Effects of Tempering Temperature on the Microstructure and Mechanical Properties of MIM-4605 High-Strength Low-Alloy Steel

This research focuses on the effects of different tempering temperatures (200 degrees C, 300 degrees C, 400 degrees C, and 500 degrees C) on the microstructure and mechanical properties of MIM-4605 steel. The results show that the matrix of as-sintered MIM-4605 steel is primarily composed of a nickel-rich phase, ferrite, and pearlite, with a large number of nodular iron oxide particles with a diameter of around 1 mu m dispersed in the matrix. However, the matrices of the as-quenched MIM-4605 steel and of the as-tempered MIM-4605 steel tempered at the different temperatures are primarily composed of lath martensite, as well as some needle martensite structures. It is worth noting that after tempering of the as-quenched MIM-4605 steel at 200 degrees C for 4 h, a large amount of fine nodular epsilon-carbide precipitates can be found in the martensite matrix. The epsilon-carbide precipitates are only 5-10 nm in size and form a semi-coherent interface with the matrix, resulting in a drastic improvement of tensile strength. However, as the tempering temperature increases, the growth of the epsilon-carbide precipitates becomes coarser, which gradually leads to a decrease in the tensile strength of the MIM-4605 steel.