How can we prevent defects caused by induction hardening of workpieces using high-frequency induction heating machines?

In order to improve the service life and wear resistance of the workpiece, we usually use a high-frequency induction heating machine to perform induction heat treatment such as quenching and tempering on the workpiece. However, during the heat treatment process, affected by factors such as the environment and manual operations, some defect. Today, we will focus on what defects will occur during the heat treatment process? How should we solve these problems?

1. The edges of the hardened layer are cracked and dropped.

If the end of a simple-shaped cylindrical part is not chamfered and has sharp edges, the edges will be overheated during incorrect scanning and quenching, especially when the sensor will separate from the part after quenching. A large amount of internal stress is formed on the edges, causing cracks and sometimes falling off in a ring shape. This is the phenomenon of cracking and falling circles at the edges of the hardened layer. In addition to not overheating the edges during quenching, the solution to the problem is that the ends must be chamfered in terms of product design.

2. Peeling off of hardened layer

The boundary spalling from the surface of the hardened layer to the entire depth of the original tissue, or spalling at a smaller depth, is called hardened layer spalling. The reason for this defect is that there is large internal stress in the parts. The solution is that after the parts are quenched with a high-frequency induction heating machine, they should be tempered in time, or self-tempering should be used; in terms of product design, the appropriate depth of the hardened layer should be selected.

3. Grinding cracks appear in induction hardened parts

When using high-frequency induction heating power for quenching heat treatment, many induction quenched parts did not find cracks in magnetic particle inspection after quenching, but cracks appeared after grinding, and the cracks were perpendicular to the movement direction of the grinding wheel. Generally, it is judged as grinding cracks. Check whether the grinding feed amount is too large, grinding wheel particle size, hardness, blunt grinding and failure to grind in time and other factors. Generally, it can be solved after taking measures according to the machining and grinding specifications.

Looking at the factors from the aspect of induction quenching, wear and tear is most likely to occur when there is high tensile stress on the surface of the hardened area; failure to temper in time, or inappropriate tempering temperature and time are often one of the factors. There are tensile stress areas on both sides of the hardened area of the crankshaft journal. After induction quenching, quenching cracks along the circumferential direction have appeared (crankshaft journal without fillet quenching).

4. Collapse of hardened layer

Network cracks appear on the surface of the part, and then pieces of metal flakes collapse along the cracks, like surface peeling. This phenomenon is called hardened layer collapse. Collapse of the hardened layer mostly occurs after grinding, especially during large feeds. This is often a grinding defect, but can also occur when quenching is overheated.