SELECTABLE STRENGTH IN THE LONGITUDINAL DIRECTION OF STEEL BAR REALIZED BY PARTIAL INDUCTION HARDENING

Steel bars with selectable strengths in the longitudinal direction were realized by partial induction hardening. The strength difference in one steel bar can induce damage to the target lower-strength region without affecting the higher-strength region, which economizes the steel consumption compared to the traditional cross-sectional difference. This study introduced the specimen with the target yield strengths of 600 and 1200 MPa (600-1200 specimen), and of 800 and 1200 MPa (800-1200 specimen) from the viewpoint of heat treatments. All the single regions satisfied the target yield strengths with great ductility. However, unexpectedly, the 600-1200 specimen’s strength transition region became a weakness.