Exotic Steel Materials

[nullack]

Gday folks,

For my next knife I was thinking about doing something in an exotic material. Im looking at Aermet 100 as its got a good strength vs toughness score.

I'd like to get peoples opinions on what an optimal material properties hard use knife would have. Any responses should be in *measurable* properties and use *standard* material science terms.

To me theres three important things:

1. Hardness
2. Strength (especially the elastic region of the stress . strain curve)
3. Toughness

While I understand edge retention is important I dont see how it can be measured and tested in a standard way.

I'd like to understand what peoples views are about how important each property is relative to another. For example, the compromise between hardness and becoming brittle with loosing ductility (having the knife shatter in plastic failure).

 

[mete]

Typo ( having the knife shatter in BRITTLE failure).
Typically as hardness increases toughness decreases.Edge retention is related to strength and wear resistance .Wear resistance is greatly dependent on carbides.
The choice of steel depends first on the use .

 

[nullack]

Thanks mate. Im very interested in your expertise and anyone elses here. I make hard use hobby knives designed for camping and backpacking where carrying lots of knives isnt an option for weight.

Im especially interested in what migh be considered an optimal ratio of importance between balancing strength, toughness and hardness.

cheers

 

[Carcara]

Look at spec for Aermet 100 since I had not come across it before. It has only .23
percent carbon and in the hardened state only gets to 55 rockwell C. Does not sound like much of a knife steel, not much in the way of carbides for edge retention.

 

[69_knives]

I make hard use hobby knives designed for camping and backpacking.


cheers

What do you make them out of currently and what makes you believe that the material or knives are inferior?

I would consider that ease of sharpening would be just as important as toughness in a hard use knife.

As for edge retention testing - sharpen X number of knives exactly the same way with something like an edge pro that you can set an angle with, when they're all sharp, start cutting 1" manilla rope until you can't cut no more; repeat with the next blade.

 

[nullack]

Look at spec for Aermet 100 since I had not come across it before. It has only .23
percent carbon and in the hardened state only gets to 55 rockwell C. Does not sound like much of a knife steel, not much in the way of carbides for edge retention.

Thanks Carcara. So do you consider an optimal balance of the three material attributes to require high hardness in preference to toughness and strength?

 

[nullack]

Mete, I would greatly appreciate your expertise on this. Im looking for a super high strength and toughness knife material. Problem is the online materials databases seem to have values missing so I cant just enter my parameters into one material database and be confident what the search finds is the best available.

On the carpenter datasheet the aermet tooling steel has same dam high numbers (killing s5 in some areas):

http://cartech.ides.com/ImageDispla...al.gif&IMGTITLE=Typical+Mechanical+Properties

http://cartech.ides.com/datasheet.aspx?i=103&e=121&c=TechArt

The only thing Im not huge on is the HRC values. As for the carbon - cant carbides be formed from other than carbon??

 

[cotdt]

Im especially interested in what migh be considered an optimal ratio of importance between balancing strength, toughness and hardness.

cheers

You would need the data for each steel, like torsional impact vs. charpy impact vs. RC hardness. It would be different for each steel, but I can't find much data on the vast majority of steels. 1095, for example, is more chip-resistant at 65 than at 60 based both on anecdotes and the graphs, so you can't always assume softer is tougher. A2 is another example of harder also being stronger/tougher.

 

[nullack]

Thanks Cotdt. What exactly is torsional impact? Ive never seen that being reported on material properties. I know there is three forces in solid mechanics - compression, tension and shear. Torsion is a blend of those.

Mate I appreciate yours words on hardness not always being an inverse relationship to tougness. I looked up A2 and its scientifically proven that it has a jump in toughness at HRC60 as opposed to say HRC 58! Nice!

 

[cotdt]

Thanks Cotdt. What exactly is torsional impact? Ive never seen that being reported on material properties. I know there is three forces in solid mechanics - compression, tension and shear. Torsion is a blend of those.

Mate I appreciate yours words on hardness not always being an inverse relationship to tougness. I looked up A2 and its scientifically proven that it has a jump in toughness at HRC60 as opposed to say HRC 58! Nice!

There's tension impact, bending impact (Charpy test) and torsion impact. This talks about the torsion test:

http://www.instron.us/wa/applications/test_types/torsion/default.aspx?

It seems to correlate well with edge chipping resistance. Here's a graph for 1095:

Yes 1095 knives at 65 have been found to be very chip resistant.

 

[mete]

Torsion impact - you're in your car making a fast getaway but on gravel so your wheels are spinning and you're moving slowly. Suddenly you hit clean dry pavement and the wheels suddenly grab - that's torsion impact - a good way to break your axel !!!

 

[nullack]

Mete Im very interested in your expertise RE possible application of aermet tooling material to knives. As Carcara has pointed out it does have only .23% carbon, but it does have significant nickel and cobalt. It isnt super hard, but then again, it certainly is hard and demonstrated tremendous strength and toughness at the hardness level it can do.

 

[mete]

There are better choices . Try CPM 3V for an exotic steel with excellent performance.

 

[nullack]

CPM 3V has poor toughness compared with say S5.

Im primarily interested in strength, toughness and then hardness.

Aermet tooling alloys have been used in industrial tooling - blanking dies and other cold work dies for example.

Mate what do you think would be the problem? Excessively poor abrasion resistance?