Hi
Assuming I have a piece of mild steel plate and want to put a sharp edge on it, how do I go about it?
The sharp edge isn't a problem, how do I harden the steel to keep it sharp?
Heat it up & plunge it in oil/water etc??? What colour - red hot, white hot?
Dave
Way OTT!
You are taking me back to metalwork lessons 40+ years ago.
The colours I recall refer not to incandescence but to the colour of the oxide film on the surface of the workpiece.
However looky here:
Grind it sharp afterwards.
HTH
DG
Normally you cannot harden mild steel, you require a high carbon steel, but a quick search on google "harden mild steel" does show a 'super quench' method. The way I have done it in the past is to use Kasenit compound and follow the instructions on the tin.
Regards Jeff
When I was at school we used some hardeing compound that I seem to remeber you dipped the hot metal into. THis was called by our teacher case hardeing.
Rick
| On Sun, 28 Aug 2005 22:56:03 GMT, "david lang" | wrote: | | >Hi | >
| >Assuming I have a piece of mild steel plate and want to put a sharp edge on | >it, how do I go about it? | >
| >The sharp edge isn't a problem, how do I harden the steel to keep it sharp? | >
| >Heat it up & plunge it in oil/water etc??? What colour - red hot, white | >hot? | >
| >Dave | >
| | When I was at school we used some hardeing compound that I seem to | remeber you dipped the hot metal into. THis was called by our teacher | case hardeing.
Case hardening is a tricky process, IMO best avoided. Get a bit of better steel.
You can't harden mild steel. It won't harden on its own, and you'll have a hard job finding Kasenit these days. I suggest you search out the rec.knives FAQs, which have a great deal of information.
The _best_ steel to use for this might be O-1, which is an oil-hardening steel available from good engineerng suppliers. It's surface ground already and is the standard workshop material for making hardened jigs etc. OTOH, not exactly cheap (but not too bad).
The _cheapest_ material for big stuff is van leaf spring from a scrappy. This is probably a bit thick though.
The _easiest_ material may be old kitchen knife blades, drum lawnmower blades, woodworking chisels, or general scrap steel that you know was originally intended to be hardened.
The other way is to hard-surface the steel by running a good bead of MIG weld along the edge, then working on that. Lots of people hereabouts have little benchwork equipment, but do have welders.
Harden it by heating to a moderate red on the kitchen cooker, then oil quenching. Old motor oil in a tin box with a lid - yes it will light, just shut the lid down and leave it to get on with things.
A more accurate temperature gauge is by heating to just above the "Curie point". Fasten a magnet to a bit of coathanger wire and heat the steel until it stops being magnetic. Then quench.
Tempering is a much harder task and needs some knowledge of what you're using it for. If it mustn't be brittle, then temper it. If it needs to be sharp rather than strong and your hardening is a little dubious anyway, then don't try it.
To temper it, let it cool and then polish the surface shiny with some emery or wet-and-dry. Then heat it gently and watche for the oxide colours forming. Yellowish brown for sharp stuff, blue for anything you're likely to break. Then quench in water.
Accurate heat treatment is of course rather more complex than all this.
You can't harden mild steel without increasing the carbon content using some form of case hardening compound. That's no good for tools because the instant you sharpen it you'll grind through the thin case-hardened layer back into the soft steel below.
You need a high carbon steel. Round stuff usually sold as "silver" steel and the flat stuff as "gauge plate". People like J&L Industrial sell it. Can be hardened and tempered as described in any basic metalwork book.
teacher
Case hardening is dead easy with the simplist of equipment. Heat item to cherry red - dip in Kasenit compound - reheat to cherry red - plunge into water. That'll give you 2-3 thou of higher carbon steel on the surface. Repeat to increase the case depth. The surface after the plunge should be glass hard and will turn a file.
WWll prisoners used to case harden mild steel for wire cutters using sugar as the carbon source and heated with a spirit blowlamp - if they could do it with such basic kit, given a tin of Kasenit it's a doddle.
AWEM
fingernails are
Fingernail (or hoof) works better than leather or bone. Rawhide is better than leather, but both of them really need some calcining (roasting) before being used.
Bone is pretty much useless, unless you're working on an industrial scale. There's just not enough organic material in it, compared to the minerals.
I thought all you needed was a steady supply of slaves into whose giblets you could plunge your blade?
That's tempering, which relies on a copious supply of URHB (urine of a red-haired boy, the rec.knives mythical panacea tempering fluid).
One of my older sword books does have a suggested diagram for how to get most efficient use of a condemned prisoner for sword testing.
Very useful thing to have, especially now that condemmed prisoners are in such short supply.
Owain
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