PREPARATION OF NON-NORMALIZED THICK STEEL PLATE FOR 80 KILOGRAM GRADE WELD STRUCTURE

摘要

PURPOSE:To obtain the titled thick steel plate to which excellent welding cracking resistance and low temp. toughness are imparted, by a method wherein a steel slab mainly containing C, Si, Mn, Sol. Al and Ti is heated to a predetermined temp. to be rolled and, thereafter, a rolling finish temp. region is prescribed to further perform rolling. CONSTITUTION:A steel slab containing, on the basis of a wt%, 0.05-0.15 C, 0.1-1.0 Si, 0.5-3.0 Mn, 0.005-0.060 Sol. Al, 0.03-0.20 Ti and, according to circumferences, further containing one or more of Nb, V and B or Ni, Cu and Cr or Mo, Ca and REM respectively in a predetermined ratio is prepared. In the next step, this steel slab is heated to 1,200-1,800 deg.C to be rolled and rolling is finished in a temp. region of 600-700 deg.C. By this method, the production of a thick steel plate is availably enabled directly from the rolling of the thick plate without necessitating normalizing treatment such as quenching or tempering after hot rolling. Tensile strength is also obtained in an objective strength level of 80kg f/mm.2 and excellent welding cracking resistance and low temp. toughness such that welding crack index P is CM 0.22% or less and Trs is -60 deg.C or less at a transient temp. can be imparted.