LINEAR SHAPE STEEL EXCELLENT IN JOINT FATIGUE CHARACTERISTICS AND PRODUCTION METHOD THEREFOR

摘要

A production method for a linear shape steel having joints (2) each consisting of a ball hook (21) and a curved hook (20) at the end of a web, the method comprising the steps of hot-rolling a steel material vertically symmetrically to form a shaped bloom having flanges (2A) at the ends of a web (1) (first step), hot-rolling the bloom vertically non-symmetrically to adjust the web in size and form the flanges into shape joints (2B) including projecting ridges (20A) (second step), and hot-bend-forming-rolling the projecting ridges to form curved hooks (20) (third step), wherein the steel material contains 0.01-0.20 mass% of C, up to 0.8 mass% of Si, up to 1.8 mass% of Mn, up to 0.030 mass% of P and up to 0.02 mass% of S, and a hook bending start temperature in the third step is set to be over Ar3 or up to Ar3-50 DEG C so that the depth of a wrinkle (10) present on the inner side of the hook is made up to 0.5mm.