Softening Behavior of H13 Steel by Thermal Cycling between Molten ADC12 Al-alloy and Spray Cooling Chamber
The thermal cycling(1000~10000 cycles)testing of H13 steel between molten ADC12 Al-alloy(670~730℃)and spray cooling chamber was conducted in this paper.The microstructure evolution and hardness change of H13 steel were studied against the cycling process,and then,a quantitative model of hardness change was established based on the kinetics of solid phase transformations theory.The results indicate that H13 steel undergoes softening along with the thermal cycling.At the beginning of the cycling,the softening of the matrix is mainly due to the decrease of dislocation density.With the in-crease of the cycling times,the softening at the middle and late stages was mainly due to the coarsening of carbides,the broadening of martensite lath and the growth of sub-grains.During different cycling tests,in-creasing the temperature of the molten Al-alloy may accelerate the softening of the matrix.According to the kinetics equation of solid phase transformations,the calculated phase transformation activation energy of the H13 steel is 200.78 kJ/mol,which is similar to the diffusion activation energy of alloy elements Cr,V,and Mo in ferrite,indicating that the softening rate of H13 steel depends on the diffusion of these elements.
metallic materialsH13 steelthermal cyclingmicrostructurehardnesskinetics of phase transformation