Production method of extra-thick plate with strength larger than 460 MPa

Abstract

The invention discloses a production method of an extra-thick steel plate with the strength larger than 460 MPa. The steel comprises, by mass, 0.12%-0.14% of C, 0.20%-0.35% of Si, 1.45%-1.60% of Mn, smaller than or equal to 0.010% of P, smaller than or equal to 0.005% of S, 0.020%-0.050% of AlT, 0.040%-0.050% of Nb, 0.055%-0.065% of V, 0.008%-0.015% of Ti, 0.50%-0.60% of Ni, 0.10%-0.15% of Cr and the balance Fe and essential residual elements. The technological process comprises the steps of converter smelting, LF refining, VD / RH vacuum treatment, continuous casting, slab heating, rolling and heat treatment. Through the chemical component design of adding Nb, V, Ti, Cr and Ni alloy and the LF + VD process, the cleanliness of steel is guaranteed, the produced super-thick steel plate with the thickness of 180-220 mm is larger than or equal to 460 MPa in yield strength, larger than 570 MPa in tensile strength, larger than or equal to 17% in elongation, larger than or equal to 35% in thickness tensile strength, larger than or equal to 60 J in impact value at the temperature of-40 DEG C and low in steel plate manufacturing cost.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and heat treatment, and relates to a production method of an extra-thick plate with a strength greater than 460 MPa. Background Art

[0002] Extra-thick plates have become indispensable materials in modern social and economic development, national defense construction, and major national engineering construction, and are widely used in coal machinery, shipbuilding, boiler containers, wind power generation, bridges, high-rise construction and other industries. With the implementation of the national policy of "carbon peak and carbon neutrality", the development of wind energy and hydrogen energy is accelerated. As an important wind power base, the Northwest region has a broad market space for high-quality extra-thick plates. At present, the annual demand for extra-thick plates above 150mm in the steel market is very large and has a rising trend. For example, the wind power industry that has grown rapidly in the Northwest region in recent years has a certain proportion of extra-thick plate demand in its tower manufacturing.

[0003] However, during the smelting process of extra-thick plates, as the thickness of the steel plates increases, the size of the continuous casting ingots of the rolled extra-thick plates increases accordingly, resulting in element segregation during the solidification process, which seriously deteriorates the quality of the ingots. It is very easy to have center segregation, shrinkage holes and looseness, which affect the flaw detection pass rate of the steel plates. At the same time, during the rolling process of the extra-thick plates, the rolling force has difficulty penetrating along the thickness direction, the deformation of the core is insufficient, and the performance differences in the thickness direction are large. The problems are mainly reflected in the instability of strength and impact properties.

[0004] Chinese patent CN200910089346.2 discloses a 460MPa yield strength low yield ratio extra thick steel plate for construction and a manufacturing method, the chemical composition mass percentage of which 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%, and the balance is iron and unavoidable impurities. Its design is suitable for -20℃ impact, and the thickness of the embodiment is unclear, which cannot meet the production requirements of thick steel plates. Summary of the invention

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

[0006] The technical solution of the present invention: A production method for extra-thick plates with a strength greater than 460 MPa, the chemical composition of the steel in 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% - 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; it includes the following process steps: 1) LF refining: Large slag amount is adopted for slag making, and the white slag holding time is controlled above 15 min; 2) Ingot casting: The bottom-pouring molten steel ingot casting method is adopted, and the qualified molten steel after LD-LF-VD smelting is poured into the ingot mold with cold materials fixed, and the overheat at the start of ingot casting is controlled at 35 ± 3 °C; 3) Heating: The target heating temperature is 1270 °C, and the holding time ≥ 400 min; 4) Rolling: The starting rolling temperature in the first stage > 1100 °C, the final rolling temperature in the first stage > 950 °C, and the reduction in the last two passes ≥ 30 mm; Intermediate water cooling is adopted before the second-stage rolling to reduce the surface temperature and increase the internal deformation. The starting rolling temperature in the second stage ≤ 880 °C, and the thickness of the intermediate billet ≥ 1.0 times the finished product thickness + 50 mm; 5) Heat treatment: The Q+T process is adopted, the quenching temperature is 910 ± 10 °C, the holding time is 100 - 130 min, water quenching is carried out at a speed of 1.8 m / min when discharging from the furnace, and swing cooling is carried out in the low-pressure area for 60 min. The tempering temperature is 610 ± 10 °C, the holding time is 100 - 130 min, and air cooling is carried out after discharging from the furnace.

[0007] Advantages of the invention: 180 - 220 mm extra-thick steel plates are obtained through the above production process, with a yield strength ≥ 460 MPa, a tensile strength greater than 570 Mpa, an elongation rate ≥ 17%, a thickness elongation ≥ 35%, and an impact value at -40 °C ≥ 60 J. The manufacturing cost of the steel plate is low and it is suitable for large-scale production. Description of the drawings

[0008] Figure 1 Optical microscopic metallographic structure diagram (500 times) of the 1 / 4 thickness position of the steel plate prepared in Example 1. Detailed implementation mode

[0009] Example 1: Production method of 180 mm thick steel plate The chemical composition percentage of the steel 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: 1) LF refining: Large slag amount is adopted for slag making, and the white slag holding time is controlled at 19 min; 2) Ingot casting: The bottom-pouring liquid steel ingot casting method is adopted. The qualified liquid steel after LD-LF-VD smelting is poured into the ingot mold with cold materials fixed. The superheat at the start of ingot casting is controlled at 35 ± 2 °C; 3) Heating: The heating temperature is 1266 °C, and the holding time is 420 min; 4) Rolling: The starting rolling temperature in the first stage is 1170 °C, the final rolling temperature in the first stage is 1020 °C, and the reduction in the last two passes is 32 mm and 35 mm; Intermediate water cooling is adopted before the second-stage rolling to reduce the surface temperature and increase the internal deformation. The starting rolling temperature in the second stage is 878 °C, and the thickness of the rolled intermediate billet is 245 mm; 5) Heat treatment: The Q + T process is adopted. The quenching temperature is 910 ± 10 °C, the holding time is 110 min, and it is water-cooled quenched at a speed of 1.8 m / min after being taken out of the furnace. It is cooled with swing in the low-pressure area for 60 min. The tempering temperature is 610 ± 10 °C, and the holding time is 110 min. Then it is taken out of the furnace and air-cooled.

[0010] The performance test results of the produced steel are shown in Table 1.

[0011] Example 2: Production method of 220-mm-thick steel plate The chemical composition percentage of the steel 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%, 1) LF refining: Large slag amount is adopted for slag making, and the white slag holding time is controlled at 20 min; 2) Ingot casting: The bottom-pouring liquid steel ingot casting method is adopted. The qualified liquid steel after LD-LF-VD smelting is poured into the ingot mold with cold materials fixed. The superheat at the start of ingot casting is controlled at 35 ± 2 °C; 3) Heating: The heating temperature is 1268 °C, and the holding time is 430 min; 4) Rolling: The starting rolling temperature in the first stage is 1160 °C, the final rolling temperature in the first stage is 1020 °C, and the reduction in the last two passes is 31 mm and 33 mm; Intermediate water cooling is adopted before the second-stage rolling to reduce the surface temperature and increase the internal deformation. The starting rolling temperature in the second stage is 870 °C, and the thickness of the rolled intermediate billet is 280 mm; 5) Heat treatment: Adopt the Q+T process, with a quenching temperature of 910±10°C, a holding time of 115 minutes, water-cooled quenching at a speed of 1.8 m / min when taken out of the furnace, swing cooling in the low-pressure area for 60 minutes, a tempering temperature of 610±10°C, and a holding time of 180 minutes, then air-cooled when taken out of the furnace.

[0012] The performance test results of the produced steel are shown in Table 1.

[0013] Table 1 Mechanical property test results of the steel produced in the examples 。

Claims

1. A method for producing extra thick steel plates with a strength greater than 460 MPa, characterized in that: The chemical composition of the steel 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%~0.065%, Ti=0.008%~0.015%, Ni=0.50%~0.60%, Cr=0.10~0.15%, and the rest are Fe and essential residual elements; the process steps include the following: 1) LF refining: a large amount of slag is used for slag making, and the white slag retention time is controlled to be more than 15 minutes; 2) Mold casting: Use the pouring molten steel mold casting method to cast the qualified molten steel after LD-LF-VD smelting into the ingot mold with the cold material fixed, and the superheat of the mold casting is controlled at 35±3℃; 3) Heating: Target heating temperature 1270℃, holding time ≥400min; 4) Rolling: The first-stage rolling temperature is greater than 1100°C, the first-stage final rolling temperature is greater than 950°C, and the last two-pass reduction is ≥30mm; intermediate water cooling is used before the second-stage rolling to reduce the surface temperature and increase the internal deformation. The second-stage rolling temperature is ≤880°C, and the thickness of the rolling intermediate billet is ≥1.0 times the finished product thickness + 50mm; 5) Heat treatment: Q+T process is adopted, quenching temperature is 910±10℃, holding time is 100~130min, water cooling quenching is carried out at a speed of 1.8m / min after being taken out of the furnace, swing cooling is carried out in the low-pressure zone for 60min, tempering temperature is 610±10℃, holding time is 100~130min, and air cooling is carried out after being taken out of the furnace to obtain 180~220mm extra-thick steel plates with yield strength ≥460MPa, tensile strength greater than 570Mpa, elongation ≥17%, thickness stretching ≥35%, and -40℃ impact value ≥60J.

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