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Welding different metals
- Thread starter madax
- Start date
Well, both are weldable steels but they have significantly different yield strengths. A36 has a yield strength of 36ksi or slightly greater while A913 Gp3 material will have a yield of 65ksi or better. The filler metal you propose actually has a yield strength between those two base metals. If your design considers the structural need for only the lower strength of all of those, then perhaps it makes sense; however, you are clearly mixing two distinctly different steels with significantly different mechanical properties. In short, one side of your structure will have ductile properties while one side will have more brittle properties.....not necessarily a good idea.
This is considered undermatching and is covered in AWS D1.1 Section 3.3.
A913 can be welded to A992 or A36 but sound engineering judgment should come into play in some undermatching situations.
The FCAW electrode classification you have is for the lower strength Group and that is what is typically used when undermatching occurs. FCAW is generally considered a low hydrogen process.
Bear in mind that D1.1 Section 3 is for prequalified joints.
By the way, is this for a prequalified seismic connection?
A913 can be welded to A992 or A36 but sound engineering judgment should come into play in some undermatching situations.
The FCAW electrode classification you have is for the lower strength Group and that is what is typically used when undermatching occurs. FCAW is generally considered a low hydrogen process.
Bear in mind that D1.1 Section 3 is for prequalified joints.
By the way, is this for a prequalified seismic connection?
Madax:
Why don’t you show us a sketch of what you are trying to do, with some loads, dimensions, and a description of the conditions. I have no qualms about doing something like that, but it is a bit of a tricky condition. Look at the stresses at the various levels in your cross section. The welding process and filler metal must be compatible with both materials in terms of chemistry and low hydrogen process, etc., so as not to seriously degrade the stronger material or welds. And now, depending on the joint detail, you may have several different weld areas (throats) which you have to check, at different mixed weld metal allowable stress, for min. weld strength. Depending upon what you are doing and what control you have over materials, etc., you might look at the mill certs. of the A36 and justify a higher min. yield stress for the joint design, and unless the filler metal matches the 65ksi+, you probably can’t justify using that higher yield stress in the joint design. If this is a hybrid plate girder, for example; at the top of the bot. flg. you might find the stress level is approaching the cert. value of the A36, so things could be o.k. Also, consider that as long as the flange material has not yielded, it will try to return down the stress/strain curve when unloaded, causing a residual stress condition. The weaker web material will follow the flg. material up the curve in terms of strain, and back down, but at some point it may have yielded a bit, but can’t get worse than following the strain of the flg. material. The web material will now be working from a point higher on its stress/strain curve, but it will still be working on the std. slope (approx. 29,000ksi). In many cases this situation is not particularly detrimental, as long as you are not working too far up the plastic plateau of the web material, or the height of the web material involved is not too great.
Why don’t you show us a sketch of what you are trying to do, with some loads, dimensions, and a description of the conditions. I have no qualms about doing something like that, but it is a bit of a tricky condition. Look at the stresses at the various levels in your cross section. The welding process and filler metal must be compatible with both materials in terms of chemistry and low hydrogen process, etc., so as not to seriously degrade the stronger material or welds. And now, depending on the joint detail, you may have several different weld areas (throats) which you have to check, at different mixed weld metal allowable stress, for min. weld strength. Depending upon what you are doing and what control you have over materials, etc., you might look at the mill certs. of the A36 and justify a higher min. yield stress for the joint design, and unless the filler metal matches the 65ksi+, you probably can’t justify using that higher yield stress in the joint design. If this is a hybrid plate girder, for example; at the top of the bot. flg. you might find the stress level is approaching the cert. value of the A36, so things could be o.k. Also, consider that as long as the flange material has not yielded, it will try to return down the stress/strain curve when unloaded, causing a residual stress condition. The weaker web material will follow the flg. material up the curve in terms of strain, and back down, but at some point it may have yielded a bit, but can’t get worse than following the strain of the flg. material. The web material will now be working from a point higher on its stress/strain curve, but it will still be working on the std. slope (approx. 29,000ksi). In many cases this situation is not particularly detrimental, as long as you are not working too far up the plastic plateau of the web material, or the height of the web material involved is not too great.
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