I’m a frequent visitor to Trad Gang, as well as a professional knifemaker. Please allow me to assist in flattening out your learning curve here a little bit on getting your steel hard.
It can be a rather daunting task to get things all identified and controlled, but with just the simplest of actions, you can make a serviceable blade.
First and foremost, you need to identify your steel type/classification. Different steel types contain different alloys and these effect the manner in which they will harden. Different temperatures and quenching media all come into play.
Here’s a basic procedure:
Heat up a piece of steel until it becomes non-magnetic and then cool quickly.
Simple, right?
At first glance.
One good thing is that all ferrous steel becomes non-magnetic at 1413 degrees. That is easily demonstrated! Heat up a piece of steel until a magnet no longer sticks to it!
That proves that atomically you have changed the condition of the steel. It is at that point that, depending on the steel type, you need to drop it’s temperature in only a few seconds to below 900 degrees.
Some need to make this drop in as little as 1 second, and others take as long as 4 seconds.
Too slow - no cigar.
Too fast - no cigar.
That is where the proper quench oil comes into play.
Firstly, canola oil is for cooking French fries.
Quenching oil is for cooling steel.
It is basically mineral oil, BUT! with special additives that absorb heat at a particular rate for the steel at hand. That is why there are different quenching oils for different steels, due to the rate of cooling necessary for that steel’s alloy content.
Have a known steel, but use the wrong oil, and you will fail.
W1 steel – quench in Water! O1 steel – quench in oil! A2 steel – air quench! And so on.
Then there are different oils for different steels speeds.
Here’s what happens – you bring a piece of steel up to that non-magnetic temperature and you have changed the steels condition. If you just let it cool slowly, it RETURNS to the same condition it was in when you started – soft.
You can watch it go black, and with your magnet, check as it slowly returns to a magnetic state.
But, if you heat it up to that non-magnetic condition and then quench it quickly in the appropriate quench media and cool it to below 1000 degrees at the proper rate for THAT steel, you “freeze” the steel atoms in a condition that is hard, because you stopped it from RETURNING to the condition it WANTED to go to – SOFT.
However, you have paid a price. It is really hard, but also brittle. It is not happy here.
So, we “temper” the steel to slightly soften and relieve the hardening stresses that have been induced in the alloy matrix.
Somewhere above I saw the temp of 1650 degrees or something like that. That’s way to high for the simple steels you will normally be using. A high temp for a chromium steel is 1525.
And, the mentioned tempering temp of 300 is way to low. More like 350 – 425 depending on how hard it got and the steel type.
Search you area for a gallon or two of medium speed quenching oil. A gallon can be ordered from Brownelle’s. I guess in a pinch, you would use Vet grade mineral oil from your local feed store. It will work for medium speed steels, but not the high carbon tool steels.
See, some oils remove the heat too slowly for “fast” steels. The steel will actually return to that “soft” state faster than a medium speed oil can remove the heat! Get it?
Some tool steels require the heat to be removed from 1500 degrees or so down to under 1000 degrees in less that 1 second!
Medium speed oils like mineral oil just won’t handle it.
That’s why so many new makers get frustrated by having good quality steel, but are quenching in the wrong media and can’t seem to get the steel hard! The oil is too slow.
Some guys quench in water and the blade cracks! The water is too fast!
Or, they don’t get that steel up to non-magnetic and change the steels condition. In that case, it won’t harden even if you have the correct quench media.
Lot of stuff to consider.
Know your steel.
Have the right quench media.
Get it up just past non-magnetic.
Hold it at the temp as long as you can without going too high.
Quench in the right stuff.
Do your research!
Good luck, guys.
Topic: Knife blade hardining. (Read 7158 times)
