Evaluating the efficiency of hardening treatment of cylindrical parts made of structural steels

The investigated objects are solid and hollow notched cylindrical specimens made of structural steels surface-hardened with the use of two techniques: hydraulic shot blasting and air shot blasting. The subject of the investigation is the residual stresses in the surface layer of the specimens after hardening. The purpose of the work is to investigate the influence of residual stresses on high-cycle fatigue and to establish the possibility of using the developed calculation methods for the evaluation of surface hardening efficiency. Residual stress distribution in the surface layer and high-cycle fatigue resistance of cylindrical specimens were analyzed using calculation and experimental methods. The use of calculation methods for evaluating the efficiency of hardening treatment showed that the difference between the calculated and experimental values of the endurance limit increments due to hardening of cylindrical specimens with semicircular notches does not exceed 8% in the case of hydraulic shot blasting (steel 40X) and 11% in the case of air shot blasting (steel 20). The use of calculation methods for defining the endurance limit increment makes it possible to evaluate the efficiency of surface hardening with practical accuracy without long- run and expensive fatigue tests