CN115094298A - Production method of 600 MPa-grade low-carbon equivalent hydroelectric steel - Google Patents

Abstract

The invention discloses a production method of 600 MPa-grade low-carbon equivalent hydroelectric steel, which comprises the following chemical components by mass percent, C = 0.05-0.07%, Si = 0.15-0.30%, Mn = 1.50-1.60%, P is less than or equal to 0.015%, S is less than or equal to 0.005%, Alt = 0.020-0.050%, Nb = 0.020-0.030%, V = 0.040-0.050%, Ti = 0.012-0.020%, Ni = 0.20-0.30%, Cr = 0.10-0.15%, Mo = 0.30-0.40%, Cu is less than or equal to 0.05%, and the balance is Fe and indispensable residual elements, wherein CE is less than or equal to 0.45%; the process comprises the following steps: converter smelting → LF refining → VD vacuum processing → continuous casting → slab heating → rolling → heat treatment. According to the invention, Nb, V, Ti, Ni, Cr and Mo are added, and an LF + VD process is adopted to ensure the cleanliness of steel, so that the steel plate with the thickness of 30-60 mm, the yield strength of more than or equal to 550MPa, the tensile strength of 640-830 MPa, the elongation of more than or equal to 17%, and the impact value at-20 ℃ and the strain aging impact value of more than or equal to 100J is produced.

Description

Production method of 600 MPa-grade low-carbon equivalent hydroelectric steel

Technical Field

The invention belongs to the technical field of metallurgy and heat treatment, and relates to a production method of 600 MPa-grade low-carbon equivalent hydroelectric steel.

Background

With the development of socio-economic, the demand of steel sheets for containers is increasing. The large-scale pressure vessels are increasing, and more strict technical requirements are put forward on the welding performance and the obdurability of the steel plates. In practical engineering application, the requirements of design specifications on the mechanical properties of materials are often strict with the requirements of relevant standards. From the technical aspect, a higher carbon equivalent is disadvantageous to the welding performance; the carbon equivalent is reduced, the weldability and the impact toughness can be improved, and the safety of equipment is further improved.

Disclosure of Invention

The invention aims to provide a production method of 600 MPa-level low-carbon equivalent hydroelectric steel, which can meet the technical requirements of a steel plate for a pressure container, has the yield strength of more than or equal to 550MPa, the tensile strength of 640-830 MPa, the elongation of more than or equal to 17 percent, and the impact value at minus 20 ℃ and the strain aging of more than or equal to 100J.

The technical scheme of the invention is as follows:

the production method of 600 MPa-grade low-carbon equivalent hydroelectric steel comprises the following chemical components, by mass, 0.05-0.07% of C, 0.15-0.30% of Si, 1.50-1.60% of Mn, less than or equal to 0.015% of P, less than or equal to 0.005% of S, 0.020-0.050% of Alt, 0.020-0.030% of Nb, 0.040-0.050% of V, 0.012-0.020% of Ti, 0.20-0.30% of Ni, 0.10-0.15% of Cr, 0.30-0.40% of Mo, less than or equal to 0.05% of Cu, less than or equal to 0.45% of CE, and the balance Fe and essential residual elements; the method comprises the following process steps:

(1) smelting in a converter: controlling the tapping temperature to be more than or equal to 0.05 percent and the tapping P to be less than or equal to 0.015 percent, and the point blowing times to be less than or equal to 2 times;

(2) LF refining: slagging is carried out by adopting a large amount of slag, and the white slag retention time is controlled to be more than 15 min;

(3) and (3) vacuum treatment: refining under the pressure of less than or equal to 0.5tor for more than or equal to 25 min;

(4) casting: the superheat degree is 10-20 ℃, and the dynamic light pressure is 5% -8%;

(5) heating: the temperature of a hearth of the heating furnace is less than or equal to 1200 ℃, the soaking temperature is 1150-1180 ℃, and the soaking time is 40-80 min;

(6) rolling: the initial rolling temperature of the first stage is 1000-1180 ℃, the final rolling temperature of the first stage is more than 950 ℃, and the reduction rate of the last two passes is more than or equal to 18 percent; the second-stage initial rolling temperature is less than 900 ℃, the thickness of the rolled intermediate blank is more than or equal to 2.0 times of the thickness of the finished product, and the final rolling temperature is less than or equal to 840 ℃;

(7) and (3) heat treatment: and (2) performing Q + T process, quenching at the quenching temperature of 910-930 ℃ for 25-50 min, water-cooling quenching at the speed of 3m/min after discharging, carrying out water-cooling quenching at the speed of 550-600 m/h on 2 groups of gaps, carrying out upward and downward water proportioning at a ratio of 1:1.4, carrying out high-density water proportioning at 16 groups at a ratio of 250-270 m/h, carrying out upward and downward water proportioning at a ratio of 1:1.45, tempering at the tempering temperature of 620-660 ℃, and carrying out heat preservation for 25-50 min for air cooling after discharging.

CE=C＋Mn/6＋Si/24＋Ni/40＋Cr/5＋Mo/4＋V/14

The invention principle is as follows: c is an element for improving the strength of the steel, but the content of C is high, so that the welding performance and the toughness of the steel are not facilitated, the hardenability of the steel plate is improved by controlling the content of C within a reasonable range, and the strength and the toughness of the steel are ensured. Si is a solid solution strengthening element, and is beneficial to improving the hardenability and the strength of the steel plate. Mn is a solid-solution strengthening element and is advantageous for improving both the strength and toughness of the steel sheet. Nb in steel mainly forms fine carbonitrides with C, N to improve the strength and toughness of steel, in controlled rolling microalloy steel, the effect of Nb element on grain size refinement and the capability of delaying austenite recrystallization are most prominent, and a trace amount of Nb has a strong inhibiting effect on austenite recrystallization. As Nb plays a role in carbide precipitation hardening in steel, the steel grains can be obviously refined and the normal-temperature tensile strength and yield strength of the steel can be improved by containing trace amount of Nb. Vanadium and iron form a continuous solid solution, an austenite phase region is strongly reduced, vanadium, carbon, nitrogen and oxygen have extremely strong affinity, the vanadium, the carbon, the nitrogen and the oxygen mainly exist in the steel in the form of carbide or oxide and nitride, the content of vanadium in austenite, the number of undissolved carbide and the actual grain size of the steel are changed by controlling austenitizing temperature, the hardenability of the steel can be adjusted, and the steel still keeps a fine grain structure at higher temperature because the vanadium forms stable and insoluble carbide, so that the overheating sensitivity of the steel is greatly reduced; titanium is a strong deoxidizer in steel, and can compact the internal structure of the steel and refine the grain strength; the aging sensitivity and the cold brittleness are reduced, and the welding performance is improved; chromium significantly increases strength, hardness and wear resistance, but simultaneously decreases plasticity and toughness. Chromium also improves the oxidation resistance and corrosion resistance of the steel. P is high and is unfavorable to welding performance, and the steel has certain cold brittleness, belongs to harmful elements in the steel grade and is controlled to be low in content as much as possible. S is easy to form MnS inclusions, so that the steel has certain hot brittleness, belongs to harmful elements in the steel, and is controlled to be as low as possible.

The invention has the beneficial effects that: the internal quality of the blank is ensured through continuous casting billet production, the low-cost chemical component design of only adding Nb, V, Ti and Cr alloy is selected, and the cleanliness of steel is ensured through the LF + VD process. Through the effective implementation of the technical measures, the low yield ratio quenched and tempered container steel plate is successfully produced; the thickness of the produced steel plate is 6-60 mm, the yield strength is more than or equal to 415MPa, the tensile strength is 550-690 MPa, the elongation is more than or equal to 22%, and the impact value at minus 20 ℃ is more than or equal to 100J.

Drawings

FIG. 1 is a metallographic (500 times) photograph of an optical microscopic metallographic photograph of a steel sheet 1/4 prepared in example 1 at a thickness position.

FIG. 2 is a metallographic (500 times) photograph of an optical microscopic metallographic photograph of a steel sheet 1/4 prepared in example 2 at a thickness position.

Detailed Description

The following examples are further illustrative.

Example 1: production of 600 MPa-grade low-carbon equivalent hydroelectric steel

The process comprises the following steps:

(1) smelting in a converter: tapping C =0.05%, tapping P =0.009%, tapping temperature 1665 ℃, and point blowing times are 1 time;

(2) LF refining: keeping the white slag for 18 min;

(3) vacuum treatment: VD, the vacuum degree is 0.48tor, and the holding time is 16 min;

(4) casting: pouring molten steel in a tundish, wherein the superheat degree of the molten steel in the tundish is 13-18 ℃, and continuously casting a casting blank with the thickness of 260 mm; the smelting chemical composition of the steel is shown in table 1;

(5) heating: setting the temperature of a hearth to 1190 ℃, the soaking temperature to 1170 ℃, and the soaking time to 50 min;

(6) rolling: the initial rolling temperature of the first stage is 1100 ℃, the reduction rates of the last three passes are respectively 18%, 23% and 26.5%, and the final rolling temperature is 980 ℃. The second stage has the rolling start temperature of 880 ℃, the thickness of the rolled intermediate blank is 80mm, the finishing temperature is about 830 ℃, and the thickness of the rolled finished product is 30 mm;

(7) and (3) heat treatment: heating the steel plate from room temperature to 920 ℃, preserving heat for 30min, discharging from the furnace, cooling to room temperature by water, tempering at 660 ℃, preserving heat for 40min, discharging from the furnace, and air cooling.

The properties of the resulting steel sheet are shown in Table 2.

Example 2: production of 600 MPa-grade low-carbon equivalent hydroelectric steel

(1) Smelting in a converter: : tapping by a converter for C =0.06%, tapping P =0.010%, tapping temperature is 1670 ℃, and point blowing times are 1 time;

(2) LF refining: keeping the white slag for 20 min;

(3) vacuum treatment: VD, the vacuum degree is 0.48tor, and the holding time is 16 min;

(4) casting: the superheat degree of molten steel in a continuous casting tundish is 14-18 ℃, a casting blank with the thickness of 300mm is obtained, and the smelting chemical components of the steel are shown in table 1;

(5) heating: setting the furnace temperature at 1200 ℃, the soaking temperature at 1170 ℃, and the soaking time at 60 min;

(6) rolling: the first stage of the rolling temperature is 1070 ℃, the final three-pass reduction rate is respectively 18 percent, 21 percent and 23.5 percent, and the final rolling temperature is 970 ℃; the second stage has the rolling temperature of 860 ℃, the thickness of the rolled intermediate blank is 130mm, the finishing temperature is about 820 ℃, and the thickness of the rolled finished product is 60 mm;

(7) and (3) heat treatment: and heating the steel plate from room temperature to 930 ℃, preserving heat for 30min, discharging from the furnace, cooling to room temperature by water, tempering at 630 ℃, preserving heat for 30min, discharging from the furnace, and air cooling.

The properties of the resulting steel sheet are shown in Table 2.

Table 1 chemical composition of example steels%

。

TABLE 2 results of mechanical property measurements of the steels of the examples

。

The product produced by the method has the advantages of 6000 tons in total, excellent surface quality, 100 percent of first-grade flaw detection qualification rate, 100 percent of performance qualification rate and 100 percent of customer inspection qualification rate.

Table 1 shows: the components of each embodiment meet the design requirements; shown in Table 2: the tensile and impact properties of each example are stable, and the steel plate has uniform properties.

Claims (1)

1. A production method of 600 MPa-level low-carbon equivalent hydroelectric steel is characterized by comprising the following steps: the steel comprises the following chemical components, by mass, 0.05-0.07% of C, 0.15-0.30% of Si, 1.50-1.60% of Mn, 0.015% or less of P, 0.005% or less of S, 0.020-0.050% of Alt, 0.020-0.030% of Nb, 0.040-0.050% of V, 0.012-0.020% of Ti, 0.20-0.30% of Ni, 0.10-0.15% of Cr, 0.30-0.40% of Mo, 0.05% or less of Cu, and the balance Fe and indispensable residual elements, wherein the content of CE is 0.45% or less; the method comprises the following process steps:

(1) smelting in a converter: controlling the C to be more than or equal to 0.05 percent and the P to be less than or equal to 0.015 percent during tapping, controlling the tapping temperature to be more than or equal to 1650 ℃ and controlling the point blowing frequency to be less than or equal to 2 times;

(2) LF refining: slagging is carried out by adopting a large amount of slag, and the white slag holding time is controlled to be more than 15 min;

(3) and (3) vacuum treatment: refining under the pressure of less than or equal to 0.5tor for more than or equal to 25 min;

(4) casting: the superheat degree is 10-20 ℃, and the dynamic light pressure is 5% -8%;

(5) heating: the temperature of a hearth of the heating furnace is less than or equal to 1200 ℃, the soaking temperature is 1150-1180 ℃, and the soaking time is 40-80 min;

(6) rolling: the initial rolling temperature of the first stage is 1000-1180 ℃, the final rolling temperature of the first stage is more than 950 ℃, and the reduction rate of the last two passes is more than or equal to 18 percent; the second-stage initial rolling temperature is less than 900 ℃, the thickness of the rolled intermediate blank is more than or equal to 2.0 times of the thickness of the finished product, and the final rolling temperature is less than or equal to 840 ℃;

(7) and (3) heat treatment: and (2) performing Q + T process, quenching at the quenching temperature of 910-930 ℃ for 25-50 min, water-cooling quenching at the speed of 3m/min after discharging, carrying out water-cooling quenching at the speed of 550-600 m/h on 2 groups of gaps, carrying out upward and downward water proportioning at a ratio of 1:1.4, carrying out high-density water proportioning at 16 groups at a ratio of 250-270 m/h, carrying out upward and downward water proportioning at a ratio of 1:1.45, tempering at the tempering temperature of 620-660 ℃, and carrying out heat preservation for 25-50 min for air cooling after discharging.

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