PURPOSE: To obtain a thick steel plate which has an excellent shape and adhesion property of scale by regulating the thickness of the scale after the end of rolling in production stages for rolling a heated billet having a specific compsn. by a reversible hot rolling mill.
CONSTITUTION: A steel for structural purposes which consists, by weight %, 0.01 to 0.20 C, 0.03 to 1.00 Si, 0.30 to 2.00 Mn, 0.005 to 0.10 Al, 0.001 to 0.01 N and the balance Fe and is heated to Ac3 or above after solidification is rolled by the reversible hot rolling mill. The steel plate to be rolled in such production stages is subjected to descaling under an impingement pressure of ≥1.2kg/cm2 near the bite side of the hot rolling mill and thereafter, is immediately hot rolled. Such steel plate is then cooled at a cooling capacity of ≥500 kgcal/m2.hr.°C right after the rolling near the bite side of the hot rolling mill and such rolling is executed in plural passes back and forth. The rolling is ended at Ar3 or above. The high-temp. stagnation time from the rolling end temp. up to 650°C is confined within 70 seconds prior to execution of the accelerated cooling thereafter, by which the thickness of the average scale within the plate prior to the heating and cooling is reduced to ≤10μm.
ISHIKAWA TADASHI
ABE MASAKAZU
