A method for producing a super-thick plate having a strength of more than 460 MPa

Abstract

The application discloses a production method of a super-thick steel plate with a strength greater than 460MPa, and the chemical components of the steel are as follows: C=0.12%-0.14%, Si=0.20%-0.35%, Mn=1.45%-1.60%, P<=0.010%, S<=0.005%, AlT=0.020%-0.050%, Nb=0.040%-0.050%, V=0.055%-0.065%, Ti=0.008%-0.015%, Ni=0.50%-0.60%, Cr=0.10-0.15%, and the rest is Fe and inevitable residual elements; and the technological process is converter smelting-LF refining-VD / RH vacuum treatment-continuous casting-slab heating-rolling-heat treatment.The application realizes the chemical component design of adding Nb, V, Ti, Cr and Ni alloys, guarantees the cleanliness of the steel through the LF+VD process, and produces the super-thick steel plate with a thickness of 180-220mm, a yield strength greater than or equal to 460MPa, a tensile strength greater than 570Mpa, an elongation greater than or equal to 17%, a thickness tensile strength greater than or equal to 35%, and an impact value at-40 DEG C greater than or equal to 60J, and the production cost of the steel plate is low.

Description

Technical Field

[0001] This invention belongs to the field of metallurgy and heat treatment technology, and relates to a method for producing extra-thick plates with a strength greater than 460MPa. Background Technology

[0002] Extra-thick steel plates have become indispensable materials in modern socio-economic development, national defense construction, and major national engineering projects, finding widespread application in industries such as coal mining machinery, shipbuilding, boiler containers, wind power generation, bridges, and high-rise buildings. With the implementation of the national policy of "carbon peaking and carbon neutrality," and the accelerated development of wind and hydrogen energy, the Northwest region, as an important wind power base, has a vast market potential for high-quality extra-thick steel plates. Currently, the annual demand for extra-thick steel plates (150mm and above) in the steel market is very large and shows a continuous upward trend. For example, the rapidly growing wind power industry in the Northwest region in recent years has a certain proportion of demand for extra-thick steel plates in its tower manufacturing.

[0003] However, in the smelting process of extra-thick plates, as the thickness of the steel plate increases, the size of the continuously cast billet of the extra-thick plate increases accordingly, which leads to severe element segregation during solidification, deteriorating the quality of the billet and making it easy for central segregation, shrinkage cavities and porosity to occur, affecting the pass rate of the steel plate's flaw detection. At the same time, during the rolling process of extra-thick plates, the rolling force has difficulty penetrating along the thickness direction, the core deformation is insufficient, and the performance difference in the thickness direction is large. The main problems are reflected in the instability of strength and impact performance.

[0004] Chinese patent CN200910089346.2 discloses an extra-thick steel plate for construction with a low yield strength ratio of 460 MPa and a manufacturing method thereof. Its chemical composition (mass percentage) is: C 0.14–0.18%, Si 0.35–0.45%, Mn 1.40–1.50%, Nb 0.025–0.035%, V 0.040–0.050%, Ti 0.010–0.020%, P < 0.020%, S < 0.008%, with the balance being iron and unavoidable impurities. It is designed to withstand impact at -20°C, but the thickness of the example is not specified, which cannot meet the requirements for producing large-thickness steel plates. Summary of the Invention

[0005] The purpose of this invention is to provide a production method for extra-thick plates with a strength greater than 460MPa. The method employs a comprehensive production process to ensure that the steel plate has a yield strength ≥460MPa, a tensile strength greater than 570MPa, an elongation ≥17%, a thickness tensile strength ≥35%, and an impact value ≥60J at -40℃.

[0006] The technical solution of the present invention:

[0007] A method for producing extra-thick plates with a strength greater than 460 MPa, wherein the chemical composition of the steel is as follows (mass percentage): C = 0.12%–0.14%, Si = 0.20%–0.35%, Mn = 1.45%–1.60%, P ≤ 0.010%, S ≤ 0.005%, AlT = 0.020%–0.050%, Nb = 0.040%–0.050%, V = 0.055%–0.065%, Ti = 0.008%–0.015%, Ni = 0.50%–0.60%, Cr = 0.10%–0.15%, with the remainder being Fe and essential residual elements; the method includes the following process steps:

[0008] 1) LF refining: Large slag volume is used for slag formation, and the white slag holding time is controlled to be more than 15 minutes;

[0009] 2) Molten casting: The qualified molten steel after LD-LF-VD smelting is poured into the steel ingot mold with the cold material fixed. The overheating temperature at the start of the casting is controlled at 35±3℃.

[0010] 3) Heating: Target heating temperature 1270℃, holding time ≥400min;

[0011] 4) Rolling: The initial rolling temperature of the first stage is >1100℃, the final rolling temperature of the first stage is >950℃, and the reduction of the last two passes is ≥30mm; intermediate water cooling is used before the second stage rolling to reduce the surface temperature and increase the internal deformation. The initial rolling temperature of the second stage is ≤880℃, and the thickness of the intermediate billet is ≥1.0 times the thickness of the finished product +50mm.

[0012] 5) Heat treatment: Q+T process is adopted, quenching temperature is 910±10℃, holding time is 100~130min, water quenching is performed at a speed of 1.8m / min after taking out of the furnace, low-pressure zone swing cooling is performed for 60min, tempering temperature is 610±10℃, holding time is 100~130min, and air cooling is performed after taking out of the furnace.

[0013] Beneficial effects of the invention: The above production process yields extra-thick steel plates of 180~220mm, with a yield strength ≥460MPa, tensile strength greater than 570MPa, elongation ≥17%, thickness tensile strength ≥35%, and impact value ≥60J at -40℃. The steel plates have low manufacturing costs and are suitable for large-scale production. Attached Figure Description

[0014] Figure 1 The image shows the metallographic structure of the steel plate at 1 / 4 thickness as shown in Example 1 (500x magnification). Detailed Implementation

[0015] Example 1: Production method of 180mm thick steel plate

[0016] The steel's chemical composition (percentage) is C=0.12%, Si=0.25%, Mn=1.49%, P=0.008%, S=0.005%, AlT=0.032%, Nb=0.042%, V=0.057%, Ti=0.010%, Ni=0.52%, Cr=0.12%. Key process steps:

[0017] 1) LF refining: Large slag volume is used for slag formation, and the white slag holding time is controlled at 19 minutes;

[0018] 2) Molten casting: The qualified molten steel after LD-LF-VD smelting is poured into the steel ingot mold with the cold material fixed. The overheating temperature of the mold casting is controlled at 35±2℃.

[0019] 3) Heating: Heating temperature 1266℃, holding time 420min;

[0020] 4) Rolling: The first stage rolling temperature is 1170℃, the first stage finishing rolling temperature is 1020℃, and the reduction of the last two passes is 32mm and 35mm respectively; before the second stage rolling, intermediate water cooling is used to reduce the surface temperature and increase the internal deformation. The second stage rolling temperature is 878℃, and the thickness of the intermediate billet is 245mm.

[0021] 5) Heat treatment: Q+T process is adopted, quenching temperature is 910±10℃, holding time is 110min, water quenching is performed at a speed of 1.8m / min after taking out of the furnace, low-pressure zone swing cooling is performed for 60min, tempering temperature is 610±10℃, holding time is 110min, and air cooling is performed after taking out of the furnace.

[0022] The performance test results of the produced steel are shown in Table 1.

[0023] Example 2: Production method of 220mm thick steel plate

[0024] The steel's chemical composition (percentage) is: C=0.13%, Si=0.25%, Mn=1.56%, P=0.006%, S=0.003%, AlT=0.036%, Nb=0.046%, V=0.056%, Ti=0.011%, Ni=0.55%, Cr=0.13%.

[0025] 1) LF refining: Large slag volume is used for slag formation, and the white slag holding time is controlled at 20 minutes;

[0026] 2) Molten casting: The qualified molten steel after LD-LF-VD smelting is poured into the steel ingot mold with the cold material fixed. The overheating temperature of the mold casting is controlled at 35±2℃.

[0027] 3) Heating: Heating temperature 1268℃, holding time 430min;

[0028] 4) Rolling: The first stage rolling temperature is 1160℃, the first stage finishing rolling temperature is 1020℃, and the reduction of the last two passes is 31mm and 33mm; before the second stage rolling, intermediate water cooling is used to reduce the surface temperature and increase the internal deformation. The second stage rolling temperature is 870℃, and the thickness of the intermediate billet is 280mm.

[0029] 5) Heat treatment: Q+T process is adopted, quenching temperature is 910±10℃, holding time is 115min, water quenching is performed at a speed of 1.8m / min after taking out of the furnace, low-pressure zone swing cooling is performed for 60min, tempering temperature is 610±10℃, holding time is 180min, and air cooling is performed after taking out of the furnace.

[0030] The performance test results of the produced steel are shown in Table 1.

[0031] Table 1. Test results of mechanical properties of the steel produced in the examples.

[0032] .

Claims

1. A method for producing extra-thick steel plates with a strength greater than 460 MPa, characterized in that: The steel's chemical composition by mass percentage is: C = 0.12%–0.14%, Si = 0.20%–0.35%, Mn = 1.45%–1.60%, P ≤ 0.010%, S ≤ 0.005%, Alt = 0.020%–0.050%, Nb = 0.040%–0.050%, V = 0.055%, Ti = 0.008%–0.015%, Ni = 0.50%, Cr = 0.10–0.15%, with the remainder being Fe and essential residual elements; the process includes the following steps: 1) LF refining: Large slag volume is used for slag formation, and the white slag holding time is controlled to be more than 15 minutes; 2) Molten casting: The qualified molten steel after LD-LF-VD smelting is poured into the steel ingot mold with the cold material fixed. The overheating temperature at the start of the casting is controlled at 35±3℃. 3) Heating: Target heating temperature 1270℃, holding time ≥400min; 4) Rolling: The initial rolling temperature of the first stage is >1100℃, the final rolling temperature of the first stage is >950℃, and the reduction of the last two passes is ≥30mm; intermediate water cooling is used before the second stage rolling to reduce the surface temperature and increase the internal deformation. The initial rolling temperature of the second stage is ≤880℃, and the thickness of the intermediate billet is ≥1.0 times the thickness of the finished product +50mm. 5) Heat treatment: The Q+T process is adopted, with a quenching temperature of 910±10℃ and a holding time of 100~130min. After exiting the furnace, the steel plate is water-quenched at a speed of 1.8m / min, followed by low-pressure zone oscillation cooling for 60min. The tempering temperature is 610±10℃ and the holding time is 100~130min. After exiting the furnace, the steel plate is air-cooled to obtain an extra-thick steel plate of 180~220mm, with a yield strength greater than 460MPa, a tensile strength greater than 570MPa, an elongation ≥17%, a thickness tensile strength ≥35%, and an impact value of ≥60J at -40℃.

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