Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making. |
03-15-2012, 09:50 PM
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Salt quench
How do you set up, use and maintain a salt quench bath?
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03-16-2012, 08:58 AM
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Location: Hubbardston, MI
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Rog, do mean a brine quench setup or do you mean a salt bath heat treating system?
Brine would be a matter of mixing around 9% brine with water for your quenchant, I would suggest a non metallic container to avoid rapid destruction due to corrosion. This would only be useful for very simple steels like 10XX and W series, and would be far too intense for most modern alloys. Even the 10XX and W can be successfully hardened in knife thickness in the right oils that were made to handle these shallow hardening steels.
If you mean salt baths, I am not certain I have the room here to cover the topic in a more general sense. I would say that for most knifemakers it is kind of overkill and a whole lot of expense, work and maintenance compared to just a good oven and some oil. I have used both electric and gas fired salt baths and have helped other makers and production heat treaters get set up. What the system consists of is a very solidly welded container (preferably of a very low carbon stainless) that is filled with heavy metal salts (solid at room temp). This container sits inside an enclosure that heats it (either gas fired burn chamber or electric kiln) to a temperature range above the melting point of the salts. The whole setup is really missing the point is it does no incorporate an electronic controller to run it for you. This is a digital programmable unit into which a thermocouple is wired so that it can read the temperature of the salts and regulate the electricity or gas supply and accurately maintain the temperature. Salts come in various chemistries for different temperature ranges that can be used for heating, quenching and tempering. Most folks separate them into two categories- high, for heating, and low temp for quenching and tempering. By far the most useful of the two for producing better results in blades is the high temp which will allow very precise and even heating.
Describing the full process of setting one up would be a very long and involved thread indeed and it may be best to find somebody who has done it to make a visit to.
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03-16-2012, 01:34 PM
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Thank you again Kevin. Sorry about the vague question. I am going to try it with some 1095, and test for quality.
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03-16-2012, 02:20 PM
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The brine should harden the 1095, maybe a bit too well, if you follow my meaning (ping). I know there are many folks who do the water base and are quite happy but so far all the successful recipes I have seen involved undersoaking to avoid that ping with modern steels.
If you meant the low temp salt bath for quenching, it is really meant for oil hardening steels. I have tried every way imaginable to get 10XX to work in low temp salts but have yet to overcome a healthy amount of pearlite and obtain a hardness level that I would find acceptable.
The best results I have gotten so far with 1095, both metallurgically and in knife performance, has been from a proper controlled soak at 1475F and a quench in a fast quenching oil. Very high hardness (65-67 as-quenched), excellent strength vs. toughness for the given steel after tempering to the appropriate level.
Last edited by Kevin R. Cashen; 03-16-2012 at 02:25 PM.
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03-16-2012, 05:34 PM
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My whole reason for thinking about the salt quench is that I was told 1095 is not for rookies, and needed areal quick quench. This I know now. I have been making knives for more than 6 years, using the magnet and Goddard's goop, (thank you $50 knife shop) Any way, I was warned off 1095, because I was told that I must use Park's 50, or the salt quench. Being a habitual "stand back boys, I got this" kinda guy I just thought I would try it for the experience.You have helped me a great deal, and I appreciate it to no end (all you guys out there) It seems I'll be settling on 1085 and 6150 for big stuff and 440C and 01 for folders. And I will be testing too. Kevin, thanks again, I'm sure well be talking some more.
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03-21-2012, 05:01 PM
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Rog, if you want to try 1095 go ahead and try it. If you haven't purchased it yet, I would recommend that you get it from The New Jersey Steel Baron. What Aldo carries was made up for knife making. Other 1095 that you find out there may not have enough manganese to shove the nose of the IT diagram far enough to the right to give time enough to miss it without having to go with something real aggressive. As Kevin said you could end up cracking a few blades but round off inner corners and grind out to 220 grit before hand and you may be able to do it. You could also see how well the steel will harden in vegetable oil first and go to brine only if you can't get it hard enough.
Doug
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03-26-2012, 09:48 PM
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Thanks for the info Doug!
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