| High speed steel specimens containing various niobium content are put to heat treatment. The hardness of these specimens measured by Rockwell hardness equipment reveals the incidence regularity caused by quenching temperature and tempering temperature. The type and chemical composition of main carbides in high speed steel are studied through X-ray diffraction analysis, microstructure observation and EDS method.The experiment results are as follow. The best quenching temperature of high speed steel is 1100-1150℃, when the hardness peak of high speed steel appears; The best tempering temperature of high speed steel is 500-525℃, when secondary hardening effect appears; The types of main carbides in high speed steel containing niobium include: MC, M6C and M7C3. The contribution of niobium as: heighten the quenching temperature of high speed steel, accelerate MC forming, and improve the hardness of high speed steel.
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