Hardness behavior of W. Nr. 1.7709 steel, oil quenched and tempered between 475°C and 575°C

Department of Mechanical Engineering, University of West Attica, 250 Thivon & Petrou Ralli Ave. 12244 Egaleo, Greece

Abstract

Steel components frequently involve a heat treatment to improve mechanical properties. In order to meet difficult working conditions, several components are hardened by quenching. W. Nr. 1.7709 is a representative structural steel with very low thermal conductivity among EN wrought alloy steels, which is extensively used after hardening and tempering. Although the steelmakers provide technical information about their heat treatment sequence, the tempering diagram of the specific grade has not been designed yet. The present paper analyses the temper resistance of the specific steel after oil quenching and tempering at high temperatures. Samples of identical chemical compositions were accordingly prepared and randomized. Five groups of ten specimens were austenitized at 960°C, hold for 30 minutes and were quenched in oil. They were tempered for two hours at different temperatures between 475°C and 575°C. Specific temperatures are interesting to the heat treaters, as they could allow certain transformations which take place during tempering. Hardness measurements were carried out and statistically processed. The tempering diagram was plotted to the specified temperature range. The influence of tempering temperature on steel hardness was analysed and the resistance to tempering back of the steel was discussed. The tempering diagram is critical for metallurgists as it represents a guide to define the proper tempering parameters so that the hardness predicted according to the mechanical property requirements are obtained.