welding crack issue 3

[fusitexa]

hi,

the customer have a hollow cylinder and stepped button (our product)welded together. both of the cylinder and stepped button are made of 316L SS. and they have a lap joint. the size of hollow cylinder is 14mm long and 0.3mm thick; and its diameter is about 9mm; our product is 2.5mm thick and has same diamater with the cylinder; is i know little about the welding process. the customer had tried a few pcs, and they are 100 percent failed, all they have a central line crack in WM. the customer complained its the problem of our product, and the material is not 316L SS. i made a EDS test both to the cylinder and stepped button, and the results shows they are similar with each other. chemical analysis needs more time and money, so i firstly chose to do EDS test. attached photo shows one of the crack. any one could help to give me an instruction on how these cracks fomred, and what we can do to prevent them to happen, thanks.

sorry for my poor english.

BR

 

[fusitexa]

one more crack photo

 

[Guest102023]

Looks like hot cracking, possibly because (I strongly suspect) the weld was made autogenously (i.e., no filler metal added) and there was poor fit-up and/or high joint restraint.

I'd like more information about the design and weld joint, as well as the weld process.

"If you don't have time to do the job right the first time, when are you going to find time to repair it?"

 

[fusitexa]

brimstoner,

thanks. yes, according to my observation, i think it has no filler metal, and was welded autogenously.
i know little about the welding parameters. attached is schematic of weld design, pls. check.
thanks again.

 

[fusitexa]

cross section of the weld connection

 

[fusitexa]

crack initiated from the outside of the weld metal and propagate to the inside,as attached file shows. and also smaller crack found near the large one. it should be hot cracking.

 

[metengr]

I agree with the comments above because this type of autogenous weld joint configuration along with 316L stainless base materials can be very susceptible to hot cracking because little ferrite is present based on the base metal composition. I would use 316 filler metal to eliminate the potential for hot cracking.

 

[gtaw]

Consider checking the precleaning operation before the parts are welded. Autogenous welds in austenitic materials are prone to hot cracking when low melting point contaminates are present. When thinking of contaminates think of cutting fluids, oils, sulfur bearing compounds, etc.

Best regards - Al

 

[StoneCold]

You might want to change the joint design to either a half V weld or a full V weld so you can add filler metal to the joint. I wonder if you could get away with the existing configuration if you pre-heated the parts first??? That is a long shot. Is the joint under a lot of stress in use or is it a cosmetic type of plug??

Regards
StoneCold

 

[fusitexa]

metengr, gtaw, thanks. always learn a lot from you.
stonecold, i don't know the application of the product. but i can tell you cracking happend when it was being welded.
metengr, could you give me a simple explaination on how these cracks formed, always tensile stress effect? and how delta ferrite can resiste hot cracking to happen? thank again.

BR

 

[fusitexa]

as we can see that the width of crack in the outside of weld metal is larger than that of internal part of the crack. could that be a proof that there is a tensile stress which promote the propagation of the crack? according to the weld design, during welding, the internal part of the weld metal cooled faster than the outside, so there is a compress stress existed in the weld metal. and also, if there is a applied tensile stress existed, considering cooling situation, the outside/surface, could initiate a crack at a critical condition and this crack would propagte in the following further cooling.

i review a paper titled "formation of hot cracks in asutenitic stainless steel welds-solidification cracking". i am not finished yet, but i learned from the previous part of the paper that 316 has a susceptability to form hot crack, and its solidification mode is FA. and its ferrite number is 2.6-2.8. according the paper, 316L should be better than 316 considering the susceptbility. so metengr, why do you chose 316 as the filler metal?

in the paper, it also metioned backfilled crack, what does that mean, does that mean liquid crack? cracking is drived by applied strain in the paper by the way.

 

[metengr]

fusitexa;
My filler metal requirement would be 316L, as you mentioned. I must have missed the L when I typed the response above. The hot cracks are formed when there is little to no ferrite present during solidification of the weld region resulting in cracks/tears to the much lower strength austenite matrix. Yes, tensile stresses are involved to promote cracks/tears because of the type of partial penetration weld joint design and welding over a parting line. Contaminants in the parting line usually produce porosity or outgassing of the weld region versus a series of straight centerline defects.

In your current joint design with an autogenous weld, you have no option to add elements to promote ferrite formation. This was the reason for modifying your joint design to accommodate adding filler metal.

 

[fusitexa]

metengr,
thank again.