JFE Steel Corporation

A method for etching steel includes a first etching process of performing electrolytic etching on steel in a basic solution having a pH of more than 7.0 and a second etching process of bringing the steel, which has been subjected to the first etching process, into contact with an acidic solution having a pH of less than 7.0.

A high-strength hot rolled steel sheet has a chemical composition containing, in % by mass, C: 0.04 to 0.18%, Si: 0.1 to 3.0%, Mn: 0.5 to 3.5%, P: more than 0% and 0.050% or less, S: more than 0% and 0.010% or less, Al: more than 0% and 1.5% or less, N: more than 0% and 0.010% or less, O: more than 0% and 0.003% or less, and Ti: 0.040 to 0.150%, with the balance being Fe and incidental impurities. The steel sheet has a steel microstructure in which bainite is a main phase and in which the volume fraction of retained austenite is less than 3%. (The amount of solute Ti/the total amount of Ti) is 0.30 or more and less than 0.80, and the amount of Ti present as precipitates having a diameter of 100 nm or more is 0.010 to 0.030% by mass.

A non-oriented electrical steel sheet is produced by hot-rolling a slab and then performing hot-band annealing and cold rolling thereon to obtain a cold-rolled sheet, and further performing finishing annealing. The finishing annealing is performed by setting the dew point D H is in the range from 500° C. to 800° C. in a heating zone to −20° C. or lower, and setting the dew point D S in the range from above 800° C. to the soaking temperature in the heating zone, as well as in a region where the steel sheet is in a soaking zone, to −40° C. or lower, and also controlling the dew points D H and D S so that the relationship of D H >D S is satisfied, thereby suppressing the oxidation of the surface of the steel sheet after the finishing annealing. Thus, a non-oriented electrical steel sheet with low iron loss is stably obtained as a high-grade material with a high Si content.

A grain-oriented electrical steel sheet having excellent coating adhesion properties is provided, and methods for manufacturing the same are provided. The grain-oriented electrical steel sheet can include a forsterite coating and an insulating coating that are disposed, in this order, starting from a surface side of the steel sheet, wherein a frequency of formation of cracks propagating through the insulating coating in a region extending 100 μm toward a widthwise middle of the grain-oriented electrical steel sheet from a widthwise edge of the grain-oriented electrical steel sheet is less than or equal to 3.0 times the frequency of formation of cracks propagating through the insulating coating in a region extending toward the widthwise middle from a widthwise position more than 100 μm from the widthwise edge to a widthwise position 500 μm from the widthwise edge, where the frequency is expressed as a number per mm.

A laser cutting method is for cutting, using a laser cutter, the vicinity of a joint ( 2 ) at which a trailing end of a preceding steel strip ( 1 A) is joined to a leading end of a succeeding steel strip ( 1 B), and includes an edge position detection process of detecting an edge position of the preceding steel strip and of the succeeding steel strip, a cutting track determination process, and a cutting execution process. In the cutting track, an oscillation start position of a laser is set outward from the edge position by a first predetermined distance in a width direction of the steel strip, an oscillation end position of the laser is set outward from the edge position by a second predetermined distance in the width direction of the steel strip, and a penetration angle of the laser is set to a predetermined angle or less.

A resistance spot welded joint is formed by welding two or more steel sheets including at least one high strength steel sheet. The high strength steel sheet has a specific chemical composition, and the nugget diameter of a weld and the width of a softened portion of a heat-affected zone satisfy the relation of: width (mm) of softened portion of heat-affected zone>nugget diameter (mm)×0.2. The hardness X of a softest portion of the heat-affected zone and the hardness of the base material of the high strength steel sheet satisfy the relation of: X (HV)<hardness (HV) of base material of high strength steel sheet× 0.95 . The total average number density of NbC, TiC, VC particles having a diameter of 100 nm or less in the heat-affected zone is 80 particles/μm 2 or more

Provided herein is a stainless steel seamless pipe for oil country tubular goods. A method for manufacturing such a stainless steel seamless pipe is also provided. The stainless steel seamless pipe has: a composition that contains, in mass %, C: 0.10% or less, Si: 0.5% or less, Mn: 0.05 to 0.50%, P: 0.030% or less, S: 0.005% or less, O: 0.0040% or less, Ni: 3.0 to 8.0%, Cr: 10.0 to 14.0%, Mo: 0.5 to 2.8%, Al: 0.1% or less, V: 0.005 to 0.2%, N: 0.10% or less, Cu: 0.01 to 1.0%, Co: 0.01 to 1.0%, and Ca: 0.0005 to 0.0030%, and in which the balance is Fe and incidental impurities; a microstructure containing at most 20 non-metallic inclusions having a predetermined composition ratio of CaO and Al 2 O 3 and a major axis of 5 μm or more per 100 mm 2 ; and a yield stress of 655 MPa or more.

In the production of a grain-oriented electrical steel sheet by heating a steel slab containing, in mass %, C: 0.02 to 0.10%, Si: 2.5 to 5.5%, Mn: 0.01 to 0.30%, S: 0.0010 to 0.040%, Se: 0 to 0.040%, sol. Al: 0.010 to 0.040%; and N: 0.004 to 0.020% to 1300° C. or higher; subsequently performing hot rolling, hot-band annealing as necessary, cold rolling, and primary recrystallization annealing which also serves as decarburization annealing; applying an annealing separator on the surface of the steel sheet; and performing finishing annealing, edge cracks that may occur in the hot rolling are effectively prevented by keeping a slab lateral face temperature at a time of starting rough rolling during the hot rolling equal to or lower than a temperature T e defined by the following Expression T e =−120000 [% S] 2 +1400 (1) and carrying out width reduction after at least one pass in the rough rolling.

A converter steelmaking method has molten pig iron subjected to dephosphorization process for dephosphorized molten iron, dephosphorized molten iron is subjected to decarburization process for molten steel. For dephosphorization process, a first cold iron source in amount meeting Formula (1) is charged into first converter-type vessel, then undephosphorized molten pig iron is charged and subjected to dephosphorization process. Dephosphorized molten iron is discharged and held in molten metal receiving vessel. After second cold iron source is charged into first converter-type vessel in which dephosphorization process has been performed, the dephosphorized molten iron held in molten metal receiving vessel is charged and subjected to decarburization process. % W s0 ≤0.1186T−134 (% W s0 ≥0) . . . (1), where % W s0 : a ratio (%) of first cold iron source to sum of first cold iron source and charge amount of undephosphorized molten pig iron, and T: a temperature (° C.) of undephosphorized molten pig iron.

A battery case for being mounted under a floor of a vehicle body and storing a battery includes: a main body formed of a bottomed frame body having side walls facing each other in a vehicle width direction in a state of being mounted on the vehicle body; and a battery case cross member configured to extend between the facing side walls in the main body and to reinforce the main body. The battery case cross member includes a hat-shaped section part including a top portion, side wall portions, and flange portions, the flange portions abutting on a bottom surface of the main body, a resin patched on or coating a full length of an inner surface and/or outer surface of the hat-shaped section part, and a reinforcement arranged to cover the resin and adhered to the resin.