CN113186455A

CN113186455A - Production method of high-strength steel plate for nuclear energy safety container

Info

Publication number: CN113186455A
Application number: CN202110337854.9A
Authority: CN
Inventors: 刘立彪; 李建宇; 何航; 贾进; 张勇伟; 张计谋; 汪后明; 徐琛; 刘晓玮
Original assignee: Hunan Valin Xiangtan Iron and Steel Co Ltd
Current assignee: Hunan Valin Xiangtan Iron and Steel Co Ltd
Priority date: 2021-03-30
Filing date: 2021-03-30
Publication date: 2021-07-30

Abstract

The production method of the high-strength steel plate for the nuclear energy safety container comprises the following chemical components, by mass, equal to or less than 0.20% of C, equal to or less than 0.15-0.55% of Si, equal to or less than 0.85-1.7% of Mn, equal to or less than 0.015% of P, equal to or less than 0.005% of S, equal to or less than 0.080% of V, equal to or less than 0.60% of Ni, equal to or less than 0.30% of Mo, equal to or less than 0.010-0.030% of Ti, equal to or less than 0.010-0.050% of Nb, equal to or less than 0.30% of Cr, equal to or less than 0.35% of Cu, equal to or less than 0.0010% of B, equal to or less than 0.020-0.060% of Alt, and the balance of Fe and inevitable impurities; the carbon equivalent Ceq is less than or equal to 0.50. The process comprises the steps of converter smelting, LF refining, vacuum degassing treatment, continuous casting/die casting, slab heating, rolling, quenching and tempering heat treatment. The grain size of the steel is above 8.0 grade; the nonmetallic inclusions of A class, B class, C class and D class are all less than 1.5 grade; lateral impact AKV at-12 ℃ in delivery state and die-welding state₈Average value is more than or equal to 54J, drop weight test T_NDTThe temperature is less than or equal to-28 ℃, and the method can be applied to the manufacture of a safety container of a thorium-based molten salt reactor nuclear energy system.

Description

Production method of high-strength steel plate for nuclear energy safety container

Technical Field

The invention belongs to the technical field of metallurgy, and particularly relates to a production method of a high-strength steel plate for a nuclear energy safety container.

Background

The nuclear energy is used as a novel energy source, has the characteristics of cleanness, no pollution and the like, and is promoting the global revival of the nuclear energy by energy conservation, emission reduction and low-carbon economy. The molten salt reactor is one of 6 candidate reactors of a fourth-generation advanced reactor, and the thorium-based molten salt reactor has the advantages and the potential of efficient thorium utilization, high-temperature hydrogen production, no water cooling, suitability for small-size modular design and the like. The development of thorium-based molten salt heaps would help address both energy and environmental challenges. The invention is very necessary to invent the steel plate suitable for the fourth generation nuclear power technology, and is very important to promote the development of the nuclear power technology.

Disclosure of Invention

The invention aims to provide a production method of a high-strength steel plate for a nuclear energy safety container, in particular to a production method of a high-strength steel plate for a safety container of a thorium-based molten salt reactor nuclear energy system, and the produced steel has high normal-temperature tensile strength and high-temperature strength of 150 ℃ in delivery state and die-welding state, and simultaneously has good low-temperature impact toughness below-12 ℃ and non-plastic transition temperature T below-28 DEG C_NDT。

The technical scheme of the invention is as follows:

the production method of the high-strength steel plate for the nuclear energy safety container comprises the following chemical components, by mass, equal to or less than 0.20% of C, equal to or less than 0.15-0.55% of Si, equal to or less than 0.85-1.70% of Mn, equal to or less than 0.015% of P, equal to or less than 0.005% of S, equal to or less than 0.080% of V, equal to or less than 0.60% of Ni, equal to or less than 0.30% of Mo, equal to or less than 0.010-0.030% of Ti, equal to or less than 0.010-0.050% of Nb, equal to or less than 0.30% of Cr, equal to or less than 0.35% of Cu, equal to or less than 0.0010% of B, equal to or less than 0.020-0.060% of Alt, and the balance of Fe and inevitable impurities, and equal to or less than 0.50% of carbon equivalent Ceq; the method comprises the following process steps:

a. smelting in a converter: slag stopping and tapping, wherein the tapping C is more than or equal to 0.06 percent, and the tapping P is less than or equal to 0.012 percent;

b. LF refining: the white slag is kept for more than 15min, and the S discharged is less than or equal to 0.005 percent;

c. vacuum degassing treatment: the holding time is more than or equal to 15min under the condition that the vacuum degree is less than or equal to 0.5 tor; after the air is broken, Ca treatment is carried out, and a pure calcium line is fed to be more than or equal to 200 m; the soft argon blowing time is more than or equal to 15 min;

d. continuous casting: protecting and casting in the whole process; the superheat degree of the molten steel of the tundish is 8-18 ℃; adopting dynamic soft reduction technology, wherein the reduction is more than 6 mm; the die casting adopts an argon protection pouring technology, the superheat degree of molten steel is 30-40 ℃, a heating agent is added into a riser after pouring, heat preservation is carried out, the steel ingot is taken off line, and stacking and slow cooling are carried out for 48-72 hours by using a heat preservation cover;

e. heating a continuous casting blank: the heating temperature of the plate blank before rolling is 1180-1220 ℃, and the heating speed is 7-12 min/cm; heating the die-cast steel ingot: filling steel ingots, closing a furnace door, braising the steel for 1h, heating to 850 +/-10 ℃ at the speed of 1.8-2 ℃/min, preserving heat for 2-2.5 h, then heating to 1000 ℃ at the heating speed of <2 ℃/min, directly heating to 1260-1300 ℃ at the temperature of 1000 ℃, and preserving heat for 5-13 h until tapping;

f. rolling a continuous casting blank: the first-stage initial rolling temperature is more than or equal to 1050 ℃, the first-stage final rolling temperature is more than 980 ℃, the final reduction rate of three passes is more than 15%, and the thickness of the intermediate blank is more than or equal to 2 times that of the finished product; the initial rolling temperature of the second stage is less than or equal to 900 ℃, and the final rolling temperature is 780-850 ℃; rolling the die-cast steel ingot: the first-stage initial rolling temperature is more than or equal to 1050 ℃, the first-stage final rolling temperature is more than 980 ℃, the thickness of the intermediate blank is more than or equal to 2 times of the thickness of the finished product, the second-stage initial rolling temperature is 840-880 ℃, and the final rolling temperature is 780-820 ℃;

g. and (3) heat treatment: quenching and tempering heat treatment processes are adopted, the quenching temperature is 900-930 ℃, the heat preservation time is 10-40 min, and then a quenching machine is adopted for water quenching; tempering at 630-680 ℃, keeping the temperature for 30-200 min, and then air cooling.

The calculation formula of the carbon equivalent Ceq is as follows: ceq = C + Mn/6+ (Cr + Mo + V)/5+ (Ni + Cu)/15.

The high-strength steel plate product standard for the safety container of the thorium-based molten salt reactor nuclear energy system refers to the related technical standard of the steel plate for the safety container of the thorium-based molten salt reactor nuclear energy system test platform project, and the mechanical properties of the plate delivery state and the die welding state meet the following requirements: the normal-temperature stretching Rp0.2 is more than or equal to 415MPa, Rm = 585-705 MPa, and A50 is more than or equal to 20%; the high-temperature stretching at 150 ℃ is performed, wherein Rp0.2 is more than or equal to 360Mpa, and Rm is more than or equal to 528 Mpa; -12 ℃ transverse impact AKV₈The average value is more than or equal to 54J; drop weight test T_NDTAt most-28 ℃. The non-metallic inclusions in A, B, C and D of the steel plate are less than 1.5 grade.

The invention has the beneficial effects that: through reasonable chemical composition design, Ceq is less than or equal to 0.50 percent; the cleanliness of the steel is ensured through an LF refining and vacuum degassing treatment process; the process of controlled rolling, quenching and tempering is adopted, the structure of the tempered sorbite is finally obtained, the grain size reaches 9.0-10.0 grade, and nonmetallic inclusions of A class, B class, C class and D class are all less than 1.5 grade; the normal-temperature tensile strength of the thorium-based molten salt nuclear energy system in the delivery state and the simulated postwelding state reaches more than 585MPa, the high-temperature tensile strength at 150 ℃ is more than 528MPa, and the high-strength steel plate has good low-temperature toughness and is used for the safety container of the thorium-based molten salt nuclear energy system with the thickness of 10-150 mm.

Drawings

FIG. 1 is a structural view of a steel of example 1 of the present invention.

Detailed Description

The present invention will be described in further detail with reference to examples.

Example 1: production method of high-strength steel plate for thorium-based molten salt reactor nuclear energy safety container

The implementation process of the steel-making process comprises the following steps: converter tapping C =0.06%, and P = 0.010%. The holding time of LF refining white slag is 20min, S =0.0040% when the slag is out of the refining station, VD vacuum degree is 0.5tor, vacuum maintaining time is 16min, a pure Ca wire is fed for 250 m treatment after the vacuum breaking, and soft argon blowing time is 16 min. And continuously casting a casting blank with the thickness of 260mm, wherein the superheat degree of molten steel in a continuous casting tundish is 11-12 ℃, the reduction amount under dynamic soft reduction is 6.3mm, and the smelting components are shown in table 1.

The steel rolling process comprises the following implementation processes: the heating speed of the casting blank is 9.0min/cm, the tapping temperature is 1195 ℃, the initial rolling temperature of the first stage is 1060 ℃, the reduction rates of the last three passes are respectively 20%, 21% and 20%, the final rolling temperature is 1000 ℃, and the thickness of the rolled intermediate blank is 110 mm. The second stage is at the initial rolling temperature of 820 ℃, the accumulated reduction rate is 50 percent, the final rolling temperature is 815 ℃, and the thickness of the rolled product is 50 mm.

The implementation process of the heat treatment process comprises the following steps: heating the steel plate from room temperature to 910 ℃, preserving heat for 20 minutes, and then quenching the steel plate to room temperature by a quenching machine; tempering at 660 ℃, preserving the heat for 35 minutes, and then cooling in air. The results of the non-metallic inclusion test of the steel sheets obtained are shown in Table 2, and the properties thereof are shown in Table 3.

Example 2: production method of high-strength steel plate for thorium-based molten salt reactor nuclear energy safety container

The implementation process of the steel-making process comprises the following steps: converter tapping C =0.09%, and P = 0.009%. Keeping the LF refining white slag for 18min, leaving S =0.0038%, keeping the VD vacuum degree at 0.5tor, keeping the vacuum degree for 17min, feeding a pure Ca wire for 250 m treatment after breaking the vacuum, and blowing argon for 16min in a soft blowing way. And continuously casting a casting blank with the thickness of 260mm, wherein the superheat degree of molten steel in a continuous casting tundish is 12-15 ℃, the reduction under dynamic soft reduction is 6.2mm, and the smelting components are shown in table 1.

The steel rolling process comprises the following implementation processes: the heating speed of the casting blank is 9.1min/cm, the tapping temperature is 1190 ℃, the initial rolling temperature of the first stage is 1070 ℃, the reduction rates of the last three passes are respectively 21%, 19% and 20%, the final rolling temperature is 1005 ℃, and the thickness of the rolled intermediate blank is 70 mm. The second stage is at the initial rolling temperature of 895 ℃, the cumulative reduction rate of 49 percent and the final rolling temperature of 830 ℃, and the thickness of the rolled product is 20 mm.

The implementation process of the heat treatment process comprises the following steps: heating the steel plate from room temperature to 900 ℃, preserving heat for 13 minutes, and then quenching the steel plate to room temperature by a quenching machine; tempering at 680 deg.c for 35 min, and air cooling. The results of the non-metallic inclusion test of the steel sheets obtained are shown in Table 2, and the properties thereof are shown in Table 3.

Example 3: production method of high-strength steel plate for thorium-based molten salt reactor nuclear energy safety container

The implementation process of the steel-making process comprises the following steps: converter tapping C =0.08%, and P = 0.009%. The holding time of LF refining white slag is 16min, S =0.0036% at the station, VD vacuum degree is 0.5tor, vacuum maintaining time is 18min, 250 m pure Ca wire is fed for processing after breaking the vacuum, and soft argon blowing time is 20 min. And casting 35 tons of ingot steel ingots in a die casting way, wherein the superheat degree of molten steel is 36 ℃, the ingot steel is demoulded after being cooled in a heaping way for 60 hours, and the smelting components are shown in table 1.

The steel rolling process comprises the following implementation processes: and (3) after the surface of the steel ingot is subjected to flame cleaning, putting the steel ingot into a furnace for carrying out steel sealing for 1 hour, heating to 850 ℃ at the speed of 2 ℃/min, preserving the heat for 2.1 hours, then heating to 1000 ℃ at the heating speed of 1.8 ℃/min, heating to 1280 ℃ at the speed of 3.0 ℃/min, preserving the heat for 9 hours, and then tapping. The first stage is at the beginning temperature of 1095 ℃ and the final temperature of 1005 ℃ and the thickness of the rolled intermediate billet is 320 mm. The second stage has the initial rolling temperature of 855 ℃, the final rolling temperature of 800 ℃ and the thickness of a rolled product of 150 mm.

The implementation process of the heat treatment process comprises the following steps: heating the steel plate from room temperature to 930 ℃, preserving heat for 25 minutes, and then quenching the steel plate to room temperature by a quenching machine; tempering at 640 deg.c, maintaining for 180 min and air cooling. Finally, the detection result of the non-metallic inclusions of the steel plate is shown in table 2; the properties are shown in Table 3; the metallographic structure is shown in figure 1, and the structure is tempered sorbite with grain size of 8-9 grade.

Table 1 chemical composition (wt.%) of the steels of the examples

。

TABLE 2 results of non-metallic inclusion test of steels of examples

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TABLE 3 test results of properties of steels of examples

。

The room temperature tensile and Charpy V-notch impact tests in Table 3 were conducted in accordance with ASME SA 370. Example 2 round tensile specimens were taken and tested in high temperature tensile according to ASME E21; examples 1 and 3 drop weight tests were conducted using P-2 type samples; example 2 drop weight test a P-3 type sample was used. All samples were perpendicular to the direction of rolling of the steel sheet, with the longitudinal axis of the sample being greater than the sheet thickness 1/4. The simulated postweld heat treatment process of the as-welded test sample in table 2 is as follows: the temperature of the sample in the furnace is less than or equal to 425 ℃, and the heating rate is less than or equal to 55 ℃/h; the temperature is kept at 610 +/-10 ℃, the temperature keeping time is 10-10.5 h, and then the product is cooled to below 425 ℃ at a cooling rate of less than or equal to 55 ℃/h.

As shown in Table 1, the carbon equivalent Ceq of each example was less than 0.50%.

As shown in figure 1, the steel of the invention is a stable tempered sorbite structure, and the grain size is above 8 grades.

As shown in Table 2, the nonmetallic inclusions of A-, B-, C-and D-types in the examples were all less than 1.5.

As shown in Table 3, in each example, the room-temperature elongation Rp0.2 is not less than 415MPa, Rm = 585-705 MPa, and A50 is not less than 20%; the high-temperature stretching at 150 ℃ is performed, wherein Rp0.2 is more than or equal to 360Mpa, and Rm is more than or equal to 528 Mpa; -12 ℃ transverse impact AKV₈The average value is more than or equal to 47J, and the steel plate has no plastic transition temperature T_NDTAt most-28 ℃. The steel has good high-temperature strength and low-temperature toughness, meets the requirements of various mechanical properties in delivery state and die welding state, has good internal and surface quality, and meets the requirement of a thorium-based molten salt nuclear reactor energy system testThe steel plate for the safety container of the Taiji project has the relevant technical standard requirement, and can be used for manufacturing the safety container of the thorium-based molten salt reactor nuclear energy system.

Claims

1. The production method of the high-strength steel plate for the nuclear energy safety container is characterized by comprising the following steps of: the steel comprises the chemical components of, by mass, equal to or less than 0.20% of C, equal to or less than 0.15-0.55% of Si, equal to or less than 0.85-1.70% of Mn, equal to or less than 0.015% of P, equal to or less than 0.005% of S, equal to or less than 0.080% of V, equal to or less than 0.60% of Ni, equal to or less than 0.30% of Mo, equal to or less than 0.010-0.030% of Ti, equal to or less than 0.010-0.050% of Nb, equal to or less than 0.30% of Cr, equal to or less than 0.35% of Cu, equal to or less than 0.0010% of B, equal to or less than 0.020-0.060% of Alt, and the balance of Fe and inevitable impurities, and equal to or less than 0.50% of carbon equivalent Ceq; the method comprises the following process steps: