CN103160732A - Steel for nuclear power pressure-bearing equipment and manufacturing method thereof - Google Patents

Abstract

The invention discloses a steel for nuclear power pressure-bearing equipment and a manufacturing method thereof. The weight percent of the chemical composition of the steel is: 0.12%-0.18% C; 0.15%-0.35% Si; 1.20%-1.65% Mn; ≤ 0.015% P; ≤0.010% S; 0.50%-0.85% Ni; ≤0.15% Cr; 0.020%-0.050% Al; ≤0.02% V; ≤0.02% Ti, and the rest is Fe and Impurities are unavoidable, and non-metallic inclusions in steel are controlled at the same time to ensure that inclusions of types A, B, C, and D are ≤ 1.5. The manufacturing method mainly includes steel smelting, rolling, quenching and tempering treatment. The present invention further optimizes the chemical composition, heat treatment process, and reduces the gas and non-metallic inclusions in the steel, so that the mechanical properties of the steel plate in the heat treatment state, the simulated post-weld heat treatment state and the high temperature state of 200 ° C are maintained at a high level, fully meeting the requirements of the technical indicators Requirements; at the same time, the impact absorption energy at 0°C remains at a relatively high level, reflecting a good match between the strength and toughness of the steel plate, and is completely suitable for the needs of steel for nuclear power pressure equipment.

Description

A kind of steel for nuclear power pressure-bearing equipment and its manufacturing method

technical field

The invention belongs to the field of ferrous metal materials, in particular to steel for nuclear power pressure-bearing equipment and a manufacturing method thereof.

Background technique

With the rapid economic development of all countries in the world, nuclear energy, as a clean, safe and stable energy source, has been paid more and more attention by all countries. It has become a trend to use nuclear energy safely and vigorously develop nuclear power. The application of nuclear power technology has also made considerable progress. It has developed from the original "second generation" technology to the current "second generation plus" and "third generation" technology, which has greatly improved the safety performance.

Among the many nuclear power units built according to different nuclear power technologies, steel for nuclear power pressure equipment plays a pivotal role as a supporting material for nuclear reactor pressure vessels, voltage stabilizers, various pipelines, boxes, tanks, tanks and other important equipment. The safety of its operation and the stability of its performance will directly affect whether the whole unit can operate safely.

From the current point of view, there are many materials used as steel for nuclear power pressure equipment, such as: A42, A52, P295GH, P355GH and S355J0, etc. The above-mentioned steel types are basically carbon steel, and the tensile strength is mostly controlled between 400-550MPa. It can effectively reduce the radiation embrittlement effect caused by the addition of alloying elements. However, as a pressure-bearing equipment, it needs to undergo long-term stress-relieving treatment and test its high-temperature tensile properties, and the strength of the above-mentioned steel types will decrease to varying degrees after long-term stress-relieving treatment or under high-temperature conditions. It is difficult to meet the requirements. It is only suitable for supporting materials for manufacturing nuclear power supporting equipment and auxiliary equipment, and it is far from meeting the needs of pressure-bearing steel for the key equipment of the nuclear island of the existing "second generation plus" and "third generation" nuclear power units. For example, after normalizing the S355J0 steel plate with a plate thickness of 60mm, the yield strength (Rel) and tensile strength (Rm) are 360N/mm ² and 525N/mm ² respectively (the index requirements Rel≥330N/mm ² , Rm≥510N /mm ² ); after simulated post-weld heat treatment, the yield strength (Rel) and tensile strength (Rm) are 340N/mm ² and 500N/mm ² respectively (indicator requirements Rel≥330N/mm ² , Rm≥510N/mm ² ); when stretched at a high temperature of 200°C, the yield strength (Rel) and tensile strength (Rm) are 255N/mm ² and 470N/mm ² , respectively. From the perspective of the three processes, the strength of the steel plate after normalizing treatment fully meets the index requirements, and has a certain margin. However, after simulated post-weld heat treatment, the strength of the steel plate drops significantly, especially the tensile strength can no longer meet the index requirements; at 200°C, the strength of the steel plate, especially the yield strength, drops more obviously, indicating that the high temperature resistance of this steel is relatively low. Low, can no longer meet the needs of nuclear power key equipment construction.

Contents of the invention

The invention provides a steel for nuclear power pressure-bearing equipment and its manufacturing method. By further optimizing the chemical composition, heat treatment process, and reducing gas and non-metallic inclusions in the steel, the steel plate can be used in the heat treatment state, simulated post-weld heat treatment state, and high temperature of 200 ° C. The mechanical properties of the state are maintained at a high level, fully meeting the requirements of technical indicators; at the same time, the impact absorption energy at 0°C remains at a high level, reflecting a good match between the strength and toughness of the steel plate, and is completely suitable for nuclear power pressure equipment demand for steel.

A kind of steel for nuclear power pressure-bearing equipment provided by the present invention and its manufacturing method can solve the problems existing in the prior art, and the specific technical scheme is:

Steel for nuclear power pressure equipment, containing the following components by weight percentage: 0.12%-0.18% C; 0.15%-0.35% Si; 1.20%-1.65% Mn; ≤0.015% P; ≤0.010% S 0.50%-0.85% Ni; ≤0.15% Cr; 0.020%-0.050% Al; ≤0.02% V; ≤0.02% Ti, and the rest is Fe.

The present invention also requires that H≤1.5ppm and O≤30ppm in the steel.

At the same time, non-metallic inclusions in steel are controlled to ensure that inclusions of types A, B, C, and D are ≤ 1.5 (inspected according to ASTM E45 method A, the same below).

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

(1) C: The C content in the steel is the main element to ensure the strength of the steel plate. If the C content is low, the strength may not meet the requirements, especially after a long time simulated post-weld heat treatment and operation at a high temperature of 200°C, the strength must be obtained to a certain extent. Therefore, the present invention requires that the C content in steel should be controlled at 0.12%-0.18%, preferably 0.14%-0.18%.

(2) Si: Si is an effective strengthening element and is also a cheap element. Therefore, from the perspective of ensuring that the strength change of the steel plate at different stages can meet the index requirements, the Si content is controlled at 0.15%-0.35%, preferably 0.20% -0.35%.

(3) Mn: In addition to strengthening the matrix, the Mn element in the steel can also effectively improve the hardenability of the steel. Therefore, the Mn content in the actual production steel is controlled at 1.20%-1.65%, preferably 1.35%-1.65%.

(4) Ni: Ni can significantly improve the low-temperature toughness of steel, and at the same time improve the low-temperature toughness of thick-section steel plates (especially steel plates above 100mm), so that the steel plate has sufficient strength and high toughness at the same time, meeting the requirements of the index Therefore, starting from actual needs, the present invention requires that the Ni content in the steel be controlled at 0.50%-0.85%, preferably 0.65%-0.85%.

(5) Cr: Cr in steel can significantly improve the oxidation resistance of steel and increase the corrosion resistance. At the same time, the austenite phase area is reduced to improve the hardenability of the steel. However, Cr can also significantly increase the brittle transition temperature of the steel and promote temper brittleness. Therefore, the present invention requires that the Cr content in the steel be ≤0.15%, preferably 0.05%-0.15%.

(6) Al: Al is mainly used as a deoxidizing and nitrogen-fixing agent in steelmaking, and can refine grains, inhibit the aging of low-carbon steel, and improve the toughness of steel at low temperature. At the same time, the Al content should not be too much. In order to avoid Al ₂ O ₃ inclusions. Usually the Al content in the steel is controlled at 0.020%-0.050%, preferably 0.020%-0.035%.

(6) V, Ti: Steel for nuclear power is required to be fine-grained steel. Fine-grained steel is less brittle than coarse-grained steel. Adding V and Ti to steel can refine grains and increase grain coarsening temperature. Therefore, the content of V and Ti in the steel is required to be ≤0.02%, preferably 0.005%-0.02%.

(7) P: Irradiation tests show that P is also very sensitive to radiation embrittlement. At the same time, the high P content is also easy to aggravate the center segregation and center porosity in the steel. Therefore, the lower the P content in the steel, the better. Well, it is controlled to be ≤0.015%, preferably ≤0.010%.

(8) S: S forms S compound inclusions in the steel, which reduces the impact toughness of the steel, affects the welding performance, and at the same time aggravates the occurrence of defects such as center segregation and porosity. Therefore, it is required that the S content in the steel should be as low as possible, and the control is ≤0.010%, preferably ≤0.003%.

(9) Gases H and O: Generally speaking, they are harmful to the performance of steel, and at the same time increase the effect of radiation embrittlement, so it is hoped that their content should be reduced to a minimum level. The present invention requires that H≤1.5ppm and O≤30ppm in steel.

Realize that the present invention takes the following technical measures in the production process:

Steel smelting:

The steel plate thickness ≤ 80mm is produced by converter and continuous casting process; the steel plate thickness > 80mm is produced by electric furnace and die casting process. Refining outside the furnace and vacuum degassing are used in the production process.

Rolling aspects of steel plate:

The continuous casting slab adopts two-stage controlled rolling in the recrystallization zone and the non-recrystallization zone. 20°C, accumulative deformation ≥ 50%, natural cooling after rolling;

Die-cast steel ingots are produced by rolling ingots. The heating temperature of the steel ingots is 1150-1200 ° C. During the rolling process, high-temperature and fast rolling is used, and natural cooling after rolling.

Steel plates need to be tempered after rolling to make the structure more uniform, the grains smaller and the performance more stable.

The quenching and tempering treatment process is: quenching temperature 940±10°C, holding time 2-3min/mm, tempering temperature 590±10°C, holding time 2-4min/mm.

The invention provides a steel for nuclear power pressure-bearing equipment and a manufacturing method thereof. The thickness of the produced steel plate is 20-120mm, and the width and length can be produced according to actual needs. Compared with the prior art, the beneficial effects are as follows:

(1) After quenching and tempering treatment, the steel grade of the present invention has a better strength level under different conditions. The steel plate has been quenched and tempered, the yield strength (Rel) ≥ 400N/mm ² , the tensile strength (Rm) is between 560-625N/mm ² ; after the simulated post-weld heat treatment, the yield strength (Rel) ≥ 360N/mm ² , The tensile strength (Rm) is between 530-600N/mm ² ; when stretched at a high temperature of 200°C, the yield strength (Rel) ≥ 340N/mm ² , and the tensile strength (Rm) is between 510-580N/mm ² . Judging from the three states, the decrease in strength of the steel plate is small, and the different states can meet the index requirements. Compared with other steel types, it has been greatly improved.

(2) After the quenching and tempering treatment of the steel grade of the present invention, the impact absorption energy at 0°C under different conditions also remains at a relatively high level. The impact absorbed energy after steel plate quenching and tempering treatment and simulated post-weld heat treatment is kept above 200J, which not only meets the requirements of the index, but also has a large margin.

Detailed ways

A steel for nuclear power pressure-bearing equipment and a manufacturing method thereof are specifically implemented as follows:

Embodiment one

The steel for nuclear power pressure-bearing equipment in this embodiment, the molten steel is smelted in a converter, refined outside the furnace (LF, VD), cast into a continuous casting slab, and the finished steel plate is rolled with a specification of 20mm. Its composition, rolling and heat treatment process, and mechanical properties are shown in Tables 1, 2, and 3, respectively.

Table 1 Chemical Composition (%)

Table 2 Rolling and heat treatment process

Table 3 mechanical properties results

At the same time, non-metallic inclusions in steel are inspected: Class A 0.5, Class B 0.5, Class C 0.5, Class D 1.0.

Through the test of the mechanical properties of the 20mm plates in different states after heat treatment, the results all meet the requirements of the indicators, and have a certain margin, which fully meets the requirements of nuclear power pressure equipment materials.

Embodiment two

The steel for nuclear power pressure-bearing equipment in this embodiment, the molten steel is smelted in a converter, refined outside the furnace (LF, VD), cast into a continuous casting slab, and the finished steel plate has a specification of 40 mm. Its composition, rolling and heat treatment process, and mechanical properties are shown in Tables 4, 5, and 6, respectively.

Table 4 Chemical Composition (%)

Table 5 Rolling and heat treatment process

Table 6 mechanical properties results

At the same time, non-metallic inclusions in steel are inspected: Class A 0.5, Class B 1.0, Class C 0.5, Class D 1.0.

Through the test of the mechanical properties of the 40mm plate in different states after heat treatment, the results all meet the requirements of the indicators, and have a certain margin, which fully meets the requirements of nuclear power pressure equipment materials.

Embodiment three

The steel for nuclear power pressure-bearing equipment in this embodiment, the molten steel is smelted in a converter, refined outside the furnace (LF, VD), cast into a continuous casting slab, and the finished steel plate is rolled with a specification of 60 mm. Its composition, rolling and heat treatment process, and mechanical properties are shown in Tables 7, 8, and 9, respectively.

Table 7 Chemical Composition (%)

Table 8 Rolling and heat treatment process

Table 9 mechanical properties results

At the same time, non-metallic inclusions in steel are inspected: Class A 0.5, Class B 1.5, Class C 0.5, Class D 1.0.

Through the test of the mechanical properties of the 60mm plate in different states after heat treatment, the results all meet the requirements of the indicators, and have a certain margin, which fully meets the requirements of nuclear power pressure equipment materials.

Embodiment Four

The steel for nuclear power pressure-bearing equipment in this embodiment, the molten steel is smelted in a converter, refined outside the furnace (LF, VD), cast into a continuous casting slab, and the finished steel plate has a specification of 80 mm. Its composition, rolling and heat treatment process, and mechanical property results are shown in Tables 10, 11, and 12, respectively.

Table 10 Chemical Composition (%)

Table 11 Rolling and heat treatment process

Table 12 mechanical properties results

At the same time, non-metallic inclusions in steel are inspected: Class A 1.0, Class B 1.0, Class C 0.5, Class D 0.5.

Through the test of the mechanical properties of the 80mm plate in different states after heat treatment, the results all meet the requirements of the indicators, and have a certain margin, which fully meets the requirements of nuclear power pressure equipment materials.

Embodiment five

The steel for nuclear power pressure-bearing equipment in this embodiment, the molten steel is smelted in an electric furnace, refined outside the furnace (LF, VD), cast into a steel ingot, and directly rolled into a finished steel plate with a specification of 100 mm. Its composition, rolling and heat treatment process, and mechanical properties are shown in Tables 13, 14, and 15, respectively.

Table 13 Chemical Composition (%)

Table 14 Rolling and heat treatment process

Table 15 Mechanical properties results

At the same time, non-metallic inclusions in steel are inspected: Class A 0.5, Class B 1.0, Class C 0.5, Class D 1.0.

Through the test of the mechanical properties of the 100mm plate in different states after heat treatment, the results all meet the requirements of the indicators, and have a certain margin, which fully meets the requirements of nuclear power pressure equipment materials.

Embodiment six

The steel for nuclear power pressure-bearing equipment in this embodiment, the molten steel is smelted in an electric furnace, refined outside the furnace (LF, VD), cast into a steel ingot, and directly rolled into a finished steel plate with a specification of 120 mm. Its composition, rolling and heat treatment process, and mechanical properties are shown in Tables 16, 17, and 18, respectively.

Table 16 Chemical composition (%)

Table 17 Rolling and heat treatment process

Table 18 Mechanical Properties Results

At the same time, non-metallic inclusions in steel are inspected: Class A 0.5, Class B 1.5, Class C 0.5, Class D 1.5.

Through the test of the mechanical properties of the 120mm plate in different states after heat treatment, the results all meet the requirements of the indicators, and have a certain margin, which fully meets the requirements of nuclear power pressure equipment materials.

Claims (4)

1. A steel for nuclear power pressure equipment, characterized in that it comprises the following components by weight percentage: 0.12%-0.18% of C; 0.15%-0.35% of Si; 1.20%-1.65% of Mn; ≤0.015% of P; ≤0.010% S; 0.50%-0.85% Ni; ≤0.15% Cr; 0.020%-0.050% Al; ≤0.02% V; ≤0.02% Ti, the rest is Fe and unavoidable impurities , while controlling H≤1.5ppm and O≤30ppm in steel, and non-metallic inclusions ensure that A, B, C, and D inclusions are ≤1.5. 2. The steel for nuclear power pressure equipment according to claim 1, characterized in that it comprises the following components by weight percentage: 0.14%-0.18% of C; 0.20%-0.35% of Si; 1.35%-1.65% 0.65%-0.85% Ni; 0.05%-0.15% Cr; 0.020%-0.035% Al; 0.005%-0.02% V; 0.005%-0.02% Ti. 3. A method for manufacturing steel for nuclear power pressure equipment as claimed in claim 1, mainly comprising steel smelting, rolling, quenching and tempering treatment, characterized in that the steel plate thickness≤80mm is carried out by converter and continuous casting process Production, the production process adopts refining outside the furnace and vacuum degassing treatment; the continuous casting slab adopts two-stage controlled rolling in the recrystallization zone and the non-recrystallization zone, the heating temperature of the billet is 1150-1200 ℃, and the final rolling temperature in the recrystallization zone is ≥1000°C, the rolling temperature in the non-recrystallized area is controlled at 850±20°C, the cumulative deformation is ≥50%, and it is cooled naturally after rolling; the quenching and tempering treatment process is: quenching temperature 940±10°C, holding time 2-3min/mm , the tempering temperature is 590±10°C, and the holding time is 2-4min/mm. 4. A method for manufacturing steel for nuclear power pressure-bearing equipment as claimed in claim 1, mainly comprising smelting, rolling, quenching and tempering treatment of steel, characterized in that steel plate thickness > 80mm is carried out by electric furnace and die casting process Production, refining outside the furnace and vacuum degassing are used in the production process; die-cast steel ingots are produced by ingot rolling, the heating temperature of the steel ingot is 1150-1200 ° C, high temperature and fast rolling are used in the rolling process, and natural cooling after rolling; The quenching and tempering treatment process is: quenching temperature 940±10°C, holding time 2-3min/mm, tempering temperature 590±10°C, holding time 2-4min/mm.