Weld Repair for 4330 Mod

[jackboot]

Has anyone ever done a weld repair on 4330 mod?

We have a heavy block that needs a small gouge filled. The weld will not contribute to any strength and will only fix a dinged sealing surface.

The ys and ts are 150 to 165 psi and the hardness approximately 330 BHN.

Since the weld is so small (~.125in) I was going to specify a stainless filler 316 with a GTAW process. Preheat to 600 F and then slow cool.

Any suggestions would be appreciated.

jackboot

 

[GRoberts]

I would recommend either 309L filler or ERNiCr-3 filler so that you don't get martensite formation as you would with 316, and then the weld would be less likely to crack. And if at all possible, I would PWHT at about 50F below the previous tempering temperature to help temper the HAZ, reduce stresses, and reduce hydrogen. The 309L might sensitize, but since you don't need corrosion resistance, that's ok. If you can't PWHT, keep it at about 500F for 6 hours to let the hydrogen out, even though GTAW is very low hydrogen anyway, but it will also relieve a small percentage of the residual stresses.

 

[jackboot]

Why would the 309L or ERNiCr-3 limit the martensite formation?

Wouldn't the martensite formation be from the "contact quench" of the hot arc on the base material? Or would the 309L capture more of the carbon so that it would tend to limit this martenisitic structure?

We can do the PWHT, but since we are welding a spot (very small) I didn't feel the PWHT is necessary. But I forgot the need to chase out the hydrogen.

jackboot

 

[GRoberts]

With the dilution from the base metal, 316 falls into the A+F+M region of the Schaffler diagram. 309 and NiCr-3 fall into the austenitic or the A+F region of the diagram. It can be affected by the cooling rate, but composition is the main criteria for Austenite, Ferrite, or Martensite formation in welds.

 

[jackboot]

Yes - I see.

I was just looking at the diagram when I saw your reply.

Thanks,

jackboot

 

[stanweld]

ERNiCr-3 is an excellent choice and agree that ER316 is a poor choice for the reasons given by GRoberts.

I have also successfully used E7018 with SMAW and ER70S-2 with GTAW and a 600F minimum preheat and 600F dehydrogenation heat treatments. I also used a temper bead technique followed by grinding to remove the temper bead after performing the dehydroghenation treatment. In these cases the dissimilar (high alloy) metals could not to tolerated for the service.