Welding 4130 chromoly with a 400f Preheat 

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A hot job came in the shop the other day...

and it involved tig welding some pretty thick chunks of 4130 chromoly.

my machinist friend and job shop owner needed a thick piece of 4130 chromoly steel welded in order to meet a customers deadline.

So I thought I would bring you along with me.

It was a simple job, but there are still a few things to talk about...

like...

Filler metal selection for tig welding 4130 chromoly, preheat, and more

A quick talk with my friend and I learned that this part would be black oxide coated after welding and stress relief.  (I made a video a while back showing the black oxide process)

That meant that I needed to weld it with a rod that would respond to black oxide coating.

I might have chosen an ER309 filler for this job but ER309 filler metal contains too much chromium and will not blacken the same as the 4130 base metal.

I also learned what the part does in service. and that it will be load tested to 900 lb.

900 lb is not that much for 2 - .250" leg fillet welds much so that was not really a concern as far as matching filler metal to match the strength of the base metal.

And, the part was only going to have a furnace stress relief type heat treatment ...not a strengthening heat treatment....so using 4130 filler material was not a requirement.

So I chose er70s-2. and a 400f preheat

er70s-2 wire will blacken, and will provide a ductile weld that is unlikely to crack.

I used 2 passes on each side to meet the .250" fillet weld requirement on the drawing....and I kept the heat above 400f during the whole welding operation.

Then I reheated the entire part and let cool slowly to room temperature before delivering the part.

Welding Procedure for Tig Welding 4130 chromoly

Base Material Type/Thickness. 4130 chromoly / 1-1/4" thick


Prep Method - machined surface, acetone wipe only


Filler Metal Type/Size - ER70S-2 3/32". (32mm)


Tungsten size and prep 3/32" (2.4mm) 2% lanthanated blunt taper 60 degree


Gas Type and Flow Rate - argon 25cfh


Cup size #12 clear furick cup


Current/Polarity 160-170 amps DCEN


Length of Arc. - 3/32" (2.4mm) or less


Angle of Travel 15-20 degree


Manipulation/Technique - move, pause, dip for first pass, lay wire wave second pass


Speed of Travel -6-7 inches per minute

preheat - 400F min

Similar project with AISI 4140 and preheat

grab a tig finger at weldmonger.com

A few years ago, I welded a part for this same job shop owner made out of 4140 steel.

4140 is very similar to 4130 except that has a bit more carbon content and therefore sometimes requires a higher preheat.

In this video, I used a 500f preheat.  First, I warmed the part up on a propane cooker, and then I used a rosebud torch to reach over 500f.

These parts were a tight fit so I heated the part with the hole first, then inserted the round part and heated it all to around 550f so that I could be sure it was at least 500f before welding.

I kept the temp up to 500f until welding was done, then reheated and let cool slowly.

I chose er70 filler rod for these parts also for the same reasons as the 4130 part...black oxide coating, and because the strength was taken care of with smart design.

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