The effects of destabilizing heat treatment temperature and natural aging treatment on the microstructure and properties of high chromium cast iron were studied, and the artificial aging treatment process to effectively improve the hardness of high chromium cast iron was discussed. In addition, the carbide stability and theoretical hardness of Fe2 xcrxc (x = 1 ~ 2) alloy are analyzed combined with the first principle to provide theoretical guidance for experimental phenomena. The conclusions are as follows:
(1) After heating the high chromium cast iron to 900 ℃ ~ 1050 ℃ for 1h, take out the water cooling quenching to room temperature. The microstructure of the experimental material is martensite + eutectic carbide (M7C3) + secondary carbide (m3c + M23C6) + residual austenite. With the increase of quenching temperature, the macro hardness of high chromium cast iron first increases and then decreases. When the quenching temperature is 950 ° C, the hardness reaches the maximum. The content of secondary carbides first increased and then decreased with the increase of temperature, and the particles gradually coarsened into spherical and rod shapes. At 1050 ℃, the content of secondary carbide decreases significantly. High chromium cast iron is a brittle material, and its impact properties are less affected by heat treatment temperature, and the fracture mode is brittle fracture.
(2) The high chromium cast iron was kept at 900 ℃ ~ 1000 ℃ for 1 hour and quenched to room temperature before natural aging treatment. During natural aging treatment η- (Fe, Cr) 2C precipitates from martensitic matrix, which increases the macro hardness of high chromium cast iron by 2 ~ 3HRC and decreases the micro hardness of matrix. However, high chromium cast iron increases slightly after being kept at 950 ℃ for 1 hour and then maintained at 80 ℃ for 2-5 hours. When the temperature is kept at 80 ℃ for 3h, the hardness reaches the maximum value, which is 66.8hrc.
(3) Cr atom reduces the formation energy of carbides in Fe2 xcrxc (x = 1 ~ 2) alloy and makes η- Formation energy ratio of (Fe, Cr) 2C carbide η- The formation energy of Fe2C carbide is low. So, η- (Fe, Cr) 2C carbide stability ratio η- Fe2C good. And η- The hardness of Fe (2C) alloy can be improved.