Residual Stress Measurement in Welded Spheroidal Graphite Cast Iron by Inherent Strain Method

Abstract

  Residual stress in welded spheroidal graphite cast iron was measured by the inherent strain method. Spheroidal graphite cast iron plates, which are equivalent to JIS-FCD400 and FCD700, were welded using SUS309 stainless steel and carbon steel wires by the MIG bead-on-plate method. Distribution of residual stress through out the bead and substrate was estimated precisely using a small cut-off specimen by the inherent strain method. The residual stress distribution corresponded closely to the structure in the welded cast irons. The residual stresses in the welded bead and the heat-affected zone (HAZ) were tensile and compressive, respectively. On the other hand, the residual stress in the bead was compressive when welded using carbon steel wire. The compressive residual stress in HAZ was derived by the formation of martensite. The residual stress in the cast iron welded with carbon steel was released by annealing at 873K for 10.8ks, whereas the cast iron welded with SUS309 stainless steel remained as the residual stress caused by the difference in shrinkage between the SUS309 steel and cast iron after annealing at 873K for 10.8ks.