Stainless is much less conductive than carbon steel. Google thermal conductivity of metals.

If you saw my welds, you wouldn't want more advice from me, either.

thank you ill try that i am greatfull for any help

What filler metal/material did you use? 309?

yes 309 L or H im not shure but it is what the company uses on a day to day thing all materials were correct but my bends failed. the roots were solid and clean they looked great not the first test ive taken prob the 100th but i know alot and cant figure this one out.

How about the actual spec on the "carbon steel"? It's not a Cr-Mo plate or anything, is it? What about pre and post heat treatment?

You might be on to something there. What was the carbon content of the "carbon steel? what was the alloy?

milo

im not a metalergist, but on the carbon plate it was from a standerd off the shelf 3/8" structural steel. as of pre heating the plate ive never heard of anybody preheating such small coupons. i have a question. is there a way i can get this problem im having to expert welders and more of a veriety of profesionals. (no offence) but i was just curious. thank you.

You mentioned that you have welded 100's of stainless welds, but perhaps you have never welded NOR have had your welds tested with dissimilar. Your apparent lack of details/knowledge on "metallurgy" suggest you have never been tested before (no offence).

http://www.sperkoengineering.com/html/articles/Sage%20Advice%20on%20SWPSs.pdf

Variety of professionals I guess you are right, there are only 3 persons on this forum and we are all high school students.

Even after your offensiveness , I will try to help you out more - because you have not been helpful in return by not specifying details and by asking a very open ended question.

Download the Nickel Institute Document 14018 - GUIDELINES FOR WELDING DISSIMILAR METALS (1991) @

http://www.nickelinstitute.org/index.cfm/ci_id/11931/la_id/1.htm

and you will see the discussion on pre and post heat.

And another paper discussioning hydrogen

http://www.aws.org/wj/supplement/AREFAE_1/INDEX.HTM

This is the work of professional (and unfortunately doesn't seem like many are there)

We regularly get the activity done but not for such a thick plate (1 3/8 = 35mm thick) our activity is limited to a few cases of pipe or flange joints.

Had a informal talk with our welding engg.

- The welding is perfectly possible and feasible. But very complex.

- Whether proper pre-heat and post heat was done?

- The type of wire used (flux cored, solid ..), the Gas for MIG ?

- Did it pass Radiography? It must have failed on the carbon steel side ?

- 309 Electrode is OK.

- can only be done under strict WPS guidelines developed for the process. And as a foot note, If i have to do it, he will stand here and get it done but of course that i can not do in your case.

Let us wait for some one who has a WPS for it. For us, as I said, it is not tried out, so no WPS as on date.

BTW: is this a regular practice at his works? do those samples pass the bend test?

I am a metallurgist, and given that the plate was 1-3/8" in the initial post, and now it is 3/8", and given that you have not described the failure mode all that well so that we can diagnose if indeed the failure initiated adjacent to the weld at the HAZ, and the fact that you have just discounted the testimony of several people all of whom have inquired with best intentions about the use of pre or post heat, including one demonstratedly knowledgeable professional (Albeit gremlin) named sb who went so far as to ask his companies welding engineer, I 'm going to pass. It is pointless to attempt to help when no one is listening..

try http://weldingweb.com/

Maybe you can hear what they are saying.

Good luck.

milo

too much science is not good

I'm guessing a little. It may be carbon embrittlement due to chilling of the weld. Does the break look brittle? Have you tried preheat/postheat? The differing thicknesses may be too disparate without additional heat.

yes! i know about separating my tools because of contamonation. the company did not seem that concerded about it. i asked a few peaple. but i did use my own tools so i did separate them. i used ER-309 on the tig, and i started by walking the cup but could not continue because of comfort, so i had to free hand. Your the first true welder i got an answer from. most of them were scientists not really knowing what i meant. well i retook the tests fri. so i wil let you know of the results, (i think i got them this time). thank you.l

If he is welding mild steel to ss would a stainless brush help all that much mr. pipewelder?

One important question is did it break in the middle of the bead or the toe of the weld. This needs to be answered before you talk about heat and other problems. What position was the test taken in.

I agree with the part about knowing where and how the weld broke but although welding in different positions can make a weld more difficult the position should have nothing to do with why it failed IMO. It either was a good weld or not no matter what position it is welded in. Destructive bend testing can be a brutal way of testing a weld and I would rather take a test that was to be x-rayed on any day. Bending not only finds the indications it also puts them under a huge stress that usually makes them grow much larger when the coupon is bent. Actually if it breaks in the base metal the weld test would pass. I am assuming it broke in the toe of the weld being it did not pass and this is usually where it would break with MIG welding. Weld metal is always stronger than the base metal if the welding procedure is any count. Unless the poster is incorrect when he said it was a clean weld I would doubt it broke in the middle of the weld. Either way the advice I gave about using the appropriate procedure, electrode and welding parameters is sound and would apply to any weld.

well if it broke in the middle of the weld then he could have too much heat. If it broke in the toe he may not have hesitated on the sides long enough or the base metal was not hot enough. A mig weld sometimes can be manipulated to look like a good weld but not have any strength if volts are too low etc.

That's why Pipewelder told him to spray-arc. Too much heat in laying down a bead in short-arc transfer usually results in large beads that lack fusion due to turbulence in the puddle. Voltage applied to attain spray-arc modes will heat the base material more, and fuse with the deposited metal better.

Isn't short-arc transfer suppose to be much cooler due to the cycle that the arc is actually extinguished.Usually poor fusion is the result of the welder not leading the edge of the puddle with his wire. Let's be honest. With his lack of details in the first post it could be anything if the weld zone was not clean he would have had visible porosity guaranteed. That are too many variables. He could use a different shield maybe 10% helium that allows for a hotter arc on SS. And having had probably a thousand welds x-rayed it is much easier to pass the bend than the machine especially with migs tendancy for micro porosity.

I was assuming he used the normal tri=-mix gas for stainless steel MIG. It would have been a much easier test if he was using FCAW (flux cored wire with a argon/carbon dioxide 75/25 % shielding gas) Instead of GMAW ( solid bare wire MIG with Argon, Helium and carbon Dioxide tri-mix gas) In the old days we would have tested with SMAW (stick) and that was very hard electrode to master. With stainless he probably won't see porosity as much as carbon steel and it many times can be sub surface porosity. ER 309 tends to get have a gas hole occur instead of cluster porosity when it dose happen. Ther is an old welders trick where you can even run a E 309 on a carbon steel weld and it will fill in hot passI would think the weld coupon failed from lack of fusion instead of porosity because this is nearly always the case with stainless MIG. If you get right down to it though nearly all weld defects could be seen as lack of fusion in that it is not 100% metal in any particular void in a weld.