How to heat small part

[JDJones]

Hi Gents
Some general info Re. hardening and tempering Propane/Air Flame approx temperature is 2.000 Centigrade, Propane/Oxy Flame 2.500 c Oxy/Acet flame 3.500 c. When I started out considered to be the hottest flame in Industry.
Oil Quenching, the oil forms a gaseous shield around the component which slows down cooling, water speeds up cooling allowing the water to contact the component faster Saline water, salt water, sea water allows the cooling to be much faster by creating small explosions when contacting the component Old Black smiths then re-heated the component to temperature by a colour code, which required a vast amount of skill and experience and of course the type of steel. All the Best Des Jones

 

[Maker]

colour code

I think the technical name is Blackbody radiation?
Anyway, according to the book, it goes like this:

220°C Very light straw.
225°C Light straw.
230°C Pale straw.
235°C Straw.
240°C Dark straw.
245°C Dark yellow.
250°C Very dark yellow.
255°C Yellow-brown.
260°C Yellowish brown.
265°C Reddish brown.
270°C Brown-purple.
275°C Light purple
280°C Full purple.
285°C Dark purple.
290°C Very dark purple.
295°C Full blue.
300°C Dark blue.

400°C Dull red, visible in the dark.
475°C Dull red, visible in half-light.
525°C Dull red, visible in normal daylight.
580°C Dull red, visible in sunlight.
700°C Dark red.
800°C Dull cherry red.
900°C Cherry red.
1000°C Bright cherry red.
1100°C Orange-red.
1200°C Yellow-orange.
1300°C Whitish yellow.
1400°C White welding heat.
1500°C Brilliant or dazzling white.

220°C-300°C was taken from the tempering colour table, 300°C is used for springs and wood saws, 220°C is for scrapers and lathe tooling for brass. It lists the uses for everything in between but I can't be bothered to type it all up.
It also says, for hardening steel, depending on the carbon content, the temperature should be 760°C to 800°C. It should be slowly brought up to temperature and quenched, and subsequently tempered to the desired hardness. It is important they are not heated above the hardening temperature otherwise they will have to be annealed before attempting hardening again.

 

[Bill Edwards]

?How do you quench evenly something like that? A thin walled long tube, something has to give, or distort.

Asking because I do not know, but would like to.

The best you can do is as with something such as a knife blade.
Drop it in while holding it vertically and ONLY move it up and down in the liquid, never slosh it round (bad practice anyway).

 

[hareng]

I was under the impression the colour started around 220 degrees and went out by 280 degrees. 275 being a light blue.

Springs no way we dumped in a bearing oil from cherry red to orange, wiped off then heated whale oil that burnt at 150 degrees to temper. Ultra rarely a breakage on the finest springs made.
Modern spring steel equivalent needed for similar strength hardening in water, then whale oil. Spates of breakages were put down to the time of year usually peak winter where the oil was cold, evident when others done slightly later being ok as oil warmed up.

 

[Wendelspanswick]

When we did engineering at school we were taught to harden and temper items in 2 separate processes, then when I did my blacksmithing apprenticeship I was taught the single hardening and tempering process used for chisels etc.-
You start with your round or hex stock and heat to red hot (not white hot) and draw down the end to form your chisel point, when you are happy with the shape you heat the tool back up to red hot and then plunge just the shaped end into your water bath to cool, moving it in a slow figure of eight motion until the end is cool, you then remove the chisel from the water and quickly file the tip till its bright. While you are doing this the residual heat from the body of the chisel (which you haven't cooled) is flowing back into the point of the chisel and this is when you watch for the temper colours on your freshly filed end.
When it reaches the correct colour you quench the tool again, tip first and then slowly lowering the whole tool into the water bath.
The advantages with this method is its quick, as you only heat the tool once and it leaves the point hardened and tempered and more importantly the body and the striking end of the chisel are left unhardened so no risk of chips flying off when struck with a hammer.

The trick is to leave enough heat in the body of the chisel to flow out to the point, easy in big chisels, harder to do in scribers and fine punches.

Very satisfying to do, especially if you have a batch of them to make.

We were lucky enough that the agricultural college next door would dump all their broken tractor bits into our skip, some of my best chisels, taper punches and hot and cold sets were made from unidentified bits of agricultural machinery!