Development of a High Hardness Soft-Magnetic Stainless Steel K-M57

Voices of our customers in late 1990s requiring soft-magnetic steels with high hardness for high wear resistance and high durability drove us to launch research and development and we have succeeded in developing a new steel K-M57, Fe-15Cr based precipitation-hardened ferritic steel by modifying a base steel with high hardness above 400HV but not quite satisfactory concerning magnetic properties and manufacturability. A simple relationship between concentrations of alloy elements and matrix phase has been found around the composition of base steel which gave us a confirmation about stability of ferritic matrix and helped us to design the new steel. Newly developed K-M57 has both high hardness (>350HV) and high performance soft-magnetic properties (Hc2500μH/m, B2000>1.2Tesla) simultaneously, which satisfy the requirements of magnetic cores of various types of solenoid valves including fuel injectors of automobiles. It also has high corrosion resistance and high electric resistivity (ρ[congruent with]90μΩ-cm) suitable for highly responsive devices. K-M57 has also good manufacturability due to low hardness (