What issues should be paid attention to during the heat treatment of construction machinery castings?

During the heat treatment of construction machinery castings, many aspects need to be paid attention to to ensure the quality and performance of the final product. Temperature control is crucial. Different materials and casting types require different heating and cooling temperatures. Any temperature deviation may lead to performance degradation or defects. The heating rate should be determined according to the material, size and shape of the casting. Too fast heating rate may cause excessive internal stress, cracks or deformation, while too slow heating rate will affect production efficiency. After reaching the required temperature, a certain holding time is required to ensure that the entire cross-section of the casting is evenly heated to achieve the expected organizational transformation and performance. Too short holding time may lead to incomplete organizational transformation, while too long holding time may cause problems such as grain growth.

The cooling rate is also important. Different heat treatment processes (such as quenching, annealing, and tempering) have different requirements for cooling rate. Too fast cooling rate may cause quenching cracks, while too slow cooling rate may not achieve the expected hardness and strength. Selecting the right heat treatment medium (such as water, oil, air, polymer solution, etc.) is crucial to controlling the cooling rate and avoiding casting defects. Different media will affect the cooling rate, stress distribution and final material properties.

The thermal stress and structural stress generated during the heat treatment process must be controlled, and deformation and cracking of the castings can be prevented by slow heating and cooling, insulation treatment and other measures. At high temperatures, the surface of the casting is easily oxidized or decarburized, affecting its performance and appearance. The surface can be protected by using a protective atmosphere (such as nitrogen, argon) or coating a protective layer.