Although welding stresses exist in a welded specimen both during and after welding, only those remaining after the specimen has completely cooled have been much discussed, and many works have been done to measure the distribution of residual stresses in welded joints.
If, however, one wants to make clear weld cracking. behaviours, the most important thing to be done is to inquire minutely into the proceses of generation and growth of welding stresses.
The following are researches on the dynamic measurements of the generation process of stresses in weld which are produced in welding mild steel under the restrained conditions. In measuring the process a trially-made experimental restraint apparatus indicated in Fig. 3 was used.
The conclusions obtained from the above experiments are as follows.
Though the tensile stresses were slightly produced by the contraction of deposit metal at temperatures higher than that of the Ar' transformation, they were soon counteracted by compressive stresses due to the Ar' transformation.
Consequently, restraint stresses are evidently considered to be generated really aftet the Ar' transformation has been finished ; the so called Heyn's "Grenze Temperatur" of plastic and elastic deformation is 500-450°C.
When deposit metal cools down below 500-450°C, restraint stresses are rapidly generated. They keep growing up to the yield point of mild steel while the deposit metal cools down to the room temperature.