Abstract: A steel sheet excellent in mechanical strength, workability and thermal stability and suited for use as a raw material in such fields of manufacturing automobiles, household electric appliances and machine structures and of constructing buildings, and a manufacturing method thereof are provided. The steel sheet is a hot-rolled steel sheet of carbon steel or low-alloy steel, the main phase of which is ferrite, and is characterized in that the average ferrite crystal grain diameter D (?m) at the depth of ¼ of the sheet thickness from the steel sheet surface satisfies the relations respectively defined by the formulas (1) and (2) given below and the increase rate X (?m/min) in average ferrite crystal grain diameter at 700° C. at the depth of ¼ of the sheet thickness from the steel sheet surface and said average crystal grain diameter D (?m) satisfy the relation defined by the formula (3) given below: 1.2?D?7??formula (1) D?2.7+5000/(5+350·C+40·Mn)2??formula (2) D·X?0.

Abstract: A steel sheet excellent in mechanical strength, workability and thermal stability and suited for use as a raw material in such fields of manufacturing automobiles, household electric appliances and machine structures and of constructing buildings, and a manufacturing method thereof are provided. The steel sheet is a hot-rolled steel sheet of carbon steel or low-alloy steel, the main phase of which is ferrite, and is characterized in that the average ferrite crystal grain diameter D (?m) at the depth of ¼ of the sheet thickness from the steel sheet surface satisfies the relations respectively defined by the formulas (1) and (2) given below and the increase rate X (?m/min) in average ferrite crystal grain diameter at 700° C. at the depth of ¼ of the sheet thickness from the steel sheet surface and said average crystal grain diameter D (?m) satisfy the relation defined by the formula (3) given below: 1.2?D?7??formula (1) D?2.7+5000/(5+350·C+40·Mn)2??formula (2) D·X?0.

Abstract: A cold-rolled steel sheet of carbon steel or low-alloy steel comprising C: 0.01 to 0.25% by mass with a ferrite main phase is has an average ferrite crystal grain diameter D (?m) at the depth of ¼ of the sheet thickness from the steel sheet surface satisfying formulas (5,6) and the increase rate X (?m/min) in average ferrite crystal grain diameter at 700° C. at the depth of ¼ of the sheet thickness from the steel sheet surface and D (?m) satisfying formula (3): 1.2?D?9.3??(5) D?5.0?2.0·Cr+5000/(5+350·C+40·Mn)2??(6) D·X?0.1??(3) and, at said ¼ inch depth, the area percentage of ferrite crystal grains the crystal grain diameter d (?m) of which satisfying formula (4) is at least 80%: D/3?d?3D??(4) wherein C, Cr and Mn represent mass % of the respective elements in the steel.

Abstract: A steel sheet excellent in mechanical strength, workability and thermal stability and suited for use as a raw material in such fields of manufacturing automobiles, household electric appliances, machine structures, and of constructing buildings, and a manufacturing method thereof is provided. The steel sheet is a hot-rolled steel sheet of a carbon steel or low-alloy steel, the main phase of which is ferrite, and is characterized in that the average ferrite crystal grain diameter D(?m) at the depth of ¼ of the sheet thickness from the steel sheet surface satisfies the relations respectively defined by formulas (1) and (2) given below and the increase rate X (?m/min) in average ferrite crystal grain diameter at 700° C. at the depth of ¼ of the sheet thickness from the steel sheet surface and said average crystal grain diameter D(?m) satisfy the relation defined by the formula (3) given below: 1.2?D?7??formula (1) D?2.7+5000/(5+350·C+40·Mn)2??formula (2) D·X?0.

Abstract: A steel sheet excellent in mechanical strength, workability and thermal stability and suited for use as a raw material in such fields of manufacturing automobiles, household electric appliances and machine structures and of constructing buildings, and a manufacturing method thereof. are provided. The steel sheet is a hot-rolled steel sheet of carbon steel or low-alloy steel, the main phase of which is ferrite, and is characterized in that the average ferrite crystal grain diameter D (?m) at the depth of ¼ of the sheet thickness from the steel sheet surface satisfies the relations respectively defined by the formulas (1) and (2) given below and the increase rate X (?m/min) in average ferrite crystal grain diameter at 700° C. at the depth of ¼ of the sheet thickness from the steel sheet surface and said average crystal grain diameter D (?m) satisfy the relation defined by the formula (3) given below: 1.2?D?7??formula (1) D?2.7+5000/(5+350.C+40.Mn)2??formula (2) D·X?0.

Abstract: A steel sheet excellent in mechanical strength, workability and thermal stability and suited for use as a raw material in such fields of manufacturing automobiles, household electric appliances and machine structures and of constructing buildings, and a manufacturing method thereof are provided. The steel sheet is a hot-rolled steel sheet of carbon steel or low-alloy steel, the main phase of which is ferrite, and is characterized in that the average ferrite crystal grain diameter D (?m) at the depth of ¼ of the sheet thickness from the steel sheet surface satisfies the relations respectively defined by the formulas (1) and (2) given below and the increase rate X (?m/min) in average ferrite crystal grain diameter at 700° C. at the depth of ¼ of the sheet thickness from the steel sheet surface and said average crystal grain diameter D (?m) satisfy the relation defined by the formula (3) given below: 1.2?D?7??formula (1) D?2.7+5000/(5+350.C+40.Mn)2??formula (2) D·X?0.

Abstract: A steel sheet excellent in mechanical strength, workability and thermal stability and suited for use as a raw material in such fields of manufacturing automobiles, household electric appliances and machine structures and of constructing buildings, and a manufacturing method thereof are provided. The steel sheet is a hot-rolled steel sheet of carbon steel or low-alloy steel, the main phase of which is ferrite, and is characterized in that the average ferrite crystal grain diameter D (?m) at the depth of ¼ of the sheet thickness from the steel sheet surface satisfies the relations respectively defined by the formulas (1) and (2) given below and the increase rate X (?m/min) in average ferrite crystal grain diameter at 700° C. at the depth of ¼ of the sheet thickness from the steel sheet surface and said average crystal diameter D (?m) satisfy the relation defined by the formula (3) given below: 1.2?D?7??formula (1) D?2.7+5000/(5+350·C+40·Mn)2??formula (2) D·X?0.

Abstract: A steel sheet excellent in mechanical strength, workability and thermal stability and suited for use as a raw material in such fields of manufacturing automobiles, household electric appliances and machine structures and of constructing buildings, and a manufacturing method thereof. are provided. The steel sheet is a hot-rolled steel sheet of carbon steel or low-alloy steel, the main phase of which is ferrite, and is characterized in that the average ferrite crystal grain diameter D (?m) at the depth of ¼ of the sheet thickness from the steel sheet surface satisfies the relations respectively defined by the formulas (1) and (2) given below and the increase rate X (?m/min) in average ferrite crystal grain diameter at 700° C. at the depth of ¼ of the sheet thickness from the steel sheet surface and said average crystal grain diameter D (?m) satisfy the relation defined by the formula (3) given below: 1.2?D?7 ??formula (1) D?2.7+5000/(5+350·C+40·Mn)2 ??formula (2) D·X?0.