Toe cracking in 4130

[csa178]

I have been welding 3/4" x 6000# threadolets into some 10" dia tubes and getting cracks along the toe of the reinforcing fillets. All the materials are AISI 4130. The WPS that I followed called for preheat of 150 deg C and I used GTAW ER80S-D2 for the root pass and filled the rest of the joint with SMAW E10018-D2. The tiny cracks were detected by dry powder MPI immediately after welding and grinded away and rewelded. When MPI was done again the cracks did not appear. However, after post weld heat treatment the cracks reappeared and had to be grinded away again. Can anybody please provide some sound advice as to how to weld these olets without getting toe cracks?

 

[metengr]

Increase the preheat to 200 deg C and MAINTAIN it for 15 minutes BEFORE welding. Sounds like underbead cracking related to hydrogen entrapment.

 

[GRoberts]

Also, make sure that your SMAW consumables have been stored and conditioned properly in order to maintain their low hydrogen properties. Also maintain preheat after welding for half an hour or at least slow cool to allow any remaining hydrogen to escape.