The influence of the shielding gas on the properties of a laser-melted surface of austenitic stainless steel

Recent investigations on the laser surface treatment of nickel-based alloys and austenitic stainless steels had shown that it is possible to increase additionally their pitting and erosion-corrosion resistance and also wear resistance as a result of laser surface alloying and laser surface melting. Austenitic stainless steel is one of the most widely used ferrous materials for structural applications in mild to very severe oxidizing environments due to its excellent corrosion resistance, mechanical strength and ductility. Therefore, an experimental investigation on ASTM 304 stainless steel was carried out to determine the influence of surface melting parameters, using a novel diode laser with rectangular and uniform energy distribution across the beam spot, on the shape, penetration depth, structure and microhardness of surface layers. The sample surface was treated using the continuous-wave high-power diode laser with a maximum output power of 2.5 kW. The surface of 304 stainless steel was melted in argon, nitrogen and air atmospheres using different laser output powers at a scanning speed of 500 mm/min. Surface layers after laser melting presented higher microhardness compared with the untreated material. In laser surface melting, a rapidly resolidified surface layer with refined grains of 300 μm thickness was obtained, and the penetration depth of surface layers was in the range 0.3-5.0 mm.