Patent ID: 11866798
Assignee: PROTERIAL, LTD.
Field: Materials, metallurgy (Chemistry)
Classification: CPC C  B  G  H | IPC B  C  G

Claim 10:
11. A method for manufacturing a magnetostrictive torque sensor shaft mounting a sensor portion of a magnetostrictive torque sensor, the method consisting of:
conducting heat treatment on a shaft material comprising chrome steel or chrome-molybdenum steel by carburizing for one time, quenching, and tempering for plural times such that the surface of the shaft material includes both austenite and martensite; and
conducting shot peening on the shaft material after the heat treatment at least on a continuous surface where the sensor portion is to be mounted,
wherein the shot peening is conducted by firing shot with a particle size of not less than 0.6 mm and not more than 0.8 mm and a Rockwell hardness of not less than 60 at a jet pressure of not less than 0.4 MPa and not more than 0.6 MPa for a jet exposure time of not less than 2 minutes only once such that further martensitic transformation occurs on the shaft material,
wherein the shot peening is conducted until a peak value of martensite in the shaft material with a Miller index of (200) is greater than a peak value of austenite in the shaft material with a Miller index of (200),
wherein before the shot peening is conducted, the peak value of martensite in the shaft material with a Miller index of (200) is smaller than the peak value of austenite in the shaft material with a Miller index of (200),
wherein peak values of martensite in the shaft material with a Miller index of (200) after conducting shot peening and martensite in the shaft material with a Miller index of (211) after conducting shot peening are not less than 1.15 times peak values of martensite in the shaft material with a Miller index of (200) and martensite in the shaft material with a Miller index of (211) before conducting shot peening, such that sensitivity of the resulting magnetostrictive torque sensor is not less than 4 mV/Nm,
wherein hysteresis error of the magnetostrictive torque sensor is not more than 3% FS in a range of not less than −40° C. and not more than 150° C.,
wherein the hardness of the shaft material after the heat treatment step is an HRC of not less than 59 and not more than 62, and
wherein the shaft surface after the shot peening step has a surface roughness Ra of not more than 0.2 μm.