Why we use Grade 440C and S30V Steel in our knives here at Alaska Guide.
Lessor Grades identified as "440A and 440B" are identical except for slightly lower carbon contents (0.60 - 0.75% and 0.75 - 0.95% respectively); these have lower attainable hardnesses but slightly higher corrosion resistances. Although all three versions of this grade are standard grades, in practice 440C is more available than the A or B variants.
A free-machining variant 440F (UNS S44020) also exists, with the same high carbon content as 440C. Again this grade is not readily available in Alaska.
Martensitic stainless steels are optimised for high hardness, and other properties are to some degree compromised. Fabrication must be by methods that allow for poor weldability and usually also allow for a final harden and temper heat treatment. Corrosion resistance is lower than the common austenitic grades, and their useful operating temperature range is limited by their loss of ductility at sub-zero temperatures and loss of strength by over-tempering at elevated temperatures.
CPM S30V is a martensitic powder-made wear and corrosion resistant stainless steel developed by Dick Barber of Crucible Materials Corporation in collaboration with knifemaker Chris Reeve.  Its chemistry promotes the formation and even distribution of vanadium carbides, which are harder and more effective at cutting than chromium carbides. These vanadium carbides give the steel a very refined grain, further improving the sharpness and toughness of its edge. Knifemakers use CPM S30V because its composition makes it easy to consistently heat treat as well as easier to grind although the carbides wear down the grinder belts. Its composition is as follows: Carbon 1.45%, Chromium 14.00%, Vanadium 4.00%, Molybdenum 2.00%
These properties are specified for bar product in ASTM A276. Similar but not necessarily identical properties are specified for other products such as plate and forgings in their respective specifications.
Table 1. Composition ranges for 440 grade stainless steels.
Table 2. Mechanical properties of 440C grade stainless steels.
Table 3. Typical physical properties for 440 grade stainless steels.
Table 4. Grade specifications for 440 grade stainless steels.
Table 5. Possible alternative grades to 440 stainless steel.
Good resistance to the atmosphere, fresh water, foods, alkalies and mild acids. Best resistance in the hardened and tempered and passivated condition. A smooth polished surface also assists.
The corrosion resistance of grade 440C approximates that of grade 304 in many environments.
Not recommended for use in temperatures above the relevant tempering temperature, because of reduction in mechanical properties by over-tempering.
Annealing - Full anneal - 850-900°C, slow furnace cool to about 600°C and then air cool. Sub-critical Annealing - 735-785°C and slow furnace cool.
Hardening - Heat to 1010-1065°C, followed by quenching in warm oil or air. Oil quenching is necessary for heavy sections. Immediately temper at 150-370°C to obtain a wide variety of hardness values and mechanical properties as indicated in the accompanying table.
Tempering in the range 425-565°C is to be avoided because of reduced impact resistance and corrosion resistance. Tempering in the range 590-675°C results in lower hardness (the product become machinable) and high impact resistance.