Welding heat treated 4130

[Guanton75]

If I have two 1/4" thick 4130 plates that I've quenched from 1600F and tempered at 900F. I then take these two plates and stick weld them together using a 4130 rod. Is the resulting weld likely to be stronger or weaker then had the two pieces been annealed in the first place. If it's likely to be weaker is it due to a more or less random heat treat resulting from the weld or weld related stresses?

I am building a replacement drum for our battle robot, Redrum (

http://www.teamentropy.com).

We hope to use 1/4" thick plate rolled to a cylinder with 1/4" "teeth" sticking out radially. Our nemesis has similar construction but is unheat treated so I am tempted to add this extra step to give us an edge but I'm worried about replacing the teeth because they will come off in combat. One option I've considered is to locally heat treat the teeth with a torch after assembly or repair.

Thanks for the help you offer now or in the past,
-Seth

 

[nousakmj]

A 4130 filler metal is intended to be heat treated. In the as-welded condition, the weld metal deposit and the heat-affected-zones (HAZs) will both have lower strengths and hardnesses than the unaffected base metal.
It is generally easier to weld annealed 4130 than a quenched and tempered 4130 -- you are less likely to crack the material along the HAZs. For your application, you would appear to be better off welding annealed material with the 4130 electrode and THEN heat treating the entire weldment -- you'll be giving up nothing in the area of the weld and you can tailor the temper cycle to suit your application.

Matt Nousak, P.E.
Senior Staff Engineer
Middough Associates Inc.
nousakmj@middough.com

 

[Guanton75]

I'd like to clarify, I'm worried about replacing teeth after a bout. I'm looking to avoid the cost of reannealing and reheat treating to weld on replacement teeth if possible.

Thank you,
Seth

 

[GRoberts]

Since your plates are only 1/4" thick, you won't have to preheat too much before welding, but you might want to get it up to around 200F before welding. After welding, whether it is welded in the annealed condition or Q&T condition, since you will definately need toughness, it should recieve a PWHT. This can be done locally though. PWHT is usually done at 25-50F below the previos tempering temperature. We do weld on Q&T materials similar to 4130 quite often, and as long as appropriat precautions are taken (mostly adequte preheat), it is not a problem. If you Q&T after welding, then you will want to use a matching filler metal such as ESAB 4130. Be aware though, that as a machined part, the dimensions will all change during the Q&T heat treatment much more than either a general or local stress relief. One way to avoid heat treatment after replacing teeth would be to overlay the 4130 material with a low alloy steel in ther areas that teeth would be welded to with an alloy that would not require PWHT, such as 9018M or 90T1-K3. The overlay areas (at least 3/16" thick) could recieve a PWHT, then teeth could be welded to the overlay without PWHT.

 

[nousakmj]

If strength isn't a basic requirement for the drum, but hardness on the teeth, i.e. how hard you can bite, is the issue, then why not use carbon steel base materials for the drum and "tooth" stub, and then hardface the tooth -- or for that matter, simply create teeth using hardfacing filler metals?
There are any number of hardfacing filler metals out there, from tungsten carbides to chromium-molybdenum alloys, that would give you plenty of "bite". You could shape the profile of the hardfaced tooth by grindingj -- both originally and when performing repairs. That would seem to be less costly and easier to do up front, and also easier and cheaper during repairs. Just re-hardface the tooth stub. Some nickel-base filler metals might also do the job.
What welding processes are available to accomplish this work?

Matt Nousak, P.E.
Senior Staff Engineer
Middough Associates Inc.
nousakmj@middough.com