Welding creates residual stresses and distortion through the elasto-plastic response of the object to the transient, localized thermal expansion and contraction. The volume of plastically deformed material can be quite large, roughly the size of the region experiencing temperature changes greater than 100°C. Fabricators must allow for distortion during design, or resort to expensive post-weld treatments. Various strategies minimize distortion, but a basic understanding of the deformation is required. Distortion depends on the geometry and welding conditions as well as the material properties of the object being welded. A qualitative understanding of the role played by the thermal and mechanical properties would be instructive. Welding. stainless steels causes approximately three times the distortion experienced in low carbon steels for the same arc current, voltage, speed, etc. Differences in thermal properties (1)t such as the thermal conductivity, k, and volumetric specific heat, C, , as well as mechanical properties such as the yield strength, oy, coefficient of thermal expansion, a, and Young’s modulus, E, are responsible. At temperatures below SOOT, k for AISI 304 stainless steel is lower than that of low carbon steel. Thus, for a given heat flux, thermal gradients will be higher in the stainless steel. C, is also lower for AISI 304 stainless steel, leading to higher temperatures for a given energy input. The isotherm pattern seen in stainless steel welds might be expected to be narrower, enclosing higher temperatures and showing steeper thermal gradients and lower cooling rates. The effect of this on welding distortion is not clear. The difference in the yield strength of the two materials is of little importance. Lower yield strengths cause larger regions of plastic deformation. This is offset by the lower level of residual stress present in the larger