Microstructural, magnetic and mechanical property changes in an AISI 444 stainless steel aged in the 560 °C to 800 °C range

AISI 444 steel is an 18Cr–2Mo ferritic stainless steel, containing Ti and Nb as stabilizing elements. The effects of aging in the 560–800 °C range on the microstructure, mechanical and magnetic properties were investigated. The material was not susceptible to sigma phase formation until 100 h of exposure. Slight hardening at 560 °C and progressive softening in the 650 °C–800 °C range were observed. At these temperatures, Mo-rich phases such as Fe2Mo and FeMoSi precipitate. The increase of particle sizes with the increase of temperature above 650 °C is responsible for the decrease of hardness. Precipitation of the Mo-rich phases increases the coercive force.