HELP-Weld Hot Cracking

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I have been trying to weld hot rolled mild to stainless at work. using TIG at 175 amps. and 309L rod.  and i get hot cracking at the end of the crater and also throughout the weld.  we did try switching the hot rolled mild to pickiling oil mild and it works perfectly but the blue print calls for hot rolled to be used and they wont let us change it to pickling oil mild, we need to find a way to stop the cracking using the hot rolled  if possible.  please help . thanks alot
Reply:Are you getting rid of the scale before you weld it?
Reply:Is the cracking right down the centerline of the weld?  That would be typical hot cracking.  Hot cracking in SS is related to low melting temperature tramp elements such as sulfur and phosphorus, and since they are they last to solidify, they get pushed to the weld centerline and leave a weak crack path that the weld contraction pulls apart.  This is more of a problem with fully austenitic weld metal, since austenite has a low solubility for sulfur and phosphorus.  Some ferrite in the weld will help keep the S&P in solution, and help prevent hot cracking.  I think 312 SS filler will help promote more ferrite in the weld than 309.There was a great article in the September AWS welding journal by Damien Kotecki (spelling?), a past AWS president, Lincoln Electric expert on SS, etc.  As I recall he addressed a problem just like yours.   The dilution of the weld metal with the CS did not add enough ferrite forming elements (Fe, Cr, Mo, Si) to offset the austenite forming elements (Ni, N, C, Mn).  You'll have to check the details yourself.This brings to mind, that since nitrogen is an austenite former, you could be promoting too much austenite by simply not having adequate inert gas shielding, since the atmosphere is around 78% nitrogen. Also, weld chemstry is a direct funtion of how much CS and SS base metal is melted, and how much filler you add.  Also as you noted, the chemistry of the CS may be a factor, and for that matter the chemistry of SS are you welding.  Another method of CS of SS welding is to butter the CS with SS first, probably 312, then weld the joint with 308 or 309.So stuff to think about.  Check out the WJ article, you can get it online at AWS.org if you're a member.
Reply:yes i am  grinding off the hot rolled scale and it doesnt help.  i am  def gonna try using 312 and see if that helps,  but i definately just thinks its  some of the components of hot rolled mixing poorly with SS, becuz the pickiling oil mild works beautifully,  so thansk alot pulser  ur advice has  given me alot to think about and to try out . i just wish the company were building these for would let us use pickiling oil  it jsut makes everything so much easier.  and i dont have access to that article ur talking about , but thansk anywyas. im gonna print off ur reply and show it to my boss on tuesday .  again thanks alot