Effects of Heat Treatment Process Parameters on Microstructure and Mechanical Properties of DP440 Cold Rolled Strip

In order to optimize the production process, improve the production efficiency and accelerate the development and application of the domestic dual-phase steel, the effects of heat treatment process parameters on micro-structure and mechanical properties of DP440 cold rolled strip were studied by the CAS-300 simulated continuous annealing equipment. When the heating rate increased from 5 to 100 °C/s, both the tensile strength and yield strength increased because of the decreased grain size. When the intercritical annealing temperature increased from 780 to 850 °C, the martensite content decreased so that the tensile strength decreased first, then increased, and the yield strength increased. When the rapid cooling rate increased from 25 to 100 °C/s, because the martensite content increased, the tensile strength increased, while the yield strength decreased. When the overaging temperature increased from 260 to 400 °C, the tensile strength decreased, while the yield strength increased. When the overaging time increased from 240 to 480 s, the tensile strength decreased a little, while the yield strength increased a little.