Stainless filler to TIG 4140?

[Investigator]

I'm making a steady rest for my 12" Logan.
I'm starting with a cut off of 4140 basically 4.75" OD, 3.25" ID.
That I will clean up and make pretty on the lathe, the weld a base to it with support of hot rolled steel.
I'm familiar enough with 4140 to know welding can lead to cracks in the HAZ. I'm planning to tack it together and put the whole assembly in the oven to 350*F. Then weld, and then back into the oven, letting it sit at 350 then simply turn the oven off and not open it for several hours.
The welds won't need to be machined after. I don't need any special strength from the 4140, it's just what I have to work with.

So, finally my question.... welding. I can stick weld it with low hydrogen rods, or TIG weld it with stainless, likely 309. Other than a slow cool down I can't post heat treat. Is stainless my best option? If not what would you suggest?

 

[Aukai]

Interesting project.

 

[den-den]

Low hydrogen stick or TIG with 70S-? should be good enough. Your pre-heat and controlled cool down is important, 309 filler should work but is not necessary. Higher strength filler than 70S is available but it doesn't sound like you need it.

 

[cathead]

I cast one vote for stick welding it.

 

[Ulma Doctor]

+1 on 309 filler

 

[machPete99]

I think 4130 is easier to weld, but needs similar process.

 

[MrWhoopee]

Another vote for 309. I've gotten to where I use stainless filler on all steel (and even CI) unless it needs black oxide.
It just flows nicely and doesn't crack.

 

[Daligas]

I have had really good results TIG welding 4130 using ER70S-2 filler.

 

[G-ManBart]

I was considering using 4140 for a project and looked into the pre/post heat recommendations. Everything I saw suggested 400*F for pre-heat and an immediate post-heat from 1000-1200*F so I'm not sure the post-heat of 350*F will help you much.

 

[verbotenwhisky]

I'm making a steady rest for my 12" Logan.
I'm starting with a cut off of 4140 basically 4.75" OD, 3.25" ID.
That I will clean up and make pretty on the lathe, the weld a base to it with support of hot rolled steel.
I'm familiar enough with 4140 to know welding can lead to cracks in the HAZ. I'm planning to tack it together and put the whole assembly in the oven to 350*F. Then weld, and then back into the oven, letting it sit at 350 then simply turn the oven off and not open it for several hours.
The welds won't need to be machined after. I don't need any special strength from the 4140, it's just what I have to work with.

So, finally my question.... welding. I can stick weld it with low hydrogen rods, or TIG weld it with stainless, likely 309. Other than a slow cool down I can't post heat treat. Is stainless my best option? If not what would you suggest?

I found these 2 articles helpful at one time and book marked them. Article 1 & Article 2.