Scratch resistances of compacted graphite iron with plasma nitriding, laser hardening, and duplex surface treatments

Compacted graphite iron is an interesting material class for automotive applications. CGI-450 grade cast iron was subjected to various surface treatments: plasma nitriding (PN), laser hardening (LH), and PN followed by LH (PN+LH). The resulting tribological behaviors were evaluated by means of linear scratch testing under progressive loading (40–70 and 70–95 N). The PN+LH treatment yielded the lowest friction coefficient and shallowest scratching. In this case, the outermost layer was composed of oxide phases (Fe2O3 and Fe3O4), underlain by a compound layer (oxides + nitrides + martensite) and a high-resistance martensitic layer with accompanying nitrides and carbides. These underlying layers provided high load capacity for the external layers, allowing them to function as solid lubricants. •Different surface treatments were applied on the CGI-450 compacted graphite iron.•Scratch tests revealed best performance of duplex treatment (PN + LH).•Hematite phase could act as a solid lubricant.•Critical load for nitrided layer was higher, above 80 N.