Steels

I'm not sure if you need a general tutorial, or just use what you know and ask the occasional question here.

Steel that's recycled from scrap has hard spots, somewhere between occasionally and often. I haven't run into any, but my dad found ball bearings in some of his once, and I've heard reports here of someone finding a tap -- still identifiable as to diameter and thread -- buried in some angle iron.

I suspect it's just something you have to accept.

You may be thinking of me. We found a tap in a piece of steel -- I no longer remember the grade, but it was graded barstock -- back around 1974. I've mentioned it here a couple of times. It's hell on endmills.

But you're right, the junk is mostly in recycled steel, particularly in structural grades. I have never put a piece of A36 on a machine tool and I doubt if I ever will.

The fact that a piece of steel is an AISI or SAE grade is not a guarentee that it will be free of high-temperature junk, like cutting tools and such, but it's pretty good assurance that the steel is homogonized, and won't have varying amounts of carbon. The only sure way to avoid both is to buy electric remelt -- electroslag or vacuum-arc. But that's almost exclusively tool steel grades, except for some special military and aircraft materials, and it costs like the devil.

You can see the exceptions in the other replies, but the only material that I've used which fairly consistently had a number of very hard spots in it, was OBF old bed frame angle.

The OBF stuff doesn't MIG weld well, either, IME. I've had deeply penetrated welds pull out completely, to the root.

Some stainless seel alloys work harden during cutting, and can dull a HSS cutting tool edge instantly if feed force is paused, but other common steels don't.

I always use a reliable cutting lubricant, not oil or some other improvised fluid, and generally keep feeding pressure steady 'till the cutting is completed.

Any new hot rolled that I've bought in recent years, still has the scale on it. I'll grind the scale away for weld areas, otherwise I just clean it well, and paint. Diluted muriatic/hydrochloric acid (available in many retail stores for etching concrete, etc) is effective at removing the scale when the parts can be submerged in the acid solution. After treating with the diluted acid, I generally rinse with baking soda water, then fresh water rinse, quickly/force dry and apply oil (new 30W).

The same acid treatment generally works well for rusty steel and cast iron parts, although with light rust, I often treat similarly with a diluted phosphoric acid/metal etch solution, then dry as mentioned previously.

Back to Chuck's question, what would you recommend for general fixture and machine building? Looking over McMaster, O1 seems to be pretty versatile, available in decent sized bars and about twice as expensive as A36.

I've had good luck threading and making shafts out of 303.

I do a lot with 1018.

i

I'm not the guy to ask on that one, Jim. I rarely do any milling these days, and when I have made fixtures, I usually used 2024 aluminum tooling plate or other shapes in medium-hardness aluminum.

But I can mention some general principles. From the OP's question it doesn't sound like he needs to harden the pieces, so for free machining and good surface finishes, you can't beat 12L14 (Ledloy; C12L14). But it costs a lot more than the scrap he's trying to use, so that may be a problem.

O1 and other oil-hardening tool steel grades are good if you need to harden the steel, although for fixture parts, you have to avoid sharp corners and wide differences in thickness. It hardens easily but it will crack in difficult sections like that. For commercial work, A1 or other air-hardening grades are preferred because they're very safe to harden and they distort the least.

I can't think of any reason to use 1018 or other basic carbon steels over

12L14, unless you can get it a lot cheaper. If you're going to case-harden anything, 12L14 can be case hardened, as can most any low- to medium-carbon steel. 1018 or 1020 also will give you a good case without significant distortion.

But what's the job? If you need hardness for wear resistance somewhere, the picture changes. If you don't, and if you don't need to worry about temperature stability, aluminum is lighter and much easier to machine.

A few other relevant facts regarding 1018 vs. 12L14:

12L14 is only available in round, square and hex; 1018 is available in those shapes, plus rectangles in finely graduated sizes from 1/8x1/4 up to at least 4x8 1018 is easy to weld; welding 12L14 is not recommended

There's not much price difference between the two.

The cold finishing processes leaves 1018 with internal stresses that can cause nasty surprises if you don't keep that fact in mind, especially when making slender and/or asymmetrical parts.

Except you cannot weld 12L14.

i

Well, you can, but as Ned said, it's not recommended. You get lead migration and unless you're good, you'll get enough of it to cause trouble.

But, yes, that would be a good reason to choose 1018 over 12L14.

Regardless of general usage, hot-rolled and cold-rolled are FINISHES, not steel GRADES. You can get various grades of steel in both finishes. If you just need a low carbon steel, 1018 is available in both finishes. Hot rolled can be had in either scaled condition or pickled and polished, which is closer to the cold-rolled finish. If you want to do extensive machining and don't want to machine all surfaces to avoid warpage, hot-rolled is highly recommended. Cold- rolled stock has a lot of stress locked up in it, would need annealing to relieve it before machining, which leaves you with about the same material and surface condition as hot-rolled.

If you want to make some sort of cutting tools, one of the tool steel grades would be what you want. Low-carbon steel can be case-hardened if you need easy machining combined with a wear surface.

As far as what steel to use where, Carpenter Steel had a book on their tool steels and where to use them, title escapes me right at the moment.

As far as fixtures, you could use continuous cast iron shapes on up, just depends on what you're doing and what kind of load it has to endure.

Stan