Si effect in the cracking of weld zone

Date 02-01-2008 14:54

Since you refernce A5.4 I assume you are doing SMAW?
What are the requirements for the overlay? Does the customer specify a composition, or just a material?
What manufacturer and type of electrode, size, current are you using?
Are your cracks only crater cracks or cracks throughout the weld?
I assume the cracks are forming during cooling and are hot cracks. I'm not sure what you mean by centrifugal though. Are you overlaying a round part and getting centerline cracks along the length of the weld as well as across it?
What is the ASTM grade of base metal?

Any other info you can supply will only help with a diagnosis.

By gaydonat (*)

Date 02-04-2008 09:05

We are doing SMAW and cladding stainless over carbon steel. The requirements of overlay are to be nonmagnetic, stand against corrosion with just one pass layer, be stable up to the service temp. of 110 Celcius. The type of the electrode is rutile and we force the electrode by using 110 amperes for 1/32 inch diameter for more deposition. The cracks start from crater then goes through the centerline along the weld. The cracks occur during cooling so yes you are right they are hot cracks. The ASTM grade is A285 Grade A.

We are also suspicious of ferrite number, it is around %15. Although we have low Sulphur and Phosphorus in composition. We may have intermetallic corrosion. Should we keep ferrite number lower or higher against cracking? What is the mechanical behaviour of ferrite phase in stainless steels?

By GRoberts (***)

Date 02-05-2008 00:00

Well, ASTM A285 is not anything unusuall with regards to Si content. While it is not specified, it would be extremely unusual for Si to be anywhere close to 1%. Typical values are around .25%, with most being under .5% for carbon steel plates in the same strength range as A285 (I don't have any specifically A285 MTRs available). And since your elecrode should be .90% max, something is way out of whack. Get both your plate and electrode tested to find out which one it is.

I believe your 1/32" diameter electrode is a typo? If you are using 3/32" electrode, 110 amps is way too high for stainless steel, and you are probably having a hard time getting craters filled properly, and that could be a big part of your problem Concave (improperly filled) craters lend themselves to crater cracks.

The 309L is designed to have 8-20FN typically. This is by design in order to prevent hot cracking when welding to or over carbon steel among other things. So the 15% (or is this FN) is an ordinary number for this type of weld. Depending on composion, you typically want at least 3-5FN in your weld to help prevent cracking. 15FN is not determental in most cases (for corrosion), and will typically only help with cracking problems. However, it will be about 15% magnetic. Your overlay will never be entirely non-magnetic because of the underlying carbon steel. What sort of magnetic properties are you looking for?

Are you testing for corrosion, or is this in-service? What sort of environment is being used in testing or production? 309L stainless steel should be metallurgically stable up to 110C and above, but corrosion wise, it all depends on what it is exposed to. It depends on the environment, crevices, flow velicity, temperature, etc. I'm not sure exactly what you mean by intermetallic corrosion. Intermetallics are phases formed by various elements that are found in stainless steel such as Cr & Mo. They are preferential corrosion sites, but are not a type of corrosion per-se. Are you referring to intergranular corrosion.

By gaydonat (*)

Date 02-05-2008 12:14

Sorry electrode diameter is 5/32 ''. After the pass we come back in order to fill the crater and make it convex but still we have the problem. Non magnetic is a wrong term we have a gauss limit and we try to stay in that limit. I mean intergranular corrosion but we have enough ferrite number against hot crack.

By CWI555

Date 02-01-2008 15:15

If I read your post correctly, your doing a 309 L stainless cladding over carbon.
"centrifugal and longitudional cracks in the weld zone" and by centrifugal do you mean centerline?

By gaydonat (*)

Date 02-04-2008 09:08

We are cladding 309L stainless over carbon. I mean we have centerline cracking starting from crater and goes through the end.

By CWI555

Date 02-04-2008 13:27 Edited 02-04-2008 13:41

Cr and Si are both ferrite formers, and Cr is also a carbide former. Nickel and Carbon are Austenite formers, An excess of Si will cause an increase in carbon due to graphitization, which if I am not mistaken, in a binary alloy will lead to excess formation of marstenite making the weld more brittle and subject to lower toughness, and centerline (hot) cracking.
All standard PMI methods don't have the ability to measure carbon content as the element is to light to be accurately picked up. What I suggest is wet chemical analysis in a lab. I believe with proper analysis your going to find an excess of carbon. Cranking up your heat isn't helping matters either, and just giving more time for carbon to wreck havoc on your weld.

However; you can skip to the chase and just get a qualified material and put a stop to it all. I may be wrong here, but I don't think there is filler classified in the 300 series that allows 1.3 percent Si.
If someone else has a different take on this, please feel free to speak up.

Regards,
Gerald

By js55

Date 02-04-2008 15:55

First of all your saying that you're overlaying carbon steel. What carbon steel? You're welding carbon steel with 309L and your Si is at 1.3%? Holy moley!!!
Given that your dilution from SMAW is going to be in the neighborhood of 15% to 40%,(probably on the high side since many people have a tendency to increase amps with SS fillers to compensate for the sluggish puddle which is not generally conducive to effective one pass corrosion properties).
The Si in your substrate has to be really high.
This also tells me two things. Your're running way too hot. This increases dilution, (not good for corrosion), and also will increase the silicon from the substrate into the weld metal, (not good for hot cracking). But not to 1.3%.
Also, if you wanna one pass overlays SMAW is not the best choice, or if you use one pass SMAW you need to punch your alloy content to compensate for dilution. 309 won't get it.
A better choice is pulse GMAW (dilution maybe 10% to 20%-sometimes less if your really controlling your process-but you risk non fusion) or ESW (dilution at maybe 5% to 8%). Even with those processes many people still punch the alloy content.

By CWI555

Date 02-04-2008 16:45

It may well be that the Si is high in the substrate. But there is absolutely no promise that it is. The one thing I can see for certain is, to much heat, and to much Si whatever the source.

By Aspirate (**)

Date 02-05-2008 03:55

agree with you guys. dilution may be too excessive.

By rafael Angarita (*)

Date 02-04-2008 19:37

Not only alloys elements originate cracks; also thickness, geometry, pre and postweld heat treatment can became critical and provide cracks formation.
May be not Si thr problem.
Can you put on more information?

By gaydonat (*)

Date 02-05-2008 13:01

The geometry of the piece is 100*100 mm(width and length) and the thickness is 250 mm. We pre heat the material up to 200 Celcius Degrees. The point is we try another brand electrode there is no problem with that. But the boss wants to work with the other brand. There is an analyze difference between them. So that we quess there may be fault at ferrite number and Si content. When we come to the point of dilution we tried with low amperages in order to prevent high dilution. But the problem still continues with that brand electrode.

By js55

Date 02-05-2008 14:58

And analysis difference between fillers within the range established by AWS 5.4 will not be enough to cause unpreventable hot cracking. Thats pretty much part of the reason the committee, backed up by mountains of emperical data established those ranges.
If your Si is sittin at 1.3% deposit, with hot SMAW near maybe 50% dilution, a quick calc, not knowing or counting the base metal Si content(which would actually increase it slightly), would be a filler chemistry of >2% Si.
310, if memory serves, allows up to 1.5%, and perhaps some exotic SS's will allow more, I can't think of any offhand. But >2% is extreme. Though I believe it should still be weldable. You may have two problems.
If your boss is insisting on that filler you may need to test, as Gerald advised, and you are clearly running too hot as Greg mentioned. Also, for 1/4" thickness there is little need to preheat. In fact, this would only contribute to the segregation of those very contituents that contribute to hot cracking by slowing down the cooling rate. Si, P, S, and other more exotic nasties.

By DaveBoyer (*****)

Date 02-06-2008 04:19 Edited 02-06-2008 04:22

In the above post gaydonat mentioned 250 mm thickness, did You mistake that for .250" ? Or did I misunderstand something?

By ssbn727 (*****)

Date 02-06-2008 08:32

That's almost ten inches thick!!! In fact, we're talking 9.843 inches (rounded off to the nearest thousandth of an inch) thick... In other words: 9.843" X 3.937" X 3.937" correct???
I mean that's what my conversion comes out to be according to what gaydonat gave in millimeters (250mm X 100mm X 100mm).

First and foremost, what is the base metal composition because without knowing this, one can only speculate on what the root cause of the cracking is!!! No one in here has the ability to assist you in finding out the cause of your problem if you do not include complete, and specific details.

Another question I have is where did you come up with the preheat temperature of 200 degrees C??? Also, can you describe in detail how you are measuring this, and where on the Base metal are you measuring the temps???

Everybody else is giving you some excellent advice yet without more specific details, we can only guess some of the potential causes for the cracking you are experiencing.
Please include as many details as possible. ;)

Respectfully,
Henry

By js55

Date 02-06-2008 14:45 Edited 02-06-2008 14:48

Dave,
LMAO!!!!!
Thanks
Yes I did in fact impose a decimal point where there was none. Huge difference between 1/4" and 10". A temporary case of cerebral rectumitis.
Er,,,,uh,,,,,nevermind....... Preheat seems reasonable. Not to mention I changed mm to inches. Good lord.