CN114000056A - Marine steel plate with yield strength of 960MPa grade and low yield ratio and preparation method thereof - Google Patents

Marine steel plate with yield strength of 960MPa grade and low yield ratio and preparation method thereof Download PDF

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CN114000056A
CN114000056A CN202111253774.1A CN202111253774A CN114000056A CN 114000056 A CN114000056 A CN 114000056A CN 202111253774 A CN202111253774 A CN 202111253774A CN 114000056 A CN114000056 A CN 114000056A
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steel plate
temperature
less
yield ratio
rolling
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尚成嘉
郭晖
喻异双
李秀程
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Yantai Institute Of Industrial Technology Beijing University Of Science And Technology
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Yantai Institute Of Industrial Technology Beijing University Of Science And Technology
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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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/46—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling metal immediately subsequent to continuous casting
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/58—Roll-force control; Roll-gap control
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/26—Methods of annealing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—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
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • 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
    • 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
    • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
    • 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
    • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite

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  • Physics & Mathematics (AREA)
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  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

The embodiment of the invention discloses a marine steel plate with yield strength of 960MPa grade and low yield ratio and a preparation method thereof, wherein the steel plate comprises the following chemical components in percentage by mass: c: 0.10 to 0.20%, Si: 0.10 to 0.30%, Mn: 1.00-1.50%, P: less than or equal to 0.010 percent, S: less than or equal to 0.005 percent, Cu: 0-0.50%, Cr: 0.20-0.60%, Ni: 0.50-3.00%, Mo: 0.20-0.80%, Co: 0.20 to 1.00%, Nb: 0-0.050%, V: 0.020 to 0.100%, Ti: 0.005-0.015%, B: 0.0005-0.0020%, and the balance of Fe and inevitable impurities, and carbon equivalent CEV is less than or equal to 0.75%. Based on the components, the medium and thick steel plate with high strength and toughness and low yield ratio is prepared through smelting, controlled rolling and controlled cooling processes, and (alpha + gamma) two-phase region annealing, complete austenitizing quenching and medium and low temperature tempering treatment processes. The yield strength R of the steel plate prepared by the inventioneHNot less than 960MPa, tensile strength Rm1100MPa or more, yield ratio YR or less than 0.95, elongation A after fracture of 12% or more, and impact toughness at-40 ℃ of 69J or more. Compared with the prior 960 MPa-grade medium plate, the invention has the advantages of good matching of strong plasticity and toughness, lower yield ratio and suitability for medium plate production.

Description

Marine steel plate with yield strength of 960MPa grade and low yield ratio and preparation method thereof
Technical Field
The invention relates to the technical field of steel materials, in particular to a marine steel plate with yield strength of 960MPa and low yield ratio and a preparation method thereof.
Background
With the intense investment in national infrastructure construction in recent years, high-strength grade structural steel has been widely used in the fields of engineering machinery, mining, crane trucks, ocean platforms, and the like, and thus higher requirements have been made on the mechanical properties of high-strength structural steel. The steel structure is required to have high strength to meet the requirement of light structure, and also has low yield ratio, excellent low-temperature toughness, weldability, corrosion resistance and the like to meet the requirements of safety, reliability, long service life and the like of the steel structure.
The 960 MPa-grade high-strength marine steel with good comprehensive performance and higher added value has obvious demand trend and is a hot steel grade researched and developed by various steel factories and scientific research institutions at present. Some advanced foreign iron and steel enterprises can stably supply materials at the level and have excellent performance, while domestic enterprises still have some defects in the aspect of production technology, and especially have technical bottlenecks in the production of plates with thicker specifications and steel plates with higher performance stability requirements.
Aiming at marine steel with yield strength of 960MPa, the conventional production process mainly comprises two processes of controlled rolling and controlled cooling (DQ + T) and quenching and tempering. The controlled rolling and controlled cooling (DQ + T) process can fully utilize the refining effect of austenite deformation on a quenched martensite structure during controlled rolling to improve the toughness of the steel plate, so that the addition of alloy can be reduced compared with the traditional quenched and tempered steel plate. However, since the reduction amount of the large-thickness steel sheet is small, the grain refinement is limited, the structure in the sheet thickness direction is not uniform, and finally, the mechanical properties in the sheet thickness direction are greatly different. The traditional quenching and tempering heat treatment (quenching and high-temperature tempering) has certain advantages on steel plates with higher requirements on production performance stability and uniformity, but after the hot rolled steel plates are quenched, the grain refinement degree is limited, and meanwhile, the yield ratio is increased due to the high-temperature tempering, so that the engineering application with the requirement on low yield ratio cannot be met.
In summary, the existing marine steel with 960 MPa-grade yield strength has the defects of poor structure uniformity and performance stability, high yield ratio and the like. To simultaneously achieve the yield strength ReHNot less than 960MPa, tensile strength RmThe alloy has the comprehensive performance requirements of more than or equal to 1100MPa, the yield ratio YR less than or equal to 0.95, the elongation A after fracture more than or equal to 12 percent and the impact toughness at minus 40 ℃ more than or equal to 69J, and has good structure uniformity and performance stability, and the existing alloy component design and process route are difficult to meet. It is urgently needed to develop 960MPa grade high-performance marine steel suitable for stable industrial production so as to meet the requirement of industry development.
Disclosure of Invention
The invention aims to provide a low yield ratio marine steel plate with yield strength of 960MPa and a preparation method thereof, wherein the microstructure of the steel plate is regulated and controlled through alloy component design and controlled rolling, controlled cooling and heat treatment processes, so that a medium steel plate with good strength-ductility-toughness matching, a lower yield ratio and a certain weather resistance is obtained.
The invention provides a low yield ratio marine steel plate with yield strength of 960MPa, which comprises the following chemical components in percentage by mass: c: 0.10 to 0.20%, Si: 0.10 to 0.30%, Mn: 1.00-1.50%, P: less than or equal to 0.010 percent, S: less than or equal to 0.005 percent, Cu: 0-0.50%, Cr: 0.20-0.60%, Ni: 0.50-3.00%, Mo: 0.20-0.80%, Co: 0.20 to 1.00%, Nb: 0-0.050%, V: 0.020 to 0.100%, Ti: 0.005-0.015%, B: 0.0005 to 0.0020 percent, and the balance of Fe and inevitable impurities, and the carbon equivalent CEV is less than or equal to 0.75 percent, and the weather resistance index I is more than or equal to 6.0 percent.
The alloy of the invention has complex component design and high alloy content, and is added with a plurality of microalloy elements. The following detailed analysis shows the selection of the main alloy components contained in the low yield ratio marine steel plate with yield strength of 960MPa grade and the dosage:
c: c is one of main elements for ensuring the strength of the steel plate, and when the content of C is too low (lower than 0.10 percent), the strength of the steel plate cannot be ensured; when the C content is too high (more than 0.20%), the low temperature toughness and weldability of the steel are degraded. Therefore, the content range of C in the invention is 0.10-0.20%.
Si: si is an essential element for steel-making deoxidation, and can play a role in solid solution strengthening and improve the strength of the steel plate. When the Si content is less than 0.10%, the deoxidation and solid solution strengthening effects are insufficient; when the Si content is more than 0.30%, cleanliness of steel is reduced, ductility and toughness of the steel sheet and welding properties are deteriorated, and quality of a final product is affected. Therefore, the Si content of the invention is 0.10-0.30%.
Mn: mn is an austenite stabilizing element, is an effective element for improving the strength and toughness, and has a remarkable effect on improving the strength of steel under the low-carbon condition. When the Mn content is less than 1.00%, the strength of the steel plate is low; when the Mn content is more than 1.50%, it is very likely to cause severe center segregation in the steel, affecting the structural uniformity and impact toughness of the steel. Therefore, the Mn content range of the invention is 1.00-1.50%.
P: p is a harmful element in steel, the content of P is strictly controlled, and higher content of P can obviously improve the weather resistance of the steel, but also increase the cold brittleness tendency of the steel, reduce the toughness of the steel and deteriorate the processing and welding performance of the steel. Therefore, the P content of the invention is controlled below 0.010%.
S: s is a harmful element in steel, is easy to form sulfide inclusion and structure segregation with elements such as Mn and the like in the steel, reduces the strength and toughness of the steel, and deteriorates fatigue and welding performance. An excessively high S content tends to cause hot shortness, and the S content should be minimized. Therefore, the S content of the present invention is controlled to 0.005% or less.
Cu: cu improves hardenability of steel, and can significantly improve core strength of thick steel plate, and Cu is also an important element for improving corrosion resistance. When the Cu content exceeds 0.50%, hot embrittlement occurs during heating, which causes surface quality problems and also reduces the toughness of the weld heat affected zone of the steel sheet. Therefore, the Cu content of the invention is in the range of 0-0.50%.
Cr: cr can effectively improve the strength of steel and obviously improve the corrosion resistance of the steel. In addition, Cr can improve the hardenability of steel, and when Cr is added in combination with Ni and Cu, the hardenability and the corrosion resistance of steel can be improved. When the Cr content is less than 0.20%, the effect cannot be effectively exerted; however, when the content is too high (more than 0.60%), the difficulty of welding increases, and the impact toughness in the heat affected zone decreases. Therefore, the Cr content range of the invention is 0.20-0.60%.
Ni: ni can improve the hardenability of steel, has a certain strengthening effect, can obviously improve the low-temperature toughness and corrosion resistance of the steel, and can effectively prevent the network fracture caused by the hot brittleness of Cu. When the Ni content is low (less than 0.50 percent), the improvement on the low-temperature toughness of steel is not obvious, especially for thick-specification steel plates; however, too high a Ni content may significantly increase the alloy cost. Therefore, the Ni content of the invention is in the range of 0.50-3.00%.
Mo: mo can improve the hardenability of steel, inhibit the generation of polygonal ferrite and pearlite, promote the formation of ferrite or bainite with a large amount of dislocations in the crystal in a larger cooling range, generate the effects of phase transformation strengthening and dislocation strengthening, and obviously improve the strength and the structural uniformity of the steel; meanwhile, Mo can effectively inhibit the tempering brittleness of martensite. When the content of Mo is less than 0.20%, the improvement on the strength and the structural uniformity of the steel is not remarkable; however, when the Mo content is too high, the carbon equivalent increases, which is disadvantageous in welding and increases the alloy cost. Therefore, the Mo content of the invention is 0.20-0.80%.
Co: although Co is an element for enlarging a gamma phase region, proper amount of Co can effectively promote the precipitation of alloy carbide, increase the dispersion degree of the alloy carbide and improve the secondary hardening effect; meanwhile, the addition of Co can refine the grain size and improve the low-temperature toughness of the steel. Therefore, the Co content of the invention is 0.20-1.00%.
Nb: nb is a strong carbonitride forming element and increases the austenite recrystallization temperature of steel, and austenite can be rolled at a higher rolling temperature. In addition, the Nb has precipitation strengthening effect in the continuous cooling process of rolling control, and austenite grains can be fixed through strain-induced precipitation of Nb carbonitride, so that the austenite grains are refined, and the strength and the low-temperature toughness are improved. When the Nb content is more than 0.050%, the yield ratio of the steel is significantly increased, and the alloy cost is increased. Therefore, the Nb content of the invention is in the range of 0 to 0.050%.
V: v is a strong carbon nitrogen compound forming element, and a proper amount of V has an obvious precipitation strengthening effect and reduces the yield ratio. When Nb and V are added compositely, the occurrence of transverse cracks can be obviously reduced, and the recrystallization temperature of the steel is obviously improved. When the content of V is too high, impact toughness of the weld affected zone may be deteriorated. Therefore, the V content range of the invention is 0.020-0.100%.
Ti: ti is a strong carbonitride forming element, forms carbon and nitride precipitated particles, can effectively pin grain boundaries, prevent the growth of austenite grains, and plays the roles of refining the grains and improving the toughness and low-temperature toughness of the steel. When the Ti content is less than 0.005 percent, the nitrogen fixation effect is poor, and the effect of grain refinement cannot be achieved; when the content exceeds 0.015%, the nitrogen fixation effect is saturated, and the toughness of the steel is deteriorated by the excessive Ti. Therefore, the Ti content of the invention is in the range of 0.005-0.015%.
B: b is a strong hardenability element, and the strength of the steel can be obviously improved by adding a trace amount of B. B may interact with Nb, Mo, and other elements to strongly suppress the formation of proeutectoid ferrite and promote the formation of martensite or bainite. When the content of B is less than 0.0005%, the hardenability effect in steel is not obvious, and the improvement on the strength of steel is limited; when the content of B is more than 0.0020%, toughness and weldability of the steel are deteriorated. Therefore, the content range of B in the present invention is 0.0005 to 0.0020%.
The yield strength R of the marine steel plate with yield strength of 960MPa grade and low yield ratioeHNot less than 960MPa, tensile strength Rm1100MPa or more, yield ratio YR or less than 0.95, elongation A after fracture of 12% or more, and impact toughness at-40 ℃ of 69J or more.
The microstructure of the marine steel plate with yield strength of 960MPa grade and low yield ratio mainly comprises tempered martensite and auxiliary tempered bainite, and the microstructure comprises a small amount of M/A.
The thickness of the marine steel plate with yield strength of 960MPa grade and low yield ratio is 10-100 mm.
The preparation method of the marine steel plate with yield strength of 960MPa grade and low yield ratio comprises the following steps:
(1) controlled rolling and cooling process
And (3) cogging the continuous casting slab or the cast ingot, then putting the cast slab or the cast ingot into a heating furnace for heating, wherein the heating temperature is 1100-1150 ℃, the heat preservation time is 120min, roughly rolling and finely rolling the slab to a thickness of 10-100 mm, and then directly quenching the slab to room temperature to obtain the hot rolled plate. Wherein the initial rolling temperature of rough rolling is 1050-1100 ℃, the final rolling temperature is 1000-1050 ℃, the rolling is carried out for 3-5 times, and the pass reduction rate is 15-20%; the finish rolling temperature is 900-950 ℃, the finish rolling temperature is 850-900 ℃, the rolling is carried out for 3-5 times, and the pass reduction rate is 20-25%.
(2) Heat treatment process
The heat treatment process comprises three procedures of (alpha + gamma) two-phase region annealing, complete austenitizing quenching and medium-low temperature tempering. Wherein the annealing heat preservation temperature of the two-phase region is Ac1+20～(Ac1+Ac3) 2 ℃ and the heat preservation time is not longerHeating the steel plate for less than 60min, and then air cooling or water quenching; the temperature of the complete austenitizing quenching is Ac1Heating the steel plate and then quenching with water at the temperature of 30-50 ℃ for 30-180 min; and (3) carrying out medium and low temperature tempering at the heat preservation temperature of 200-400 ℃ for 30-120 min, and air cooling the tempered steel plate to room temperature.
The preparation method of the marine steel plate with yield strength of 960MPa grade and low yield ratio comprises the following process control principles:
the principle of the controlled rolling and controlled cooling process related by the invention is as follows: and (2) cogging the continuous casting slab or the cast ingot, then putting the continuous casting slab or the cast ingot into a heating furnace for heating, wherein the heating temperature is 1100-1150 ℃, the heat preservation time is 120min, roughly rolling and finely rolling the continuous casting slab or the cast ingot to a thickness of 10-100 mm, and then directly quenching the continuous casting slab or the cast ingot to room temperature to obtain the hot rolled plate. Wherein the initial rolling temperature of rough rolling is 1050-1100 ℃, the final rolling temperature is 1000-1050 ℃, the rolling is carried out for 3-5 times, and the pass reduction rate is 15-20%; the finish rolling temperature is 900-950 ℃, the finish rolling temperature is 850-900 ℃, the rolling is carried out for 3-5 times, and the pass reduction rate is 20-25%.
The heat treatment process principle related by the invention is as follows: the heat treatment process comprises three procedures of (alpha + gamma) two-phase region annealing, complete austenitizing quenching and medium-low temperature tempering. Wherein the annealing heat preservation temperature of the (alpha + gamma) two-phase region is Ac1+20～(Ac1+Ac3) At the temperature of 2 ℃, the heat preservation time is not less than 60min, and the steel plate is air-cooled or water-quenched after being heated; the temperature of the complete austenitizing quenching is Ac1Heating the steel plate and then quenching with water at the temperature of 30-50 ℃ for 30-180 min; and (3) carrying out medium and low temperature tempering at the heat preservation temperature of 200-400 ℃ for 30-120 min, and air cooling the tempered steel plate to room temperature. The tissue regulation and control principle of each procedure is as follows:
(α + γ) two-phase region annealing: the steel plate can refine grains through annealing in an (alpha + gamma) two-phase region to obtain a non-uniform structure, the structure consists of martensite/bainite enriched with alloy elements and critical ferrite barren with the alloy elements, and the steel plate is characterized in that the enrichment degrees of the alloy elements at different phases and interfaces are different. The inhomogeneous structure formed by annealing in the two-phase region is used for preparing the structure for subsequent complete austenitizing quenching, is favorable for the formation of granular reversed austenite at the interface in the subsequent heating process, and can haveEffectively refine grains. The annealing holding temperature of the two-phase region is set as Ac1+20～(Ac1+Ac3) 2 ℃ in order to obtain a certain amount of reversed austenite; the heat preservation time is not less than 60min, which is to ensure that elements can be fully distributed into reversed austenite in the heat preservation process, and finally obtain an uneven structure.
And (3) complete austenitizing and quenching: the steel plate is annealed in a two-phase region and then reheated to Ac1And keeping the temperature for 30-180 min at the temperature of + 30-50 ℃, and then quenching. The steel plate is quenched by complete austenitization, the prior austenite grains are effectively refined, and finally, a structure which takes quenched martensite (hard phase) as a main phase, bainite (soft phase) as an auxiliary phase and a small amount of M/A (hard phase) is obtained, and the structure enables the steel plate to have a lower yield ratio.
Medium and low temperature tempering: and heating the steel plate subjected to complete austenitizing quenching to 200-400 ℃, preserving heat for 30-120 min, and performing medium-low temperature tempering. The steel plate is tempered at medium and low temperature to separate out nano carbides, so that the yield strength is improved; meanwhile, the medium-low temperature tempering can avoid dislocation over-recovery and M/A decomposition, and the tensile strength of the steel plate is ensured. After the steel plate is tempered at medium and low temperature, a structure with tempered martensite (hard phase) as a main part, tempered bainite (soft phase) as an auxiliary part and a small amount of M/A (hard phase) is obtained, and the steel plate is ensured to have high strength and toughness and simultaneously obtain low yield ratio.
The innovation points of the embodiment of the invention comprise:
1. the alloy components of the invention adopt low-carbon design, thus ensuring the toughness and welding performance of the steel plate; the toughness and the corrosion resistance of the steel are improved by adding weather-resistant elements such as Cu, Ni, Cr, Mo and the like; nb, V and Ti are subjected to composite micro-alloying, and grains are refined; b microalloying treatment is carried out to improve hardenability; the alloy components which are low-carbon, easy to weld and weather-resistant are designed.
2. By adopting a reasonable rolling and cooling control process, an (alpha + gamma) two-phase region annealing process, a complete austenitizing quenching process and a medium-low temperature tempering heat treatment process and controlling the rolling and heat treatment process parameters, the steel plate obtains good strong plastic toughness matching and lower yield ratio, namely yield strength ReHNot less than 960MPa, tensile strength RmMore than or equal to 1100MPa, yield ratio YR less than or equal to 0.95, elongation A after fracture more than or equal to 12 percent and-40 DEG CThe impact toughness is more than or equal to 69J.
3. The steel plate prepared by the alloy components and the treatment process has the advantages that the microstructure is mainly tempered martensite and secondarily tempered bainite and consists of a small amount of M/A, the structure is uniform in the thickness direction, the performance fluctuation is small, and the steel plate with the thickness of 10-100 mm can be produced.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. It is to be understood that the drawings in the following description are merely exemplary of some embodiments of the invention. For a person skilled in the art, without inventive effort, further figures can be obtained from these figures.
FIG. 1 is a schematic view of a heat treatment process (T) used in an embodiment of the present invention0＝1100～1150℃，t0Is 120 min; t is1＝Ac1+20～(Ac1+Ac3)/2℃，t1Not less than 60 min; t is2＝Ac1+30～50℃，t2＝30～180min；T3＝200～400℃，t3＝30～120min；t0、t1、t2And t3For the holding time);
FIG. 2 is a schematic view of a scanning electron microscope structure of a steel of the composition of example 1 of the present invention under the heat treatment process condition of the present invention (sample 2);
FIG. 3 is a schematic view of an electron back-scattered diffraction structure of a steel of the composition of example 1 of the present invention under the heat treatment process conditions of the present invention (sample 2).
Detailed Description
The technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. It is to be understood that the described embodiments are merely a few embodiments of the invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.
It is to be noted that the terms "comprises" and "comprising" and any variations thereof in the embodiments and drawings of the present invention are intended to cover non-exclusive inclusions. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those steps or elements listed, but may alternatively include other steps or elements not listed, or inherent to such process, method, article, or apparatus.
The invention provides a marine steel plate with yield strength of 960MPa grade and low yield ratio and a preparation method thereof. The following provides a detailed description of embodiments of the invention.
The steel of the invention is smelted by a vacuum induction furnace, and the chemical components are shown in table 1. Forging and cogging (80mm), rolling the billet in a laboratory in two stages to form plates with the thickness of 12mm, and finally performing water quenching to room temperature. The main process parameters such as heat treatment temperature and cooling mode after heat treatment are shown in Table 2. The transverse tensile strength and the-40 ℃ longitudinal impact energy of the heat-treated steel sheets are shown in Table 3, and all the values reach the yield strength ReHNot less than 960MPa, tensile strength Rm1100MPa or more, yield ratio YR or less than 0.95, elongation A after fracture of 12% or more, and impact toughness at-40 ℃ of 69J or more.
TABLE 1 chemical composition (wt.%) of low yield ratio marine steel sheet with yield strength of 960MPa grade
Figure BDA0003323210000000071
TABLE 2 Heat treatment process of low yield ratio marine steel plate with yield strength of 960MPa
Figure BDA0003323210000000072
TABLE 3 mechanical properties of the marine steel sheet with yield strength of 960MPa grade and low yield ratio
Figure BDA0003323210000000073
The system and apparatus embodiments correspond to the system embodiments, and have the same technical effects as the method embodiments, and for the specific description, refer to the method embodiments. The device embodiment is obtained based on the method embodiment, and for specific description, reference may be made to the method embodiment section, which is not described herein again. Those of ordinary skill in the art will understand that: the figures are merely schematic representations of one embodiment, and the blocks or flow diagrams in the figures are not necessarily required to practice the present invention.
Those of ordinary skill in the art will understand that: modules in the devices in the embodiments may be distributed in the devices in the embodiments according to the description of the embodiments, or may be located in one or more devices different from the embodiments with corresponding changes. The modules of the above embodiments may be combined into one module, or further split into multiple sub-modules.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (5)

1. A marine steel plate with yield strength of 960MPa grade and low yield ratio and a preparation method thereof are characterized in that the steel plate comprises the following chemical components by mass percent: c: 0.10 to 0.20%, Si: 0.10 to 0.30%, Mn: 1.00-1.50%, P: less than or equal to 0.010 percent, S: less than or equal to 0.005 percent, Cu: 0-0.50%, Cr: 0.20-0.60%, Ni: 0.50-3.00%, Mo: 0.20-0.80%, Co: 0.20 to 1.00%, Nb: 0-0.050%, V: 0.020 to 0.100%, Ti: 0.005-0.015%, B: 0.0005 to 0.0020 percent, and the balance of Fe and inevitable impurities, and the carbon equivalent CEV is less than or equal to 0.75 percent, and the weather resistance index I is more than or equal to 6.0 percent. Wherein the content of the first and second substances,
CEV(％)＝C+Mn/6+(Cr+V+Mo)/5+(Ni+Cu)/15，
I(％)＝26.01Cu+3.88Ni+1.20Cr+1.49Si+17.28P-7.29Cu×Ni-9.10Ni×P-33.39Cu2。
2. steel plate for maritime work with yield strength of 960MPa grade and low yield ratio according to claim 1, wherein the steel plate has yield strength ReHNot less than 960MPa, tensile strength Rm1100MPa or more, yield ratio YR or less than 0.95, elongation A after fracture of 12% or more, and impact toughness at-40 ℃ of 69J or more.
3. The low yield ratio marine steel sheet having a yield strength of 960MPa grade according to claim 1, wherein the microstructure is mainly tempered martensite and secondarily tempered bainite and consists of a small amount of M/A.
4. The steel plate for marine engineering with yield strength of 960MPa grade and low yield ratio of claim 1, wherein the thickness of the steel plate is 10-100 mm.
5. The method for preparing the low yield ratio marine steel plate with the yield strength of 960MPa grade according to claim 1, is characterized by comprising the following steps:
(1) controlled rolling and cooling process
And (2) cogging the continuous casting slab or the cast ingot, then putting the continuous casting slab or the cast ingot into a heating furnace for heating, wherein the heating temperature is 1100-1150 ℃, the heat preservation time is 120min, roughly rolling and finely rolling the continuous casting slab or the cast ingot to a thickness of 10-100 mm, and then directly quenching the continuous casting slab or the cast ingot to room temperature to obtain the hot rolled plate. Wherein the initial rolling temperature of rough rolling is 1050-1100 ℃, the final rolling temperature is 1000-1050 ℃, the rolling is carried out for 3-5 times, and the pass reduction rate is 15-20%; the finish rolling temperature is 900-950 ℃, the finish rolling temperature is 850-900 ℃, the rolling is carried out for 3-5 times, and the pass reduction rate is 20-25%.
(2) Heat treatment process
The heat treatment process comprises three procedures of (alpha + gamma) two-phase region annealing, complete austenitizing quenching and medium-low temperature tempering. Wherein the annealing heat preservation temperature of the (alpha + gamma) two-phase region is Ac1+20～(Ac1+Ac3) At 2 deg.C, maintaining for at least 60min, heating steel plateAir cooling or water quenching; the temperature of the complete austenitizing quenching is Ac1Heating the steel plate and then quenching with water at the temperature of 30-50 ℃ for 30-180 min; and (3) carrying out low-temperature tempering at the temperature of 200-400 ℃, carrying out heat preservation for 30-120 min, and carrying out air cooling on the tempered steel plate to room temperature.
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