What kind of steel is this?

Last Sunday I found these steel bars at the local flea market. The price was very good and I bought them. I had no expectation about the quality, I wanted use them for welding. But then I noticed that the edges are sharp. Like on HSS bars. I tried to scratch them with a file and it is quite hard. Not as hard as a silver HSS tools but for sure it is not mild steel.

I read somewhere that the sparks created when you grind it can give some clues about the material. Here I compared one bar with mild steel (right) and the best HSS tool I have (left).

If they are 13" long they are probably silver steel.

Most likely gauge-plate - oil-hardening tool-steel ground to accurate sizes but here appallingly neglected.

It is supplied annealed, and is machineable but very tough. It can be used as it is for wear-resistant machine-parts (one long-established model-engineering application is for valve-gear expansion-links); and oil-hardened and tempered as it is designed to be for various edge-tools such as form-tools.

Don't try welding it. It is not a welding-grade steel, at least not in the ordinary way. You might get away with it but I would not trust the weld's strength or the risk of brittleness, and the weld itself (which would be a very peculiar alloy) might well be very hard.

They are about 10" long. But there are small differences both in length and thickness.

Sounds like an interesting stuff. Can I use it to make lathe tools? In the past weeks I was thinking to make a boring bar that would fit in a 7-8mm hole but I couldn't decide to waste a new HSS bar for this. I'm not sure about the result and they are not cheap. Now with all these bars I can try something.

Edited By Sonic Escape on 16/05/2023 22:32:36

Carefully clean it without removing steel.

If it is what I think it is, you may find traces of grinding on the wide surfaces, and circular-sawn edges. Gauge-plate is made in large sheets and cut to widths. (In a previous employment I had sometimes to cut two-foot squares of 6mm gauge-plate into four equal squares. With a Startrite vertical-bandsaw and hand-feeding. Took a long time.)

You can make lathe-tools from it. It is similar to silver-steel, but intended for oil-quenching.

The different lengths may simply be due to its previous owner having used some of it.

So after machining it, it is heated and quenched and you get a case hardened tool? Sounds handy

It will be through hardened, not case hardened.

Andrew

Could be 'key steel', if you heat treat a sample and it remains soft (relatively), that'd be my guess.

Steve

Cut a bit off, get it red hot and quench. If it's pot hard it's gauge plate or similar high carbon

Edited By duncan webster on 17/05/2023 00:22:14

In a similar vein to AJ, he means ‘anneal’. Heat treatment can cover a multitude of separate events, so can be hardening or softening.

10" long does sound like gauge plate which is often cut into 500 or 250mm lengths

Spangly sparks suggest med/high carbon, low alloy... but could be wrong. Can't tell if it oil or water hardening. Welding will work but will be weak.

Doesn't look like stainless.

In my opinion stuff like this is more trouble than it's worth - you don't know what the alloy is, or how it's been treated.

Could well be Gauge Plate, but it needs to be tested. Without wasting time machining it, test if it will cut with a file or hacksaw. If it does, it will be useful for something! If it cuts, heat a sample up following the usual instructions for hardening Gauge Plate, and quench it in oil. If a file bounces off, it's at least some form of tool-steel, and might be useful.

What separates Gauge Plate from other tool-steels is it's less fussy about temperatures and timing than other hardenable steels. They're fussier, calling for accurate heating and timing, and more likely to crack and warp during a botched quench. The clue it's a tricky one is mixed results - works well and then fails on the next try.

If it is hardenable, don't expect it to be as good as HSS. For use as a cutting tool, my first choice is HSS, because Silver Steel is general-purpose handy rather than high-performance. But it does make at lot of jobs easier.

Problem with scrap is it can make jobs much harder. If the alloy is designed for some other purpose it may not cooperate. I'm not sure it's smart to waste time and money annealing a lump of hardened scrap steel in hope it will machine nicely afterwards, and still be fit for purpose.

Another booby trap, some modern steels contain Boron; makes them extra strong, but difficult to weld which can come as a nasty surprise.

Working with scrap is OK as long as the operator quickly recognises it's unsuitable and doesn't waste time or damage tools with it.  The only way to find out is to experiment.

Dave

Edited By SillyOldDuffer on 17/05/2023 11:35:06

Yes. Do not put hundreds or even tens of hours into anything you make this this stuff. Always start valuable projects with known materials.

I hesitate - following comments elsewhere - to offer advice, but ...

If it is ordinary carbon steel (such as gauge plate, silver steel, etc) then you can heat it red-hot and quench it. It will then be glass-hard and, I'm sorry, will also be glass-tough. Use for tooling would be dangerous as it will snap leaving sharp edges and sharp bits flying about.

If you harden it and then draw the temper (also called just 'tempering' you can add toughness at the expense of hardness. The traditional way to do this is slow heating of the item, leaving a clean (ground or filed) surface open to the air. A range of colours will appear, starting with pale golden, through straw and brown, then blue and purple, and finally black. The 'best' colour depends on what you wish to use it for.

Thick books have been written on the process, and starting from a guess is not always helpful.

One further comment: If you hope to make tools for lathe work (etc) where the rate of cutting is enough to heat up the tool above about boiling point, the sharpness will be destroyed. There are fancy steels with added ingredients, which will stand such heating, though. They are called Tool Steel or HSS, and tend not to be left lying about to get rusty.

PS: anyone feeling the need to pick holes in my grammar is invited to stick something large up an orifice and leave it there. Especially if they are a moderator.

Regards, Tim

Edited By Tim Stevens on 17/05/2023 14:50:06

With the help of a furnace and a harness tester you can guesstimate the general class of steel. I did this with some scraps of unknown "tool steel" by water quenching and tempering at increasing temperatures. It matched typical "chrome moly" and I've used it as such for parts that needed strength but wouldn't kill me if it failed.

Simpler tools will give a rougher estimate, but that might be enough for your needs.

I don't plan to use this steel to anything important. Actually nothing that I do is important

I thought it was interesting because it looks different from what I usually see in stores. And the fact that I paid only 4 euro for the whole bag was also a factor here. I don't have a way to heat it red hot. I doubt a barbeque fire would be enough. I started to read about different hardening methods and various types of steels. But it is a huge domain! It's interesting but I'll let it for later.

To make things more complicated now I realized that HSS is not a single type of steel. I have one HSS tool, the left one in the video that has a silver color. The file slides on it without scratching it. I have also HSS tools that are black. Not on the cutting edge. I guess they oxidized or something. They can be scratched a little.

I have found the best freely available HSS to be 5% cobalt, ok on the lathe and superb on the shaper

I have a decent chunk of stellite 100 that turned up at the bottom of a box of junk, very impressive but it's quite rare. Not a spot of rust on it and almost mirror shiny lying at the bottom of a box of rusty tat.

Almost but not quite as good as carbide tooling when used on a lathe

I would ujst add one comment to Tim's offering, and that is, when tempering these steels, don't hang about before quickly cooling the tool. The colour changes at the cutting edge can be so darned quick that almost before you've recognised, eg straw colour, the tool has gone past it and is now in the purple region!

How do I know? I'll leave that to your imagination!

Peter G. Shaw

Yes - the important thing is to be aware of the possibility that not all metal cuts well.

Apart from there being thousands of different alloys, metals can be heat-treated, work hardened, age hardened, and otherwise processed. Also possible a bar could be a composite, such as tool-steel enveloping a tougher core. Very confusing.

I think what turns up as scrap depends hugely on where you live. The lucky ones live in places where scrap comes mostly from machine shops and structural work, and what they put in the bin is mostly suitable. However, if local industry specialises where you live, perhaps aerospace, military, food processing or making chemical componentry, the scrap could be downright unfriendly. My area has no industry to speak of, so the scrap comes from domestic sources and old cars. Here scrap metal is unpredictable, anything between wonderful and vile, mostly poor stuff.

I've scrapped many a printer and scanner for the ground-steel runners inside. With one exception, they've all turned and cut beautifully. The exception looks identical to the others, but for some reason it's so hard that carbide struggles to cut it. Now I don't trust scrap at all. I mostly buy known metal. When tempted to use scrap because it's cheap, it's tested first. Any sign of trouble, such as a file bouncing off, or it work-hardening under a bluntish hacksaw, and I walk away. Almost the worst thing a beginner can do is persist with a nasty bit of scrap.

Dave