Abstract
A new inclusion rating method by the tensile test with the hydrogen-precharged specimens is proposed. The method is essentially based on the statistic extremes method of inclusion rating in which the maximum inclusion is found by the simple tensile test with the hydrogen-precharged specimens. In order to verify the validity of the new inclusion rating method, that is the tensile test method with the hydrogen-precharged specimens, tensile tests and fatigue tests were carried out for bearing steel (JIS-SUJ2, Vickers hardness HV=682, 611, 559, 447, 346) and the inclusions appeared on the fracture surface were investigated. It was confirmed that the distribution of extreme values of Al2O3·(CaO)X inclusions obtained by the tensile test method with the hydrogen-precharged specimens coincided with that obtained by the fatigue test method. On the other hand, the distribution of extreme values of inclusions obtained by the optical microscope method was different from those obtained by the tensile test method with the hydrogen-precharged specimens or fatigue method. The inclusion rating method by the fatigue test can be replaced by the tensile test method with hydrogen-precharged specimens. The proposed method is more convenient and reliable than other existing inclusion rating methods.
