In order to obtain ADI material with stable structure and performance, the salt bath used for isothermal transformation should have the following characteristics:
① The salt bath shall be equipped with a device to prevent local overheating or local supercooling of salt bath to ensure the temperature of each area in the salt bath is uniform;
② The proportion of bath salt shall have enough heat capacity. When the casting is quenched into the salt bath, the temperature rise of bath salt shall not be higher than 20 ℃, and it is better to control within 10 ℃, and the mass ratio of parts and bath salt shall not be higher than 1:10, so as to ensure that the temperature fluctuation of bath salt before and after the casting is quenched into the salt bath can be minimized;
③ Bath salt should be cleaned more, and the cooling capacity of bath salt caused by pollution should be avoided as far as possible;
④ Bath salt should be added properly and added regularly to improve the chilling effect of bath salt. Among them, the salt composition and temperature of the ductile iron are commonly used in isothermal quenching.
By using proper tempering treatment (180-200 ℃), the martensite structure in the matrix of the Equitemperature quenched ductile iron can be transformed into tempered martensite, and some unstable unaltered austenite can be further transformed into austenite and stable high carbon austenite, and the internal stress of the material of isothermally quenched ductile iron can be effectively eliminated.