Production method of thin steel plate for nuclear containment vessel

Abstract

The invention discloses a production method of a thin steel plate for a nuclear containment vessel. The steel plate comprises the following chemical components in percentage by mass: less than or equal to 0.20% of C, 0.40-0.50% of Si, 0.75-1.50% of Mn, less than or equal to 0.030% of P, less than or equal to 0.010% of S, less than or equal to 0.003% of Nb and less than or equal to 0.003% of V. Ti < = 0.003%; alt is greater than or equal to 0.30%; alt / N is greater than or equal to 4, and the balance is Fe and inevitable impurities. The production method comprises the procedures of smelting and rolling. The smelting process adopts an LF + VD external refining process; a single-phase region high-temperature fast rolling process is adopted in the rolling procedure. The produced thin steel plate for the nuclear containment vessel with the thickness of 5-10 mm meets the requirement for low yield strength, the low-temperature toughness at the temperature of-40 DEG C is good, the normal-temperature tensile ReH is 300-330 MPa, Rm is larger than or equal to 450 MPa, and A is larger than or equal to 40%; the transverse impact energy at-40 DEG C is greater than or equal to 100J.

Description

Technical Field

[0001] The present invention belongs to the field of metallurgical technology and relates to a production method of thin steel plates for nuclear containment vessels. Background Art

[0002] In the field of nuclear power generation, the nuclear containment vessel is the last physical barrier of the nuclear reactor, playing a key role in preventing the leakage of radioactive substances, withstanding external extreme events such as earthquakes and aircraft impacts, and the internal high-pressure and high-temperature environment. Its structural materials require excellent comprehensive mechanical properties and long-term service stability and other stringent requirements. At present, low-alloy high-strength steels are generally used for the steel plates of nuclear containment vessels, and the target mechanical properties are achieved through normalizing or quenching and tempering treatments. However, the traditional process not only has high costs, but also has problems such as the contradiction between low yield and high plastic toughness and insufficient tissue uniformity under heat treatment, which affects the performance consistency of the steel plates and increases the risk of local failure of the containment vessel.

[0003] Therefore, there is an urgent need to develop a production technology for special steel plates for nuclear containment vessels based on the normalizing rolling process. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a production method of thin steel plates for nuclear containment vessels. This technology can enable the steel plates to obtain uniform microstructures after rolling and control the grain size within a reasonable range. The thickness specification of the steel plates is 5 - 10 mm; the steel plates still meet the performance requirements after normalizing treatment during subsequent processing and manufacturing: when the steel plates are sampled for simulated normalizing treatment, the mechanical properties still meet the requirements of normal temperature tensile ReH = 300 - 330 MPa, Rm ≥ 450 MPa, A ≥ 40%; the transverse impact energy at -40°C ≥ 100 J; the grain size of the steel plate structure is 5 - 8 grades.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is: 1. A production method of thin steel plates for a low containment vessel, characterized in that: the mass percentage content of the chemical components of the steel plates is C ≤ 0.20%, Si = 0.40% - 0.50%, Mn = 0.75% - 1.50%, P ≤ 0.030%, S ≤ 0.010%, Nb ≤ 0.003%, V ≤ 0.003%; Ti ≤ 0.003%; Alt ≥ 0.30%; Alt / N ≥ 4, and the balance is Fe and inevitable impurities; the thickness specification of the steel plates is 5 - 10 mm; when the steel plates are sampled for simulated normalizing treatment, the mechanical properties still meet the requirements of normal temperature tensile ReH = 300 - 330 MPa, Rm ≥ 450 MPa, A ≥ 40%; the transverse impact energy at -40°C ≥ 100 J; the grain size of the steel plate structure is 5 - 8 grades; the key process steps include: (1)Smelting: The LF+VD secondary refining process is adopted; in the LF process, ferrosilicon manganese alloy is first used for deoxidation, and the addition amount of ferrosilicon manganese alloy per ton of molten steel is ≥10 kg; then aluminum wire is used for deep deoxidation, and the white slag holding time is ≥20 min; (2)Rolling: The billet thickness is ≤150 mm, and the billet holding temperature is 1260 - 1300 °C; the single-phase region high-temperature rapid rolling process is adopted, the starting rolling temperature is ≥1220 °C, the finishing rolling temperature is ≥950 °C, and it is air-cooled to ≤600 °C after rolling and then stacked for slow cooling.

[0006] The thickness specification of the steel plate produced by the present invention is 5 - 10 mm; the steel plate produced still meets the performance requirements after normalizing treatment during subsequent processing and manufacturing: the mechanical properties still meet the requirements of normal temperature tensile ReH = 300 - 330 MPa, Rm ≥ 450 MPa, A ≥ 40%; the transverse impact energy at -40 °C is ≥100 J; Innovation points and beneficial effects: 1) Control the addition of grain-refining elements Nb, V, Ti, and ensure the strength basis through C and Mn elements; at the same time, increase the addition of Si and Al, which play a role in inhibiting the precipitation of carbides and promoting the precipitation of ferrite structure. However, in order to prevent the large precipitation of AlN under high Al content, the present invention limits Al / N ≥ 4, because experiments have proved that when Al / N is too low, the residual N is easy to react with Al.

[0007] 2) In the LF process, an innovative phased deoxidation is adopted, using ferrosilicon manganese alloy and aluminum wire for deep deoxidation to balance the deoxidation effect and the effect of high purity; using VD degassing to further remove the nitrogen content in the steel.

[0008] 3) Adopt the single-phase region high-temperature rapid rolling process, and control the finishing rolling temperature above 950 °C, that is, in the recrystallization region. On the one hand, the structure is uniform during the recrystallization process, and on the other hand, the structure in the recrystallization region can be coarsened to ensure that the structure of the rolled thin plate is controlled at 5 - 8 grades.

[0009] 4) After rolling, it is first air-cooled and then stacked for slow cooling. The slow cooling process can promote the growth of ferrite structure. At the same time, in order to avoid the precipitation of a large amount of second phases such as AlN during the slow cooling process, the high-temperature region is avoided, and slow cooling is carried out at a temperature below 600 °C. Finally, a steel plate with excellent comprehensive performance is obtained, which meets the requirements of low yield, high tensile strength, high plasticity and high toughness, and meets the needs of the nuclear power market. Specific embodiments

[0010] The present invention will be further described in detail below with reference to specific embodiments.

[0011] Examples 1 - 6: The thickness and chemical composition of the thin steel plates for nuclear safety containment vessels in Examples 1 - 6 are shown in Table 1.

[0012] The key process steps of the production method of the thin steel plate for low-cost nuclear containment include: (1) Smelting: Adopt the LF+VD secondary refining process; in the LF process, first deoxidize with ferrosilicon manganese alloy, and the addition amount of ferrosilicon manganese alloy per ton of molten steel is ≥10 kg; then deeply deoxidize with aluminum wire, and keep the white slag time ≥20 min.

[0013] (2) Rolling: The thickness of the billet is ≤150 mm, and the billet holding temperature is 1260-1300 °C; adopt the single-phase zone high-temperature rapid rolling process, the starting rolling temperature is ≥1220 °C, the finishing rolling temperature is ≥950 °C, and air-cool after rolling to ≤600 °C and then stack and slow-cool.

[0014] Table 1 Steel plates of the examples and their chemical compositions Wt% , Table 2 Production process parameters of the steel plates of the examples , Table 3 Mechanical properties of the steel plates of the examples , The specific process parameters of Examples 1 to 6 are shown in Table 2, the performance test results of the thin steel plates for nuclear containment are shown in Table 3, the thin steel plates for low-cost nuclear containment are sampled for simulated normalizing treatment, the holding temperature is 890-950 °C, and the mechanical property results are shown in Table 4: Table 4 Mechanical properties of the steel plates of the examples after simulated normalizing .

Claims

1. A production method of thin steel plates for a nuclear containment vessel, characterized in that: The mass percentage of the chemical composition of the steel plate is C≤0.20%, Si = 0.40% - 0.50%, Mn = 0.75% - 1.50%, P≤0.030%, S≤0.010%, Nb≤0.003%, V≤0.003%; Ti≤0.003%; Alt≥0.30%; Alt / N≥4, and the balance is Fe and inevitable impurities; The key process steps include: (1) Smelting: Adopt the LF+VD secondary refining process; in the LF process, first deoxidize with silicomanganese alloy, and the addition amount of silicomanganese alloy per ton of molten steel is ≥10 kg; then deeply deoxidize with aluminum wire, and keep the white slag time ≥20 min; (2) Rolling: The thickness of the billet is ≤150 mm, and the billet holding temperature is 1260 - 1300 °C; adopt the single-phase zone high-temperature and fast-rolling process, the starting rolling temperature is ≥1220 °C, the finishing rolling temperature is ≥950 °C, and after rolling, air-cool to ≤600 °C and then stack and slow-cool.