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The Newbies Arena Are you new to knife making? Here is all the help you will need.

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  #1  
Old 09-14-2017, 10:45 PM
KevBooth KevBooth is offline
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Good target hardness for A2...

I ran into a bunch of A2 cutoffs for free, and am hoping to turn it into blades. I've done a little A2 in the past, but to say I was stabbing around in the dark would be an understatement.
The vast majority of the steel is 5"X1", some 6"X1". So the blades will be B&T style, or small drop points. Basically smaller knives, Flat ground. The most likely applications would be utility and hunting. Not much chopping, I would think.
My question is, what's a good target hardness, for A2 on a smaller knife? My Web reasearch shows a large range depending on the temperature of the tempering process. I'm just hoping to get some experienced opinions on the subject.
Thanks in advance.
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  #2  
Old 09-15-2017, 12:00 AM
Bob Hatfield Bob Hatfield is offline
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Since you plan to make them for utility or hunting I would harden to 59-60RC.


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  #3  
Old 09-15-2017, 12:04 PM
samuraistuart samuraistuart is offline
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A2 has a toughness/hardness intersection at around 61HRC. For a bird/trout/hunting sort of knife, I personally like them harder, even with all carbon steels. 63-64HRC. The best thing for you to do is make one, temper it for 64-64, use it, and see how you like it. If it's too chippy (I haven't found A2 to be), then back down the HRC with a higher temp temper.

If you were making a larger knife that would see more heavy use, then 60-61HRC. I personally do no believe most any steel should be left below 60HRC. If more toughness is needed, go with a different steel, ala 5160, 80CrV2 (1080+), etc. A2 is VERY tough, even at high hardness levels.

Recommend at least a sub zero treatment immediately after the quench to eliminate retained austenite. If you have access to "cryo" (LN2), even better, but not a must. There is quite a bit of retained austenite in A2 after a quench, and is not a desirable structure in cutlery.
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Old 09-15-2017, 01:41 PM
KevBooth KevBooth is offline
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Quote:
Originally Posted by samuraistuart View Post
A2 has a toughness/hardness intersection at around 61HRC. For a bird/trout/hunting sort of knife, I personally like them harder, even with all carbon steels. 63-64HRC. The best thing for you to do is make one, temper it for 64-64, use it, and see how you like it. If it's too chippy (I haven't found A2 to be), then back down the HRC with a higher temp temper.

If you were making a larger knife that would see more heavy use, then 60-61HRC. I personally do no believe most any steel should be left below 60HRC. If more toughness is needed, go with a different steel, ala 5160, 80CrV2 (1080+), etc. A2 is VERY tough, even at high hardness levels.

Recommend at least a sub zero treatment immediately after the quench to eliminate retained austenite. If you have access to "cryo" (LN2), even better, but not a must. There is quite a bit of retained austenite in A2 after a quench, and is not a desirable structure in cutlery.
Good to know, thank you. I agree a test piece is the way to go.
I know I may The opening a canna worms here. But you mentioned a subzero treatment. What can I use besides cryo-that would work?


Thanks
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  #5  
Old 09-15-2017, 01:59 PM
dtec1 dtec1 is offline
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Ideally cryo (liquid nitrogen) is best ....depends how low the steel has to go I am not familiar with a2 but I do a liquid nitrogen soak on all my stainless (stainless is 90% of my work) However some steel are ok doing what I call a "sub zero" treatment wich is a mixture of dry ice and acetone....some guys prefer to use alcohole in place of acetone.....It has always been easy for me to get liquid nitrogen from a weld supply store....Now I have a dewar (container for liquid nitrogen) it takes about 3-4 months for the 35 liters to evaporate. However if you have a weld supply near by that has liquid nitrogen before I had the dewar I used a strofoam cooler (NOT the one you can get at the gas station) I used the ones that they pack dry ice in and ship food. The walls of it are about 3 in thick...however the liquid nitrogen will evaporate in 24 hours in a cooler. so I used to get 8-10 blades ready for heat treat and do all at once....I always felt liquid nitrogen was best but like I said dry ice and acetone or alcohol will work for some steels
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  #6  
Old 09-16-2017, 11:41 AM
samuraistuart samuraistuart is offline
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Whether to cryo (LN2) or sub zero (dry ice) is really not complicated, but I understand how confused I was at first.

What are we trying to accomplish with these 2 things? It is the transformation of retained austenite into untempered martensite (that gets tempered later). Which one you pick will be simply determined by the steel itself, due to it's alloying. The more alloyed the steel, the more you NEED to go below -100F to convert that RA. Only the most heavily alloyed steels NEED, or I should say "should", get an LN2 soak. Think along the lines of S110V and the like. Steels like A2 and AEB-L, and honestly...MOST, of the steels we normally use do NOT NEED LN2. The dry ice slurry will be cold enough to convert most of the RA that needs to be converted. A2 falls easily into this category. However, more RA CAN be converted with LN2 over sub zero, but again, if it's a mid alloy steel like A2,D2, AEBl, etc, then sub zero does well enough.

However there is an added benefit when using LN2 over sub zero. Not only do you get a more complete RA conversion on all steels, but the LN2 WITH soak will allow the precipitation of extremely small "eta" carbides upon tempering. This BOTH increases toughness AND wear resistance. So with A2 and LN2 for example, you will get a theoretical 100% conversion of RA PLUS the extra eta carbides within the matrix after tempering. I say theoretical 100%, because even with XRAY diffraction they can only detect down to around 2% RA remaining.

Buying an LN2 dewar, one the right size and right mouth size, can be expensive. Plus finding a place to fill it. Dry ice is cheap, and the denatured alcohol is re-used over and over and over.
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