COLD-ROLLED STEEL SHEET THERMALLY TREATED IN BATCH ANNEALING FURNACE AND METHOD OF MANUFACTURING SAME

摘要

A method of manufacturing a cold-rolled steel sheet thermally treated in a batch annealing furnace according to an embodiment of the present invention provides a cold-rolled steel sheet containing 0.050 to 0.080 wt% of carbon (C), more than 0 wt% and 0.03 wt% or less of silicon (Si), 1.5-1.7 wt% of manganese (Mn), more than 0 wt% and 0.03 wt% or less of phosphorus (P), more than 0 wt% and 0.006 wt% or less of sulfur (S), 0.01-0.06 wt% of aluminum (Al), more than 0 wt% and 0.006 wt% or less of nitrogen (N), 0.005-0.015 wt% of niobium (Nb), and the balance of Fe and inevitable impurities. With the cold-rolled steel sheet, a batch annealing furnace thermal treatment is carried out, which includes a first heating step, a first heat maintaining step, a second heating step, a second heat maintaining step, and a cooling step. In the first heat maintaining step, the heat is maintained at heat maintaining temperatures of 350±10°C for heat maintaining hours of 4 to 8 hours. In the second heat maintaining step, the heat is maintained at heat maintaining temperatures of 660±10°C for heat maintaining hours of 8 to 12 hours. As a result, the cold-rolled steel sheet thermally treated in the batch annealing furnace has a yield strength of 265 MPa or higher, a tensile strength of 440 MPa or higher, and an elongation rate of 30 or higher.;COPYRIGHT KIPO 2016