Precipitation hardening (PH) martensitic stainless steel generally contains alloying elements such as copper, lead, molybdenum, and titanium that form a hardened phase. These alloying elements have greater solubility in austenite, but very little in martensite. Therefore, the heat treatment of precipitation hardening martensitic stainless steel should first be solid solution treatment to fully dissolve the hardened phase precipitated in the as-cast state. Then the precipitation hardening treatment is carried out to precipitate the secondary hardening phase, thereby improving the strength of the stainless steel casting and making it have good corrosion resistance. In addition, solution treatment will also improve the cutting performance of precipitation hardening stainless steel castings.
Characteristics of Heat Treatment of Precipitation Hardening Stainless Steel Castings:
- 1) Before solution treatment, it needs to be preheated to 650℃, and then quickly heated to a predetermined temperature. Castings can also be loaded into furnaces at high temperatures.
- 2) The solid solution temperature is generally 1020-1060°C, and the holding time is calculated according to the corresponding increase of 1 hour for every 25 mm increase in wall thickness. For castings with complex shapes, the solid solution temperature can be reduced to about 930°C.
- 3) In order to eliminate the non-uniformity of dendritic structure and component segregation in large steel castings, it is best to perform high temperature homogenization treatment before solid solution.
- 4) The temperature of the aging treatment can be appropriately selected according to the requirements of the strength, hardness and toughness of the casting.
- 5) In order to improve the mechanical properties of precipitation hardening stainless steel castings, after solution treatment, air cooling at 700-810°C for 2 hours, and then air cooling at 620°C for 4 hours. This can significantly improve the cutting performance of castings.
Post time: Sep-04-2021