Dis-similar metal issues?

[radkins]

I need to weld a short extension to the tang on my receiver project (4140 material) and I was wondering about coloration problems with the bluing? I have the equipment to do this properly and I have been a welder for many years so procedure is not a problem nor is heat control to protect the main part of the receiver from heat damage, my question is will using ER70S wire or an equivalent rod for Oxy/Acetylene cause a mis-match of the welded area when the time comes for bluing?

[JCHannum]

There is a good chance that it could cause a difference in the bluing in the weld area. Bluing itself will vary from job to job as well as material to material and is not always predictable.

You can mimimize the chances by keeping the gap as small as possible, V-ing out the backside and putting most of the weld there rather than on the front where it will be more visible if there is a difference.

[38_Cal]

Not familiar with the wire/rod you're looking at...will it blue? Lay a few inches of bead on some scrap and file it smooth, then try cold blue on it. You may still have color differences between your added-on part, the weld and the action. Rust bluing will often eliminate/minimize the differences, though.

David

[rolland]

Brownell's has a 3 1/2 % nickel rod that works very well with 4140 and "normally" blue up nicely. You might try some of that. I have no idea what ER70S is so I could not comment on how it compares.

[JCHannum]

Brownell's has a 3 1/2 % nickel rod that works very well with 4140 and "normally" blue up nicely. You might try some of that. I have no idea what ER70S is so I could not comment on how it compares.

ER70S is standard TIG, MIG and gas welding rod for mild steel. The S indicates silicone content and it has a copper plate, either of which could cause bluing problems.

The Brownell rod works nicely, but is expensive. You might check for a comparable rod at your local welding supply.

[radkins]

ER70S is standard TIG, MIG and gas welding rod for mild steel. The S indicates silicone content and it has a copper plate,

[either of which could cause bluing problems].

That is what I was wondering about, guess I will scrap that idea.

Last night I was drilling a 7/8" hole to 1" in another piece of 4140 I am using for a shaft coupling and I noticed some really heavy "curls" coming off this, possibly these could be used as filler for TIG welding? :confused: Also I will check with Brownells and see what it is they have.


Thanks

[Mike Hunter]

Two issues you need to deal with when bluing welded parts:

Steel differences, all steels do not take blue the same, normally I deal with older frames made out of low carbon steel, I have had the best luck using like material for filler.

Heat from welding will cause localized hardening of the material esp with thru hardening steel such as 4140. I’ve found annealing the parts after welding really helps.

Mike

[markkw]

ER70S6 is going to stand out like a big red clown nose, it'll blue but not to the same color as the 4140. TIG is the way to go and use 4140 filler if needed. Heat is not only going to spot-harden/anneal but will also cause issues with bluing in the HAZ (Heat Affected Zone) and can also raise hardness issues on either side as well as within the HAZ that can pose mechanical safety issues depending upon the service duty of the part. Yes, it can be done but be sure you know how to do it properly so the end product is safe.

[radkins]

Safety is not really an issue here since this is just a short extension of the tang and, with control measures, the heat will not affect the main part of the receiver at all. I used the heavy swarf from the drilling operation as filler metal and welded it using Oxy/Acetylene so the filler is a perfect match having come from the same chunk of 4140 as the receiver. I then used the torch to enlarge the HAZ slightly and create a gradual transition of the affected metal being careful not to let it creep into the main body then cooled it slowly, after that I reblued using the temporary cold bluing and there appears to be no color issues. However I am aware that cold blue is vastly different than the finial hot blue process so I guess I have no choice but to try it and hope for the best.

[Bob Ford]

Radkins

From your description I think the bluing will turn out fine and I doubt very much that you have done any damage. The tempering of the action material was close to 1,000° to achieve R C 30.

Bob

[markkw]

Radkins

Sounds like a winner, I don't think you'll have any problems with the blue.

[radkins]

Thanks for the encouragement!


Just out of curiosity since I have no reason to be concerned about my receiver but while welding that small piece I was wondering how hot 4140 pre-hard has to get before before the heat treating would be ruined?

[Bob Ford]

Radkins

Read my last post!
Bob

[radkins]

It would have to reach close to 1000 deg then before the heat treating would be affected? I was just unsure if the HT specs could be changed significantly at a temperature well below the range it was taken to during the treating process.

[Bob Ford]

Radkins

My Machinery's Handbook 21first edition page 2123, standard steels chart for 4140.

tempering temperatures Hardness number

400° 510
600° 445
800° 370
1000° 285
1200° 230

Bob

[radkins]

Thank you, that one just went into my notes!