Possible factors for surface hardness deviation
The problem is that during the heating and quenching cycle, the heat treatment personnel notice that the surface hardness of the quench shaft changes significantly after the first induction quenching, whether the parts are rotated or not.
Solution: There are at least two possible causes of this hardness change:
(1) non-uniformity of austenite before quenching;
(2) Uneven quenching.
A: The austenite uniformity around the parts can be improved by increasing the rotation speed or replacing the traditional single-quench inductor with the snake inductor.
B: In order to improve the uniformity of quenching, it is necessary to redesign the spray quenching device and try to cover the surface of the workpiece as far as possible. At the same time, change the speed at quenching (for example, increase by 25% and then decrease by 25%) and compare the results.
It is suitable for the above two situations simultaneously: too slow or too fast rotation speed of workpiece during quenching will lead to non-uniform circumferential quenching, which may cause corresponding surface hardness deviation around the workpiece heated uniformly. Excessive swing of parts due to bearing wear can also adversely affect heating and quenching and produce surface hardness deviations on the circumference.
Example: Austenite heterogeneity on the workpiece surface