Effect of Cr–N precipitations on thermal fatigue behaviour of GX-8 steel nitrided layer

Abstract

Two types of nitrided layers with different nitride precipitates were prepared by salt bath nitriding on the surface of GX-8 steel. The microstructure of the nitrided layers was investigated by SEM, XRD, grazing-incidence XRD and TEM. A cyclic thermal fatigue test system was used to evaluate the influence of nitrides on the thermal fatigue properties of the two nitrided layers. Under the operation of alternating thermal cycles from ambient temperature to 600 °C on the surface, the nitrided surface with a compound layer composed of ε-Fe2-3N phase and strip-shaped CrN had more cracks and spalling than that of the nitrided layer with nanoscale nitrides. Further analysis revealed that the tessellated stress caused by different thermal expansion coefficients of CrN and α-Fe in the interlayer was responsible for the interlaminar deformation, cracking and spalling of the surface.

Keywords

• Salt bath nitriding
• GX-8 steel
• Thermal fatigue
• Cr–N precipitations
• Tessellated stress