80/ A METHOD FOR MANUFACTURING HOT ROLLED STEEL SHEET OF TENSILE STRENGTH 80kg/ GRADE WITH EXCELLENT WEATHER RESISTANCE AND WORKABILITY

摘要

PURPOSE: Provided is a hot rolled steel sheet of tensile strength 80kg/mm¬2 grade with excellent weather resistance and workability, which is appropriate for use in vehicle container. CONSTITUTION: The method includes the steps of: (i) reheating a steel slab comprising C 0.02-0.12wt.%, Si 0.7wt.% or less, Mn 0.5-2.0wt.%, P 0.05wt.% or less, S 0.01wt.% or less, Al 0.01-0.07wt.%, Nb 0.09wt.% or less, Ti 0.05wt.% or less, Ni 0.1-0.5wt.%, Cu 0.1-0.5wt.%, Cr 0.5-1.5wt.%, Ca .001-0.005wt.%, balance Fe, and other inevitable impurities in the temperature range of 1100 to 1300C; (ii) finish hot rolling in the temperature range of 900 to 800C; (iii) quenching at cooling rate of higher than 2 0C/sec; (iv) coiling in the temperature range of 450 to 550C. Optionally, vanadium is added in an amount of 0.01 to 0.07wt.%.