Some observations on bainitic hardening of 18-4-1 high speed steel

High speed tool steels containing bainitic structure have been shown to have better properties than tools of the same steel heat treated by conventional quenching of high speed steel due to the stabilization of austenite martensite reaction. In this paper various parameter have been investigated with a view to getting maximum amount of bainite in 18/4/1 high speed steel. It was observed that a maximum amount of 75-80% bainite, termed primary bainite was obtained by direct isothermal transformation treatment at 230°C-315°C temperature range for a maximum period of 16 hours. In addition, it was further observed that additional amount of bainite termed as secondary bainite can be formed by isothermally treating the steel followed by tempering at 600°C and then again holding at the transformation temperature for an additional period of time to get secondary bainite. Thus by giving judicious combination of iso-thermal transformation and tempering, high-speed steel containing 100% bainite was obtained. The hardness of the conventional heat-treated specimens consisting of primary martensite and secondary bainite and secondary bainite, and the results have been discussed. (Dr. R.K. Dubey, Scientist, Mr. P.S. Nag, Senior Laboratory Assistant, Mr. P.K. Gupte, Scientist, National Metallurgical Laboratory, Jamshedpur)