Austenitic stainless steel cannot be strengthened by heat treatment, but it can be strengthened by cold working deformation (cold work hardening, deformation strengthening), which will increase the strength and reduce the plasticity. After austenitic stainless steel or products (springs, bolts, etc.) are strengthened by cold working deformation, there is a large processing stress. The existence of this stress increases the sensitivity of stress corrosion when used in a stress corrosion environment, and affects the small size of the scale. stability. To reduce stress, stress relief treatment can be used. - Generally, it is heated to 280 ℃ ~ 400 ℃ for 2h ~ 3h and then air-cooled or slowly cooled. The stress relief treatment can not only reduce the stress of the workpiece, but also improve the hardness, strength and elastic limit without changing the elongation greatly.
First of all, attention should be paid to the reasonable selection of the heating temperature for the solid solution treatment of austenitic stainless steel. In the material standard of austenitic stainless sodium, the specified range of solid solution heating temperature is wide. In the actual heat treatment production, the specific composition of the steel, Factors such as content, use environment, possible failure form, etc., reasonably select the optimal heating temperature. However, care should be taken to prevent the heating temperature from being too high due to melting, because the heating temperature of the solution treatment is too high, which may cause the grains of the materials that have been refined by forging to grow. The coarsening of the grains can cause some undesirable consequences.
Secondly, attention should be paid to the effect of stabilization treatment on the properties of the solid solution state. For austenitic stainless steel containing stabilizing elements, the mechanical properties will tend to decline when the solution heat treatment is followed by stabilization treatment. Strength, plasticity, and toughness have this phenomenon. The reason for the decrease in strength may be that during the stabilization treatment, the strong carbide-forming element titanium combines with more carbon to form TiC, which reduces the strengthening degree of carbon in austenite solid solution, and TiC will also be in the process of heating and heat preservation. Agglomerates grow, which also has an effect on strength.
Thirdly, the heating temperature for stabilization treatment should not be too high, generally between 850°C and 930°C. Austenitic stainless steel should not be subjected to multiple solution treatment, because multiple solution heating will cause grain growth and adversely affect the properties of the junction material. At the same time, attention should be paid to pollution during processing. Once contaminated, measures should be taken to eliminate pollution. In order to better eliminate the intergranular stress, the use of heat preservation bright annealing heat treating machine can be considered. According to processing data from clients of Hangao Tech (SEKO Machinery), the temperature difference of each point in the heat preservation area is controlled within plus or minus 1-2 degrees Celsius, so as to ensure that the steel can be heated completely, the grains can be completely melted, and a better metallographic structure can be obtained.
