1095 and that one second

samuraistuart

samuraistuart

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Dec 21, 2006
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Just trying to make sure I understand this principle properly. I may be all wet....so I kindly ask your correction if needed. 1095 requires a super fast quench to harden properly, especially if the Mn count is really low. I've heard that you have less than a second to get below 900F, or the pearlite nose (whatever that is for 1095). Here is the question.....is it the quench medium itself that has less than one second to do it's job? Or does that "less than once second" mean "you have less than one second to get your blade from 1475F inside the forge to below 900F"? Which I would think is just damn near impossible.

I was thinking that once 1095 had reached it's austenitizing temp of 1475F or thereabouts, you need to move as quick as you can from the forge to the quench, but if that takes a second...you are still OK.....because the temperature of the steel is hopefully going to still be above where it needs to be. Not saying to dilly dally. If it takes one second to go from forge to quench....it is the quench medium itself that now has less than one second to go from the temp it is at (which is going to be below 1475F due to the time it takes for you to go from forge to quench) down to 900F or whatever?

I hope that makes sense. Thanks for your help in understanding this correctly.
 
The second begins when the hot steel is quenched into the quenchant, not from when it is sitting in the forge or kiln. Although you need to move somewhat quickly from heat source to quenchant, you have much more time than one second.
 
Thank you very much guys. I thought that was right...just wanted to make sure. I do recall when I first started making knives and learning about heat treating...that i had it backwards....thinking you had one second to go from the flame to 900F. Good to know that it is the QUENCH that must reduce the temp in less than a second....and not my clumsy movement from the heat source to the oil.
 
This question got me curios, so I've been going back through all my HT info. Most say get to the quench as soon as possible.
I would also think that ambient temperature would be a factor on the steel cooling once out of the forge, i.e. get to the quench faster in the winter than in the summer. However if you have a climate controlled shop it shouldn't make to much of a difference.




So i guess it's a good idea to keep your oil near by.:)
 
You are on the right track and right train, Rusty. Absolutely....when it comes to 1095 and the like....get from your heat source to the quench ASAP. And I mean as fast as possible without any hiccups. But THAT DOES NOT MEAN YOU HAVE LESS THAN ONE SECOND TO GO FROM 1475f TO 900F. It is the quenchants job to get below the pearlite nose....and I think some guys heat treating knives are mis-understanding this.
 
You need to get the 1095 into the quenchant before any phase changes start, so guessing, you have to get it in before you get below 1400f or so. If you cool to 1200 before getting into the quench, then pearlite forms, and this cannot be undone (changed to martensite). If you get it in and you cross the pearlite nose on the way down you will get some pearlite as well. Once you get below 900f, the pearlite conversion swings way wide in terms of time, so you are good to go to get to Ms without much trouble.
 
I've often wondered how much heat is lost on the way from the forge to the quenchant. I always go as fast as I can. With thinner stock, heat loss is faster in the air or the quenchant.
 
Air is an insulator. It will cool the steel slowly as it's obviously cooler than the steel. Cooling to black is about 900f, and that takes a while in air. If you lose more than 1-2 shades of red between the kiln/forge and the quench, you are too slow. Hope that helps.
 
Look at this- the chart shows the time/temp. interaction.
http://www.cashenblades.com/steel/1095.html
For me, it's a pretty clear illustration of where that "one second" thing comes from, and just what has to take place within that second.
It's pretty easy to lose a lot of heat from a thin edge on the way to the quenchant, but my testing so far shows that I'm making it in time.
 
Warren & elementfe are right. Watch your blade as closely as possible from the heat source to the quench. If the edge or tip lose much color before you get to the quench then you probably wont miss the Pearlite nose, especially in that area of the blade.
That's another reason to grind bevels on anything 1/8" or thinner after H/T.
 
Metallurgically:
While soaking at 1475-1500F, 1095 is austenite. When taken from the forge/oven, it will cool rather slowly in the air. You have several seconds before it drops below 1350F. As long as it gets under the quenchant before that, you are OK. Once in the quenchant, the rate of cooling for 1095 is less than one second to drop to 900-1000F. This narrow range is called the pearlite nose. If it cools fast enough, the steel stays austenite. If it cools too slow some or all of the steel becomes pearlite. Once the steel has passed the nose, it is called super-cooled austenite. The cooling rate now should be a bit smoother, and you have minutes if needed to drop to 400F. At 400F the steel starts converting to martensite...and finishes that conversion around 200F. By room temp, the steel is called brittle martensite, and is very fragile. With two one hour tempers at about 400F, the steel is converted into tough tempered martensite.
 
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I was talking to my wife about this last night (yeah....she has the blank look on her face the whole time!!), guessing which temperature the steel cools to before you've lost it......I figured 1350F was right. Thanks for the metallurgy refresher Stacy...and the verification. Geez...maybe I am starting to get this stuff. After ALLLLLLLLL this time.
 
Whether you get it quickly or not, the big thing is that you care about it. That means you will want to figure out what the parameters are before doing something. This leads to better knives.
 
I found that moving too fast(from heat to quench) could cause uneven cooling due to the wicking effect of moving air. I also notice that my edges stayed hotter longer if I held the blade spine down. I stumbled upon this while taking someone's advice for avoiding "tip-dip" or reverse sori.
 
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Ok Rick i know your speaking words but, could you explain a little more. Like what's tip-dip?
 
I hope it isn't rude to answer for someone, I am guilty of that. I'm not trying to steal Rick's thunder, just trying to give an answer quickly. Rick...if I may and then you fill in where needed. "Tip dip" is when the tip of a blade actually bends down toward the ground (or toward the edge), due to the fact that the edge is cooling faster than the spine (as in hamon formation). Interestingly, when steel is quenched in oil, the "tip dips" down (negative sori), while a water quench causes the "tip dip" upwards (positive sori), as in the curve of a samurai sword.
 
Stuart has it, right. It mostly happens with dirk shaped geometry with a thin edge and thick spine. When using oil, quenching spine first and leaving a bit of stock have virtually eliminated it for me. Like Stu said, water quenching is more severe and doesn't usually have this effect.
 
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