Welding 316L to A36 2

[steris]

Hi All,

In our application we are MIG welding an A36 bar to one side of a 1/4" thick plate of 316L. The side of the plate without the bar is exposed to a corrosive environment. Currently we have two approved processes for joining A36 to 316L - one uses a 316L consumable and the other uses a 309L consumable. My understanding is that 309 is generally better because it contains a higher chromium content and acts as a better transition metal to help prevent chromium depletion from within the welded stainless part. My question is when should one consumable be used at opposed to the other. Is there a situation where you would want to use 316L wire to join a P1 material to a P8 material? If the main goal is to preserve corrosion resistance of the 316L plate in the HAZ, is there a better consumable than 309L? Thanks for the help!

Best,
Steris

 

[kingnero]

I would start with a Schaeffler / De Long / WRC 92 / Bystram diagram, and see how that turns out.
What is the thickness of the 316L part? What is the dilution on either side? What's the weld detail?

 

[metengr]

Typically, the consumable for joining dissimilar metal - austenitic stainless steel to carbon or low alloy is 309, not 316L. The 309 provides the necessary dilution to avoid solidification cracking along the austenitic side of the weld and reduced harmful martensite in the weld fusion zone, on the ferritic side of the weld.

 

[metengr]

.....Exposure of the 316L plate to the corrosive environment will be on the side opposite the weld so filler metal selection is based on what I mentioned above. For the side of the plate exposed to corrosion, I would remove the heat tint after welding to ensure maximum corrosion resistance of the 316L.

 

[steris]

Kingnero - The 316L plate is 1/4" thick. The weld is a 1/4" fillet. I'm not sure what the dilution ratio is. How would the dilution ratio affect the filler metal specification?

Metengr - Thanks for the replies! We remove the oxide that forms on the non-welded side with a mechanical polish followed by a pickling/passivation process. I know that by using 316L base and 309L filler the reduced carbon content will help prevent chromium carbide precipitation. I have read some sites that talk about annealing/stress relieving to help maximize corrosion resistance. Do you have any thoughts on this or other means to further increase corrosion resistance?

Thanks for all of the help!

 

[metengr]

steris;
For DMW joints, your best bet is to keep heat input low to reduce sensitization and to use 309L for service temperature at or below 700 deg F. For service temperature above 700 deg F, I prefer a nickel-base electrode. Second comment, you are better off leaving the DMW in the as-welded condition. A proper solution treatment for austenitic stainless steel will affect the carbon steel material.

 

[wegm]

Steris,
With regard to your question for annealing/stress relieving, please have a look at SFA-5.4, A7.12, E309L that states: "Embrittlement or cracking can occur if these dissimilar steel welds are subjected to a post weld heat treatment or to service above 700 degree F". So, as Metengr told, either you shall use E309L without PWHT or in case that you shall perform PWHT or it is for high temperature application you shall use a nickel based consumable (e.g. AWS 5.14, ErNiCr-3)
Please have a look at this link:

http://www.weldinguide.com/gdanastasiadis/viewtopic.php?f=5&t=32

regards
wegm

 

[steris]

Hi Wegm,

Thanks for that information! I wasn't aware of that PWHT could cause cracking in the joint. Just one of the many reasons I love this forum. Thanks so much!

-Steris