According to the different chemical composition, heat treatment, the purpose of, austenitic stainless steel is often used heat treatment method of solution treatment, stabilizing annealing treatment, eliminate stress and sensitizing treatment etc.
1 solution treatment
Austenitic stainless steel bar solution treatment is the steel is heated to fully dissolve excess phase to solid solution in a certain temperature, keep a certain time after the rapid cooling technique. Austenitic stainless steel is the purpose of the solution heat treatment to the precipitation in different processing procedures before or carbide alloy, such as (FeCr) 23 c6 and sigma phase to dissolve into austenite, access to a single austenitic organization (some) there may be a small amount of delta ferrite, to ensure that the material has good mechanical properties and corrosion resistance, fully eliminate stress and cold work hardening phenomenon. Solution treatment is suitable for any component and the grades of austenitic stainless steel.
2 stabilizing annealing
Stabilizing annealing is to contain the stabilizing element titanium or niobium austenitic stainless steel heat treatment methods. With the purpose of this approach is the use of titanium, niobium and carbon strong combination properties, stable carbon and make it as far as possible don’t combine with chromium, ultimately achieve the goal of stable chromium, improve the stability of chromium in austenite, avoid from grain boundary precipitates, ensure material corrosion resistance.
Austenitic stainless steel cooling method and cooling rate on the stabilization of stabilizing treatment effect is not much, so, in order to prevent the complicated shape workpiece deformation or to guarantee minimum stress of the workpiece, can use smaller cooling speed, such as air cooling or furnace cooling.
3 eliminating stress
Austenitic stainless steel to eliminate stress treatment method, should be used according to the type of material, environment, the purpose of eliminating stress size and shape of the workpiece, etc., pay attention to grasp some principles.
Remove after the machining process of stress or remove the residual stress. Can use solution treatment temperature and rapid cooling, class I and class II austenitic stainless steel can be adopted slower cooling pipe. In order to ensure the final size of the workpiece stability. Can use low heating temperature and slow cooling rate. To eliminate a lot of residual stress. Eliminate the new stress may be produced in the working environment of the residual stress of workpiece or to eliminate the welding stress, with large cross-section weldments should be used for melting temperature, class III austenitic stainless steel must be fast. This kind of circumstance had better choose class I or class II austenitic stainless steel, slow cooling after heating, the effect of eliminating stress better. Can use local heating mode only to eliminate the residual stress of workpiece. Should take the way of low temperature heating and slow cooling.
4 sensitizing treatment
Sensitization processing actually does not belong to the austenitic stainless steel or its products should be used in the process of manufacturing methods of heat treatment. But as in the test of austenitic stainless steel intergranular corrosion resistance testing when used by a program.
Sensitization processing is essentially make austenitic stainless steel is more sensitive to intergranular corrosion of processing. For, use some special occasions, for more strictly check material intergranular corrosion resistance, in certain standards, to austenitic rust sodium sensitization system more strict, according to temperature and material artifacts for future use and whether in the carbon containing clamp element factors and adopt different system of sensitization. Some of sensitizing treatment, cooling speed control. So, in the judgement inclination of intergranular corrosion of austenitic stainless steel, the sensitization system should be paid attention to.
Five austenitic stainless steel cold work to strengthen and to deal with stress
Austenitic stainless steel can’t use heat treatment to strengthen, but can be reinforced by cold deformation (cold work hardening, deformation strengthening), can make the strength increase and the decrease of the plastic. Austenitic stainless steel (spring, bolts, etc.) or after cold deformation strengthening, there is a big process stress, the existence of this kind of stress in the stress corrosion environment, increase the sensitivity of stress corrosion, influence the stability of small feet. To reduce stress, can be used to deal with stress. – as is heated to 280 ℃ ~ 400 ℃ for 2 h to 3 h after air cooling or slow cooling. To deal with the stress not only can reduce the stress of the parts, will be no big change in the elongation, hardness, strength and elastic limit was improved.
Notice first austenitic stainless steel solution treatment selection of proper heating temperature, sodium in austenitic stainless material in the standard, the regulation of solution temperature range is wide, the actual heat treatment production, can consider the specific composition of steel, content, use environment, factors such as possible failure modes, reasonably choose the best heating temperature. However, attention should be paid to prevent because of heat melting temperature is too high, because the solution treatment temperature is too high, may make the material has fine grains after forged grain growth. Grain coarsening can cause some adverse consequences.
Second stabilizing treatment should be paid attention to affect the performance of solid solution state, stabilizing element containing austenitic stainless steel, solid solution heat treatment after the stabilization treatment, can make the mechanical properties have a downward trend. Strength and plasticity and toughness have this phenomenon. Intensity decreased, may be stabilizing, titanium is strong carbide forming elements combine with more carbon into the TiC, reducing the degree of carbon in austenite solid solution strengthening, and TiC will gather grew up in the process of heat insulation, this will also affect intensity.
Third, the heating temperature is unfavorable and exorbitant, stabilizing treatment is generally choose between 850 ℃ ~ 930 ℃. Austenitic stainless steel is unfavorable to carry on the solution treatment, many times because of solid solution heat for many times, can cause grain growth, and material properties. At the same time, pay attention to the pollution in the process of machining, once polluted, measures should be taken to eliminate pollution.