MANUFACTURE OF BAKING HARDENING TYPE STEEL SHEET WITH COMPOSITE STRUCTURE SUITABLE FOR DEEP DRAWING

摘要

PURPOSE: To economically manufacture cold rolled steel sheet having desired strength characteristic as well as an excellent deep drawing characteristic without adding Ti, Nb, B, etc. ;CONSTITUTION: The steel, containing 0.002-0.010% C, ≤1.0% Si, 0.2-2.5% Mn, ≤0.20% P and 0.005-0.10% Al are contained, and of which the remainder is composed of Fe and inevitable impurities, is hot rolled and cold rolled; successively in continuous annealing, heated not less than transformation point but not more than Ac₃ point: cooled to 500-750°C at an average cooling rate of 20°C/sec; and cooled to the transportation point Ms or less at the average cooling rate of 20°C or above. Consequently, the structure composed of ferrite and martensite of not less than 0.1% and not more than 5% in volume percentage is obtained. This steel sheet is provided with a necessary material characteristic as a cold rolled sheet steel for which deep drawing characteristic is required, and it is excellent especially in strength characteristic.;COPYRIGHT: (C)1993,JPO&Japio