| 摘要 |
<p>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. Providing an appropriate bearing steel evaluated by the method for evaluating large-sized inclusions is a second object. Further, eliminating short lifetime- and broken-products and providing a rolling bearing of a longer lifetime of the entire bearing is a third object. In order to achieve the first object, a round bar formed of a bearing steel to be evaluated and an ultrasonic are placed in an ultrasonic transmission medium, and the sizes and number of large-sized inclusions that are present in the flaw detection volume are measured to estimate the presence 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 produced. The bearing is made of a seamless steel tube, as material, having a diameter of 180 mm or less and a wall thickness of 25 mm or less, the steel tube being guaranteed that it does not include a flaw having a length of 1 mm or more at its material stage.</p> |
