Effects of controlled cooling process on Microstructure and Mechanical Properties of Engineering Machinery Steel Q690D

摘要

By choosing properly the accelerated cooling process,the high strength structural steels were obtained coming up to China's National Standards Q690D.as included in GB/ T16270—1996.Discussed the effects of controlled cooling,i.e.the finish cooling temperature and the cooling rate,on the mechanical properties of the test steel,and the microstructure of the steel was investigated by virtue of OM(optical microstructure),SEM(scanning electron microscope) and EPMA(electron probe microprobe analyser).Lath bainite was easily obtained by increasing the cooling rate and reducing the finish cooling temperature,which can effectively improve the plate,the formation of acicular ferrite was helpful to the improvement of low temperature impact toughness and uniformly distributed equiaxed M/A islands were less detrimental to low temperature impact toughness; the massive M/A islands were formed in high finish cooling temperature and low cooling rate,which can easily produce stress concentration and crack,meanwhile,lead to lower toughness and ductility of the steel.