CN112746158A - YP460MPa thick steel plate with low cost, high crack resistance and high weldability and manufacturing method thereof - Google Patents

YP460MPa thick steel plate with low cost, high crack resistance and high weldability and manufacturing method thereof Download PDF

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CN112746158A
CN112746158A CN201911400865.6A CN201911400865A CN112746158A CN 112746158 A CN112746158 A CN 112746158A CN 201911400865 A CN201911400865 A CN 201911400865A CN 112746158 A CN112746158 A CN 112746158A
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steel plate
low
rolling
cooling
temperature
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刘自成
刘斌
钟武波
胡战
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Baosteel Zhanjiang Iron and Steel Co Ltd
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Baosteel Zhanjiang Iron and Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

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Abstract

A YP460MPa thick steel plate with low cost, high crack resistance and high weldability and a manufacturing method thereof, wherein low C-low Si-medium high Mn-Nb series low alloy steel is used as a base, and Mn/C is controlled to be more than or equal to 17, (% C) x [1+1.72 (% Mn) +6.17 (% P)1/2+11.36(％P)1/2]Not less than 0.52, not less than 20 and not more than 40 of B/N, micro Ti treatment, Ca treatment with Ca/S ratio controlled between 1.0 and 3.0 and (% Ca) × (% S)0.28≤1.0×10‑3(ii) a Optimizing the TMCP Process, i.e. [ T ]Beginning rolling×1.4×(％Ceq)×VCooling rate]/(ξ×TStopping cooling) Not less than 0.105, the microstructure of the finished steel plate is uniform and fine ferrite and bainite distributed in a dispersion way, the average grain size of the microstructure is below 15 mu m, the base steel plate obtains high strength, excellent low-temperature toughness and excellent large heat input weldability, and meanwhile, the steel plate and a welding heat affected zone have excellent low-temperature toughness and crack arrest characteristics, so that the steel plate is particularly suitable for shells of ice breaking ships, ocean platforms, sea-crossing bridges, offshore wind power structures, marine machinery and the like in ice sea areas, and can realize stable batch industrial production with ultralow cost.

Description

YP460MPa thick steel plate with low cost, high crack resistance and high weldability and manufacturing method thereof
Technical Field
The invention relates to a YP460MPa thick steel plate with low cost, high crack resistance and high weldability and a manufacturing method thereof, wherein the plate thickness of the steel plate is more than or equal to 80mm, the yield strength is more than or equal to 460MPa, the tensile strength is more than or equal to 570MPa, the Charpy impact energy (single value) at minus 50 ℃ is more than or equal to 100J, Kca (-20℃), and more than or equal to 6000N/mm3/2And can realize large heat input welding and low-cost manufacturing.
Background
As is well known, low-carbon (high-strength) low-alloy steel is one of the most important engineering structural materials, and is widely used in petroleum and gas pipelines, offshore platforms, ship manufacturing, bridge structures, boiler pressure vessels, building structures, automobile industry, railway transportation and machinery manufacturing. The properties of low carbon (high strength) low alloy steel depend on its chemical composition, the process regime of the manufacturing process, where strength, toughness and weldability are the most important properties of low carbon (high strength) low alloy steel, which ultimately depend on the microstructure state of the finished steel. With the continuous forward development of science and technology, people put forward higher requirements on the toughness and weldability of steel, namely, the comprehensive mechanical property and the service performance of the steel plate are greatly improved while the lower manufacturing cost is maintained, so that the consumption of steel is reduced, the cost is saved, and the self weight, the stability and the safety of steel components are reduced. At present, the research surge of developing a new generation of high-performance steel materials is raised in the world, and better microstructure matching is obtained through alloy combination design, a rolling control/TMCP (thermal mechanical control processing) technology and a heat treatment process, so that the steel plate has better strength and toughness, strong plasticity matching, seawater corrosion resistance, welding performance and fatigue resistance; the steel plate provided by the invention is a wide and thick steel plate for heavy steel structures, which is developed at low cost by adopting the technology, has high toughness, strong plastic matching and excellent low-temperature toughness and can be welded by high heat input.
In The prior art, when a medium steel plate with yield strength of more than or equal to 420MPa and low-temperature impact toughness of more than or equal to 34J at-60 ℃ is manufactured, a certain amount of Ni or Cu + Ni element (more than or equal to 0.30%) is generally added into The steel [ The fire (1986) international Symposium and inhibition on offset metals and arc Engineering, 1986, Tokyo, Japan, 354; "DEVELOPMENTS IN MATERIALS FOR ARCTIC OFFSHORE STRUCTURES"; "Structural Steel Plates for arrangement Use Produced by Multipurose accepted Cooling System" (Japanese), Tokawasaki iron technology, 1985, Nos. 168-72; "Application of accessed consistent For Producing 360MPa Yield Strength Steel plates of up to 150mm in Thickness with Low Carbon Equivalent", accessed consistent Rolled Steel, 1986, 209-219; "High Strength Steel Plates For Ice-Breaking Vessels Produced by Thermo-Mechanical Control Process", Accelerated Co-vibrating Rolled Steel, 1986, 249-260; "420 MPa Yield Strength Steel Plate with Superior frame Structure for extraction offset Structure", Kawasaki Steel technical report, 1999, No.40, 56; "420 MPa and 500MPa Yield Strength Steel Plate with High HAZ to microwave Process by TMCP for offset Structure", Kawasaki Steel technical report, 1993, No.29, 54; "Toughness Improvement in Bainite Structure by Thermo-Mechanical Control Process" (Japanese) Sumitomo Metal, Vol.50, No.1(1998), 26; "Steel plate for ocean platform Structure used in icy sea area" (Japanese), Steel research, 1984, No. 314, 19-43 ] to ensure excellent low temperature toughness of the base steel plate, and when welding with heat input less than 50KJ/cm, the toughness of the HAZ in the heat affected zone can reach Akv ≥ 34J at-60 ℃; however, when welding is carried out with an ultra-high heat input (not less than 100KJ/cm), the low-temperature toughness of the welding Heat Affected Zone (HAZ) is generally difficult to achieve, and the low-temperature toughness of the Heat Affected Zone (HAZ) is seriously degraded. A large number of Patent documents only describe how to achieve low-temperature toughness of a base steel plate, how to obtain excellent low-temperature toughness of a Heat Affected Zone (HAZ) under welding conditions is less, how to ensure less and less low-temperature toughness of the Heat Affected Zone (HAZ) particularly when welding with ultra-high heat input, and in order to ensure low-temperature toughness of the steel plate, a certain amount of Ni or Cu + Ni element is generally added to the steel, and the low-temperature toughness of the Heat Affected Zone (HAZ) of the steel plate with ultra-high heat input can rarely reach-60 ℃ (japanese Patent nos. sho 63-93845, sho 63-79921, sho 60-258410, japanese Patent publication No. 4-285119, japanese Patent publication No. 4-308035, hei 3-264614, hei 2-250917, hei 4-143246, US Patent nos. US 4855106, US Patent nos. 5183198 and US Patent No. 4137104).
At present, only the Nippon Nissian iron company adopted the oxide metallurgy technology (U.S. Pat. No.4, 4629505, WO 01/59167A1) to improve the low temperature toughness of the Heat Affected Zone (HAZ) of the welded steel plate with ultra-large heat input, namely, in the process of welding with large heat input, TiN particles are dissolved and lose effect due to the action of high temperature for a long time in the vicinity of a fusion line, and Ti2O3More stable than TiN and does not dissolve even when reaching the melting point of steel. Ti2O3The particles can become the needle ferrite nucleation positions in the austenite crystals, promote the needle ferrite (acicular ferrite-AF) nucleation in the austenite crystals, effectively divide the austenite crystals, refine the HAZ structure, form a high-strength high-toughness needle ferrite structure, or pin the ultra-high temperature austenite crystal boundary by adopting MgO particles, ensure that the austenite crystals are fine and uniform in the ultra-high heat input welding heat cycle process, ensure that the welding heat affected zone is uniform and fine in structure, and have higher low-temperature toughness and crack arrest characteristics; however, the technology does not basically relate to the condition of ultra-large heat input welding of ultra-thick steel plates. .
Chinese patent application No. zl201410300713.x, ZL201310244712.3, ZL201310244706.8, ZL201310124065.2, ZL201310244713.8, ZL201210209637.2, ZL201410815614.5, 201710183350.X, and application No.201910149978.7, all of which are various low temperature steel plates developed by Bao steel and capable of being welded in large heat input, in order to ensure the low temperature toughness of the heat affected zone of the large heat input welding, a certain amount of precious alloy elements Cu and Ni are added in the steel plates (especially super thick steel plates), when the yield strength YP reaches 460MPa, a small amount of Mo is properly added, although the high heat input welding performance of the steel plates is better, the toughness of the heat affected zone of the welding, especially the low temperature toughness of the heat affected zone of the super thick steel plates welding is not too stable, certain fluctuation exists, especially the crack arrest characteristic is high (Kca (-20 ℃) and is not less than 6000N/mm under the condition of-20 ℃), and3 /2) Not only does the base metal steel plate not relate to, but also has high crack arrest characteristics of a welding heat affected zone HAZ; in addition, the manufacturing cost of the super-thick steel plate is higher, and the high crack arrest characteristic of the super-thick steel plate is not involved.
Disclosure of Invention
The invention aims to provide a YP460MPa thick steel plate with low cost, high crack arrest and high weldability and a manufacturing method thereof, wherein the contradiction between low alloy cost and high strength, high crack arrest characteristic, excellent low-temperature toughness (especially high crack arrest characteristic) and excellent weldability (especially larger heat input weldability) is successfully solved by adding a small amount of Ni, Cu and Mo noble elements, designing the combined components at low cost and matching with a TMCP (thermal mechanical control processing) process; is particularly suitable for icebreaking ship shells, ocean platforms, cross-sea bridges, offshore wind power structures, marine engineering machinery and the like in ice sea areas, and can realize stable batch industrial production with ultra-low cost
In order to achieve the purpose, the technical scheme of the invention is as follows:
the invention starts from alloy combination design, adopts low-C-low-Si-medium high Mn-Nb series low alloy steel as a base, and controls Mn/C to be more than or equal to 17, (% C) x [1+1.72 (% Mn) +6.17 (% P)1/2+11.36(％P)1/2]Not less than 0.52, not less than 20 and not more than 40 of B/N, micro Ti treatment, Ca treatment with Ca/S ratio controlled between 1.0 and 3.0 and (% Ca) × (% S)0.28≤1.0×10-3(ii) a Optimizing the TMCP Process, i.e. [ T ]Beginning rolling×1.4×(％Ceq)×VCooling rate]/(ξ×TStopping cooling) Not less than 0.105, the microstructure of the finished steel plate is uniform and fine ferrite and bainite distributed in a dispersion way, and the microstructure is averageThe grain size is below 15 mu m, the base steel plate obtains high strength, excellent low-temperature toughness, excellent large heat input weldability, and the steel plate and the welding heat affected zone have excellent low-temperature toughness and crack arrest characteristics.
Specifically, the YP460MPa thick steel plate with low cost, high crack resistance and high weldability comprises the following components in percentage by weight:
C：0.050％～0.090％
Si：0.01～0.10％
Mn：1.40％～1.70％
P：≤0.013％
S：≤0.0030％
Cu：≤0.30％
Ni：0.10％～0.35％
Mo：≤0.15％
Nb：0.010％～0.030％
Ti：0.008％～0.015％
B：0.0015％～0.0030％
N：0.0050％～0.0080％
Al：≤0.010％
Ca：0.0010％～0.0030％，
the balance of Fe and other inevitable impurities; and the content of the elements must satisfy the following relation at the same time:
Mn/C≥17；
(％C)×[1+1.72(％Mn)+6.17(％P)1/2+11.36(％P)1/2]≤0.52；
0.20≤B/N≤0.40；
[Tbeginning rolling×1.4×(％Ceq)×VCooling rate]/(ξ×TStopping cooling) Not less than 0.105, wherein,
Tbeginning rollingRolling temperature, T, controlled for non-recrystallizationBeginning rolling760-0.30t, unit is;
ceq is the carbon equivalent of the carbon,
(％Ceq)＝(％C)+(％Mn)/6+(％Si)/24+(％Ni)/40+(％Cr)/5+(％Mo)/4+(％V)/14；
Vcooling rateThe accelerated cooling speed of the steel plate is expressed in the unit of ℃/s;
xi is the accumulated rolling reduction rate of non-recrystallization controlled rolling, and the unit is percent;
Tstopping coolingTo accelerate the cooling-down temperature, TStopping cooling400-0.75t, unit is;
t is the thickness of the finished steel plate in unit mm;
ca treatment and Ca/S ratio controlled between 1.0 to 3.0, and (% Ca) × (% S)0.28≤1.0×10-3。
Mn/C is more than or equal to 17: the microstructure form of the super-thick steel plate is improved, and the eutectoid ferrite grains are homogenized and refined; meanwhile, the precipitation size of the internal carbide of the tempered bainite is reduced, the distribution and the morphology of the internal carbide of the bainite under tempering are improved, the intrinsic low-temperature impact toughness of the bainite is improved, the uniform and fine grains and excellent intrinsic toughness of a complex phase structure (ferrite and a small amount of bainite) of the super-thick steel plate are ensured, and the ductile-brittle transition temperature of the steel plate is lower than minus 50 ℃.
(％C)×[1+1.72(％Mn)+6.17(％P)1/2+11.36(％P)1/2]Less than or equal to 0.52: the method comprises the following steps of inhibiting the degree of C, Mn, P and S conjugate segregation in the molten steel solidification process, firstly, improving the C, Mn, P and S conjugate segregation in the molten steel solidification process, improving the "three properties" -soundness, homogeneity and purity of the inner quality of the super-thick steel plate, and improving the low-temperature toughness, crack arrest property and weldability of the super-thick steel plate; secondly, the precipitation of carbon nitride in the welding thermal cycle process is promoted, the formation of M-A islands is inhibited, the number of the M-A islands is reduced (especially the number of blocky M-A islands is reduced), the size of the M-A islands is reduced, the low-temperature toughness and crack arrest characteristics of a large heat input welding heat affected zone are improved, and the safety and reliability of a steel structure, especially a heavy steel structure are improved; this is one of the key technologies of the present invention.
B/N is more than or equal to 0.20 and less than or equal to 0.40: the method ensures that the large heat input welding heat affected zone of the super-thick steel plate has enough and dispersed BN precipitates, and simultaneously, the base metal steel plate and the welding heat affected zone have certain existence of solid solution B atoms. The following effects are realized: A) under the conditions of low carbon and low carbon equivalent, the balance of high strength, high strength and low temperature toughness of the super-thick base metal steel plate is ensured through the high hardenability of the solid solution B; secondly, solid solution B inhibits the formation of ferrite of the side plate strip with thick austenite crystal boundary in a large heat input welding heat affected zone, promotes the formation of ferrite in austenite crystal, and improves the low-temperature toughness of the large heat input welding heat affected zone; B) in the process that the steel plate is welded by large heat input, BN dispersed in a welding heat affected zone promotes ferrite nucleation in austenite crystal, divides coarse prior austenite crystal grains in the heat affected zone, refines the microstructure of the heat affected zone and improves the low-temperature toughness of the heat affected zone by large heat input; this is one of the key technologies of the present invention.
[TBeginning rolling×1.4×(％Ceq)×VCooling rate]/(ξ×TStopping cooling) Not less than 0.105: 1) ensuring that the controlled rolling effect of the super-thick steel plate is obvious, and the eutectoid ferrite grains are uniform and fine; 2) by the deformation of ferrite + austenite two-phase region, the proeutectoid ferrite grain forms stronger (110)<111>，(100)<011>Cold rolling texture, improving impact toughness and crack arrest characteristics of the super-thick steel plate under low temperature condition; 3) the phase change of fine and uniform proeutectoid ferrite is promoted, simultaneously, carbon-rich austenite is generated in the non-phase-changed austenite, the phase change of the carbon-rich austenite is ensured to be generated at lower temperature, lower bainite is formed, a uniform and fine ferrite and lower bainite complex phase structure which is in dispersion distribution is formed, and the super-thick steel plate is ensured to have excellent strength and toughness/strong plasticity matching, low-temperature toughness and crack arrest characteristics. In a word, the high strength, the high toughness (high crack arrest characteristic) and the excellent weldability (can bear high heat input welding) of the super-thick steel plate are realized under the conditions of low C content, low carbon equivalent and relatively low cost by refining the grain size of the super-thick steel plate, cold rolling texture toughening and a ferrite/lower bainite complex phase structure, which is one of the key technologies of the invention.
Ca treatment and Ca/S ratio controlled between 1.0 to 3.0, and (% Ca) × (% S)0.28≤1.0×10-3: the influence of the inclusions on low-temperature toughness and weldability is reduced to the minimum while the spheroidization of the sulfide is ensured, and meanwhile, Ca (O, S) particles are uniformly and finely distributed in the steel, so that the growth of austenite grains in a large heat input welding heat affected zone is inhibited, and the low-temperature toughness and crack arrest characteristics of the welding heat affected zone are improved.
The component data in the above relational expression is calculated according to percentage, for example, the carbon content is 0.10%, and when the relational expression is calculated, the calculation is carried out by substituting 0.10.
In the composition design of the steel of the invention:
c has great influence on the strength, low-temperature toughness, crack arrest characteristics, elongation and weldability of the TMCP type super-thick steel plate, particularly on the large heat input weldability, and the C content in the steel is expected to be controlled to be lower from the aspects of improving the low-temperature toughness, crack arrest characteristics and large heat input weldability of the TMCP type super-thick steel plate; however, from the aspects of the strength of the super-thick steel plate, the control of the microstructure in the production and manufacturing process and the manufacturing cost, the content of C is not suitable to be controlled to be too low; too low C content easily causes too high grain boundary mobility, coarse grains of the microstructure of the base metal steel plate and the welding HAZ, and too low C content in the steel causes the weakening of the grain boundary, thus seriously deteriorating the low-temperature toughness of the base metal steel plate and the welding HAZ; therefore, the reasonable range of the C content is 0.050 to 0.090 percent.
Si promotes molten steel deoxidation and can improve the strength of the super-thick steel plate, but Si deoxidation effect is not large by adopting Al deoxidation molten steel, Si can improve the strength of the super-thick steel plate, but Si seriously damages the low-temperature toughness, crack arrest characteristics, elongation and weldability of the super-thick steel plate, particularly Si not only promotes M-A island formation, but also forms massive M-A islands with large size and uneven distribution under the condition of high heat input welding, and seriously damages the low-temperature toughness and crack arrest characteristics of a welding heat affected zone, so that the Si content in steel is controlled to be as low as possible, and the Si content is controlled to be 0.01-0.10% in consideration of the economy and operability of a steel making process.
Mn, the most important alloying element, improves the strength of the super-thick steel sheet, expands the austenite phase region, and reduces Ar in the steel3Point temperature, refining TMCP type super-thick steel plate microstructure to improve low-temperature toughness and crack-arrest characteristic, promoting low-temperature phase transformation structure formation to improve super-thick steel plate strength; however, Mn is easily segregated during the solidification of molten steel, and particularly, when the Mn content is too high, not only is casting operation difficult, but also conjugate segregation with elements such as C, P, S is easily generated, and particularly, when the C content in steel is high, segregation and porosity at the central part of a cast slab are increased, and serious central region segregation of the cast slab easily forms an abnormal structure during subsequent rolling, accelerated cooling and welding processes, resulting in a low super-thick steel plateThe temperature toughness and the crack arrest characteristic are low, and the welded joint has cracks and embrittlement; therefore, the Mn content is between 1.40 and 1.70 percent.
P as harmful impurities in steel has great damaging effect on the mechanical properties of steel plates (especially ultra-thick steel plates), especially low-temperature impact toughness, crack arrest characteristics, elongation and weldability (especially high heat input weldability), and the lower the requirement is, the better the theoretical requirement is; however, considering the steel-making workability and the steel-making cost, the P content is preferably in the range of 0.013% or less.
S has great damage effect on low-temperature toughness and crack arrest characteristics of steel plates (especially ultra-thick steel plates) as harmful inclusions in steel, more importantly, the S is combined with Mn in the steel to form MnS inclusions, and particularly when the Mn content in the steel is high, the formed MnS inclusions are numerous and have huge size; in the hot rolling process, the plasticity of MnS enables MnS to extend along the rolling direction to form long-strip MnS inclusions along the rolling direction, so that the low-temperature impact toughness and the crack arrest characteristic of a steel plate (especially an ultra-thick steel plate) are seriously damaged (the MnS is not only a crack starting point, but also reduces the energy required by crack propagation and greatly reduces the propagation resistance of a crack), the elongation, the Z-direction performance and the weldability (especially the large heat input weldability), and meanwhile, the S is also a main element generating hot brittleness in the hot rolling process, and the lower the theoretical requirement is; however, considering the steel-making operability, steel-making cost and the principle of smooth material flow, the S content needs to be controlled to be less than or equal to 0.0030 percent.
As an austenite stabilizing element, a small amount of Cu may be added to reduce Ar3The point phase transition temperature, and simultaneously, the strength of the steel plate is improved (mainly realizing the composite superposition strengthening effect together with other alloy elements), and the low-temperature toughness is improved without damaging the weldability; however, the excessive addition of Cu not only increases the manufacturing cost, but also causes the formation of GP precipitation zones of Cu in the hot rolling and TMCP processes, which damages the low-temperature toughness of the steel plate and may cause copper brittleness; if the Cu content is too small, the composite improvement effect on the strength and the toughness of the super-thick steel plate is small, and the Cu content is controlled to be less than or equal to 0.30 percent by comprehensively considering the factors.
Ni is an indispensable alloy element for obtaining excellent ultralow temperature toughness of the super-thick steel plate, can reduce the ferrite dislocation low temperature P-N force, promotes 1/2<111> (110) dislocation cross slip and improves the low temperature ferrite intrinsic plastic low temperature toughness and the steel plate crack arrest characteristic; besides, Ni and other alloy elements realize composite superposition strengthening effect, the low-temperature toughness and crack arrest characteristics of a large heat input welding heat affected zone of the steel plate are improved, and the influence on weldability is small. Therefore, theoretically, the higher the Ni content in the steel is, the better the steel is, but Ni is a very expensive alloy element, and the addition amount is preferably 0.10 to 0.35% from the viewpoints of low cost, mass production and high heat input weldability.
The addition of Mo can greatly improve the hardenability of the steel plate and promote the formation of bainite in the accelerated cooling process, but Mo is used as a strong carbide forming element to promote the formation of bainite, increase the size of bainite crystal groups, reduce the meta-position difference of the formed bainite laths and reduce the resistance of cracks passing through the bainite crystal groups; therefore, Mo greatly improves the strength of the super-thick steel plate and simultaneously reduces the low-temperature toughness and the elongation of the TMCP steel plate; and when Mo is excessively added, not only elongation, high heat input weldability, and weld joint properties of the steel sheet are seriously impaired, but also production cost of the steel sheet is increased. But the Mo element is added, so that the C content is reduced to balance the strength and toughness and strong plasticity matching of the super-thick steel plate, and the ultralow temperature toughness and weldability of the super-thick steel plate are effectively improved; therefore, the phase change strengthening effect of Mo, the influence on the low-temperature toughness, the elongation and the weldability of the base steel plate and cost factors are comprehensively considered, and the content of Mo is controlled to be less than or equal to 0.15 percent.
The purpose of adding trace Nb element in the steel is to control and roll the grain size of the super-thick steel plate without recrystallization, and improve the strength, low-temperature toughness and crack arrest characteristics of the TMCP type super-thick steel plate; when the addition amount of Nb is less than 0.010 percent, the strengthening and toughening capabilities of the TMCP type super-thick steel plate are insufficient besides the effect of controlling rolling and refining crystal grains (particularly crystal grains at the central part of the super-thick steel plate) which cannot be effectively exerted; when the addition amount of Nb exceeds 0.030%, the formation of upper bainite (Bu) and the secondary precipitation embrittlement of Nb (C, N) are induced under the condition of high heat input welding, and the low-temperature toughness and crack arrest characteristics of a high heat input welding heat affected zone of the super-thick steel plate are seriously damaged; therefore, the Nb content is controlled to be between 0.010 and 0.030 percent, the optimal effect of controlling rolling and refining the grain size of the super-thick steel plate is obtained, the toughness of a large heat input welding heat affected zone is not damaged while the strength and toughness/plasticity matching of the TMCP type super-thick steel plate is realized.
The affinity of Ti and N is far greater than that of B and N, when a small amount of Ti is added, N is preferentially combined with Ti to generate TiN particles which are dispersed and distributed, thereby inhibiting austenite grains from excessively growing in the TMCP process and improving the low-temperature toughness and crack arrest characteristics of the steel plate; more importantly, the growth of crystal grains in a heat affected zone (a zone far away from a fusion line) in the large heat input welding process is inhibited to a certain extent, and the low-temperature toughness and the crack arrest characteristic of the heat affected zone are improved; the effect of adding too little Ti (0.008%) is not great, and when the Ti content is added too much (0.015%), the BN particles in the steel are inhibited from being separated out, so that the quantity of the BN particles is rare, and the low-temperature toughness of a large heat input welding heat affected zone cannot be improved; in addition, when the content of Ti in the steel is extremely high, most of N in the steel is combined by Ti, so that the content of solid solution B in the steel is too high, and the low-temperature toughness and the high heat input weldability of the steel plate are influenced; therefore, the suitable Ti content range is 0.008 to 0.015 percent.
In order to ensure that certain solid-solution B atoms in the steel are partially aggregated at an austenite crystal boundary in the TMCP process, inhibit the formation of grain boundary-like ferrite, promote the formation of low-temperature phase-change structure bainite/martensite in the TMCP process and realize high strength under the conditions of low carbon and low carbon equivalent; secondly, enough solid solution B atoms in the steel are combined with N atoms in the welding heat circulation process to generate a certain amount of BN particles which are dispersedly distributed, so that ferrite grains are formed in austenite crystals (the BN particles are used as heterogeneous nucleation points of ferrite in the austenite crystals) in the large heat input welding process, the original coarse austenite grains are segmented, the microstructure of a large heat input welding heat affected zone is refined, and the low-temperature toughness of the ultra-thick steel plate welding heat affected zone is improved; therefore, the content of the B element in the steel is not less than 0.0015 percent; however, when the B content in the steel is too high, a large amount of coarse Fe is precipitated on the prior austenite grain boundary23(CN)6The cold and hot processing characteristics, the service bearing and the crack resistance and crack arrest characteristics of the steel plate are rapidly deteriorated due to the low-temperature toughness, crack arrest characteristics and plasticity of the base metal steel plate and the welding heat affected zone which are seriously embrittled, and the steel plate is over-serviceThe safety in the process can not be guaranteed, so the content of the steel plate B can not exceed 0.0030 percent.
Enough BN particles are ensured to promote ferrite nucleation in a large heat input welding heat affected zone, coarse prior austenite grains in the heat affected zone are segmented, the microstructure of the large heat input welding heat affected zone is refined, the low-temperature toughness of the large heat input welding heat affected zone is improved, and the content of N in steel is not less than 0.0050%; however, when the content of N in the steel is too high, all B atoms in the steel are combined with N atoms, and after BN particles are generated, solid solution B atoms do not exist in the steel, so that the strength of the steel plate with ultralow C and low carbon equivalent components is low, and the development requirement cannot be met; in addition, the excessive N content in the steel reaches the increase of solid solution N atoms in a large heat input welding heat affected zone, and the low-temperature toughness of the welding heat affected zone is seriously degraded; therefore, the N content in the steel cannot exceed 0.0080%.
In order to ensure that a sufficient amount of BN particles are formed in the steel and to suppress the generation of a large amount of AlN particles, the upper limit of the Al content in the steel must be controlled; therefore, Al in the steel should not be higher than 0.010%.
The Ca treatment of the steel can further purify the molten steel on one hand, and the modification treatment of the sulfide in the steel on the other hand can lead the sulfide to become non-deformable, stable and fine spherical sulfide, inhibit the hot brittleness of S, improve the low-temperature toughness, the elongation and the Z-direction performance of the steel plate and improve the anisotropy of the toughness of the steel plate. The addition amount of Ca depends on the content of S in steel, the addition amount of Ca is too low, and the treatment effect is not great; the addition of Ca is too high, the formed Ca (O, S) has too large size and increased brittleness, and can be used as a starting point of fracture crack, reduce the low-temperature toughness and elongation of steel, and simultaneously reduce the purity of the steel and pollute molten steel; therefore, the appropriate range of the Ca content is 0.0010% to 0.0030%.
The invention relates to a method for manufacturing YP460MPa thick steel plates with low cost, high crack resistance and high weldability, which comprises the following steps:
1) smelting and casting
Smelting and continuously casting the components into a plate blank;
2) heating the plate blank, wherein the heating temperature is controlled to be 1050-1130 ℃;
3) rolling, the total compression ratio (slab thickness/finished steel plate thickness) of steel plate is more than or equal to 3.0
The first stage is common rolling, and the accumulated reduction rate is more than or equal to 50 percent;
in the second stage, rolling is controlled by adopting non-recrystallization, the rolling start temperature is controlled to be 760-0.3t, the rolling pass reduction rate is more than or equal to 7 percent, the accumulated reduction rate is more than or equal to 50 percent, and the final rolling temperature is 750-0.3 t; wherein t is the thickness of the finished steel plate and the unit is mm;
4) cooling down
After rolling control is finished, conveying the steel plate to cooling equipment, then carrying out accelerated cooling on the steel plate, wherein the finish rolling temperature of the steel plate is 740-0.3t, the cooling speed is more than or equal to 3 ℃/s, the stop cooling temperature is less than or equal to (400-0.75t), then naturally air-cooling the steel plate to 350 ℃, and then carrying out slow cooling, wherein the slow cooling process is that the temperature of the steel plate is kept for at least 24 hours under the condition that the temperature surface of the steel plate is more than 300 ℃; wherein t is the thickness of the finished steel plate and the unit is mm.
According to the components of the steel plate, the heating temperature of the plate blank is controlled between 1050 ℃ and 1130 ℃, so that the austenite grains of the plate blank do not grow abnormally while the Nb in the steel is completely dissolved into austenite in the heating process of the plate blank.
The total compression ratio (slab thickness/finished steel plate thickness) of the steel plate is more than or equal to 3.0, so that rolling deformation is ensured to penetrate through the core part of the steel plate, and the microstructure and the performance of the central part of the steel plate are improved.
The first stage is common rolling, continuous rolling is carried out by adopting the maximum rolling capacity of a rolling mill, the cumulative reduction rate is more than or equal to 50 percent, the deformed billet is ensured to be recrystallized, and austenite grains are refined.
In the second stage, non-recrystallization controlled rolling is adopted, according to the content range of the Nb element in the steel, in order to ensure the non-recrystallization controlled rolling effect, the controlled rolling initial rolling temperature is controlled to be (760-0.3t) DEG C, the rolling pass reduction rate is more than or equal to 7 percent, the accumulated reduction rate is more than or equal to 50 percent, and the final rolling temperature is (750-0.3t) DEG C; wherein t is the thickness of the finished steel plate and the unit is mm.
After the controlled rolling is finished, the steel plate is immediately conveyed to accelerated cooling equipment, and then accelerated cooling is carried out on the steel plate; the steel plate is cooled at the temperature of 740-0.3t and the cooling speed is more than or equal to 3 ℃/s, the accelerated cooling and cooling stopping temperature is 400-0.75t, then the steel plate is naturally cooled to 350 ℃ and then is subjected to slow cooling hydrogen diffusion treatment, and the slow cooling process is that the temperature of the steel plate surface is kept for at least 24 hours under the condition that the temperature is more than 300 ℃; wherein t is the thickness of the finished steel plate and the unit is mm.
The invention has the beneficial effects that:
according to the invention, by adding a small amount of precious alloy elements Cu, Ni and Mo, designing the composition at low cost and matching with a corresponding TMCP (thermal mechanical control processing) process, YP460MPa super-thick steel plates with excellent mechanical properties and weldability are successfully produced in batches; the steel plate manufacturing technology not only greatly reduces the manufacturing cost of the whole process, shortens the manufacturing period of the steel plate, creates great value for enterprises, and realizes the green and environment-friendly manufacturing process. The high-performance and high-added-value of the super-thick steel plate is intensively shown in that the super-thick steel plate has high strength, excellent low-temperature toughness and crack arrest characteristics, meanwhile, the weldability (especially the large heat input weldability) of the steel plate is also excellent, the key technical problems that the low C content, the low carbon equivalent, the low cost (namely, the high-temperature and high-temperature steel plate does not contain or contains trace precious alloy elements such as Cu, Ni and Mo) and the high strength are mutually conflicted in component design and process design and are difficult to harmonize are successfully solved, and the safety and stability of a large heavy steel structure are greatly improved; the good weldability (especially the large heat input single pass welding) saves the manufacturing cost of the user steel component, greatly shortens the manufacturing time of the user steel component and creates great value for users.
Drawings
FIG. 1 is a photograph of a microstructure (1/4 thickness) of example 5 of the present invention;
FIG. 2 is a photograph showing the microstructure (heat input 100kJ/cm) of the weld heat affected zone in example 5 of the present invention.
Detailed Description
The invention is further illustrated with reference to the following figures and examples.
The steel plate components of the embodiment of the invention are shown in table 1, tables 2 to 3 are process parameters of the embodiment of the invention, and table 4 is performance parameters of the steel of the embodiment of the invention.
As can be seen from FIG. 1, the microstructure of the steel sheet is uniform and fine ferrite + bainite distributed in a dispersed manner, the average grain size of the microstructure is 15 μm or less, the base steel sheet has high strength, excellent low-temperature toughness, excellent large heat input weldability, and excellent low-temperature toughness and crack arrest characteristics with respect to the weld heat affected zone.
According to the invention, by adding a small amount of precious alloy elements Cu, Ni and Mo, designing the composition at low cost and matching with a corresponding TMCP (thermal mechanical control processing) process, YP460MPa super-thick steel plates with excellent mechanical properties and weldability are successfully produced in batches; the steel plate manufacturing technology not only greatly reduces the manufacturing cost of the whole process, shortens the manufacturing period of the steel plate, creates great value for enterprises, and realizes the green and environment-friendly manufacturing process. The high-performance and high-added-value of the super-thick steel plate is intensively shown in that the super-thick steel plate has high strength, excellent low-temperature toughness and crack arrest characteristics, meanwhile, the weldability (especially the large heat input weldability) of the steel plate is also excellent, the key technical problems that the low C content, the low carbon equivalent, the low cost (namely, the high-temperature and high-temperature steel plate does not contain or contains trace precious alloy elements such as Cu, Ni and Mo) and the high strength are mutually conflicted in component design and process design and are difficult to harmonize are successfully solved, and the safety and stability of a large heavy steel structure are greatly improved; the good weldability (especially the large heat input single pass welding) saves the manufacturing cost of the user steel component, greatly shortens the manufacturing time of the user steel component and creates great value for users.
The super-thick steel plate is mainly used for low-temperature hull structural steel, ocean platforms, cross-sea bridges, offshore wind power pile leg structures, harbor machinery, steel structures in cold regions and the like, and can realize stable batch industrial production with low cost.
With the development of national economy and the requirement of building a conservation-oriented harmonious society in China, ocean development has reached the daily agenda, ocean engineering construction (such as offshore wind power engineering) and related equipment manufacturing industry in China are not fully developed at present, and key materials of the ocean engineering construction and the related equipment manufacturing industry, namely, super-thick steel plates which can be welded by large heat input and are prevented from cracking at low temperature, have wide market prospects.
Figure BDA0002347413830000131
Figure BDA0002347413830000141
Figure BDA0002347413830000151

Claims (6)

1. The YP460MPa thick steel plate with low cost, high crack resistance and high weldability comprises the following components in percentage by weight:
C：0.050％～0.090％
Si：0.01～0.10％
Mn：1.40％～1.70％
P：≤0.013％
S：≤0.0030％
Cu：≤0.30％
Ni：0.10％～0.35％
Mo：≤0.15％
Nb：0.010％～0.030％
Ti：0.008％～0.015％
B：0.0015％～0.0030％
N：0.0050％～0.0080％
Al：≤0.010％
Ca：0.0010％～0.0030％，
the balance of Fe and inevitable impurities; and the content of the elements must satisfy the following relation at the same time:
Mn/C≥17；
(％C)×[1+1.72(％Mn)+6.17(％P)1/2+11.36(％P)1/2]≤0.52；
0.20≤B/N≤0.40；
[Tbeginning rolling×1.4×(％Ceq)×VCooling rate]/(ξ×TStopping cooling) Not less than 0.105, wherein,
Tbeginning rollingRolling temperature, T, controlled for non-recrystallizationBeginning rolling760-0.30t, unit is;
ceq is the carbon equivalent of the carbon,
(％Ceq)＝(％C)+(％Mn)/6+(％Si)/24+(％Ni)/40+(％Cr)/5+(％Mo)/4+(％V)/14；
Vcooling rateThe accelerated cooling speed of the steel plate is expressed in the unit of ℃/s;
xi is the accumulated rolling reduction rate of non-recrystallization controlled rolling, and the unit is percent;
Tstopping coolingTo accelerate the cooling-down temperature, TStopping cooling400-0.75t, unit is;
t is the thickness of the finished steel plate in unit mm;
ca treatment, and the Ca/S ratio is controlled to be between 1.0 and 3.0 and (% Ca) × (% S)0.28≤1.0×10-3。
2. The low-cost, high crack-arresting and high-weldability YP460MPa grade steel plate according to claim 1, characterized in that the microstructure of said steel plate is uniform and fine ferrite + bainite distributed in dispersion, and the average grain size of the microstructure is below 15 μm.
3. The low-cost, high crack-arresting and high-weldability YP460 MPa-grade thick steel plate according to claim 1 or 2, characterized in that the plate thickness of the steel plate is 80mm or more, the yield strength is 460MPa or more, the tensile strength is 570MPa or more, and the Charpy impact energy (single value) at-50 ℃ is 100J, Kca (-20 °) > 6000N/mm or more3/2。
4. The method for manufacturing a low-cost, high crack arrest and high weldability YP460MPa grade thick steel plate according to claim 1, characterized by comprising the steps of:
1) smelting and casting
Smelting and continuously casting the components according to the claim 1 into a slab;
2) heating the plate blank, wherein the heating temperature is controlled to be 1050-1130 ℃;
3) rolling, wherein the total compression ratio of the steel plate, namely the thickness of the plate blank/the thickness of the finished steel plate is more than or equal to 3.0
The first stage is common rolling, and the accumulated reduction rate is more than or equal to 50 percent;
in the second stage, rolling is controlled by adopting non-recrystallization, the rolling start temperature is controlled to be 760-0.3t, the rolling pass reduction rate is more than or equal to 7 percent, the accumulated reduction rate is more than or equal to 50 percent, and the final rolling temperature is 750-0.3 t; wherein t is the thickness of the finished steel plate and the unit is mm;
4) cooling down
After rolling control is finished, conveying the steel plate to cooling equipment, immediately carrying out accelerated cooling on the steel plate, wherein the steel plate is cooled at the temperature of 740-0.3t DEG C at the cooling speed of more than or equal to 3 ℃/s and the cooling stop temperature is (400-0.75t) ° C, then naturally cooling the steel plate to 350 ℃ in air, and then slowly cooling the steel plate, wherein the slow cooling process is that the temperature is kept for at least 24 hours under the condition that the temperature surface of the steel plate is more than 300 ℃; wherein t is the thickness of the finished steel plate and the unit is mm.
5. The method for producing a low-cost, high crack-arresting and high-weldability YP460 MPa-grade thick steel plate as claimed in claim 4, wherein the microstructure of said steel plate is uniform and fine ferrite + bainite distributed in a dispersed manner, and the average grain size of the microstructure is 15 μm or less.
6. The method for producing a low-cost, high crack arrest and high weldability YP460MPa grade thick steel plate according to claim 4, characterized in that the plate thickness of said steel plate is 80mm or more, the yield strength is 460MPa or more, the tensile strength is 570MPa or more, the Charpy impact energy (single value) at-50 ℃ is 100J, Kca (-20 °) > 6000N/mm or more3/2。
CN201911400865.6A 2019-12-30 2019-12-30 YP460MPa thick steel plate with low cost, high crack resistance and high weldability and manufacturing method thereof Pending CN112746158A (en)

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20060016526A1 (en) * 2004-07-21 2006-01-26 Yasushi Mizutani High-strength steel for welded structures excellent in high temperature strength and method of production of the same
JP2012172258A (en) * 2011-02-24 2012-09-10 Nippon Steel Corp Method for manufacturing thick steel plate
CN104046899A (en) * 2014-06-27 2014-09-17 宝山钢铁股份有限公司 550MPa-grade steel sheet capable of being welded at high heat input and manufacturing method thereof

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20060016526A1 (en) * 2004-07-21 2006-01-26 Yasushi Mizutani High-strength steel for welded structures excellent in high temperature strength and method of production of the same
JP2012172258A (en) * 2011-02-24 2012-09-10 Nippon Steel Corp Method for manufacturing thick steel plate
CN104046899A (en) * 2014-06-27 2014-09-17 宝山钢铁股份有限公司 550MPa-grade steel sheet capable of being welded at high heat input and manufacturing method thereof

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