Abstract: In order to investigate the phase transformation law of high carbon steel wire rod during isothermal quenching in salt bath, the cooling curves of high temperature wire rod after entering molten salt was measured by taking 92Si steel as the research object, and the convective heat transfer coefficient between the wire rod and molten salt was calculated by using Deform software, and then the cooling law of wire rod in molten salt was analyzed. In addition, the effects of heating temperature and salt bath isothermal temperature on microstructure and mechanical properties of the wire were studied. The results show that the phase transformation heat is difficult to be transferred quickly during isothermal quenching, which leads to the continuous non-isotermal phase transformation of wire rod in molten salt. The heat transfer capacity of the molten salt can be improved by reducing molten salt temperature, and then the cooling effect of the wire rod can be improved. The tensile strength of the wire rod after salt bath isothermal quenching is mainly determined by the molten salt temperature, and reducing the molten salt temperature in the pearlite transformation temperature range leads to smaller pearlite lamellar spacing and higher tensile strength. The plasticity of the wire rod is mainly determined by the heating conditions before phase transformation. With the increase of heating temperature, the prior austenite grain size becomes larger, the size of pearlite colony and block in the wire rod after phase transformation increases, and the percentage reduction of area of the wire rod decreases.

Key words: salt bath, isothermal quenching, phase transformation temperature, tensile strength, percentage reduction of area