What heat treatment defects may occur during induction hardening? How to prevent it?

The heat treatment defects of steel after induction hardening are similar to those of ordinary heat treatment. Common defects and preventive measures are as follows.
(1) Unqualified hardness
The reason is that the carbon content of steel is low; Improper cooling operation results in a pre cooling time before rapid cooling of the surface layer, leading to the formation of pearlite structure; Insufficient cooling quantity or low water pressure, resulting in low cooling speed; The heating temperature (austenitization temperature) is low, and the carbon concentration in austenite is uneven. For such defects, metallographic examination, chemical composition analysis, and proper heat treatment engineering control can be used.
(2) Quenching crack
① Overheating. Due to the fact that the sharp corners, key slots, circular holes, and edges of the designed parts are prone to local overheating and cracking during induction heating. Design improvements or protective measures can be taken to avoid the presence of hazardous sections.
② Repeated quenching. The parts with unqualified hardness after quenching were reheated and quenched without annealing or normalizing.
③ The cooling rate is too fast. For high carbon steel and alloy steel parts, a faster cooling rate is adopted. Improvements can be made by replacing the cooling medium, adjusting the water pressure and cooling time of the sprinkler, and changing the cooling method.
④ The high carbon content or presence of large inclusions in steel can easily cause surface cracking.
⑤ Grinding and grinding cracks. It is caused by excessive grinding during heat treatment or grinding, and excessive rapid cooling during cooling.
(3) Shape distortion
Uneven original organization (normalizing or isothermal annealing), uneven heating, and uneven cooling are generally caused by measures such as eliminating internal stress, increasing the rotation speed of the part, continuous quenching and heating, and making the relative distance between the part and the inductor equal.