Group question on machining something

Don't get the wrong impression, Wayne. I'm not hot, nor was I upset by your response. Just adding more comments to what is a good conversation and a learning experience for everyone that isn't familiar. I figure you and I have exchanged views long enough that we understand one another.

To quote what you said earlier:

The material in question here is actually 4130, not 4140 or the others (4340 is chrome nickel moly). 4130 is low enough in carbon that it won't heat treat hard enough to create the problems the others do, and *can* be welded reliably.

Harold

Giuys..Ive got lots more of it..so Ill take some chunks and see if it welds ok. Ill try SS filler first.

Ill get back to yall on it.

Gunner

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

I'd make it in two pieces as you did, drill holes and insert locator pins, and silverbraze it with EasyFlo45. Holler by email with snailmail addy if you'd like a foot or three of that, Jerry Martes gave me a lifetime supply I'd be happy to share some of. It's good shit, Maynard! Stronger than a good TIG weld in some sits.

Agreed.

Ok. I'll buy that. All of my higher alloy stock like that is unknown so I can't pin down the exact alloy. Experience has taught me how to recognize that it's one of the chrome molly alloys when I do run across it though.

Wayne Cook Shamrock, TX

Right on. Some of the most interesting posts are the ingenious ways that folks do things with what they have in their garage, lacking a full CNC shop with waterjet, EDM, CNC plasma, laser, E-beam welding.......

Ever try "railroad rod" with Ferro-Flux and O/A? I wouldn't say that it's better than good brazing, but it works quite well and affords perfect color match -- which doesn't matter if the piece is painted.

I've used it to repair some intricate "lacey" cast iron things, like cracked foot treadles for antique sewing machines. It doesn't really puddle, you kind of mush it in. It's hard to find.

No I've never tried it. I do have some of the rod but I don't think I've got any of the flux (there's a lot of different kinds of flux out there but I don't remember that kind).

In situations where you want a color match and don't care about the hardness I'm sure it's great.

Wayne Cook Shamrock, TX

It's about like the parent metal in hardness, is easily worked with a file.

Ok. I wasn't sure since cast iron does like to get really hard when treated improperly.

Wayne Cook Shamrock, TX

Just to add to this discussion...

I walked out to the garage and took a look. My old Schwinn Probe mountain bike frame claims to be True Temper Chrome Molly 4130. As you can imagine, it has quite a few welds on it. This was only a low end bike a good many years ago now when Chrome Molly frames were quite popular. The frame has held up well (~40,000 miles) and is quite stiff. For the price I paid for it (~$350), it can't be too difficult to weld.

Airframe builders weld 4130 routinely, usually with O/A. Bikebuilders do too, usually with TIG.

4130 was developed specifically for aircraft applications in the 1920s. It was designed for reliable welding, good ductility, toughness, and strength, generally in thin sections, primarily as tubing. It can take heavy shock loads very well.

Initially it was expected to be welded with O/A. Through the 1930s, many tubular aircraft spaceframes, including those for military aircraft, were welded with stick -- yes, stick.

It has a quirk. It has a slow quench-hardening rate, approaching that of air-hardening steels. So welds can wind up hard, with a transition to a soft, more-or-less annealed heat-affected zone (HAZ), and then with another transition to the parent metal, which usually is normalized and a bit harder than annealed. It depends on weld thickness and welding method.

So there is a long-standing controversy over whether to "stress-relieve" the welds. Most aircraft weldors today say not to, in sections thinner than

1/8".

FWIW I ran some informal, non-scientific tests on TIG-welded 4130, 3/4" tubing with 0.065" wall thickness (16 guage) a few years ago. I smashed them with a hammer on an anvil until they were flatter than a road-killed 'possum. The welds were the qualification samples my welding instructor had performed for an Air Force airframe-repair re-certification, and they were really good welds. It was an experiment/demonstration for the class.

They did not crack until I had them smashed about dead flat, and then the cracks started on the surface and did not penetrate. The parent tubing was beginning to crack at the same stage of smashing. So much for all of the controversy, as far as I'm concerned.

-- Ed Huntress

I agree----but *only* with 4130. The higher carbon content of 4140 and greater changes all of that. That was my original point.

Harold

That could well be true, probably in proportion to a similar increase in carbon in plain-carbon grades.

Keep in mind that chromium increases the hardening potential of carbon, so the material's carbon-related properties are somewhat higher than you would have for 1030 or 1040, respectively.

-- Ed Huntress

The problem with welding 4140 is that the surrounding cold metal quenches the weld too fast and you get stresses and hard spots in the wekd because of the higher carbon content. A simple solution for welding 4140 is to preheat the metal to about 400 degrees F. so that it will not quunch the weld and make it brittle.

John

There's a nice article in one of the 80's Projects in Metal issues that covers just this procedure. I believe another poster here has already described something similar, but if you want the article, let me know, I'll email it to you.