連続焼鈍法によるプレス成形性の優れた 35∿40kgf/mm^2級高張力冷延鋼板の製造(製造技術)(<特集>高強度薄鋼板)

概要

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Dual phase (DP) steels with low yield to tensile strength ratio of 45% and extra deep drawing high strength (EDDH) steels with high γ^^-- value above 2.0 have been successfully produced in a multipurpose continuous annealing line with cooling rate of 40℃/s by gas jet. Dent resistance of trunk lid panel made from 1.2Mn-0.5Cr DP steel sheets of 0.70mm thickness is higher than that made from Al killed mild steels of 0.90mm thickness. In order to obtain tensile strength between 40 to 46 kgf/mm^2, it is effective to control C content within 0.025∿0.040%, and to adjust annealing temperature precisely just above 740℃. Excellent deep drawabilities are attained by reducing C content down to 0.004% or less in 0.03Nb-0.06P-0.05Al EDDH steels. In actual production, the extremely low carbon content is attained by the combination of decarburizing with bottom blown vessel (down to 0.015%C) and subsequently with reformed RH degasser in about 15 min (less than 0.003%). The EDDH steels have lower yield strength than 20 kgf/mm^2 and higher elongation than 42%. In the multipurpose continuos annealing line, the strip tensions in soaking section and rapid cooling section in the furnace are regulated in dependently to avoid heat buckling at 830℃ and fluttering caused by gas jet, respectively.
社団法人日本鉄鋼協会の論文
1982-07-01