Forecasting an increment in the parts’ endurance limit due to surface hardening

Rolling with various forces influence on the endurance limit of specimens made of steel 20 of 50 mm diameter with cuts of various radiuses and pressurized bush has been examined. The estimation of the surface hardening influence on the specimens endurance limit has been carried out using two criterions, namely: residual stresses on the dangerous section surface and the average integral residual stresses through the dangerous section thickness, equal the fatigue non-propagating crack critical depth. On base of carried out experiments it’s been established that the employment of the average integral residual stresses criterion is more rightful for the endurance limit prediction of surface hardened cylindrical specimens made of steel 20 with diameter 50 mm with cuts and pressurized bush taking into account the concentration degree. The residual stresses on the concentrator surface is not acceptable as a criterion for the endurance limit prediction of surface hardened specimens made of steel 20 with cuts and pressurized bush because the corresponding coefficient of the criterion influence on the endurance limit has a essential dispersion. Besides, the dependence of the fatigue non-propagating crack critical depth on the specimen (part) dangerous cross-section sizes has been confirmed.