CN111621694B - Low-cost high-crack-resistance super-thick steel plate and manufacturing method thereof - Google Patents
Low-cost high-crack-resistance super-thick steel plate and manufacturing method thereof Download PDFInfo
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Abstract
The low-cost and high-crack-arresting super-thick steel plate comprises the following components in percentage by weight: c: 0.050% -0.080%, Si is less than or equal to 0.15%, Mn: 1.65-1.95 percent of Ni, less than or equal to 0.013 percent of P, less than or equal to 0.003 percent of S, less than or equal to 0.20 percent of Cu, less than or equal to 0.20 percent of Ni, less than or equal to 0.15 percent of Mo, Ti: 0.006% -0.015%, Nb: 0.015-0.030%, N is less than or equal to 0.0050%, Al: 0.035-0.065%, Ca: 0.0010 to 0.0040 percent, and the balance of Fe and inevitable impurities. The invention adopts a component system of ultralow C, low Si, high Mn, Nb microalloying and ultramicro Ti treatment, and obtains a high crack arrest steel plate (Kca (-10 ℃) with excellent weldability and more than or equal to 8000N/mm, wherein the yield strength of the steel plate is more than or equal to 460MPa, the tensile strength of the steel plate is 570-720 MPa, the summer specific impact energy (single value) at minus 50 ℃ is more than or equal to 100J, and the weldability is more than or equal to 8000N/mm3/2】。
Description
Technical Field
The invention relates to a low-cost high-crack-arrest super-thick steel plate and a manufacturing method thereof, which are particularly suitable for manufacturing large VLCC container ships, large offshore wind power pile legs, offshore platforms (including offshore engineering machinery and marine floating cranes) and steel structures of sea-crossing bridges.
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 strength and toughness/strong plasticity matching, crack resistance, fatigue resistance and weldability (especially large heat input weldability) of steel, namely, the comprehensive mechanical property and service performance of the steel plate are greatly improved while the lower manufacturing cost is maintained, so that the cost is saved by reducing the consumption of steel, and the self weight, stability and safety of steel components are reduced. At present, the research surge of developing a new generation of high-performance steel materials is raised worldwide, and better microstructure matching is obtained through alloy combination design, innovative controlled rolling/TMCP technology and heat treatment process, so that the steel plate has better strength and toughness, strong plasticity matching, seawater corrosion resistance, welding property, fatigue resistance and crack arrest property.
The prior art has a microstructure of thick Steel plate with Yield Strength of 415MPa or more, which is mainly ferrite + pearlite or ferrite + pearlite (including transformed pearlite) + a small amount of bainite, and The production process includes normalizing, normalizing rolling, thermomechanical rolling (TMR) and TMCP, The Steel plate has excellent (ultra) Low temperature toughness, weldability and cold-hot processing characteristics, and is widely applicable to large heavy Steel STRUCTURES such as building STRUCTURES, bridge STRUCTURES, ship STRUCTURES and ocean platforms (see The fire (1986) international Symposium and extreme on offset properties and Engineering, 1986, Tokyo, Japan, 354, DEVELOPMENT IN MATERIALS FOR ARCTIC OFFSHORUCTURES, Structural Steel Plates FOR Engineering by multi-purpose Steel product and lightweight alloy Engineering, 1986, Tokyo, Japan, and 354, The technical report of Steel Engineering systems, Japan, Inc. 168, Japan, and Steel manufacturing, Inc. 72, and Steel manufacturing by Steel manufacturing method, manufacturing and manufacturing method, manufacturing and manufacturing method of manufacturing, manufacturing and manufacturing process of manufacturing, manufacturing, accelerated Cooling 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; US Patent 4629505, WO 01/59167a1), but the steel sheet does not relate to brittle crack propagation resistance, i.e. high crack arrest performance. Japanese Sumitomo successfully developed a thick steel plate FCA (Steel plate with fatigue crack propagation suppression, No. 3298544) with excellent weldability, fatigue crack propagation resistance, and yield strength of 355 MPa; a thick steel plate having excellent fatigue crack-inhibiting properties, Japanese patent application laid-open No. Hei 10-60575; japan Ship building institute culture collection Vol.2001(2001) No.190, P507; まてりあ Vol.43(2014) No.2, P148, has achieved good practical effects and realized mass production, but the development of steel plates has not been concerned with the high crack arrest characteristics of super thick steel plates.
The series disclosed by Chinese patents ZL201410300713.X, ZL201310244712.3, ZL201310244706.8, ZL201310124065.2, ZL201310244713.8, ZL201210209637.2 and ZL201410815614.5 and application number 201710183350.X can weld various low-temperature steel plates under high heat input, in order to ensure the low-temperature toughness of a welding heat affected zone under high heat input, a certain amount of noble alloy elements Cu and Ni are added into the steel, the steel plate has better welding performance under ultra-high heat input, but the toughness of the welding heat affected zone has certain fluctuation, the manufacturing cost of the steel plate is higher, and the crack arrest characteristic of the super-thick steel plate is not involved.
Disclosure of Invention
The invention aims to provide a low-cost high-crack-arrest super-thick steel plate and a manufacturing method thereof, which are particularly suitable for hull structures, ocean platforms, bridge structures, building structures, ocean wind tower structures, maritime work machines and the like in ice sea areas and can realize low-cost stable batch industrial production when high strength, high toughness, excellent weldability and high crack arrest characteristics are obtained.
In order to achieve the purpose, the technical scheme of the invention is as follows:
the reason why the super-thick steel plate with high crack resistance is one of the most difficult varieties in thick plate products is that the steel plate not only requires ultralow C and low carbon equivalent Ceq, high strength, excellent low-temperature toughness and weldability (especially high heat input weldability), but also has excellent crack resistance, especially the super-thick steel plate can resist crack propagation, so that bending and crack tip passivation are continuously generated in the crack propagation process, and the crack resistance of the super-thick steel plate is improved. The method not only requires that the microstructure of the super-thick steel plate is uniform and fine and has a certain amount of low-carbon bainite with reasonable distribution, but also the microstructure and the texture in the plate thickness direction present certain gradient distribution, the surface of the steel plate and the 1/4 thickness area have uniform and fine microstructures, and the central part of the steel plate has more developed (100) <011> - (112) <110> texture groups; how to realize uniform and fine ferrite and bainite (F + B) two-phase structures, and controlling the quantity, hardness, morphology and distribution of bainite reasonably, and simultaneously, the microstructure and texture of the steel plate along the plate thickness direction present certain gradient distribution, and the balance among high strength, excellent low-temperature toughness, crack arrest characteristics and weldability of the super-thick steel plate is one of the biggest difficulties of the product under the condition of ultralow C and low carbon equivalent Ceq, and is also a key core technology.
Therefore, in the aspects of key technical route, components and process design, the invention integrates key factors influencing the chemical components (ultralow C and low carbon equivalent Ceq), the strength, the low-temperature toughness, the weldability, particularly the crack arrest characteristic and the like of the super-thick steel plate, starts from the chemical component design of the super-thick steel plate, creatively adopts the ultralow-carbon C-low-Si-high-Mn-Nb series low alloy steel as the base, and controls the (% C) x [4.15 (% Si) + (% Mn)]≤0.21、10≤[(Ar3+30℃)×ξ1]/[ξ2×H]≤37、220≤[(Ar3-30℃)×ξ2]H ≦ 420 (where ξ1The rolling reduction is the accumulated rolling reduction rate of the austenite single-phase zone without recrystallization and rolling control, and the unit is; xi2Rolling accumulated pressure for ferrite/austenite two-phase regionLower rate, unit is%; h is the thickness of the steel sheet in mm), Ca treatment is performed and the Ca/S ratio is controlled to be 1.0 to 3.0 (% Ca) x (% S)0.28≤2.5×10－3Optimizing TMCP process to make the microstructure of the finished steel plate be a ferrite + bainite evenly dispersed and distributed, the average grain size of the microstructure is below 10 μm, and the central part of the steel plate has developed (100)<011>～(112)<110>And (4) texture groups.
Specifically, the low-cost and high-crack-arrest super-thick steel plate comprises the following components in percentage by weight:
C：0.050％～0.080％
Si：≤0.15％
Mn：1.65％～1.95％
P：≤0.013％
S：≤0.003％
Cu：≤0.20％
Ni：≤0.20％
Mo：≤0.15％
Ti：0.006％～0.015％
Nb：0.015％～0.030％
N：≤0.0050％
Al：0.035％～0.065％
Ca：0.0010％～0.0040％
the balance of Fe and inevitable impurities; and the content of the elements must satisfy the following relation at the same time:
(％C)×[4.15(％Si)+(％Mn)]≤0.21；
10≤[(Ar3+30℃)×ξ1]/[ξ2×H]less than or equal to 37, wherein,
Ar3＝910-310(％C)-80(％Mn)-20(％Cu)-15(％Cr)-55(％Ni)-80(％Mo)-0.35(H-8)；ξ1the rolling reduction is the accumulated rolling reduction rate of the austenite single-phase zone without recrystallization and rolling control, and the unit is; xi2The rolling reduction is the accumulated rolling reduction rate of a ferrite/austenite two-phase region controlled rolling, and the unit is percent; h is the thickness of the steel plate, and the unit is mm;
220≤[(Ar3-30℃)×ξ2]h is less than or equal to 420, wherein,
Ar3＝910-310(％C)-80(％Mn)-20(％Cu)-15(％Cr)-55(％Ni)-80(％Mo)-0.35(H-8)；ξ2the rolling reduction is the accumulated rolling reduction rate of a ferrite/austenite two-phase region controlled rolling, and the unit is percent; h is the thickness of the steel plate, and the unit is mm;
ca treatment, and the Ca/S ratio is controlled to be 1.0-3.0 and Ca x S0.28≤2.5×10－3。
The microstructure of the steel plate is a dual-phase structure of ferrite and bainite evenly dispersed and distributed, the average grain size of the microstructure is less than 10 mu m, and the central part of the steel plate has (100) <011> - (112) <110> texture groups.
The yield strength of the steel plate is more than or equal to 460MPa, the tensile strength is 570-720 MPa, the single value of the Charpy impact energy at-50 ℃ is more than or equal to 100J, Kca (-10 ℃), and the single value of the Charpy impact energy at-50 ℃ is more than or equal to 8000N/mm3/2。
In the composition design of the steel plate of the invention:
c is used as an important alloy element in steel and plays an important role in improving the strength of the steel plate, promoting the formation of second phase bainite and the uniformity of a microstructure, so that the steel must contain a certain amount of C; however, when the content of C in the steel is too high, the internal segregation of the steel plate is deteriorated, the low-temperature toughness and weldability of the steel plate are reduced, the control of the hardness, morphology, quantity and distribution of the second phase bainite is not facilitated, and the weldability, low-temperature toughness and crack arrest characteristics of the steel plate are seriously deteriorated; therefore, the proper content range of C is controlled to be 0.050% -0.080%.
Si can improve the strength of the steel plate, and more importantly, Si expands a medium-temperature phase transformation area, thereby being beneficial to controlling the quantity, the appearance, the hardness and the distribution of bainite; however, when the Si content in steel is high, segregation, low-temperature toughness, weldability, and crack arrest characteristics of the steel sheet are seriously deteriorated; therefore, the content range of Si is controlled to be less than or equal to 0.15 percent.
Mn as the most important alloying element in the steel not only improves the strength of the steel sheet, but also expands the austenite phase region and reduces Ar3Point temperature, refining TMCP steel plate ferrite grains and bainite crystal groups to improve the low-temperature toughness of the steel plate and promote the formation of bainite, and particularly when the content of C is low, the function of Mn is particularly obvious; however, Mn is easily added during solidification of molten steelSegregation (Mn segregation is not easy to eliminate or relieve in the subsequent manufacturing process), particularly when the content of C, Mn is high, not only is casting operation difficult, but also C-Mn-P-S conjugate segregation is easy to occur, so that serious solidification segregation and porosity occur in the central part of a casting blank, the serious casting blank central segregation is easy to form an abnormal structure (upper bainite with high carbon) in the subsequent TMCP and welding processes, so that the low-temperature toughness of a steel plate is deteriorated, and a welding joint is easy to crack and severe cracking of crack arrest characteristics, therefore, when the content of C is lower than 0.09%, the Mn content suitable for the cost is 1.65-1.95%.
P has great damage effect on low-temperature impact toughness, elongation, weldability and crack arrest characteristics of steel as harmful impurities in the steel, and the lower the requirement is, the better the theory is; but the content of P is controlled to be less than or equal to 0.013 percent in consideration of steelmaking operability and steelmaking cost.
S has great damage effect on low-temperature toughness and crack arrest characteristics (mainly strip-shaped sulfides) of steel as harmful inclusions in the steel, more importantly, the S is combined with Mn in the steel to form MnS inclusions, MnS plasticity enables MnS to extend along the rolling direction in the hot rolling process to form MnS inclusion strips along the rolling direction, the low-temperature impact toughness, crack arrest characteristics, elongation, Z-direction performance and weldability of a steel plate are seriously damaged, and meanwhile, the S is also a main element generating hot brittleness in the hot rolling process, and the lower the requirement is better in theory; but considering the steel-making operability, the steel-making cost and the principle of smooth material flow, the content of S is controlled to be less than or equal to 0.0030 percent.
According to the invention, Cu of not more than 0.20 percent, Ni of not more than 0.20 percent and Mo of not more than 0.15 percent can be properly added according to the thickness of the steel plate, the medium-low temperature regulation and control of a microstructure and the formation of bainite in the TMCP process are promoted, and the quantity, the size, the morphology and the distribution condition of two phases of ferrite and bainite are controlled, so that the strength, the low-temperature toughness and the crack arrest characteristic of the steel plate are improved.
The affinity of Ti and N is very large, 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 processes of heating and hot rolling a plate blank and improving the low-temperature toughness of a 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 toughness of the heat affected zone is improved; the effect of adding too little Ti (0.006%) is not great, when the addition amount of Ti exceeds 0.015%, the effect of further increasing the Ti content in the steel on refining the grains of the steel plate and improving the weldability of the steel plate is not great, and even when the Ti/N is too large, the Ti/N is not beneficial to refining the grains of the steel plate and even deteriorates the weldability of the steel plate; therefore, the suitable Ti content range is 0.007 to 0.015 percent.
The purpose of adding trace Nb element in the steel is to perform non-recrystallization controlled rolling, promote the formation of refined steel plate microstructure and bainite, improve the strength and toughness of the TMCP steel plate and improve the fatigue crack propagation resistance of the steel plate; when the addition amount of Nb is less than 0.010 percent, the forming capability of the steel plate bainite is small and the phase change strengthening capability is insufficient besides the rolling control effect which cannot be effectively exerted; when the amount of Nb added exceeds 0.030%, weldability of the steel sheet is seriously impaired, and therefore the Nb content is controlled to be between 0.015% and 0.030%.
The control range of N corresponds to the control range of Ti, and the Ti/N is optimal between 1.5 and 3.0 in order to improve the grain refining effect of the steel plate and improve the weldability of the steel plate. When the N content is too low and the Ti content is too high, the generated TiN particles are small in quantity and large in size, cannot play a role in improving the weldability and grain refinement of steel, and are harmful to the weldability and grain refinement of a steel plate; however, when 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 a large heat input welding condition, so that the low temperature toughness and crack arrest characteristics of the HAZ are seriously impaired, and the weldability of the steel is deteriorated; in addition, when the content of N is high, the surface of the plate blank has serious cracks, and the plate blank is scrapped when the surface of the plate blank is serious. Therefore, the content of N is controlled to be less than or equal to 0.0050 percent.
Als in steel can fix free [ N ] in steel]Removal of weld Heat Affected Zone (HAZ) free [ N ]]Improving the low temperature toughness and crack arrest characteristics of the welded HAZ; therefore, the lower limit of Als is controlled to be 0.035%; 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 impair the soundness of the steel sheet internal structure, low-temperature toughness, weldability, and crack arrest characteristics, and therefore the upper limit of Als is controlled to 0.065%.
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 of the steel plate, improve the crack arrest characteristic, 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, simultaneously reduce the purity of the steel, pollute molten steel and deteriorate the crack arrest characteristics of a steel plate; therefore, the appropriate range of the Ca content is 0.0010% to 0.0040%.
(% C) × [4.15 (% Si) + (% Mn) ] is less than or equal to 0.21, 1) inhibits the conjugate segregation of C, Mn, P and S in the process of molten steel solidification, reduces the segregation of the central part of a steel plate and associated inclusions (mainly MnS, aluminum silicon oxide and the like), improves the low-temperature toughness and crack arrest characteristics of the steel plate, and improves the weldability of the steel plate, particularly the weldability with large heat input; 2) the critical cooling speed of bainite phase transformation is reduced, ferrite/austenite (namely bainite) separation type phase transformation is promoted in the processes of ferrite/austenite two-phase zone controlled rolling and accelerated cooling, and ferrite and bainite (F + B) two-phase groups are realized, which is one of the key technologies of the invention.
10≤[(Ar3+30℃)×ξ1]/[ξ2×H]Less than or equal to 37, 1) ensuring that the microstructure of the super-thick steel plate is uniform and fine and has two-phase tissues with reasonable quantity, size and distribution; 2) the microstructure and texture in the thickness direction of the steel sheet showed a certain gradient distribution, the surface and 1/4 thickness regions of the steel sheet had a uniform and fine microstructure, the microstructure in the center of the steel sheet was slightly coarser than the surface and 1/4 thickness regions, but the center (100)<011>～(112)<110>The texture is developed, and the crack propagation inhibition and texture strengthening effects are strong; the full thickness of the super-thick steel plate is ensured to have high strength, high toughness and excellent crack arrest characteristics, which is one of the key technologies of the invention; wherein Ar is3＝910-310(％C)-80(％Mn)-20(％Cu)-15(％Cr)-55(％Ni)-80(％Mo)-0.35(H-8)；ξ1The rolling reduction is the accumulated rolling reduction rate of the austenite single-phase zone without recrystallization and rolling control, and the unit is; xi2The rolling reduction is the accumulated rolling reduction rate of a ferrite/austenite two-phase region controlled rolling, and the unit is percent; h is the thickness of the steel plate and is in mm.
220≤[(Ar3-30℃)×ξ2]the/H is less than or equal to 420, the proportion, the appearance and the distribution of a ferrite/bainite two-phase structure are reasonable while the size of a microstructure of the super-thick steel plate is further refined and homogenized; more importantly, the central part (100) of the super-thick steel plate is ensured<011>～(112)<110>When the texture group is developed, the amount of ferrite eutectoid in advance is proper and severe rolling deformation does not occur, so that the steel plate is ensured to have excellent low-temperature toughness, crack arrest characteristics and texture strengthening effect, and the crack arrest and crack arrest characteristics of the steel plate are also excellent while the super-thick steel plate obtains high strength and excellent toughness at low temperature, which is one of the key technologies of the invention; wherein the content of the first and second substances,
Ar3＝910-310(％C)-80(％Mn)-20(％Cu)-15(％Cr)-55(％Ni)-80(％Mo)-0.35(H-8)；ξ2the rolling reduction is the accumulated rolling reduction rate of a ferrite/austenite two-phase region controlled rolling, and the unit is percent; h is the thickness of the steel plate, and the unit is mm;
ca treatment and controlling the Ca/S ratio to be 1.0-3.0 and Ca x S0.28≤2.5×10－3: the method ensures the spheroidization of the sulfide, reduces the influence of inclusions on low-temperature toughness and weldability to the minimum, simultaneously, uniformly and finely distributes Ca (O, S) particles in the steel, refines the grain size of the steel plate, improves the crack arrest characteristic of the steel plate, inhibits the growth of austenite grains in a welding heat affected zone, and improves the weldability of the steel plate and the low-temperature toughness and the crack arrest characteristic of the welding heat affected zone.
The invention relates to a manufacturing method of a low-cost and high-crack-arrest super-thick steel plate, which comprises the following steps:
1) smelting and casting
Smelting and casting the components into a plate blank;
2) heating the plate blank, wherein the heating temperature is controlled to be 1080-1130 ℃;
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 3.5
The first stage is common rolling, continuous rolling is carried out by adopting the maximum rolling capacity of a rolling mill, the yield of a rolling line is improved to the maximum extent, and meanwhile, the deformed billet is ensured to be recrystallized, and austenite grains are refined;
the second stage of non-recrystallization controlled rolling in the single-phase austenite region, the rolling start temperature of controlled rolling is controlled at Ar3+50℃～Ar3+20 ℃, rolling pass reduction rate is more than or equal to 7%, cumulative reduction rate is more than or equal to 50%, and final rolling temperature is Ar3+30℃～Ar3；
The third stage is controlled rolling in ferrite/austenite two-phase region, and the rolling start temperature of controlled rolling is controlled at Ar3-40℃～Ar3Rolling pass reduction rate is more than or equal to 7 percent at minus 10 ℃, cumulative reduction rate is more than or equal to 28 percent, and final rolling temperature is Ar3-50℃～Ar3-20℃；
4) After the controlled rolling is finished, the steel plate is immediately conveyed to accelerated cooling equipment to carry out accelerated cooling on the steel plate; open cooling temperature Ar of steel plate3-60℃～Ar3The cooling speed is more than or equal to 6 ℃/s at minus 30 ℃, the cooling stopping temperature is 300-450 ℃, and then the steel plate is slowly cooled, wherein the slow cooling process is that the temperature of the steel plate surface is more than or equal to 250 ℃ and the temperature is kept for at least 24 hours.
In the manufacturing process of the steel plate of the invention:
according to the content ranges of C, Mn, Nb and Ti, the heating temperature of the plate blank is controlled between 1080 ℃ and 1130 ℃, so that the austenite grains of the plate blank are not abnormally grown while the Nb in the steel is completely dissolved into austenite in the heating process of the plate blank;
in the rolling process, the total compression ratio (slab thickness/finished steel plate thickness) of the steel plate is more than or equal to 3.5, 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; three-stage rolling is adopted, wherein,
the first stage is common rolling, continuous rolling is carried out by adopting the maximum rolling capacity of a rolling mill, the yield of a rolling line is improved to the maximum extent, and meanwhile, the deformed billet is ensured to be recrystallized, and austenite grains are refined;
the second stage of rolling in single-phase austenite region without recrystallization and controlled rolling according to the Nb content range in the steel to ensure the effect of rolling without recrystallizationThe rolling temperature is controlled at Ar3+50℃～Ar3+20 ℃, rolling pass reduction rate is more than or equal to 7%, cumulative reduction rate is more than or equal to 50%, and final rolling temperature is Ar3+30℃～Ar3。
The third stage is controlled rolling in a ferrite/austenite two-phase region.
The invention has the beneficial effects that:
the invention adopts a component system of ultralow C, low Si, high Mn, Nb microalloying and ultramicro Ti treatment, and obtains a high crack arrest steel plate (Kca (-10 ℃) with excellent weldability and more than or equal to 8000N/mm, wherein the yield strength of the steel plate is more than or equal to 460MPa, the tensile strength of the steel plate is 570-720 MPa, the summer specific impact energy (single value) at minus 50 ℃ is more than or equal to 100J, and the weldability is more than or equal to 8000N/mm3/2】。
The steel plate of the invention is combined with a special TMCP manufacturing process through the combined design of low-cost alloy elements, not only can produce the high-crack-arrest TMCP super-thick steel plate with excellent comprehensive performance with high efficiency and low cost, but also can greatly shorten the manufacturing period of the steel plate, create great value for enterprises and realize the green environmental protection of the manufacturing process. The high performance and high added value of the steel plate are collectively shown in that the steel plate has high strength, excellent low-temperature toughness and weldability, particularly has excellent crack arrest characteristic, realizes the manufacture with low alloy cost and low manufacturing process cost, successfully solves the problem of brittle fracture of a large heavy steel structure, and ensures the safety and reliability of the steel structure in the long-term service process; the good weldability saves the manufacturing cost of the user steel member, reduces the manufacturing difficulty of the member and shortens the manufacturing time of the user steel member.
Drawings
FIG. 1 is a photograph of a microstructure of a steel sheet of example 3 of the present invention multiplied by 500 times (1/4 thickness).
FIG. 2 is a photograph of a microstructure of a steel sheet of example 3 of the present invention multiplied by 500 times (1/2 thickness).
Detailed Description
The invention is further illustrated by the following examples and figures.
The compositions of the steel sheets of the examples of the present invention are shown in Table 1, tables 2 to 4 show the manufacturing processes of the steel sheets of the examples of the present invention, and Table 5 shows the performance parameters of the steel sheets of the examples of the present invention.
As can be seen from FIGS. 1 and 2, the microstructure of the steel sheet of the present invention is a two-phase structure of ferrite and bainite uniformly dispersed therein, the average grain size of the microstructure is 10 μm or less, and the central portion of the steel sheet has texture groups of (100) <011> to (112) <110 >.
The steel plate is combined with a special TMCP (thermal mechanical control processing) manufacturing process through simple low-cost alloy combination design, so that the ultra-thick steel plate with excellent comprehensive mechanical property and weldability and high crack-arrest performance is produced at low cost, the manufacturing period of the steel plate is greatly shortened, great value is created for enterprises, and the green environmental protection of the manufacturing process is realized. The high performance and high added value of the steel plate are collectively shown in that the steel plate has high strength, excellent low-temperature toughness and weldability, particularly has excellent crack arrest performance, can effectively inhibit crack propagation, eliminates brittle fracture of the steel plate, realizes low alloy cost and low manufacturing process cost, successfully solves the problem of poor crack arrest performance of a large heavy steel structure, and ensures the safety and reliability of the steel structure in a long-term service process; the good weldability saves the manufacturing cost of the user steel member, reduces the manufacturing difficulty of the member and shortens the manufacturing time of the user steel member.
The steel plate is mainly used for large heavy steel structures such as hull structures, ocean platforms, cross-sea bridges, offshore wind tower structures, port machinery and the like, and can realize stable batch industrial production with low cost.
With the development of national economy in China, ocean development and offshore large-capacity wind power construction have reached the daily agenda, at present, ocean engineering, offshore large-capacity wind power construction and related equipment manufacturing industry in China are not well developed, and high crack arrest ultra-thick TMCP steel plates, which are key materials in ocean engineering, offshore large-capacity wind power construction and related equipment manufacturing industry, have wide market prospects.
Claims (4)
1. The low-cost and high-crack-arresting super-thick steel plate comprises the following components in percentage by weight:
C：0.050％～0.080％
Si：≤0.15％
Mn：1.65％～1.95％
P：≤0.013％
S：≤0.003％
Cu：≤0.20％
Ni：≤0.20％
Mo：≤0.15％
Ti：0.006％～0.015％
Nb：0.015％～0.030％
N：≤0.0050％
Al：0.035％～0.065％
Ca：0.0010％～0.0040％
the balance of Fe and inevitable impurities; and the content of the elements must satisfy the following relation at the same time:
(％C)×[4.15(％Si)+(％Mn)]≤0.21；
10≤[(Ar3+30℃)×ξ1]/[ξ2×H]less than or equal to 37, wherein,
Ar3＝910-310(％C)-80(％Mn)-20(％Cu)-15(％Cr)-55(％Ni)-80(％Mo)-0.35(H-8)；ξ1the rolling reduction is the accumulated rolling reduction rate of the austenite single-phase zone without recrystallization and rolling control, and the unit is; xi2The rolling reduction is the accumulated rolling reduction rate of a ferrite/austenite two-phase region controlled rolling, and the unit is percent; h is the thickness of the steel plate, and the unit is mm;
220≤[(Ar3-30℃)×ξ2]h is less than or equal to 420, wherein,
Ar3＝910-310(％C)-80(％Mn)-20(％Cu)-15(％Cr)-55(％Ni)-80(％Mo)-0.35(H-8)；ξ2is ironThe accumulated reduction rate of the ferrite/austenite two-phase zone controlled rolling is expressed in unit; h is the thickness of the steel plate, and the unit is mm;
ca treatment, and the Ca/S ratio is controlled to be 1.0-3.0 and Ca x S0.28≤2.5×10－3；
The microstructure of the steel plate is a dual-phase structure of ferrite and bainite evenly dispersed and distributed, the average grain size of the microstructure is below 10 mu m, and the central part of the steel plate has (100) <011> - (112) <110> texture groups; the steel sheet is obtained by a manufacturing method comprising:
1) smelting and casting
Smelting and casting the components into a plate blank;
2) heating the plate blank, wherein the heating temperature is controlled to be 1080-1130 ℃;
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 3.5
The first stage is common rolling, continuous rolling is carried out by adopting the maximum rolling capacity of a rolling mill, the yield of a rolling line is improved to the maximum extent, and meanwhile, the deformed billet is ensured to be recrystallized, and austenite grains are refined;
the second stage of non-recrystallization controlled rolling in the single-phase austenite region, the rolling start temperature of controlled rolling is controlled at Ar3+50℃～Ar3+20 ℃, rolling pass reduction rate is more than or equal to 7%, cumulative reduction rate is more than or equal to 50%, and final rolling temperature is Ar3+30℃～Ar3；
The third stage is controlled rolling in ferrite/austenite two-phase region, and the rolling start temperature of controlled rolling is controlled at Ar3-40℃～Ar3Rolling pass reduction rate is more than or equal to 7 percent at minus 10 ℃, cumulative reduction rate is more than or equal to 28 percent, and final rolling temperature is Ar3-50℃～Ar3-20℃；
4) After the controlled rolling is finished, the steel plate is immediately conveyed to accelerated cooling equipment to carry out accelerated cooling on the steel plate; open cooling temperature Ar of steel plate3-60℃～Ar3The cooling speed is more than or equal to 6 ℃/s at minus 30 ℃, the cooling stopping temperature is 300-450 ℃, and then the steel plate is slowly cooled, wherein the slow cooling process is that the temperature of the steel plate surface is more than or equal to 250 ℃ and the temperature is kept for at least 24 hours.
2. The low-cost, high crack-arresting super-thick steel plate as claimed in claim 1, wherein said steel plate has a yield strength of 460MPa or more, a tensile strength of 570-720 MPa, a charpy impact energy of-50 ℃ of 100J or more, and a Kca of 8000N/mm or more at-10 ℃3/2。
3. The method for manufacturing a low-cost, high crack arrest super thick steel plate as claimed in claim 1, comprising the steps of:
1) smelting and casting
Smelting and casting a slab according to the composition of claim 1;
2) heating the plate blank, wherein the heating temperature is controlled to be 1080-1130 ℃;
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 3.5
The first stage is common rolling, continuous rolling is carried out by adopting the maximum rolling capacity of a rolling mill, the yield of a rolling line is improved to the maximum extent, and meanwhile, the deformed billet is ensured to be recrystallized, and austenite grains are refined;
the second stage of non-recrystallization controlled rolling in the single-phase austenite region, the rolling start temperature of controlled rolling is controlled at Ar3+50℃～Ar3+20 ℃, rolling pass reduction rate is more than or equal to 7%, cumulative reduction rate is more than or equal to 50%, and final rolling temperature is Ar3+30℃～Ar3；
The third stage is controlled rolling in ferrite/austenite two-phase region, and the rolling start temperature of controlled rolling is controlled at Ar3-40℃～Ar3Rolling pass reduction rate is more than or equal to 7 percent at minus 10 ℃, cumulative reduction rate is more than or equal to 28 percent, and final rolling temperature is Ar3-50℃～Ar3-20℃；
4) After the controlled rolling is finished, the steel plate is immediately conveyed to accelerated cooling equipment to carry out accelerated cooling on the steel plate; open cooling temperature Ar of steel plate3-60℃～Ar3The cooling speed is more than or equal to 6 ℃/s at minus 30 ℃, the cooling stopping temperature is 300-450 ℃, and then the steel plate is slowly cooled, wherein the slow cooling process is that the temperature of the steel plate surface is more than or equal to 250 ℃ and the temperature is kept for at least 24 hours.
4. The low cost of claim 3The manufacturing method of the super-thick steel plate with high crack resistance is characterized in that the yield strength of the steel plate is more than or equal to 460MPa, the tensile strength is 570-720 MPa, the single value of the Charpy impact energy at minus 50 ℃ is more than or equal to 100J, and the Kca at minus 10 ℃ is more than or equal to 8000N/mm3/2。
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