Hardness of Carbon?

J

Jered

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Dec 26, 2005
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I'm new to these pages and I was hoping to get some information and thought I'd go right to the experts. I'm a culinary student and work at a cutlery shop by my school and there has recently been a debate relating to the general hardness of carbon vs. high-carbon stainless and just plain stainless knives specifically in chef's cutlery (Wusthof / Kikuichi / old Sabatier / etc). Some of the employees feel that carbon is the hardest of the three materials and others feel that stainless is the hardest. Another thought that the hardness of carbon related to what kind of carbon the blade was made out of. Any thoughts or information would be greatly appreciated.

Jered
 
Carbon is the chief alloy element that makes steel, both carbon and stainless hardable. With proper heat treat most times stainless blades are harder than carbon steels, but not always. Depends on specific heat treat and working hardness of particular steel and steel alloy. Edge holding is relative to hardness, but not the only thing relating to edge holding. Grain size has a lot to do with edge holding also. Edge geomitry and intened use has a lot to do with working hardness also. An axe needs a thicker and softer edge than a hunter, a fine pocket knife blade can have a thiner and harder blade than a bowie. The trick is to get as hard as posible without the edge chiping in use. Chrome in stainless and some high alloy steels increase hardability, and in the case of stainless has enough to make it stainless. Unfortunatly for stainless the amounts of chrome nessisary for stainless properties makes for larger carbides, even in the CPM steels, which are finner than has previously been posible with stainless. That's why many carbon steels when heat treated rite will come very close to the edge holding ability of a lot of the super stainless steels but be far easier to sharpen. The finner the grain at the proper working hardness the better the edge holding and easier to sharpen and tougher. That's one reason CPM S30V holds such a good edge, but even with the amounts of chrome it is still a bear to sharpen and not as tough as a properly heat treated carbon steel. I'm sure Mete will step in and correct any blunders I may have made.

Carbon carbides are softer than Chrome carbides if that helps. But there is a lot more to knives than hardness. Hardness is a benchmark for the knifemaker, but it is only one of many. Differant alloys afect the steel in differant ways. Also each steel has an ideal hardness where it's sometimes stronger at a higher hardness than a slightly lower hardness.
 
Jered, I wonder if you really mean 'hardness' or a combination of properties. Steel by definition is an alloy of iron and carbon. Stainless steel by definition is one that contains at least 12% chromium, and in knives usually 13-15%.Hardness is generally proportional to carbon content.In any cutting tool there is a compromise between edge retention and ease of sharpening.It's been some years since I used carbon kitchen knives but I remember some old ones that were VERY soft.On the other hand knives made of 1095 are excellent to me . Easy to sharpen and hold an edge well.Stainless steels of typical european make like Henkels have about .50C and are a good combination of sharpening and edge retention but I've retired my Henkels and now use Shun knives of VG 10.They are still easy to sharpen but hold an edge much better....But there are many carbon steels and many stainless steels and different ways to heat treat them.The knife is a basic tool in cooking so spend some money to get good knives , learn to use them properly and take very good care of them !!!
 
Jared, In my chef days I learned many things about knives that help me as a maker.The most important is that there are three things that affect the ability of a knife to cut.(1) the metal it is made from.(2) the sharpening skills of the user. (3) the skill of the user in cutting. The first makes the least difference. Learn to put a good edge on the steel.Learn how to use your knives efficiently and effectively.I have old carbon steel knives I love,and I have ones I make from S30V that are hold an edge well and stay sharp.Both have their places.
For your information,I make most professional cutlery from ATS34 or S30V.I make blades in 1095 by special order.
Make your motto this: "Good scalpels don't make good surgeons any more than good knives will make good chefs."
Stacy
 
Unfortunately, the description of the knife (carbon, high carbon stainless, stainless, etc.) says nothing about the hardness of the knife. All knives have carbon in them, and as far as I know, "high carbon" actually means nothing more (technically) than "carbon" when it comes to describing a knife steel.

"Stainless" does mean that the steel contains at least 10.5% chromium (the percentage varies according to whom you ask, but SSINA says 10.5%), but this doesn't help with hardness levels.

Generally speaking, you cannot get stainless steels as hard as non-stainless steels. One reason is because the chromium makes the steel more brittle, so a 62HRC stainless blade would be more brittle than a 62HRC 1095 knife. So, again generally speaking, non-stainless ("carbon") steels are usually "harder" than stainless.

There are also other properties such as edge retention and sharpness, which you may mean when you talk about "hardness." (Many people assume that harder steels/materials are sharper, but this is not true.)
 
So, basically, the answer is that it depends on many many factors. But we all talked at the shop today and all your info was discussed in length and greatly appreciated.

Jered
 
I haven't seen a real wide variety of carbon steel (nonstainless) alloys used in kitchen knives. Lately I have only seen a couple varieties in common knives. Most carbon steel kitchen cultery made in the US is made from 1095 alloy (with about .95% carbon in the mix with iron). This is usually hardened more than common American or European stainless steel kitchen knife blades. From sharpening these blades I would estimate that they are often in the 58 to 60 Rockwell C-scale hardness range. European and American stainless steel kitchen knife blades are commonly in the 52 to 57 RC range. The French Sabatier blades are made from a slighly softer alloy (something like 1085 with .85% carbon) which takes a wicked edge. I would estimate that they are hardened into the 56 to 58 RC range.

These are guesstimates, mostly from hand sharpening experience. Even though they are harder the carbon steel blades are usually easier to sharpen than all but the softest stainless blades. That is because the large amount of chrome in the stainless blades slows down the sharpening process (and often doesn't take as fine an edge as the carbon steel). Since they are harder (and often sharper to begin with) the carbon steel blades can hold an edge longer than stainless. They also respond better to steeling than stainless blades. The way that they lose out to stainless is that they can go dull via corrosion if they are not dried frequently. They can also give a metalic taste to acidic fruits and vegetables.

Japanese stainless is often in a different class (or several different classes) from European and American stainless kitchen cutlery. They tend to add more alloying elements like vanadium, molybdenum, and tunsten to the mix. This makes a lot of Japanese stainless as hard as 1095 carbon steel and it doesn't corrode. Its primary weakness is that hard stainless like this may chip if you use it on something like hard bone. This also makes it a bad bet for steeling. The Japanese also make kitchen knives from some very hard carbon steels as well. For most purposes I go for Japanese stainless cutlery.
 
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