Stainless Steel to Mild Steel.

By jon20013 (*****)

Date 02-23-2006 13:27

Sounds like your on the right track with either the 309 or 309Mo for the dissimilar metals joint and it should also be okay for the 304 / 304 work.

By MDG Custom Weld (***)

Date 02-23-2006 17:16

You are very close, but I would recommend that you use 309L to go along with the L in the 304. The L is for low carbon. We manufacture OEM fabricated manifolds and 304L to carbon steel is almost standard for all 300 series fabricated manifolds. The 316L will work, but the Mo really only helps in the watercraft applications for better corrosion resistance. Also, 316 has about 3-5% less Cr and over 1% less Ni than the 309L

By JBOLDUC Date 02-23-2006 17:56

For TIG welding of carbon steel to stainless, one thing which is probably as important as the filler metal selection is the dillution. In dissimilar welding, the resulting weld is a new alloy composed of X%CS + Y%SS + Z%filler metal. The % are controled by the dillution. If you have too much CS and not enough SS filler metal, you will end-up with martensitic weld (hard & brittle). With other welding process, the dillution is always relatively low and limited by the fact that you have to melt the electrode to make a weld. The use of 309 filler metal (more nickel and chrome to compensate for dillution) is then enough to avoid the problem. With TIG however, the dillution can be as much as 100% if you want(no filler metal). To avoid problems, keep the dillution (penetration) low on carbon steel side and make sure to apply 309X filler metal to compensate for the dillution.

By awill4wd (**)

Date 02-24-2006 08:11

Thanks for all your information everyone, it's pointed me in the right direction for sure.
Regards Andrew.

By aevald

Date 02-24-2006 08:32

Hello jboldduc, I really appreciated your response on this thread. I hadn't quite looked at the dilution issue in the sense that you explained it here. I tend to be a nuts and bolts sort of person and your post was very concise and easily understood. I would imagine a great many others would not have thought of the difference with GTAW when compared to other welding processes in this case or others similar in nature. Thank You. Regards, aevald

By - Date 03-03-2006 15:28

Your response is well taken, but may I offer some comments also. The martensitic structure of a SS to CS weld is determined by the carbon content of both base metals and the filler metal. For example, even when welding a 2205 Duplex material with ELC (extra low carbon) to virtually any CS using a 2209 Duplex filler metal, martensite will be above the recommended hardness for the SS side of the weld metal regardless of the welding process used. Using a 309 filler metal would promote more martensite than if one used a 309L filler with the lower allowable carbon content. The 309 filler metal, with the higher nickel and chrome, is used primarily for welding SS to CS and is preferred to compensate for the difference in thermal expansion and contraction during the welding process. I respectfully disagree that using a 309 filler metal to join SS to CS will eliminate the formation of martensite. The degree of martensitic formation would be determined, as you said, by the dilution but moreso by the content of carbon. That is why a PWHT is used...to soften the martensitic structure and relieve any stresses attributed to the welding process. From a metallurgical standpoint, autogenous welding (no filler metal) is never recommended for joining SS to CS.

By terkivatan Date 03-03-2006 07:39

in our project electrode classification is : ASME/AWS A 5.4 309 MoL-16
as far as i know, this type is suitable for dissimiliar metal joint.i want to learn if i use 309 MoL-16 in ss to ss welding, what kind of welding defects will occur? thanks.

By - Date 03-03-2006 16:02

A5.4 is an ANSI/AWS (not ASME) Specification for Covered Electrodes. The 309MoL, whether it is the -15, -16, or -17 coating, is primarily used for joining SS that contains moly to CS. Normally, the 309MoL is also used to join dissimilar grades of stainless steel. I.E., 304 to 316, 316 to 2205 Duplex, 316 to 254 SMO. Although it can be used to join SS to CS, it is also used to join stainless steels that contain moly to other stainless steels that do not contain moly. The moly offers added pitting corrosion protection under most corrosion environments. A urea environment is a case where moly is more detrimental than beneficial. But, to specifically answer your question about what defects you will incur if you use 309MoL to weld SS to SS is.....probably none.