CN108950387B - steel with excellent high-temperature performance and thick specification for nuclear power safety injection box and manufacturing method thereof - Google Patents

Abstract

The invention discloses a steel with excellent high-temperature performance and a thick gauge nuclear power safety injection box and a manufacturing method thereof. Steel contains C: 0.14%～0.20%, Si: 0.10%～0.60%, Mn: 0.30%～0.40%, P≤0.008%, S≤0.002%, Mo: 0.30%～0.60%, Ni: 0.45%～ 0.90%, Cr: 0.50%-0.80%, Cu≤0.05%, _Alt≤0.04 %, H≤0.00015%, O≤0.0020%, and the rest are Fe and unavoidable impurities. Steel ingot is heated to 1150-1350°C, heat preservation>2h, compression ratio of steel plate>3:1, start rolling temperature≥1100°C, finish rolling temperature≥920°C, rolling speed 1.0-1.5m/s; quenching temperature 850-925 ℃, holding time 1~4min/mm; tempering temperature 630~670℃, holding time 3~7min/mm. After quenching and tempering heat treatment and 16-hour simulated post-weld heat treatment, the 80-150mm thick steel plate has good comprehensive mechanical properties.

Description

Thick-gauge nuclear power safety injection box steel with excellent high-temperature performance and manufacturing method thereof

technical field

The invention belongs to ferrous metal materials, and in particular relates to a steel for a nuclear power safety injection box with excellent high-temperature tensile properties and a manufacturing method.

Background technique

The nuclear power safety injection tank is an advanced equipment that injects cooling water into the accident equipment when an accident occurs in a nuclear power plant. The safety injection tank contains boron-containing water, and the upper cavity is filled with nitrogen. When the pressure of the reactor coolant system drops below the pressure of the safety injection tank , Boron-containing water is injected into the cold section of the reactor coolant system by nitrogen pressure, which can submerge the core in a short time and avoid melting of fuel rods, thereby ensuring the safety and integrity of the reactor system. Its manufacturing requirements are very strict, the process control is extremely harsh, and the acceptance inspection procedures are quite strict. At present, the steel plates for the head of the injection box and the cylinder are almost entirely dependent on imports, which are expensive and have a long delivery time. There are mainly two problems in the following aspects: one is that according to the plate design requirements, the head and cylinder plates are ultra-wide plates (plate width 4.5m), so there are strict requirements on the equipment and capabilities of the manufacturing plant; After more than 16 hours of simulated post-weld heat treatment, the strength of the steel plate has dropped significantly, especially the tensile strength of the 150°C high-temperature tensile is lower than the index requirement, but due to the limitation of imported steel plates, the index has to be lowered.

CN201410098857.1 is titled "a steel plate for nuclear power plant pressure vessel and its manufacturing method", which mainly discloses a steel for nuclear power plant pressure vessel and its manufacturing method. % Si, 0.60%~1.40% Mn, P≤0.020%, S≤0.010%, Ni≤0.30%, Cu≤0.18%, Cr≤0.30%, Mo≤0.08%, V≤0.020%, Nb≤0.020 %, 0.008%-0.030% Ti, 0.020%-0.050% Alt, N≤0.012%, Ni+Cu+Cr+Mo≤0.70%, and the rest are Fe and unavoidable impurities. The steel plate has good low temperature toughness and high temperature resistance, excellent and stable welding performance, cold and hot processing performance, good radiation embrittlement resistance and low cost. However, in the composition design of this invention, the content of C, Ni, Mo and other elements is low, and the normalizing heat treatment or controlled rolling method is adopted for production, resulting in low strength of the designed steel plate, and no attention has been paid to the performance of the steel plate after long-term simulated post-weld heat treatment .

CN201210387824.X is titled "18MND5 nuclear power low-alloy structural steel and process control method", which discloses a 18MND5 nuclear low-alloy structural steel and process control method. The composition of the chemical composition including the following weight percentage content: C≤0.22%, 0.10%～0.30% of Si, 1.15%～1.60% of Mn, S≤0.012%, P≤0.012%, Al≤0.04%, 0.43%～ 0.57% Mo, Cu≤0.08%, 0.50%～0.80% Ni, V≤0.01%, N≤0.008%, H≤1.5ppm, O≤30ppm, N≤0.013%, Cr≤0.25%, Co≤0.08 %, B≤0.0018%, As≤0.010%, Sb≤0.002%, Sn≤0.010%, and the rest are Fe and unavoidable impurities. The mechanical properties of the 18MND5 material produced by the invention are obviously superior to other steel types, and can be used as 18MND5 high-strength low-alloy structural steel for nuclear power pressure bearing. The above-mentioned patent adopts the electric furnace smelting-forging-heat treatment process, the production rhythm is low, and the production cycle is long, which is not suitable for continuous mass production, and the applicable steel plate thickness range is not specified in the examples.

CN201010276502.9 is titled "A Steel for Nuclear Reactor Containment Head and Cylinder", which discloses a steel for nuclear reactor containment head and cylinder. The weight percentage of its chemical composition is: C≤0.20%, 0.15%～ 0.55% Si, 0.90%~1.60% Mn, P≤0.025%, S≤0.025%, Ni≤0.60%, Cr≤0.30%, Mo≤0.30%, Nb≤0.04%, V≤0.07%, Cu≤ 0.35%, V+Nb≤0.08%, the remaining content is Fe and unavoidable impurities, the carbon equivalent in steel is 0.40%~0.44%, and the carbon equivalent calculation formula is CE=C+Mn/6+(Cr+Mo+V )/5+(Ni+Cu)/15, control non-metallic inclusions in steel, A, B, C, D type inclusions ≤ 1.5 level. The invention effectively ensures that the steel plate has high strength and also has uniform and stable toughness, especially after a long time stress relief treatment, the strength of the steel plate will not be significantly reduced, and the index requirements can still be met. The thickness of the steel plate in this embodiment of the invention is 42mm, there is no record of a thicker steel plate, and the simulated post-weld heat treatment time is relatively short, and the high temperature tensile index is not mentioned.

Contents of the invention

The object of the present invention is to overcome the deficiencies of the prior art, to provide a kind of steel with excellent high-temperature performance for the safety injection box of nuclear power with thick specification and its manufacturing method. The thickness of the steel plate can reach 80-150 mm. Reducing the content of gas and non-metallic inclusions in the steel can effectively ensure that the steel plate has excellent comprehensive mechanical properties, especially after the steel plate has undergone 16h simulated post-weld heat treatment, the 150°C high temperature tensile and -50°C low temperature impact indicators can still be fully Meet the manufacturing requirements of nuclear power safety injection tank equipment.

The specific technical solutions are:

Thick-gauge nuclear power safety injection box steel with excellent high-temperature performance contains the following components by mass percentage: C: 0.14% to 0.20%, Si: 0.10% to 0.60%, Mn: 0.30% to 0.40%, P≤0.008% , S≤0.002%, Mo: 0.30%～0.60%, Ni: 0.45%～0.90%, Cr: 0.50%～0.80%, Cu≤0.05%, Al _t≤0.04 %, H≤0.00015%, O≤0.0020% , the remaining content is Fe and unavoidable impurities.

The reasons for adopting the above-mentioned composition design are as follows:

C: is the main element to ensure the strength of the steel plate. It can effectively improve the strength and hardenability of the steel, but at the same time it also reduces the plasticity, toughness and weldability of the steel. Therefore, the present invention requires that the C content be 0.14% to 0.20%.

Si: It is a strengthening element in steel, which is beneficial to improve the strength of the steel plate, but too high Si content will damage the low-temperature toughness of the steel plate, and will increase the irradiation brittleness, so it is better to control the Si content at the lower limit. In the present invention, Si Element control is 0.10% ~ 0.60%.

Mn: Mn in steel can not only strengthen the matrix, but also effectively improve the hardenability of the steel plate, and the cost is low, but too high Mn content will increase the temper brittleness sensitivity of the steel, and make the grain coarser Therefore, the present invention requires that the Mn content in the steel be controlled at 0.30% to 0.40%.

P and S: are harmful elements in steel. P in steel will aggravate the generation of center segregation and center porosity. The sulfide inclusions formed by S are very detrimental to the impact toughness and welding performance of steel. Therefore, the lower their content is, the better it is good. In the present invention, the P content is controlled to be P≤0.008%, and the S content is controlled to be S≤0.002%.

Mo: It can improve the hardenability and heat resistance of the steel plate, and can also work together with Cr and Mn to reduce or suppress temper brittleness. Therefore, the content of Mo is controlled at 0.30%-0.60% in the present invention.

Ni: can significantly improve the low-temperature toughness of the steel plate, and at the same time increase the hardenability of the steel plate, but Ni will reduce the A3 line temperature of the steel and increase the irradiation effect, so the present invention requires that the Ni content in the steel be controlled at 0.45% to 0.90% .

Cr: can significantly improve the oxidation resistance and corrosion resistance of steel, and can improve the hardenability of steel plates, but Cr can also significantly increase the brittle transition temperature of steel, and promote temper brittleness, so the present invention requires that the Cr content in steel be controlled to 0.50% to 0.80%.

Cu: Cu is the most harmful element to radiation embrittlement, which reduces the mechanical properties of steel and causes oxidation of the metal surface when heated, affecting the quality of steel. Therefore, it is generally required that the Cu content in steel for nuclear power should not be higher than 0.05%.

Al _t : Al is a commonly used deoxidizer in steel, which can refine the grain size and improve the impact toughness of the steel plate. However, if the Al content is too high, the content of inclusions will increase and the weldability of the steel plate will be affected. Therefore, the present invention requires The Al _t content is controlled to be ≤0.04%.

H and O: Both H and O are harmful to the performance of steel and will increase the radiation embrittlement effect, so the lower their content, the better. The present invention requires that H≤0.00015% and O≤0.0020% in steel.

The manufacturing method of steel for nuclear power safety injection box includes smelting, casting, heating, rolling, and heat treatment. The following technical measures are taken in the production process to realize the present invention:

Smelting and rolling: deep desulfurization treatment of molten iron, electric furnace smelting, LF and VD refining outside the furnace after tapping, and then pouring. The steel ingot is heated to 1150-1350°C in the chamber furnace, and the billet is opened after the holding time is >2 hours. The intermediate billet is slowly cooled and destacked and then rolled to effectively ensure that the compression ratio of the finished steel plate is >3:1, and the rolling temperature is ≥1100 ℃, finish rolling temperature ≥ 920℃, rolling speed controlled at 1.0-1.5m/s, natural stacking and slow cooling after rolling.

Heat treatment: Quenching and tempering heat treatment is carried out by quenching and tempering to obtain a fine and uniform structure. The quenching and tempering heat treatment process is: quenching temperature 850-925 ℃, holding time 1-4min/mm; tempering temperature 630-670 ℃, holding time 3-7min/mm, after sufficient tempering time, can obtain fine grain, Tempered bainite with uniform structure, high toughness and moderate strength can further eliminate the internal stress of the steel plate. At the same time, carbides formed by alloying elements such as Mo and V will precipitate, which increases the effect of precipitation strengthening, so that the steel plate has sufficient strength. toughness.

Beneficial effect:

The invention provides a thick specification nuclear power safety injection box steel with excellent high-temperature performance and a manufacturing method. The thickness of the produced steel plate is 80-150mm, and the width and length can be produced according to actual needs. Compared with the prior art, the beneficial effects are as follows:

(1) The thickness of the steel plate of the present invention is 80-150 mm, which is produced by billet rolling of steel ingots. By controlling the alloy elements in the steel, the gas content and the content of non-metallic inclusions are reduced, and the maximum thickness of 150 mm with a compression ratio> 3:1 can be obtained The finished steel plate has excellent high-temperature tensile properties and toughness. Among them, the 80-150mm finished quenched and tempered steel plate can reach 500-530MPa high-temperature tensile yield strength and 610-635MPa tensile strength at 150°C. After 16 hours of simulated post-weld heat treatment, the tensile yield strength of the steel plate at 150°C high temperature can reach 500-520MPa, the tensile strength can reach 610-625MPa, and the impact toughness of the steel plate at -50°C can be achieved in both states Between 185 and 277J, the reduction of area can reach 60 to 85%.

(2) After quenching and tempering heat treatment and 16-hour simulated post-weld heat treatment, the steel grade of the present invention has better strength levels in different states. The tensile yield strength and tensile strength at 150°C of 120mm thick specification steel plate after quenching and tempering treatment are 529MPa and 635MPa respectively; after simulated post-weld heat treatment, the tensile yield strength and tensile strength at 150°C of The results show that the high temperature tensile strength of steel plates at 150°C in different states has been greatly improved compared with other steel types.

(3) The impact absorption energy and cross-sectional fiber ratio of the steel type of the present invention are also maintained at a relatively high level under different conditions. The -50°C impact absorbed energy of the 120mm steel plate after quenching and tempering treatment and simulated post-weld heat treatment is more than 200J, and the cross-sectional fiber ratio can reach more than 65%, which shows that the steel type of the present invention has good low-temperature toughness.

(4) The Z-direction reduction of area of the steel grade of the present invention has a relatively high level, and the Z-direction reduction of area of the 120mm steel plate after quenching and tempering treatment can reach 67.3%, indicating that the steel grade of the present invention has better resistance to lamellar tearing ability.

(5) The present invention is produced by selecting low-P and low-S molten iron, and carrying out deep desulfurization treatment of molten iron, removing desulfurization slag, electric furnace smelting, refining outside the furnace, vacuum treatment and rolling process for production, so the cleanliness of molten steel is guaranteed higher.

Description of drawings

Fig. 1 is the metallographic structure of Example 3; the microstructure is tempered bainite.

Detailed ways

The following examples are used to specifically illustrate the contents of the present invention, and these examples are only general descriptions of the contents of the present invention, and do not limit the contents of the present invention.

The smelting chemical composition of each embodiment steel of the present invention is as shown in table 1;

Table 1 steel smelting chemical composition mass% of each embodiment

Example C Si mn P S Mo Ni Cr Cu Al_T h o 1 0.16 0.10 0.30 0.005 0.0009 0.42 0.50 0.55 0.017 0.016 0.00010 0.0019 2 0.14 0.30 0.40 0.008 0.0009 0.55 0.75 0.60 0.015 0.028 0.00015 0.0016 3 0.18 0.28 0.35 0.006 0.0010 0.50 0.62 0.78 0.016 0.030 0.00008 0.0018 4 0.20 0.40 0.32 0.004 0.0007 0.35 0.55 0.70 0.018 0.025 0.00009 0.0020 5 0.15 0.55 0.36 0.005 0.0010 0.48 0.65 0.66 0.012 0.020 0.00009 0.0015

The molten steel is smelted in an electric furnace, refined outside the furnace, and vacuum-treated, and cast into ingots, and the finished steel plate is rolled with a specification of 80-150mm. The simulated post-weld heat treatment process is a temperature of 615±5°C, a holding time of 16h, and a heating and cooling rate of ≤55°C/h above 400°C.

The rolling process of each embodiment steel of the present invention is as shown in Table 2, and the heat treatment of each embodiment steel is as shown in Table 3; the 150 ℃ high temperature tensile properties of each embodiment steel plate of the present invention are as shown in Table 4; each embodiment of the present invention The -50°C impact properties of the steel plates of the examples are shown in Table 5; the Z-direction tensile and cold bending test properties of the steel plates of each example of the present invention are shown in Table 6.

Table 2 Rolling process

Table 3 heat treatment process

Table 4 Results of tensile properties of steel plates at 150°C high temperature

Table 5 -50℃ impact performance results of steel plate

Table 6 Z-direction tensile and cold bending test performance results of steel plate

After quenching and tempering heat treatment and 16-hour simulated post-weld heat treatment, the 80-150mm thick steel plate has good comprehensive mechanical properties, and all performance indicators fully meet the requirements for nuclear power safety injection box equipment manufacturing.

Claims (3)

1. A kind of steel with excellent high-temperature performance and thick gauge nuclear power safety injection box, characterized in that the chemical composition in the steel is: C: 0.15%-0.20%, Si: 0.40%-0.60%, Mn: 0.32% ~0.40%, P≤0.008%, S≤0.002%, Mo: 0.30%～0.60%, Ni: 0.55%～0.90%, Cr: 0.50%～0.80%, _Cu≤0.05 %, Alt: 0.016%～0.04 %, H≤0.00015%, O≤0.0020%, and the rest are Fe and unavoidable impurities; after simulated post-weld heat treatment, the tensile strength of the steel plate at 150°C high temperature reaches 610~625MPa, and the impact toughness at -50°C reaches 185~ 277J, the reduction of area reaches 60% to 85%. 2. The steel for nuclear power safety injection box with excellent high-temperature performance and thick specifications as claimed in claim 1, characterized in that the thickness of the steel plate is 80-150mm. 3. A production method as claimed in claim 1 or 2 with excellent high-temperature performance thick specification nuclear power safety injection box steel, the production process of steel plate is: smelting, casting, heating, rolling, heat treatment, it is characterized in that, Deep desulfurization treatment of molten iron, smelting in an electric furnace, LF and VD refining outside the furnace after tapping, and then pouring; the steel ingot is heated to 1150-1350 ° C, the holding time is > 2 hours, and the billet is opened after the heat preservation, and the intermediate billet is slowly cooled and destacked. Rolling, the compression ratio of the finished steel plate is > 3:1, the starting rolling temperature is ≥1180°C, the final rolling temperature is ≥920°C, the rolling speed is controlled at 1.0-1.5m/s, and the rolling is naturally stacked and slowly cooled; Quenching and tempering heat treatment is carried out in the way of quenching and tempering. The quenching temperature is 850-925°C, and the holding time is 1-4min/mm; the tempering temperature is 635-660°C, and the holding time is 3-7min/mm.