Effect of quenching on microstructure and properties of modified Al-bearing high boron high speed steel

In this paper, the effects of different quenching temperatures on the microstructure, hardness, and wear resistance of modified Al-bearing high boron high speed steel were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), a hardness tester, and an MM-200 block-on-ring wear testing machine. The results showed that the as-cast microstructure of modified Al-bearing high boron high speed steel consisted of martensite, ferrite, pearlite and continuous network eutectic borocarbides which were distributed at the grain boundary. The eutectic borocarbides mainly included M₂B and M₇(C, B)₃. With an increase of quenching temperature, the matrix turned into martensite, and the continuous network structure of eutectic borocarbides were gradually broken and changed to the spherical; the secondary borocarbides M₂₃(C, B)₆ were precipitated from the matrix. After quenching at 1150°C, eutectic borocarbides were clearly visible as a broken network and spheroidal in shape, and the distribution was more uniform. When the quenching temperature was in a range of 1000°C to 1150°C, the hardness and wear resistance of the alloy obviously increased. When the quenching temperature attained 1150°C, hardness reached the highest 64.3 HRC, and the wear resistance was best.