This paper studies the best tempering process and provides guidance for the industrial application of modified Al-bearing high boron high-speed steel (AB-HSS) in the future. The microstructure, hardness and wear resistance of modified AB-HSS after quenching at 1150 °C and tempering in the different condition were investigated. The results showed that the matrix of modified AB-HSS consisted of tempered martensite after once tempering at 500 °C and 530 °C for four hours. Small granular secondary M 23 (C, B) 6 type borocarbides were precipitated from the matrix. With the increase of tempering temperature, the macro-hardness, micro-hardness and wear resistance of modified AB-HSS all decreased gradually. With the increase of tempering times and tempering holding time, a part of tempered martensite was decomposed into ferrite, and the macro-hardness and microhardness all decreased slowly. Appropriate tempering process of modified AB-HSS was once tempering at 500 °C-530 °C for four hours.

The microstructure of Al-bearing high-boron high speed steel (AB-HSS) contains a large amount of borocarbides, which makes it have high hardness, superior wear resistance and thermal stability. But the borocarbides are coarser and continuously distribute along the grain boundary which seriously destroys the toughness of AB-HSS. In this paper, the microstructure and properties of AB-HSS were regulated by adding modifiers and quenching and tempering heat-treatment. The modifier was RE-Mg, Ti and N elements. The microstructure and properties of AB-HSS were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), the electron probe microanalysis (EPMA), hardness testing, wear testing, and impact testing. The results show that the borocarbides in as-cast AB-HSS are found in intergranular networks showing different degrees of continuity after adding different types of modifiers. The matrix of as-cast AB-HSS all is composed of ferrite, pearlite and martensite, and the borocarbides all consist of M2(B,C) and M7(C,B)3 after adding different types of modifiers. After high-temperature heat treatment, the borocarbides in the microstructure of RE-Mg modification AB-HSS appear as discontinuous networks showing signs of spheroidization and the distribution of the borocarbides is more uniform. The matrix of RE-Mg modification AB-HSS is martensite and the borocarbides consist of M2(B,C), M7(C,B)3 and M23(C,B)6. The hardness of RE-Mg modification AB-HSS reaches 61.7 HRC, and impact toughness increases by 52%, and has excellent comprehensive mechanical properties.