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Shed Machinist
10-11-2003, 03:21 PM
Is it best to quench mild steel in water, or oil?

Tony
10-11-2003, 03:39 PM
is this a trick question?

jfsmith
10-11-2003, 04:13 PM
This depends on the steel type. some are oil quench and some are air quench.

If you are forging a piece of steel, to keep the steel at a workable temperature I use water to cool the steel.

To harden and cool the oil quench stuff, I use a mix of 30 weight motor oil, ATF and olive oil. Many of the commercial formulas work well, I was taught by a blacksmith, so my formula is home made and does work well.

The air stuff, I place that on fire place bricks.

Jerry

Al Messer
10-11-2003, 04:46 PM
Shed, mild steel usually does not have enough Carbon content in it to make any difference if it is quenched or not. I assume that you are still in knife-making mode and are asking about how to harden and temper the blade once you have forged it to shape. In that case, and you are using a piece of steel with a Carbon content similar to an old file, jfsmith has already given you very good advise.

pgmrdan
10-11-2003, 05:53 PM
.

[This message has been edited by pgmrdan (edited 03-08-2004).]

Evan
10-11-2003, 07:19 PM
Shed,

As Al said, mild steel does not have enough carbon to matter. That's why it's called mild steel. But, you can change that. If you make a knife blade from mild steel you can harden it. Sharpen it first, to the best edge you can. Then put it in a metal container that is almost completely sealed. A piece of black iron plumbing pipe (not galvanized!) with end caps AND a small hole drilled in one of the caps will do. Don't leave out the hole!!! I suggest you buy the parts at different stores 'cause someone might think you are building a pipe bomb. It shouldn't cost more than a few dollars. Put the caps on very loosely. Fill the pipe with ground up charcoal briquets and put the blade in it and screw the cap on loosely. Start yourself a barbeque and put the pipe in it. Get out the hamburger and make lunch on it. Keep it going as long as you can. Make supper on it. Let it burn out overnight, this is a must. Next day you will have a case hardened knife blade. You may hone it very lightly to improve the edge but the case is only a few thousands of an inch deep so don't go grinding it.

If you really want to harden deep do this several days in a row.

BTW, the thin cutting edge will pick up the carbon quite well and so will withstand some light sharpening.

darryl
10-11-2003, 09:10 PM
I was given a small quantity of hardening powder by a local macnine shop. Procedure is to heat metal red hot, then grind it into the powder, reheat, grind it in, do a few times, more often for deeper penetration of the powders. You'd have to take a piece of sheet metal, fold it into a tight vee, and lay the powder into the vee, so the blade can be pressed into it, catch what falls out the ends and reuse it. Most of the powder will be pressed into the edge of the blade, where you want it. Don't burn yourself. I was amazed at how hard it was able to make a nail, hard enough to resist a file. If you can find this powder, add it to the ground up briquettes, and do as Evan has laid out. It will just make it better.

Evan
10-11-2003, 11:06 PM
The powder that Darryl speaks of is Casenit or Quick Hard. Both are Sodium Ferrocyanide. It is not as dangerous as it sounds, it only releases cyanide if mixed with strong acid. The MSDS says it can be disposed in the regular garbage. That stuff will truly harden a blade (or any other steel) but the blade must be heated to bright red heat for it to work. This requires a real forge or an acteylene torch. The barbeque trick will work, slower, but it will work and is way cheaper.

Tony
10-12-2003, 05:32 AM
i've heard stories of being able to case harden with only an oxy-acet torch. if i recall, the idea was to coat the workpiece (knife blade, in this instance) with carbon from a rich (or purely acetylene) flame. once coated, it was to be burned off, with a hot neutral flame. this process, repeated often enough, was supposed to "embed" carbon in the material surface.

anyone know if this is true?

-knucklehead.

Evan
10-12-2003, 08:47 AM
Sure, it should sort of work. Carbon is carbon, but the depth won't be much. I don't look forward to all the little carbon "floaties" in the shop though.

JCHannum
10-12-2003, 09:28 AM
Kasenit is advertised as containing no cyanide.
Use of carbonaceous materials for case hardening as described is somewhat effective, but temperatures in the range of 1650-1700*F must be attained and held. This is in the bright red range. Then reheating and cooling, and reheating and quenching is recommended.
There is quite a bit of information in Machinist Handbook on heat treating steels.

Evan
10-12-2003, 10:47 AM
JCH,

Kaseint IS sodium ferrocyanide. Here is the MSDS.

https://www.travers.com/htdocs/msds/pdf/81-003-001.pdf

Hardending, Tempering and Heat Treatment, WORKSHOP PRACTICE SERIES, #1

By Tubal Cain.



[This message has been edited by Evan (edited 10-12-2003).]