Need help welding heat treated steels

[Retired Gunsmith]

For about 30 years, I have been working on M-1 and M1A rifles. One of the tasks is to weld a recoil lug onto the rear of the receiver. I had a certified welder and he developed the process with the assistance of the Metallurgy Department at his day job. He commented on the process several times, but I never wrote it down. He died suddenly, and I am now trying to remember/recreate the process to work with a new welder.
The receivers are carburized 8620, the lugs are 1018, rod is Linde 65, this I know. My memory of the procedure is to tack the lug in two corners, preheat to 800degF, weld the lug in one pass on each side and then water quench. We had done several hundred receivers, without any failures and I know the process worked. Mostly, I am looking for validation that I remember the process correctly.
Can you assist?

 

[MFAMET]

your preheating and water quenching practices appear good. Just make sure the welding temperature does not exceeds 1000F during quenching. These two dissimilar(1018 and 8620) metals may not cause severe galvanic corrosion issue due to the light difference of electrode potentials.

 

[mfgenggear]

Retired gunsmith
Generally it's not recommended to weld on carburized surfaces. Are you certain that area is carburized. And Is it a non critical area.

The temper of carburize is low approximately 300 degrees f. To prevent cracking, the area welded
Needs to be drawed back. Soften, and the steel
Needs to be preheat at 300 degrees f before welding. Depending on the depth of the case, it would help to grind some off. To prep for weld.
But at best this is a tricky weld, and is prone to cracking. So no guarantee. And your are taking responsibility.

See link

http://www.interlloy.com.au/our-products/case-hardening-steels/8620-case-hardening-steel/

 

[kingnero]

I'm not sure I agree with the tacking before preheating, even though neither alloy has a tendency to harden excessively. But the carburizing treatment might do so!
The 800°F (over 400 °C) seems very high. Do you have an idee of the carbon content on the surface?
Also, a quick google says that Linde 65 is an oxy-acetylene filler. Shouldn't be used for GTAW, but I don't know the Linde products, so that might be incorrect. Either way, any common ER70S-x rod will most likely be fine. A 307/309/312 filler might also be an option, depending on the actual chemistry of the carburized part. But you have a validated (by experience) methodology, so no reason to change.

 

[TugboatEng]

Silver brazing is often used to join hardened steels.

 

[Retired Gunsmith]

Gentlemen,
Thank you for the prompt and helpful replies.
mfgenggear- Has helped me remember that we would grind a bevel into the area to be welded, to reduce the available carbon in the bead.

kingnero- May be correct about the preheat temperature. 350-400F does seem more realistic, the 800F was a memory of something I thought I heard many years ago. The Linde 65 rod came from the Metallurgy Dept at Garrett Airesearch almost 40 years ago. I cannot comment other than it has worked all this time. Hatcher's Notebook says carburizing was .012-.018 depth and Rockwell D 59-67, but doesn't specify actual carbon content.

Any other info will be appreciated.

 

[MFAMET]

In order to avoid the cracking during welding and to alleviate the effect of(residual) thermal stressing after quenching, 800F pre-heat is an appropriate process. But it could also reduce the hardness of carburized workpiece in the heat affected zone by the formation of more tempered martensite. You could try both ways (preheat at 350 F or 800F) to see the best results.

 

[mfgenggear]

800 degrees f will temper the hardness.
Guesing probably HRc 40

Carburize is normally 300 degrees f
Temper.

 

[MFAMET]

I though we were talking about the pre-heat prior to welding for already carburized parts instead of the tempering during the manufacturing processes.
The preheat itself should take much shorter time than tempering. So, the hardness dropping may not be necessary profound.

 

[mfgenggear]

MfAMET
Yes it's about the preheat, it should not go above the temper. I run test
There is an OG trick to carburize all over and temper the carburize area to HRc 40, then machine away some of the excess stock. The case maybe HRc 40 but the core hardness really drops.
Could be dead soft less then HRc 10