2008 巻 (2008) 53 号 p. 45-56
The method for measuring a decarburized zone depth is conventionally listed as follows; (1) Micro structure observation by optical microscope, (2) Measurement of hardness distribution, (3) Measurement of carbon concentration by EPMA analysis. The second method is considered to be convenient for easy and practical handling. In some cases, this hardness measuring method is specified in the inspection agreement between a supplier and a customer. Because of the restriction of applicable loads and measuring pitch in Vickers hardness tests, this method is deemed to be difficult for the measurement of small decarburized depth which is often seen in oil quenched and tempered wires for springs, though it can be used for measurement of large decarburized depth in general carbon steels. Round robin tests were carried out in the committee for the oil tempered and quenched wires, and the following conclusions were obtained. It was clarified that the present measurement accuracy of Vickers hardness was suitable for judging large differences such as 100HV or more, but not suitable for judging small difference such as 50HV or less. In order to insure accurate decarburized depth measurements in the latter case, an error inspection by using the reference blocks should be carried out, and statistical processing should be used on a larger number of measurement.