welding consumable selection

Date 03-22-2011 16:48

My first thought is to use what the WPS calls out. My second thought is that there must not be a WPS if you're asking this question. My third thought is that you need to go have this conversation with the EOR and get a determination from him/her. My fourth thought...you don't want to know it. :grin:

By jarcher (**)

Date 03-22-2011 17:16

I take it you are developing a WPS or doing some welding under the farm code. The more usual choice for FCAW would be E71T-1 for gas shielded all position and ER70S-2 or ER70S-6 for GMAW in a wire size appropriate to your application. Generally, E70 or ER70 wire are used for as filler wire for this class of steels.

By zambrota (**)

Date 03-22-2011 21:41

Thanks Jarcher,

You are correct. E71T-1 & ER70S are the only wires available on market. I'm interested why we do not have lower strength wires to match base metal. Do we need in this case double-overmatching weld metal? Does it make sense?

Thanks

By MBSims

Date 03-24-2011 03:01

It is very common to use an overmatching strength filler for the lower strength carbon steels and does not present a problem with quality of the weld. If the weld is sound and the welded joint is stressed to the point of failure, the failure should occur in the base metal. Are you trying to design a weld joint that will fail in the weld instead? Or are you concerned that you would be wasting money on the extra unused tensile and yield strength in the filler metal?

By zambrota (**)

Date 03-24-2011 06:49

I guess, if I use lower strength filler, weld joint failure is reduced?

By Ddenis Date 03-24-2011 11:34

It's common practise for brazed joints to get joint's strength lower than strength of parent metal. Talking about welding, you should use fillers so that the strength of weld matel would be higher than the strength of base.

By MBSims

Date 03-24-2011 17:28

I guess I'm not following the "if I use weaker weld material, the overall assembly will be stronger" philosophy. An interesting idea, but it would seem to suggest a failure would not necessarily occur at the weld if the material were homogenous. But failure would then be more likely at a change in geometry, such as a change in thickness at the weld or base metal, or other feature.

By 803056

Date 03-26-2011 16:36

There are occasions where it is prudent to under match the weld. I will often intentionally under match the weld when the repair involves a highly restrained joint when low carbon or high strength low alloy steels.

When the first weld bead is deposited, it will shrink as it solidifies and further contract as it cools to the preheat temperature (ambient if no preheat is utilized). When the joint is highly restrained either because of the mass of the base metal or the configuration of the joint (think of a circular patch in the wall of a vessel), something has to move as the weld shrinks and further contracts. If the weld is as strong as the base metal or possibly stronger than the adjacent base metal, the movement is accommodated initially by the hot weld metal. However, as the weld cools and recovers tensile strength, the adjacent heat affected zone is forced to accommodate the forces resulting from the contraction of the weld and surrounding base metal as the assembly cools. In many instances, the properties of the HAZ are over whelmed by the stresses introduced by the contraction of the much stronger weld and a crack develops in the HAZ.

It can be an advantage to use an under matched filler metal when the joint is highly restrained so the residual stressed resulting from the contraction that occurs during cooling is accommodated by the weld rather than the adjacent HAZ. The weld often has a geometry that permits plastic deformation to occur without cracking better than the adjacent HAZ. As the under matched weld is subjected to plastic deformation, there will be some stain hardening in the weld as it cools, thereby increasing the tensile strength somewhat at the expense of ductility. However, the effects of strain hardening and loss of ductility will be reduced somewhat by the second layer of weld deposited over the initial root bead. The process will continue, i.e., each weld bead is strain hardened as it cools, but the mechanical properties are improved by the tempering effects of successive weld beads.

If the weld joint is not highly restrained, there is little to be gained by under matching the weld.

Best regards - Al