Grade 440C stainless steel is a high carbon martensitic stainless steel. It has high strength, moderate corrosion resistance, and good hardness and wear resistance. Grade 440C is capable of attaining, after heat treatment, the highest strength, hardness and wear resistance of all the stainless alloys. Its very high carbon content is responsible for these characteristics, which make 440C particularly suited to such applications as ball bearings and valve parts.

Applications

Typical applications include:

Rolling element bearings

Valve seats

 High quality knife blades

Surgical instruments

Chisels

Heat Treatment

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.

Welding

If welding is necessary pre-heat at 250°C and follow welding with a full anneal. Grade 420 filler will give a high hardness weld (although not as high as the 440C), but 309 or 310 will produce soft welds with higher ductility.

Machining

In the annealed condition this grade is relatively easily machined; approximately the same as for high speed steel. Chips are tough and stringy so chip breakers are important. If these grades are hardened machining becomes more difficult and probably impossible.

Principal Design Features This is a high carbon martensitic stainless with moderate corrosion resistance good strength and the ability to obtain and keep excellent hardness (Rc 60) and wear resistance.