Mechanical Properties in the Tempering Process of a Low-alloy Quenched and Tempered Steel

Effect of tempering temperature on mechanical properties and microstructure of a lowalloy quenched and tempered steel was investigated.The results show that the as-quenched status is lath martensite with self-tempered precipitates,which possesses both good strength and toughness.The amount of plate-like precipitates increases when tempered at around 250℃,and the yield strength gets a certain rise thereby.Carbide film precipitated along lath boundaries at 400℃inducing tempered martensite embrittiement.The lath morphology still remains generally after high temperature tempering,while laths in some local areas have merged to block ferrite grains.A large amount of nano-scale carbide precipitates was observed above 550℃,and cementite particles were coarsened apparently.Fine grain strengthening and precipitation strengthening are the main strengthening mechanisms of the steel.The microstructure evolvement and precipitation characteristics influence the tensile curve shape and n value directly.