Steel product for induction hardening, induction-hardened member using the same, and methods for producing them

[0070] No. 1-31 steels having the composition shown in Table 1 were smelted by a converter, and formed into billets with a cross-sectional size of 300×400 mm by continuous casting. After the billet is rolled into a 150 mm square billet through the billet opening process, it is rolled into a bar steel of 24-60 mmφ according to the hot working conditions shown in Table 2.

[0071] Select a rotating bending fatigue test piece with a diameter of 8mmφ at the parallel part from the steel bar, and use an induction quenching device with a frequency of 15kHZ for the test piece and quench it under the induction quenching conditions shown in Table 2-1 and Table 2-2 Thereafter, a tempering treatment at 170° C.×30 m was performed to manufacture a sample of No. 1-43 steel material. For these samples, an Ono-type rotational bending tester was used to change the stress conditions at a rotational speed of 3000 rpm to conduct a rotational bending fatigue test, and the measured life was 1×10 8 Sec