Evaluation of mechanical properties and metallurgical changes, which occur in AISI 431 martensitic stainless steel as a result of the welding processes consisting of electron beam welding (fusion welding) and friction welding (solid state welding) is carried out. In addition, the influence of post weld heat treatments on microstructure and mechanical properties has also been investigated. Weld center in EB welding exhibited a cast dendritic structure with ferrite network in a matrix of un tempered martensite. In friction welding, the weld center exhibited thermo mechanical effected structure consists of fine intragranular acicular martensite in equiaxed prior austenite grains. In both the welding processes, post weld tempering treatment resulted in coarsening of the martensite which increases with increase in tempering temperature. In the as weld condition, both EB and Friction welds exhibited high strength and hardness and poor impact toughness. Increase in impact toughness and decrease in strength and hardness is observed with an increase in tempering temperature. However, high strength and hardness observed in friction welds as compared to EB welds, which may be due to fine grain size of the welds due to thermo mechanical work the weld undergoes during welding. Low impact toughness is observed in friction welds as compared to EB welds, due to presence of fine grained martensite.