Research on Welding Residual Stresses, Report 1

Effects of Welding Conditions on Residual Strain in Weldments

Abstract

This research was aimed at surveying the differences of welding residual stresses due to the differences of welding conditions in connection with the research on welding cracks conducted by the author. The variations of welding conditions prefered were those for the kinds of electrodecore-rods, the diameter of core-rods, the kinds of base metals and the local heat-treatment after welding.
Single beads were deposited on the surfaces of many rectangular. specimens of mild steel and ducol steel.
These specimens were subdivided into strips perpendicular or parallel to the bead line after depositing.
The differences of the distances between two point-marks before and after subdividing, namely residual strains, were measured.
The distributions of residual welding, stresses were determined from these measurements by an approximate calculation formula of elasticity.
The main points of the results obtained are as follows:
1) The residual stresses perpendicular-to weld lines are in compression at both edge-portions and in tension at the central portion of the plate.
2) The. residual stresses parallel to weld, lines are in compression at. both sides and in tension in the. vicinity of weld lines.
3) These is no great variation in the residual stress distributions between mild steel and ducol steel.
4) The amounts of residual stresses are changed considerably by the differences of electrodes. And even if the core rods are equally mild steel, there are pretty large differences in residual stresses between the cases for 5mm and 3.2mm diameter core rods. Namely, the maximum tensile stress perpendicular to the bead line by the former is greater than. the latter, and the maximum tensile stress parallel to the bead line by the former is smaller than the latter.
When the amounts of residual stresses by Cr-Mo. steel electrodes, mild steel electrodes and 18-8 atstenitic steel electrodes are compared, the maximum values of tensile stresses for both directions are arranged from large to small in order of this description. Therefore, it is understood that onefactor for the suitability of austlnitic steel type electrodes for the welding of alloy steel, especially high tensile alloy steel, is a small amount of residual stresses.
5) There is no great change in the distribution of mean residual stresses in the macroscopic field even when the weld line is locally post-heated by gas-flames.
However, the maximum tensile stress parallel to the weld line of ducol steel plates is increased considerably by local postheating. This phenomenon is considered to be due to the tempering of hardened zones.
6) Local heating at the center line of steel plates, which seemed to have no initial stress, gives much the same distribution of residual stresses as in the case of welding.
The author examined the relation between the results obtained and the types and prevention of welding cracks.