Does chromium reduce the toughness of a blade steel?

[mb]

For instance, the only dramatic difference I can see in the composiiton of ATS-34 and A2 (both air-hardening I believe) is the higher amount of chromium in ATS-34. Is this difference the reason why A2 has a reputation for being noticeably tougher than ATS-34 (assuming proper heat treating for each)?

 

[Cobalt]

I think that A-2 has a great rep for toughness because it is usually maintained at a Rc of 56 to 58, while too many people use ATS at a Rc of 61. I have heard that when you drop the Rc of ATS 34 to the high 50's it gets really tough.

 

[Samurai6]

As I understand it, certain alloying elements, Chromium in particular, tend to form large carbide crystals, and the alignment and size of these crystals can tend to give the entire matrix a large "grain" size with continuous and distinct grain boundaries. These large and distinct grain boundaries weaken the steel and are the cause of stainless steel's tendency to be brittle at high hardness. Another thing that contributes to stainless lower strength potential is that the more complex molecular transformations that take place during hardening slow the transformations down, allowing, again, large clusters of carbide molecules to form. Stainless, high-alloy steels generally require more complex and carefully controlled heat treatment in order to perform well.

ATS-34 is about 18% alloys while A-2 is around 8%. ATS-34 can actually be quite tough at 61 RcH, but it has to be cryogenically quenched, soaked at a temperature as far below zero as possible, and triple tempered to make the grain structure in the blade as homogenous as possible. Some makers like Jerry Hossom, Ernie Mayer, and Tom Mayo make short swords and machetes out of ATS-34, and they serve well.

[This message has been edited by Steve Harvey (edited 05-25-2000).]

 

[Jerry Hossom]

What Steve says is true, but with proper heat treating and cryogenic quenching, the grain structure of ATS-34 can be quite refined. Still, at the same hardness it is not as tough as A2. Having said all that about the problems of chrome, one of the toughest steels around is CPM-3V which has 7-1/2% chrome while A2 has just 5%. D2 which has 11% chrome is more brittle than 440C which has 17%.

BTW, ATS-34 also has 4% Molydenum, which is another carbide forming element that contributes to hardness.

Steel defies simple logic.



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Jerry Hossom
www.hossom.com