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OwnerTatsuo Yokoi, Natsuko Sugiura +3inventors
InventorsTatsuo Yokoi, Natsuko Sugiura, Naoki Yoshinaga, Koichi Tsuchihashi, Takehiro Nakamoto
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The present invention provides a thin steel sheet, for automobile use, excellent in notch-fatigue strength, and a method for producing said steel sheet. Specifically, the present invention is a thin steel sheet for automobile use excellent in notch-fatigue strength, said steel sheet containing, in mass, 0.01 to 0.3% C, 0.01 to 2% Si, 0.05 to 3% Mn, 0.1% or less P, 0.01% or less S and 0.005 to 1% Al, with the balance consisting of Fe and unavoidable impurities, characterized in that, on a plane at an arbitrary depth within 0.5 mm from the surface of said steel sheet in the thickness direction thereof, the average of the ratios of the X-ray diffraction strength in the orientation component group of {100}<011> to {223}<110> to random X-ray diffraction strength is 2 or more and the average of the ratios of the X-ray diffraction strength in the three orientation components of {554}<225>, {111}<112> and {111}<110> to random X-ray diffraction strength is 4 or less and that the thickness of said steel sheet is in the range from 0.5 to 12 mm, and a method for producing said steel sheet by subjecting a steel slab containing aforementioned chemical components to rolling at a total reduction ratio of 25% or more in a temperature range of the Ar3 transformation temperature+100° C. or lower.
A thin steel sheet, for automobile use, excellent in notch-fatigue strength, characterized in:
A thin steel sheet for automobile use excellent in notch-fatigue strength, the steel sheet containing, in mass, 0.01 to 0.3% C, 0.01 to 2% Si, 0.05 to 3% Mn, 0.1% or less P, 0.01% or less S and 0.005 to 1% Al, with the balance consisting of Fe and unavoidable impurities, characterized in that, on a plane at an arbitrary depth within 0.5 mm from the surface of the steel sheet in the thickness direction thereof, the average of the ratios of the X-ray diffraction strength in the orientation component group of {100}<011> to {223}<110> to random X-ray diffraction strength is 2 or more and the average of the ratios of the X-ray diffraction strength in the three orientation components of {554}<225>, {111}<112> and {111}<110> to random X-ray diffraction strength is 4 or less and that the thickness of the steel sheet is in the range from 0.5 to 12 mm.
A method for producing a thin steel sheet for automobile use excellent in notch-fatigue strength characterized in that a steel slab containing, in mass, 0.01 to 0.3% C, 0.01 to 2% Si, 0.05 to 3% Mn, 0.1% or less P, 0.01% or less S and 0.005 to 1% Al, with the balance consisting of Fe and unavoidable impurities, is subjected, in a hot rolling process, to rough rolling and then to finish rolling at a total reduction ratio of 25% or more in terms of steel sheet thickness in the temperature range of the Ar3 transformation temperature +100° C. or lower, that, on a plane at an arbitrary depth within 0.5 mm from the surface of the steel sheet in the thickness direction thereof, the average of the ratios of the X-ray diffraction strength in the orientation component group of {100}<011> to {223}<110> to random X-ray diffraction strength is 2 or more and the average of the ratios of the X-ray diffraction strength in the three orientation components of {554}<225>, {111}<112> and {111}<110> to random X-ray diffraction strength is 4 or less and that the thickness of the steel sheet is in the range from 0.5 to 12 mm.
A method for producing a thin steel sheet, for automobile use, excellent in notch-fatigue strength, characterized in that a steel slab containing, in mass, 0.01 to 0.3% C, 0.01 to 2% Si, 0.05 to 3% Mn, 0.1% or less P, 0.01% or less S and 0.005 to 1% Al, with the balance consisting of Fe and unavoidable impurities, is subjected to rough rolling, then finish rolling at a total reduction ratio of 25% or more in terms of steel sheet thickness in the temperature range of the Ar3 transformation temperature +100° C. or lower, pickling, cold rolling at a reduction ratio of less than 80% in terms of steel sheet thickness and then annealing for recovery or recrystallization comprising the processes of retaining the cold-rolled steel sheet for 5 to 150 sec. in the temperature range from the recovering temperature to the Ac3 transformation temperature +100° C. and then cooling it, that, on a plane at an arbitrary depth within 0.5 mm from the surface of the steel sheet in the thickness direction thereof, the average of the ratios of the X-ray diffraction strength in the orientation component group of {100}<011> to {223}<110> to random X-ray diffraction strength is 2 or more and the average of the ratios of the X-ray diffraction strength in the three orientation components of {554}<225>, {111}<112> and {111}<110> to random X-ray diffraction strength is 4 or less and that the thickness of the steel sheet is in the range from 0.5 to 12 mm.
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