EFFECT OF PRE-QUENCHING AND PRE-NORMALIZATION ON MICROSTRUCTURES AND MECHANICAL PROPERTIES OF 40Cr STEEL AFTER ZERO-TIME-HOLDING QUENCHING

Pre-quenching and pre-normalization are selected as pre-treatment processes. Microstructures, the tensile strength and hardness of zero-time-holding quenched 40Cr steel with different pre-treatment are investigated. The results show that the zerotime- holding 40Cr steel quenched by prequenching is fine martensite and exhibits higher tensile strength and hardness than that with pre-normalization. The mechanical properties of the zero-time-holding 40Cr steel quenched by prequenching are better than that with prenormalization. The effect of pre-treatment on the mechanical properties of zero-time-holding quenched 40Cr steel becomes prominent when the zero-time-holding quenching temperature decreases. The mechanical properties of zero-timeholding 40Cr steel quenched at 860-890 degrees C can be improved with austenite inverse transformation.