Metallurgy Question for the experts...

[tobnpr]

So many terms used in metallurgy, and it's fairly complicated so I'll try to phrase my question/info I'm seeking in a way that makes sense...

I weld (MIG) a lot of bolt bodies for the Mosin-Nagant. Dozens per week.
Unlike the Mauser, the MN does not have an integral bolthead- so the concern about heat transfer affecting temper of the bolthead lugs doesn't exist.

However, there may (or may not) be an issue of "wear resistance", as relates to the cocking cam at the rear, and front notched section of the bolt body that engages the bolthead to rotate it into, and out of, battery.

This is not an issue of "strength", or "hardness", or "brittleness", in my non-expert opinion, because there is very little in the way of external forces applied to these parts.

I use a simple, aluminum heatsink that I insert into the bolt body "just because", but to the point of my question: I have been unable to find with my "Google-fu", the temperature at which steel becomes "softened" (don't know if that is the correct technical term) and it's wear resistance is affected.

I've done over 1,000 of these, have had two weld failures (two too many- but they were at the beginning), and never an issue related to wear brought to my attention by a customer.

But as my Daddy said long ago- anything worth doing, is worth doing "right"- so I'd like to know what this critical temperature is. It will be simple enough for me to check both ends of the bolt body after welding with my IR thermometer to see what I've got. The MIG process goes very quickly and the steel never gets red hot, so I'm probably overthinking this, just want to be sure I'm turning out the best product possible.

Edit to add: Bolts are allowed to slowly air-cool. No quenching with oil/water, wet rags, etc...

[BobCat45]

You are not screwing anything up doing what you are doing.

To soften the steel, assuming it was heat treated in the first place, you need to heat it above the temperature at which it was tempered. For many common steels this will be in the ballpark of 1,000ºF - tool steels much lower, maybe closer to 5-600ºF. Depends on what the steel is and how it was processed.

Carbon and low alloy steels (and tool steels - different animal) are strengthened (hardened) by austenitizing (heating above roughly 1350ºF - depends on carbon content), quenching (in water or oil - depending on carbon and alloy content and section thickness), then tempering - re-heating to a moderate temperature, well below the austenitizing temperature. And (usually) air cooling - the only reason people sometimes cool more rapidly from tempering is to avoid long dwell times in intermediate (so-called temper embrittlement) temperatures - applicable to very thick sections. Tempering temperature and time depend on carbon and alloy content and the purpose to which the steel will be put.

Go to http://www.dtic.mil/dtic/ and search (upper right) for "heat treatment iron and steel" without the quotes.

The first hit should be National Bureau of Standards Monograph 88 - Heat Treatment and Properties of Iron and Steel. It is the clearest, most succinct explanation I've seen, and will clarify lots of things if you have the patience to read it.

But, unless I'm totally misunderstanding what you are doing welding these bolts, I think your procedure is proper and you have nothing to worry about.

[Dixie Gunsmithing]

Generally, just from welding, you'll only see temperatures high enough to harm temper close to the weld, on either side of it, which is the heat affected zone, or HAZ. There, you can see the welded steel turning from a dark gray, at the weld, to blue, then brown, and finally yellow, on both sides, before there's no color change at all, which means that nothing past the color change was hot enough to be affected. You would have to get a bolt handle really hot, and keep it there for a good amount of time, for enough heat to be transmitted, to where you would see the steel start to change color into the tempering ranges, and especially spread to the bolt itself.

One could mark the top of the bolt handle, with a 300-350 degree F. Temple crayon, and watch for it to melt. I highly doubt it will, but if it did, that would be a sign that you have reached about the highest you can go, before getting into the tempering range of tool steel, where in reality, the bolt tempering temperature will probably be much higher, more closer to spring hardness, in the purple to blue range.

From Wikipedia:



and:

https://en.wikipedia.org/wiki/Tempering_(metallurgy)

[tobnpr]

Thanks, gentlemen.

I've bookmarked the "Heat Treatment of Iron and Steel" doc and will start going through it. If I get hung up, I'll just ask my youngest son to explain it to me

I got curious about this because of the other post currently where the OP says that his smith is vehemently opposed to welding bolts- and I've run into that before, never quite understanding it. It has to be a pretty s***** welding job for a bolt handle to come apart, given the very minor stresses they're subjected to compared to what a proper weld is supposed to be able to withstand (if I have any doubt as to weld pentration, I chuck it into the vise at the end of the 300 lb. workbench and try to lift it. Not very scientific, but...)

I get the concern over the Mauser lugs, but they're still a good distance from the handle weld area. Perhaps, this is a holdover from the "old" days when acetylene was used to weld, instead of MIG/TIG.

[Gunplummer]

Russian bolt bodies are case hardened. There is no real difference between welding them or a Mauser bolt. I have welded a bridge on the receiver of Russians and still retained the case around the weld. I silver soldered a Remington style bolt handle BEHIND the bridge on a modified bolt and had no problem. Carbon steel and low carbon steel react differently to heat. You can burn the carbon off of cased, low carbon steel with too much heat (Red hot) for too long, but I don't see that happening with what you are doing. I have welded a lot of bolt handles and receivers and used both gas welding and stick welding to do it. If you are really worried about it, put small beads on and then cool it in between welds. I have never had a failure. The fear of heating up the steel is usually where the problems start. MIG welding also has poor penetration. I would grind the two areas to a point and fill it in with weld. Rule #1 is know what material you are dealing with. Looking at charts and graphs is worthless if you do not have some kind of idea what the steel is. Kind of like using a Machinists Handbook. It tells you all the thread specs, but you better already know how to thread.

[tobnpr]

MIG welding also has poor penetration.

Poor MIG welds, have poor penetration.
When correctly done, that's not the case. Thing about MIG, is the welds can look fine, with minimal penetration. Definitely took me some experience to learn the correct sounds, and correct combinations of WFS and voltage, stickout, positioning ,as well as gas CFH to get optimal results.

And they say TIG is harder to learn. Can't wait...that's next...

[James K]

Just a suggestion, but you might find a copper heat sink more effective than an aluminum one. You can make one from a ground rod and a foot or so will be enough. You can make several heat sinks from a piece of rod and shape them to different bolts.

Jim

[Dixie Gunsmithing]

tobnpr, TIG is not a lot different than Gas. The torch is held at about a 10 degree angle, from vertical, and the wire is brought into the arc, at around 30 degrees from the work. It's then, just watching the droplets hit the work, and adding wire to the arc as you need more weld metal.

If you get a TIG machine, make sure it has a high frequency arc starter. Scratch starting is for the birds on this setup, and will ruin the tip on Tungsten electrodes pretty quickly. They need a sharp point for the arc to easily start.

There is a video link, on here, that I posted about TIG. It is one of the better ones that I've seen.

[Gunplummer]

No, MIG welders have poor penetration. Do some reading. There is no reason to have an unwelded area on something as small as a bolt handle. The center of that area should be welded. Stick welding would penetrate, but I always ground a "V" and slowly built the weld between cooling to avoid heat sink. I remember one time I turned a brass slug to put in a shortened receiver. I could not even (Gas weld) get the area hot enough to weld. I believe a stick welder would have done it, but I have my doubts about a Mig. There is no reason to do the complete weld at one time. It is easier to weld in steps and then you can actually see what the inside of your weld will look like. With case hardened materials, I just run the head of the bolt under water between beads until the whole bolt is cooled off.

[tobnpr]

I'm not going to argue with you about the effectiveness of MIG welding.
If the machine is powerful enough for adequate penetration of the thickness of the material being welded they produce perfectly acceptable welds; sometimes multiple passes are required.
The thicker the material, the more powerful (higher amperage) the machine that is required.
Tell Miller, Hobart, and Lincoln to just stop making them, that MIG is garbage.

And who said anything about an "unwelded area"?

You stay with you stick welder.... I'll stay with my MIG.

[Gunplummer]

If your bolt handles broke off, that indicates an unwelded area. Basically, they were "Tacked on" and were not welded in the center area. I used to work in a machine shop and the sales reps for welding rigs used to come around and hand out literature for welding set ups/applications. Mig welding was described as having the least penetration of all the various welding methods.

[tobnpr]

^^^
If you read my post, I said I had two weld failures "at the beginning".
They were part of the learning curve, and I haven't had one in over 800 bolts since (at least, I assume a customer would let me know).

MIG can be very deceiving- I agree with that- but to dismiss all MIG welds as having poor penetration is simply not a factual statement.

MIG is also limited- but with a 300+ amp machine, .045 wire and a 98% Argon mixture can go to 1/2" and more.

[Gunplummer]

Why did you even bother with the original post?