Welding 400 series stainless

Date 05-08-2003 13:58

Both ferritic and martensitic stainless steels fall in 400 series. I’m not sure does martensitic stainless steels is magnetic or not and if somebody tell me the answer I would like to appreciate him/her.
And your answer, ferritic stainless steels can be welded very well by austenitic fillers but keep your heat input as low as possible.

By GRoberts (***)

Date 05-08-2003 14:35

If the tube is martensitic or ferritic, the magnet should stick just as well as it would to carbon steel. If it is only slightly attracted, I would guess you have austenitic tube there, probably 304. 304 is the most susceptable to martensite transformation during cold working. The strain placed on the tube while forming the sheet into a tube probably transformed some of the austenite into martensite which you are picking up with your magnet.

By Lawrence (*****)

Date 05-08-2003 14:48

Good point!

I've seen something similar; We discovered a batch of 347 (AMS5680) that responded to a magnet. After freaking out and pulling the stock off the shelf, analysis determined that the recipie was indeed correct. What happened was this; the welding wire while being drawn down to 0.035 inch dia. was cold worked to the point that it became magnetic.

By George-kh (**)

Date 05-08-2003 19:11

Grobert
I found you an expert in stainless steels. So let me ask a question.
As you know stainless steels are susceptible to precipitation of chromium carbides in the range of 400 to 800C. On the other hand martensitic stainless steels must be preheated before welding and if carbon content be high enough they must be PWHT after welding. Certainly, because of preheating and PWHT chromium carbides will be precipitated. Is it right? If so, after welding the HAZ and maybe entire of base metal because of PWHT can not be a stainless steel. What can we do for this problem?

By GRoberts (***)

Date 05-08-2003 22:22

It is strange that carbide precipitation problems are seldom mentioned in welding literature regarding martensitic stainless steel. Far from being an expert, I can only give you my observations.

Since martensitic stainless steel has only moderate corrosion resistance as compared to austenitic stainless steel, I would imagine that carbide precipitation would not be as important since the environment is not a severe. The most common uses for martensitic stainless are high temperatures, where oxidation and strength are the main concerns, and high hardness applications where moderate corrosion resistance is required. Of course an austenizing heat treatment after welding would improve corrosion resistance if corrosion resistance is important and other stainless steels are not suitable. Also, not all martensitic stainless steels require preheat. Cast Stainless CA6NM, and forged stainless F6NM (much less common) can be welded without preheat. PWHT is recommended though in all but a few cases, and it can be beneficial to heat it up quickly and water quench.

As far as the mechanisms involved, this is a guess, but I think that microstructure has something to do with it. Since austinite has a much higher solubility for carbon than ferrite or martensite, the austenite can retain the carbon in solution to room temperature, then when heated to the sensitization temperatures, the increased mobility of the carbon allows it to diffuse to grain boundaries where it combines with chrome because chromium carbides are a more stable form than free carbon (lower free energy). Martensite on the other hand doesn't want to retain carbon in solution, so if carbides form, it is probably during cooling after transformation from austenite, and the carbides are dispersed thought instead of in one place. So when welding, there would be less free carbon in the matrix available for precipitation, and the carbides that have already formed do not deplete one specific region. Does anyone else know the mechanisms as to carbon reactions in martensitic stainless????

One thing I do know though is that for high temperature martensitic alloys, they sometimes add vanadium and tungsten, which preferentially form carbides over chromium as a strengthening mechanism.

By boring

Date 05-08-2003 22:48

Wow,
I learned a lot in this string!!! Lincoln makes a rod for joining 304, I guess I'll go with that.
Thanks for all the info.!

Mike

By medicinehawk01 (**)

Date 05-17-2003 15:23

Try 308L rod for welding this frame as I believe you are using some form of 304 base material. Because the magnet only has some attraction (and not wanting to actually stick to the material) then 308L is the welding wire you want to use as you can get it in stick or tig rod form. The mechanical properties of this welding wire are more closely matched than any other rod.