CK 45 steel surface hardening using 1064 fiber laser

A fiber laser of 30 W power was employed in this work to treat the surface of CK45 steel, to study the effect of varying different parameters determined after a set of pilot studies. The parameters that have been manipulated were power ratio (P) of (30, 50, and 70)%, traverse speed (SS) of (1000,1500 and 2000) mm/sec, and the overlapping ratio (OL) of (0, 25, and 50)%. The responses of these parameters were analyzed using Box-Behnken design which is one of the surface response methodologies, by using the obtained results from different experimental characterizations; OM, Microhardness, and Roughness. The higher hardness value was 766.75 HV (obtained at P 50%, SS 1500 mm/sec, and OL 25%) which is more than double the base hardness value of 328.3 HV. While, the lowest value was 282.75 HV (obtained at P 70%, SS 2000 mm/sec, and OL 25%). Roughness was examined in two directions, inline and perpendicular on laser lines. The highest roughness values were obtained with increasing the hardness. The roughness increased from 0.844 µm to 3.43 µm in the perpendicular direction over laser path, and from 1.402 µm to 2.341 µm in case of the inline laser direction. With using different parameters, the roughness value decreased to 0.749 µm in the case of the inline laser direction which is about 46.57% from the roughness of the untreated area 1.402 µm. On the other hand, the coloring test shows wide colors ranging between bright to dark brown was obtained after fiber laser treatment of the material, due to the formation of different elements oxides on the surface layer. Finally, the FESEM image showed that a very thin layer was affected by this process, i.e., very small hardened depth.