Is there a Material Engineer in the house? [Steel Question]

[Hobot]

This is related to my Ethical Dilemma thread.

The knives I was selling were supposedly made of the best steel money can buy. According to the Vector/Cutco training manual, they have a steel grade of 440A with a Rockwell Hardness of 56-57 degrees Celsius (which is the ideal hardness for a knife according to them). They then go on to say that Henckels (a German high quality cutlery company) knives are inferior as they use 420A steel. However, when I did my research some sites indicated that 440C is actually the best and that 420A steel is very cheap and used in the most inexpensive knives so Cutco must be lying about the quality of steel Henckels uses.

I'd just like to know if anyone can confirm or repudiate these findings.

[TheFeniX]

Can't help on the Stainless part (But I have been told by numerous people that 440 is about the best you can get). I do know that true Carbon Steel is much stronger than Stainless. Try some of these links:

1
2

Hope this helps. Links found using the magic of Google.

[aerius]

440A is a good stainless steel if corrosion resistance is the the top priority, unfortunately it's on the soft side and not very wear resistant due to the lower carbon content among other things. A Rockwell C hardness of about 55-57 is optimal for 440A.

Their claims of Henckels being made from 420A are completely false, you can't make a knife out of 420A. 420A is structural steel, it's quite strong but very soft and wears easily. The only 420 series steels suitable for knives are 420J2 and 420HC, the former is found in junk fleamarket knives while the latter is about the same quality as 440A.

420HC (high carbon) and 440A will both make pretty decent kitchen knives. Food is not exactly abrasive so wear resistance isn't much of an issue, and a Rockwell C hardness of 55-57 is enough to deal with bones. Both steels are also decently tough so that if you cut into a ceramic plate or chop into frozen bone wrong, the edge just gets bent a bit instead of fracturing and chipping out. The corrosion resistance is also important since many foods have corrosive juices, and the wet kitchen environment doesn't help either. Most good kitchen knives are made from a steel similar to this.

440C is a higher carbon version of 440A, it's harder and a lot more wear resistant but it corrodes a bit easier. No production kitchen knives I know of use 440C, it's only used by custom makers such as George Tichbourne, who makes some amazing custom kitchen knives among other things.

And then we move on to the high end steels, such as 154CM and BG-42. These are even harder and more wear resistant than 440C, while being a bit more brittle. These are used in high end production knives and many custom ones as well. You can take a small pocketknife made of these steels and cut a popcan to pieces and it'll still be sharp enough to shave with. A larger knife can be used to chop through a steel bar without any real damage. This is performance on par with M2 tool steel, which is a steel used in bits for milling, drilling, and cutting other steels. This level of performance is overkill for almost everyone. There's a company that makes kitchen knives out of VG-10, which is comparable to the above steels.

Then you get to the fancy particle metallurgy steels such as S30V, CPM-3V, and A11. Similar hardness to the above at about Rockwell C 60-62, but far more wear resistant and tougher as well. These super steels are hideously expensive and a bitch to work with, but they give the best performance money can buy. Very few knives are made from these steels, and they cost an arm and a leg.

To summarize, unless you're a looney like me you won't need anything better than 420HC or 440A.

[Darth Wong]

I don't know much about knives or the requirements for cutting meat and bone, but 440C has 2% elongation to failure. It's really very brittle, and it has a martensitic microstructure. I don't know much about specialty knives, but anything with a martensitic microstructure is a bad idea from a toughness standpoint. Then again, maybe knives don't need to be very tough; I tend to think about metal from a structural engineering standpoint.

Processing after the fact could change a lot of these parameters anyway. A blade made out of a ductile steel and then case-hardened might work fine. But since Hobot's problem was with the ethics of dealing with a MLM company, I'd say that's the real problem anyway. You can't trust anything a MLM company says.

[Crayz9000]

Well, my family has been using a set of RH Forschner/Victorinox knives since before I was born, and I've seen Forschner knives used in culinary institutions as well.

According to the Victorinox website... "All Victorinox knives are high carbon, stainless, first grade, A-quality stainless steel, x 50 CrMo. They are tempered to a 55-56 HRC hardness for optimum edge retention."

[aerius]

I don't know much about knives or the requirements for cutting meat and bone, but 440C has 2% elongation to failure. It's really very brittle, and it has a martensitic microstructure. I don't know much about specialty knives, but anything with a martensitic microstructure is a bad idea from a toughness standpoint. Then again, maybe knives don't need to be very tough; I tend to think about metal from a structural engineering standpoint.

A knife is not a prybar, nor is it a hammer, and unless you're using it as one you don't need much toughness. Practically all knives are made from martensitic steels, as that's the only way to get the required carbides and grain structure needed for high hardness and wear resistance. Knives are more similar to tool steels such as M2, A2, D2, etc. than anything else since their primary function is to cut things without wearing away.

Processing after the fact could change a lot of these parameters anyway. A blade made out of a ductile steel and then case-hardened might work fine.

It's been done but it doesn't really work that well. You'll get the hardness of a martensitic steel but not the wear resistant carbides and grain structure found in those steels. They've done some fancy stuff with nitriding and carburization of steels to case-harden & treat them but it hasn't worked out that well for knives. Does wonders for tool bits and some other cutting tools though.

[Zoink]

My Applegate combat knife is made from ATS-34 steel, which is supposidly better than 440C:

http://www.planet.eon.net/~matth/ATS34.htm

[Zoink]

I don't know much about knives or the requirements for cutting meat and bone, but 440C has 2% elongation to failure. It's really very brittle, and it has a martensitic microstructure. I don't know much about specialty knives, but anything with a martensitic microstructure is a bad idea from a toughness standpoint. Then again, maybe knives don't need to be very tough; I tend to think about metal from a structural engineering standpoint.

My japanese chef's knife is made from very brittle high-carbon steel, layered on either side with multiple layers of stainless steels, then ground to create a "damascus" pattern on the blade. Its a similar process that they use for the samurai swords. You get a razor sharp cutting surface protected by the stainless steel. It not good for bones however, as the edge can chip.

[kojikun]

I have a feeling that if Mike were to engineer a knife, it would be capable of cutting through other knives, and you could drop a tonne right down onto the tip of it and the knife wouldn't break.

[Admiral Valdemar]

I have a feeling that if Mike were to engineer a knife, it would be capable of cutting through other knives, and you could drop a tonne right down onto the tip of it and the knife wouldn't break.

Bah, I'd rather just make a handheld version of the hydrocutters my dad's workplace uses.

I wonder if a 2mm wide, 65,000 PSI jet of water going at Mach 3+ and around 100 degrees C would cut other knives...

[kojikun]

Bah, I'd rather just make a handheld version of the hydrocutters my dad's workplace uses.

I wonder if a 2mm wide, 65,000 PSI jet of water going at Mach 3+ and around 100 degrees C would cut other knives...

With fine sand mixed into the water.. cuts a perfect cut every time without using a single blade.. omgs i thinking im getting horny thinking about it

[Admiral Valdemar]

Bah, I'd rather just make a handheld version of the hydrocutters my dad's workplace uses.

I wonder if a 2mm wide, 65,000 PSI jet of water going at Mach 3+ and around 100 degrees C would cut other knives...

With fine sand mixed into the water.. cuts a perfect cut every time without using a single blade.. omgs i thinking im getting horny thinking about it

The UK Fire Brigade uses a sort of abrasive hydrocutter "water knife" (the ones at father's work don't need the abrasive since they cut much softer materials like cardboard) that puts fires out through walls. Reminds me of MGS2 with Metal Gear RAY being the amphibious assault mecha that has a fuck-off huge hydrocutter in the mouth, imagine that thing attacking ships.

Course, the CAD dept. at the factory uses laser cutters for making stereos used for printing, but lasers, plasma cutters and normal knives aren't too good on food and textiles that can combust or blunt stuff easily.