Do you know what defects will occur when the connecting rod bolts are heat treated with a medium frequency induction heating machine?

The connecting rod bolt is a key component in the engine's working process. It cooperates with the crankshaft to complete the movement of the piston, allowing the engine to obtain power. During the working process, the bolts are subject to uniform tensile stress. Therefore, the bolts are required to have sufficient tensile strength, yield strength and good toughness. In order to meet the working requirements of bolts, we usually use medium frequency induction heating machines to heat treat them, and the effect is very good. However, in the process of operation, due to the influence of the surrounding environment and its own factors, the bolts may have some defects. Today, the editor will analyze these defects for you.

1. Surface decarburization is caused by the fact that during the heating process using a medium frequency induction heating machine, the heating medium is oxidizing, which causes oxidative decarburization on the surface of the bolt in the oxidizing atmosphere, with less granular carbides than in the center. The existence of decarburization will cause the strength of the plastic deformation zone at the root of the thread to decrease, and its plasticity is lower than the core, reducing the fatigue strength and cold fatigue resistance, inducing cracks under stress and becoming a crack source. Therefore, during the heat treatment process, the atmosphere in the furnace must be strictly controlled to be reducing or neutral to prevent surface decarburization.

2. Excessive free ferrite or undissolved carbides. The heating temperature is low or the holding time is short. The spherical pearlite is not transformed into austenite structure. The carbides are not fully dissolved. Such defects appear during quenching and cooling.

3. Overheating or overburning is mostly related to the high heating temperature or long time during hot stamping. Therefore, the heating temperature and holding time of this process should be strictly controlled.

Defects produced during the heat treatment of bolts can at least reduce the service life of the bolts, or at worst cause the workpiece to be scrapped. Therefore, they should be avoided during the heat treatment of bolts.