| 摘要 |
PROBLEM TO BE SOLVED: To provide a hot rolled steel sheet having a high yield strength satisfying a yield ratio YR of≥0.8 and excellent impact absorbing properties and shape fixability, and suitable as the stock for automobiles or the like, and to provide a method for producing the same. SOLUTION: The steel sheet is composed of a carbon steel or a low alloy steel comprising one or more kinds selected from Ti, Nb, Mo and V of≤0.05% in total, and containing ferrite as a main phase. The average crystal grain diameter D (μm) of the ferrite in the depth position of the 1/4 of the sheet thickness from the surface of the steel sheet satisfies the following inequalities (1) and (2), a yield ratio YR satisfies≥0.8, and the average plastic tangential slope H' satisfies the following inequality (3). The inequality (1) is 1.2≤D≤7, the inequality (2) is D≤2.7+5000/(5+350*C+40*Mn)<SP>2</SP>, and the inequality (3) is 0.1≤H'/TS≤-2×YR+3.1, wherein C and Mn denote the contents (unit: mass%) of the respective elements in the steel; H' denotes an average plastic tangential slope; TS denotes tensile strength (MPa); and YR denotes a yield ratio. COPYRIGHT: (C)2008,JPO&INPIT
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