The 440 grades form a series of high carbon martensitic stainless steels. They have basic corrosion resistance and extremely high hardness and wear resistance.
Approximate Composition – 16% Cr, 0.60-1.0% C plus Mo and V in EN grades (Exact composition ranges vary between EN and ASTM standards. Equivalents much looser than for most grades).
This grade combines the following characteristics:
- Basic corrosion resistance. Lower than other martensitic grades like 431
- Very high hardness increasing with carbon content. 440C capable of 60 Rockwell HRC (~700 HV)
- Very high strength up to 2000 MPa UTS, 1900 MPa 0.2% PS
- Low elongation 4%
- Low toughness 10J
- Very high wear resistance
- Difficult to weld
- Difficult to machine
This series of grades give the highest level of strength/hardness in any martensitic stainless steel. Consequently, they are used where a basic level of corrosion resistance is required coupled with high wear resistance or blade sharpness. They are usually supplied in the annealed condition for improved machinability and then hardened and tempered to develop the high hardness.
Applications which illustrate these features include:
Bearings, valves, knife blades, surgical instruments, tools, moulds, dies.