July 15, 2023
Problems and Countermeasures of High-frequency Induction Quenching
High-frequency Induction quenching, as a mature heat treatment process, plays an important role in the industrial field. While it brings us convenience, some problems often occur in the manufacturing process.
Usually, the problems occurring in induction quenching are ① quenching cracks; ② soft spots; ③ spalling, etc.
For details, please refer to the article described below.
Never overheat when quenching at high frequency. Overheating is likely to occur around corners, keyways, and holes, and thus quench cracks are easily caused. To avoid quenching cracks, you can make these parts round, or put copper sheets in keyways and holes, etc.
Because high-frequency induction quenching is when the surface layer is heated and the surface layer is quenched, the surface layer is the place where thermal stress and tissue stress work together. If only the surface layer is heated without hardening, tensile stress will be generated on the surface layer; if it is hardened, the thermal stress will be greater than the phase transformation stress, and compressive stress will be generated.
Therefore, cracks rarely occur when hardened; on the contrary, thermal cracks occur when hardened. How to harden it through high-frequency induction heating is an important issue.
If the parts after high-frequency induction quenching are subjected to high-frequency induction tempering, the same cracks as grinding cracks will occur on the surface. Therefore, it is safer to temper the parts after high-frequency induction quenching in the electric furnace. If high-frequency induction tempering is necessary, low-frequency heating must be used.
High-frequency induction quenched parts sometimes produce dark purple bands on the surface, which appear like a barber's front sign when they are rotated and quenched. These colored places are quenched soft spots with low hardness. If these colors are removed after a little grinding, the soft spots still exist.
This is caused by the water jet hole being blocked by dust and the inappropriate size and number of holes. This phenomenon can be overcome if the water jet is changed to a slit type, or if water-soluble quenching liquid is used instead of the water jet.
If the hardness gradient of the section changes sharply, the hardening layer process will cause spalling. Therefore, it is preferable to deepen the hardened layer by preheating. It is convenient to use an inductive coil to preheat first during preheating.
In addition, if the quenching and tempering treatment is done before high-frequency quenching, the hardenability can be uniform and the hardening can be deep, which is effective in preventing spalling.
