| 摘要 |
High tensile strength hot-rolled steel sheet suitable for use in interior materials for automobiles and a method for producing the same, in which bake hardenability, fatigue resistance, crash resistance, and resistance to room temperature aging are improved, containing 0.01% to 0.12% by weight of carbon, 2.0% by weight or less of silicon, 0.01% to 3.0% by weight of manganese, 0.2% by weight or less of phosphorus, 0.001% to 0.1% by weight of aluminum, and 0.003% to 0.02% by weight of nitrogen and subjected to hot rolling and cooling at a cooling rate of 50° C./s or more within 0.5 second after hot rolling; the hot-rolled steel sheet has a structure including a ferrite having an average grain diameter of 8 mum or less as a primary phase, the amount of solute Nitrogen ranges from 0.003% to 0.01%, and the ratio, Ngb/Ng, of an average concentration Ngb of nitrogen dissolved in the ferrite grain boundary to an average concentration Ng of nitrogen dissolved in ferrite grains ranges from 100 to 10,000.
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