Controlling deformation and residual stresses in a TIG joint for Invar steel molds

Abstract

Invar steel is used to produce molds for composite materials for its thermal expansion coefficient similarity to those materials. These molds show wear resistance, provide good dimensional accuracy of produced parts, and they are produced with tungsten inert gas (TIG) welding. In this study, welding deformation and residual stress optimization of an Invar steel TIG welded butt joint were studied experimentally and numerically. Results show that deformation can be controlled effectively with the appropriate welding sequence from both sides to the middle of the joint when compared to sequential welding. When double welding guns are used to weld concurrently from both ends along the same welding path in segmental welding, deformation developed is minimum, while deformation increases significantly at the weld segmental area. When segmental bidirectional welding is used, deformation is slightly increased, but the highest deformation area can be avoided compared to segmental unidirectional welding, and residual stresses can be improved. The equivalent stresses were reduced following heat treatment, and especially stress concentration in the weld, with optimal values reached for heat treatment at 420 °C.