| 摘要 |
PURPOSE: A method for preparing a sheet of deep drawing quality special killed-fully stabilized type steel of uniform enhanced strength and good formability and weldability is provided. CONSTITUTION: The method comprises providing an essentially unalloyed interstitial free carbon steel melt having C 0.001-0.01%, Mn 0.15-0.50%, Si 0.005-0.03%, AL 0.02-0.06%, S 0.002-0.015%, N 0.001-0.01%, O 0.001-0.01% and Fe balance; adding to the steel melt a strengthening element selected from Ti, Nb, V and mixtures thereof in total amount from about 0.01-0.3 free atomic percent available strengthening element uncombined with other elements; casting and hot rolling or hot rolling followed by cold rolling the steel; coiling the rolled sheet; annealing the rolled sheet at about 1275-1350 °F; treating the annealed sheet in an open coil annealing furnace in an isothermal step at a nitriding temperature about 800-1250 °F with a nitriding gas to nitride the steel through at least a portion of the sheet thickness; recirculating the nitriding gas; controlling the strengthening of the steel sheet as a function of steel composition, the nitriding gas composition, nitriding time, nitriding temperature, thickness of the steel sheet and depth of strengthening desired to provide a steel sheet having an 0.2% off-set yield strength after temper rolling of at least about 45 ksi and a r value in excess of about 1.8 for the cold rolled sheet.
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