Increasing fatigue resistance of case hardened component

摘要

A method of improving the fatigue resistance of a case hardened component, which is subjected to rolling or sliding contact, abrasion, bending and/or pitting, involves: (a) determining the load acting on the component; (b) determining the corresponding fatigue strength values and the applied fatigue stress values at the component surface and at a number of pre-selected points along the case thickness 't'; and (c) imparting a residual compressive stress profile, which extends from the component surface to the case thickness 't' and which comprises an upper, a lower and several intermediate residual compressive stress profiles, such that the residual compressive stresses at the surface and the pre-selected points respectively have sufficient size to achieve a resulting overall stress of /- 25 % less than the corresponding fatigue strength. Preferably, step (c) involves imparting a carbon gradient by either (i) variation of the carbon potential of the atmosphere during carburising; o r (ii) thermal spraying of a functional gradient material (FGM) coating of thickness 't' and with a carbon gradient profile extending from the new surface to thickness 't', the FGM being a ceramic, metal and/or cermet. Also claimed are a case hardened component and a case hardened gear wheel having the above characteristics.