Step 6. Cooling *Cooling in still air is good enough to obtain high hardness. step 7. Hardness test *After the dies cool down to room temperature, test the hardness of die edge by a file or a scriber *lf the desired hardness might not be obtained, refer to the following. Case 1. If an excessive hardness be obtained, temper the die at a temperature 150-200 C Case 2. If the hardness be lower than the desired one, following two causes are considered. (1) Caused by poor heating Return to the Step 5 and the die edge is heated at a higher temperature than the previous one. (2) Caused by overheat a)Polish the die edge surface to a depth sufficient to remove overheated surface layer. b)After annealing the die or tempering it at 650°C return to the Step 5 and heat the die edge at a lower temperature than the previous one.