When the medium frequency induction hardening machine quenches the workpiece, what stresses will be generated and how are they distributed?

Anyone who often does heat treatment knows that after the workpiece is induction quenched with a medium frequency induction hardening machine, some stress will be generated. These stresses have a great impact on the heat treatment quality of the workpiece. Therefore, understanding what stresses are on the parts during quenching and how they are distributed is crucial to our heat treatment work. Today, the editor will tell you the answer.

The stress produced by surface quenching parts during the quenching process with a medium frequency induction hardening machine is caused by thermal stress and tissue stress. The residual stress caused by thermal stress is generally not large (the residual compressive stress on the surface is about 98- 147MPa, the internal residual tensile stress is also roughly similar). Many studies have proven that after induction quenching of steel parts, there is residual compressive stress in the hardened layer. At the surface, its value can reach 686-784MPa. Generally, the compressive stress becomes smaller the further away from the surface. When the depth exceeds the hardened layer, the residual stress transforms into tensile stress.

The residual compressive stress after surface quenching improves the fatigue strength of the specimen or part. On the contrary, residual tensile stress is harmful. When the tensile stress reaches a certain value, it can cause cracks in the parts.

Regarding the hardness and residual stress on the boundary of the quenched part, through multiple tests, we found that the surface residual compressive stress within the quenching zone is equal to 539-588MPa, and the compressive stress near the boundary of the quenched layer is reduced and converted into tensile stress. , the maximum value of tensile stress is located 10mm away from the edge of the hardening zone, and its maximum value reaches 147MPa. And we also get the following relationship. As the total depth of the quenched layer increases, that is, the heating depth increases and the heating speed decreases, the maximum compressive stress in the center of the quenching zone increases, and the tensile stress near the quenching zone decreases.