Abstract: A method for manufacturing a hot-rolled sheet attains grain refinement of the steel sheet whose grain size is extremely fine. In particular, a ferrite grain size of less than average 2 ?m is obtained, which is not laminar but has ferrite grains with equiaxed morphology and exhibits high formability in forming. The method comprises the steps of rolling and cooling, wherein the rolling reductions, cooling steps, and temperature are closely regulated. A hot rolled sheet made from the method of manufacturing has a controlled ferrite grain in different regions of sheet thickness.

Abstract: A multi-phase hot-rolled steel sheet has a metallurgical structure having a main phase of ferrite with an average grain diameter of at most 3.0 ?m and a second phase including at least one of martensite, bainite, and austenite. In the surface layer, the average grain diameter of the second phase is at most 2.0 ?m, the difference (?nHav) between the average nanohardness of the main phase (nH?av) and the average nanohardness of the second phase (nH2nd av) is 6.0-10.0 GPa, the difference (??nH) of the standard deviation of the nanohardness of the second phase from the standard deviation of the nanohardness of the main phase is at most 1.5 GPa, and in the central portion, the difference (?nHav) between the average nanohardnesses is at least 3.5 GPa to at most 6.0 GPa and the difference (??nH) between the standard deviations of the nanohardnesses is at least 1.5 GPa.

Abstract: A high-strength steel sheet has a chemical composition comprising C: 0.05-0.20%, Si: 0.02-3.0%, Mn: 0.5-3.0%, P: at most 0.5%, S: at most 0.05%, Cr: 0.05-1.0%, sol. Al: 0.01-1.0%, one or more elements selected from the group consisting of Ti, Nb, Mo, V, and W: a total of 0.002-0.03%, and a remainder of Fe and impurities. The sheet has an average grain diameter of ferrite of at most 3.0 ?m at least in a region of 100-200 ?m in the sheet thickness direction from the surface of the steel sheet. The average spacing in the sheet thickness direction of the remaining structure in this region is at most 3.0 ?m. Mechanical properties include at least 750 MPa tensile strength and at least 13,000 MPa·% (tensile strength×elongation).

Abstract: A multi-phase hot-rolled steel sheet having improved strength in an intermediate strain rate region has a chemical composition comprising, in mass percent, C: 0.07-0.2%, Si+Al: 0.3-1.5%, Mn: 1.0-3.0%, P: at most 0.02%, S: at most 0.005%, Cr: 0.1-0.5%, N: 0.001-0.008%, at least one of Ti: 0.002-0.05% and Nb: 0.002-0.05%, and a remainder of Fe and impurities. The area fraction of ferrite is 7-35%, the grain diameter of ferrite is in the range of 0.5-3.0 ?m, and the nanohardness of ferrite is in the range of 3.5-4.5 GPa. A second phase which is the remainder other than ferrite contains martensite and bainitic ferrite and/or bainite. The average nanohardness of the second phase is 5-12 GPa, and the second phase contains a high-hardness phase of 8-12 GPa with an area fraction of 5-35% based on the overall structure.

Abstract: A method for manufacturing a hot-rolled sheet is provided, wherein the method attains grain refinement of the steel sheet containing C, Si, and Mn, wherein the grain size thereof is set to particularly below average of 2 ?m, which has ferrite grain with equiaxed morphology, which has high formability in forming, and the ferrite grain-size deviation in the thickness direction is uniformed down to the level not higher than a predetermined amount whereby uniform formability in forming is high. The method includes a first rolling for rolling the sheet such that the total rolling reduction is 80% or more or the average grain size is 30 ?m or less in a form of single phase of austenite, a second rolling of a single-pass, a third rolling being conducted thereafter, and a following cooling.

Abstract: An austenitic heat resistant alloy, which contains, by mass percent, C?0.15%, Si?2%, Mn?3%, Ni: 40 to 80%, Cr: 15 to 40%, W and Mo: 1 to 15% in total content, Ti?3%, Al?3%, N?0.03%, O?0.03%, with the balance being Fe and impurities, and among the impurities P?0.04%, S?0.03%, Sn?0.1%, As?0.01%, Zn?0.01%, Pb?0.01% and Sb?0.01%, and satisfies the conditions [P1=S+{(P+Sn)/2}+{(As+Zn+Pb+Sb)/5}?0.050], [0.2?P2=Ti+2Al?7.5?10×P1], [P2?9.0?100×O] and [N?0.002×P2+0.019] can prevent both the liquation crack in the HAZ and the brittle crack in the HAZ and also can prevent defects due to welding fabricability, which occur during welding fabrication, and moreover has excellent creep strength at high temperatures. Therefore, the alloy can be used suitably as a material for constructing high temperature machines and equipment, such as power generating boilers, plants for the chemical industry and so on.

Abstract: A high strength, ductile, and tough Ni-base heat resistant alloy comprises by mass percent, C: 0.1% or less, Si: 1% or less, Mn: 1% or less, Cr: not less than 15% to less than 28%, Fe: 15% or less, W: more than 5% to not more than 20%, Al: more than 0.5% to not more than 2%, Ti: more than 0.5% to not more than 2%, Nd: 0.001 to 0.1% and B: 0.0005 to 0.01%, with the balance being Ni and impurities. Impurity contents of P, S, Sn, Pb, Sb, Zn and As are P: 0.03% or less, S: 0.01% or less, Sn: 0.020% or less, Pb: 0.010% or less, Sb: 0.005% or less, Zn: 0.005% or less and As: 0.005% or less, and formulas of [0.015?Nd+13.4×B?0.13], [Sn+Pb?0.025] and [Sb+Zn +As?0.010] are met.

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 Ni-base heat resistant alloy, which comprises by mass percent, C: 0.1% or less, Si: 1% or less, Mn: 1% or less, Cr: not less than 15% to less than 28%, Fe: 15% or less, W: more than 5% to not more than 20%, Al: more than 0.5% to not more than 2%, Ti: more than 0.5% to not more than 2%, Nd: 0.001 to 0.1% and B: 0.0005 to 0.01%, with the balance being Ni and impurities, in which the contents of P, S, Sn, Pb, Sb, Zn and As among the impurities are P: 0.03% or less, S: 0.01% or less, Sn: 0.020% or less, Pb: 0.010% or less, Sb: 0.005% or less, Zn: 0.005% or less and As: 0.005% or less, and further satisfies the formulas of [0.015?Nd+13.4×B?0.13], [Sn+Pb?0.025] and [Sb+Zn+As?0.010] is an alloy in which much higher strength than the conventional Ni-base heat resistant alloy can be achieved, the ductility and toughness after a long period of use at a high temperature are remarkably improved, and moreover the zero ductility temperature and the hot workability are also further improved.

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: According to a low alloy steel of the present invention, compositional elements thereof are limited, and a metal structure thereof comprises bainite or martensite. Further, proper amounts of Nd inclusions are formed by appropriately selecting timings of deoxidation and Nd addition in melting a steel. Consequently, compatibility between high-temperature creep strength and long-term creep ductility, which is hardly established in conventional steels, can be achieved even in hostile conditions. Accordingly, the low alloy steel of the present invention can be widely applied as the material for the heat-resistant structural member used for a long time under the high-temperature and high-pressure conditions such as power plant boilers, turbines, and nuclear power plants.

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: An austenitic heat resistant alloy, which comprises, by mass percent, C?0.15%, Si?2%, Mn?3%, Ni: 40 to 80%, Cr: 15 to 40%, W and Mo: 1 to 15% in total content, Ti?3%, Al?3%, N?0.03%, O?0.03%, with the balance being Fe and impurities, and among the impurities P?0.04%, S?0.03%, Sn?0.1%, As?0.01%, Zn?0.01%, Pb?0.01% and Sb?0.01%, and satisfies the conditions [P1=S+{(P+Sn)/2}+{(As+Zn+Pb+Sb)/5}?0.050], [0.2?P2=Ti+2Al?7.5?10×P1], [P2?9.0?100×O] and [N?0.002×P2+0.019] can prevent both the liquation crack in the HAZ and the brittle crack in the HAZ and also can prevent defects due to welding fabricability, which occur during welding fabrication, and moreover has excellent creep strength at high temperatures. Therefore, the alloy can be used suitably as a material for constructing high temperature machines and equipment, such as power generating boilers, plants for the chemical industry and so on.

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: The present invention provides a method for manufacturing the hot-rolled sheet, which includes: a step A including a first rolling in which a steel sheet containing 0.04-0.20% C, 0.01-2.0% Si, 0.5-3.0% Mn by mass, and the reminder being Fe and inevitable impurities, is rolled by successive multi-pass rolling at a total rolling reduction of 80% or more while keeping the steel sheet at temperatures not lower than the para-equilibrium transformation temperature Ae3; a step B including a second rolling in which a single-pass rolling is carried out at a rolling reduction of 30-55% when an entry side temperature is not lower than the para-equilibrium transformation temperature Ae3; a step C including a third rolling in which a single-pass rolling is carried out at a rolling reduction of 35-70% when an entry side temperature is set within a predetermined range; and a step D in which within 0.2 seconds after the third rolling, the rolled sheet is cooled at a cooling rate of 600 degree C.

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: According to a low alloy steel of the present invention, compositional elements thereof are limited, and a metal structure thereof comprises bainite or martensite. Further, a proper amounts of Nd inclusions are formed by appropriately selecting timings of deoxidation and Nd addition in melting a steel. Consequently, compatibility between high-temperature creep strength and long-term creep ductility, which is hardly established in conventional steels, can be achieved even in hostile conditions. Accordingly, the low alloy steel of the present invention can be widely applied as the material for the heat-resistant structural member used for a long time under the high-temperature and high-pressure conditions such as power plant boilers, turbines, and nuclear power plants.