水素チャージした試験片を用いた引張試験による新しい非金属介在物検査法

摘要

機械や構造物における破壊事故の約80％が疲労破壊によるものだと言われており，疲労破壊による事故を未然に防ぐことは極めて重要な課題である。ピッカース硬さHV＝400以上の高強度鋼で製造された部品・部材では，部品・部材中に含まれる最大寸法の非金属介在物が疲労破壊起点となることが知られているり。%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 Al_2O_3-(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.