How to measure the depth of hardened layer of inductively hardened parts?

According to the provisions of GB/ t5617-2005, the depth of the hardened layer of High frequency induction heating machine quenching parts is determined by the method of measuring the hardness of the part section. That is, the distance from the part surface to 0.8 times the hardness lower limit (HVMS) with vickers hardness tester (9.8n load) is used as the effective hardness layer depth (Ds), which can be expressed as the following formula:

HVHL HVMS = 0.8

Where HVMS—- the lower limit of hardness required by the part (minimum hardness value);

HVHL– ultimate hardness value.

There is a principle difference between measuring the effective hardness layer with the hardness method and measuring the depth of the hardness layer with the metallographic method we used in the past.The former is according to the technical requirements of the hardness of the lower limit, the latter is more than 50% (area fraction) of the martensitic tissue as the depth of the hardened layer, it is basically fixed.