RACK BAR, STEERING DEVICE AND ELECTRIC POWER STEERING DEVICE USING THE RACK BAR

PROBLEM TO BE SOLVED: To provide a rack bar that is inexpensive, excellent in bending deforming performance, and can be preferably used for a steering device. SOLUTION: A rack teeth forming portion 22 is machined on a main body 20 of a round bar shape having a diameter D formed by using steel subjected to hardening and tempering for a short time. Carbon content of the steel is 0.50 to 0.60 mass %. High frequency hardening and tempering are given to the rack teeth forming portion 22 to provide a hardening layer 25. The surface hardness of the rack teeth forming portion 22 is 680 to 800HV. At a part 27 wherein the depth of the rack teeth forming portion 22 from a surface of a back surface portion 26 is 3/4 D, total area percentage of a tempering bainite structure and a tempering martensite structure is 30 to 100%, and reproduction pearlite structure is 0 to 50% in area percentage. The total area percentage of the tempering bainite structure, the tempering martensite structure, and the reproduction pearlite structure is 50 to 100%. COPYRIGHT: (C)2005,JPO&NCIPI