HARD ORIGINAL SHEET FOR SURFACE TREATMENT HAVING HIGH BH CHARACTERISTIC AND SUPERIOR WORKABILITY

摘要

PURPOSE: To obtain a surface treated steel sheet having high BH characteristic and superior workability by forming the structure of a carbon steel sheet of specific composition into a mixed structure of soft ferrite and hard hardened structure, refining ferrite grain size, and regulating the amount of solid-solution carbon to a specific value or above. ;CONSTITUTION: As a steel sheet to be subjected to surface treatment, such as tin plating and chromating a steel sheet having a composition consisting of, by weight, 0.070-0.200% C, ≤0.30% Si, 0.50-1.50% Mn, ≤0.030% P, ≤0.025% S, 0.002-0.100% sol.Al, ≤0.0120% N, and the balance Fe is produced. At this time, at the time of continuous annealing after cold rolling, cooling after recrystallization annealing is executed at (100 to 500)°C/sec cooling rate. By this procedure, the structure is formed into a mixed structure of soft ferrite and hardened structure and ferrite grain size is regulated to ≤5μm and also the amount of solid-solution carbon is regulated to ≥40ppm, by which the steel sheet for surface treatment, which has BH characteristic as high as ≥56kgf/mm yield strength and superior workability, can be produced.;COPYRIGHT: (C)1994,JPO&Japio