Problems and Countermeasures of High Frequency Induction Hardening

Problems and Countermeasures of High Frequency Induction Hardening

 

 

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 arise during the production process.

 

Usually, during high-frequency induction quenching, the problems that occur are: ① quenching cracks; ② soft spots; ③ peeling, etc. Please see the following article for details.

 

① Quenching cracks

 

Never overheat during high-frequency induction hardening. Overheating is likely to occur around edges, keyways, and holes, which can easily cause quenching cracks. It is necessary to make these parts round, or to put copper sheets in the keyways and holes.

 

Because high-frequency induction quenching causes the surface layer to be heated and the surface layer to be quenched, the surface layer is where thermal stress and tissue stress work together. If the surface layer is only 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 change stress, and compressive stress will be generated.

 

Therefore, cracks are unlikely to occur during quenching; conversely, thermal cracking will occur when the material is not quenched. How to harden it through high-frequency induction heating is an important issue.

 

If parts after high-frequency induction quenching are subjected to high-frequency induction tempering, cracks similar to grinding cracks will occur on the surface. Therefore, it is safer to temper parts after high-frequency induction quenching in an electric furnace. If high-frequency induction tempering is necessary, low-frequency induction heating must be used.

 

②  Quenching soft spot

High-frequency induction quenching parts sometimes produce dark purple bands on the surface, and spiral bands like the sign in front of a barber shop appear during rotation and movement quenching. These colored areas are quenching soft spots with low hardness. If they are slightly ground, these colors will disappear, but the soft spots will still exist.

 

This is caused by the water spray holes being blocked by dust and the size and number of holes being inappropriate. This phenomenon can be overcome by changing the water nozzle to a slit type or using water-soluble quenching fluid instead of water spray.

 

③ Surface peeling

 

If the cross-section hardness gradient changes sharply, spalling will occur during the hardened layer process. Therefore, it is best to use preheating to deepen the hardened layer. It is very convenient to preheat the inductor coil first during preheating.

 

Also, if the quenching and tempering treatment is done before high-frequency induction quenching, the hardenability can be uniform and deep, which is effective in preventing peeling.

 

This article shares with you the three most common problems that occur during high-frequency induction quenching. They also often occur in production. This is a point worthy of our attention.