The Study on Laser Processing of the Surface Layer of Grey Cast Iron Machine Parts

The following monography refers to laser processing of the surface layer of grey cast iron. It is focused on the process involving by implementing selected element(s) or substances into the surface layer. The presented monography is divided into two parts. The first one raises the issue of exploratory research about the influence of example substances implemented during laser treatment on the effects in the surface layer of grey cast iron and the second present the example of the possibility of the surface layer improvement in the aspect of increasing wear resistance by laser alloying. The aim of first part was to determine the differences in the surface layer effects after the laser treatment with the same heating conditions but with four different, selected substances (silicon, cobalt, silicon nitride and titanium). Here were showed the effects in the surface layer of nodular iron after laser treatment with the same heating conditions between four chosen alloying substances (silicon, cobalt, silicon nitride and titanium). The treatment was performed with a molecular laser. As the microstructure observation revealed, the greatest amount of the implemented elements was diluted during the treatment in a solid solution. In all cases (except alloying with cobalt), in the alloying zone, fine and homogeneous microstructure was found. Cobalt in the alloying zone counteracted the formation of the martensitic microstructure so effectively that austenite turned into exclusively fine perlite (or bainite at most). The size of the obtained alloyed zone was different despite the same laser heat treatment parameters. A 30% smaller depth of the zone after laser alloying with silicon nitride than the alloying with cobalt or silicon was observed. The highest strengthening of the alloyed zone could be expected when silicon (hardness was approx. 980HV0.1 and the modulus of elasticity was 208GPa) and titanium (hardness was approx. 880HV0.1 and the modulus of elasticity was 194GPa) were used. The lowest hardness (700HV0.1) was observed for the zone alloyed with cobalt due to pearlite (or bainite) existence. The aim of second part was to evaluate the influence of the laser alloying on the abrasive wear resistance of the example machine part. Coulter flap was chosen as an object of this investigation. To produce the alloyed layer on the most exposed to wear area of the flap a diode laser was used as a source of heat. Investigation showed that laser alloying with chromium and titanium can increase the wear resistance of components working in abrasive conditions. Smaller mass loss after the wear tests in abrasive conditions of soil could be expected. The laser alloyed layer (with a depth of approx. 400 mm) was characterized by martensite micro-structure (mainly), homogenous morphology and fine grains. A 5-fold increase of hardness (approximately 1050HV) in comparison to the hardness of core material and doubled in comparison to the original ledeburitic surface layer of coulter flap was noted. Some changes after laser alloying in the surface stereometry were observed (a decrease in roughness parameters is possible). Roughness parameter values after the wear test decreased in the case of original and alloyed coulter flaps.