Cracking Temperature of Mild Steel Arc Welds during Cooling

Abstract

From the result that the back reflection patterns obtained from the surfaces of shrihkage cracks in various mild steel arc welds show the mergence of K_α doublets to continuous broad lines as shown in Photo. 1, which indicates large lattice distortions, it was first asumed with the ordinary knowledge on physical metallurgy that these shrinkage cracks did riot ctake place above the A₃ transformation temperature.
In order to prove the assumption, back reflection photograms from the fractures of weld metals broken by applied loads at various temperatures, viz from room temperature to 900°C, were taken. The results show that the extinguishment of K_α doublets is seen in the specimens broken at 500°C or below irrespective of the modes of breaking, as in Photo. 3 and 4. From these results, it was concluded that many of the blued cracks took place at temperatures from about 300°C to 600°C.
And the author introduced the X-ray back reflection photography as a new method for the determination of cracking temeperatures of mild steel arc welds during cooling.