A high-strength steel sheet that has a predetermined component composition, that has a steel microstructure in which an area percentage of ferrite ranges from 5% to 50% in a thickness cross-section in a rolling direction, a total area percentage of fresh martensite and retained γ ranges from 2% to 30%, each of the fresh martensite and the retained γ has an average grain size of 5 μm or less, and a ratio of the fresh martensite and the retained γ adjacent only to ferrite with respect to the fresh martensite and the retained γ from a surface to 200 μm in the thickness direction is 30% or less in total area percentage, and that has a yield strength of 550 MPa or more.

A high-strength galvanized steel sheet includes a base steel sheet and a galvanized layer on a surface thereof. The base steel sheet has a predetermined chemical composition and a microstructure in which an area fraction of martensite is 30% or less, an area fraction of pearlite is 1% or less, a total area fraction of tempered martensite and carbide-containing bainite is 30% or more and 99% or less, an area fraction of retained austenite is 1% to 20%, and a total area fraction of ferrite and non-carbide-containing bainite is 45% or less in the steel sheet microstructure in a predetermined region and in which an area fraction of retained austenite grains having two or more crystal orientations is 40% or less in all the retained austenite grains in a predetermined region.

A thin steel sheet has a steel structure which has a ferrite area fraction of 30% or less, a bainite area fraction of 5% or less, a martensite and tempered martensite area fraction of 70% or more, and a retained austenite area fraction of 2.0% or less and in which the ratio of the dislocation density in the range of 0 μm to 20 μm from a surface of the steel sheet to the dislocation density of a through-thickness central portion of the steel sheet is 90% to 110% and the average of the top 10% of the sizes of cementite grains located in a depth of up to 100 μm from a surface of the steel sheet is 300 nm or less. The maximum camber of the steel sheet sheared to a length of 1 m in a longitudinal direction of the steel sheet is 15 mm or less.

Iron-based alloys and articles in strips, sheets, workpieces and the like are converted into high strength steel with a minimum of cost, time and effort, including producing dual phase materials. This is achievable by extremely rapid micro-treating of low, medium, and high carbon iron-based alloys and articles by rapid heating and rapid cooling at least a portion of the alloy/article. This heating step involves nearly immediately heating the iron-based alloy to a selected temperature above its austenite conversion temperature. Then, the alloy is immediately quenched, also at an extremely fast rate, on at least a portion of the iron-based alloy in a quenching unit adjacent the heating unit. This procedure forms high strength alloy in a desired area, depending upon where the treatment was performed.

A surface-treated steel sheet of the present invention includes a base steel sheet and a Ni—Co—Fe alloy-plated layer on at least one surface of the base steel sheet, in which, in the alloy-plated layer, a Ni coating weight is 7.1 to 32.5 g/m.sup.2, a Co coating weight is 0.65 to 5.2 g/m.sup.2, and a total of the Ni coating weight and the Co coating weight is in a range of 9.0 to 35.0 g/m.sup.2. In an outermost layer of the alloy-plated layer, a Co concentration is in a range of 20 to 60 atom %, and a Fe concentration is in a range of 5 to 30 atom %. In the alloy-plated layer, a region having a thickness of 2 μm or more, in which a total of a Ni concentration and the Co concentration is 10 atom % or more and the Fe concentration is 5 atom % or more, is present, and the base steel sheet has a predetermined chemical composition, and a ferrite grain size number is 9.0 or more.

A surface-treated steel sheet of the present invention includes a base steel sheet and a Ni—Co—Fe alloy-plated layer on at least one surface of the base steel sheet, in which, in the alloy-plated layer, a Ni coating weight is 7.1 to 18.5 g/m.sup.2, a Co coating weight is 0.65 to 3.6 g/m.sup.2, and a total of the Ni coating weight and the Co coating weight is in a range of 9.0 to 20.0 g/m.sup.2. In a surface layer of the alloy-plated layer, a Co concentration is in a range of 20 to 60 atom %, and a Fe concentration is in a range of 5 to 30 atom %. In the alloy-plated layer, a region having a thickness of 2 μm or more, in which a total of a Ni concentration and the Co concentration is 10 atom % or more and the Fe concentration is 5 atom % or more, is present. The base steel sheet has a predetermined chemical composition, and a ferrite grain size number is 10 or more.

A conveyance system for tensioning to post-treat a rapidly-solidified metal strip, and a method for post-treating the metal strip with the conveyance system is provided. The conveyance system comprises a tension roller assembly and a tensioning assembly, between which the metal strip is conveyed to be continuously post-treated under a predetermined tensile stress. The tension roller assembly comprises a single drive roller and a freely-rotating pressing roller. The metal strip is conveyed over an angle of wrap α on the drive roller, and, with respect to the drive roller, the pressing roller is arranged at a contact point of the metal strip that defines one end of an angle of wrap α. The method can include bridging the distance between the tensioning assembly and the tension roller assembly amid the insertion of the metal strip into the tension roller assembly, after a post-treatment region in space and in time.

A method for manufacturing a thin strip component, including a processing step of processing an amorphous thin strip member into a dimension shape larger than a target shape, and a heat treating step of heat treating and contracting the amorphous thin strip member processed in the processing step to form the amorphous thin strip member into a thin strip component of the target shape. A thin strip component which is a magnetic laminate in which a plurality of plate-shaped thin strip component members of the same shape are laminated, and has a recess over an entire side surface of the magnetic laminate is used. A motor including the thin strip component, a plurality of coils disposed on the thin strip component, and a rotor disposed between the plurality of coils is used.

Provided is a method for producing a grain-oriented electrical steel sheet with which it is possible to obtain a grain-oriented electrical steel sheet exhibiting excellent magnetic properties. This method for prod producing a grain-oriented electrical steel sheet involves subjecting a surface of a grain-oriented electrical steel sheet which does not have a forsterite film thereon to a film formation treatment, and performing the film formation treatment while imparting tension to the grain-oriented electrical steel sheet which does not have a forsterite film thereon.

Iron-based alloys and articles in strips, sheets, workpieces and the like are converted into high strength steel with a minimum of cost, time and effort, including producing dual phase materials. This is achievable by extremely rapid micro-treating of low, medium, and high carbon iron-based alloys and articles by rapid heating and rapid cooling at least a portion of the alloy/article. This heating step involves nearly immediately heating the iron-based alloy to a selected temperature above its austenite conversion temperature. Then, the alloy is immediately quenched, also at an extremely fast rate, on at least a portion of the iron-based alloy in a quenching unit adjacent the heating unit. This procedure forms high strength alloy in a desired area, depending upon where the treatment was performed.