The effect of alloying elements such as Cr and Ni in austenitic stainless steel causes the Ms point to drop below room temperature (-30 to -70℃). To ensure the stability of the austenite structure, no phase change occurs above room temperature during heating and cooling. Therefore, the main purpose of heat treatment of austenitic stainless steel is not to change the mechanical properties, but to improve corrosion resistance.

1. Solution treatment of austenitic stainless steel
Process:
In the GB1200 standard, the recommended heating temperature range is relatively wide: 1000~1150℃, usually 1020-1080℃. Considering the specific grade composition, whether it is a casting or a forging, etc., the heating temperature should be appropriately adjusted within the allowable range. If the heating temperature is low, C-Cr carbides cannot be fully dissolved. If the temperature is too high, there will also be problems with grain growth and reduced corrosion resistance.

Cooling method: 

Cooling should be done at a faster speed to prevent carbides from re-precipitating. In the standards of my country and some other countries, "fast cooling" after solid solution treatment is indicated. Combining different literature and practical experience, the scale of "fast" can be mastered as follows:

• C content ≥ 0.08%; Cr content > 22% and Ni content is relatively high; C content < 0.08%, but effective size > 3mm, should be water-cooled;

• C content < 0.08% and size < 3mm, can be air-cooled;

• Effective size ≤ 0.5mm can be air-cooled.

2. Stabilization heat treatment of austenitic stainless steel
Stabilization heat treatment is limited to austenitic stainless steel containing stabilizing elements Ti or Nb, such as 1Cr18Ni9Ti, 0Cr18Ni11Nb, etc.

Process:
Heating temperature: This temperature should be higher than the dissolution temperature of Cr23C6 (400-825℃), lower than or slightly higher than the starting dissolution temperature of TiC or NbC (such as the dissolution temperature range of TiC is 750-1120℃). The stabilization heating temperature is generally selected at 850-930℃, which will fully dissolve Cr23C6, so that Ti or Nb will be combined with C, while Cr will continue to remain in austenite.

Cooling method: 

Generally, air cooling is used, and water cooling or furnace cooling can also be used, which should be determined according to the specific situation of the parts. The cooling rate has no significant effect on the stabilization effect. From our experimental research results, when cooling from the stabilization temperature of 900℃ to 200℃, the cooling rate is 0.9℃/min and 15.6℃/min. Compared with each other, the metallographic structure, hardness, and intergranular corrosion resistance are basically the same.

3. Stress relief treatment of austenitic stainless steel
Process:
When conditions permit, solution treatment and stabilization treatment can effectively eliminate stress (solid solution water cooling will also produce certain stress). However, this method is sometimes not allowed, such as pipe fittings in the circuit, complete workpieces without margins, and parts with particularly complex shapes that are easy to deform. In this case, the stress relief method of heating at a temperature below 450°C can be used to eliminate some stress. If the workpiece is used in a strong stress corrosion environment and must completely eliminate stress, this should be considered when selecting materials, such as using steel containing stabilizing elements or ultra-low carbon austenitic stainless steel.

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