Microstructure Evolution and Mechanical Properties of Advanced High Strength Steel for Automobile under Ultra-fast Cooling with Different Aging Temperature

摘要

We describe here the effect of aging temperature on microstructure evolution and mechanical properties of advanced high strength steel for automobile when the ultra-fast cooling rate was 500℃/s and the annealing temperature was 820℃.Experimental studies obtained that high strength of more than 1100 MPa can be obtained through judicious selection of aging temperature.Experiments indicated that with the increasing of the aging temperature,the tensile strength was decreased while the yield strength was increased.The tensile strength decreased from 1164MPa to 896MPa and the yield strength increased from 614MPa to 729MPa when the aging temperature increased from 240℃to 320℃.The underlying reason is that the volume faction of martensite decreased gradually with the increasing of aging temperature.When the aging temperature increased from 240℃ to 320℃,the volume faction of martensite decreased from 64.5％ to 47.5％.And the grain size increased within the investigative aging temperature,it increased from 3.9μm to 5.4μm.The microstructural characterization indicated that the quantity and the average size of precipitates was increased with the aging temperature increased.