How hot tester

This is where the oil that you use gets important again, also that you have consistency in that oil. A good formulated quenchant will drop you through that upper range we have discussed and then slow down the cooling as you approach the lower ranges. Yes, they do to this I have plenty of first hand experience that they can engineer oils to behave this way.

For interrupting the quench do a few practice runs and figure out the speed of your oil by counting off seconds and then removing the steel. My fast oils are usually around a seven count. When you pull the blade from the oil it should be well coated and have slight vapors coming off it. It should not heavily smoke- that is too hot! Most oils have active vapor points at around 400F so you should have a wet blade that is giving off light vapors.

Another test to perform in conjunction with this is to bend the blade; I recommend this anyhow since it will give you a good feel and make a believer out of you that there really is austenite still there and that the blade is very moveable. You will be able to feel that blade set up as martensite forms and things get increasingly stiffer. So put your gloves on and play with some hot steel. If you notice the steel burns your gloves and takes a VERY long time to start resisting you’re bending, you are interrupting too quickly.

Why interrupt? Well while it is not the best way to attempt marquenching it is a way to get within the ballpark. What this does is allows the martensite transformation to occur much more evenly throughout the blade and allows for a condition known as autotempering. Perhaps as much as 40% of the martensite will from at temperatures where the thermal mass of the blade will actually help get a jump start on tempering, greatly reducing stress and other issues. It is for this reason that I am not as paranoid as others about getting to the tempering before O1 cools too much. I have noticed a distinct increase in impact toughness in some steel that have been marquenched. But beyond all of that it is wonderful to know that you can straighten any warps that develop after the quench but before the blade fully hardens. The down side is that there could be a wee bit more tendency for retained austenite, but triple tempering seems to do a very good job at correcting much of this.
 
Kevin R. Cashen said:
Why interrupt? Well while it is not the best way to attempt marquenching it is a way to get within the ballpark. What this does is allows the martensite transformation to occur much more evenly throughout the blade and allows for a condition known as autotempering. Perhaps as much as 40% of the martensite will from at temperatures where the thermal mass of the blade will actually help get a jump start on tempering, greatly reducing stress and other issues. It is for this reason that I am not as paranoid as others about getting to the tempering before O1 cools too much. I have noticed a distinct increase in impact toughness in some steel that have been marquenched. But beyond all of that it is wonderful to know that you can straighten any warps that develop after the quench but before the blade fully hardens. The down side is that there could be a wee bit more tendency for retained austenite, but triple tempering seems to do a very good job at correcting much of this.
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It really is soft as butter! Thanks Kevin great info. I wonder if heatbath is as friendly to deal with about marquenching oils as they are about Parks50.
 
wow dady this is getting good. im working with 5160 and want to realy understand how and why not Just stick a magnet to it and dip in oil. thanks so much for all the info. right now im using vet grade minaral oil is that ok? which is like water thickness when heated up.
 
I interrupt all my 1070-1095 blade quenches. After about 5 seconds I slap them on the anvil and give them a couple of gentle taps with a polished face hammer, then grab them with the gloved hands and bend/twist/tweak as needed until straight. I then drop them back into the tank and let finish cooling.They are removed at tank temperature(130) quickly cleaned, and put into the oven for a snap temper. I rarely have a warp problem this way, and I agree that the blades seem to have a better martensitic structure.
Stacy
 
Jarod, in order to get a good handle on 5160 let's first simplify it and remove the chromium. Now you have 1060 and you will have to cool it very quickly but the soaking temp will be a matter of heating to 1500F holding for a couple of minutes to dissolve any extra ferrite (actually fill it with carbon since it is the solvent not the solute) and then quenching it. The main thing to remember before putting the chromium back in is that slight hold time to deal with that ferrite.

With the chromium put back in there to make it 5160 you now have shifted all the Arrest (A) lines on the diagrams in a very dramatic way. The temperature to soak it at will now be around 25F higher and the carbon will take a little more time to get into solution, however this will also result in the carbon being more sluggish on the way down so you will have around five more seconds to get below 900F to avoid pearlite, and in quenching that is a very long time.

You can get 5160 to harden cooling from the Currie temperature (above 1414F where it loses magnetism) but you will not maximize its potential. Yes it will skate a file real nice and even Rockwell out good as-quenched, but there will still be a little untapped potential left that you will probably notice in hardness after the tempering. But then again with the number of folks making 5160 knives with just the magnet and selling them quickly, who am I to say that it isn't "good enough". Just I have always been the kind of guy who obsesses over that last bit of leftover potential.

I will not get into whether mineral oil will or will not work for you, as that never seems to be a very productive discussion with a clean resolution. I will just say that I used many other things before going to actual heat treating oils, but once I did I never looked back, so I am more qualified to tell you about the results using one of those quenchants than I am with mineral oil. If other folks have done a good amount of studying Rockwell hardness of various thicknesses and microscopy of the results of using mineral oil instead they would be the ones to ask.
 
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