Advice on Heat Treating

[Ramon WilsonParticipant @ramonwilson3]

Hopper, as you rightly infer there are as many shades of cherry in the basket as there are cherries! Knowing which one to pick is another matter

As Dave says there is skill and judgement required but it's not a difficult process in the home workshop. The main thing to be aware of is overheating the part. If it's felt taht is the case just let it cool slightly before plunging into the oil bath. Simply dropping parts in is not a good idea as if the part is thin and goes in at even a slight angle to the surface of the oil distortion usually occurs.

I've said on many occasions I still get a buzz out of making a cutting tool and seeing it work as hoped for.

Like most I use silver steel and for most small cutters never bother to temper so as to have maximum hardness. Though it is intended as water hardening steel I always quench in oil basing this on an experience at work. At one time we produced a largish (for us) batch of small 12 mm diameter 'cams' with a 4 mm hex socket broached in one end. Quenched to manufacturer recommendations a very high percentage of them cracked on use around the hex socket.

The new batch were quenched in oil with a 100% success rate. Since then I have always quenched in oil for that reason. Yes the resultant hardness factor is not quite the same but it has always proved more than enough to do the job in hand. It has to be said that usually said tools are only for the one job so the risk of cracking is outweighed by the hardness of the cutting edge – for me. Were it to be something intended for long time use then it would get tempered.

Besides that occurance with Silver Steel, in the many thousands of tool steel parts heat treated over several years I only witnessed cracking of one batch of components. Because that was only one of the four batches out of the oven treated it was quickly realised that this was the first batch quenched into oil that was at ambient temperature. It had been a very cold night and though a modern factory the oil temp was well below what it would have been normally. From that point on a cube of steel was heated at the same time and dropped ito the oil to take the chill off before that first batch went in. Obviously that oil increased in temperature as each batch was done but no variation in hardness was experienced as a result.

Most, though not all of our steels but including silver steel came from Uddeholm and all our heat treatment followed their procedures as closely as possible. Heat treatment was a regular occurence in the machine shop that I ran not so much daily but certainly weekly – along time ago now but still quite fresh in my minds eye

Happy days – certainly miss the grinding facilities!

Tug

[Rod RenshawParticipant @rodrenshaw28584]

I read somewhere that back in the day when the colour of "Cherry Red" was originally used as a description of metal temperature, most of the apprentices being taught would only have been familiar with the glace cherries they saw on the Sunday tea table. Apparently fresh cherries would not have been seen in industrial cities at that time.

Rod

[egaParticipant @ega]

Has the use of a magnet to test for temperature been mentioned? This avoids the uncertainty of cherries, etc.

Tubal Cain's little book has excellent photos of the various temperatures and it just happens to be number one in the series.

[Martin KyteParticipant @martinkyte99762]

Niel once made the usefull alternative as cooked carrots to cherry red which may even have started out as cheery red, who knows.?

With most propane torches and hearths it equates to as hot as you can get it. I can't say I have ever managed to 'over cook' but then I'm not sure I would know if I had. Everything always comes out hard except the odd time I've picked up a lump of stainless thinking it was silver steel.

Probably more important to hold or soak at the top temperature. An hour for each inch of thickness rings a bell.

regards Martin

[HopperParticipant @hopper]

Posted by Ramon Wilson on 18/03/2021 10:18:37:

.. silver steel … Though it is intended as water hardening steel I always quench in oil basing this on an experience at work.

I'm glad to hear I'm not the only one who does this. I have always used oil when making cutters etc out of silver steel, in line with what we did at work many years ago. Been told by well informed types since that silver steel is water hardening and oil will make it brittle etc etc etc but that has never happened to me.

One thing I see some people doing is using a tiny cup of oil (or water) for quenching, and bubbling and boiling and smoking going on as a result. I use a large bucket, or at least a half gallon tin, and don't just drop the job in. Plunge it under the surface held in a pair of pliers and move it quickly up and down under the surface while moving it around in a circle near the outer edge of the container. This helps stop vapor bubbles forming on the hot job and slowing down the heat transfer so vital for quenching.

[HopperParticipant @hopper]

Posted by Martin Kyte on 18/03/2021 10:51:43:

Niel once made the usefull alternative as cooked carrots to cherry red which may even have started out as cheery red, who knows.?

Carrots I cook are orange, another colour again from dark cherry red or even bright glaced cherry red. As ega says, maybe best to use a magnet as Tubal Cain suggests. And like Martin, I find with a propane torch and firebricks and largish lumps (eg stress relieving my fabricated steel dividing head body) I will be happy with whatever shade of red I can struggle to achieve. No choice but a nice dull red usually.

[Anonymous]

Posted by Hopper on 18/03/2021 11:07:33:

Plunge it under the surface held in a pair of pliers and move it quickly up and down under the surface while moving it around in a circle near the outer edge of the container.

Likewise I use a large bucket. For expediency I use brine for quenching both silver steel and gauge plate. I'd agree that agitation is vital. To achieve maximum hardness, mid sixties Rc, the agitation needs to be vigorous. Anything less will result in a measured hardness around the mid forties Rc. I always temper, but don't worry about keeping the part above a certain temperature after quenching. I temper within an hour or two of hardening; basically the time taken for the electric furnace to cool down to tempering temperature. These are what I use to measure hardness:

Andrew

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