A 1000mpa grade water and electricity steel plate with a thickness of 120mm and a manufacturing method thereof

Abstract

The present application relates to a kind of 1000MPa grade thickness reaches 120mm hydroelectric steel steel plate and its manufacturing method, chemical composition is according to mass percentage: C:0.10~0.13%, Si:0.05~0.20%, Mn:0.95~1.20%, P≤0.007%, S≤0.002%, Al:0.04~0.07%, V:0.035~0.060%, Cr:0.40~0.70%, Cu:≤0.30%, Ni:1.80~2.40%, Mo:0.30~0.60%, B:≤0.0020%, the balance is Fe and inevitable impurity, element content satisfies carbon equivalent Ceq≤0.60%. Yield strength ≥870MPa, tensile strength 920~1130MPa, elongation ≥14%, plate thickness 1 / 4 place-60 ℃ transverse impact energy KV2≥120J, plate thickness 1 / 2 place-60 ℃ transverse impact energy KV2≥100J.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of iron-based alloys, and particularly relates to a thick-gauge hydroelectric steel plate with high strength and excellent low-temperature impact toughness and a manufacturing method thereof. BACKGROUND

[0002] With the continuous upgrading of the level of hydropower stations, the severity of the service environment increases, and the level requirements for high-toughness hydroelectric station steel are also increasingly high. The strength level gradually transitions from the 600MPa level to the 800MPa level, and then to the 1000MPa level. With the continuous increase in the installed capacity of hydropower, the thickness of hydroelectric steel is also increasing. Hydroelectric station steel used in ultra-high strength level and ultra-low temperature environment has become a bottleneck for the development of steel for large-scale hydropower station construction.

[0003] The performance requirements for steel plates for large-scale hydropower station construction are increasingly high. In addition to requiring high strength (yield strength ≥ 870MPa, tensile strength 920-1130MPa), high toughness (steel plate transverse impact energy KV2 at -60℃ ≥ 70J), and easy weldability.

[0004] The patent document with the patent publication number CN 113652607A discloses a 1000MPa grade quenched and tempered hydroelectric steel plate with a maximum thickness of 56mm, a performance of yield strength ≥ 885MPa, tensile strength 950-1130MPa, and steel plate transverse low-temperature impact at -60℃ ≥ 100J. The strength is high, and the toughness is good, but the production thickness of the steel plate only reaches 56mm.

[0005] The patent document with the patent publication number CN 113399948A discloses a method for producing 1000MPa hydroelectric steel with a thickness of 100mm or more. The method adopts two 250-350mm thick continuous casting blanks that are welded to form a blank, and then subjected to rolling and heat treatment, to produce 1000MPa grade high-strength thick hydroelectric steel with a thickness of 100mm or more. The method adopts a composite blank manufacturing process, which is complex, significantly increases the manufacturing cost, and the low-temperature toughness corresponds to a test temperature of -40℃, which does not reach the impact toughness test temperature of -60℃.

[0006] The existing 1000MPa grade hydroelectric steel produced by the continuous casting process has a small thickness, which cannot meet the needs of the large-scale hydropower station market. The production of thick plates by mold casting, electroslag remelting, and composite blanking has problems such as high production cost, long cycle, poor practicality, insufficient strength, and low low-temperature impact toughness. SUMMARY

[0007] In view of the problems existing in the prior art, the present application provides a 1000MPa grade hydroelectric steel plate with a thickness of 120mm and a manufacturing method thereof, which has the characteristics of high strength, excellent low-temperature toughness, excellent welding performance, low production cost, and short cycle.

[0008] The chemical composition of the 1000MPa grade steel plate for hydroelectricity with a thickness of 120mm designed by the present application is as follows in terms of mass percentage: C: 0.10-0.13%, Si: 0.05-0.20%, Mn: 0.95-1.20%, P≤0.007%, S≤0.002%, Al: 0.04-0.07%, V: 0.035-0.060%, Cr: 0.40-0.70%, Cu: ≤0.30%, Ni: 1.80-2.40%, Mo: 0.30-0.60%, B: ≤0.0020%, and the balance of Fe and inevitable impurities, and the content of the corresponding elements satisfies Ceq=[C]+[Mn] / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14≤0.60%.

[0009] The performance of the 1000MPa grade steel plate for hydroelectricity with a thickness of 120mm designed by the present application satisfies the following conditions: yield strength≥870MPa, tensile strength 920-1130MPa, elongation≥14%, transverse impact energy KV2 at 1 / 4 thickness at-60℃≥120J, and transverse impact energy KV2 at 1 / 2 thickness at-60℃≥100J. The microstructure of the steel plate is as follows: the surface layer is martensite, the 1 / 4 thickness layer is martensite+ bainite, and the 1 / 2 thickness layer is bainite.

[0010] The chemical composition is the main factor affecting the performance of the ultra-thick steel plate, and in order to ensure that the ultra-thick steel plate of the present application has excellent comprehensive mechanical properties, especially low-temperature toughness, the main elements of the present application are specified, and the main principles are as follows:

[0011] Carbon: C is a traditional strengthening element in low-carbon steel, which can effectively improve the strength and hardness of the steel plate. When the carbon content is high, it will have an adverse effect on the plasticity, toughness and weldability of the steel plate. Therefore, the carbon content is controlled to be 0.10-0.13% in the present application under the premise of ensuring the strength.

[0012] Silicon: Si can improve the strength of the steel, and its solid solution in austenite can strengthen the structure and significantly improve the strength and hardness of the steel. For low-alloy steel, the tensile strength of hot-rolled steel can be increased by about 8MPa for each increase of 0.10% of Si. When the Si content exceeds 0.50%, the impact toughness and the reduction of area will decrease, and at the same time, the iron oxide skin will be formed on the surface of the steel, thereby affecting the surface quality of the steel. Therefore, the Si content is controlled to be 0.05-0.20% in the present application.

[0013] Manganese: Mn is a solid solution strengthening element in steel, which can refine the grain, reduce the brittle ductile transition temperature, and promote the solid solution of Nb, V, Ti and other micro-alloy elements in austenite. It is the main element to improve the strength of low alloy high strength steel. The strength of steel increases with the increase of manganese content. Within the range of 1.0%, the toughness improves with the increase of manganese content. Exceeding the range, the toughness will decrease. At the same time, manganese elements lead to intracrystalline segregation and center segregation during the solidification and cooling of molten steel, which reduces the thermal conductivity of steel and easily forms coarse grains. Therefore, the Mn content in the present application is controlled within 0.95-1.20%.

[0014] Chromium: In the quenched and tempered structural steel, the main role of chromium is to improve the hardenability of steel, so that the steel has good comprehensive mechanical properties after quenching and tempering treatment. At the same time, the addition of chromium in steel can significantly improve the oxidation resistance and corrosion resistance of steel. However, when the chromium content is too high, it will also increase the temper brittleness of steel, and reduce the toughness and weldability of steel. Therefore, the Cr content in the present application is controlled within 0.40-0.70%.

[0015] Aluminum: It is usually added to steel as a deoxidizer. When Al is solid-solved in steel, it can play a solid solution strengthening role, enhance the fatigue strength and low temperature toughness of steel. Therefore, the Al content in the present application is controlled within 0.04-0.07%.

[0016] Boron: B in solid solution in steel mainly can enhance the hardenability of steel, replace and reduce the addition of some precious metals such as Ni, Cr, Mo, thereby reducing the cost of steel. B has a great affinity with N in steel, and appropriate addition of boron can reduce the aging brittleness phenomenon of steel. In the present application, the content of B is ≤0.0020%.

[0017] Copper: It can improve the strength and low temperature toughness of the base and weld metal, and can better play the corrosion resistance with Ni. However, too high content will significantly reduce the plasticity. Therefore, the content of Cu is ≤0.30%.

[0018] Nickel: Ni is an indispensable element to improve the low temperature toughness of steel, and it is also the most effective element. It is mutually soluble with iron, which can refine the α phase grain, strengthen the ferrite and refine the pearlite structure, and can significantly improve the low temperature toughness of steel, especially the low temperature impact toughness after long time mold welding treatment. At the same time, it can reduce the tendency of casting crack caused by the addition of Cu. However, Ni is a precious element, and too much Ni will significantly increase the production cost of steel. Therefore, the Ni content in the present application is controlled within 1.80-2.40%.

[0019] Molybdenum: It can improve the tempering stability and grain refinement of steel, especially the mechanical properties of steel plate after mold welding, and prevent the significant decrease of strength. At the same time, appropriate amount of Mo element can also improve the toughness of welded joint. However, as a precious metal, too much Mo will significantly increase the cost of steel. Therefore, the Mo content in the present application is controlled within 0.30-0.60%.

[0020] Vanadium: It has strong binding force with C and N, and forms corresponding stable carbide, nitride or carbonitride, which can refine grain and prevent primary austenite grain from coarsening, and improve the strength and toughness of the steel. Therefore, the content of V in the present application is controlled at 0.035-0.060%.

[0021] Phosphorus and sulfur: Generally, S and P are harmful elements in steel, which are easy to produce center segregation, inclusions and other defects, and have adverse effects on the mechanical properties and welding performance of the steel plate. For thick steel plates with low temperature toughness requirements, the lower the content of S and P, the better. Therefore, the content of P in the present application is controlled at ≤0.007%, and the content of S is controlled at ≤0.002%.

[0022] The main manufacturing process of the 1000MPa grade steel plate with a thickness of 120mm for hydropower is as follows: KR pre-desulfurization, BOF converter smelting, LF refining, RH vacuum treatment, thick slab continuous casting, continuous casting blank cover slow cooling, continuous casting blank heating, rolling, steel plate cover slow cooling, flaw detection, quenching and tempering treatment, flaw detection, performance test, and the specific requirements are as follows:

[0023] (1) Steelmaking and continuous casting: after the molten iron is pretreated by KR, the content of [S] is ensured to be ≤0.02%, and the tapping temperature of the converter is controlled at 1620-1700℃; the LF refining time is ≥40 minutes, the molten steel is deoxidized by aluminum wire, and the content of [O] in the molten steel is ensured to be ≤20ppm, vanadium iron, chromium iron and other alloys are added during the LF refining, the vacuum treatment time is ≥25 minutes, the content of H in the molten steel is ≤0.9ppm after the RH vacuum treatment, calcium wire is fed after the treatment, the soft blowing is ≥15 minutes, the casting speed is controlled at 0.45-0.55m / min during the continuous casting, the superheat is strictly controlled at 10-30℃, the thick blank is cast, and the blank is slow cooled with a cover.

[0024] (2) Rolling and slow cooling: the thick blank is heated to 1220-1270℃ and kept for more than 4 hours, after the blank is discharged, the high-pressure water is used for descaling, the blank after descaling is rolled in two stages, the total reduction rate of the first stage rolling is ≥55%, the strong reduction is used, the single pass reduction rate of the last three passes is ≥16%, the maximum single pass reduction rate is ≥23%, the surface of the blank is cooled by high-pressure descaling water before each pass of rolling, and the finish rolling temperature is 980-1050℃; the total reduction rate of the second stage rolling is ≥30%, the starting rolling temperature is 900-980℃, the surface of the blank is cooled by high-pressure descaling water before each pass of rolling, and the finished thickness steel plate is rolled; after the rolling is completed, the blank is air cooled and straightened. After the straightening, the blank is air cooled to 550-650℃ on the cooling bed, then enters the cover, and is slow cooled by the way of laying on the bottom and covering on the top, the slow cooling time is ≥72 hours, and the blank is taken out of the cover after the slow cooling to the surface temperature of 100-150℃.

[0025] (3) Quenching and tempering treatment: quenching heating temperature 890-930 DEG C, in furnace time 1.9-2.5 min / mm, using quenching machine water quenching to steel plate surface temperature ≤100 DEG C after air cooling to room temperature, tempering is carried out using continuous furnace, tempering temperature 580 DEG C-610 DEG C, in furnace time 2.0-3.5 min / mm, after furnace air cooling to room temperature.

[0026] The present application aims at the demand of high strength, high toughness and easy welding of steel plate for large hydropower station with high water head and high parameter, adopts low carbon equivalent high hardenability composite microalloying component design, ensures that the steel plate has good hardenability, high strength, high toughness and good weldability and other characteristics, controls the inclusions and gas content in molten steel through ladle furnace+vacuum double refining mode, adopts low superheat pouring during continuous casting, matches scientific casting speed and light press-down process, realizes high purity high-quality continuous casting billet manufacturing, adopts low-speed large-press-down rolling technology to the casting billet, refines the organization grain, finally carries out quenching and tempering treatment, strengthens the microstructure of the super-thick steel plate, thereby improving the comprehensive performance of the steel, and the 120mm-thick super-thick hydropower steel plate of the present application meets the requirements of high strength, high toughness and easy welding.

[0027] Compared with the existing production technology and patent, the present application has the following characteristics and advantages:

[0028] (1) Compared with the production of super-thick steel plate by adopting ingot, electroslag remelting and composite billet, the present application directly uses continuous casting billet to manufacture 120mm-thick high strength and toughness hydropower steel, significantly reduces the production cost, obviously shortens the production cycle, and greatly improves the competitiveness of the medium plate product.

[0029] (2) The present application adopts low carbon equivalent high hardenability composite microalloying component design, and through advanced pure steel smelting technology, ladle furnace+vacuum double refining mode, low-speed large-press-down rolling process, high-efficiency quenching+tempering technology, develops 120mm-thick super-thick hydropower steel, which has strong operability and applicability.

[0030] (3) The carbon equivalent of the hydropower steel of the present application

[0031] Ceq=[C]+[Mn] / 6+Si / 24+Ni / 40+Cr / 5+Mo / 4+V / 14 ≤0.60%, the performance meets the requirements of yield strength ≥870MPa, tensile strength 920-1130MPa, elongation ≥14%, transverse impact energy KV2 at 1 / 4 plate thickness at-60 DEG C ≥120J, transverse impact energy KV2 at T / 2 plate thickness at-60 DEG C ≥100J, has high strength, excellent low-temperature toughness, excellent weldability and other characteristics, and has a wider application range. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1The surface metallographic structure of the 120mm thick steel plate of Example 1 is mainly martensite.

[0033] Figure 2 The metallographic structure at 1 / 4 of the 120mm thick steel plate of Example 1 is mainly martensite + bainite.

[0034] Figure 3 The metallographic structure at 1 / 2 of the 120mm thick steel plate of Example 1 is mainly bainite.

[0035] Figure 4 The Y-type bevel groove crack sensitivity test welded joint dissection diagram of the 120mm thick steel plate of Example 1. DETAILED DESCRIPTION

[0036] The application will be further described in conjunction with preferred embodiments, which are exemplary and intended to explain the application, and cannot be understood as a limitation of the application.

[0037] Example 1

[0038] This example relates to a 1000MPa grade steel plate for hydropower, and the main production process is KR pre-desulphurization → BOF converter smelting → LF refining → RH vacuum treatment → thick slab continuous casting → continuous casting slab cover slow cooling → continuous casting slab heating → rolling → steel plate cover slow cooling → flaw detection → quenching and tempering treatment → flaw detection → performance test.

[0039] The 1000MPa grade steel plate for hydropower related in this example is produced with a thickness of 120mm, and the chemical components and mass percentage contents thereof are as follows: C: 0.12%, Si: 0.15%, Mn: 1.05%, P: 0.003%, S: 0.002%, Cr: 0.45%, Ni: 2.00%, Cu: 0.15%, Mo: 0.35%, Al: 0.045%, V: 0.040%, Ca: 0.0014%, N: 0.0031%.

[0040] The molten iron is smelted in a top and bottom combined blowing converter, and then subjected to refining treatment, deoxidation and alloying, and finally subjected to vacuum degassing in a vacuum furnace to remove gaseous elements, soft blowing to make large inclusions fully float and remove, and then subjected to light pressing and full-process protection pouring to form a continuous casting slab.

[0041] The thick continuous casting billet is heated to 1240-1270 DEG C, total furnace time is greater than or equal to 560 min, soaking time is greater than or equal to 270 min; after descaling, rolling is started, high-pressure descaling water is used to cool the surface of the billet before each pass, the pass reduction is 50-60 mm after three passes of rough rolling, and the finish rolling temperature is 980-1050 DEG C; the rough rolling temperature is 880-960 DEG C, and the steel plate is rolled into a 120 mm thick steel plate; after rolling, the steel plate is air-cooled and straightened, and is air-cooled to 550-650 DEG C and then is slowly cooled (lowered and covered) to room temperature.

[0042] The steel plate is subjected to quenching and tempering heat treatment, the quenching heating temperature is 890-930 DEG C, the tempering heating temperature is 580-610 DEG C, and the steel plate is air-cooled to room temperature after being discharged.

[0043] Table 1 Mechanical properties of the steel plate of Example 1

[0044]

[0045] As shown in Table 1, the 1000 MPa grade 120 mm thick steel plate for water and electricity has good comprehensive performance, the yield strength is greater than or equal to 870 MPa, the tensile strength is 920-1130 MPa, the elongation A is greater than or equal to 14%, the average value of KV2 at 1 / 4 of the plate thickness at-60 DEG C is greater than or equal to 120 J, and the average value of KV2 at 1 / 2 of the plate thickness at-60 DEG C is greater than or equal to 100 J.

[0046] The steel plate is subjected to Y-type groove welding crack sensitivity test, and the results are shown in Table 2.

[0047] Table 2 Results of Y-type groove welding crack sensitivity test of the steel plate of Example 1

[0048]

[0049] As shown in Table 2, the 1000 MPa grade 120 mm thick steel plate for water and electricity has good weldability, and no cracks are generated when the welding preheating temperature is greater than or equal to 100 DEG C.

[0050] Figures 1 to 3 The microstructure of the 120 mm thick steel plate at the surface, 1 / 4 of the plate thickness and 1 / 2 of the plate thickness is shown, and the grains are finer, which not only ensures that the steel has sufficient strength, but also makes the steel plate have excellent low-temperature toughness.

[0051] The 1000 MPa grade 120 mm thick steel plate for water and electricity has a microstructure that changes in the thickness direction, and the steel plate has excellent comprehensive mechanical properties, and can be widely used in water and electricity, bridges, large steel structures, containers, ocean engineering structures and the like under low-temperature environment.

Claims

1. A 1000 MPa grade water power steel plate having a thickness of 120 mm, characterized in that: The chemical composition in percentage by mass is: C: 0.10-0.13%, Si: 0.05-0.20%, Mn: 0.95-1.20%, P: ≤0.007%, S: ≤0.002%, Al: 0.04-0.07%, V: 0.035-0.060%, Cr: 0.40-0.70%, Cu: ≤0.30%, Ni: 1.80-2.40%, Mo: 0.30-0.60%, B: ≤0.0020%, the balance being Fe and inevitable impurities, and the element content satisfies carbon equivalent Ceq: ≤0.60%; the surface metallographic structure of the steel plate is martensite, the metallographic structure at 1 / 4 thickness of the steel plate is martensite + bainite, and the metallographic structure at 1 / 2 thickness of the steel plate is bainite; The mechanical properties of the steel plate are: yield strength: ≥870 MPa, tensile strength: 920-1130 MPa, elongation: ≥14%, transverse impact energy KV2 at 1 / 4 thickness of the plate at-60℃: ≥120 J, and transverse impact energy KV2 at 1 / 2 thickness of the plate at-60℃: ≥100 J.

2. Steel sheet according to claim 1, characterized in that: Y-type groove welding crack sensitivity test: no welding cracks when the welding preheating temperature is ≥100℃.

3. A method of manufacturing the steel sheet according to claim 1, characterized by: The process flow is KR pretreatment→BOF converter smelting→LF refining→vacuum degassing treatment→continuous casting→continuous casting blank cover slow cooling→continuous casting blank heating→rolling→slow cooling→quenching and tempering treatment, and the specific operation is as follows: (1) Steelmaking and continuous casting: the molten iron is desulfurized by KR pretreatment to ensure that [S] is ≤0.02%; the molten iron is smelted in a converter, and the converter tapping temperature is controlled to be 1620-1700℃; the LF refining time is ≥40 minutes, the molten steel is deoxidized by feeding aluminum wire, and [O] is ensured to be ≤20ppm; alloy elements are added during refining to adjust the alloy element composition to the target value; the vacuum treatment time is ≥25 minutes, the H content in the molten steel after vacuum treatment is ≤0.9ppm, calcium wire feeding is performed after the end of the treatment, and soft blowing is continued for ≥15 minutes to further remove inclusions; the molten steel is cast into a continuous casting blank; (2) Rolling and slow cooling: the blank is heated to 1220-1270℃ and kept for ≥4 hours, after being discharged, high-pressure water is used for descaling, two-stage rolling is performed, the total reduction rate of the first stage rolling is ≥55%, strong reduction rolling is used, the reduction rate of the last three passes is ≥16%, the maximum reduction rate is ≥23%, the surface of the blank is cooled before each pass of rolling by using high-pressure descaling water, and the finish rolling temperature is controlled to be 980-1050℃; the total reduction rate of the second stage rolling is ≥30%, the start rolling temperature is controlled to be 900-980℃, the surface of the blank is cooled before each pass of rolling by using high-pressure descaling water, and the blank is rolled into a finished thickness steel plate; after rolling, the steel plate is air cooled and straightened, the steel plate is air cooled to 550-650℃ after being straightened, the steel plate is stacked in a lower-paving upper-covering manner in a cover for slow cooling, and the slow cooling time is ≥72 hours, and the steel plate is taken out of the cover after being slowly cooled to a surface temperature of 100-150℃; (3) Quenching and tempering heat treatment: the blank is quenched and tempered to obtain a water and electricity steel plate with a surface layer of martensite and a center layer of bainite.

4. The method of claim 3, wherein: Step (1), control the casting speed at 0.45-0.55 m / min and the superheat at 10-30 ℃ during continuous casting to obtain the casting blank with cover slow cooling.

5. The method of claim 3, wherein: Step (3), quenching heating temperature 890-930 ℃, furnace time 1.9-2.5 min / mm, water quenching to ≤100 ℃ using quenching machine, and then air cooling to room temperature, tempering is carried out using continuous furnace, tempering temperature 580-610 ℃, furnace time 2.0-3.5 min / mm, and then air cooling to room temperature.

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