I'm making a couple small leaf springs. After a bit of searching, I've settled on 1095 steel for my project. It needs to be heat treated for spring properties, but I'm not finding info on tempering. The best page I've found has a HUGE range for tempering.
Does anyone have information for a procedure to treat this for best spring properties?
The classic way to heat treat objects small enough to burn in the torch flame is to put them on a larger piece of iron. which is heated to the necessary temperature, and is then tipped so the parts fall directly into the waiting oil or water quench bath.
Tempering is much the same, except no abrupt dump into fluid.
From Machinery's temper colour temperatures for plain carbon steel, full blue 560F (293C), dark blue 570F (299C). IIRC a usual recommendation is to hold the part at the tempering temperature for 1 hour per inch of thickness.
That can be done with a torch, with care. But it will be easier on a larger hunk of iron.
What they mean by tempering to a color is that after heating to incandescence and quenching, one cleans the black scale off a convenient surface (or all surfaces) down to bare metal, and then reheats the metal while watching the color of light reflected off a clean spot.
At something like 600 to 700 degrees F, the color will be a deep blue. These colors are generated by optical interference in the oxide film grown on the hot steel, and are a measure of the thickness of the oxide film. The steel is not emitting visible light during tempering.
Tempering to straw color can be done in a domestic oven, as this requires only 400 to 500 degrees F.
The page you mentioned showed tempering temps from 700 to 1300F, quite a range. Take a look at the various tempering temps on these links
What you are looking for is a plot of RC and Kpsi against ductility. Straight from the oil bath is 46 RC and extremely brittle. Temper at
700F will relieve the stresses, not much else. Here's the range you want to look at:
I've lost the original question, but in general, you need to read the specs for the metal in question to determine these factors.
Typically -- how long is determined by the thickness, usually specified as "N minutes per inch of thickness". The temper is also held for a time proportional to thickness (to allow the full piece of metal, from outside to center to reach the desired temperature).
And the *temperature* for the tempering is determined in part by the desired final hardness.
If you can get the book from the manufacturer, it will have good information on this.
I've not hardened 1095 -- but most recently hardened D2 (an air hardening steel which still requires a few tricky steps during hardening.
As an apprentice boy one of the things we learned was how to make our own tools and particularly for boring bars it was common to find them in the shop, mainly bars made for some particular task that a commercial bar wouldn't handle.
The accepted technique was to forge the bar to shape, rough grind it and then harden and temper. As we had no ovens and did it all in a forge the hardening was by heating to "cherry red" and quenching and then polishing and tempering to a "light straw" color and re-quench.
An accomplished tool maker could harden and temper in a single heat by quenching the cutter portion of the tool and then quickly hit it on the grinder (to see the colors) and let the colors run down the shank
- from the unquenched portion - and when the correct color reached the cutting edge stick it back in the water.
I am certain that we never got as constant result in dong it this way but I will say that it was a common method for making tools for a hundred years or more.