Nitralloy issues 1

[3lilaggies]

Having some issues welding A355 nitralloy. Overlay of Stellite 6 with a 600 Degree F preheat is causeing some major warpage in the 3 inch diameter rod that I am welding on. Is the 600 Degree F nessisary for this small of diameter? The rod its self ranges from 24" to 52" in length, and 1" to 3" in diamter. Any suggjestions?

 

[metengr]

3lilaggies;
The 600 deg F is not the problem, your distortion is from the Stellite 6 weld shrinkage stresses. You have asked this question before regarding welding; thread292-154891.

You might want to try another approach using an Inconel 82 butter layer over the A355 Nitralloy, using the same preheat. After the butter layer, go with the Stellite hardfacing. This may help.

 

[3lilaggies]

Thanks for that tip Metengr, I will have to check with the customer to see if that can be allowed.

 

[3lilaggies]

It is the rod itself that is warping from the 600 Degree preheat. As I heat the area to be welded it is causeing distortion, and thus changing the overall dimension. that is the issues arise.

 

[metengr]

3lilaggies;
Ok. Are you applying the preheat uniformly, and holding this temperature before welding? Yes, the bar(s) will grow in dimension (radially and axially) because of heat. The excessive distortion you mentioned could also be from residual stresses in the bar(s), prior to welding. Unfortunately, you relieve these residual stresses from heat (welding or preheat, it makes no difference).

What you need to do is to obtain this material in an annealed condition to avoid having the bar supplied with inherent residual stresses. The Inconel butter layer that I recommended will help to reduce residual stresses from the Stellite 6 overlay.

 

[3lilaggies]

Thanks again metengr for all your help. We do receive the nitralloy in the annealed condition. I am not familiar with buttering is it referenced in ASME section 8 or 9 any where?

 

[GRoberts]

You will have warping on any bar that is welded. Preheat only serves to reduce distortion when it is applied. Are you welding 100% of the bar around the circumfrence? The only way to keep it relatively straight is to make sure that all welding is equally distributed around the neutral axis of the bar. Then allow for machining to get the bar straight when finished.

 

[metengr]

3lilaggies;
Yes, and in addition to GRoberts information, buttering is a weld overlay. The Inconel 82 is very ductile and will reduce weld shrinkage stresses of Stellite 6 by absorbing the stresses. This should help to reduce distortion and reduce problems with depositing Stellite 6. The more I think about this weld build-up of Nitralloy, the Inconel interface layer makes sense. Again, treat the Inconel/Stellite hardfacing as a two layer weld build-up or overlay, and qualify this two layer weld build-up welding procedure using ASME Section IX as a guide.