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.

Applications Ball bearings and races, gage blocks, molds and dies, cutlery, valve components, knives and measuring instruments.

Machinability Best machined in the annealed condition. Tough, stringy chips can be best handled by the use of chip breakers. Carbide or ceramic tooling is recommended.

Welding This alloy is not commonly welded due to its tendency to air harden. If it must be welded, preheat to 500 F (260 C) and post weld treat at 1350-1400 F (732-760 C) for 6 hours followed by a slow furnace cooling to avoid cracking. Use similar filler metal and high heat inputs during operations.

Hot Working Pre-heat to 1400 F (760 C), then bring slowly up to 1900-2200 F (1038-1204 C)before proceeding. Do not work this material below 1700 F (927 C). Cool material slowly after working and once at room temperature, anneal fully.