Scratch test analysis of coated and uncoated nitrided steel

The mechanical properties of duplex-coated steel, nitrided steel and untreated steel were characterised by means of scratch testing. It was obtained that upon nitriding, the yield stress of steel increases from 2.7 to 7 GPa and the ductility decreases. For the duplex-coated steel, which consists of a 1 μm Cr2N layer on nitrided steel, the adhesion of the Cr2N layer was very good, despite the presence of some iron nitride at the coating–substrate interface. The influence of the Cr2N layer on the mechanical properties of the nitrided steel is discussed. The Cr2N coating slightly affects the hardness of the specimen and the friction of the sliding indenter. However, the crack patterns in the scratch tracks are influenced considerably.