圧延用ロールの疲労強度に及ぼす鋳造欠陥の影響とその極値統計評価法

概要

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Steel making mill rolls usually contain shrinkage defects. The design of mill rolls is currently based on the empirically modified formulae. However, fatigue fractures of mill rolls from shrinkage defects have been experienced in service even based on the empirical design method. Many studies have shown that the effects of defects such as nonmetallic inclusions and graphite nodules on the fatigue strength can be effectively evaluated by paying attention to the geometrical parameter √<area>, the square root of area of defects onto the plane perpendicular to the principal stress. Different from that of nonmetallic inclusions, shrinkage defects generally have extremely complex three-dimensional shapes, and accordingly the projection of their shapes onto the plane perpendicular to the principal stress is very irregular. In this study, the tension compression fatigue tests are carried out with the specimen materials cut out from a real mill roll. Based on the propagation properties of cracks emanating from shrinkage defects, the effective geometrical parameter √<area>_<eff> for complex shrinkage defects is defined. The rule for estimating the maximum √<area>_<eff> of shrinkage defects to be contained in a real roll by the statistics of extremes is proposed.
一般社団法人日本機械学会の論文
2003-08-25