Micro-alloy Low-temperature Secondary Hardening Mechanism

The heat treatment technique which can result in secondary hardening phenomenon at low temperature tempering of 50CrV steel has been studied. And a series of experiments were designed to analyse the fonnation character of second phase particles which was formed during the temperring. From all of this analyses, we can obtain the necessary factors which may result in secondary hardening at low temperature and we also enumerated all kinds of curve shape that maybe exist.From the graphs which we mensurated through special heat treatment technique, we can draw conclusions that to different materials 'the low temperature' is reletive, and the optimal temperature is at 180~ 190 C for 50CrV steel which the secondary hardening can be observed.In order to explain the secondary hardening at low temperature which exists in the SOCrV, 9CrV steel .We designed the comparative experiment and observed the microstructure of the sample which has occurred the secondary hardening. The last experiment results were determined by three factors : the second phase precipitation, die decompound of martensite, martensitic transformation of remnant austenite. Especially, the microalloyed elements, which were made the second phase precipitation equally. There would be found distinct second hardening apex in the curve when .In a brief, dirogh a special heat treatment technique die strcngdiening by precipition of microalloyed carbide can compensate die falling of hardening, so the optimal mechanical property of the steel was acquired .