Is there any way I can tell CPM M4 from standard M2

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Feb 19, 2019
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I have a batch of blades all hardened to 66 Rc and the markings are burned off. Is there anything I could do to tell between them?
 
If this data is correct .......................
CPM M4 - Density 0.286 lb/in3 (7916 kg/m3)
M2 - Density 0.294 lb/in3 (8138 kg/m3)
 
Lick them - the M2 is more bitter tasting due to the nickel content.

Seriously, I don't think there is any way short of spectrograph to tell them apart because they are so close. The only real difference is that M2 has some nickel. I would divide the batch in half and call the right half M2 and the left half M4 .. or is nit the other way around?
 
Find somebody who is allergic to most 925 sterling silver, and rub it on their arms, whichever one makes them react is the M2.
That should work right Stacy.
 
Actually, it is the old white gold alloy that had about 5% nickel. They banned that alloy about 40 years ago.
Sterling is 92.5% silver and 7.5% copper. People who are "allergic" to silver are really allergic to copper. Despite what many people say, copper is a very rare allergy.

Fun fact - 14 karat yellow gold is 25% copper.
 
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Hmmm???
I see nickel on the Zknife charts for M2, and it is mentioned in the steel's discussion on a couple websites.
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, but not in the data sheet for M2

ASTM M2 Tool Steel Chemical Composition Properties

ASTM A600CMnPSSiCrVMoW
M2 regular C0.780.880.150.400.030.030.200.453.754.501.752.204.505.505.506.75
DIN ISO 4957CMnPSSiCrVMoW
1.33430.860.940.453.804.501.702.104.705.205.906.70
JIS G4403CMnPSSiCrVMoW
SKH510.800.880.400.030.030.453.804.501.702.104.705.205.906.70
 
The Zknives app is made by a knife enthusiast, it is not a perfect representation of steel chemistry requirements. The AISI spec allows a maximum of 0.3% Ni for both M2 or M4. The Zknives app shows this as simply 0.3% Ni for whatever reason with M2 and leaves it off for M4.
 
Actually, it is the old white gold alloy that had about 5% nickel. They banned that alloy about 40 years ago.
Sterling is 92.5% copper and 7.5% silver. People who are "allergic" to silver are really allergic to copper. Despite what many people say, copper is a very rare allergy.

Fun fact - 14 karat yellow gold is 25% copper.
always thought it was the other way around? 92.5% silver and 7.5% copper? no? thanks.
 
Thanks for the catch. It was a typo. 92.5% silver/7.5% copper.

Coin silver (mostly used to make silverware and serving pieces) is 90% silver and 10% copper to make it harder and last longer. Some countries, like Canada used only 80% silver in their coins.
 
The Zknives app is made by a knife enthusiast, it is not a perfect representation of steel chemistry requirements. The AISI spec allows a maximum of 0.3% Ni for both M2 or M4. The Zknives app shows this as simply 0.3% Ni for whatever reason with M2 and leaves it off for M4.
Just as a sidebar, would Ni be a good thing to have in there for knives? In theory at least
 
Thanks for the catch. It was a typo. 92.5% silver/7.5% copper.

Coin silver (mostly used to make silverware and serving pieces) is 90% silver and 10% copper to make it harder and last longer. Some countries, like Canada used only 80% silver in their coins.
True. The Canadian 5 cent piece used to be about the size of a dime and made of 80% silver.
In 1921 they recalled them and switched to the nickel. I bought one of the few hundred that survived with my paper route money when I was a kid. I sold it about 10 years later to buy alcohol and other essentials.
 
Just as a sidebar, would Ni be a good thing to have in there for knives? In theory at least
The danger with nickel additions is that it is a strong austenite stabilizer so retained austenite becomes a concern.
 
True. The Canadian 5 cent piece used to be about the size of a dime and made of 80% silver.
In 1921 they recalled them and switched to the nickel. I bought one of the few hundred that survived with my paper route money when I was a kid. I sold it about 10 years later to buy alcohol and other essentials.
Are they still nickel? Bet they would be worth a lot more as scrap.
 
Are they still nickel? Bet they would be worth a lot more as scrap.
I quit collecting in the early 80s. According to Google they were 99.9 percent nickel for a range of dates up to 1981. Apparently now they are mostly steel with some nickel plating.
 
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