Cracking in 347 SS

Date 01-08-2009 18:17

Welcome to the wonderful world of 347, lovingly referred to as Crackalloy.
You might do well however to give us a little more detail as to crack description and welding parameters.
Heavy wall will also have great restraint imposed on it.

By THOR Date 01-08-2009 21:06

We are currently welding the repairs with Avesta E347-16 1/8" SMAW rod at 100 amps. We use a preheat of 100 degrees farenheit and a max interpass temperature 350 degrees fareinheit. All the cracks occuring are transverse in the weld metal and stop before the parent material.

By js55

Date 01-09-2009 18:11

HAZ cracking (remember in multipass welds you have HAZ's in the weldmetal) is not unheard of in 347. My understanding is that its liquation/segregate related, and related to grain size. The usual remedy is to keep heat inputs low. And I also understand that C content can aggravate the problem. If you happen to have a higher C content it will tend to be more problematic.
It may be a transverse crack but I'll gues that if you look really close the crack path will be jagged which is typical of hot intergranular cracking.
Go to smaller wires. Run stringers. Do not try and fill the cavity in single layers.

By Fredspoppy (**)

Date 01-09-2009 13:34

Can you explain the reason for the "baked at 899 degree's celsius" portion of the procedure? That equates to ~1650F. How long did you hold at the 899C temperature?

By js55

Date 01-09-2009 14:31

High temps from welding re-solutions all carbides (close to the fusion line-knifeline attack is the concern) that will then precipitate preferrentially as M23C6 upon reheating in multipass welds, taking Cr out of solution. Re-heating to this temp range re-solutions the M23C6, preserving Cr, and precipitates Nb carbides, which is the intent of the stabilized alloy.

By Stephan (***)

Date 01-10-2009 14:57 Edited 01-10-2009 15:00

Carl + Jeff,

first off, happy new year to both of you.

It shouldn't be too late for this.

I have posted a similar question already yesterday, but addressed to THOR, then I have deleted it again due to not wanting to run into the risk to be finally "downrated" to 10^-9 some day.

However, here I am again, since it wouldn't have been me if I had let this be the final word at this.

Thus once again my question, and this time a bit more "differentiated" and asked to both of you as you are two of the most experienced forum fellow members in this field.

How are e.g. cap- or even the layers beneath the cap-layer (in a multiple pass joint on cracking susceptible steel stainless steel grades e.g. pure austenitics) being removed to get access to a flaw lying e.g. in the centre of the transversal cross section of the joint, e.g. slag inclusions. Is it being performed by grinding? And if so, what are the precautions to avoid a contamination of the layer to be repair welded with e.g. ... sulphur, originated from the binder of the grinding wheel. This again forming very low melting Nickelsulphide-Eutectics or even Nickelcarbosulphide-Eutectics? Are there special grinding wheels used or is the weld metal being removed by machining which must be accomplished again without hydrocarbon containing cooling agents?

However, if, which is just an assumption, a grinding wheel was used containing binders which are containing sulphur again, then, again just my assumption, it would be explainable why the material was free of cracks before it was repair welded and full of cracks subsequently to the repair. And if, so my assumption, once sulphur is within the material and being diluted again by each repair weld, then, so my assumption, it might be a hard untertaking to get crack free repairs at the end of the day, since each repair welded layer would dilute at least traces of it into the layer underneath the welded one.

I am sure that THOR is an outstanding expert as well and his company or employer has the appropriate means for repairing, thus please see this my question just as a very general questioned one - just for my personal interest, so to speak.

Stephan

By js55

Date 01-12-2009 13:42

Stephen,
Good to hear from you again.
I don't remember the metallurgical mechanism for HAZ cracking of 347(early desciptions even utilized terms such as similar to underbead cracking). But given the description of transverse cracking which is usually H2 related though would probably not be with an austenitic, it is conceivable that an HAZ crack could follow a transverse path along the HAZ related to the the stress involved in filling cavities for weld repairs which is very high.

By Stephan (***)

Date 01-12-2009 19:47

Thanks a lot Jeff!

Good feeling to find a free minute - at least at the moment - to join the forum once again.

Cheers also for your explanation. Yes, this would make sense.

However, what has wondered me was the fact described by THOR, that the cracks have occurred in the "weld metal" to "stop before the parent material".

This again has let grown the idea that eventually an undesired reaction between some contaminants induced from the grinding wheel or whatsoever in combination with the already welded + cracking susceptible alloy could have led to this phenomenon. As I said, just an idea.

Anyhow, it were nonetheless interesting to get some idea of how the removing of solidified weld metal from a joint at cracking susceptible material is accomplished to enabling a subsequent repair weld.

I guess this should be regulated as well...

Stephan