This study aims to identify any effects of temperature temperatures on the toughness and the hardness of 4340 steel, by steady temperatures and holding time to the hardenning process, thereafter using variations in temperature and holding time. This research administered the heat treatment hardening and tempering. In ordet to get hardness results by using rockwell's hardness test and toughness by using the impact test. Analysis of the test data was using Analysis of Variance (Anova). From the results of this study it was found that the hardness value decreased after theprocess tempering with the lowest hardness value at a temperature of 650C with a value of 29 HRC, while the value of toughness increased after the tempering process was carried out at a temperature of 650˚C with a value of 0.1483 J/mm2.