Centerline cracks! 1

[NickE]

just a question of interest.

Has anyone noticed centerline cracking recently in SAE631 Stainless. Specifically 0.050"?

 

[mcguire]

Help those of us who don't use SAE as a spec for stainless. What is SAE631? I know of a number of centerline cracking problems.

 

[metengr]

I believe the SAE 631 stainless steel is 17-7 PH.

 

[unclesyd]

Just to start you off, a couple of the main reasons for center line cracking in thins sections is not enough weld metal or constraint. Not enough weld metal is common in autogenous welds and is usually very evident. Constraint can come from many sources and is hard to verify in a post mortem analysis, it is most likely to be detected by observing the welding process. If there is delayed cracking I would look at the weld metal compatibility if filler is added. There are other metallurgical concerns dealing with the 17/7.

What is the Condition of the 17/7 when you are attempting to weld it?.

 

[NickE]

This isn't weld centerline cracking, its lamination or centerline cracking from the caster or the hotmill.

We just had a 50lb order of sheet (17-7 condition C) undergo de-lamination in the dead center of the thickness. This occured after wire EDM of the part and also after a light forming step. There really is nothing we can do now, my purchaser cannot find anymore 17-7condC in .050" though. I just posted the question to inquire if anyone else has seen this recently, our supplier is stating that they've got two heats with the same problem.


Thanks for the interest.
nick

 

[mcguire]

17-7PH is really a difficult grade to produce for the steelmaker. The aluminum addition makes it quite different from normal austenitics. If the producer made it on a caster which is not equipped with electromagnetic stirring, the solidification segregation can be excessive and irreversible.
The mill that made these heats got out of its league and all such material should go back to it as a claim. You can't fix it.

 

[EdStainless]

We have seen some real banding in strip that is in this thickness range. We work with 0.035"-0.134" material. Since we anneal/cold draw/anneal we are making tubes) prior to aging we get enough diffusion to minimize the effects.

Was your material really in the C condition? Had it been cold rolled/annealed/cold finished? I have seen 17-7 that had lamination from the rolling. Did yours actually come apart in the center or was it about 1/4th of the way in?
I hate to ask, but which mill produced it? They each have a different set of problems.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be slowed down.

 

[NickE]

We got the steel from a secondary, w/o mill certs.. Yes it is condition C, it has to be, the spring is really really stressfull (itself and for the engineers).

Dead center (or therabouts) .0285 - .0235 on .051 (Caliper meas. not accurate but shows how even the cracking was)

Thanks Mcguire, our supplier is refunding the order. I wondered if this was a particularly hard grade to produce, seems to have great properties but there is'nt alot around.


nick

 

[EdStainless]

NickE, they have to tell you the producing mill if your require it in your PO. For a lot of our aircraft work we get strip from re-rollers, but require the original CMTRs for tracability reasons.
Well straight down the center eliminates one of the comestic mills, theirs is always offset.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[unclesyd]

I would come up with a specification on the 17/7 material you need prior to any more purchases.

You might want to checkout these sites.

Hamilton supplied us with a lot of material with never any problems.

http://www.hpmetals.com/allyspcs.asp

These people did the same except larger sizes.

http://www.eaglealloys.com/stainlesssteelalloys.html

Here is the daddy of the PH steels. I haven’t delt with them in several years but at one time they were a great resource. Two good pieces of information on this page.

http://www.aksteel.com/markets_products/stainless_precipitation.asp