A method for eliminating ring patterns in austenitic stainless steel

Abstract

The present invention discloses a method for eliminating ring patterns in austenitic stainless steel. 1Cr18Ni9Ti electroslag steel is subjected to pre-forging, high-temperature homogenization, and final forging in sequence, ultimately yielding 1Cr18Ni9Ti austenitic stainless steel with a ring pattern that reaches Class A in its macrostructure. By optimizing the hot working forging and high-temperature homogenization processes, the present invention reduces the ring pattern in the electroslag ingot while achieving stable production, resulting in excellent mechanical properties and meeting the current demand for high-quality 1Cr18Ni9Ti in the nuclear power and aviation sectors both domestically and internationally.

Description

Technical Field

[0001] The invention belongs to the technical field of macrostructure improvement of austenitic stainless steel, and in particular relates to a method for eliminating annular patterns of austenitic stainless steel, in particular 1Cr18Ni9Ti austenitic stainless steel. Background Art

[0002] 1Cr18Ni9Ti is a widely used 18-8 austenitic stainless steel with excellent corrosion resistance, thermal stability, atmospheric oxidation resistance, weldability, and cold working properties. It is primarily used in the manufacture of welding equipment, superheater piping, corrosion-resistant containers, and their structural components. Due to its harsh service environment, 1Cr18Ni9Ti requires excellent corrosion resistance. The presence of Ti in the steel forms stable carbides, TiC, thereby preventing the precipitation of Cr23C6 at grain boundaries and causing intergranular corrosion. Solution and stabilization treatments can mitigate this tendency toward intergranular corrosion, but this can also lead to the formation of titanium nitride inclusions in the steel. Especially when the TiN is distributed in a chain-like pattern, this can cause cracking in the steel.

[0003] To address the TiN inclusion problem in 1Cr18Ni9Ti, an electroslag remelting process is used to remelt the ingot a second time to improve its purity. However, during the electroslag remelting process, the melting rate of the electrode remelting fluctuates, changing the solidification structure of the steel and reducing the compositional uniformity of the steel. After low-magnification etching, a ring-like pattern appears on the cross-section of the electroslag ingot. Major manufacturers at home and abroad generally address this ring-like pattern by modifying electroslag equipment and adjusting voltage and current parameters to stabilize the remelting rate. However, the high viscosity of 1Cr18Ni9Ti molten steel leads to large fluctuations in the melting rate during remelting, and alloying elements are not easily diffused, resulting in a clear ring-like pattern observed during low-magnification testing.

[0004] While many experts and scholars have studied the formation mechanism and solutions for ring patterns in martensitic steels, few have focused on ring patterns in austenitic steels. Therefore, it is urgent to develop a method to eliminate ring patterns in austenitic stainless steels, particularly 1Cr18Ni9Ti austenitic stainless steel, in order to further improve the overall performance of austenitic stainless steels. Summary of the Invention

[0005] In view of the above-mentioned defects existing in the prior art, the purpose of the present invention is to provide a method for eliminating the ring pattern of austenitic stainless steel. By optimizing the hot working forging and high-temperature homogenization process, the ring pattern of the electroslag ingot is reduced while achieving stable production, so that it has excellent mechanical properties and meets the current domestic and foreign nuclear power and aviation fields. The actual demand for high-quality 1Cr18Ni9Ti.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] The invention provides a method for eliminating ring patterns in austenitic stainless steel. 1Cr18Ni9Ti electroslag steel is subjected to pre-forging, high-temperature homogenization treatment, and final forging in sequence to finally obtain 1Cr18Ni9Ti austenitic stainless steel with a ring pattern in a macrostructure reaching A level.

[0008] Preferably, during the pre-forging process, the 1Cr18Ni9Ti electroslag steel is heated to 1160-1200° C. and kept warm for 300-480 minutes, and then subjected to 1-2 times of upsetting and drawing.

[0009] Preferably, during the pre-forging process, the forging ratio of a single upsetting and drawing is 2 to 4, and the total forging ratio of the pre-forging is greater than 4.

[0010] Preferably, in the high-temperature homogenization treatment, the intermediate billet obtained by pre-forging is heated to 1220-1270° C., kept at this temperature for 8-15 hours, and then air-cooled.

[0011] Preferably, during the final forging process, the intermediate billet after high-temperature homogenization treatment is heated to 1100-1140° C., kept warm for 120-180 minutes, and then subjected to multi-fire forging.

[0012] Preferably, in the final forging process, the forging ratio of the last fire is ≥2, and the total forging ratio of the final forging is ≥4.

[0013] Preferably, the 1Cr18Ni9Ti austenitic stainless steel has a tensile strength Rm ≥ 590 MPa at room temperature and a specified plastic extension strength Rp 0.2 >240MPa, section shrinkage Z>70%, impact absorption energy KU2>285J.

[0014] Preferably, in the macrostructure of the 1Cr18Ni9Ti austenitic stainless steel, the radial segregation level reaches A level, the grain size level reaches above 7.5, and the fine inclusions of non-metallic inclusions of types A, B, and D are below level 0.5.

[0015] The beneficial effects of the method for eliminating annular patterns in austenitic stainless steel provided by the present invention are as follows:

[0016] 1. The method for eliminating annular patterns in austenitic stainless steel provided by the present invention improves the density of the material by pre-forging, reduces the diameter of the electroslag ingot, and thus improves the high-temperature homogenization treatment effect;

[0017] 2. The method for eliminating annular patterns in austenitic stainless steel provided by the present invention fully diffuses the alloying elements of the intermediate blank through high-temperature homogenization treatment, thereby improving the structural uniformity of the intermediate blank;

[0018] 3. The method for eliminating the ring pattern of austenitic stainless steel provided by the present invention refines the grains through final forging and improves the mechanical properties of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0020] Figure 1 This is a low-magnification horizontal photograph of the first type of 1Cr18Ni9Ti produced without adopting the method of the present invention;

[0021] Figure 2 This is a horizontal low-magnification photograph of a second type of 1Cr18Ni9Ti produced without adopting the method of the present invention;

[0022] Figure 3 A low-magnification horizontal photograph of the third type of 1Cr18Ni9Ti produced without adopting the method of the present invention;

[0023] Figure 4 A low-magnification horizontal photograph of the first type of 1Cr18Ni9Ti prepared by the method for eliminating the ring pattern of austenitic stainless steel according to the present invention;

[0024] Figure 5 A low-magnification horizontal photograph of the second type of 1Cr18Ni9Ti prepared by the invented method for eliminating the ring pattern of austenitic stainless steel;

[0025] Figure 6 Low-magnification horizontal photograph of the third type of 1Cr18Ni9Ti prepared by the invented method of eliminating the ring pattern of austenitic stainless steel. DETAILED DESCRIPTION

[0026] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below with reference to embodiments.

[0027] The present invention provides a method for eliminating ring patterns in austenitic stainless steel, wherein 1Cr18Ni9Ti electroslag steel is subjected to pre-forging, high-temperature homogenization treatment, and final forging in sequence, ultimately obtaining 1Cr18Ni9Ti austenitic stainless steel having a ring pattern in a macrostructure reaching Grade A. The specific process is as follows:

[0028] (1) Pre-forging: Heat 1Cr18Ni9Ti electroslag steel to 1160-1200℃ and keep it warm for 300-480min, then perform 1-2 times of upsetting and drawing to obtain an intermediate billet, where the forging ratio of a single upsetting and drawing is 2-4, and the total forging ratio of pre-forging is ≥4.

[0029] (2) High temperature homogenization treatment: Heat the intermediate billet obtained by pre-forging to 1220-1270°C, keep it at this temperature for 8-15 hours and then air cool it.

[0030] (3) Final forging: The intermediate billet after high temperature homogenization treatment is heated to 1100-1140°C, kept warm for 120-180 min, and then subjected to multiple forgings to obtain 1Cr18Ni9Ti austenitic stainless steel with a macrostructure and annular pattern reaching Class A; the forging ratio of the last forging is ≥2, and the total forging ratio of the final forging is ≥4.

[0031] The 1Cr18Ni9Ti austenitic stainless steel prepared by the above process has no obvious ring pattern and has excellent mechanical properties; the 1Cr18Ni9Ti austenitic stainless steel has a tensile strength Rm ≥ 590MPa at room temperature and a specified plastic elongation strength Rp 0.2 >240MPa, section shrinkage Z>70%, impact absorption energy KU2>285J. In the macrostructure of 1Cr18Ni9Ti austenitic stainless steel, the grain size level is above 7.5, and the fine inclusions of non-metallic inclusions A, B, C, and D are below 0.5 level.

[0032] Combine Figure 1 、 Figure 2 、 Figure 3 Horizontal low-power photograph of 1Cr18Ni9Ti produced by the method, and Figure 4 、 Figure 5 、 Figure 6 This is a low-magnification horizontal photograph of 1Cr18Ni9Ti prepared by the method for eliminating ring patterns in austenitic stainless steel of the present invention. It can be clearly seen that the 1Cr18Ni9Ti austenitic stainless steel prepared by the present invention has no obvious ring patterns.

[0033] The method for eliminating the ring-shaped pattern of austenitic stainless steel of the present invention is further described below with reference to specific examples.

[0034] Example 1

[0035] The 1Cr18Ni9Ti austenitic stainless steel in this embodiment is prepared by the following steps:

[0036] (1) Pre-forging: Heat the 1Cr18Ni9Ti electroslag ingot to 1180℃ and keep it for 300min, then perform one upsetting and drawing to obtain the intermediate billet. The forging ratio of a single forging and drawing is 4, and the total forging ratio of pre-forging is 4.

[0037] (2) High temperature homogenization treatment: heat the intermediate billet to 1250°C, keep it at this temperature for 12 hours and then air cool it;

[0038] (3) Final forging: The intermediate billet is heated to 1140°C and kept at this temperature for 120 min. 1Cr18Ni9Ti austenitic stainless steel is obtained by forging in three passes. The forging ratio of the last pass is 2, and the total forging ratio of the final forging is 6.

[0039] The chemical composition of the 1Cr18Ni9Ti austenitic stainless steel prepared in this embodiment is shown in Table 1, and the comprehensive properties of the 1Cr18Ni9Ti austenitic stainless steel are shown in Tables 2 to 5.

[0040] Example 2

[0041] The 1Cr18Ni9Ti austenitic stainless steel in this embodiment is prepared by the following steps:

[0042] (1) Pre-forging: Heat the 1Cr18Ni9Ti electroslag ingot to 1180℃ and keep it for 300min, then perform one upsetting and drawing process. The forging ratio of a single forging and drawing process is 3, and the total forging ratio of pre-forging is 3.

[0043] (2) High temperature homogenization treatment: heat the intermediate billet to 1230°C, keep it at this temperature for 14 hours, and then air cool it;

[0044] (3) Final forging: The intermediate billet is heated to 1140°C and kept at this temperature for 150 min. 1Cr18Ni9Ti austenitic stainless steel is obtained by forging twice. The forging ratio of the last fire is 3, and the total forging ratio of the final forging is 5.

[0045] The chemical composition of the 1Cr18Ni9Ti austenitic stainless steel prepared in this embodiment is shown in Table 1, and the comprehensive properties of the 1Cr18Ni9Ti austenitic stainless steel are shown in Tables 2 to 5.

[0046] Example 3

[0047] The 1Cr18Ni9Ti austenitic stainless steel in this embodiment is prepared by the following steps:

[0048] (1) Pre-forging: Heat the 1Cr18Ni9Ti electroslag ingot to 1200℃ and keep it for 480min, then perform two upsetting and drawing operations. The forging ratio of a single forging and drawing operation is 3, and the total forging ratio of pre-forging is 6.

[0049] (2) High temperature homogenization treatment: heat the intermediate billet to 1260°C, keep it at this temperature for 10 hours, and then air cool it;

[0050] (3) Final forging: The intermediate billet is heated to 1150℃ and kept warm for 180min. 1Cr18Ni9Ti austenitic stainless steel is obtained by forging twice. The forging ratio of the last fire is 2, and the total forging ratio of the final forging is 5.

[0051] The chemical composition of the 1Cr18Ni9Ti austenitic stainless steel prepared in this embodiment is shown in Table 1, and the comprehensive properties of the 1Cr18Ni9Ti austenitic stainless steel are shown in Tables 2 to 5.

[0052] Comparative Example 1-2

[0053] Comparative Examples 1 and 2 did not adopt the ring pattern elimination method of the present invention to prepare 1Cr18Ni9Ti. The chemical composition is shown in Table 1, and the comprehensive properties of 1Cr18Ni9Ti are shown in Tables 2 to 5.

[0054] In Tables 2 to 5, the specifications for stainless steel and heat-resistant steel bars for aviation use specified in GJB 2294A-2014 are used as the standard.

[0055] Table 1 Chemical composition of 1Cr18Ni9Ti (wt%)

[0056]

[0057] Table 2 Mechanical properties of 1Cr18Ni9Ti at room temperature

[0058]

[0059] Table 3 Qualified levels of macrostructure

[0060]

[0061] Table 4 Qualified levels of non-metallic inclusions

[0062]

[0063] Table 5 Grain size

[0064] standard No coarser than level 5 Comparative Example 1 7.5-3 Comparative Example 2 7-2.5 Example 1 8 Example 2 7.5 Example 3 8

[0065] As shown in Tables 2 to 5, the comprehensive performance of the 1Cr18Ni9Ti austenitic stainless steel prepared in the embodiment is significantly better than that of the 1Cr18Ni9Ti prepared in the comparative example. It can be seen that the method for eliminating the ring pattern of austenitic stainless steel of the present invention, by optimizing the hot working forging and high-temperature homogenization process, reduces the ring pattern of the electroslag ingot while achieving stable production, so that it has excellent mechanical properties, meeting the current domestic and foreign nuclear power and aviation fields and other fields for high-quality 1Cr18Ni9Ti.

[0066] Those skilled in the art should recognize that the above embodiments are merely intended to illustrate the present invention and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A method for eliminating ring patterns in austenitic stainless steel, characterized in that: The 1Cr18Ni9Ti electroslag steel is subjected to pre-forging, high temperature homogenization treatment and final forging in sequence, and finally the 1Cr18Ni9Ti austenitic stainless steel with annular pattern reaching A grade in macrostructure is obtained. During the pre-forging process, the 1Cr18Ni9Ti electroslag steel is heated to 1160-1200° C. and kept at this temperature for 300-480 minutes, and then subjected to 1-2 times of upsetting and drawing. During the pre-forging process, the forging ratio of a single upsetting and drawing is 2 to 4, and the total forging ratio of the pre-forging is ≥4; During the high-temperature homogenization treatment, the intermediate billet obtained by pre-forging is heated to 1220-1270° C., kept at this temperature for 8-15 hours, and then air-cooled; During the final forging process, the intermediate billet after high temperature homogenization treatment is heated to 1100-1140° C., kept at this temperature for 120-180 minutes, and then subjected to multi-fire forging; During the final forging process, the forging ratio of the last fire is ≥2, and the total forging ratio of the final forging is ≥4; In the macrostructure of the 1Cr18Ni9Ti austenitic stainless steel, the grain size level reaches above 7.5, and the fine inclusions of non-metallic inclusions A, B, C, and D are below level 0.

5.

2. The method for eliminating annular patterns of austenitic stainless steel according to claim 1, characterized in that: The 1Cr18Ni9Ti austenitic stainless steel has a tensile strength Rm ≥ 590 MPa and a specified plastic extension strength Rp at room temperature. 0.2 >240MPa, section shrinkage Z>70%, impact absorption energy KU2>285J.

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