Provided is a high strength steel sheet that has a predetermined chemical composition and is manufactured under optimum conditions, the high strength steel sheet having a steel microstructure including, by area, ferrite: 30% or more and 80% or less, martensite: 5% or more and 35% or less, and retained austenite: 8% or more, wherein the quotient of the area fraction of grains of the retained austenite, the grains having an aspect ratio of 2.0 or more and a minor axis length of 1 μm or less, divided by the total area fraction of the retained austenite is 0.3 or more, wherein the quotient of the average Mn content (mass %) in the retained austenite divided by the average Mn content (mass %) in the ferrite is 1.5 or more.

Provided is a high strength steel sheet that has a predetermined chemical composition and is manufactured under optimum conditions, the high strength steel sheet having a steel microstructure including, by area, ferrite: 30% or more and 80% or less, martensite: 5% or more and 35% or less, and retained austenite: 8% or more, wherein the quotient of the area fraction of grains of the retained austenite, the grains having an aspect ratio of 2.0 or more and a minor axis length of 1 μm or less, divided by the total area fraction of the retained austenite is 0.3 or more, wherein the quotient of the average Mn content (mass %) in the retained austenite divided by the average Mn content (mass %) in the ferrite is 1.5 or more.

Provided are a hot-rolled steel sheet for an electric resistance welded steel pipe and a method for manufacturing the same, an electric resistance welded steel pipe and a method for manufacturing the same, a line pipe, and a building structure. The hot-rolled steel sheet has a chemical composition containing, by mass %, C: 0.030% or more and 0.20% or less, Si: 0.02% or more and 1.0% or less, Mn: 0.40% or more and 3.0% or less, P: 0.050% or less, S: 0.020% or less, N: 0.0070% or more and 0.10% or less, and Al: 0.005% or more and 0.080% or less, the balance being Fe and incidental impurities, in which N dissolved in steel is contained in an amount of 0.0010% or more and 0.090% or less, and letting a sheet thickness be t, a steel microstructure at a ½t position has an average grain size of 20.0 μm or less.

Disclosed is a high corrosion-resistance strip steel, comprising a carbon steel base layer and a corrosion-resistance cladding layer roll-bonded with the carbon steel base layer, the corrosion-resistance cladding layer being austenitic stainless steel or pure titanium, the thickness of the corrosion-resistance cladding layer being 0.5% to 5% of the total thickness of the strip steel. In addition, further disclosed is a manufacturing method for the described high corrosion-resistance strip steel, comprising the steps of: (1) obtaining a base layer material and a cladding layer material; (2) assembling billets (3) pre-heating: pre-heating the billets at a temperature of 1150° C. to 1250° C., so that elements of the corrosion-resistance cladding layer and elements of the carbon steel base layer diffuse at the interface to form a stable transition layer, and then slowly cooling to room temperature; (4) secondary heating and rolling; and (5) water-cooling and then winding. The high corrosion-resistance strip steel finally provides, by means of rational component design, thickness design, and process design, the obtained steel plate or steel strip with a high corrosion-resistance surface and good interlayer bonding performance, and the steel plate or steel strip has good mechanical properties and processability.

Disclosed is a high corrosion-resistance strip steel, comprising a carbon steel base layer and a corrosion-resistance cladding layer roll-bonded with the carbon steel base layer, the corrosion-resistance cladding layer being austenitic stainless steel or pure titanium, the thickness of the corrosion-resistance cladding layer being 0.5% to 5% of the total thickness of the strip steel. In addition, further disclosed is a manufacturing method for the described high corrosion-resistance strip steel, comprising the steps of: (1) obtaining a base layer material and a cladding layer material; (2) assembling billets (3) pre-heating: pre-heating the billets at a temperature of 1150° C. to 1250° C., so that elements of the corrosion-resistance cladding layer and elements of the carbon steel base layer diffuse at the interface to form a stable transition layer, and then slowly cooling to room temperature; (4) secondary heating and rolling; and (5) water-cooling and then winding. The high corrosion-resistance strip steel finally provides, by means of rational component design, thickness design, and process design, the obtained steel plate or steel strip with a high corrosion-resistance surface and good interlayer bonding performance, and the steel plate or steel strip has good mechanical properties and processability.

The present invention relates to an RFeB-based sintered magnet having a composition including: 24-31% by mass of at least one element selected from the group consisting of Nd, Pr, La and Ce; 0.1-6.5% by mass of at least one element selected from the group consisting of Dy and Tb; 0.8-1.4% by mass of B; 0.03-0.2% by mass of at least one element selected from the group consisting of Zr, Ti, Hf and Nb; 0.8-5.5% by mass of Co; 0.1-1.0% by mass of Cu; and 0.1-1.0% by mass of Al, with a remainder being Fe and unavoidable impurities, in which the composition has a total content of Cu and Al being higher than 0.5% by mass.

The present invention relates to an RFeB-based sintered magnet having a composition including: 24-31% by mass of at least one element selected from the group consisting of Nd, Pr, La and Ce; 0.1-6.5% by mass of at least one element selected from the group consisting of Dy and Tb; 0.8-1.4% by mass of B; 0.03-0.2% by mass of at least one element selected from the group consisting of Zr, Ti, Hf and Nb; 0.8-5.5% by mass of Co; 0.1-1.0% by mass of Cu; and 0.1-1.0% by mass of Al, with a remainder being Fe and unavoidable impurities, in which the composition has a total content of Cu and Al being higher than 0.5% by mass.

A non-oriented electrical steel sheet with an average magnetostriction λ.sub.p-p at 400 Hz and 1.0 T of not more than 4.5×10.sup.−6, and area ratio of recrystallized grains at a section in rolling direction of steel sheet of 40 to 95% and an average grain size of 10 to 40 μm is obtained by subjecting a steel slab containing, in mass %, C: not more than 0.005%, Si: 2.8 to 6.5%, Mn: 0.05 to 2.0%, Al: not more than 3.0%, P: not more than 0.20%, S: not more than 0.005%, N: not more than 0.005%, Ti: not more than 0.003%, V: not more than 0.005% and Nb: not more than 0.005% and satisfying Si—2Al—Mn≥0 to hot rolling, hot-band annealing, cold rolling and finish annealing under adequate cold rolling and finish annealing conditions, and a motor core is manufactured by such a steel sheet.

A non-oriented electrical steel sheet with an average magnetostriction λ.sub.p-p at 400 Hz and 1.0 T of not more than 4.5×10.sup.−6, and area ratio of recrystallized grains at a section in rolling direction of steel sheet of 40 to 95% and an average grain size of 10 to 40 μm is obtained by subjecting a steel slab containing, in mass %, C: not more than 0.005%, Si: 2.8 to 6.5%, Mn: 0.05 to 2.0%, Al: not more than 3.0%, P: not more than 0.20%, S: not more than 0.005%, N: not more than 0.005%, Ti: not more than 0.003%, V: not more than 0.005% and Nb: not more than 0.005% and satisfying Si—2Al—Mn≥0 to hot rolling, hot-band annealing, cold rolling and finish annealing under adequate cold rolling and finish annealing conditions, and a motor core is manufactured by such a steel sheet.

A Super Invar alloy includes Ni of 30 to 35 percent by mass, Co of 3 to 6 percent by mass, Ti of 0.02 to 1.0 percent by mass, Mn of 0 to 0.2 percent by mass, an inevitable impurity including S, and the balance Fe. The Super Invar alloy does not include an additive other than Ti and Mn, as an additive. The Super Invar alloy includes the Ni of 32.3 to 32.5 percent by mass, the Co of 4.4 to 5.1 percent by mass, the Ti of 0.02 to 1.0 percent by mass, and the S of 0.007 to 0.1 percent by mass. The Super Invar alloy is an alloy having good high temperature ductility, low hot crack sensitivity, and low thermal expansibility of equal to or lower than 1 ppm/° C. It is applicable to use Zr or Hf instead of Ti.