Laser surface pretreatment of 100Cr6 bearing steel - hardening effects and white etching zones

In order to achieve a surface pretreatment of the bearing steel 100Cr6 (1 - 1.5 wt. - % Cr) a laser-based process was used. The obtained modification may result in an optimization of the adhesive properties of the surface with respect to an anticorrosion polymer coating on the basis of PEEK (poly-ether-ether-ketone), which is applied on the steel surface by a laser melting technique. This work deals with the influence of the laser-based pretreatment regarding the surface microstructure and the micro-hardness of the steel, which has been examined by scanning electron microscopy (SEM), light microscopy and automated micro-hardness testing. The most suitable parameter set for the laser-based pretreatment leads to the formation of very hard white etching zones (WEZ) with a thickness of 23 mm, whereas this pretreatment also induces topographical changes. The occurrence of the white etching zones is attributed to near-surface re-austenitization and rapid quenching. Moreover, dark etching zones (DEZ) with a thickness of 32 mm are found at the laser path edges as well as underneath the white etching zones (WEZ). In these areas, the hardness is decreased due to the formation of oxides as a consequence of re-tempering.