Method for improving drawing performance of welding wire steel for nuclear power

Abstract

The 10Mn2NiMo is mainly used for welding wire steel in the nuclear power field, not only requires higher purity, but also requires better drawing performance. However, when the steel is used initially, the drawing performance of the material is poor, and the purity of the material is determined to be improved through research, so that the steel needs to be strictly controlled in the smelting and refining processes; meanwhile, the rolled material is subjected to annealing treatment, so that on one hand, the hydrogen content in the steel is reduced, and on the other hand, the structure is reformed, the yield strength and the tensile strength are reduced, and the yield ratio is reduced; and the drawing performance of the material is obviously improved, and the product quality is accepted by customers.

Description

Technical Field

[0001] The invention belongs to the steelmaking field of the metallurgical industry and relates to a method for improving the drawing performance of welding wire steel for nuclear power. The method can be used to produce wires with excellent drawing performance. Background Art

[0002] In recent years, with the development of material science, customers have put forward higher requirements for materials. For example, 10Mn2NiMo welding wire steel for nuclear power not only needs to have a high purity, but also needs to have good drawing performance. To prevent wire breakage during the drawing process. Therefore, the steel needs to be planned and designed during the smelting and refining process. For example, slag must be prevented during the converter steel tapping process; high-basicity Al2O3 slag system is used during LF refining, and the amount and method of Al addition are strictly controlled. The steel tapping process is fully added once to avoid subsequent aluminum supplementation and the generation of Al2O3 inclusions; during vacuum treatment, the vacuum degree and holding time need to be strictly controlled; at the same time, the wire is annealed to reduce the hydrogen content in the steel on the one hand, and to reorganize the organization on the other hand. Thereby improving the process performance of the material.

[0003] The invention provides a method for improving the drawing performance of 10Mn2NiMo welding wire steel for nuclear power. By adopting the method, the drawing performance of the welding wire steel can be significantly improved, the drawing force can be reduced, and the breakage phenomenon can be prevented. Summary of the invention

[0004] The purpose of the present invention is to provide a method for improving the drawing performance of welding wire steel for nuclear power in view of the above problems.

[0005] The object of the present invention is achieved in this way: a method for improving the drawing performance of welding wire steel for nuclear power, comprising the following steps: step one: improving the purity of steel: 1) converter smelting: slag is strictly prohibited during steel tapping, and steel retention operation is performed during steel tapping, with 8-10 tons of steel retained to prevent slag; 2) high vacuum degree is controlled according to ≤100Pa, and the high vacuum retention time is 20-25min; 3) slag system is adjusted; 4) unstable oxides in refined slag are reduced: the unstable oxides FeO and MnO in the refined slag are required to be ≤0.5% and ≤0.5%; step two: annealing process: heating the wire at a heating rate of ≤100℃ / h, heating the wire to a temperature of 660-700℃ and keeping the temperature for 3-4 hours, and then cooling the wire at a cooling rate of ≤50℃ / h, cooling the wire to below ≤500℃ and cooling the wire out of the furnace.

[0006] In step 1, 3) adjusting the slag system specifically involves using high basicity slag, maintaining the basicity between 4 and 6, and controlling the Al2O3 content in the slag between 16 and 20%.

[0007] The beneficial effects of the present invention are as follows: the present invention discloses a method for improving the drawing performance of 10Mn2NiMo welding wire steel for nuclear power. In order to improve the drawing performance, it is first necessary to improve the purity of the material and appropriately adjust the smelting slag system; at the same time, the gas content, especially the hydrogen content, is strictly controlled to ensure that it is ≤1ppm at the end of vacuum and ≤0.7ppm when sampling on the material; in addition, annealing treatment is required to adjust the structure of the material and eliminate the internal stress of the structure. In the production process, a new design scheme is adopted to prevent the material from breaking during the wire drawing process and ensure the performance of the product. DETAILED DESCRIPTION

[0008] 1. To improve the purity of steel and reduce the inclusions in steel, the following measures were decided: (1) Slag is strictly prohibited during converter tapping: Due to the low carbon content and the user's requirement of P ≤ 0.006%, molten steel is prone to overoxidation during the smelting process. In order to prevent overoxidized slag from entering the ladle, steel retention is required during tapping. It is stipulated that about 8-10 tons of steel should be retained, and oxidized slag is strictly prohibited.

[0009] (2) The high vacuum degree is controlled at ≤100Pa, and the high vacuum holding time is 20-25min.

[0010] (3) Adjust the slag system: Use high basicity slag, maintain the slag basicity between 4-6, and control the Al2O3 content in the slag between 16-20%.

[0011] (4) Reducing unstable oxides in refined slag: The unstable oxides in the slag are required to be FeO ≤ 0.5%, and MnO ≤ 0.5%.

[0012] 2. Annealing treatment: In order to prevent the wire from breaking due to the high strength of the material, the wire needs to be annealed. The annealing process is as follows: heat at a heating rate of ≤100℃ / h, heat to 660-700℃ for 3 hours, and then cool to ≤500℃ at a cooling rate of ≤50℃ / h before taking out of the furnace for cooling.

[0013] After the wire is annealed, the yield strength and tensile strength are significantly reduced, and the drawing performance is improved. Example 1

[0014] (1) The production process is: converter smelting - LF refining - RH degassing - die casting 8.4t flat ingot - red delivery initial rolling - uniform heating - billet opening - annealing - cutting - fine grinding - stainless wire factory heating - rolling - inspection - delivery to warehouse. In the later stage of converter smelting, steel retention operation was carried out, and the steel retention amount was 8.7 tons. No slag phenomenon occurred during steel tapping.

[0015] (2) The high vacuum degree is controlled at 67Pa, and the high vacuum holding time is 23min; (3) The slag system is adjusted: high basicity slag is used, the basicity is maintained at 4.8, and the Al2O3 content in the slag is controlled at 17.8%; (4) The unstable oxides FeO≤0.5% and MnO≤0.5% in the refined slag; the billet specifications are: 200×1050×3200mm. After rolling the wire, the following inspections and analyses are carried out, and the specific results are as follows: (1) Gas content analysis: The hydrogen content in the steel was sampled and analyzed, and the analysis result was 0.5PPm, achieving the purpose of vacuum treatment.

[0016] (2) Inspection of inclusions: Two volumes were inspected separately. The specific results are shown in the following table.

[0017]

[0018] From the results, it can be seen that the inclusion level is significantly low, indicating that the steel is pure and has the conditions for producing high-grade welding wire.

[0019] (3) The mechanical properties of the materials were analyzed: two performance tests were conducted. The first test was conducted directly on the wire after rolling, and the second test was conducted on the wire after heat treatment (see Table 2).

[0020]

[0021] After direct sampling and inspection, the yield strength and tensile strength of the material were obviously too large, and after the customer's wire drawing test, drawing became difficult; in addition, the elongation of the material was too small, so wire breakage often occurred during the drawing process, so the material was annealed, and the annealing process was as follows: Annealing process: heating at a heating rate of 80℃ / h, heating to 680℃ and keeping warm for 3.5 hours, and then cooling to 450℃ at a cooling rate of 40℃ / h before taking out of the furnace for cooling.

[0022] The performance results after annealing are shown in the following table.

[0023]

[0024] After annealing, the yield strength and tensile strength are significantly reduced, and the elongation is significantly increased, which is beneficial to the improvement of drawing performance.

[0025] After being drawn by the customer, no wire breakage accidents occurred, production was smooth, and customer satisfaction was high.

[0026] The above description is only a specific embodiment of the present invention, but the structural features of the protection scope of the present invention are not limited thereto. Any changes or modifications made by any technician in the field of the present invention are all covered by the patent scope of the present invention.

Claims

1. A method for improving the drawing performance of welding wire steel for nuclear power, characterized in that: The following steps are involved: Step 1: Improve the purity of steel: 1) Converter smelting: slag is strictly prohibited during steel tapping. During steel tapping, steel should be retained, with 8-10 tons of steel retained to prevent slag; 2) High vacuum degree is controlled at ≤100Pa, and the high vacuum retention time is 20-25min; 3) Adjust the slag system; 4) Reduce unstable oxides in refined slag: FeO≤0.5% and MnO≤0.5% of unstable oxides in refined slag are required; Step 2: Annealing process: Heat the wire at a heating rate of ≤100℃ / h, heat to 660-700℃ and keep warm for 3-4 hours, then cool at a cooling rate of ≤50℃ / h, cool to ≤500℃ and then take out of the furnace for cooling.

2. A method for improving the drawing performance of welding wire steel for nuclear power according to claim 1, characterized in that: In step 1, 3) adjusting the slag system specifically involves using high basicity slag, maintaining the basicity between 4 and 6, and controlling the Al2O3 content in the slag between 16 and 20%.

Images