2results about How to "Excellent stretch-flangeability" patented technology

This invention provides a high-strength steel plate with excellent tensile flange properties, bending and LME resistance, and capable of manufacturing parts with high dimensional accuracy. The high-strength steel plate of the present invention has the following composition: it contains C, Si, Mn, P, S, Al, N, Nb, Ti and B in specified amounts, such that [%Si] / [%Mn] is 0.10 to 0.60, the amount of free Ti is 0.001% by mass or more, and the remainder is composed of Fe and unavoidable impurities; it has the following steel structure: the total amount of Nb dissolved in the surface layer and the amount of precipitation below 100 nm is 0.002% by mass or more, at the 1 / 4 position of the plate thickness, the area fraction of martensite is 78% or more, the area fraction of ferrite is 10% or less, the volume fraction of retained austenite is less than 10.0%, the ratio of the grain size in the rolling direction to the grain size in the thickness direction of the original austenite grains is 2.0 or less, and the hardness variation frequency per 1500 μm in the width direction at the 200 μm position of the plate thickness is 10 times or less; and the high-strength steel plate has a tensile strength of 1180 MPa or more.

There is provided a hot-rolled steel sheet having excellent stretch flangeability. A hot-rolled steel sheet has a chemical composition containing, by mass%, C: 0.10% or less, Si: 2.0% or less, Mn: 2.0% or less, P: 0.100% or less, S: 0.02% or less, Al: 1.5% or less, and O: 0.0025% or less, the balance being Fe and incidental impurities, in which a main phase is ferrite, and a maximum orientation density of grains is 2.1 or less.