Solid Solution Treatment
The main purpose of solution treatment is to dissolve carbides or other precipitated phases in solid solution to obtain a supersaturated single-phase structure. Castings of austenitic stainless steel, austenitic manganese steel and precipitation hardening stainless steel should generally be solid solution treated. The choice of solution temperature depends on the chemical composition and phase diagram of the cast steel. The temperature of austenitic manganese steel castings is generally 1000 ℃ - 1100 ℃; the temperature of austenitic chromium-nickel stainless steel castings is generally 1000℃-1250℃.
The higher the carbon content in cast steel and the more insoluble alloying elements, the higher its solid solution temperature should be. For precipitation hardening steel castings containing copper, the hardness of the steel castings increases due to the precipitation of hard copper-rich phases in the as-cast state during cooling. In order to soften the structure and improve the processing performance, the steel castings need to be solid solution treated. Its solid solution temperature is 900℃-950℃.
Precipitation Hardening Treatment
Precipitation hardening treatment is a dispersion strengthening treatment carried out within the tempering temperature range, also known as artificial aging. The essence of precipitation hardening treatment is that at higher temperatures, carbides, nitrides, intermetallic compounds and other unstable intermediate phases are precipitated from supersaturated solid solution and dispersed in the matrix, thus making the cast steel comprehensive Improved mechanical properties and hardness.
The temperature of aging treatment directly affects the final performance of steel castings. If the aging temperature is too low, the precipitation hardening phase will precipitate slowly; if the aging temperature is too high, the accumulation of the precipitated phase will cause overaging, and the best performance will not be obtained. Therefore, the foundry should select the appropriate aging temperature according to the cast steel grade and the specified performance of the steel casting. The aging temperature of austenitic heat-resistant cast steel is generally 550℃-850℃; the aging temperature of high-strength precipitation hardening cast steel is generally 500℃.