Microstructural origin of the outstanding durability of the high nitrogen bearing steel X30CrMoN15-1

The high nitrogen bearing steel X30CrMoN15-1, marketed under commercial names such as Cronidur30, VC444, NitroMax and N360, is well-known for its outstanding rolling contact fatigue and corrosion properties. More importantly, there are no reports about failure by white etching cracks for this alloy, although this premature failure mode is frequently observed in conventional high carbon bearing steels. To understand the origin of this superior performance, we analyze in the current paper its microstructure prior to rolling contact fatigue by means of scanning electron microscopy, atom probe tomography and nano-indentation, and relate this to its thermal processing history. The origin of the exceptional white etching crack resistance of this alloy is rationalized in terms of the mechanical and thermodynamic stability of the precipitates, the different grain boundary segregation behavior between nitrogen and carbon as indicated by the atom probe results, and the cleanliness of the steel.