METHOD FOR EVALUATING LARGE-SIZED INCLUSIONS IN A STEEL FOR USE IN BEARING

摘要

A first object is to provide a method for evaluating large-sized inclusions in a bearing steel. The method enables quantitative evaluation of large-sized inclusions even if the steel has a high degree of cleanliness. Further, a second object is to provide an appropriate bearing steel evaluated by the method for evaluating large-sized inclusions. Further, a third object is to provide a rolling bearing capable of eliminating short life products and cracked products and providing longer lifetime for entire bearings. In order to achieve the first object, a round bar formed of a bearing steel to be evaluated and an ultrasonic probe are placed in an ultrasonic transmission medium, and the size and number of large-sized inclusions that are present in the flaw detection volume are measured to estimate the existence probability of large-sized inclusions in the bearing steel to be evaluated. The second object is achieved by specifying large-sized inclusions that are present in the bearing steel in accordance with the method for evaluating large-sized inclusions. Further, to achieve the third object, a rolling bearing is manufactured from a seamless steel tube, as material, having a diameter of 180 mm or less and a wall thickness of 25 mm or less, and ensured that it does not include a defect having a length of 1 mm of more at its material stage.