Influence of laser-hardening on microstructure and hardness of plasma-nitrided compacted graphite iron

[Display omitted] •Surface treatments of plasma nitriding followed by fiber laser hardening performed on grade 450 compacted graphite iron.•Effect of plasma nitriding duration and laser hardening power investigated in the absence of surface remelting.•Duplex treatment led to deeper hardening than regular nitriding and higher surface hardness than solely laser hardening.•Partial solubilization of the nitrided layer by laser processing.•Reduction in the hardness gradient between the surface and substrate. Duplex surface treatments involving plasma nitriding (PN) followed by laser hardening (LH) were performed in this work on grade 450 compacted graphite iron (CGI) to investigate the effects of PN duration (1 and 3 h) and LH power (400, 449, and 514 W) on microstructure evolution, nitrogen profile, and hardening depth of CGI. X-ray diffraction (XRD) phase analysis indicated a reduction in and partial decomposition of ε and γ’ nitrides corresponding to an increase in laser power. The existence of a new nitrogen-rich austenitic phase—FeN0.076—was observed along with the identification of certain iron oxides. The proposed duplex treatment of CGI was found to facilitate the establishment of duplex layers with higher surface hardness (826–951 HK 0.05) and greater hardening depths (300–750 μm). Additionally, a reduction in the hardness gradient was observed between the surface and substrate. This affords a major advantage in applications involving operations on mechanical components.