| 摘要 |
PURPOSE:To obtain the member having the bending strict on the necessary shape without generating cracks in press forming by using the very high strength steel plate having specific chemical component and tensile strength and specific yielding ratio and bore expand rate. CONSTITUTION:The composition of a cold rolled steel sheet contains 0.08-0.25%(weight) C, 0.5-3.0% Si and 0.5-3.0% Mn. It contains further, as occasion demands, at least one kind of the element selected among the group consisting of 0.01-0.15% P, 0.05-1.0% Cr and 0.05-0.6% Mo, and/or at least one kind selected from the group consisting of 0.02-0.25% Ti, 0.02-0.25% Nb and 0.08-0.40% V and the balance Fe with inevitable impurities. The cold rolled steel sheet having >=80kg f/mm<2> tensile strength, >=0.65 yielding ratio and >=35% bore expand rate is then subjected to strong bending by the press forming whose limitation bend R in 45 deg. V bend test is <=1.0.
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