Heating time of quenching is one of the most important parameters when designing the quenching process of die steel, directly related to its quenching quality. Customarily, when the furnace temperature t1 is below the Ac3 of pearlitic steel, the quenching time should be t2≥2t1, and when t1≥Ac3, t2≥15-20min; When the furnace temperature T1 is lower than the A1 of bainite steel, the quenching time should be t2 2T1, and when t1≥A1, t2≥10-15min; When the furnace temperature T1 is below the Ms of martensite steel, the quenching time should be t2≥2t1, and when t1 is greater than or equal to Ms when t2 is not lower than 15-20 min.
When the working temperature is lower than the above requirements, the time should not be less than 1h. The heating time of die steel should not only be determined according to the above requirements, but also the size and shape of the parts, the composition of die steel, the temperature and humidity of the atmosphere and the use of quenching medium should also be taken into account.
When the working temperature is lower than the A1 of the bainite steel, if the workpiece is small, the heating time can be appropriately shortened; on the contrary, it should be appropriately lengthened. The shape design of the parts should be based on the requirements of quenching size and hardness.
If the quenching medium is used with quenching oil, the heating temperature should be slightly higher than normal. The temperature of the furnace should be strictly controlled at the temperature range of about 150 degrees lower than the optimal quenching temperature of die steel. The humidity of the atmosphere should be controlled at about 70 percent in order to prevent the thermal deformation of die steel.
Heating time is an important technical indicator in heat treatment process. It affects the performance of die steel directly. Before heat treatment, the factors such as size, shape, composition, quenching medium, temperature and humidity should be considered carefully to provide scientific and rational heating time. Only in this way can we obtain good quenching effect.
