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I've read that when making a knife from a railroad spike, it needs to be quenched in "SuperQuench" or a similar solution. I'm wondering, what happens if you quench in oil rather than Superquench? Does it harden but not as hard? Does it do nothing? Just curious on why the different quenching liquids for different steels.

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Greg, im sure the others will chime in with their collective genious, but i would recommend first doing a lengthy search and some reading. There are some really great threads here on the subject.  To me, a rr spike is less than average quality steel, so using superquench would be overkill? Not sure but i believe its designed for higher quality steels. As far as using "oil", i wouldnt use motor oil because of the fumes and impurities, i would use simple and cheap canola oil. Works great for leaf spring and 5160 which seem to be readily available when starting to forge. If you did use motor oil or trans fluid ,im sure it would harden, but you may get unexpected results. Superquench was developed for the metal industry for good quality repeatable results.

Tom

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Speed is the primary issue.  For carbon steels there is a knee in the Time/Temperature diagram that happens at about 900 degrees F.  If you can cool the steel below that point in the proper amount of time, the steel will convert to martensite and become hard.  The T/T diagram is different for different steels, some need to be faster, some can be a bit slower.  1095 needs to get to the knee in about .3 seconds, 1080 needs to get there in about 3 seconds.

Oils can be slow or fast depending on formulation, canola is not particularly fast, but works OK for most of the simple carbon steels, water is much faster (way too fast for steels like 5160), brine (salt water) is faster still and SuperQuench is faster still.

Because RR spikes don't really have enough carbon to get hard (a whole other issue) you need SQ to get anything out of them.  It makes things made out of them tough, but not hard when compared to a properly heat treated piece of 1080.

That is a thumbnail of the information needed to understand making a blade hard.  It is the central mystery in our craft.

 

Geoff

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35 minutes ago, Geoff Keyes said:

Speed is the primary issue.  For carbon steels there is a knee in the Time/Temperature diagram that happens at about 900 degrees F.  If you can cool the steel below that point in the proper amount of time, the steel will convert to martensite and become hard.  The T/T diagram is different for different steels, some need to be faster, some can be a bit slower.  1095 needs to get to the knee in about .3 seconds, 1080 needs to get there in about 3 seconds.

Oils can be slow or fast depending on formulation, canola is not particularly fast, but works OK for most of the simple carbon steels, water is much faster (way too fast for steels like 5160), brine (salt water) is faster still and SuperQuench is faster still.

Because RR spikes don't really have enough carbon to get hard (a whole other issue) you need SQ to get anything out of them.  It makes things made out of them tough, but not hard when compared to a properly heat treated piece of 1080.

That is a thumbnail of the information needed to understand making a blade hard.  It is the central mystery in our craft.

 

Geoff

It's posts like this that keep me readin'. Thanx!

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To add to Geoff's informative (as always) post, standard RR spikes are around 0.2% carbon and can't be hardened.  The vaunted HC spikes are only high carbon compared to ordinary spikes, weighing in at 0.35%.  Superquench will harden those.  Superquench is ONLY for steels of less than around 0.35% carbon and will destroy real blade steels, often explosively.

Spikes are tough due to added silicon, but were never meant to be hardenable.  They look cool, though.

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Anecdote:

I made exactly one rr spike knife (out of having over 100 rail road spikes at one point), I quenched it in cold brine and I was able to do a 2x4 chop test with it. I left the handle area square though so it gave me blisters. I leave it out by the forge to cut open bags of coal and charcoal as I need to.

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3 hours ago, Alan Longmire said:

will destroy real blade steels, often explosively

I have to try it with 52100 now. :rolleyes:

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Super Quench is cool stuff.  I've successfully used on on two RR spike "Letter Openers".   Got hard enough to take an edge and cut paper easily.   Makes a crazy sound during the quench.    I would definitely  be careful with it though,  And Jeremy, if you do try it with 52100, please do take a video from behind bullet proof glass so we can all see the results :) 

I imagine the fumes are none to healthy either if you are too close.  I think the experts here have already answered the question at hand.

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