hardening/tempering a bit of steel

I'm going to be making a 12mm countersink tool ,I'm wondering what the best way to harden/temper the tool,I only have a small gas torch .

Sean

Assuming the steel is high carbon, silver steel, it first needs to be hardened by heating bright red and quenching rapidly in water. Then tempered to light or medium straw colour on a cleaned section near the cutting edge by careful heating. A sand-bed or similar is good for this.

Afterwards, sharpening will be required.

From your description of your gas-torch as "small", I suspect that you will have some difficulty with reaching a sufficient temperature for the initial hardening.

Best of luck though.

The first thing you need to check is that you are using a suitable steel. It must have a high enough carbon content, silver steel (drill rod in some countries) is the normal choice although there are others. Mild steel does not have enough carbon and will not through harden although it may be possible to harden the surface (called case hardening)..

Stage one is to heat to red heat and then quench (usually in water or brine). This fixes the atoms in the steel into a very hard but brittle state. Your torch will need to be powerful enough to get the countersink red hot.

The second stage is to gently heat the part to get the right compromise between hadness and brittleness. This usually entails getting the surface to a nice clean shiny state and watching the colour as you gently heat the part. In this case I suggest a straw colour would be right. Once the colour is there quench to stop it overheating.

Metalurgist will go into much greater detail but this might help get you started.

Sorry for the repeated info Clive beat me to it.

Edited By Roger Woollett on 02/01/2018 14:19:32

Hi Sean You can easily harden small item with a blow torch. Just have a clear area with fireproof floor a can of oil to quench the item in, an old pair of pliers that you don't mind burning, a good pair of strong leather gloves. You hold the item in the flame until it reaches an orange colour and hold it there for a few minutes then quench it in the oil vigorously shaking it about under the surface of the oil till reasonably cool quenching it in water can cause it to fracture. You then have clean the item of scale etc I use a scouring pad till it is as bright as you can get. Then to temper by heating it slowly whatching the colours change till it goes light brown and then quench it in water to stop the process. If the shank goes a bit blue it dosnt matter as long as the cutting edges are hard.

David

Edited By David George 1 on 02/01/2018 14:28:54

If you have a gas stove and the part is not too large you can also use that. After waiting until you have the house for yourself, just remove the cap of the largest burner which will give you a good hot flame. Niko.

Heating is much more effective if you can surround the part with heatproof insulation while you heat it. I have a couple of mica bricks I bought years ago, but you could use some scraps of firebrick. Don't use housebrick, it can spit shards at you when it gets hot. As David says, it needs to be orange - carrot colour is often quoted - and held there for a few minutes for the heat to penetrate and the crystalline changes to occur.

Sounds like it may already have been hardened. If so, step one is to soften it by annealing. That means holding the item at a steady red heat for a few minutes and then letting it cool as slowly as possible. Normally done in a furnace and not easy with a small torch.

After machining, the item can be re-hardened as described in the other posts.

Not a good idea to work with unknown materials if you can possibly avoid it. There are an awful lot of steels that don't heat-treat or machine well. I've had a few that were vile, including a rod that defeated carbide. By all means try it, but don't blame your equipment if the job goes pear-shaped. Much easier to use Silver Steel bought for the purpose.

Dave

Edited By SillyOldDuffer on 02/01/2018 16:19:59

It should be mentioned that it is only necessary to heat the operating end of the tool to temperature, shielding as suggested which concentrates the heat, then quench Also to temper , do not heat this end but heat the other and allow the heat to conduct down the tool until the desired colour is reached, then quench immediately.

Like your style

Sean

Regarding the hardening part of the process; I read in the M.E. Years ago that when the material is held at red heat for long enough, then the material will no longer be attracted by a magnet. It seems to work.

Maurice.

Sean, over the years I have made lots of similar tools and pretty well everything has been said regarding the heat treatment, David G is spot on with the oil quench, water is too harsh for most tool steels, silver steel in particular.
Have a look in my albums at "rimming cutter" a similar tool made from SS hardened in oil with Bullfinch torch and the aid of a few fire bricks. I would add the tempering colour on this cutter is a little dark in the photo, you need to temper to a pale straw -- the photo looks a dark straw which it was not. For tempering it is essential that the work is clean and bright -- wire wool or brush will not do -- and free from oil or finger prints.

I would strongly advise against using an unknown steel, you are going to put quite bit of time into making the cutter and for the sake of a very small £sum you may be disappointed and have a lump of scrap. If you feel you must use the steel you have then I would cut of a short length and harden it then test with a file -- it should skid over the surface, you will at least then know the steel will harden.

Hope this helps a little

John

With the greatest respect there is no evidence that what Sean is proposing to use is silver steel!

There are various simple tests for silver steel.

If Sean's material is not silver steel then a lot of the above is academic, as is Sean's aim to harden and temper the material he has.

Cheers,

Julian