440B is almost identical to 440A, but has a higher carbon content range compared to 440A 440C is considered a high-end stainless steel. It is very resistant to corrosion and is one of the most common stainless alloys used for knife making. … 440C has highest carbon content in 440 group.
I’ve seen these designations as a source of confusion in the knifemaking field for decades, and it’s time to set some things straight. First, there is no “440” stainless steel. Without the letter designation, it’s like claiming your car is a 20th century version (not identifying the year or the model)! Yes, I drive a 1900’s car; it’s a great car; it was built in the 1900s. How ridiculous is that? Yet I’ve seen this again and again in not only individual knife maker’s sites, but in knife manufacturer’s advertisements as well. The numbers 440 without the A, B, or C designation after them are essentially meaningless. Just Google the term 440 steel and see the endless list of makers and manufacturers that are proud to spew their ignorance about this type of steel, calling it surgical stainless, dive stainless, or other terms that demonstrate their lack of knowledge about the term they are attempting to define.
440A: this is a hardenable stainless steel alloy, hardenable to a higher hardness than 420 series stainless steels (which are only hardenable to 52 HRC). 440A has good corrosion resistance, and is used in less expensive bearings and in harder surgical tools (rare). It has 0.6 to 0.75 percent carbon, about the same carbon content as most steel springs. Its advantage is that is cheaper than 440B and slightly more corrosion resistant.
440B: this is a hardenable stainless steel alloy, hardenable to a higher hardness than 440A. It has good corrosion resistance and is used in cutlery (economy), valves, and instrument bearings, where high wear is less important than high corrosion resistance. It has 0.75 to 0.95 percent carbon.
440C: this is also a hardenable stainless steel alloy, hardenable to a higher hardness than 440B. It has good corrosion resistance, and is used in ball bearing balls and races, high pressure nozzles, valve seats and high wear components. It has 0.95 to 1.20 percent carbon. As detailed in the Machinery’s Handbook: “This steel has the greatest quenched hardness and wear resistance upon heat treatment of any corrosion-resistant or heat-resistant steel.”
All three of these steels have the same amount of chromium, from 16 to 18 percent. They are all high chromium martensitic standard stainless steels. All of their other alloy elements are about the same, including manganese, silicon, phosphorus, sulfur, and molybdenum. Clearly, the difference in these three is the carbon content, which is substantial. The higher carbon content in 440C yields a much more wear resistant knife blade. More about carbon on my “Heat Treating and Cryogenic Processing of Knife Blade Steels” page.