Relevant knowledge of heat treatment and smelting of steel castings
The steel castings can only be used after heat treatment. There will be other casting defects such as air holes, cracks, shrinkage cavities, shrinkage porosity, coarse grains and so on in the as cast steel castings, which can greatly reduce the strength, plasticity and toughness of the steel castings. In order to refine some grains or even structure and eliminate internal stress, steel castings must be normalized or annealed. The steel degree and mechanical properties after normalizing treatment also need to be annealed, and its cost is relatively low, so it is widely used. Normalizing treatment will cause greater internal stress than annealing, and is only suitable for steel castings with carbon content less than 0.35%.
At the same time, because the plasticity of low carbon steel castings is relatively good, they will not crack easily during the cooling process. In order to reduce the internal stress, it is necessary to conduct high temperature tempering after normalizing. If the carbon content is greater than 0.35%, the steel castings with complex structure or easy to crack can only be annealed. As long as you remember that the steel casting is not easy to quench, otherwise it is easy to form cracks.
The equipment used for steel casting smelting is generally open hearth furnace, electric arc furnace, induction furnace, etc. The open hearth furnace is characterized by large capacity and can use scrap as raw material The control of the composition of steel and the ability to smelt high-quality steel and low-alloy steel are all used to smelt large steel castings with high quality requirements. It is convenient to open and shut down three-phase electric arc furnace, which can ensure the composition and quality of molten steel. Therefore, the requirements for furnace charge will not be very strict, and it is a common equipment for producing steel castings.
If power frequency or medium frequency induction furnace is used, high alloy steel and steel with low carbon content can be smelted. In the process of using the induction furnace, the smelting speed is relatively fast, the alloy element burning loss is relatively small, and the energy consumption will be less, so the quality of the molten steel will be relatively high, which is suitable for small steel casting workshops.