stainless filler rod with mild steel

[jjense15]

I am tig welding mild steel tubing with stainless filler rod (was told by a welding engineer that I could do this). I had been getting some contamination using mild steel filler rod, and was told that the stainless sort of acts like a cleaner. Does this make sense? The welds look perfect, but I am wondering if there are any structural issues when using the stainless. I talked with another experienced welder and he never heard of doing this.

Thanks,
Jason

[ASKANDY]

Jason,
Kind of depends on the use of your weldment. There are better ways to assure good welds. In short, you are trying to mix an apple and an orange. Yes they are both fruit but the resulting bead integrity will give you a lot of strength and little or no elongation %. Normally you would want to match base metal characteristics to the filler. Tensile and Elongation requirements. Your SS filler has a much higher Tensile and may cause cracking under load. I most definitely would NOT use this filler for any chassis or roll cage construction. Those items need to have higher elongation %s(stretch) incase of impact. The bead must stretch with the basemetal. Your beads will look great with the SS, but we are after performance, not looks. Or maybe your applications is strictly visual. You will need to evaluate that.

Thanks for the question and welcome!

Andy

[jjense15]

stainless on mild steel

Thanks Andy. I'm concerned now, since my project is a back half on a drag car and the work is just completed. Is there anything I can do now, grind the stainless and then go back over with the correct filler? The last thing I need is to have ladder bar brackets breaking off the rear end, etc.

[ASKANDY]

It was definitely mild steel right? Not Chrome-moly? If it was CM and not mild steel, the SS filler might work. It's still not the best but at least the base metals would be a better mix. Otherwise, I too would be concerned. Here'a a little story about a major NASCAR team that TIG welds their chassis. Not naming anyone but they thought the same as you. Welded 4 new chassis with a SS blended filler cause it looks great and flowed nice. Went to test at a track and after teardown later in the week found stress cracks. Hence, 4 scrap chassis and a change back to ER70S-2 and ER80S-D2 fillers. This race team was given the proper filler recommendations by me but decided to take the advice of the shop forman who was hired from an INDY car team. Indy cars do not use mild steel on anything. They performed destructive tests and came to the conclusion that I was right all along. Sometimes "looks good" doesn't perform good.

You may be fine on some of the chassis points but I would rather you remake the ladder bar and attachments as that will see a regular amount of fatigue and impact with the race track.

Sorry.

Anyone else with EXPERIENCE on this might offer an additional view or alternative fix. At the very least, Stress relieve the welded areas.

Andy

[jjense15]

Yes, mild steel. Looks like I am going to cut everything up and start over. Makes me sick to my stomach! I know who I WONT be going to advice from now on. Better to get right though. Thanks for the education Andy.

[arcdawg]

i have been GUILTY of usIng stainless rod on mild steel rod. it flows so much nicer then mild steel rod. but doing some thinking / resarch the chemical makeup of any stainless compared to mild steel is so diffrent from each other, i guess that its the chromium, correct me if im wrong,

i have ran into poristity with mild steel and rod even after thtoughly cleaning base and filler and having proper gass coverage

so after much babbling what causes this ? and how do i cure this problem...

thanks for the eye opener andy.

i dont feel bad now knowing that nascar guys SREW UP TOO !!

BRIAN

[HAWK]

Andy,

Let ask a question: A few years back I had to to get a 6G, 3/4" plate certificate for a contract job. We only ran vetical uphill progression and overhead which covered all postions. There were 2 coupons: (1) Mild steel to Stainless A304L and (2) Mild steel to Mild steel. The procedure called for 309 SS stick for both coupons. I never really gave it much thought and did as asked. Both coupons were bend test only. I wonder why the choice of SS 309 for joining A36 to A36. Any ideas? It really makes me wonder after reading this post. Yes, this was SMAW rather than GTAW, but the same scenario as far a filler is concerned.

[ASKANDY]

I would agree. Not sure of the application but it purely must have been for tensile or burst not impact or vibration. Ya think?
I could think of much better rods to use than that on the mild steel. Could be number of things to, like they want to see if they can get away with purchasing one type of rod, or they thought that with the thickness of plate the 309 would prevent quench cracking, or they too were under the impression that the strongest bead wins. All I can say is that with tubing like race car stuff, you will not get enough base metal dilution to give the toes adequate fusion for any decent amount of elongation.

Thoughts?

Andy

[Rob]

Jason,

Sorry to hear of your misfortune, but better than hearing of a suspension failure on the big end of a drag strip. Take Andy's advice and make your chassis safe.

To Andy/Hawk,
Another thought on Hawk's experience with the stainless rod requirement is that the heat input per total weldment volume would have been much greater on 3/4" plate, which means cooling rate would be reduced greatly. The result would be a broader, less pronounced heat affected zone. Since it works almost like a post heat, the weldment would have fewer heat-induced stress risers.

Thinner material such as chassis tubing requires less heat input and it's very localized. Heat affected zones are narrow and pronounced, which is a serious stress riser, and makes stress relieving more important. Stress relieving is especially important on mild steel since it's more prone to hardening than low alloy steels, which is one reason chromoly is such a good material for high strength weldments in thin-wall structures.

There are a lot of variables involved in creating a welding procedure. Change any variable and the results will be affected, sometimes a little, other times a lot.

Rob