Hardening Steel

[SparkyLB]

I got some 1.5 mm round stock from the big box store and had at it with my lathe and gravers.  My intention is to make a set of pin gauges for jewel hole measuring. 

After a dozen or so attempts, I was able to turn a .15mm specimen. 

I tried a stiff slurry of Borax and Isopropyl, brought to red-hot, in the hopes of eliminating scale.  The slurry just formed a "hard candy shell" and seems to be fixed on quite permanently. 

I took all my steel scraps and placed them on a thick sheet of steel, and mounded it so that the newly-made pin was off the bottom, and encased in the steel shavings so oxidation was somewhat ruled out.  This worked much better, but I'm looking for something more respectable.  Once red-hot, I confirmed a magnet wouldn't stick, and quenched the pin. 

There's no foreign material on the outside now, which I'm happy about.  Furthermore, a file won't leave a mark and it's certainly hardened.  Next step is to eventually blue  (red hot, polish, straw to blue. .)

Could someone lend me some advice on hot blueing steel?  What methods do you use that get you success? If so, would you mind describing them? 

Thank you, all. 

 

Larry. 

Edited February 1, 2020 by SparkyLB

[Philbird]

I'm a big fan of the curved sheet of brass held in pliers manuever for tempering. Place the piece to be tempered in the sheet of brass, heat over a torch and watch like a hawk for colour change. You want straw coloured probably, so watch when it just starts to turn and then quench immediately or it'll go right to blue. Good luck.

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[yankeedog]

Hot blueing? Pretty  nasty operation.consider parkerizing.or maybe even  a cold  phosphate  coating. There is a product  called ospho.that gives you a dull  blue  black finish and a degree of rust proofing. 

[saswatch88]

There is a color chart you should refer to when hardening metal. Each color is for what you are trying to harden something small enough to fit in a pivot hole should not be made red hot, that will cause them to brake very easily even if you temper them. I believe the color you are looking for is a medium yellow at about 420 degrees. Quench in oil not water, you will have to do it again in order to temper it.

[rodabod]

I thought Borax was usually used as a flux, and yes, it does forma glass-like surface. Can you not just use soap?

 

For pin gauges, I'd temper over a flame and very slowly bring them towards blue (or whatever colour you like). They don't need to be super hard, and aesthetics aren't your top priority.

[nickelsilver]

You can use a pure soap, but I prefer charcoal powder. I grind wood charcoal in an espresso grinder as fine as possible, then that goes in a steel tube with the part, heated to orange, dump in oil, fish out with magnet. The part will be an even grey color, clean off oil then temper in a tray of brass filings over an alcohol lamp until blue.

 

The tube is from a Nitrous oxide canister for whipped cream makers, so about 20mm diameter 45mm long, welded to a rod as handle. Can't find a pic right now.

 

You want to temper as soon as possible after hardening.

 

Are you sure your steel is hardenable? Most hardware stores will sell the lowest grade of steel.

[jdm]

Great practical info here, which interest me much. But I'm still to try anything. Thanks all.

[SparkyLB]

rodabod, I'm going by information from the internet, before I found this place.  I never saw the borax solution liquify, but maybe my torch is hotter.

Nickelsilver, thank you for the perfect tutorial.  When you say soap, do you mean liquid?  I happen to make my own.  I'm going to see if I can obtain a nitrus oxide "test tube," a great idea.  Cutting wheel on a grinder and I'm in business.  As for your question, I will use my grinding wheel to see if the carbon level is high enough.  Does heating accomplish nothing of the steel is too low in carbon?

saswatch, I'll try the medium yellow and compare it to the grey I got last night.  That's the "straw yellow" color, right?  I'll use oil for quenching.  I never knew when to use water or oil, but read about both. 

Yankee dog, if you're referring to hot bluing a la gunsmiths with tubs of solution; I'm not referring to that.  I just mean bluing by means of heat, not chemicals. 

Thank you, philbird.  Good info, saswatch agrees on the color. 

[Tmuir]

I get the idea of making gauges for jewel holes, but why don't you just start with blue steel and machine that to dimension then you don't need to harden and temper.

Yes Blue steel will blunt you gravers quicker, but its what you use to make balance staffs anyhow, so its good practice as trying to harden and temper things that small is not easy.

It sounds like the steel you have is carbon steel as you say a file won't touch it after hardening, but if you have a bench grinder there is an easy test you can do to see if the steel you have is carbon steel so can be hardened. It is called 'The spark test'.

Putting it simply mild steel when put on the grinder will give only small sparks, straight line that just disappear.

Carbon steel gives 'sparkly sparks' what I mean by this is the spark will come of the grinder and then branch out into more sparks, a bit like a growing tree branch. If you get some carbon steel and then just a mild steel nail and put them on the grinder one after the other you will see what I'm talking about.

[nickelsilver]

Ah missed that it passes the file test. Should be ok then. As said by Tmuir the traditional way to make such things is with steel prehardened and tempered to blue, but you can heat treat after too.

[SparkyLB]

52 minutes ago, nickelsilver said:

Ah missed that it passes the file test. Should be ok then. As said by Tmuir the traditional way to make such things is with steel prehardened and tempered to blue, but you can heat treat after too.

Where does one obtain prehardened blue steel? 

[nickelsilver]

Where does one obtain prehardened blue steel? 

Watch material houses have it.
I personally don't like it, if I really want to make something from prehardened steel I make it myself.

[SparkyLB]

niclesilver,I had a question about the use of charcoal in hardening.  Does it not turn to ash? 

I've got plenty of fine powder at the bottom of my bag of pyrolized natural lump charcoal.  

Edited February 1, 2020 by SparkyLB

[nickelsilver]

 

 

 

niclesilver,I had a question about the use of charcoal in hardening.  Does it not turn to ash? 

I've got plenty of fine powder at the bottom of my bag of pyrolized natural lump charcoal.  

 

Hmm not like when you do a bbq. It all goes in the oil red hot, after a while I decant the oil and pitch the old oily charcoal (which is quite black).

 

As long as it's wood charcoal powder and not from the pressed briquettes it's fine.

 

[Redwood]

Charcoal is a carbon and will case harden steel used by blacksmiths for hundreds of years, if the steel looses it’s magnetic value when heated and when quenched leave a file test hardened steel then the bar stock steel probably has more carbon than mild steel, how much carbon is hard to tell. When tempering steel leave it cool slowly, if you cool it in water it will cause stress fracture. If it was me I would go straw rather than blue first

[nickelsilver]

Wood charcoal might elevate the carbon content of the steel if left for a long time but not at the length of time watch parts are held at red heat. It does prevent oxidation of the steel surface very effectively though. Blacksmiths use bone charcoal for case hardening.

There are many types of hardenable steel. Some are air hardening, some oil hardening, some water hardening. The designations of the 3 most common seen in North America A2, O1, and W1 are self explanatory. Air hardening will harden when left to cool from red hot. W1 and O1 need to be quenched in water or oil respectively to become hard.

When tempering by color the clean grey steel will go from a very light straw to brown, then purple, then blue, light blue then almost grey again.

Straw would be for cutting tools. A dark brown for punches. Purple if you're French and want to **BLEEP** off future repairmen. Blue is typical for almost all watch parts from staffs to pinions to springs. A lighter blue is good for screws for a bit more resistance to breakage when tightening.

If you want brown and get to blue you need to reharden. If you want blue and get to grey you need to reharden. If you want to anneal heat treated steel it needs to be brought up to hardening temp and then cooled as slowly as possible.

[vinn3]

  if you can get " drill rod ",    it uses water or oil quench.   an oxy acetalene "jewelers"  torch is ideal for small stuff.   vin

[saswatch88]

8 hours ago, SparkyLB said:

 

saswatch, I'll try the medium yellow and compare it to the grey I got last night.  That's the "straw yellow" color, right?  I'll use oil for quenching.  I never knew when to use water or oil, but read about both. 

Yes straw yellow. Oil is way better than water there is reason why something about the molecules i forgot. Just think how the ancient Japanese made their katana blades. They used oil. When tempering you have to hold the temperature for a few hours then let it slowly cool down. Quenching is used when hardening, but you really must temper or you will be breaking these things very easily.

[nickelsilver]

Sparky, you do not want straw color for a pivot gage or pivot or any functional part in a watch for that matter. I say it again as it's been mentioned several times to temper to straw, that is incorrect. Also, you 100% do need to get to red/orange heat to harden. Also, you do not need to hold the tempering temperature for a few hours, a few minutes (even one) is plenty.

[Philbird]

Nicklesilver and sparky, I seem to have been working with ignorance on my part-I was giving general tool tempering advice, which did not pertain to the situation at hand. I hope no damage has been done? Sorry about that.

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[nickelsilver]

Nicklesilver and sparky, I seem to have been working with ignorance on my part-I was giving general tool tempering advice, which did not pertain to the situation at hand. I hope no damage has been done? Sorry about that.

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Ha don't worry Philbird- you're technique is good! Color just a bit light.

[SparkyLB]

This thread is immensely informative. 

[rodabod]

If you are turning annealed steel to size (like we are here) and it doesn't need to be extremely hard, but have enough carbon content to harden and temper, then I can recommend EN8. It is sometimes referred to as "medium carbon" or sometimes even "mild" but it has sufficent carbon content to harden and also to produce vivid colour if aesthetics are of consideration. The benefit here is that it is easier to turn than silver-steel / high carbon steel.

As I mentioned in the 4th post, you don't need to temper to be very hard. And why would you? It'll only break.

Take a piece of scrap rod of similar diameter and experiment with tempering. If you heat only at one end, you'll get a rainbow effect and can see how brittle it is as it transitions in colour.

Only for larger parts with great thermal mass do you need to hold the heat (whether hardening or tempering) for a longer time to make sure that it is consistent all the way through. It's a bit like cooking a large piece of meat in the oven compared to frying a small piece. It might look cooked on the outside, but it might feel a bit different on the inside if it's large!

[vinn3]

Quote

 

     a book like "the  machinery hand book "    will spell it out for you.   vin

[SparkyLB]

23 hours ago, vinn3 said:

     a book like "the  machinery hand book "    will spell it out for you.   vin

I checked that book out at the library a few months ago but didn't know this was in there.  I'll have to check it out again.  Thank you.