You’ve seen the old carbon steel chefs knives, the ones stained with black spots, and washed grey with age. Have you ever wondered why you still see them being used when there is a seemingly endless selection of new shiny stainless options available? If you’re someone that uses edged metals often you probably already know the answer. Many chefs, barbers, and wood workers often opt out of the trendy stainless for the old standby – carbon steel.
What’s the attraction? Why would someone prefer one over the other. Most often it becomes a choice of maintenance. Carbon steel will take a keener edge than stainless, and you will be able to acquire that edge in a much quicker fashion. Here is a photo taken with an SEM (Scanning Electron Microscope) that shows an ultra close up view of a commonly used stainless blade steel manufactured by Sandvik. The stuff that looks like moon debris going across center is actually chromium carbides protruding from the surfaced edge of the steel. These large carbides contribute to the wear resistance of the steel but, at the same time, they also reduce the toughness and the sharpness potential of the blade. The large carbides make the knife very difficult to sharpen and tend to fall or be ripped out of the cutting edge during use and sharpening. As a result, most knife blades made from common stainless steels become micro-serrated making it very difficult to acquire an edge that can match that of a carbon steel knife. (Photo courtesy Sandvik Materials)
These carbides are extremely hard. Knife hardness is rated using a Rockwell tester on the C scale. For arguments sake let’s say you have a Wusthof chef knife with a Rockwell of 58rc. Those carbides you see in that photo, which are essentially what you are trying to sharpen, may actually test up to a hardness of 70rc. Most knives, carbon or stainless, average around 56-60rc, so you can imagine why 10rc points adds a new level of difficulty when sharpening stainless steels.
Many stainless users attack this problem with diamond stones. Yes, there is actually real diamond grit on the face of these plates, which is one of the reasons they are so expensive. However, a problem still exists. If one is not patient during the sharpening process, and simply pushes down harder to expedite the process, the diamond grit will rip the carbides right off the edge of the blade, creating that “toothy edge” and an even longer sharpening process.
So that leads us to the next question- Why then would someone prefer stainless over carbon. The most obvious reason is corrosion (rust) resistance. The other main one is abrasion resistance. Those carbides protect the surrounding softer metal and provide an improved wear resistance essentially creating an edge that will last longer.
Read this Bladeforums post to the left put up by a moderator there who operates under the username “Knarfang”. He explains it much better than I, and provides a good analogy for carbides and wear resistance.
In the end it is completely up to the user and their intentions with their blade. If you cut carpet all day and need a high abrasion resistance, stainless would be the best choice. If you are slicing sashimi and tomatoes that requires a refined edge it would have to be carbon steel.
Next post should hopefully include some testing and comparisons between stainless and carbon. In the meantime don’t buy any knives (or swords for that matter) off the home shopping network. Thanks for reading- chris
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