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

Abstract

Abstract 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.