A cold-rolled and heat-treated steel sheet-having a microstructure consisting of, in surface fraction: between 10% and 30% of retained austenite, said retained austenite being present as films having an aspect ratio of at least 3 and as Martensite Austenite islands, less than 8% of such Martensite A islands having a size above 0.5 m, at most 1% of fresh martensite at most 50% of tempered martensite and recovered martensite containing precipitates of at least one element chosen among niobium, titanium and vanadium.

It also provides a manufacturing method thereof.

An electric-resistance-welded stainless clad steel pipe or tube that is excellent in both the fracture property of the weld and the corrosion resistance of the pipe or tube inner surface as electric resistance welded without additional welding treatment such as weld overlaying after electric resistance welding is provided. An electric-resistance-welded stainless clad steel pipe or tube comprises: an outer layer of carbon steel or low-alloy steel; and an inner layer of austenitic stainless steel having a predetermined chemical composition, wherein a flatness value h/D in a 90 flattening test in accordance with JIS G 3445 is less than 0.3, and a pipe or tube inner surface has no crack in a sulfuric acid-copper sulfate corrosion test in accordance with ASTM A262-10, Practice E, where h is a flattening crack height (mm), and D is a pipe or tube outer diameter (mm).

A resistance spot welding method inhibits, in accordance with the electrode angle, the occurrence of cracking in the weld regardless of the steel grade. The resistance spot welding method satisfies relationships:
2.Math.A.Math.(t.Math.T/F).sup.1/2H when 0A<1
(3.Math.A1).Math.(t.Math.T/F).sup.1/2H when 1A<10
(A+19).Math.(t.Math.T/F).sup.1/2H when 10A<20
where H (ms) is an electrode force retaining time after completion of current passage, A (degrees) is an electrode angle of the electrodes, t (mm) is a sheet thickness of a steel sheet having a largest sheet thickness among the steel sheets, T (MPa) is a tensile strength of a steel sheet having a highest tensile strength among the two or more steel sheets, and F (N) is the electrode force.

An Al plated electric resistance welded steel pipe for hardening use suppressing the formation of scale to the inside of the plating layer while performing hot forming and an Al plated hollow member using that Al plated electric resistance welded steel pipe, wherein the Al plated electric resistance welded steel pipe for hardening use is comprised of a base material made of a tubular steel plate and having a predetermined chemical composition and an electric resistance welded zone provided at a seam portion of the steel plate and extending in a longitudinal direction of the steel plate, the base material is further provided with an intermetallic compound layer positioned on the surface of the steel plate and including an Al-Fe-Si-based intermetallic compound and an Al plating layer positioned on the surface of the intermetallic compound layer and containing Al and Si, and 70X/DY/t30 is satisfied, wherein X (m) is a thickness of the intermetallic compound layer, Y (m) is a thickness of the Al plating layer, t (mm) is a pipe thickness of the steel pipe, and D (mm) is an outside diameter of the steel pipe.

A process for joining steel plate includes providing a steel plate and joining the steel plate to another material. The steel plate includes at least one surface having an AlSi coating. The step of joining the steel plate to another material is performed while the steel plate is in an as- coated condition. Joining is performed using a forging process.

A spot weld may be formed between an aluminum workpiece and an adjacent overlapping steel workpiece with the use of opposed spot welding electrodes that have mating weld faces designed for engagement with the outer surfaces of the workpiece stack-up assembly. The electrode that engages the stack-up assembly proximate the aluminum workpiece includes a central ascending convex surface and the electrode that engages the stack-up assembly proximate the steel workpiece has an annular surface. The mating weld faces of the first and second spot welding electrodes distribute the passing electrical current along a radially outwardly expanding flow path to provide a more uniform temperature distribution over the intended spot weld interface and may also produce a deformed bonding interface within the formed weld joint. Each of these events can beneficially affect the strength of the weld joint.

An electric-resistance-welded stainless clad steel pipe or tube that is excellent in both the fracture property of the weld and the corrosion resistance of the pipe or tube inner surface as electric resistance welded without additional welding treatment such as weld overlaying after electric resistance welding is provided. An electric-resistance-welded stainless clad steel pipe or tube comprises: an outer layer of carbon steel or low-alloy steel; and an inner layer of austenitic stainless steel having a predetermined chemical composition, wherein a flatness value h/D in a 90 flattening test in accordance with JIS G 3445 is less than 0.3, and a pipe or tube inner surface has no crack in a sulfuric acid-copper sulfate corrosion test in accordance with ASTM A262-10, Practice E, where h is a flattening crack height (mm), and D is a pipe or tube outer diameter (mm).

Provided is a resistance spot welding method. The resistance spot welding method for joining a sheet set including a plurality of lapped steel sheets includes: holding the sheet set between a pair of electrodes; and energizing the sheet set under application of electrode force to thereby join the steel sheets together. At least one of the plurality of lapped steel sheets is a surface-treated steel sheet including a metal coating layer on a surface thereof. The energizing includes: a primary energizing step of performing energization to form a nugget portion; a non-energizing step in which, after the primary energizing step, the energization is suspended for an energization suspension time Tc (cycles); and a secondary energizing step of, after the non-energizing step, performing energization for reheating while the nugget portion is prevented from growing. During the energizing, the relations of a particular formula are satisfied.

An electric-resistance-welded stainless clad steel pipe or tube that is excellent in both the fracture property of the weld and the corrosion resistance of the pipe or tube inner surface as electric resistance welded without additional welding treatment such as weld overlaying after electric resistance welding is provided. An electric-resistance-welded stainless clad steel pipe or tube comprises: an outer layer of carbon steel or low-alloy steel; and an inner layer of austenitic stainless steel having a predetermined chemical composition, wherein a flatness value h/D in a 90 flattening test in accordance with JIS G 3445 is less than 0.3, and a pipe or tube inner surface has no crack in a sulfuric acid-copper sulfate corrosion test in accordance with ASTM A262-10, Practice E, where h is a flattening crack height (mm), and D is a pipe or tube outer diameter (mm).

The invention relates to a device (2) for welding hard material elements (4) onto teeth (6) of a saw blade (8), comprising a saw blade feed device (12) for moving the saw blade (8) in a feed direction (14), such that a tooth (6a) of the saw blade (8) can be brought into a target position (16) in a working region (10) of the device (2), comprising a first centering device (30) for centering the saw blade (8) transversely to the feed direction (14), comprising a second centering device (32) for centering a respective hard material element (4) transversely to the feed direction (14), comprising a resistance welding device (24) having a welding electrode (26) that can be deployed into and withdrawn from the working region (10), comprising a supply device (28) for supplying and transferring a respective hard material element (4) to the welding electrode (26), and it being possible for the welding electrode (26) to be deployed in such a way that the hard material element (4) can be brought toward the tooth (6a) to abut the tooth (6a). According to the invention, the hard material element (4) can be centered relative to the centered and fixed saw blade (8) by means of the second centering device (32), and the first and second centering device (30) are provided in a common assembly (38), such that the centering of the saw blade (8) by the first centering device (32) predetermines a centering position for the subsequent centering of the hard material element (4) by the second centering device (32).