CN112746219A - YP500 MPa-grade steel plate with low yield ratio, high toughness and high weldability and manufacturing method thereof - Google Patents

YP500 MPa-grade steel plate with low yield ratio, high toughness and high weldability and manufacturing method thereof Download PDF

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CN112746219A
CN112746219A CN201911400868.XA CN201911400868A CN112746219A CN 112746219 A CN112746219 A CN 112746219A CN 201911400868 A CN201911400868 A CN 201911400868A CN 112746219 A CN112746219 A CN 112746219A
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刘自成
钟武波
胡战
刘斌
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Baosteel Zhanjiang Iron and Steel Co Ltd
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    • 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
    • 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
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    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • 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
    • C21D2211/001—Austenite

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Abstract

A YP500 MPa-grade steel plate with low yield ratio, high toughness and high weldability is prepared from an alloy system treated by ultralow C, ultralow Si, high Mn and micro (Ti + Nb), and through reasonable combination of (Cu + Ni + Cr + Mo) matching and combining with TCMP + T processGold was used as a basis by controlling (% C) × [ (% Ceq) +0.67 (% P) +0.53 (% S) +0.59 (% Nb)]Not more than 0.046, not less than 16 Mneq/C not more than 36, Ti/N between 1.5 and 2.5, Ca treatment with Ca/S ratio controlled between 1.0 and 3.0 (% Ca) x (% S)0.28≤1.5×10‑3And the like metallurgical technical means; the TMCP process is optimized, the microstructure of the finished steel plate is a small amount of fine ferrite and lower bainite distributed in a dispersing way, the average grain size is below 15 mu m, and the obtained steel plate has high strength, low yield ratio, high toughness (especially high crack resistance and crack arrest characteristics), small performance anisotropy and excellent weldability, can be welded by large heat input, and is particularly suitable for offshore wind power, low-temperature pressure vessels, ocean platforms, bridge steel and the like.

Description

YP500 MPa-grade steel plate with low yield ratio, high toughness and high weldability and manufacturing method thereof
Technical Field
The invention relates to a YP500 MPa-grade steel plate with low yield ratio, high toughness and high weldability and a manufacturing method thereof.
Background
As is well known, low-carbon (high-strength) low-alloy steel is one of the most important engineering structural materials, and is widely applied to petroleum and natural gas pipelines, ocean platforms, shipbuilding, bridge structures, boiler containers, building structures, automobile industry, railway transportation and mechanical manufacturing; the properties of low carbon (high strength) low alloy steel depend on its chemical composition and manufacturing process, where strength, toughness, plasticity 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 metallurgical technology and field control technology, people put forward higher requirements on the toughness, plasticity and weldability of high-strength steel; namely, the steel plate has high strength, high elongation and high crack arrest characteristics (namely brittle fracture resistance and plastic instability fracture resistance) at low temperature, and meanwhile, the steel plate has excellent welding performance and can be welded at high heat input and high efficiency; under the condition of lower manufacturing cost, the comprehensive mechanical property and the service performance of the steel plate are greatly improved, the cost is saved by reducing the using amount of steel, the self weight, the stability and the safety of a steel member are reduced, and more importantly, the cold and hot workability of the strong steel and the safety and the reliability in the service process are further improved; at present, research booms for developing new-generation high-performance steel materials are raised in the range of Japanese Korea, European Union and North America, and the combination of alloy combination design optimization and a new-generation online thermomechanical treatment process technology is tried to obtain better microstructure matching, ultrafine microstructure and substructure. Under the condition of not increasing noble alloy elements (such as Cu, Ni, Mo and the like), better tissue morphology, size and substructure are obtained by matching alloy combination design optimization with a new generation TMCP process technology, so that higher obdurability and better weldability are obtained.
Conventional steel sheets having a tensile strength of greater than 590MPa (yield strength of 500MPa or more) are mainly produced by a reheat quenching and tempering (RQ + T) process, i.e., an off-line hardening and tempering process, which requires that the center portion of the steel sheet must have a sufficiently high hardenability, i.e., a hardenability index DI of 1.0 × the thickness of the steel sheet, where DI is 0.311C1/2(1+0.64Si) x (1+4.10Mn) x (1+0.27Cu) x (1+0.52Ni) x (1+2.33Cr) x (1+3.14Mo) x 25.4(mm) to ensure sufficiently high strength, excellent ultra-low temperature toughness and uniformity of microstructure and properties in the thickness direction of the steel sheet, and therefore, it is inevitable to add a certain amount of alloying elements such as Cr, Mo, Ni, Cu, etc. to the steel because Ni elements not only improve the strength and hardenability of the steel sheet, but also reduce the transformation temperature to refine the bainite/martensite lath grain size; more importantly, Ni is the only element capable of improving the intrinsic low-temperature toughness of bainite/martensite laths, increasing the orientation angle between the bainite/martensite laths, and increasing the propagation resistance of cracks in the bainite/martensite crystal groups (Japanese patent No. Sho 59-129724, Hei 1-219121).
Therefore, the steel plate has high alloy content, so that the manufacturing cost of the steel plate is high, the carbon equivalent Ceq and the welding cold crack sensitivity index Pcm are also high, great difficulty is brought to field welding, preheating is needed before welding, heat treatment is needed after welding, the welding cost is increased, the welding efficiency is reduced, and the working environment of the welding field is deteriorated; a great deal of patent documents only explain how to realize the strength and the low-temperature toughness of a base steel plate, improve the welding performance of the steel plate, obtain an excellent welding heat affected zone HAZ low-temperature toughness and have less explanation, and do not relate to how to ensure the through quenching of the central part of a quenched and tempered steel plateProperty to ensure the strength, toughness and uniformity of the strength and toughness along the thickness direction of the steel plate (Japanese Patent No. Sho 63-93845, No. Sho 63-79921, No. Sho 60-258410, No. Hei 4-285119, No. Hei 4-308035, No. Hei 3-264614, No. Hei 2-250917, No. Hei 4-143246, U.S. Pat. No. 4,4855106, U.S. Pat. No. 5183198, U.S. Pat. No. 4,4137104); at present, only the Nippon Nissian iron company (U.S. Pat. No. 4,505 and European Patent WO 01/59167A 1) which improves the low-temperature toughness of the Heat Affected Zone (HAZ) of the welded steel plate with ultra-large heat input adopts the oxide metallurgy technology (U.S. Pat. No. 4,505 and European Patent WO 01/59167A 1), namely, in the process of welding with large heat input, TiN particles are dissolved and lose effect near the fusion line due to strong high-temperature effect, 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 and form a high-strength high-toughness needle ferrite structure; the Japanese Sumitomo metal adopts technical means of adding B, controlling the B/N to be more than or equal to 0.5, low silicon content, ultralow aluminum content, medium N content and the like, solves the problem of high heat input weldability of a 60 kg-grade steel plate, obtains good effect and is successfully used for engineering achievement (iron と steel, 1978, Vol.64, P2205).
Chinese patent application numbers ZL201610463494.6, ZL201210077114.7, ZL201110181293.4, ZL201010113835.X, ZL200910196233.2, ZL200810042088.8 and ZL200810042124.0 are Bao steels, since 2008, a series of 600MPa quenched and tempered steel plates with high toughness and excellent weldability are developed successively, the steel types adopt an offline quenching and tempering heat treatment process, the problems of high toughness, crack resistance and crack arrest characteristics, excellent weldability, low-cost manufacturing, steel plate thickness specification expansion, performance uniformity in the thickness direction of an extra-thick steel plate and the like of the 600MPa quenched and tempered steel plate are mainly solved in research and development places, great breakthrough and good effects are achieved, and batch industrial production of the steel plates is achieved. The steel plate is successfully applied to the construction of important hydroelectric engineering at home and abroad (such as Sanxia Wudongde, white Crane beach hydroelectric engineering, national new power grid company pumped storage power station engineering and Israel hydroelectric engineering), ocean engineering and the manufacture of important equipment (such as a water turbine seat ring plate of a million kilowatt unit of the Wudong De and white Crane beach, a floating crane and a bridge crane for a vibro-heavy industrial large-scale ship, a giant excavator and the like), obtains good supply performance, replaces imports with partial varieties and fills up the domestic blank. The steel plate is produced by an offline quenching and tempering heat treatment process (namely RQ + T), the mechanical properties (particularly low-temperature toughness, crack resistance and crack arrest characteristics) and the weldability of the steel plate are excellent, and the quality of the product reaches the international leading level; but the yield ratio of the steel plate is higher and is more than or equal to 0.89; in addition, the steel plates are produced by an off-line quenching and tempering heat treatment process, so that the production and manufacturing processes are multiple, the manufacturing period is long, and the manufacturing cost is relatively high.
Disclosure of Invention
The invention aims to provide a YP500 MPa-grade steel plate with low yield ratio, high toughness and high weldability and a manufacturing method thereof, which successfully solve the contradiction among low alloy cost, low carbon equivalent, high strength, low yield ratio, smaller performance anisotropy (longitudinal and transverse), excellent low-temperature toughness (especially high crack resistance and crack arrest characteristics) and excellent weldability (especially larger heat input weldability); the low-temperature toughness and the crack resistance and crack resistance of the welded HAZ are also excellent under the condition of large heat input welding; the yield strength is more than or equal to 500MPa, the tensile strength is more than or equal to 630MPa, and the transverse impact toughness KV at minus 50 ℃ is higher than2Not less than 120J (shearing area FA not less than 75%), yield ratio YR not more than 0.85, and high heat input welding (not less than 50 kJ/cm).
In order to achieve the purpose, the technical scheme of the invention is as follows:
the invention starts from alloy combination design, in an alloy system processed by ultralow C-ultralow Si-high Mn-micro (Ti + Nb), based on reasonable alloying of matching combination of (Cu + Ni + Cr + Mo), by controlling (% C) x [ (% Ceq) +0.67 (% P) +0.53 (% S) +0.59 (% Nb)]Not more than 0.046, not less than 16 Mneq/C not more than 36, Ti/N between 1.5 and 2.5, Ca treatment with Ca/S ratio controlled between 1.0 and 3.0, and (% Ca) × (% S)0.28≤1.5×10-3And the like metallurgical technical means; optimizing TMCP (Thermo-mechanical control process), i.e. controlling the temperature to be less than or equal to 62 [ [ (H)Thickness of board)×(ξNot recrystallized)×(TStopping cooling)]/[(TFinish rolling)×(VCooling rate)×Ceq]319 or less, the microstructure of the finished steel plate is a small amount of fine ferrite and lower bainite which are dispersed, the average grain size is below 15 mu m, and the steel plate which has high strength, low yield ratio, high toughness (especially high crack resistance and crack arrest characteristics), small performance anisotropy, excellent weldability and larger heat input welding can be obtained.
Specifically, the YP500 MPa-grade steel plate with low yield ratio, high toughness and high weldability comprises the following components in percentage by weight:
C：0.06％～0.10％
Si：0.01～0.20％
Mn：1.35％～1.65％
P：≤0.013％
S：≤0.0030％
Cu：0.10％～0.45％
Ni：0.10％～0.50％
Cr：0.10％～0.30％
Mo：0.10％～0.30％
Nb：0.010％～0.040％
Ti：0.008％～0.015％
Als：0.025％～0.060％
N：≤0.0050％
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:
(％C)×[(％Ceq)+0.67(％P)+0.43(％S)+0.59(％Nb)]≤0.046；
Mneq/C is more than or equal to 16 and less than or equal to 36, wherein Mneq is the equivalent of manganese,
Mneq(％)＝(％Mn)+0.23(％Cu)+0.76(％Ni)；
Ti/N is between 2.0 and 3.0;
ca treatment, the Ca/S ratio is controlled to be 1.0 to 3.0, and (% Ca) × (% S)0.28≤1.5×10-3；
62≤[(HThickness of board)×(ξNot recrystallized)×(TStopping cooling)]/[(TFinish rolling)×(VCooling rate)×Ceq]Less than or equal to 319, wherein,
Hthickness of boardThe thickness of the finished steel plate is in mm;
ξnot recrystallizedThe cumulative reduction in the unrecrystallized region is expressed in units of%;
Tstopping coolingTo accelerate the cooling stop temperature, in units of;
Tfinish rollingThe final rolling temperature is the final rolling temperature of non-recrystallization controlled rolling, and the unit is;
Vcooling rateThe cooling speed for accelerating cooling is expressed in ℃/s;
ceq is the carbon equivalent of the carbon,
ceq (%) (% C) + (% Mn)/6+ (% Si)/24+ (% Ni)/40+ (% Cr)/5+ (% Mo)/4+ (% V)/14, unit%.
(％C)×[(％Ceq)+0.67(％P)+0.43(％S)+0.59(％Nb)]≤0.046：
1) The conjugate segregation among elements such as C, Mn, P, S and the like is inhibited, the solidification segregation degree of molten steel is reduced, and the low-temperature toughness and the large heat input weldability of the base metal steel plate are improved;
2) the precipitation of an M-A island in a larger heat input welding heat affected zone (particularly a blocky M-A island) is inhibited, the size of the M-A island is reduced, the number of the M-A islands is reduced, the distribution of the M-A islands is improved, and the low-temperature toughness of the HAZ in larger heat input welding is greatly improved;
3) the relation between C and Ceq is matched, so that the steel plate has high strength, high plasticity and low yield ratio while the steel plate has excellent large heat input weldability; this is one of the key technologies of the present invention.
16-36 parts of Mneq/C: the steel plate has excellent low-temperature toughness and crack resistance and crack arrest characteristics, and meanwhile, the steel plate is low in yield ratio control difficulty and large in TMCP process window.
Ti/N is between 2.0 and 3.0;
ca treatment, the Ca/S ratio is controlled to be 1.0 to 3.0, and (% Ca) × (% S)0.28≤1.5×10-3；
1) The HAZ area far away from a fusion line is ensured, the welding peak temperature is lower (less than or equal to 1200 ℃), TiN is less dissolved in the welding thermal cycle process, namely the TiN particles are not easy to Ostward ripening in the welding thermal cycle process (namely large particles swallow small particles, the particle number is greatly reduced, the particle size is increased, the pinning effect on grain boundaries is lost), the number, the size and the distribution of the TiN particles in the welding thermal cycle process are ensured to be kept stable, no obvious coarsening is generated, the austenite grain boundaries in a welding heat affected zone are effectively pinned, and the excessive growth of the austenite grains is inhibited;
2) when the HAZ area close to the fusion line, the welding peak temperature is higher (>1250 ℃), and a larger part of TiN particles are dissolved and lose the effective pinning of the austenite grain boundary of the welding heat affected zone, Ca (O, S) particles which are proper in quantity, fine in size and uniformly distributed in steel pin the austenite grain boundary of the welding heat affected zone, inhibit the austenite grain growth of the high-temperature area in the welding heat affected zone and improve the low-temperature toughness and the crack resistance of the coarse-grain heat affected zone;
3) the method ensures that sulfides are fully spheroidized, and meanwhile, the quantity of Ca (O, S) particles (namely inclusions) is excellent in low-temperature toughness, crack resistance and fatigue resistance of a base metal steel plate and a welding joint.
62≤[(HThickness of board)×(ξNot recrystallized)×(TStopping cooling)]/[(TFinish rolling)×(VCooling rate)×Ceq]≤319，
1) The low-temperature controlled rolling effect of the steel plate is ensured to be obvious, and the sizes of the eutectoid ferrite grains and the lower bainite crystal clusters are uniform and fine;
2) ensuring that the microstructure of the finished steel plate is a hardened uniform fine ferrite and uniform fine lower bainite structure, wherein the ferrite content is not more than 15 percent; therefore, the tensile curve of the steel plate shows a continuous yield state, and high strength, high toughness (crack resistance and crack arrest characteristics), low yield ratio and smaller performance anisotropy are obtained, which is one of the key technologies of the invention.
In the composition design of the steel of the invention:
c has great influence on the strength, low-temperature toughness, elongation and weldability of the TMCP steel plate, and the C content in the steel is expected to be controlled to be lower from the viewpoint of improving the low-temperature toughness and weldability of the TMCP steel plate; however, from the perspective of low yield ratio realization, strength and toughness, strong plastic matching, ultralow temperature toughness, and microstructure control and manufacturing cost in the production and manufacturing process of steel plate steel, the content of C is not easily controlled to be too low, too low C content easily causes too high grain boundary mobility, large grains of the base metal steel plate and the welding HAZ, and seriously degrades the low temperature toughness of the base metal steel plate and the welding HAZ, and the steel plate is difficult to realize low yield ratio; the reasonable range of the factor C content is 0.06% -0.10%.
Si promotes molten steel deoxidation and can improve the strength of a steel plate, but Si deoxidizes little by adopting Al, Si can improve the strength of the steel plate, but Si seriously damages ultralow-temperature toughness, elongation and weldability of the steel plate, particularly under the condition of large heat input welding, Si not only promotes M-A island formation, but also forms larger M-A islands, increases the number of M-A islands, is unevenly distributed, and seriously damages the toughness of a welding Heat Affected Zone (HAZ), so the Si content in the steel is controlled to be as low as possible, and the Si content is controlled to be 0.01-0.20% in consideration of the economy and operability of a steelmaking process.
Mn, the most important alloying element, improves the strength of the steel sheet, expands the austenite phase region, and reduces Ar in the steel1、Ar3Point temperature, refining TMCP steel plate microstructure to improve steel plate low temperature toughness, promoting low temperature phase transformation structure formation and improving steel plate strength; however, Mn is easy to segregate in the molten steel solidification process, and particularly when the Mn content is high, the Mn not only causes difficulty in casting operation and is easy to generate conjugate segregation with elements such as C, P, S and the like, so that segregation/porosity of the central part of a casting blank and enrichment of oxygen-sulfur inclusions are increased, and serious central region segregation of the casting blank is easy to form abnormal structures in the subsequent rolling and welding processes, so that low-temperature toughness of a steel plate is low and a welding joint is cracked; when the content of Mn is too high, the control of the longitudinal and transverse anisotropy and the low yield ratio of the steel plate is difficult; therefore, the Mn content is 1.35-1.65%.
P as harmful impurities in the steel has great damage effect on the mechanical properties of the steel, particularly the ultralow-temperature impact toughness, the elongation, the weldability (particularly the high heat input weldability) and the performance of a welding joint, and the lower the requirement is, the better the theoretical requirement is; however, considering the steel-making operability and the steel-making cost, the P content of the TMCP steel plate which requires large heat input welding, toughness at-50 ℃ and excellent strength toughness/strong plasticity matching needs to be controlled to be less than or equal to 0.013 percent.
S has a great damage effect on the low-temperature toughness of steel as harmful inclusions in the steel, more importantly, S is combined with Mn in the steel to form MnS inclusions, the plasticity of MnS enables the MnS to extend along the rolling direction in the hot rolling process to form MnS inclusion bands along the rolling direction, the low-temperature impact toughness, the elongation, the Z-direction performance, the weldability and the weld joint performance of a steel plate are seriously damaged, and simultaneously S is also a main element generating hot brittleness in the hot rolling process, and the lower the S is required to be, the better the S is theoretically required to be; however, considering the steel-making operability, steel-making cost and logistics smoothness principle, the S content of the TMCP steel plate which requires excellent weldability, toughness at-50 ℃ and excellent strength-toughness/strong-plasticity matching needs to be controlled to be less than or equal to 0.003 percent.
Cu is also an austenite stabilizing element, and the addition of Cu can also reduce Ar1、Ar3The point temperature improves the hardenability of the steel plate and the atmospheric corrosion resistance of the steel plate, refines the TMCP steel plate microstructure and improves the ultralow temperature toughness of the TMCP steel plate; however, the addition of Cu is too much and is higher than 0.45 percent, which easily causes the problems of copper brittleness, surface cracking of casting blanks and internal cracking and especially the performance degradation of thick steel plate welding joints; the addition amount of Cu is too small, less than 0.10%, and the effect is small; therefore, the Cu content is controlled between 0.10 percent and 0.45 percent.
The addition of Ni can not only improve the dislocation mobility in a ferrite phase, promote the dislocation cross slip and improve the intrinsic ductility and toughness of ferrite grains and bainite laths; in addition, Ni acts as a strong austenite stabilizing element, greatly reducing Ar1、Ar3The point temperature is adopted, the driving force of the phase transformation from austenite to ferrite is improved, so that the phase transformation of austenite is caused at a lower temperature, the microstructure of the TMCP steel plate is greatly refined, the orientation angle between bainite laths is increased, the expansion resistance of cracks in bainite crystal groups is improved, and the ultralow temperature toughness of the TMCP steel plate is greatly improved, so that Ni has the function of simultaneously improving the strength, the elongation and the low temperature toughness of the TMCP steel plate, particularly the crack resistance and crack arrest characteristics; ni can be added into steelSo as to reduce the copper brittleness of the copper-containing steel, reduce intergranular cracking in the hot rolling process and improve the atmospheric corrosion resistance of the steel plate. Therefore, theoretically, the higher the Ni content in the steel is in a certain range, the better the Ni content is, but the too high Ni content can harden the welding heat affected zone, and is unfavorable for the weldability of the steel plate and the SR performance of the welded joint; but also greatly improves the yield ratio of the steel plate and is very unfavorable for controlling the low yield ratio; meanwhile, Ni is a very precious element, and the content of Ni is controlled between 0.10 percent and 0.50 percent in consideration of cost performance.
Cr is used as a weak carbide forming element, and the added Cr not only improves the hardenability of the steel plate and promotes the formation of a low-temperature phase transformation product-bainite, but also increases the meta-position difference of bainite laths, increases the resistance of cracks passing through bainite crystal groups, and has the function of improving the toughness of the steel plate to a certain extent while improving the strength of the steel plate; however, when the amount of Cr added is too large, weldability of the steel sheet is seriously impaired, and particularly, weld HAZ is seriously deteriorated in large heat input welding; however, for a 60 kg TMCP steel plate, a certain Cr content is required to ensure that the steel plate has sufficient hardenability; therefore, the Cr content is controlled between 0.10 percent and 0.30 percent.
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 TMCP steel plate and simultaneously reduces the low-temperature toughness and the elongation of the TMCP steel plate; when Mo is excessively added, the elongation, the large heat input weldability and the welded joint performance of the steel plate are seriously damaged, and the production cost of the steel plate 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 steel plate, and the ultralow-temperature toughness and weldability of the steel plate are effectively improved; therefore, the Mo content is controlled between 0.10% and 0.30% by comprehensively considering the phase change strengthening effect of the Mo, the influence on the low-temperature toughness, the elongation and the weldability of the base steel plate and cost factors.
The purpose of adding trace Nb element is to control rolling without recrystallization and improve the strength and toughness of the TMCP steel plate, when the addition amount of Nb is less than 0.010 percent, the strengthening capability of the TMCP steel plate is insufficient except the rolling control function which can not be effectively exerted; when the addition amount of Nb exceeds 0.040%, not only the formation of upper bainite (Bu) and the secondary precipitation embrittlement action of Nb (C, N) under the condition of large heat input welding are induced, but also the low-temperature toughness of a heat-affected zone (HAZ) of large heat input welding is seriously damaged; but also easily causes severe anisotropy of longitudinal and transverse properties of the steel plate; therefore, the Nb content is controlled between 0.010 percent and 0.040 percent, the optimal rolling control effect is obtained, the toughness and the small longitudinal and transverse performance anisotropy of the large heat input welding HAZ are not damaged while the strength and toughness/strong plasticity matching of the TMCP steel plate is realized.
The purpose of adding a trace amount of Ti is to combine with N in the steel to generate TiN particles with high stability, control the growth of austenite grains in a welding HAZ region, inhibit the generation of coarse FSP, Bu and other brittle tissues, and improve the weldability of the steel, the low-temperature toughness and the crack resistance/crack arrest characteristics of the HAZ. The content of Ti added in the steel is matched with the content of N in the steel, and the matching principle is that TiN cannot be precipitated in liquid molten steel and must be precipitated in a solid phase; when the content of Ti added is too small (< 0.008%), the quantity of formed TiN particles is insufficient, and the defects of inhibiting the growth of austenite grains of HAZ and inhibiting the generation of coarse FSP, Bu and other brittle tissues are not enough to improve the low-temperature toughness of HAZ; when the Ti content is excessive (> 0.015%), large-size TiN particles can be separated out, and the large-size TiN particles can not inhibit the growth of the HAZ austenite grains but become the starting point of crack initiation; therefore, the optimal control range of the Ti content is 0.008 to 0.015 percent.
Als in the steel sheet can fix the free [ N ] in the steel]More importantly, the HAZ free [ N ] in the welding heat affected zone is reduced]The precipitation of ferrite in the welding cooling circulation is promoted, the formation of a massive M-A island is inhibited, and the low-temperature impact toughness effect of the large heat input welding HAZ is improved; therefore, the lower limit of Als is controlled to be 0.030%; however, excessive addition of Als to the steel not only causes casting difficulties, but also forms a large amount of dispersed acicular Al in the steel2O3Inclusions which impair the soundness of the steel sheet inner quality, low-temperature toughness and large heat input weldability; in addition, Als also promotes greater heat input weldingIn the process, the block M-A is formed, and the crack resistance/crack arrest characteristic of the welding joint is seriously deteriorated; therefore, the upper limit of Als is controlled to 0.060%.
The control range of N corresponds to the control range of Ti, and Ti/N is optimal to be 2.0-2.5 for the high heat input welded steel plate. The content of N is too low, the quantity of generated TiN particles is small, the size is large, the effect of improving the weldability of steel cannot be achieved, and the weldability is harmful; however, if the N content is too high, the free [ N ] in the steel increases, and particularly, the free [ N ] content in the Heat Affected Zone (HAZ) sharply increases under high heat input welding conditions, which seriously impairs the low temperature toughness of the HAZ and deteriorates the weldability of the steel. Therefore, the content of N is controlled to be less than or equal to 0.0050 percent.
Ca treatment is carried out on the steel, on one hand, the molten steel can be further purified, and on the other hand, the sulfide in the steel is subjected to denaturation treatment, so that the steel becomes non-deformable, stable and fine spherical sulfide, the hot brittleness of S is inhibited, the low-temperature toughness and Z-direction performance of the steel are improved, and the anisotropy of the toughness of the steel plate is improved; 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 Ca addition is too high, the formed Ca (O, S) has too large size, the number of inclusions in the steel is increased, the brittleness is also increased, the steel can become a fracture crack starting point, the low-temperature toughness and the weldability of the steel are reduced, and meanwhile, the steel purity and the polluted molten steel are also reduced; therefore, the appropriate range of the Ca content is 0.0010% to 0.0030%.
The invention relates to a method for manufacturing a YP500 MPa-grade steel plate with low yield ratio, high toughness and high weldability, which comprises the following steps:
1) smelting and casting
Smelting and continuously casting the components into a plate blank; the continuous casting soft reduction rate is controlled between 2 percent and 4 percent, and the pouring temperature of the tundish is less than or equal to 1550 ℃;
2) heating the plate blank, wherein the heating temperature is controlled to be 1080-1140 ℃;
3) rolling;
the rolling starting temperature is controlled to be 750-800 ℃, the rolling pass reduction rate is more than or equal to 7 percent, the cumulative reduction rate is more than or equal to 45 percent, and the final rolling temperature is 740-780 ℃;
4) cooling down
After rolling control is finished, the steel plate is conveyed to cooling equipment, the steel plate is rapidly cooled, the cooling temperature of the steel plate is 720-760 ℃, the cooling speed is more than or equal to 6 ℃/s, the cooling stopping temperature is less than or equal to 400 ℃, then the steel plate enters a slow cooling box or a slow cooling pit for slow cooling hydrogen diffusion treatment, and the slow cooling process is that the temperature of the surface of the steel plate is kept for at least 24 hours under the condition that the temperature is more than 300 ℃.
The casting process adopts a continuous casting process, the casting temperature is mainly controlled in the continuous casting process, the casting temperature of the molten steel in the tundish is less than or equal to 1550 ℃, and a low-temperature casting method is better so as to refine the original as-cast structure. In order to control the center conjugate segregation of the continuous casting billet, a soft reduction process is adopted, and the soft reduction amount is controlled to be between 2 and 4 percent.
In order to ensure that initial austenite grains are uniform and fine, a slab low-temperature heating process is required, and meanwhile, complete solid solution of a microalloying element Nb is also required. The heating temperature of the plate blank is controlled between 1080 ℃ and 1140 ℃, so that the austenite grain size of the original plate blank is uniform and fine.
The rolling temperature of the non-recrystallization controlled rolling is 750-800 ℃, the rolling pass reduction rate is more than or equal to 7%, the cumulative reduction rate is more than or equal to 45%, and the final rolling temperature is 740-780 ℃.
After the rolling control is finished, the steel plate is immediately conveyed to accelerated cooling equipment at the maximum conveying speed of the roller way, and then accelerated cooling is carried out on the steel plate; the steel plate is cooled at the temperature of 720-760 ℃, the cooling speed is more than or equal to 6 ℃/s, the accelerated cooling and cooling stopping temperature is less than or equal to 400 ℃, then the steel plate enters a slow cooling box or a slow cooling pit for slow cooling and hydrogen diffusion treatment, and the slow cooling process is that the steel plate is kept warm for at least 24 hours under the condition that the surface temperature of the steel plate is more than 300 ℃.
The invention has the beneficial effects that:
according to the invention, through adding a small amount of alloy elements Cu, Ni, Cr and Mo, designing the composition at relatively low cost and matching with a corresponding TMCP (thermal mechanical control processing) process, YP500MPa 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 steel plate are collectively shown in the aspects of high strength, low yield ratio, excellent low-temperature toughness (crack resistance and crack arrest characteristics) and small performance anisotropy, the weldability (especially large heat input weldability) of the steel plate is also excellent, the key technical problems that the steel plate is low in C content, high in manganese, low in carbon equivalent, low in cost, high in strength, low in yield ratio, high in toughness, small in performance anisotropy, excellent in weldability and the like, conflict with each other in component design and process design and difficult to reconcile are successfully solved, and the safety service performance of a large heavy steel structure is 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 the microstructure of the steel of 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 4 are process parameters of the embodiment of the invention, and table 5 is performance parameters of the steel of the embodiment of the invention.
As is clear from FIG. 1, the microstructure of the steel sheet was a small amount of hardened uniformly fine equiaxed ferrite + fine uniform lower bainite, and the average grain size of the microstructure was 15 μm or less.
According to the invention, through adding a small amount of alloy elements Cu, Ni, Cr and Mo, combining component design at relatively low cost and matching with a corresponding TMCP (thermo mechanical processing) process, the matching potential between the component design and the TMCP process is fully excavated, the technical advantages of equipment of a production line of the Bao steel thick plate are exerted, and the YP500 MPa-level low yield ratio TMCP steel plate with excellent mechanical property and weldability is successfully produced in batches by taking green and environment-friendly manufacturing process and service process as targets.
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 high-added-value centralized representation of the steel plate has high strength, low yield ratio and excellent low-temperature toughness (namely crack resistance and crack arrest characteristics), the weldability (especially larger heat input weldability) of the steel plate is also excellent while the high-performance high-added-value centralized representation of the steel plate has high strength, low yield ratio, excellent low-temperature toughness (crack arrest characteristics) and smaller performance anisotropy, the key technical problems that the low C content, the high manganese content, the low carbon equivalent, the low cost, the high strength, the low yield ratio, the high toughness, the smaller performance anisotropy, the excellent weldability and the like conflict with each other in component design and process design and are difficult to reconcile are successfully solved, and the safety service performance of a large heavy steel structure is 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 invention has the advantages of simple production process and easy process control without adding any equipment, can be popularized to all medium plate manufacturers with accelerated cooling equipment, and has strong adaptability, environmental protection and extremely high economy.
At present, a production line of a thick plate of 5m Bao steel stock is already supplied for 2137 tons of Wuhan Jianghhan seven-bridge engineering in batches, the maximum plate thickness reaches 65mm, and the grade of a steel plate is Q500qE (requiring-40 ℃ KV2The single value is more than or equal to 120J, the shearing area ratio FA is more than or equal to 75 percent), the steel plate processing, welding and steel member manufacturing characteristics are excellent, and particularly the low-temperature crack resistance and crack arrest characteristics, the weldability and the extremely low yield ratio of the steel plate are highly praised by users.
Figure BDA0002347413580000131
Figure BDA0002347413580000141
Figure BDA0002347413580000151

Claims (6)

1. The YP500 MPa-grade steel plate with low yield ratio, high toughness and high weldability comprises the following components in percentage by weight:
C：0.06％～0.10％
Si：0.01～0.20％
Mn：1.35％～1.65％
P：≤0.013％
S：≤0.0030％
Cu：0.10％～0.45％
Ni：0.10％～0.50％
Cr：0.10％～0.30％
Mo：0.10％～0.30％
Nb：0.010％～0.040％
Ti：0.008％～0.015％
Als：0.025％～0.060％
N：≤0.0050％
Ca：0.0010％～0.0030％，
the balance of Fe and other inevitable impurities; and, the contents of the above elements must satisfy the following relationship at the same time:
(％C)×[(％Ceq)+0.67(％P)+0.43(％S)+0.59(％Nb)]≤0.046；
Mneq/C is more than or equal to 16 and less than or equal to 36, wherein Mneq is the equivalent of manganese,
Mneq(％)＝(％Mn)+0.23(％Cu)+0.76(％Ni)；
Ti/N is between 2.0 and 3.0;
ca treatment, the Ca/S ratio is controlled between 1.0-3.0, and the (% Ca) × (% S)0.28 is less than or equal to 1.5 × 10-3；
62≤[(HThickness of board)×(ξNot recrystallized)×(TStopping cooling)]/[(TFinish rolling)×(VCooling rate)×Ceq]Less than or equal to 319, wherein,
Hthickness of boardThe thickness of the finished steel plate is in mm;
ξnot recrystallizedThe cumulative reduction in the unrecrystallized region is expressed in units of%;
Tstopping coolingTo accelerate the cooling stop temperature, in units of;
Tfinish rollingIs not knotted againThe final rolling temperature of the crystal controlled rolling is in units of;
Vcooling rateThe cooling speed for accelerating cooling is expressed in ℃/s;
ceq is the carbon equivalent of the carbon,
ceq (%) (% C) + (% Mn)/6+ (% Si)/24+ (% Ni)/40+ (% Cr)/5+ (% Mo)/4+ (% V)/14, unit%.
2. The low yield ratio, high toughness and high weldability YP500MPa grade steel sheet according to claim 1 wherein the microstructure of said steel sheet is a small amount of fine ferrite + lower bainite distributed in dispersion and the microstructure has an average grain size below 15 μm.
3. The low yield ratio, high toughness and high weldability YP500MPa grade steel plate according to claim 1 or 2, characterized in that the tensile strength of the steel plate is not less than 630MPa, the yield strength is not less than 500MPa, and the-50 ℃ transverse impact toughness KV is not less than2More than or equal to 120J (the shearing area FA is more than or equal to 75 percent) and the yield ratio YR is less than or equal to 0.85.
4. The method for producing a low yield ratio, high toughness and high weldability YP500MPa grade steel sheet 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; the continuous casting soft reduction rate is controlled between 2 percent and 4 percent, and the pouring temperature of the tundish is less than or equal to 1550 ℃;
2) heating the plate blank, wherein the heating temperature is controlled to be 1080-1140 ℃;
3) rolling;
the rolling starting temperature is controlled to be 750-800 ℃, the rolling pass reduction rate is more than or equal to 7 percent, the cumulative reduction rate is more than or equal to 45 percent, and the final rolling temperature is 740-780 ℃;
4) cooling down
After rolling control is finished, conveying the steel plate to cooling equipment, and then carrying out accelerated cooling on the steel plate, wherein the starting cooling temperature of the steel plate is 720-760 ℃, the cooling speed is more than or equal to 6 ℃/s, and the stopping cooling temperature is less than or equal to 400 ℃; and then the steel plate enters a slow cooling box or a slow cooling pit to carry out slow cooling hydrogen diffusion treatment, and the slow cooling process is to carry out heat preservation for at least 24 hours under the condition that the surface temperature of the steel plate is more than 300 ℃.
5. The method for producing a low yield ratio, high toughness and high weldability YP500MPa grade steel sheet according to claim 4 wherein the microstructure of said steel sheet is a small amount of fine ferrite + lower 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 YP500 MPa-grade steel plate with low yield ratio, high toughness and high weldability according to claim 4, characterized in that the tensile strength of the steel plate is not less than 630MPa, the yield strength is not less than 500MPa, and the lateral impact toughness KV at-50 ℃ is not less than KV2More than or equal to 120J (the shearing area FA is more than or equal to 75 percent) and the yield ratio YR is less than or equal to 0.85.
CN201911400868.XA 2019-12-30 2019-12-30 YP500 MPa-grade steel plate with low yield ratio, high toughness and high weldability and manufacturing method thereof Pending CN112746219A (en)

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CN113549828A (en) * 2021-07-13 2021-10-26 鞍钢股份有限公司 Low-yield-ratio ultrahigh-strength marine steel and manufacturing method thereof
CN115537647A (en) * 2021-06-30 2022-12-30 宝山钢铁股份有限公司 High-toughness, low-yield-ratio and low-longitudinal-transverse-strength anisotropic 600 MPa-grade steel plate and manufacturing method thereof

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JP2015098642A (en) * 2013-11-19 2015-05-28 新日鐵住金株式会社 Steel sheet

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JP2015098642A (en) * 2013-11-19 2015-05-28 新日鐵住金株式会社 Steel sheet

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Publication number Priority date Publication date Assignee Title
CN115537647A (en) * 2021-06-30 2022-12-30 宝山钢铁股份有限公司 High-toughness, low-yield-ratio and low-longitudinal-transverse-strength anisotropic 600 MPa-grade steel plate and manufacturing method thereof
CN115537647B (en) * 2021-06-30 2023-10-13 宝山钢铁股份有限公司 High-toughness, low-yield ratio and low-longitudinal-transverse-strength anisotropic 600 MPa-grade steel plate and manufacturing method thereof
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