Production method of strong and tough thick steel plate

Abstract

A steel containing predetermined components is rolled in a recrystallization temperature region or a non-recrystallization temperature region of an austenite and is subsequently subjected to repeated hot bending. Alternatively, a surface layer portion is cooled during rolling of the steel described above to an .alpha. single phase or a .gamma./.alpha. dual phase temperature region, rolling is then effected and is finished at the point of time when the surface temperature of the plate rises above an Ac.sub.3 point due to recuperative heat, and repeated bending is carried out. Still alternatively, the steel described above is rolled to a cumulative reduction ratio of at least 20% in the non-recrystallization temperature region and is then subjected to repeated bending. Further alternatively, the surface layer portion is cooled during hot rolling of the steel described above to an .alpha. single or .gamma./.alpha. dual phase temperature region, rolling is then continued at a cumulative reduction ratio of at least 20% and is finished at the point when the surface temperature of the steel plate rises less than (Ac.sub.3 point--200.degree. C.) due to recuperative heat, and subsequently, repeated bending is carried out.