High-crack-arrest easy-to-weld super-thick YP460-grade steel plate and manufacturing method thereof

Abstract

The invention discloses a high-crack-arrest easy-to-weld super-thick YP460-grade steel plate and a manufacturing method thereof, the high-crack-arrest easy-to-weld super-thick YP460-grade steel plate comprises the following components in percentage by weight: 0.030-0.060% of C, less than or equal to 0.15% of Si, 1.55-1.90% of Mn, less than or equal to 0.015% of P, less than or equal to 0.003% of S, 0.15-0.40% of Cu, 0.15-0.50% of Ni, 0.05-0.30% of Cr, 0.025-0.050% of Nb, 0.008-0.016% of Ti, 0.025-0.060% of Als, less than or equal to 0.0050% of N, 0.0010-0.0040% of Ca and the balance of Fe and inevitable inclusions, and Als / (N-0. 292 Ti) is greater than or equal to 32; the BCC crystal structure dislocation low-temperature mobility index theta is larger than or equal to 0.51, the Ca / S ratio is controlled to be 1-3, and (% Ca) * (% S) is smaller than or equal to 1.5 * 10 <-3 >. According to the method, the high strength, excellent low-temperature toughness and high crack arrest characteristic of the ultra-thick base metal steel plate are obtained, and meanwhile, the low-temperature toughness of a fusion line and the low-temperature toughness of HAZ are also excellent during large heat input welding; and the device is particularly suitable for high-power offshore wind power pile legs, ocean platforms, cross-sea bridge steel tower structures, engineering machinery and the like.

Description

Technical Field

[0001] The invention relates to the technical field of high-strength steel, and in particular to an ultra-thick YP460 grade steel plate with high crack arrestability and easy welding, and a manufacturing method thereof. Background Art

[0002] As we all know, 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 projects, bridge structures, boiler containers, 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, among which strength, toughness, plasticity, weldability and the matching between them are the most important properties of low-carbon (high-strength) low-alloy steel, which is 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 on the toughness, plasticity, especially weldability and low anisotropy of performance of high-strength steel, that is, the steel plate has the ability to resist brittle fracture and plastic instability fracture at low temperature (-40℃), while the elongation at fracture and uniform elongation reach the level of 500MPa grade steel plate, and the steel plate has excellent weldability and low anisotropy of performance, which can be To withstand large heat input welding (can withstand welding heat input ≥100kJ / cm); and under relatively low alloy content, especially precious metal content, and low manufacturing cost conditions, greatly improve the comprehensive mechanical properties and performance of the steel plate, reduce the alloy content of steel and save costs, high strength and lightweight reduce the weight, stability and safety of the steel components themselves, and more importantly, further improve the cold / hot workability of steel components and safety and reliability during service; Currently, Japan, South Korea, the European Union and North America have set off a research climax on the development of a new generation of high-performance steel materials, and strive to obtain better microstructure matching through alloy combination optimization design, control of submicrostructure fine structure and innovative manufacturing process technology, ultra-fine metallographic microstructure and substructure (dislocation substructure configuration, packet, block, etc.) fine structure, so that high-strength steel can obtain better strength-plasticity and plastic-toughness matching, weldability and low anisotropy.

[0003] In the prior art, when manufacturing thick steel plates with a yield strength of ≥420 MPa and a low-temperature impact toughness of ≥34 J at -60°C, a certain amount of Ni or Cu+Ni elements (≥0.30%) is generally added to the steel. (The Firth(1986)internationalSymposium 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 Bulletin", 1985, No. 1 68~72; "Application of Accelerated Cooling For Producing 360MPa Yield Strength Steel plates of up to150mm in Thickness with Low Carbon Equivalent", Accelerated Cooling RolledSteel, 1986, 209~219; "High Strength Steel Plates For Ice-Breaking VesselsProduced by Thermo-Mechanical Control Process”, Accelerated Cooling RolledSteel, 1986, 249~260; "420MPa Yield Strength Steel Plate with Superior FractureToughness for Arctic Offshore Structures", "Kawasaki steel technical report", 1999, No. 40, 56; "420MPa and 500MPa Yield Strength Steel Plate with High HAZtoughness Produced by TMCP for Offshore Structure", "Kawasaki steel technicalreport》, 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 Areas" (Japanese), "Steel Research", 1984, No. 314, 19-43), to ensure that the base steel plate has excellent low-temperature toughness. When welding with a heat input of <50KJ / cm, the toughness of the heat affected zone (HAZ) can also reach -60℃Akv≥34J; however, when welding with ultra-large heat input (≥100KJ / 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) is seriously deteriorated. A large number of patent documents only explain how to achieve low-temperature toughness of the base steel plate, but there are few descriptions 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 ultra-large heat input welding is used. 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 ultra-large heat input welding is rarely able to reach -60℃. (See Japanese Patents Sho 63-93845, Sho 63-79921, Sho 60-258410, Te Ping Kai 4-285119, Te Ping Kai 4-308035, Ping 3-264614, Ping 2-250917, Ping 4-143246, US Patent 4855106, US Patent 5183198, US Patent 4137104). .

[0004] At present, only Japan's Nippon Steel Corporation has improved the low-temperature toughness of the heat-affected zone (HAZ) of ultra-high heat input welded steel plates by using oxide metallurgy technology (see US Patent 4629505, WO 01 / 59167A1), that is, during high heat input welding, near the fusion line, due to long-term high temperature, TiN particles dissolve and lose their function, while Ti2O3 is more stable than TiN and will not dissolve even when the melting point of steel is reached. Ti2O3 particles can become the nucleation site of acicular ferrite in austenite crystals, promote the nucleation of acicular ferrite (AF) in austenite crystals, effectively divide austenite grains, refine HAZ structure, and form high-strength and high-toughness acicular ferrite structure.

[0005] Baosteel has developed a series of products that can weld various low-temperature steel plates with high heat input (such as Chinese patents ZL201410300713.X, ZL201310244712.3, ZL201310244706.8, ZL201310124065.2, ZL201310244713.8, ZL201210209637.2, ZL201410815614.5 and Chinese patent application No. 201710183350.X, 201910149978.7). For the low-temperature toughness of the heat affected zone in high heat input welding, a certain amount of precious alloy elements Cu and Ni are added to the steel plates (especially ultra-thick steel plates). When the yield strength YP reaches 460MPa, it is especially necessary to add a small amount of Mo. Although the processability of the steel plate with high heat input welding is good, the toughness of the heat affected zone, especially the low-temperature toughness of the heat affected zone of the thick steel plate, is not very stable (under high heat input welding conditions, Mo promotes the formation of coarse upper bainite and deteriorates the toughness of the coarse-grained heat affected zone of the welding), and the impact toughness requirement of -40℃ cannot be stably met. The manufacturing cost of thick steel plates is also relatively high.

[0006] Baosteel has applied for patents for steel plate manufacturing (such as Chinese patent application numbers 202110734971.9 and 202211365790.4). The steel plates have excellent strength, toughness, low yield strength ratio (≤0.86), transverse and longitudinal anisotropy (≤30MPa), atmospheric corrosion resistance and weldability, and have been applied in mass engineering projects (Changtai Bridge, Chaoma Bridge, etc.). The weldability and weather resistance are excellent, but the crack arrest characteristic Kca is not involved, the steel plate's ability to resist unstable expansion of plastic cracks is insufficient, and the thickness of the steel plates used in bridge engineering projects is all below 80mm. Summary of the invention

[0007] The object of the present invention is to provide a high crack arrest, easy-to-weld ultra-thick YP460 grade steel plate and a manufacturing method thereof, which can obtain high strength, excellent low-temperature toughness and high crack arrest characteristics of the ultra-thick base steel plate, and at the same time, the low-temperature toughness of the fusion line and the HAZ during welding with a large heat input is also excellent; the yield strength of the steel plate is ≥460MPa, the tensile strength is ≥590MPa, the impact energy KV2 (single value) at -40°C is ≥100J, and the Kca (-10°C) is ≥6000N / mm 3 / 2 ; Excellent weldability, no preheating before welding, can withstand welding heat input ≥50kJ / cm, heat affected zone -40℃ impact energy KV2 (single value) ≥60J; particularly suitable for high-power offshore wind power pile legs, offshore platforms, cross-sea bridge steel tower structures, hydropower metal structural components, port machinery and engineering machinery, etc., and can achieve low-cost and stable mass industrial production.

[0008] Ultra-thick steel plates with high toughness and high crack arrest are one of the most difficult types of thick plate products. The reason is that this type of steel plate not only requires ultra-low C, low carbon equivalent CEV, high strength, excellent low-temperature toughness and high crack arrest properties, but also the steel plate must be able to withstand large heat input welding (welding heat input ≥ 50KJ / cm), and the steel plate welding fusion line and heat-affected zone have high strength, excellent low-temperature impact toughness and high crack arrest properties. However, 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) between low temperature toughness, high crack arrest and large thickness, low manufacturing cost (low Ni content);

[0011] C) High strength, high crack arrest properties and good weldability, especially weldability with large heat input.

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

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

[0014] To achieve the above object, the technical solution of the present invention is:

[0015] High crack arrest, easy to weld extra 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 includes Fe and other unavoidable inclusions and must satisfy the following relationship at the same time:

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

[0031] Pcm=(%C)+(%Si) / 30+[(%Mn)+(%Cu)+(%Cr)] / 20+

[0032] (%Ni) / 60+(%Mo) / 15+(%V) / 10+5(%B);

[0033] Als / (N-0.292Ti)≥32;

[0034] The low-temperature mobility index of dislocations in BCC crystal structure is θ≥0.51.

[0035] θ=1.25(%Ni)+[1.57(%Mn)-0.69(%Mn) 2 ]+1.69(%Cu)

[0036] -3.51(%Si)-0.46[(%Cr)+(%Mo)]-2.43[(%Al)+(%Nb)+

[0037] (%Ti)];

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

[0039] Furthermore, the balance is Fe and other inevitable inclusions.

[0040] The microstructure of the steel plate of the present invention is uniform fine ferrite + a small amount of low-carbon bainite, and the average grain size is less than 20 μm.

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

[0042] In the composition design of the steel plate of the present invention:

[0043] C has a great influence on the strength, low-temperature toughness, crack arrest characteristics, elongation and weldability of TMCP ultra-thick steel plates, especially the high heat input weldability. From the perspective of improving the low-temperature toughness and high heat input weldability of ultra-thick steel plates, it is hoped that the C content in the steel can be controlled relatively low; however, from the perspective of the strength of ultra-thick steel plates and the microstructure control and manufacturing cost during the production process, the C content should not be controlled too low; too low C content can easily lead to excessively high grain boundary mobility, coarse grains in the microstructure of the parent steel plate and the welded HAZ, and easy generation of mixed crystals, and too low C content in the steel can cause grain boundary weakening, seriously deteriorating the crack arrest characteristics of the parent 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 steel plates. However, for molten steel deoxidized by Al, the deoxidation effect of Si is not significant. Although Si can improve the strength of steel plates, Si seriously damages the low-temperature toughness, crack arrest properties, elongation and weldability of weathering steel plates. Especially for high-strength and ultra-thick steel plates with high alloy content, when welding with large heat input, Si not only promotes the formation of MA islands, but also makes the formed MA islands relatively large in size and unevenly distributed, which seriously damages the low-temperature toughness and crack arrest properties of the heat affected zone (HAZ) of the steel plate. Therefore, the Si content in steel should be controlled as low as possible. Considering that Si has a certain weathering effect and the economy and operability of the steelmaking process, the Si content is controlled below 0.15%.

[0045] As the most important alloying element in steel, Mn not only improves the strength of the steel plate, but also has the functions of expanding the austenite phase region, lowering 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 and crack arrest characteristics of the steel plate (fine grain toughening), and 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, which not only makes the casting operation difficult, but also Mn is prone to conjugate segregation with elements such as C, P, and S. Especially when the C content in the steel is high, the segregation and looseness in the center of the ingot are aggravated. Severe segregation in the center of the ingot is prone to form abnormal tissue during the subsequent TMCP and welding process, resulting in low low-temperature toughness of the steel plate and cracks in the welded joints. In addition, for high-strength TMCP ultra-thick steel plates, when the Mn content is too high, not only the low-temperature toughness, crack arrest characteristics, and elongation of the steel plate deteriorate sharply, but also the weldability of the steel plate, especially the weldability with large heat input, is seriously deteriorated; in addition, when the Mn content is too high, the low-temperature mobility of ferrite dislocations is reduced, resulting in deterioration of the intrinsic toughness and crack arrest of the steel plate; therefore, the suitable Mn content is 1.55-1.90%.

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

[0047] As a harmful inclusion in steel, S has a great damaging effect on the low-temperature toughness, crack arrest characteristics and weldability of the steel plate. More importantly, S combines with Mn in the steel to form MnS inclusions. During the hot rolling process, the plasticity of MnS causes MnS to extend along the rolling direction to form a MnS inclusion belt along the rolling direction, which not only seriously damages the low-temperature impact toughness, crack arrest characteristics, elongation, Z-direction performance, fatigue resistance and other properties of the steel plate, but also causes the weldability of the steel plate (especially the weldability with large heat input) to be seriously deteriorated; at the same time, S is also the main element that produces hot brittleness during hot rolling, and theoretically the lower the better; but considering the operability of steelmaking, the cost of steelmaking and the principle of smooth logistics, for TMCP ultra-thick steel plates that require large heat input welding, high toughness (toughness at -40°C), high crack arrest characteristics (Kca at -10°C), 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 an element that improves 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 plates, and improve the low-temperature toughness and crack arrest properties of TMCP steel plates. However, if Cu is added too much, higher than 0.40%, it will not only easily cause copper brittleness, surface cracking of the ingot, internal cracking problems, and especially the impact load fracture characteristics (i.e., crack arrest characteristics) of thick steel plates; it will also cause serious deterioration of the low-temperature toughness and crack arrest characteristics of welded joints. At the same time, considering that Cu is a relatively precious alloying element, from a cost-effectiveness perspective, it is appropriate to control the upper limit of Cu to 0.40%. If Cu is added too little, lower than 0.15%, the above effects are small; therefore, the Cu content is controlled between 0.15 and 0.40%.

[0049] Adding Ni can not only reduce the friction force of the dislocation lattice of the BCC crystal structure (i.e., PN force), improve the low-temperature mobility of ferrite dislocations, promote dislocation cross-slip, and improve the intrinsic plasticity and toughness of ferrite; in addition, Ni, as a strong austenite stabilizing element, greatly reduces the Ar1 and Ar3 point temperatures, increases the driving force for the phase transformation of austenite to ferrite, causes the austenite to undergo phase transformation at a lower temperature, greatly refines the microstructure of the TMCP steel plate, increases the crack propagation resistance through the ferrite grains, and greatly improves 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 to steel can also reduce the copper embrittlement phenomenon of copper-containing steel, reduce intergranular cracking during hot rolling, and improve the atmospheric corrosion resistance of the steel plate. Therefore, theoretically, the higher the Ni content in steel is within a certain range, the better. However, too high Ni content will not only harden the welding heat affected zone, which is detrimental to the weldability of the steel plate and the low-temperature toughness of the welded joint with large heat input, but also greatly increase the manufacturing cost of the steel plate (Ni is a precious alloy element); therefore, the Ni content is 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 thick steel plates without damaging the low-temperature toughness, bending cold working and large input welding of the steel plates; but if the Cr content is too little (<0.05%), Cr contributes little to the strength of the steel plates and fails to meet the requirements of performance indicators; if too much is added (>0.30%), the low-temperature toughness, crack arrest properties, and bending cold working properties of the steel plates are damaged, especially the weldability of the steel plates, especially the large heat input weldability, and the low-temperature toughness and crack arrest properties of the welding heat affected zone are seriously deteriorated (coarse feather-like upper bainite structure is formed in the welding heat affected zone); therefore, the Cr content is controlled between 0.05 and 0.30%.

[0051] The purpose of adding trace amounts of Nb elements to steel is to carry out non-recrystallization controlled rolling, refine the grain size of the steel plate, and improve the strength and toughness of the TMCP steel plate; for ultra-thick steel plates, when the C content in the steel is low (≤0.060%), when the Nb addition is less than 0.025%, in addition to the inability to effectively play the role of controlled rolling, it is also unfavorable for the strengthening and toughening matching and crack arrest characteristics of the TMCP ultra-thick steel plate; when the Nb addition exceeds 0.050%, it not only causes the low-temperature toughness and crack arrest characteristics of the steel plate to deteriorate (too high Nb content is prone to mixed crystals) and the steel The alloy cost of the plate (Nb is also a precious alloy element) remains high; and under large heat input welding conditions, the formation of upper bainite (Bu) and the secondary precipitation embrittlement of Nb (C, N) are induced, which seriously damages the low-temperature toughness and crack arrest properties of the heat affected zone (HAZ) of the ultra-thick steel plate with large heat input. Therefore, the Nb content is controlled between 0.025 and 0.050% to obtain the best controlled rolling effect, achieve the toughness / plasticity matching of the TMCP ultra-thick steel plate, and high crack arrest properties, without damaging the high heat input weldability of the ultra-thick steel plate.

[0052] The purpose of adding a trace amount of Ti to steel is to combine with N in steel to generate highly stable TiN particles to inhibit the growth of steel plate grains and grains in the welding HAZ area; the Ti content added to the steel must match the N content in the steel, and the matching principle is that TiN cannot precipitate in liquid molten steel but must precipitate in the solid phase; therefore, the precipitation temperature of TiN must be ensured to be lower than 1400°C; when the amount of Ti added to the steel is too small (<0.008%), the number of TiN particles formed is insufficient to inhibit the growth of austenite grains during TMCP and welding thermal cycles and improve the low-temperature toughness and weldability of ultra-thick steel plates; when too much Ti is added (>0.016%), the TiN precipitation temperature exceeds 1400°C, and some TiN particles precipitate large-sized TiN particles during the solidification of the molten steel. Such large-sized TiN particles not only cannot inhibit grain growth, but instead become the starting point for crack initiation; therefore, the optimal control range of Ti content is 0.008-0.016%.

[0053] Als in steel plates can fix the free [N] in steel, reduce the free [N] in the welding heat affected zone (HAZ), and improve the low-temperature impact toughness and crack arrest characteristics of HAZ with large heat input welding; but adding excessive Als to steel will not only form a large number of dispersed needle-shaped Al2O3 inclusions in the steel, but also damage the low-temperature impact toughness and weldability of the steel plate. According to the analysis of the composition system of ultra-thick steel plates, the optimal Als content is controlled between 0.025 and 0.060%.

[0054] The control range of N corresponds to the control range of Ti, which is important for controlling the grain of steel plates, improving the low-temperature toughness, crack arrest characteristics and weldability of steel plates; if the N content is too low, the number of TiN particles generated is small and the size is large, which cannot play the role of controlling the grain of steel plates and improving the low-temperature toughness and weldability of steel plates, but is harmful to the low-temperature toughness and weldability of steel plates; however, when the N content 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 characteristics and bending cold workability of HAZ, and deteriorates the processing and use characteristics of steel. Therefore, the N content is controlled at ≤0.0050%.

[0055] Ca treatment of steel can, on the one hand, further purify the molten steel, and on the other hand, denature the sulfides in the steel, turning them into non-deformable, stable and fine spherical sulfides, inhibiting the hot brittleness of S, improving the low-temperature toughness, crack arrest characteristics, elongation and Z-direction properties of ultra-thick steel plates, and improving the weldability of steel plates. In addition, Ca treatment is used to improve the pourability of high-acid-soluble aluminum molten steel; more importantly, Ca (O, S) particles cannot condense and grow in liquid molten steel or solid steel, and are distributed in the steel in a fine and dispersed state. Such high-melting-point Ca (O, S) particles pin the growth of austenite grains in the heat-affected zone during welding with large heat input, refine the grains in the welding heat-affected zone, and greatly improve the low-temperature plastic toughness of the heat-affected zone with large heat input. The amount of Ca added depends on the S content in the steel. If the amount of Ca added is too low, the treatment effect is not great; if the amount of Ca added is too high, the size of Ca(O,S) will be too large, and the brittleness will also increase, which can become the starting point of the fracture crack, reducing the low-temperature toughness, crack arrest characteristics, elongation of the steel and the large heat input weldability of the steel plate, while also reducing the purity of the steel and polluting the molten steel. Generally, the Ca content is controlled according to ESSP = (%Ca) [1-1.25 (%O)] / 1.25 (%S), where ESSP is the sulfide inclusion shape control index, and the value range is preferably between 1.00 and 3.00, so the appropriate range of Ca content is 0.0010 ~ 0.0040%.

[0056] In particular, the contents of the above elements in the present invention must simultaneously satisfy the following relationship:

[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 is %.

[0058] It ensures that under the conditions of ultra-low carbon and low Pcm, the steel plate not only has excellent weldability; more importantly, ultra-thick steel plates can be welded with large heat input under high Nb content conditions (0.025-0.050%); the welding heat affected zone not only forms non-embrittled ultra-low carbon bainite and low M / A island content, but also the secondary precipitation embrittlement degree of Nb (C, N) is small during the multi-layer and multi-pass welding process; the low-temperature toughness and crack arrest characteristics of the ultra-thick steel plate welding heat affected zone are guaranteed.

[0059] Als / (N-0.292Ti)≥32, ensuring that during the multi-layer and multi-pass welding process with large heat input of ultra-thick steel plates, all the solid solution [N] forms fine dispersed AlN, eliminating the strong embrittlement effect of the solid solution [N] on the heat affected zone of the welding, and improving the low-temperature toughness and crack arrest characteristics of the heat affected zone of the ultra-thick steel plate welding.

[0060] The low-temperature mobility index of dislocations in BCC crystal structure is 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, the lattice friction force (i.e., PN force) of dislocation slip in the BCC crystal structure is reduced, dislocation cross slip is promoted, the low-temperature mobility of dislocation in the BCC crystal structure is improved, the plastic deformation field at the crack tip is expanded, the plastic deformation work (i.e., the value-added and slip velocity of the FR source dislocation at the crack tip) is increased, the intrinsic plastic toughness of the BCC crystal structure is increased, and the crack arrest characteristics of the steel plate are improved. This is one of the key core technologies of the present invention.

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

[0065] While ensuring sulfide spheroidization and minimizing the effect of Ca(O,S) particles on low-temperature toughness, Ca(O,S) particles are evenly and finely distributed in the steel, inhibiting the growth of austenite grains in the heat-affected zone of large heat input welding, improving the low-temperature toughness and crack arrest characteristics of the heat-affected zone of large heat input welding of the steel plate, and improving the Z-direction performance of ultra-thick steel plates.

[0066] The method for manufacturing the high crack arrest, easy-to-weld ultra-thick YP460 grade steel plate of the present invention comprises the following steps:

[0067] 1) Smelting and casting

[0068] Smelting and casting into slabs according to the above ingredients;

[0069] 2) Slab heating, the temperature is controlled at 1080~1150℃;

[0070] 3) Controlled rolling

[0071] The first stage is ordinary rolling, which uses the maximum rolling capacity of the rolling mill for continuous rolling;

[0072] The second stage adopts non-recrystallization controlled rolling, the start rolling temperature is controlled at 720-760℃, the rolling pass reduction rate is ≥7%, the cumulative reduction rate is ≥45%, and the final rolling temperature is 710-750℃; In addition to meeting the above requirements, the following relationship must also be met:

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

[0074] Where: 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 cumulative reduction rate of controlled rolling in the non-recrystallization / critical region, unit: %;

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

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

[0081] 4) Controlled cooling

[0082] After controlled rolling, the steel plate is immediately transported to the accelerated cooling equipment, and then the steel plate is accelerated cooled, the start cooling temperature is 700 ~ 740 ℃, the cooling rate is ≥ 3 ℃ / s, and the stop cooling temperature is 300 ~ 450 ℃; when the thickness of the steel plate is ≥ 80mm, the steel plate is slowly cooled, 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;

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

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

[0085] Among them, Pcm is the welding crack sensitivity index,

[0086] Pcm=(%C)+(%Si) / 30+[(%Mn)+(%Cu)+(%Cr)] / 20+

[0087] (%Ni) / 60+(%Mo) / 15+(%V) / 10+5(%B), unit is %;

[0088] T 开冷 is the starting 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, in step 1), the slab is produced by continuous casting, the tundish pouring superheat is controlled at 8°C to 28°C, the pulling speed is controlled at 0.6m / min to 1.0m / min, and the crystallizer liquid level fluctuation is controlled at ≤5mm.

[0093] In the manufacturing method of the present invention:

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

[0095] According to the above-mentioned C, Mn, Nb and Ti content range, the slab heating temperature is controlled between 1080 and 1150°C to ensure that all Nb in the steel is dissolved into the austenite during the slab heating process and that the austenite grains of the slab do not grow abnormally.

[0096] Controlled rolling:

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

[0098] The second stage adopts non-recrystallization controlled rolling. According to the Nb element content range and texture strengthening and toughening requirements in the above-mentioned steel, in order to ensure the effects of non-recrystallization controlled rolling and critical zone controlled rolling, the controlled rolling start temperature is controlled at 720-760°C, the rolling pass reduction rate is ≥7%, the cumulative reduction rate is ≥45%, and the final rolling temperature is 710-750°C.

[0099] 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; the steel plate starting cooling temperature and the final rolling temperature are 700-740℃, the cooling rate is ≥3℃ / s, and the stopping cooling temperature is 300-450℃. When the steel plate thickness is ≥80mm, the steel plate is slowly cooled. 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 addition to meeting the above requirements, the following relationships must also be met:

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

[0102] Where 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 cumulative reduction rate of non-recrystallization / critical zone controlled rolling, unit %; H is the thickness of the finished steel plate, unit mm; T 终轧 It is the final rolling temperature of non-recrystallization / critical zone controlled rolling, unit is ℃.

[0104] From formula (1), we can see that:

[0105] As the niobium content (%Nb) increases, the controlled rolling effect increases, the austenite recrystallization is inhibited to a greater extent, the austenite flattening effect is enhanced, and the dislocation density and deformation band density inside the austenite grains increase;

[0106] Secondly, with the increase of the cumulative reduction rate ξ of the non-recrystallization / critical zone controlled rolling, the dislocation density and deformation band density inside the flat austenite grains also increase significantly, resulting in an increase in the position of the ferrite phase deformation nucleus and an increase in the driving force for the austenite to ferrite phase transformation. During the accelerated cooling of the thick, Cr-containing steel plate, the coarse feathery bainite structure and the side lath Widmanstatten transformation structure are suppressed, and the fine equiaxed ferrite structure and lath bainite structure increase. In addition, with the increase of the cumulative reduction rate ξ of the recrystallization / critical zone controlled rolling, the deformation texture (100) <011> Enhanced, the texture strengthening and toughening effect is enhanced;

[0107] Third, as the austenite stabilization index Au increases, the anisotropy of the electron cloud of the outer dsp hybrid orbit of the alloy atoms decreases, the covalent bond characteristics weaken and the metallic bond characteristics enhance, the low-temperature mobility of the BCC dislocation increases, and the intrinsic plastic toughness of the steel plate is improved. At the same time, the Ar3 point temperature decreases, and the grain structure of the ultra-thick steel plate is refined.

[0108] The above results are superimposed on each other, ensuring that the ultra-thick steel plate has excellent low-temperature toughness and crack arrest properties. As the thickness H of the steel plate and the final rolling temperature increase, the controlled rolling effect weakens, the austenite flattening effect deteriorates, the dislocation density / deformation band density inside the austenite grains is low, the nucleation sites are few, the austenite stability increases, and the superimposed smaller cooling rate (due to the plate thickness) and the presence of Cr alloys promote the development of coarse feather-like upper bainite structure and side plate strip Widmanstatten structure, which deteriorates the low-temperature toughness and crack arrest properties of the ultra-thick steel plate; In summary, when all indicators meet the above formulas, it is ensured that the ultra-thick steel plate has excellent low-temperature toughness and crack arrest properties. This is one of the key core technologies of the present invention.

[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 T is the starting temperature of accelerated cooling, in °C; 停冷 is the stop temperature of accelerated cooling, unit: °C; V c is the accelerated cooling rate of the steel plate, in °C / s; H is the thickness of the finished steel plate, in mm.

[0111] From formula (2), it can be seen that as the welding crack sensitivity index Pcm increases and the cooling temperature T 开冷As the temperature rises and the cooling rate increases, the content of low-temperature phase transformation structure (such as bainite, especially lower bainite) of the steel plate increases, and the strength of the steel plate increases; and as the cooling temperature increases and the thickness of the steel plate increases (the effect is that the cooling rate is low, especially the cooling rate in the center of the ultra-thick steel plate is extremely low), the content of low-temperature phase transformation structure (such as bainite, especially lower bainite) of the steel plate is lower, and the strength of the steel plate is lower; in summary, when all indicators meet the above formula, it is ensured that the ultra-thick steel plate has high strength, high toughness, and high crack arrest characteristics, while the steel plate has excellent weldability with large heat input, and successfully eliminates the contradiction between low C, low carbon equivalent (Pcm) of the ultra-thick steel plate and high strength, high toughness, high crack arrest characteristics and excellent weldability, which are mutually opposed and difficult to be compatible. This is one of the key core technologies of the present invention.

[0112] The composition data in the above relationship is calculated as a percentage. For example, if the carbon content is 0.10%, just substitute 0.10 when calculating the relationship.

[0113] Beneficial effects of the present invention:

[0114] The present invention adopts ultra-low carbon C-low Si-high Mn low alloy steel as the basis, Pcm≤0.20%, low N content and Als / (N-0.292Ti)≥32, (Cu+Ni+Cr) alloying, BCC crystal structure dislocation low temperature mobility index θ≥0.51, Ti+Nb microalloying, Ca treatment and Ca / S ratio controlled between 1.00 and 3.00 and (%Ca)×(%S)≤1.5×10 -3 Alloy optimization combination design, matching 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 fine ferrite + a small amount of low-carbon bainite, and the average grain size of the microstructure is below 20μm.

[0115] The steel plate of the present invention reduces the content of precious alloy elements (Ni elements), matches the combination design between the main alloy elements, micro-alloy elements and inclusion elements, and combines it with the new generation TMCP manufacturing process to produce TMCP type ultra-thick crack-arresting steel plates with excellent comprehensive performance at low cost. The ultra-thick crack-arresting steel plates not only have high strength, high toughness and high crack-arresting properties, but also have excellent weldability, especially large heat input welding, which greatly shortens the manufacturing cycle of steel structures, creates huge value for construction companies, and realizes low-carbon, green and environmentally friendly steel plate manufacturing and use processes.

[0116] The high performance and high added value of the steel plate of the present invention are mainly reflected in the large thickness (≥80mm), high strength, high toughness, high crack arrest characteristics and excellent weldability of the steel plate, especially the perfect match of large heat input weldability, which successfully solves the following problems:

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

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

[0119] C) The conflict between high strength, high crack arrest characteristics and excellent weldability, especially weldability with large heat input, in composition design and TMCP process design is difficult to reconcile, which greatly improves the safety, stability and durability of large heavy steel structures; good weldability (especially welding with large heat input) saves the cost of steel structure manufacturing for user companies and shortens the time of steel structure manufacturing for users, which not only creates huge value for users, but more importantly reduces carbon emissions (no preheating before welding, no heat treatment after welding, ultra-large heat input and high-efficiency welding), so this type of steel plate is not only a high value-added, full-life green and environmentally friendly product. BRIEF DESCRIPTION OF THE DRAWINGS

[0120] Figure 1 This is a photo of the microstructure (1 / 4 thickness) of the steel of Example 5 of the present invention at 500 times magnification. DETAILED DESCRIPTION

[0121] The present invention will be further described below in conjunction with the embodiments and drawings.

[0122] The composition of the embodiment of the present invention is shown in Table 1, and the balance is Fe and unavoidable impurities. Tables 2 and 3 are the manufacturing process parameters of the embodiment of the present invention. Table 4 is the performance parameters of the embodiment 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 large heat input welding.

[0124] In summary, the present invention not only obtains high strength, excellent low-temperature toughness and high crack arrest properties of ultra-thick base steel plates, but also has excellent low-temperature toughness of the fusion line and HAZ during welding with large heat input; it particularly solves the problem of crack resistance and crack arrest properties of ultra-thick YP460 grade steel plates, and especially the steel plates have excellent resistance to unstable plastic crack expansion, ensuring the safety and reliability of large-scale steel structures, especially marine structures (large-capacity offshore wind power pile leg structures, offshore platforms, large floating cranes, icebreakers, etc.), bridge engineering structures, energy development projects, wind power projects and engineering machinery, mining machinery and heavy vehicle manufacturing, and can achieve low-cost stable mass industrial production.

[0125] With the development of my country's national economy, infrastructure construction (such as large-scale cross-sea highway and railway bridge projects), large-scale shipbuilding (such as VLCC), marine development, high-power offshore wind power projects and major equipment manufacturing have been put on the daily agenda. The world-renowned large-capacity offshore power projects in the southeast of my country use ultra-thick EH40 / EH47, and offshore wind power projects in Europe and the Middle East need to use 60-140mm ultra-thick S420+G2-Z35, S420ML-Z35, S460ML-Z35, which is YP460MPa grade high crack arrest steel plate. At present, my country's infrastructure construction, marine engineering development and major equipment manufacturing are in the ascendant; the key materials for infrastructure construction, marine engineering development and related equipment manufacturing industries---YP460 grade ultra-thick steel plates with high toughness, high crack arrest properties and excellent weldability have broad market prospects.

[0126]

[0127]

[0128]

Claims

1. High crack arrest, easy to weld, extra thick YP460 grade steel plate, the weight percentage of its components 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 balance includes Fe and other unavoidable inclusions and must satisfy the following relationship at the same time: 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; The low-temperature mobility index of dislocations in BCC crystal structure is θ≥0.

51. θ=1.25(%Ni)+[1.57(%Mn)-0.69(%Mn) 2 ]+1.69(%Cu) -3.51(%Si)-0.46[(%Cr)+(%Mo)]-2.43[(%Al)+(%Nb)+(%Ti)]; The Ca / S ratio is controlled between 1 and 3, and (%Ca)×(%S)≤1.5×10 -3 .

2. The high crack arrest, easy to weld, ultra-thick YP460 grade steel plate according to claim 1, characterized in that: The balance is Fe and other inevitable inclusions.

3. The high crack arrest, easy to weld ultra-thick YP460 grade steel plate according to claim 1 or 2, characterized in that: The steel plate microstructure is uniform fine ferrite + a small amount of low-carbon bainite, and the average grain size is less than 20 μm.

4. The high crack arrest, easy to weld ultra-thick YP460 grade steel plate according to claim 1, 2 or 3, characterized in that: The yield strength of the steel plate is ≥460MPa, the tensile strength is ≥590MPa, and the yield strength ratio is ≤0.83; the impact energy KV2 (single value) of the -40°C steel plate is ≥100J, and Kca (-10°C) is ≥6000N / mm 3 / 2 ; CTOD (-10℃) ≥ 0.35mm; excellent weldability, no preheating before welding, can withstand welding heat input ≥ 50kJ / cm, the impact energy KV2 (single value) of the heat affected zone at -40℃ ≥ 60J.

5. The method for manufacturing the high crack arrest, easy to weld ultra-thick YP460 grade steel plate according to claim 1, 2, 3 or 4, characterized in that: The steps include: 1) Smelting and casting Smelting and casting into slabs according to the composition of claim 1 or 2; 2) Slab heating, the temperature is controlled at 1080~1150℃; 3) Controlled rolling The first stage is ordinary rolling, which uses the maximum rolling capacity of the rolling mill for continuous rolling; The second stage adopts non-recrystallization controlled rolling, the starting rolling temperature is controlled at 720-760℃, the rolling pass reduction rate is ≥7%, the cumulative reduction rate is ≥45%, and the final rolling temperature is 710-750℃; In addition to the above requirements, the following relationships must also be met: [(%Nb)×Au×ξ] / [H×(%Cr)×(T 终轧 )]≥4.47×10 -4 , where: Au is the austenite stabilization 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 cumulative reduction rate of controlled rolling in the non-recrystallization / critical region, unit: %; H is the thickness of the finished steel plate, in mm; T 终轧 is the final rolling temperature of non-recrystallization / critical region controlled rolling, unit: °C; 4) Controlled cooling After controlled rolling, the steel plate is immediately transported to the accelerated cooling equipment, and then the steel plate is accelerated cooled, the start cooling temperature is 700 ~ 740 ℃, the cooling rate is ≥ 3 ℃ / s, and the stop cooling temperature is 300 ~ 450 ℃; when the thickness of the steel plate is ≥ 80mm, the steel plate is slowly cooled, 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; In addition to meeting the above requirements, the following relationships must also be met: [Pcm×(T 开冷 )×(V c )] / [(T 停冷 )×H]≥9.45×10 -3 ; Among them, Pcm is the welding crack sensitivity index, Pcm=(%C)+(%Si) / 30+[(%Mn)+(%Cu)+(%Cr)] / 20+(%Ni) / 60+(%Mo) / 15+(%V) / 10+5(%B), in %; T 开冷 is the starting temperature of accelerated cooling, in °C; T 停冷 is the stop temperature of accelerated cooling, in °C; V c is the accelerated cooling rate of the steel plate, in °C / s; H is the thickness of the finished steel plate, in mm.

6. The method for manufacturing the high crack arrest, easy to weld ultra-thick YP460 grade steel plate as claimed in claim 5, characterized in that: Step 1) The slab is produced by continuous casting, the tundish pouring superheat is controlled at 8-28°C, the pulling speed is controlled at 0.6-1.0 m / min, and the crystallizer liquid level fluctuation is controlled at ≤5 mm.

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