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AssigneeJfe Steel Corporation
InventorsYoshihiko Ono, Hideyuki Kimura, Kaneharu Okuda, Takeshi Fujita, Michitaka Sakurai
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A high-strength hot-dip galvanized steel sheet that even on the premise of ordinary CGL heat cycle, has a low yield stress and excels in resistance to natural aging and baking hardenability without reliance on the use of expensive Mo; and a process for producing the same. The constituent composition thereof comprises 0.01 to less than 0.08% C, 0.2% or less Si, more than 1.0 to 1.8% Mn, 0.10% or less P, 0.03% or less S, 0.1% or less Al, 0.008% or less N and more than 0.5% Cr so that the relationship 1.95≦Mn(mass %)+1.3Cr(mass %)≦2.8 is satisfied and comprising the balance iron and unavoidable impurities. The structure thereof has a ferrite phase and a martensite phase of 2 to 15% area ratio, and the cumulative area ratio of pearlite phase and/or bainite phase is 1.0% or less. In the production of this hot-dip galvanized steel sheet, the temperature and cooling rate are controlled during the annealing/plating operation subsequent to cold rolling.
A high strength galvanized steel sheet having a composition which contains, on a mass percent basis, 0.01% to less than 0.08% of C, 0.2% or less of Si, more than 1.0% to 1.8% of Mn, 0.10% or less of P, 0.03% or less of S, 0.1% or less of Al, 0.008% or less of N, more than 0.5% of Cr, and the balance being iron and inevitable impurities, wherein 1.95≦Mn (mass percent)+1.3Cr (mass percent)≦2.8 and the microstructure includes a ferrite phase and 2% to 15% of martensite on an area ratio basis, and the total area ratio of perlite and/or bainite is 1.0% or less.
Dependencies are inferred from the claim text.