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
Carbon steel springs are tempered blue.
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.
There is a good writeup in Machinery's Handbook.
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:
900F 39 RC 176 kpsi 10% elongation (ductility) pretty brittle!
1000F 35 RC 160kpsi 13% elongation
1100F 28 RC 140kpsi 17% elongation (getting softer)
Sounds like you want something right around 1000F
I had a good chart of the oxide colors, it disappeared.Next best
here is the red heat chart
1000F will be the very dark blue but not getting close to glowing red.
Karl Townsend wrote:
"> Does anyone have information for a procedure
to treat this for best spring
Karl, Do you need some material? I've got a
bit of C1075 that I used to make a
few thousand greenhouse clips out of last year.
It's .045 (I think) by 1/2" wide.
Got it from Mead Metals. Here is a link to
their heat treat chart--at the bottom of the
The ideal temper will depend on the stress and the number of cycles
the spring will experience. If the stress is relatively low, less than
90,000 psi, then tempering around 950F would give maximum life. The
700F temper would be appropriate if stresses are higher and shorter
life is acceptable.
I don't have any straightforward data on time, but 1/2 to 1 hour for a
small part would probably be safe.
Did you try this heat treatment as mentioned above? Did it work as
intended? How long did you hold the part at 1475 F, quench in oil, and
temper at 950 F?
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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
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.
John D. Slocomb