Effect of Heat Treatment on Microstructure and Mechanical Properties of 45 Steel
In order to optimize the comprehensive mechanical properties of 45 steel,on the basis of standardized annealing + quenching tempering,three quenching processes with different cooling were designed,including oil quenching,NaNO3 salt bath quenching and water quenching.The microstructures of steel under three quenching conditions was observed by optical microscopy and scanning electron microscopy.It was found that the cooling rate had a significant effect on the size and density distribution of the martensitic lamelae of 45 steel.The tensile strength,yield strength,ductility and impact toughness of the steel after heat treatment were tested by tensile testing machine and a gravel impact testing machine.The results show that the yield strength,tensile strength and ductility of the steel after NaNO3 salt bath quenching are superior to those after oil quenching and water quenching.The impact toughness of the steel after oil quenching is the highest.It is proved that proper control of quenching cooling rate can effectively optimize the mechanical properties of 45 steel.
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