1. Quenching and tempering heat treatment: Products with strength grades of 8.8 and above are all products of quenching and tempering heat treatment. The characteristic of this heat treatment is that the hardness is relatively uniform inside and outside. When the same material is heat treated, the higher the hardness, the worse the toughness. Therefore, it is necessary to have a safe match. While meeting the hardness, the toughness is also guaranteed.
2. Carburizing heat treatment: Self-tapping screws basically need this treatment, which is characterized by a very hard surface and a soft core; because it needs to attack a hard iron plate.
One of the possible reasons for the risk of breakage of self-tapping screws is related to the heat treatment process. Too high or too low hardness may cause the head to be twisted and broken. Of course, there are other reasons for the risk of head breakage, such as hydrogen embrittlement, too deep cross grooves, too thin heads, and stress concentration caused by the lack of chamfering at the head-neck joint.
