Residual stresses in 18CrNiMo7-6 linear friction welded high strength steel chains

Linear friction welding is a solid-state process that comprises rapid heating and cooling of the welded parts. Residual stresses (RS) as in every other welding process cannot be avoided. The presence of RS compromises the in-service performance and reliability. They influence stress corrosion cracking, fatigue strength, and the crack growth rate. Knowing the magnitude and nature of such stresses is critical for improving the quality of welded joints. Therefore, four different manufacturing stages of linear friction welded chain links were analyzed in the present study: “as forged” (F), “as welded” (A), “as welded” without flash (N), and post weld heat treated (P). The residual stress field was measured using the hole drilling (HD) method. The results of the hole drilling method showed to be independent of the measured position and symmetry with respect to the weld was observed in all evaluated regions. Close to the weld center line (WCL), the compressive stresses present in the “as forged” condition switched to tensile as a result of the welding process. However, in further regions, stresses remained almost unchanged for either A and N. The PWHT uniformizes the residual stress field along the whole weld region.