Surface treatment with laser radiation takes advantage of self-quenching effect that enables rapid cooling of the treated zone into bulk material without the need of any external quenching media [1]. The major benefits of laser hardening consist in narrow heat-affected zone due to low input energy, smooth surface after the treatment and thus no need for any post-process surface machining. In addition, microstructural features of the laser treated surfaces possess the increased strength, wear and corrosion resistance i.e. all the properties required for application of hot work tool steels used in high speed machining processes [2].

The present study deals with the effects of laser surface treatment on microstructure evolution, tribological properties and wear resistance of hot work tool steel in quenched and tempered conditions. The most upper laser-affected zone is characterized by re-melted microstructure consisting of dendrite cells with fresh non-tempered martensite, retained austenite, and inter-dendritic carbidic network. The subsolidus microstructure just beneath the re-melted zone represents the most laser surface hardened zone consisting of fresh non-tempered martensite with fine and coarse carbides as a result of overheating the original QT substrate microstructure. The highest microhardness values in the range from 775 to 857 HV were measured for the LSH microstructure and the most softened microstructure exhibited the minimum hardness of 530 HV. Figure 1 depicts the comparison of specific wear rate related to the individual materials states (AR, QT, LSH) showing the minimal value for LSH condition. This behavior of the laser-hardened surface can likely be related to the refinement of martensitic microstructure which also correlates well with the decrease of the friction coefficient at different tribological loading. The lowering of the specific tribological wear rate in the LSH condition of studied steel compared to the QT material state resulted in the increase of surface wear resistance by 35 %.

This work has been supported by the Slovak Research & Development Agency (APVV-Sk-Ua-21-0023)

References

[1] S.M. Shariff, T.K. Pal, G. Padmanabham, S.V. Joshi Surface &Coatings Technology, 2013, 228, 14-26.

[2] G. Telasang, J. D. Majumdar, G. Padmanabham, I. Manna Surface & Coatings Technology, 2015, 261, 69-78.