What is the hardest steel?

Huntsman Knife Co. LLC.

Huntsman Knife Co. LLC.

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I've been reading a lot about hardness lately and I was wondering, is there any steel out there that can be harded further than CPM 121 Rex and still be usable? I see that 121 can be hardened all the way to 72, is there any other steel that can rival this?
 
I don't know of a steel that goes higher than Rex 121.

As far as steels that are more commonly used, ZDP-189 is usually run around 65-67 HRC as a finished hardness (I believe before tempering it is around 70 HRC).
 
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The harder a steel gets the more brittle it becomes. Knifemakers try and look for the "sweet spot" when heat treating. It should have a good compromise between edge retention/edge stability, wear resistance, and toughness. Even this depends on the intended purpose of the knfie. As far as CPM 121 at 72RC goes, I would think that if you were cutting withit and hit a staple, you'd have an extremely large chip in the blade, if you dropped it, it would probably break cleanly into a couple pieces. I am probably mistaken in a couple things, but that is what I've learned in my time on BF.
 
On CPM's website, they have a quench hardness chart. The chart specifies that best toughness can be obtained between 66.5 and 70 Rockwell C, depending on hardening temp. According to the chart, this is tougher than when the steel is at 55 Rc.

They also list a few toughness comparisons:
Toughness (depending on heat treatment) approximately comparable to CPM 15V, CPM Rex 76 at maximum hardness, or conventional T15.
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Hard steel is brittle steel.

I want my knives to have strength, not just hardness.
 
riderV3 said:
Hard steel is brittle steel.
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The chart specifies that best toughness can be obtained between 66.5 and 70 Rockwell C, depending on hardening temp. According to the chart, this is tougher than when the steel is at 55 Rc.
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Not always.

Strength and hardness are related. Hardness testing is a quick way to get an idea how strong a part is, without having to do a full tensile test. It can't/shouldn't stand alone, but you can hardness test 50% of a batch and only have to destructively test maybe 1%, as an example.

Anyone know the intended use of CPM 121?
 
CPM 121: Designed for: Hobs, Broaches
Milling Cutters End Mills
Form Tools Punches and Dies
Guide Rolls Wear Parts
Hood Latch for Barbi's Corvette
 
me2 said:
Anyone know the intended use of CPM 121?
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from crucible's website:

"CPM REX 121 also bridges the performance gap between high alloy tool steels and carbide materials. It may be used in cutting tools, where high cutting speeds demand higher heat resistance, but carbide is too brittle, or in high wear tooling applications (punches and dies) where carbide tools are too fragile."
 
Carbide inclusions can raise the wear resistance of steels and Titanium alloys which come in at lower Rockwell numbers. Tungsten carbide is 72RwC. Vanadium carbide is 82 RwC. Titanium Aluminum Nitride, which is used as a blade coating (Buckcote), has a RwC hardness of 92 and is exposed on the edge of a chisel sharpened (single bevel) blade. Because the edge is so much harder than the blade, the steel wears away in preference to the coating and the knife sharpens itself.
 
tiguy7 said:
Carbide inclusions can raise the wear resistance of steels and Titanium alloys which come in at lower Rockwell numbers. Tungsten carbide is 72RwC. Vanadium carbide is 82 RwC. Titanium Aluminum Nitride, which is used as a blade coating (Buckcote), has a RwC hardness of 92 and is exposed on the edge of a chisel sharpened (single bevel) blade. Because the edge is so much harder than the blade, the steel wears away in preference to the coating and the knife sharpens itself.
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You said tungsten carbide is 72 RwC, what do you mean?
 
tiguy7 said:
Carbide inclusions can raise the wear resistance of steels and Titanium alloys which come in at lower Rockwell numbers. Tungsten carbide is 72RwC. Vanadium carbide is 82 RwC. Titanium Aluminum Nitride, which is used as a blade coating (Buckcote), has a RwC hardness of 92 and is exposed on the edge of a chisel sharpened (single bevel) blade. Because the edge is so much harder than the blade, the steel wears away in preference to the coating and the knife sharpens itself.
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Also, is that the hardness of the carbide itself, or the macrohardness of WC or VC in it's matrix?
 
rockwell C doesn't actually go that high, it is an estimated conversion from other scales like vickers

the carbide itself is the carbide itself, those aren't steels
 
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