hardening and tempering

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ChipMaker4130
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Re: hardening and tempering

Post by ChipMaker4130 » Wed Feb 19, 2020 9:27 pm

liveaboard wrote:
Tue Feb 18, 2020 4:07 pm
. . .2 rods I made for my press didn't bend at full force. . .
You don't say what function your hardened parts will perform, but if edge-loaded or if used where a bending force may be applied you definitely don't want super hard. When they break, its like an explosion - shrapnel and all! There are materials that can maintain toughness and hardness, but they are expensive and often difficult to properly heat-treat.

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tornitore45
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Re: hardening and tempering

Post by tornitore45 » Thu Feb 20, 2020 7:55 am

It's not like such a mistake would destroy a Mars probe...
Never happened before.... they built the pyramids.
Mauro Gaetano
in Austin TX

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liveaboard
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Re: hardening and tempering

Post by liveaboard » Fri Feb 21, 2020 6:09 am

ChipMaker4130 wrote:
Wed Feb 19, 2020 9:27 pm
liveaboard wrote:
Tue Feb 18, 2020 4:07 pm
. . .2 rods I made for my press didn't bend at full force. . .
You don't say what function your hardened parts will perform, but if edge-loaded or if used where a bending force may be applied you definitely don't want super hard. When they break, its like an explosion - shrapnel and all! There are materials that can maintain toughness and hardness, but they are expensive and often difficult to properly heat-treat.
I'm working an different things; the 24mm rods are good, as they're strong enough to resist bending while supporting the shelf beams at full force of the 20 ton press. Unlike the first rods I made from common mild steel.
bearing block in press.jpg
As you can see, the design puts a lot of stress on those rods; I hesitated to build it that way but I saw some commercially made ones like that and it could be done with leftover material I had.

The other parts I hardened are pivot pins for the lower arms of the 3-point lift of my tractor, and wear resistance is what I'm after more than sheer strength, as they're very oversized.

I think I just need a better idea of what heat treatment regimes bring on what combinations of hardness and ductility; and some objective method of measuring hardness would be very helpful too.

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tornitore45
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Re: hardening and tempering

Post by tornitore45 » Fri Feb 21, 2020 7:13 am

See this

viewtopic.php?t=32919

You do not need to buy one, is just a tube you drop a steel ball, the higher the bounce the harder the piece.
Mauro Gaetano
in Austin TX

johnfreese
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Re: hardening and tempering

Post by johnfreese » Sun Feb 23, 2020 10:02 pm

To get a rapid quench in water the water must be agitated or the part moved rapidly through the quench. If the part is held still and the quench is not agitate a layer of steam will form around the part which acts as an insulator.

Harold_V
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Re: hardening and tempering

Post by Harold_V » Mon Feb 24, 2020 2:55 am

Be careful about quenching long or slender items. If you expose the long face, on one side, to the quenchant, you can expect a permanent deformation (bowing) of the quenched part, thanks to one side contracting faster than the other.

When one quenches long objects, they are plunged up and down, not sideways, so that condition is minimized.

Speaking from (a bad) experience, by the way.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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liveaboard
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Re: hardening and tempering

Post by liveaboard » Mon Feb 24, 2020 5:29 pm

Thanks, I didn't know that; I was lucky this time but if I do it again I'll remember to put the material in end first.

Another thing I hadn't considered is the surface oxidization causing a little material loss.
These parts didn't have to be very accurate so I had the benefit of a cheap lesson.

Harold_V
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Re: hardening and tempering

Post by Harold_V » Tue Feb 25, 2020 5:28 pm

There's another condition to address when heat treating, especially if the heating process is long and drawn out. It's called decarburization, whereby the surface is depleted of carbon, so it won't harden. Hot rolled tool steels are often sold in what us known as a decarb free state, where, after final rolling, the surface is removed to the point where the material chemistry is as it should be.

If heating in an oxidizing atmosphere, or in a furnace without atmospheric control (rarely found in the home shop, if ever) material may lose its ability to harden (at least on the surface).

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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liveaboard
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Re: hardening and tempering

Post by liveaboard » Tue Feb 25, 2020 6:46 pm

I had some trouble with the kiln; it hadn't been used in years.
The gfi tripped off a couple of times; the bricks were full of water and the steam was condensing across the contacts outside.
Then there was a bad connection at the controler.
So the atmosphere was worse than uncontrolled; it was wet, hot, and cold again.
Ah well; we can only try.

I remember 40 years ago my friend Bob chortling happily about his diamond tip hardness test machine. I was 18 and barely able to hold a wrench, but I remember.
He recently died suddenly.
In a shed in rural NH, lie many treasures.
I have no doubt that old hardness test machine is in perfect working order.

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