict with each other in composition design and TMCP process design, and are difficult to reconcile: when reducing the C content and Pcm, it is difficult to realize the high strength and high crack arrest characteristics of the super-thick steel plate; while improving the low temperature toughness and crack arrest characteristics of the super-thick steel plate, it is difficult to realize the low manufacturing cost manufacturing (low Ni content) of the steel plate; when the super-thick steel plate obtains high strength and high crack arrest characteristics, the steel plate weldability, especially the larger heat input steel plate, is difficult to guarantee.

[0013] How to balance large thickness, low C / low Pcm, high strength, high toughness, high crack arrest characteristics and larger heat input weldability is one of the greatest difficulties of the present application, and is also a key core technology.

[0014] To achieve the above purpose, the technical scheme of the present application is:

[0015] The high crack arrest, easy-to-weld super-thick YP460 grade steel plate, the composition weight percentage is:

[0016] C: 0.030-0.060%

[0017] Si: ≤0.15%

[0018] Mn: 1.55-1.90%

[0019] P: ≤0.015%

[0020] S: ≤0.003%

[0021] Cu: 0.15-0.40%

[0022] Ni: 0.15-0.50%

[0023] Cr: 0.05-0.30%

[0024] Nb: 0.025-0.050%

[0025] Ti: 0.008-0.016%

[0026] Als: 0.025-0.060%

[0027] N: ≤0.0050%

[0028] Ca: 0.0010-0.0040%

[0029] the balance comprising Fe and other unavoidable impurities, and must simultaneously satisfy the following relationships:

[0030] welding cold crack sensitivity index Pcm ≤ 0.20%;

[0031] Pcm = (%C) + (%Si) / 30 + [(%Mn) + (%Cu) + (%Cr)] / 20 + (%Ni) / 60 + (%Mo) / 15 + (%V) / 10 + 5(%B);

[0032]

[0033] Als / (N-0.292Ti) ≥ 32;

[0034] BCC crystal structure dislocation low temperature mobility index θ ≥ 0.51,

[0035] θ = 1.25(%Ni) + [1.57(%Mn) - 0.69(%Mn) + 1.69(%Cu) - 3.51(%Si) - 0.46[(%Cr) + (%Mo)] - 2.43[(%Al) + (%Nb) + (%Ti)]; 2

[0036]

[0037] (%Ti)];

[0038] Ca / S ratio is controlled at 1-3, and (%Ca) x (%S) ≤ 1.5 x 10 -3 .

[0039] Further, the balance is Fe and other unavoidable impurities.

[0040] The steel sheet of the present application has a steel sheet microstructure of uniform fine ferrite + a small amount of low carbon bainite, with an average grain size of below 20 μm.

[0041] The steel sheet of the present application has a yield strength ≥ 460 MPa, a tensile strength ≥ 590 MPa, an impact energy KV2 (-40°C) ≥ 100 J (single value), and Kca (-10°C) ≥ 6000 N / mm 3 / 2 ​​​The steel plate has excellent weldability, no preheating before welding, can withstand welding heat input of ≥50kJ / cm, and the impact energy KV2 (single value) of the heat affected zone at -40°C is ≥60J.

[0042] In the component design of the steel plate according to the present application:

[0043] C has a great influence on the strength, low-temperature toughness, crack arrest property, elongation and weldability of the TMCP ultra-thick steel plate, especially the great heat input weldability. In order to improve the low-temperature toughness and great heat input weldability of the ultra-thick steel plate, it is desirable to control the C content in the steel to be relatively low. However, from the perspective of the strength of the ultra-thick steel plate and the control of microstructure during production and manufacturing process and manufacturing cost, the C content should not be controlled too low. Too low C content can easily lead to too high grain boundary migration rate, coarse microstructure of the base steel plate and welded HAZ and easy mixed crystal, and too low C content in the steel can cause grain boundary weakening, seriously deteriorating the crack arrest property of the base steel plate and the low-temperature toughness of the welded HAZ. Therefore, the reasonable range of C content is 0.030-0.060%.

[0044] Si promotes the deoxidation of molten steel and can improve the strength of the steel plate. However, the deoxidation effect of Si is not great when Al is used for deoxidation of the molten steel. Although Si can improve the strength of the steel plate, Si seriously damages the low-temperature toughness, crack arrest property, elongation and weldability of the weathering steel plate. Especially for high-strength ultra-thick steel plates with high alloy content, Si not only promotes the formation of M-A islands, but also forms coarse and unevenly distributed M-A islands, which seriously damages the low-temperature toughness and crack arrest property of the steel plate welded heat affected zone (HAZ). Therefore, the Si content in the steel should be controlled as low as possible. Considering the certain weather resistance of Si and the economy and operability of the steelmaking process, the Si content is controlled to be below 0.15%.

[0045] Mn is the most important alloying element in steel. In addition to increasing the strength of the steel plate, it also has the effects of expanding the austenite phase region, reducing the Ar3 point temperature, refining the TMCP steel plate grains to increase the strength of the steel plate (fine-grain strengthening effect), improving the low-temperature toughness of the steel plate, stopping crack characteristics (fine-grain toughening), promoting the formation of low-temperature phase transformation structure (phase transformation strength effect) to increase the strength of the steel plate. However, Mn is prone to segregation during the solidification of molten steel, especially when the Mn content is high. Not only does it cause casting operation difficulties, but Mn is also prone to conjugate segregation with elements such as C, P, and S. When the C content in the steel is high, the segregation and porosity in the center of the casting blank are aggravated, and severe center area segregation of the casting blank is prone to form abnormal structures during subsequent TMCP and welding processes, which can lead to low-temperature toughness and crack formation in the welded joint. In addition, for high-strength TMCP ultra-thick steel plates, high Mn content not only causes the low-temperature toughness, crack stopping characteristics, and elongation of the steel plate to deteriorate rapidly, but also leads to serious deterioration of the weldability of the steel plate, especially the weldability of large heat input. In addition, when the Mn content is too high, the low-temperature mobility of ferrite dislocations decreases, leading to deterioration of the intrinsic toughness and crack stopping properties of the steel plate. Therefore, the suitable Mn content is 1.55-1.90%.

[0046] P is a harmful inclusion in steel that has a significant damaging effect on the mechanical properties of the steel plate, especially low-temperature impact toughness, crack stopping characteristics, elongation, and weldability. In theory, the lower the better. However, considering the steelmaking operability and steelmaking cost, for TMCP ultra-thick steel plates that require large heat input welding, high toughness (-40°C toughness), high crack stopping characteristics (-10°C Kca), high strength, and large heat input welding, the P content needs to be controlled at ≤0.015%.

[0047] S is a harmful inclusion in steel that has a significant damaging effect on the low-temperature toughness, crack stopping characteristics, and weldability of the steel plate. More importantly, S combines with Mn in the steel to form MnS inclusions. During hot rolling, the plasticity of MnS causes it to extend along the rolling direction, forming MnS inclusion bands along the rolling direction, which not only severely damages the low-temperature impact toughness, crack stopping characteristics, elongation, Z-direction performance, and fatigue resistance of the steel plate, but also causes the weldability of the steel plate, especially the weldability of large heat input, to deteriorate severely. At the same time, S is also the main element that causes hot brittleness during hot rolling. In theory, the lower the better. However, considering the steelmaking operability, steelmaking cost, and smooth logistics principles, for TMCP ultra-thick steel plates that require large heat input welding, high toughness (-40°C toughness), high crack stopping characteristics (-10°C Kca), high strength, and large heat input welding, the S content needs to be controlled at ≤0.003%.

[0048] Cu is mainly an austenite stabilizing element, and also an element for improving the low-temperature mobility of ferrite dislocations. Adding Cu can also reduce the Ar1 and Ar3 point temperatures, refine the microstructure of TMCP weathering steel plate, and improve the low-temperature toughness and crack arrest characteristics of the TMCP steel plate. However, if the Cu content is too high (higher than 0.40%), it can easily cause copper brittleness, surface cracking and internal cracking of the casting blank, and especially the impact load fracture characteristics (i.e. crack arrest characteristics) of the steel plate with large thickness. Moreover, it can also lead to serious deterioration of the low-temperature toughness and crack arrest characteristics of the welded joint. Considering that Cu is a relatively valuable alloying element, the upper limit of Cu content should be controlled at 0.40% from the perspective of cost-effectiveness. If the Cu content is too low (lower than 0.15%), the above effects are small. Therefore, the Cu content should be controlled between 0.15% and 0.40%.

[0049] Adding Ni can not only reduce the BCC crystal structure dislocation lattice friction (i.e. P-N force), improve the low-temperature mobility of ferrite dislocations, promote dislocation cross-slip, and improve the intrinsic plasticity and toughness of ferrite. In addition, as a strong austenite stabilizing element, Ni can greatly reduce the Ar1 and Ar3 point temperatures, improve the driving force for the phase transformation of austenite to ferrite, cause the phase transformation of austenite to occur at a lower temperature, greatly refine the microstructure of the TMCP steel plate, increase the resistance to crack propagation through ferrite grains, and greatly improve the low-temperature toughness of the TMCP steel plate. Therefore, Ni has the effect of simultaneously improving the strength, low-temperature toughness and crack arrest characteristics of the TMCP steel plate without reducing the elongation (i.e. plasticity and toughness). Adding Ni in the steel can also reduce the copper brittleness of copper-containing steel, reduce 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 a Ni content not only hardens the weld heat-affected zone, which is not conducive to the weldability of the steel plate and the low-temperature toughness of the welded joint with large heat input, but also greatly increases the manufacturing cost of the steel plate (Ni is a valuable alloying element). Therefore, the Ni content should be controlled between 0.15% and 0.50%.

[0050] For ultra-thick steel plates, adding a certain amount of Cr (≤0.30%) can improve the strength of the thick steel plate without compromising the low-temperature toughness, bending cold workability and large input welding of the steel plate. However, if the Cr content is too low (<0.05%), the contribution of Cr to the strength of the steel plate is small, and the performance requirements cannot be met. If the Cr content is too high (>0.30%), it can compromise the low-temperature toughness, crack arrest characteristics, bending cold workability of the steel plate, especially the weldability of the steel plate, especially the large heat input weldability, and the low-temperature toughness and crack arrest characteristics of the weld heat-affected zone (the weld heat-affected zone forms coarse feather-like upper bainite structure). Therefore, the Cr content should be controlled between 0.05% and 0.30%.

[0051] The purpose of adding trace Nb element in the steel is to control the rolling without recrystallization, refine the grain size of the steel plate, and improve the strength and toughness of the TMCP steel plate. For the ultra-thick steel plate, when the C content in the steel is low (≤0.060%), and the Nb addition is less than 0.025%, the TMCP ultra-thick steel plate is not effectively controlled by rolling, and the matching of strength and toughness and the crack arrest characteristics are not good. When the Nb addition is more than 0.050%, not only the low temperature toughness and crack arrest characteristics of the steel plate are deteriorated (high Nb content is easy to produce mixed crystal), but also the alloy cost of the steel plate is high (Nb is also a valuable alloy element). Moreover, under the condition of large heat input welding, upper bainite (Bu) is induced to form and Nb(C, N) secondary precipitation embrittlement, which seriously damages the low temperature toughness and crack arrest characteristics of the heat affected zone (HAZ) of the ultra-thick steel plate under large heat input welding. Therefore, the Nb content is controlled between 0.025-0.050% to obtain the best rolling control effect, realize the matching of strength and toughness / plasticity of the TMCP ultra-thick steel plate, and have high crack arrest characteristics without damaging the large heat input welding of the ultra-thick steel plate.

[0052] The purpose of adding trace Ti in the steel is to combine with N in the steel to generate TiN particles with high stability, and to inhibit the grain growth of the steel plate and the welding HAZ. The Ti content added in the steel should match the N content in the steel. The matching principle is that TiN cannot precipitate in liquid steel and must precipitate in solid phase. Therefore, the precipitation temperature of TiN must be ensured to be lower than 1400°C. When the Ti addition in the steel is too low (<0.008%), the number of TiN particles formed is insufficient to inhibit the austenite grain growth during TMCP and welding thermal cycle and to improve the low temperature toughness and weldability of the ultra-thick steel plate. When the Ti addition is too high (>0.016%), the TiN precipitation temperature exceeds 1400°C, and part of the TiN particles precipitate in large size during the solidification of the steel liquid. Such large size TiN particles not only cannot inhibit the grain growth, but also become the starting point of crack initiation. Therefore, the optimal control range of Ti content is 0.008-0.016%.

[0053] Als in the steel plate can fix free [N] in the steel, reduce the free [N] in the welding heat affected zone (HAZ), and improve the low temperature impact toughness and crack arrest characteristics of the large heat input welding HAZ. However, excessive addition of Als in the steel will form a large number of dispersed needle-shaped Al2O3 inclusions in the steel, which will damage the low temperature impact toughness and weldability of the steel plate. According to the composition system analysis of the ultra-thick steel plate, the optimal Als content is controlled between 0.025-0.060%.

[0054] The control range of N corresponds to the control range of Ti, and is used to control the grain of the steel plate, improve the low temperature toughness, crack arrest property and weldability of the steel plate; if the content of N is too low, the amount of TiN particles generated is small and the size is large, which cannot control the grain of the steel plate and improve 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 under the condition of large heat input welding, the free [N] content in the heat affected zone (HAZ) increases sharply, which seriously damages the low temperature toughness, crack arrest property and bending cold workability of the HAZ, and deteriorates the processing and using properties of the steel. Therefore, the content of N is controlled to be ≤0.0050%.

[0055] The steel is treated with Ca, 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, crack arrest property, elongation and Z-direction performance of the ultra-thick steel plate, and improve the weldability of the steel plate. In addition, the use of Ca treatment improves the castability of high acid-soluble aluminum molten steel. More importantly, the Ca(O,S) particles cannot agglomerate and grow in the liquid steel and solid steel, and are dispersed in the steel in a fine state. The high melting point Ca(O,S) particles can pin the growth of the austenite grains in the heat affected zone during 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 large heat input. The amount of Ca added depends on the content of S in the steel. If the amount of Ca added is too low, the treatment effect is not good; if the amount of Ca added is too high, the size of Ca(O,S) formed is too large, the brittleness is also increased, and the Ca(O,S) can become the starting point of fracture cracks, which reduces the low temperature toughness, crack arrest property, elongation of the steel, and the 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 Ca is controlled according to ESSP=(%Ca)[1-1.25(%O)] / 1.25(%S), wherein ESSP is the shape control index of sulfide inclusions, and the value range is preferably 1.00-3.00, and therefore the suitable range of the content of Ca is 0.0010-0.0040%.

[0056] In particular, the above-mentioned element contents of the present application must satisfy the following relationships simultaneously:

[0057] C≤0.060%, Pcm≤0.20%; wherein Pcm is the welding cold crack sensitivity index, Pcm=(%C)+( %Si) / 30+[(%Mn)+( %Cu)+( %Cr)] / 20+( %Ni) / 60+( %Mo) / 15+( %V) / 10+5( %B), unit: %.

[0058] Ensure that in the condition of ultra-low carbon, low Pcm, the steel plate not only has excellent weldability; more importantly, the ultra-thick steel plate can be welded with large heat input under the condition of high Nb content (0.025-0.050%); the weld heat-affected zone not only forms ultra-low carbon bainite without brittleness, but also has low M / A island content, and the degree of Nb(C,N) secondary precipitation brittleness is small during multi-pass welding process; the low temperature toughness and crack arrest characteristics of the ultra-thick steel plate in the weld heat-affected zone are ensured.

[0059] Als / (N-0.292Ti)≥32, ensure that the ultra-thick steel plate can be welded with large heat input during multi-pass welding process, all solid solution [N] forms fine and dispersed AlN, eliminates the strong brittleness effect of solid solution [N] on the weld heat-affected zone, and improves the low temperature toughness and crack arrest characteristics of the ultra-thick steel plate in the weld heat-affected zone.

[0060] BCC crystal structure dislocation low temperature mobility index θ≥0.51,

[0061] θ=1.25(%Ni)+[1.57(%Mn)-0.69(%Mn) 2 ]+1.69(%Cu)-3.51(%Si)

[0062] -0.46[(%Cr)+(%Mo)]-2.43[(%Al)+(%Nb)+(%Ti)].

[0063] Under low temperature conditions, reduce the lattice friction force (i.e. P-N force) of BCC crystal structure dislocation slip, promote dislocation cross-slip, improve BCC crystal structure dislocation low temperature mobility, expand the plastic deformation field of crack tip, increase the plastic deformation work (i.e. crack tip F-R source dislocation increment and slip speed), improve the intrinsic plasticity and toughness of BCC crystal structure, and improve the crack arrest characteristics of the steel plate. This is one of the key core technologies of the application.

[0064] Ca treatment, Ca / S ratio is controlled at 1-3, and (%Ca) x (%S)≤1.5 x 10 -3 .

[0065] Ensure sulfidation spheroidization, and at the same time, Ca(O,S) particles are uniformly and finely distributed in the steel, inhibit the growth of austenite grains in the weld heat-affected zone with large heat input, improve the low temperature toughness and crack arrest characteristics of the steel plate in the weld heat-affected zone with large heat input, and improve the Z-direction performance of the ultra-thick steel plate.

[0066] The manufacturing method of the high crack arrest and easy-to-weld ultra-thick YP460 grade steel plate disclosed by the application comprises the following steps:

[0067] 1) Smelting and casting

[0068] Smelting and casting into a slab according to the above composition;

[0069] 2) Slab heating, temperature control at 1080-1150°C;

[0070] 3) Controlled rolling

[0071] The first stage is normal rolling, using the maximum rolling capacity of the rolling mill to continuously roll;

[0072] The second stage uses non-recrystallization controlled rolling, with a starting temperature of 720-760°C, a rolling pass reduction of ≥7%, a cumulative reduction of ≥45%, and a finishing temperature of 710-750°C. In addition to meeting the above requirements, the following relationship must also be met:

[0073] [(%Nb) x Au x ξ] / [H x (%Cr) x (T 终轧 )]≥4.47 x 10 -4 ,

[0074] Wherein: Au is the austenite stabilization index,

[0075] Au = 2.54 + 40.53[(%C) + (%N)] + 0.43[(%Cu) + (%Ni)

[0076] + (%Mn)] - 0.22(%Al) - 2.64[(%P) + (%S)] - 1.26[(%Cr) +

[0077] (%Mo)] - (%Si), unit %;

[0078] ξ is the non-recrystallization / critical zone controlled rolling cumulative reduction, unit %;

[0079] H is the finished steel plate thickness, unit mm;

[0080] T 终轧 is the finishing temperature of non-recrystallization / critical zone controlled rolling, unit °C;

[0081] 4) Controlled cooling

[0082] After the controlled rolling is completed, the steel plate is immediately transported to the accelerated cooling equipment, and then the steel plate is accelerated cooled, with a starting cooling temperature of 700-740°C, a cooling speed of ≥3°C / s, and a stopping cooling temperature of 300-450°C. When the steel plate thickness is ≥80mm, the steel plate is slowly cooled, with a slow cooling process of not less than 300°C for 24 hours or more, and then the steel plate is naturally air cooled to room temperature;

[0083] In addition to meeting the above requirements, the following relationship must also be met for the controlled cooling:

[0084] [Pcm x (T 开冷 ) x (V c )] / [(T停冷 ) x H] ≥ 9.45 x 10 -3 ;

[0085] Pcm = (%C) + (%Si) / 30 + [(%Mn) + (%Cu) + (%Cr)] / 20 + (%Ni) / 60 + (%Mo) / 15 + (%V) / 10 + 5(%B) in %.

[0086] Pcm = (%C) + (%Si) / 30 + [(%Mn) + (%Cu) + (%Cr)] / 20 + (%Ni) / 60 + (%Mo) / 15 + (%V) / 10 + 5(%B) in %.

[0087] Pcm = (%C) + (%Si) / 30 + [(%Mn) + (%Cu) + (%Cr)] / 20 + (%Ni) / 60 + (%Mo) / 15 + (%V) / 10 + 5(%B) in %.

[0088] T 开冷 is the start temperature of accelerated cooling, in °C;

[0089] T 停冷 is the stop temperature of accelerated cooling, in °C;

[0090] V c is the accelerated cooling rate of the steel plate, in °C / s;

[0091] H is the thickness of the finished steel plate, in mm.

[0092] Preferably, the slab is produced by continuous casting, the tundish pouring superheat is controlled at 8-28 °C, the withdrawal speed is controlled at 0.6-1.0 m / min, and the mold level fluctuation is controlled at ≤5 mm.

[0093] In the manufacturing method described in the present application:

[0094] The slab is preferably produced by continuous casting, the tundish pouring superheat is controlled at 8-28 °C, the withdrawal speed is controlled at 0.6-1.0 m / min, and the mold level fluctuation is controlled at ≤5 mm.

[0095] According to the above content ranges of C, Mn, Nb and Ti, the slab heating temperature is controlled at 1080-1150 °C, which ensures that the Nb in the steel is completely dissolved into the austenite during the slab heating process, and the slab austenite grains do not abnormally grow.

[0096] Controlled rolling:

[0097] The first stage is ordinary rolling, continuous rolling is performed using the maximum rolling capacity of the rolling mill, which maximizes the rolling line capacity while ensuring recrystallization of the deformed billet and refining the austenite grains.

[0098] The second stage adopts non-recrystallization controlled rolling. According to the content range of Nb element in the above-mentioned steel and the requirements of texture strengthening and toughening, in order to ensure the effect of non-recrystallization controlled rolling and critical zone controlled rolling, the controlled rolling starting temperature is controlled at 720-760 DEG C, the rolling pass reduction is greater than or equal to 7%, the cumulative reduction is greater than or equal to 45%, and the finish rolling temperature is 710-750 DEG C.

[0099] After the controlled rolling is finished, the steel plate is immediately transported to the accelerated cooling equipment, and then the steel plate is subjected to accelerated cooling; the steel plate open cooling temperature is the finish rolling temperature of 700-740 DEG C, the cooling speed is greater than or equal to 3 DEG C / s, and the stop cooling temperature is 300-450 DEG C; when the thickness of the steel plate is greater than or equal to 80 mm, the steel plate is subjected to slow cooling, the slow cooling process is that the temperature is kept at not less than 300 DEG C for more than 24 hours, and then the steel plate is naturally air-cooled to room temperature.

[0100] In addition to meeting the above requirements, the following relationship must also be met:

[0101] [(%Nb) x Au x ξ] / [H x (%Cr) x (T 终轧 )]≥4.47 x 10 -4 (1)

[0102] In the formula, Au is the austenite stabilization index,

[0103] Au=2.54+40.53[(%C)+(%N)]+0.43[(%Cu)+(%Ni)+(%Mn)]-0.22(%Al)-2.64[(%P)+(%S)]-1.26[(%Cr)+(%Mo)]-(%Si), unit %; ξ is the non-recrystallization / critical zone controlled rolling cumulative reduction, unit %; H is the thickness of the finished steel plate, unit mm; T 终轧 is the finish rolling temperature of non-recrystallization / critical zone controlled rolling, unit DEG C.

[0104] It can be seen from the formula (1) that:

[0105] With the increase of the content of niobium (%Nb), the controlled rolling effect increases, the degree of inhibition of austenite recrystallization is large, the austenite flattening effect is enhanced, and the dislocation density and deformation band density inside the austenite grain are increased;

[0106] Secondly, with the increase of the non-recrystallization / critical zone controlled rolling cumulative reduction ξ, the dislocation density and deformation band density inside the flattened austenite grain are also greatly increased; the nucleation position of ferrite phase is increased, the driving force of austenite to ferrite phase transformation is increased, the coarse feather-like bainite structure and side-lath Widmanstatten structure are inhibited in the accelerated cooling process of the thick and Cr-containing steel plate, the fine equiaxed ferrite structure and lath bainite structure are increased, and in addition, with the increase of the recrystallization / critical zone controlled rolling cumulative reduction ξ, the deformation texture (100)<011> is enhanced, and the texture strengthening and toughening effect is enhanced;

[0107] Thirdly, with the increase of austenite stabilization index Au, the anisotropy of the electron cloud of the outer layer dsp hybrid orbital of alloy atoms decreases, the covalent bond characteristics weaken and the metallic bond characteristics strengthen, the low-temperature mobility of BCC dislocation is improved to improve the intrinsic plasticity and toughness of the steel plate, while the Ar3 point temperature decreases, and the grain structure of the ultra-thick steel plate is refined.

[0108] The above-mentioned results superimpose each other to ensure that the ultra-thick steel plate has excellent low-temperature toughness and crack arrest characteristics. With the increase of the thickness H of the steel plate and the final rolling temperature, the controlled rolling effect is weakened, the austenite flattening effect is poor, the dislocation density / deformation band density inside the austenite grain is low, the nucleation position is less, the austenite stability increases, the superimposition of the small cooling rate (caused by the thickness of the plate) and the Cr-containing alloy promotes the development of the coarse feather-like upper bainite structure and the side plate Weishi structure, which deteriorates the low-temperature toughness and crack arrest characteristics of the ultra-thick steel plate; in combination of the above, when each index meets the above formula, the ultra-thick steel plate has excellent low-temperature toughness and crack arrest characteristics. This is one of the key core technologies of the present application.

[0109] [Pcm×(T 开冷 )×(V c )] / [(T 停冷 )×H]≥9.45×10 -3 (2)

[0110] Wherein, Pcm is the welding crack sensitivity index, Pcm=(%C)+(%Si) / 30+[(%Mn)+(%Cu)+(%Cr)] / 20+(%Ni) / 60+(%Mo) / 15+(%V) / 10+5(%B), unit is %; T 开冷 is the starting temperature of accelerated cooling, unit ℃; T 停冷 is the stop temperature of accelerated cooling, unit ℃; V c is the accelerated cooling speed of the steel plate, unit is ℃ / s; H is the thickness of the finished steel plate, unit mm.

[0111] As can be seen from formula (2), with the increase of the welding crack sensitivity index Pcm, the open cooling temperature T 开冷The content of low-temperature phase transformation organization (such as bainite, especially lower bainite) of the steel plate increases with the increase of the rising and cooling speed, and the strength of the steel plate increases; and the content of low-temperature phase transformation organization (such as bainite, especially lower bainite) of the steel plate is lower and the strength of the steel plate is lower with the higher stop cooling temperature and the larger thickness of the steel plate (which causes the lower cooling speed, especially the extremely low cooling speed at the center of the super-thick steel plate); in combination with the above, when each index meets the above formula, the super-thick steel plate has high strength, high toughness, high crack arrest property, and the steel plate has excellent weldability with large heat input, and the contradiction between low C, low carbon equivalent (Pcm) and high strength, high toughness, high crack arrest property and excellent weldability of the super-thick steel plate is successfully eliminated. This is one of the key core technologies of the application.

[0112] The component data in the above formula is calculated in percentage, for example, if the carbon content is 0.10%, 0.10 is used in the calculation.

[0113] The beneficial effects of the application are as follows:

[0114] The application adopts ultra-low carbon C-low Si-high Mn low-alloy steel as the basis, Pcm≤0.20%, low N content, Als / (N-0.292Ti)≥32, (Cu+Ni+Cr) alloying, BCC crystal structure dislocation low-temperature mobility index θ≥0.51, Ti+Nb micro-alloying, Ca treatment, and the Ca / S ratio is controlled between 1.00-3.00 and (%Ca)×(%S)≤1.5×10 -3 The alloy optimization combination design and the matched TMCP process: [(%Nb)×Au×ξ] / [H×(%Cr)×(T 终轧 )]≥4.47×10 -4 , [Pcm×(T 开冷 )×(V c )] / [(T 停冷 )×H]≥9.45×10 -3 , so that the microstructure of the finished steel plate is uniform and fine ferrite + a small amount of low-carbon bainite, and the average grain size of the microstructure is below 20 μm.

[0115] The steel plate of the application produces the TMCP type super-thick crack arrest steel plate with excellent comprehensive performance at low cost by reducing the content of valuable alloy elements (Ni element), matching combination design between main alloy elements, micro-alloy elements and inclusion elements, and combining with the new generation TMCP manufacturing process. The super-thick crack arrest steel plate not only has high strength, high toughness and high crack arrest property, but also has excellent weldability, especially large heat input welding, which greatly shortens the manufacturing cycle of the steel structure, creates great value for the construction enterprise, and realizes low carbon, green and environmental protection in the process of steel plate manufacturing and use.

[0116] The high performance and high added value of the steel plate described in this invention are mainly reflected in its large thickness (≥80mm), high strength, high toughness, high crack arrest properties, and excellent weldability. In particular, it can perfectly match the weldability with a large heat input, successfully solving the following problems:

[0117] A) Balancing ultra-low C, low Pcm with large thickness and high strength;

[0118] B) Balancing low-temperature toughness, high crack arrest, and large thickness with low manufacturing cost (low Ni content);

[0119] C) The contradiction between high strength, high crack arrest properties, and excellent weldability, especially weldability with high heat input, which is difficult to reconcile in composition design and TMCP process design, greatly improves the safety, stability, and durability of large heavy steel structures. The good weldability (especially weldability with high heat input) saves users the cost of steel structure manufacturing and shortens the manufacturing time, which not only creates huge value for users, but more importantly, reduces carbon emissions (no preheating before welding, no heat treatment after welding, and high-efficiency welding with ultra-high heat input). Therefore, this type of steel plate is not only a high-value-added product with green and environmentally friendly features throughout its entire life cycle. Attached Figure Description

[0120] Figure 1 This is a 500x magnified image of the microstructure (1 / 4 thickness) of the steel in Example 5 of the present invention. Detailed Implementation

[0121] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0122] The composition of the embodiments of the present invention is shown in Table 1, with the balance being Fe and unavoidable impurities. Tables 2 and 3 show the manufacturing process parameters of the embodiments of the present invention. Table 4 shows the performance parameters of the embodiments of the present invention.

[0123] Depend on Figure 1 It can be seen that the microstructure of the finished steel plate is uniform fine ferrite + a small amount of low carbon bainite (less than 30%), and the average grain size of the microstructure is less than 20μm. The steel plate has high strength, high toughness, and high crack arrest properties, and the steel plate has excellent weldability, especially it can be welded with large heat input.

[0124] In summary, the application obtains high strength, excellent low temperature toughness and high crack arrest characteristics of the super-thick base steel plate, and the low temperature toughness of the fusion line and HAZ is also excellent when large heat input welding is performed; the crack arrest characteristics of the super-thick YP460 grade steel plate are particularly solved, and the steel plate has excellent plastic crack instability expansion capacity, which ensures the safety and reliability of large steel structures, especially ocean structures (large capacity offshore wind pile leg structures, ocean platforms, large floating cranes, icebreakers, etc.), bridge engineering structures, energy development engineering, wind power engineering and engineering machinery, mining machinery and heavy vehicle manufacturing, and can realize low-cost stable batch industrialized production.

[0125] With the development of the national economy of China, the infrastructure construction (such as large cross-sea highway and railway bridge engineering), large ship manufacturing (such as VLCC), ocean development, large power ocean wind power engineering and major equipment manufacturing have been put on the agenda, and the super-thick EH40 / EH47 for large capacity offshore power projects in the southeast of China, 60-140mm super-thick S420+G2-Z35, S420ML-Z35, S460ML-Z35 for European and Middle East offshore wind power engineering are YP460MPa grade high crack arrest characteristic steel plates. At present, the infrastructure construction, ocean engineering development and major equipment manufacturing in China are in the ascendant; the key material of the infrastructure construction, ocean engineering development and related equipment manufacturing industry, the YP460 grade super-thick steel plate with high toughness, high crack arrest characteristics and excellent weldability has broad market prospects.

[0126]

[0127]

[0128]

Claims

1. A high crack-arrest, easy-to-weld ultra-thick YP460 grade steel plate, having the following composition in weight percent: C：0.030～0.060％ Si: ≤ 0.15% Mn: 1.55-1.90% P：≤0.015％ S：≤0.003％ Cu: 0.15-0.40% Ni: 0.15-0.50% Cr：0.05～0.30％ Nb: 0.025-0.050% Ti: 0.008-0.016% Als: 0.025-0.060% N：≤0.0050％ Ca: 0.0010-0.0040% the balance being Fe and other unavoidable inclusions, and must simultaneously satisfy the following relationships: welding cold crack sensitivity index Pcm ≤ 0.20%; Pcm = (%C) + (%Si) / 30 + [(%Mn) + (%Cu) + (%Cr)] / 20 + (%Ni) / 60 + (%Mo) / 15 + (%V) / 10 + 5(%B); Als / (N-0.292Ti) ≥ 32; BCC crystal structure dislocation low temperature mobility index θ ≥ 0.51, θ = 1.25 (% Ni) + [1.57 (% Mn) - 0.69 (% Mn) + 1.69 (% Cu) 2 + 0.69 (% Mn) + 1.69 (% Cu) -3.51(%Si) - 0.46[(%Cr) + (%Mo)] - 2.43[(%Al) + (%Nb) + (%Ti)]; The Ca / S ratio is controlled to be 1 to 3, and (%Ca) x (%S) < 1.5 x 10 -3 ; the steel plate microstructure of the steel plate is uniform fine ferrite + a small amount of low carbon bainite, with an average grain size of less than 20 μm; The steel sheet has a yield strength of ≥ 460 MPa, a tensile strength of ≥ 590 MPa, and a yield ratio of ≤ 0.83; an impact energy KV2 of ≥ 100 J at -40°C and Kca of ≥ 6000 N / mm at -10°C 3 / 2 ; a CTOD of ≥ 0.35 mm at -10°C; excellent weldability, no preheating before welding, a weld heat input of ≥ 50 kJ / cm, and an impact energy KV2 of ≥ 60 J at -40°C in the heat affected zone.

2. The method of producing a high-rupture-resistance, easy-to-weld super-thick YP460-grade steel sheet according to claim 1, characterized by, comprising the following steps: 1) smelting and casting smelting and casting into a slab according to the composition of claim 1; 2) slab heating, with the temperature controlled at 1080-1150°C; 3) controlled rolling the first stage is ordinary rolling, using the maximum rolling capacity of the rolling mill for continuous rolling; the second stage uses non-recrystallization controlled rolling, with the rolling temperature controlled at 720-760°C, the rolling pass reduction rate ≥ 7%, the cumulative reduction rate ≥ 45%, and the finish rolling temperature 710-750°C; in addition to meeting the above requirements, the following relationship must also be satisfied: [(%Nb) x Au x ξ] / [H x (%Cr) x (T 终轧 )] ≥ 4.47 x 10 -4 wherein: Au is the austenite stabilisation index, Au = 2.54 + 40.53[(%C) + (%N)] + 0.43[(%Cu) + (%Ni) + (%Mn)] - 0.22(%Al) - 2.64[(%P) + (%S)] - 1.26[(%Cr) + (%Mo)] - (%Si), unit %; ξ is the non-recrystallization / critical zone controlled rolling cumulative reduction rate, unit %; H is the finished steel plate thickness, unit mm; T 终轧 final rolling temperature for non-recrystallization / critical region controlled rolling, unit: °C; 4) controlled cooling after the controlled rolling is completed, the steel plate is immediately transported to the accelerated cooling equipment, and then the steel plate is subjected to accelerated cooling, with the cooling start temperature 700-740°C, the cooling rate ≥ 3°C / s, and the stop cooling temperature 300-450°C; when the steel plate thickness is ≥ 80 mm, the steel plate is subjected to slow cooling, with the slow cooling process being holding at no less than 300°C for 24 hours or more, and then the steel plate is naturally air cooled to room temperature; in addition to meeting the above requirements, the following relationship must also be satisfied: [Pcm x (T 开冷 ) x (V c )] / [(T 停冷 ) x H] ≥ 9.45 x 10 -3 ; wherein Pcm is the welding crack sensitivity index, Pcm = (%C) + (%Si) / 30 + [(%Mn) + (%Cu) + (%Cr)] / 20 + (%Ni) / 60 + (%Mo) / 15 + (%V) / 10 + 5(%B), unit %; T 开冷 temperature for the start of accelerated cooling, in °C; T 停冷 temperature for the acceleration of cooling, unit: °C; V c to accelerate the cooling rate of the steel sheet, in °C / s; H is the finished steel plate thickness, unit mm.

3. The method of producing a high-riεt-tert, easily-weldable, extra-thick YP460 grade steel sheet according to claim 2, characterized by, Step 1) The slab is produced by continuous casting. The superheat of the tundish is controlled at 8-28℃, the casting speed is controlled at 0.6-1.0m / min, and the liquid level fluctuation in the crystallizer is controlled at ≤5mm.

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