Method for eliminating network carbide in annealed microstructure of Cr-type martensitic stainless steel

Abstract

The invention relates to a method for eliminating network carbides in a Cr-type martensitic stainless steel annealing microstructure. The method comprises the following steps of: performing high-temperature diffusion annealing before forging a steel ingot; and after the steel ingot subjected to high-temperature diffusion annealing is forged and formed, heat treatment after forging is conducted. According to the 17% Cr type martensitic stainless steel material, high-temperature diffusion annealing is adopted to homogenize components and eliminate or reduce liquation carbides, the upsetting ratio and the total forging ratio are controlled in the forging forming process, and network carbides in the annealed microstructure of the 17% Cr type martensitic stainless steel are eliminated in combination with heat treatment after forging; the annealing microstructure form of the 17% Cr type martensitic stainless steel is remarkably improved, a uniform granular pearlite structure is obtained, a good structure foundation is laid for pre-hardening treatment, and the polishing property and corrosion resistance of the steel are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, and specifically relates to a method for eliminating network carbides in annealed microstructure of 17% Cr type martensitic stainless steel, and in particular to a method for improving the annealed microstructure morphology of 17% Cr type martensitic stainless steel and obtaining uniform granular pearlite structure. Background Art

[0002] 17% Cr type martensitic stainless steel mainly includes 3Cr17Mo, 3Cr17NiMoV, 1.2316, AISI440B, etc. These steels contain enough carbon and alloy elements, and the hardness can reach 50-60HRC after heat treatment. This type of steel has good hardenability, excellent wear resistance, polishing and corrosion resistance, and has been widely used in the production of various corrosive plastic molds, injection molds and die-casting molds. Because the steel contains 17% Cr, its liquid precipitation point E shifts to the left. During the smelting and solidification process, a large amount of liquid precipitation carbides precipitate and distribute along the dendrites. After forging deformation, they are in the form of bands or meshes. During the cooling process after forging, they are very easy to become the nucleation core of secondary carbides. Liquid precipitation carbides plus high content of secondary carbides are distributed in the steel in a mesh shape, which seriously affects its polishing and corrosion resistance. Summary of the invention

[0003] The invention provides a method for eliminating network carbides in the annealed microstructure of 17% Cr martensitic stainless steel, which significantly improves the annealed microstructure morphology of the 17% Cr martensitic stainless steel, obtains a uniform granular pearlite structure, lays a good organizational foundation for pre-hardening treatment, and improves the polishability and corrosion resistance of the steel.

[0004] In order to solve the above technical problems, the present invention provides a method for eliminating network carbides in the annealed microstructure of 17% Cr type martensitic stainless steel, characterized in that the steps are as follows:

[0005] 1) High temperature diffusion annealing is performed before forging the steel ingot;

[0006] 2) Forging the high temperature diffusion annealed steel ingot;

[0007] 3) After the forging is completed, air-cool or water-cool it to 200-450℃ and keep it for a certain period of time, heat it to 1100-1150℃ at ≤100℃ / h and keep it for 15-40 hours, air-cool or water-cool it to 200-400℃, heat it to 1020-1060℃ at ≤100℃ / h and keep it for 5-20 hours, air-cool or water-cool it to 200-400℃, finally heat it to 740-800℃ and keep it for 15-40 hours.

[0008] Beneficial effects: 17% Cr martensitic stainless steel material adopts high temperature diffusion annealing to uniform composition, eliminate or reduce liquid carbides, control the upsetting ratio and total forging ratio in the forging forming process, and eliminate the network carbides in the annealed microstructure of 17% Cr martensitic stainless steel combined with post-forging heat treatment, significantly improve the annealed microstructure morphology of 17% Cr martensitic stainless steel, obtain uniform granular pearlite structure, lay a good organizational foundation for pre-hardening treatment, and improve the polishability and corrosion resistance of steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0010] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below.

[0011] The present invention proposes a method for eliminating network carbides in the annealed microstructure of 17% Cr martensitic stainless steel, comprising the following steps:

[0012] 1) The steel ingot is subjected to high temperature diffusion annealing at 1200-1290℃ for 25-40 hours to homogenize the composition and eliminate or reduce liquid carbides.

[0013] 2) Forging the high temperature diffusion annealed steel ingot, controlling the heating temperature between 1100 and 1250°C, and ensuring that the upsetting ratio is ≥2.0 and the total forging ratio is ≥4.0.

[0014] 3) After the forging is completed, the forging is air-cooled or water-cooled to 200-450°C and kept for a certain period of time, and then heated to 1100-1150°C at ≤100°C / h and kept for 15-40 hours to fully dissolve the network carbides that precipitate along the crystals during forging and cooling after forging; then air-cooled or water-cooled to 200-400°C to inhibit the precipitation of carbides along the crystals, and then heated to 1020-1060°C at ≤100°C / h and kept for 5-20 hours to achieve recrystallization and grain refinement, and obtain uniform and fine austenite plus uniformly distributed carbide structure; then air-cooled or water-cooled to 200-400°C to obtain uniform martensite, and finally heated to 740-800°C and kept for 15-40 hours to allow the carbides to precipitate uniformly, grow and spheroidize, and obtain a uniform granular pearlite structure.

[0015] Example:

[0016] 1. Before forging, the steel ingot is subjected to high temperature diffusion annealing at 1200-1290℃ for 25-40 hours.

[0017] 2. Forge the high-temperature diffusion annealed steel ingot, control the heating temperature between 1100 and 1250°C, the upsetting ratio ≥2.0, and the total forging ratio ≥4.0.

[0018] 3. After forging, air or water cool to 200-450℃ and keep warm for a certain period of time → heat up to 1100-1150℃ at ≤100℃ / h and keep warm for 15-40 hours → air or water cool to 200-400℃ → heat up to 1020-1060℃ at ≤100℃ / h and keep warm for 5-20 hours → air or water cool to 200-400℃ → heat up to 740-800℃ and keep warm for 15-40 hours.

[0019] 4. The microstructure test results are shown in the table below.

[0020] Uniform spheroidizing annealing structure Network carbide Product 1 A2 B2 Product 2 A2 B2 Product 3 A2 B2

[0021] The present invention significantly improves the annealing microstructure of 17% Cr type martensitic stainless steel through post-forging heat treatment, obtains uniform granular pearlite structure, lays a good organizational foundation for pre-hardening treatment, and improves the polishability and corrosion resistance of the steel.

[0022] This method has been applied in batches to 17%Cr martensitic stainless steels such as 1.2316, 3Cr17Mo, 3Cr17NiMoV, and BZS816. After adopting this method, the network carbides in the annealed microstructure of 17%Cr martensitic stainless steel can be completely eliminated. According to GB / T 35840.3-2018, the uniform spheroidizing annealing structure can reach A1~A3 and the network carbides B1~B2.

[0023] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for eliminating network carbides in the annealed microstructure of 17% Cr martensitic stainless steel. It is characterized in that Here are the steps: 1) High temperature diffusion annealing is performed before forging the steel ingot; 2) Forging the high temperature diffusion annealed steel ingot; 3) After the forging is completed, air-cool or water-cool it to 200-450℃ and keep it for a certain period of time, heat it to 1100-1150℃ at ≤100℃ / h and keep it for 15-40 hours, air-cool or water-cool it to 200-400℃, heat it to 1020-1060℃ at ≤100℃ / h and keep it for 5-20 hours, air-cool or water-cool it to 200-400℃, finally heat it to 740-800℃ and keep it for 15-40 hours.

2. A method for eliminating network carbides in the annealed microstructure of 17% Cr martensitic stainless steel according to claim 1, It is characterized in that In step 2), the heating temperature is controlled between 1100 and 1250° C., and the upsetting ratio is ensured to be ≥2.0 and the total forging ratio is ≥4.

0.

3. A method for eliminating network carbides in the annealed microstructure of 17% Cr martensitic stainless steel according to claim 1, It is characterized in that In step 1), the steel ingot is subjected to high temperature diffusion annealing at 1200-1290° C. for 25-40 hours.

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