Welding Q&T 4130 w/o Post Weld Q&T 1

[tc7]

I have a requirement to develop a WPS for welding 4130 which has been heat treated to HRC 26-32 (this is the 4130 condition prior to weld). I am further instucted to weld using Mil-12018-M2 rod. No post weld heat treatment is prescribed, other than to stress relieve.

The HRC 26-32 tells me the tensile strength prior to weld is 125ksi. Use of the 12018 rod leads me to think we may expect ~120ksi weld metal strength. Since we are not using a heat treatable welding rod, we cannot PWHT to strengthen the weld to the original condition. However, I am not sure how to predict what the true joint strength (CJP T-Weld w/fillet reinforcement)will be, owing to any annealing of the base material during weld.

How can I establish the pass/fail strength criteria of the PQR tensile and bend tests? (this will be for a Mil-278 type PQR, which are very similar to ASME PQR's).

Thansk for any advice.

 

[metengr]

tc7;
The criteria for pass/fail will be based on the location of tensile failure for test specimens using a groove weld plate specimen - fracture in the weld or base metal HAZ is failure to qualify this filler metal. For design purposes, you normally want the weld to be as strong as the base metal(s). Qualification of a groove weld can be used for fillet welds.

The same would apply for the bend tests - no tears in the weld or base metal HAZ.

 

[tc7]

Agreed that success or failure will be based on fracture or bend failures in the base metal HAZ or the weld metal. I am certain that we can expect the 12018 weld metal will be stronger than heat affected area of the base material which will lose some of it's original Q&T strength and failures will be in the HAZ.

So I have a situation where, by design, the welding operation degrades the original strength of the base metal.
In this particular case, I don't believe failure in the HAZ is necessarily a total failure if we can predict the % strength reduction expected from the welding operation.

Thoughts?

 

[metengr]

tc7;
You won't be able to predict. Run the coupon to qualify the weld procedure and see what happens.

 

[tc7]

I wonder if I really have to qual a new procedure? I have many other WPS for normalized 4130, all using either a 80xx or a 90xx filler with a typical 2-hour PWHT at 1100 deg F.

Since I am not required to re-Q&T this HRC 26-32 version of 4130, why should we have to do a new PQR?

 

[metengr]

In this particular case, I don't believe failure in the HAZ is necessarily a total failure if we can predict the % strength reduction expected from the welding operation.

tc7;
Be careful here because your PWHT may indeed adversely affect the mechanical properties of the Q&T base material. So, based on your specific question above, maybe instead of a "PQR" as I originally mentioned above, you still run a coupon and perform tensile testing (and bend) to assure yourself that the weld region is strong enough and possesses adequate ductility. This is easy enough to do and provides you with no guesstimates.

 

[tc7]

Metengr-
Thankyou for kicking around some ideas. I think you have offered good advice and will proceed as you suggested.
VR
Tom

 

[GRoberts]

I'd bet you lunch that your failure was not in the HAZ if you have any thickness to your weld coupon. The softened portion of the HAZ will tend to be narrow and will be restrained from the harder portion of the HAZ sitting right next to it. Depending on you PWHT temperature, your filler metal could easily be the weak link as the 120ksi minimum tensile strength for 12018-M2 is in the as-welded condition. With the low carbon content of the weld, it can soften appreciably. It also looses a significant amount of toughness and ductility. Your bend tests could be problematic.

 

[tc7]

GR-
Not sure what you are saying in regard to the "softened portion of the HAZ will tend to be narrow and will be restrained from the harder portion of the HAZ". In a tension or bend test, where the PQR weld will be a V-groove butt weld (probably in 3/8" thick plate), how will the softened portion of the HAZ be restrained? I think the softened portion of the HAZ will extend across the entire thickness of the test plate, and therfore strength will be dictated by the softened portion of the HAZ, won't it?

Additionally, in regard to your comment on the 12018 rod - this rod is designed to provide ~120ksi strength in the as-welded condition, even considering what dilution may be expected from the 4130?? Why would you expect less than 120ksi strength from a 120ksi rod?


Need your help help GR, please comeback with clarification.
Thanks.

 

[GRoberts]

The softened portion of the HAZ will extend through the thickness of the material, but say, may be only 1-2mm wide. When pulled in a tensile test, it tries to elongate, which reduces the area of the cross section, but the harder portion of the HAZ- which will be on the weld side, and the unaffected base metal will keep it from reducing the area much. It won't be as significant on 3/8" plate as the 1 1/2" or 3" MIL-STD-248 plate that gets you unlimited thickness, but it will still have some effect.

On the 120KSI electrode, as you mentioned, it is desiged for 120KSI in the as-welded condition. You state that you will be doing PWHT.