According to the difference between the chemistry and composition of the heat treatment purpose, the heat treatment processes often used for
304 austenitic stainless steel sheets include solid solution treatment, stabilization annealing treatment, stress relief treatment and sensitization treatment.
Solution treatment
The solid solution treatment of 304 austenitic stainless steel plate is a process of heating the plate to a certain temperature at which the excess phase is fully dissolved into the solid solution, and then rapidly cooling after holding for a certain period of time. The purpose of the solution heat treatment of austenitic stainless steel plate is to redissolve the alloy carbides and σ phase formed or precipitated in the previous processing steps into the austenite structure, so as to obtain a single austenite structure, thereby ensuring Stainless steel sheets have excellent mechanical properties and corrosion resistance to maximize stress relief and cold work hardening. Solution treatment is suitable for any composition and grade of austenitic 304 stainless steel.
Stabilization Annealing
The stabilization annealing process is a heat treatment method used for austenitic 304 stainless steel sheets containing stabilization elements titanium or niobium. The purpose of using this method is to stabilize the carbon element by using the strong bonding characteristics of titanium, niobium and carbon, so as not to combine with chromium as much as possible, and finally achieve the purpose of stabilizing the chromium element and enhance the stability of chromium in the austenite structure. , to prevent precipitation from grain boundaries and ensure the corrosion resistance of stainless steel sheets.
The cooling method and cooling rate of austenitic 304 stainless steel sheet stabilization treatment will not have much influence on the stabilization effect. Therefore, in order to prevent the deformation of workpieces with complex shapes or to ensure the minimum stress of stainless steel parts, a smaller cooling rate can be used. , such as air cooling or furnace cooling.
stress relief treatment
Determining the stress relief treatment process for austenitic 304 stainless steel plates depends on the type of material, the use environment, the purpose of stress relief and the shape and size of stainless steel parts. It should be noted that some principles must be mastered.
To remove the stress generated during the processing or to remove the residual stress after processing, the solution treatment can be used to heat the temperature and cool quickly. The type I and type II austenitic 304 stainless steel plates can be cooled slowly. To ensure final dimensional stability of stainless steel workpieces, lower heating temperatures and slow cooling rates can be used. To eliminate large residual stress. To eliminate the residual stress of the workpiece that may generate new stress in the working environment or to eliminate the welding stress of the large-section weldment, the melting heating temperature should be used, and the Class III austenitic 304 stainless steel plate must be quickly cooled. In this case, it is best to use Type I or Type II austenitic 304 stainless steel plate, which is slowly cooled after heating, and the effect of stress relief is better. In order to eliminate the residual stress of the workpiece that can only be heated locally. It should be heated at low temperature and cooled slowly.
Sensitization
Sensitization treatment does not substantially belong to the heat treatment process that needs to be used in the production process of austenitic 304 stainless steel plate or its products. Rather, it is a procedure used in testing the resistance to intergranular corrosion of austenitic 304 stainless steel plates.
The sensitization treatment is essentially a treatment that sensitizes the austenitic 304 stainless steel sheet to intergranular corrosion. For some special occasions, in order to more strictly assess the intergranular corrosion resistance of the material, in some standards, the sensitization system for the austenite structure is more stringent, according to the temperature of the workpiece in the future and the content of the material. Different sensitization systems are used depending on factors such as carbon content and whether it contains clamp elements. Some also control the heating and cooling rates of the sensitization treatment. Therefore, when judging the intergranular corrosion tendency of austenitic 304 stainless steel plate, it is necessary to pay attention to the sensitization system used.
Cold working strengthening and stress relief treatment
Austenitic 304 stainless steel plate 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 of the material and reduce the plasticity. After the austenitic 304 stainless steel plate or product is strengthened by cold working deformation, it has a large processing stress. The existence of this stress will increase the stress corrosion sensitivity of the stainless steel plate material when it is used in a stress corrosion environment, thereby affecting the material. stability. To reduce stress, stress relief treatments can be used. Usually, it is heated to 280℃～400℃ for 2-3 hours and then air-cooled or slowly cooled. Stress relief treatment can not only reduce the stress of the part, but also improve the hardness, strength and elastic limit without significant change in elongation.
