CHROMIUM CARBIDE LASER-BEAM SURFACE-ALLOYING TREATMENT ON STAINLESS-STEEL

In order to improve the resistance to wear, oxidation and corrosion of a stainless steel die, chromium carbide surface-alloying treatment was carried out on a 12 % Cr stainless steel using a CO2 laser. Cr3C2 powder slurry was coated on the stainless steel and then a 3 kW CO2 laser beam was used to irradiate the specimen. The thickness of surface-alloyed layer was about 0.3 mm and the chromium concentration was about 40 % throughout the alloyed-region. Large amounts of Cr3C2 and Cr7C3 were also distributed in this alloyed layer. From the results of the isothermal oxidation test at 960-degrees-C for 100 h, it was found that the surface-alloying treatment improved the oxidation resistance by about 100 times due to the distribution of chromium carbides and the increase in the chromium concentration. The results of the cyclic oxidation test revealed that the oxidation layer was very stable on the chromium carbide surface-alloyed region, while it scaled off very easily from the substrate region due to porous oxidation products. The microhardness was about 1100 H(V) due to the dispersion and precipitation of chromium carbides in addition to the martensitic structure in the surface-alloyed region. The microhardness did not decrease much, despite heating at 960-degrees-C for 100 h. The chromium carbide surface-alloying treatment improved the wear-resistance greatly, and the results of the wear-resistance test were very consistent with those of the microhardness test.