Restraint Cracking in Automatic Welding Process

Observation for Automatic Welding Procedure of Structural Steel of Large Thickness

Abstract

It has been disturbing experience of those engaged in submarged arc welding of structural steel plates to find cracks in the weld metal. These cracks which frequently take place while the weld is still very hot, and usually while the joint is subjected to high stresses, are associated with weakness between dendrites and it is believed to be probably hot cracking caused by increasing restraint due to the larger thickness of plates.
Using large restraint specimens authors have experimented of the development of these cracks quantitatively and compared the various welding procedures with the result obtained.
Covering the experimental methods used and the results obtained, this paper presents data whose several phases are as follows :
(1) In order to prevent the restrained crack, it is more desirable the deposit of the first layer is made larger. (cf Fig. 5, 6 and 7)
Generally, speaking of the performance of joint after welded, a multi-layer weld is said better. However, in view of such fact, it seems to be somewhat dangerous to increase the number of layers too much, which may cause the dwindling of the deposit of the first layer.
(2) Among two combinations of rod and flux used in test, the low manganese rod of the combination I whose width of bead is larger is showing much better result (cf Fig. 5, 6, 10 and 11) As for the restraint crack of manual welding, better fusion and higher the deposit top is showing a better result, but a different aspect is presented in the automatic welding.
(3) In the restraint crack of manual welding, the cold crack mainly poses a problem, but in the automatic welding it is conceivable the crack develops at a fairly high temperature (cf Fig. 10, 11).