Abstract
In order to measure the case depth of carburized steels easily and non-destructively, the authors investigated an electro-magnetic method. The carburized specimens which had the known case depth were excited by alternating current and read the induced voltage in secondary coil. From this preliminary tests the relation curve between the case depth and induced voltage are obtainable. From this curve we can find the case depth of other samples nondestructively. In order to get most sensitive results, the frequency of exciting current must be proper according to the case depth.
The experiment was carried out with the specimens with the dimension, 16 mm diameter and 115 mm in length, and carburized at 850° and 950° for 2, 4, 6 and 8 hours, respectively.
The experimental results obtained are as follows:
When the case depth was smaller than 1 mm, the sensitive results could be obtainable by using high frequency exciting current, for example, 500∼1000 cycles/sec, but in the case of the depth being greater than 1 mm, the better results could be obtained by using low frequency current, namely, 100∼300 cycles/sec. And it is important that the relation curve between the case depth and induced voltage is different with the carburized conditions, namely, carburized temperature, cooling velocity, etc., because the reading results are affected by these factors, so the carburized conditions of the preliminary test sample and the samples under examination must be equal.
