One of the advantages of water-air hardening is the possibility of conducting controlled self-tempering, which in surface induction hardening provides hardening without tempering in a furnace andexclamationthe creation of the optimum conditions for heat treatment in a single production line with full automation of the process. In addition, there are no hardening craccs on the treated parts. Investigation of the influence of the quenching and self-tempering times on the surface hardness was made on shaft model samples of 45 steel. The results of the inwestigations made show that a self-tempering time in the range from 10 to 60 seconds has little influence on the change in surface layer hardness. To obtain equal hardness in self-tempering (HRC 57-58), it is necessary to use higher temperatures than in furnace tempering. For 45 steel this difference is 75-85/sup 0/C with a tempering temperature up to 300/sup 0/C and 100-250/sup 0/C at higher temperatures. A comparison of the self-tempering and furnace tempering temperatures after hardening with a water-air mixture providing equal hardnesses of 45 steel are shown.