Production method for a magnetostrictive torque sensor

A production method for a magnetostrictive torque sensor which detects steering torque applied to a steering shaft by electrically detecting distortion of a magnetostrictive film provided on a surface of the steering shaft, comprising:

• a plating step of forming the magnetostrictive film on the surface of the steering shaft;
• and
• a heat treatment step of heat-treating the magnetostrictive film on the surface of the steering shaft,
• wherein the heat treatment step decreases a weight ratio of hydrogen included in the magnetostrictive film
• wherein when a thermal desorption gas analysis is performed on at least a portion of the magnetostrictive film removed from the surface of the steering shaft which undergoes the heat treatment step, a portion of the magnetostrictive film having a thickness of 40 μm or less is heated at a temperature rise rate of 5° C. per minute,
• a weight ratio of a total amount of the hydrogen desorbed from the portion of the magnetostrictive film due to the heat treatment step to a weight of the portion of the magnetostrictive film before the heat treatment step is equal to or less than 3 ppm up to 150° C.,
• wherein the weight ratio is equal to or less than 10 ppm up to 300° C., and
• wherein the weight ratio is equal to or less than 15 ppm up to 400° C.