The forged gear must also be subjected to post-forging heat treatment after forging. The purpose of the post-forging heat treatment is firstly to soften the structure, to reduce the difficulty of roughing, and more importantly to eliminate the network secondary carbide and reduce the burden of light heat treatment.
The final forging temperature of the forged gear is above 800 °C. The forged blank can be properly cooled in the air, but it is easy to crack if the cooling temperature is too low. Therefore, it is necessary to enter the furnace before cooling to 600 ° C and maintain it in the temperature range of 600-680 ° C to complete the pearlite transformation.
This type of roll has a particularly high carbon content, and it is easy to precipitate a network of secondary carbides along the grain boundary due to slow cooling after forging. However, the reticulated carbide seriously damages the roll strength and plastic toughness, and increases the risk of roll breakage, which is not allowed to be taken up to the finished roll product. Therefore, the reticulated carbide must be eliminated in the post-forging heat treatment process. Otherwise, it is necessary to consider this task in the final heat treatment, and it is heated to a very high temperature, which brings about the disadvantages of grain and tissue coarsening.
The spheroidizing annealing treatment is performed on the forged gear in order to distribute the secondary carbide in the form of uniform fine spherical particles to obtain a granular pearlite structure. The above-mentioned purpose can be achieved in the vicinity of long-term heat preservation, and the multi-stage cold spheroidizing process can obtain a satisfactory spheroidizing effect, which has been proved by the production practice of several hundred rolls.
The forged gear blank after forging heat treatment has a hardness of 35-40, and the machining performance is also between the forged steel roll and the cast iron roll. The rough machining uses the cemented carbide insert to obtain higher processing efficiency.