Precipitation Hardening Stainless Steel heat Treatment Process
Precipitation hardening stainless steel belongs to a special group of stainless steel, which can achieve a higher mechanical strength or hardness by heat treatment to provide superior properties in applications requiring these properties and corrosion resistance. Precipitation hardening stainless steel heat treatment commonly requires a solution treatment, rapid cooling, aging and an optional annealing or bright annealing treatment. This article outlines the important parameters, the heat treatment processes, and the mechanical properties of the precipitation hardening stainless steel.
First, a solution treatment is required to uniform the composition of the precipitation hardening stainless steel material. Solution treatment involves heating the material in a protective atmosphere at a temperature above the A1 transformation temperature (usually at 1050-1150°C, depending on the grade). The material is then rapidly cooled, preferably using water or air, to prevent the formation of martensite and to homogenize the microstructure.
After the solution treatment is complete, the material is heated to a predetermined aging temperature until the material reaches the desired mechanical properties. The aging temperature is usually lower than the solutionizing temperature and is determined by the grade of precipitation hardening stainless steel. Aging times may vary from a few minutes for low aging temperatures, to several hours at higher temperatures, depending on the desired properties.
After aging is complete, the material should be cooled in air. No further heat treatment is required unless higher mechanical strength is desired. In such a case, the material must be cooled to room temperature and then reheated again to a temperature between 300°C and 450°C. The material is then cooled again in air.
The mechanical strength or hardness of the precipitation hardening stainless steel can depend on the solutionizing temperature, aging temperature, and the aging times. Generally, the higher the solutionizing temperature and aging temperature, the higher the mechanical properties of the material. Higher aging temperatures also increase the hardness, but the maximum hardness after aging does not always increase with higher aging temperatures.
Furthermore, an annealing or bright annealing treatment can also be used to improve the corrosion resistance of precipitation hardening stainless steel. The material is heated at a temperature range of between 600°C and 950°C, depending on the grade and the desired mechanical properties. The material is then cooled in air or water. After annealing, the mechanical properties and microstructure are restored and the corrosion resistance is increased.
In conclusion, precipitation hardening stainless steel heat treatment is a complex material science process that requires careful consideration and planning. The heat treatment parameters must be carefully selected based on the properties required. Solutionizing, aging, and annealing are the key steps in the heat treatment of precipitation hardening stainless steel. By selecting the proper heat treatment process, the material can be effectively hardened, preserved and made corrosion resistant.
