Fatigue Strength of Micro Pulse Induction Hardened Steel. Effect of Case-Hardened Depth on Fatigue Strength of Micro Pulse Induction Hardened S45C Thermal Refined Steel

Recently, a new super rapid heating induction hardening technique which uses MICROPULSE SYSTEM has been developed. The new induction hardening technique differs from the former induction hardning in that the new technique is very useful for controlling case-hardened depth exactly, and is attendant on little deformation after hardening.In this study, in order to clarify the fatigue strength of the notched specimens of carbon steel (S45C, α=1.6) whose effective case-hardened depth are about 0.70mm and 0.45mm, uniaxial loading fatigue tests were conducted. It was found that the fatigue strength of the hardened specimens was 670MPa for the hardning depth 0.70mm and 630MPa for the hardening depth 0.45mm. Micro pulse induction hardening improved the fatigue strength about two times higher than that of the S45C base metal. The “Fish-eye” which indicates that fatigue cracks initiated from the inside of a specimen appeared on many fracture surfaces. And the position of the “Fish-eye” coincided nearly with that of the case-hardened depth.