Abstract: This indirect spot welding is for welding members including at least two overlapping steel sheets that have a ferrite phase as a main phase by holding a welding electrode (23) against a steel sheet (21) from one side while applying pressure with the electrode (23), attaching a feeding point (24) to a steel sheet (22) at the other side at a location remote from the electrode (23), and allowing current to flow between the electrode (23) and the feeding point (24). This welding includes contacting magnetic rigid bodies (26-1, 26-2) to a peripheral area of the electrode (23) from the one side against which the electrode (23) is held and securing an overlapping region in the peripheral area of the electrode (23) by a magnetic force produced by the rigid bodies (26-1, 26-2), thereby obtaining a weld having fully satisfactory strength, regardless of the rigidity of the members.

Abstract: This indirect spot welding is for welding members including at least two overlapping steel sheets that have a ferrite phase as a main phase by holding a welding electrode (23) against a steel sheet (21) from one side while applying pressure with the electrode (23), attaching a feeding point (24) to a steel sheet (22) at the other side at a location remote from the electrode (23), and allowing current to flow between the electrode (23) and the feeding point (24). This welding includes contacting magnetic rigid bodies (26-1, 26-2) to a peripheral area of the electrode (23) from the one side against which the electrode (23) is held and securing an overlapping region in the peripheral area of the electrode (23) by a magnetic force produced by the rigid bodies (26-1, 26-2), thereby obtaining a weld having fully satisfactory strength, regardless of the rigidity of the members.

Abstract: A press forming method for a metal sheet uses dies, a surface roughness of which is an arithmetical mean roughness Ra of 7.5 ?m or smaller, which are used as a punch, an upper die, and a blank holder. Fluid with a kinematic viscosity of 500 mm2/s or lower is supplied to a space between a metal sheet and the blank holder, a space between the metal sheet and the punch, and a space between the metal sheet and the upper die. A die is detached from a workpiece in the middle of forming, and resuming the forming.

Abstract: A surface-distortion measuring device and a surface-distortion measuring method can quantitatively, rapidly, and highly accurately measure and evaluate surface-distortion distribution at all of observable points on a specular or semi-specular surface of a measurement target. The device includes pattern displaying means 2 capable of switching and displaying a plurality of kinds of light-and-shade patterns 5, capturing means 3 for capturing mirror images, reflected in the specular or semi-specular surface of a measurement target 1, of the plurality of light-and-shade patterns displayed on the pattern displaying means, and surface-distortion distribution calculating means 10 for performing image processing on the captured mirror images of the plurality of light-and-shade patterns to calculate surface-distortion distribution of the measurement-target surface.

Abstract: A press forming method for a metal sheet is provided. The method is capable of improving a forming limit at which a crack appears in a metal sheet and being easily applied to a large press machine for mass production with a low cost, without correcting the shape of dies, such as a punch and an upper die, or changing the shape or material of a blank to a special shape or material. Dies, a surface roughness of which is an arithmetical mean roughness Ra of 7.5 ?m or smaller, are used as a punch, an upper die, and a blank holder. Fluid with a kinematic viscosity of 500 mm2/s of lower (40° C.) is used as a lubricant, and is supplied to a space between a metal sheet and the blank holder, a space between the metal sheet and the punch, and a space between the metal sheet and the upper die. A die is detached from a workpiece in the middle of forming, and resuming the forming, thereby improving formability.

Abstract: A surface-distortion measuring device and a surface-distortion measuring method can quantitatively, rapidly, and highly accurately measure and evaluate surface-distortion distribution at all of observable points on a specular or semi-specular surface of a measurement target. The device includes pattern displaying means 2 capable of switching and displaying a plurality of kinds of light-and-shade patterns 5, capturing means 3 for capturing mirror images, reflected in the specular or semi-specular surface of a measurement target 1, of the plurality of light-and-shade patterns displayed on the pattern displaying means, and surface-distortion distribution calculating means 10 for performing image processing on the captured mirror images of the plurality of light-and-shade patterns to calculate surface-distortion distribution of the measurement-target surface.

Abstract: An ultra-high strength cold rolled steel sheet having a tensile strength of 880 to 1170 MPa, that consists essentially of 0.01 to 0.07% C, 0.3% or less Si, 0.1% or less P, 0.01% or less S, 0.01 to 0.1% sol.Al, 0.0050% or less N, 1.6 to 2.5% of the sum of at least one element selected from the group consisting of Mn, Cr, and Mo, by mass, and a balance of Fe, and that has an inner zone deeper than 10 &mgr;m from the surface of the steel sheet being substantially a martensitic single phase structure. Since the steel sheet has a hole expansion ratio of 75% or more, specified by the Standard of Japan Iron and Steel Federation, JFST1001-1996, the steel sheet has a tensile strength in a range of from 880 to 1170 MPa, and an excellent mechanically joining property, and is suitable for fabricating automobile seat frames.

Abstract: The present invention relates to an ultra-high strength cold rolled steel sheet having 880 to 1170 MPa of tensile strength, that consists essentially of 0.01 to 0.07% C, 0.3% or less Si, 0.1% or less P, 0.01% or less S, 0.01 to 0.1% sol.Al, 0.0050% or less N. 1.6 to 2.5% of sum of at least one element selected from the group consisting of Mn, Cr, and Mo, by mass, and balance of Fe, and that has an inner zone deeper than 10 &mgr;m from the surface of the steel sheet being substantially martensitic single phase structure. Since the steel sheet has hole expansion ratio of 75% or more, specified by the Standard of Japan Iron and Steel Federation, JFST1001-1996, tensile strength in a range of from 880 to 1170 MPa, and excellent mechanically joining property, it is suitable for automobile seat frames.