410 Stainless Weld Cracking

Date 10-07-2008 22:28

Hello. I had another post regarding 410 stainless and I appreciate the help from that one. I now have another problem with weld centerline cracking in welding 410 stainless.

Basically we have 4 90 degree segments that are roughly 3" thick and about 4 feet tall. They were put together to form a barrel. The outside vertical joints were welded using 309L. However the penetration was only about 0.120" (there was no weld cracking). The reason for this is that the welds are temporary only to hold this part in place while machining. Several tabs were also welded to the bottom of the barrel to fix it to a base plate to keep it level. Once the welds were finished, the inside of this barrell was machined. The cutter started at the top of the part and cut 1/2" into the part taking roughly 0.010" every revolution. So, this particular machining operation was going fairly quick. Now the part is off the mill and they want to weld the inside joints. This is the machined side. We grooved the joints out to about 0.150" deep because that's all we were allowed due to net part dimensions. We took a torch and pre-heated the joint until it reached 400 degrees F. We first used a 410 stainless SMAW electrode and the first weld we did cracked. We hogged the material out and used 309L - the welds still cracked. We welded 2 joints and they both cracked. The cracking occured shortly after the welding was finished as the joint was reaching ambient temperature.

We are not sure why this is happening but are looking at a few reasons. #1 - maybe we need to stick the entire part in an oven and pre-heat the entire part. #2 - maybe there is coolant in the joints from the machining process (however I would assume it would burn out as we torched the joint for a long time). #3 - since the part was machined on the inside at such a fast rate, maybe the material is now somehow work hardened and will not weld the same. #4 - the part needs to be stress relieved due to the machining process. #5 - since the OML is welded and the tabs are welded to the bottom, the part cannot contract/expand correctly to relieve the stresses during the welding, and this causes the centerline crack.

I'm not sure if any of these make sense. Any other suggestions as to why we could have cracking in this situation?

Thanks.

By 803056

Date 10-08-2008 12:18

The 410 stainless steel is a martensitic stainless steel (MSS). As you most likely know there are a few potential problems welding the material. A quick recap goes like this:
Air hardenable when cooled rapidly from austenizing temperatures (1600 to 1850ºF)
Best Welded in the annealed condition
Higher carbon content requires higher preheat (typically 400 to 600ºF)
Requires low hydrogen welding practices
May require PWHT to reduce hardness and likelihood of cracking

You stated you weld the outside of the "barrel" with 309 and you welded tabs at the bottom. You didn't mention the use of preheat. The material may be in the annealed condition as purchased, but you didn't state that fact, so I'm taking a leap of faith that it was.

The welding of the 3" thick MSS could have easily hardened the stainless because there is sufficient carbon present to cause it to air harden. You did not say you performed any PWHT on the barrel after the first welding operation so we can assume it is hardened as a result of the initial welding operation. The machining of the 410 MSS most likely involved the use of cutting fluids, either oil based or water based water soluble oil type. Cutting fluids contain all sorts of nasties when it comes to welding parts that have been contaminated with the stuff. Due to surface contamination, i.e., failure to post clean the assembly guarantees surface contamination and the failure to remove potential sources of atomic hydrogen. Did you bake the SMAW electrodes before using them? AWS D1.6 requires all stainless steel SMAW electrodes to be properly stored at 250 degrees (check the proper storage temperatures with your manufacturer). If you are using E410-15 they definately need to be stored at temperature because they use the same flux system as the typical E7018, i.e., limestone based flux.

Preheating to 400 degrees is too low for a material 3" thick and as you noted. Torch heating local areas is insufficient the maintain the proper interpass temperature. Thus, increased likelihood of hardening and cracking problems will result. Oven heating and the maintenance of the preheat temperature is recommended.

I suggest you read a copy of the book:
Welding Metallurgy and Weldability of Stainless Steel
J. Lippold and D. Kotecki, Wiley Interscience 2005

By the way, I had the pleasure of speaking to both of the authors at FabTech on Monday. Talk about rubbing elbows with the "Great Ones". Yea, I'm name dropping again!

As always the value of the advice you receive is worth exactly what you paid for it, so research this problem thoroughly before tackling this problem.

Best regards - Al

By Zeek

Date 10-08-2008 20:26

Thanks for the reply Al.

A couple more things were brought up that may have influenced this. I am learning that this material was annealed originally but was then bump formed into these segments without another annealing process afterwards. Therefore the material we are welding is in a cold worked stage.

Just to answer some of your assumptions on the last post.
#1 - You are correct, there was no preheat when we originally welded the OML with 309
#2 - You are correct, there was no PWHT after the first welding operation on the barrel - it went straight to machining.
#3 - The 410 electrodes we used were not baked out in an oven.

The part was put into the oven this morning and it took a few hours for it to reach 350. The part was removed and welded. It's currently cooling off, so we'll see if we still get centerline cracking.

Regarding Lippold's book - I actually do have that book as he was one of my professors in college. He's definitely a very smart guy.

Unfortunately, in this particular situation, these welds are temporary and they are rushing to get this part done. I'm not sure they want to preheat this particular part to 600, since a welder has to get inside it and weld. Hopefully these welds will not crack. Thanks again for your help.

Adam

By 803056

Date 10-08-2008 22:48 Edited 10-08-2008 23:11

I love welders, they taste like chicken if you cook them properly!

I believe the bending operation alone could cause the annealled SS to transform to hard martensite. I assume the bends are not in the area of the welds. That would make the welding operations nearly impossible without PWHT first.

Good luck. It's the quick temproary welds that usually lead to the problems!

Let us know how it works out, what works and what doesn't.

By the way, Ross Hancock says hello to everyone!

Best regards - Al