Thermal and metallurgical characteristics of surface modification of AISI 8620 steel produced by TIG arcing process

The influence of TIG arcing process for surface modification of AISI 8620 steel at varying arcing current and heat input was studied in this work. Weld isotherm, thermal cycle and cooling rate of the modified region was estimated by analytical modeling and experimentally validated. Thermal characteristics of the modified zone were correlated with their respective microstructure and hardness. Cooling rate as a function of area of fusion influences the microstructure and hardness of the modified region. The multi-pass TIGA process for larger area of modification on substrate was applied using optimum arcing parameters for the best possible result found in a single pass. The effect of multiple thermal cycles on phase transformation and tempering of modified matrix were studied by microstructure analysis and mapping of its influence on the hardness distribution in the matrix. Residual stresses in the modified matrix created by single pass TIG arcing were measured by standard central drill hole technique. The surface modification of AISI 8620 steel by TIGA process shows the appreciable martensitic phase transformation in the matrix that enhances the hardness of the modified zone as well as introduces compressive residual stresses in it.