Abstract: A hot-stamp formed body has a predetermined chemical composition and has a microstructure including, by area ratio, martensite: 90% to 100% and a remainder in the microstructure: 0% to 10%. The percentage of martensite having a GAIQ value of 40000 or less in all of the martensite is less than 5.0%, an average grain size of prior austenite grains is 6.0 ?m or less, and a standard deviation of grain sizes of the prior austenite grains is 2.6 ?m or less.

Abstract: The spot welding method of the present invention has steps of preliminary conduction, first conduction, second conduction, and third conduction: Preliminary conduction: Conduction method aimed at improving closeness of contact surfaces of steel sheets and reducing sheet gaps by gradually increasing the welding current (for example, upslope conduction). If rapidly applying current, current would be locally carried and that part would melt resulting in expulsion, so this is a conduction method gradually running current (for example upslope conduction) to avoid local heating. First conduction: Conduction method running a constant welding current and using the heat generated by the electrical contact resistance between steel sheets to cause the formation of a nugget when preliminary conduction results in close contact surfaces between the steel sheets.

Abstract: The spot welding method of the present invention has steps of preliminary conduction, first conduction, second conduction, and third conduction: Preliminary conduction: Conduction method aimed at improving closeness of contact surfaces of steel sheets and reducing sheet gaps by gradually increasing the welding current (for example, upslope conduction). If rapidly applying current, current would be locally carried and that part would melt resulting in expulsion, so this is a conduction method gradually running current (for example upslope conduction) to avoid local heating. First conduction: Conduction method running a constant welding current and using the heat generated by the electrical contact resistance between steel sheets to cause the formation of a nugget when preliminary conduction results in close contact surfaces between the steel sheets.

Abstract: A brazed joint having excellent tensile strength (TSS and CTS) and a method of production of the same are provided. A sheet combination 200 comprised of steel sheets 210, 220 between which a brazing filler metal 230 is clamped is heated at a temperature of the Ac3 point of the steel sheet (matrix material) or more. The Ar3 point of the regions near the brazing filler metal at the steel sheets is made higher than the Ar3 point of the steel sheets (matrix material), then the quenching start temperature X is made a temperature of the Ar3 point of the steel sheet (matrix material) or less and hot stamping is performed to produce a brazed joint.

Abstract: A overlapped body 10 comprising steel plates 1a and 1b and satisfying (TS1×t1+TS2×t2)/(t1+t2)?440 is energized while being sandwiched and pressed by a pair of electrodes 2a and 2b to form a molten pool 4b at a steel plate interface 4 and thereby to join the steel plates 1a and 1b. TS1 represents the tensile strength (MPa) of the steel plate 1a, t1 represents the thickness (mm) of the steel plate 1a, TS2 represents the tensile strength (MPa) of the steel plate 1b, and t2 represents the thickness (mm) of the steel plate 1b. An energization point 4a is formed at the steel plate interface 4, and spot welding is performed such that the molten pool 4b is formed at a position at a horizontal distance W of 20 mm or less from the energization point 4a.

Abstract: An overlapped body 10 includes at least three steel plates 1a, 1b and 1c and in which at least one steel plate interface 2a has a contact resistance different from the contact resistance of another steel plate interface 2b. A molten pool is formed at the steel plate interfaces so as to join the steel plates 1a, 1b and 1c, and an energization point 5 is formed at the steel plate interface 2b having the largest contact resistance. Initial spot welding is performed under a condition in which a branch current is generated in the energization point 5 so as to form the molten pool. By doing so, it makes it difficult to generate the expulsion and surface flash at the steel plate interface where resistive heating is large and form the molten pool having a sufficiently large size at the steel plate interface where resistive heating is small.

Abstract: A formed member is provided which can be manufactured at a low cost, which has excellent dimensional accuracy, which has excellent axial crushing properties and three-point bending properties, which has excellent bending stiffness and torsional stiffness, and which is suitable for use in a component of an automobile. The formed member (20) has a reinforcing member (35) which is joined by a weld (40) provided on a ridge portion (28). It is manufactured by joining a flat sheet blank and a flat sheet reinforcing member (35) by a weld (40) and performing bending so that the weld (40) becomes a ridge portion (28).

Abstract: The present invention is a friction welding method for friction welding of metal members characterized by starting friction welding in a state inserting an insert material between surfaces of the metal members facing each other, wherein the insert material consists of a metal having a melting point (centigrade temperature) of 60 to 80% of the melting point (centigrade temperature) of the metal members, melting the insert material, and pushing the melted insert material out from between the pair of metal members. Due to this, the adverse effects due to high temperature heating like in the past are eliminated while a quality of joint equal to or better than the past is obtained in a short time period.

Abstract: A galvanized steel sheet for hot forming, the galvanized steel sheet including a galvanized film provided on a surface of a steel sheet, wherein the steel sheet has a chemical composition consisting of, in mass %, C: 0.02% to 0.58%, Mn: 0.5% to 3.0%, sol. Al: 0.005% to 1.0%, a predetermined element(s) as necessary; Si: less than or equal to 2.0%, P: less than or equal to 0.03%, S: less than or equal to 0.004%, N: less than or equal to 0.01%, and the balance: Fe and impurities, wherein a content of Mn in a portion from an interface of the steel sheet and the galvanized film to a depth of 5 ?m is more than or equal to 0.3 mass %, wherein the galvanized film has a plating coverage of 40 g/m2 to 110 g/m2, an Al content of more than or equal to 150 mg/m2 within the galvanized film, and an Al concentration of less than or equal to 0.5 mass %, and wherein the galvanized steel sheet is used for an application in which the galvanized steel sheet is heated to 700° C. or above and is then subjected to hot forming.

Abstract: A brazed joint having excellent tensile strength (TSS and CTS) and a method of production of the same are provided. A sheet combination 200 comprised of steel sheets 210, 220 between which a brazing filler metal 230 is clamped is heated at a temperature of the Ac3 point of the steel sheet (matrix material) or more. The Ar3 point of the regions near the brazing filler metal at the steel sheets is made higher than the Ar3 point of the steel sheets (matrix material), then the quenching start temperature X is made a temperature of the Ar3 point of the steel sheet (matrix material) or less and hot stamping is performed to produce a brazed joint.

Abstract: The spot welding method of the present invention has steps of preliminary conduction, first conduction, second conduction, and third conduction: Preliminary conduction: Conduction method aimed at improving closeness of contact surfaces of steel sheets and reducing sheet gaps by gradually increasing the welding current (for example, upslope conduction). If rapidly applying current, current would be locally carried and that part would melt resulting in expulsion, so this is a conduction method gradually running current (for example upslope conduction) to avoid local heating. First conduction: Conduction method running a constant welding current and using the heat generated by the electrical contact resistance between steel sheets to cause the formation of a nugget when preliminary conduction results in close contact surfaces between the steel sheets.

Abstract: A overlapped body 10 comprising steel plates 1a and 1b and satisfying (TS1×t1+TS2×t2)/(t1+t2)?440 is energized while being sandwiched and pressed by a pair of electrodes 2a and 2b to form a molten pool 4b at a steel plate interface 4 and thereby to join the steel plates 1a and 1b. TS1 represents the tensile strength (MPa) of the steel plate 1a, t1 represents the thickness (mm) of the steel plate 1a, TS2 represents the tensile strength (MPa) of the steel plate 1b, and t2 represents the thickness (mm) of the steel plate 1b. An energization point 4a is formed at the steel plate interface 4, and spot welding is performed such that the molten pool 4b is formed at a position at a horizontal distance W of 20 mm or less from the energization point 4a.

Abstract: An overlapped body 10 includes at least three steel plates 1a, 1b and 1c and in which at least one steel plate interface 2a has a contact resistance different from the contact resistance of another steel plate interface 2b. A molten pool is formed at the steel plate interfaces so as to join the steel plates 1a, 1b and 1c, and an energization point 5 is formed at the steel plate interface 2b having the largest contact resistance. Initial spot welding is performed under a condition in which a branch current is generated in the energization point 5 so as to form the molten pool. By doing so, it makes it difficult to generate the expulsion and surface flash at the steel plate interface where resistive heating is large and form the molten pool having a sufficiently large size at the steel plate interface where resistive heating is small.

Abstract: The present invention is a friction welding method for friction welding of metal members characterized by starting friction welding in a state inserting an insert material between surfaces of the metal members facing each other, wherein the insert material consists of a metal having a melting point (centigrade temperature) of 60 to 80% of the melting point (centigrade temperature) of the metal members, melting the insert material, and pushing the melted insert material out from between the pair of metal members. Due to this, the adverse effects due to high temperature heating like in the past are eliminated while a quality of joint equal to or better than the past is obtained in a short time period.

Abstract: A galvanized steel sheet for hot forming, the galvanized steel sheet including a galvanized film provided on a surface of a steel sheet, wherein the steel sheet has a chemical composition consisting of, in mass %, C: 0.02% to 0.58%, Mn: 0.5% to 3.0%, sol. Al: 0.005% to 1.0%, a predetermined element(s) as necessary; Si: less than or equal to 2.0%, P: less than or equal to 0.03%, S: less than or equal to 0.004%, N: less than or equal to 0.01%, and the balance: Fe and impurities, wherein a content of Mn in a portion from an interface of the steel sheet and the galvanized film to a depth of 5 ?m is more than or equal to 0.3 mass %, wherein the galvanized film has a plating coverage of 40 g/m2 to 110 g/m2, an Al content of more than or equal to 150 mg/m2 within the galvanized film, and an Al concentration of less than or equal to 0.5 mass %, and wherein the galvanized steel sheet is used for an application in which the galvanized steel sheet is heated to 700° C. or above and is then subjected to hot forming.

Abstract: A formed member is provided which can be manufactured at a low cost, which has excellent dimensional accuracy, which has excellent axial crushing properties and three-point bending properties, which has excellent bending stiffness and torsional stiffness, and which is suitable for use in a component of an automobile. The formed member (20) has a reinforcing member (35) which is joined by a weld (40) provided on a ridge portion (28). It is manufactured by joining a flat sheet blank and a flat sheet reinforcing member (35) by a weld (40) and performing bending so that the weld (40) becomes a ridge portion (28).

Abstract: The welding quality classification apparatus relating to the present invention is an apparatus, wherein a data point indicating feature information of a welded joint to be classified whose welding quality is unknown is mapped to a point in a mapping space which has a dimensional number higher than the number of the features constituting the feature information, and the welding quality of a welded joint to be classified is classified based on which of regions of two welding qualities, which are formed by separating the mapping space with a decision boundary, contains the mapped point, and wherein a discriminant function is determined by adopting a weight which minimizes the sum of the classification error corresponding to classification accuracy of a training dataset and a regularization term having a positive correlation with the dimensional number of the discriminant function as weight for each feature constituting the discriminant function indicating the decision boundary.

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.