"hardened" freeze plugs

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Tony M.
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Re: "hardened" freeze plugs

Post by Tony M. »

desertland wrote:
So after hardening you give one a hammer blow and it does shatter, that could be taken as a sign that the carbon content is high enough that you have a pretty worth while baffle material. Even if its origins are from a lowly freeze plug.
If all of the plugs have the same chemistry, then yes, the issue comes in that because of the application, freeze plugs are rarely kept in lot segregation, so a single box could contain multiple alloys.
Fulmen
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Re: "hardened" freeze plugs

Post by Fulmen »

Increasing carbon content requires time and temperature, it can not be done any other way. Quenching in oil or any other material will not change carbon content.

I have just finished a furnace for heat treatment and have case hardened several parts made from mild steel. It's done in a sealed container filled with wood charcoal and 15% K/CaCO3 heated to appr 900°C. One can expect a thickness of appr. 0,1mm per hour, so it is pretty obvious that the quench cannot impart any significant amount of carbon to the material due to the short time (0,1mm per hour is the same as 30 nanometers per second).

For those who are interested, here's a little more detailed explanation. The process does not only require a source of carbon, it requires an atmosphere of carbon monoxide. This CO diffuses into the steel and reacts to form CO2 and carbon, the CO2 can then diffuse out and react with carbon to produce more CO. This is the reason for adding carbonates, it provides a source of oxygen as well as catalyze the CO2+C-reaction.

I would start by heating and quenching a plug and see what happens. No need for using a hammer, a file will tell you if it's hard or not. If a file cuts the material after quench it's not hard enough to make any difference. Choice of quenchant shouldn't be too critical considering the thickness of the material, just work fast. One can safely assume they are made from fairly simple steels, and they require a very fast quench to harden. If it doesn't work with water it won't work at all.
desertland
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Re: "hardened" freeze plugs

Post by desertland »

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Last edited by desertland on Thu May 14, 2015 9:43 pm, edited 1 time in total.
Fulmen
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Re: "hardened" freeze plugs

Post by Fulmen »

Yeah, pretty much...
Tony M.
Silent But Deadly
Posts: 368
Joined: Wed Jul 31, 2013 11:42 pm
Location: FL

Re: "hardened" freeze plugs

Post by Tony M. »

Fulmen wrote:Yeah, pretty much...
What he said.
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