A method of producing a surface-treated steel sheet is provided. The surface-treated steel sheet includes a layer that contains a metal oxide. The method is characterized by including: dipping a steel sheet for 0.1 to 10 seconds in a treatment liquid that contains at least fluoride ions and has a pH of 2 to 5; and electrically treating by flowing a direct current between the steel sheet and an electrode in a treatment liquid to form a layer that contains a metal oxide on a surface of the steel sheet. According to the present invention, there can be provided a method of producing a surface-treated steel sheet which can enhance the interfacial adhesion with an organic resin layer when the organic resin layer is formed on the metal oxide layer.

One aspect of this ferritic stainless steel sheet contains, by mass %, C: 0.03% or less, N: 0.05% or less, Si: 1% or less, Mn: 1.2% or less, Cr: 14% or more and 28% or less, Nb: 8(C +N) or more and 0.8% or less, and Al: 0.1% or less, with a balance being Fe and inevitable impurities, in which a film satisfying Expression 1 is formed in a surface thereof. Expression 1 is d.sub.fCr.sub.f+5(Si.sub.f+3Al.sub.f)2.0. In Expression 1, d.sub.f represents a thickness (nm) of the film, Cr.sub.f represents a Cr cationic fraction in the film, Si.sub.f represents a Si cationic fraction in the film, and Al.sub.f represents an Al cationic fraction in the film.

A low temperature carburizing method according to the present invention comprises: step (a) for pre-processing a metal to be processed; step (b) for inputting the metal to be processed to a reaction chamber and heating the same to a set temperature; step (c) for forming a vacuum atmosphere in the reaction chamber and introducing a reaction gas thereinto at a predetermined pressure to accelerate carburization; step (d) for supplying the reaction gas to the reaction chamber at a pressure equal to or lower than the pressure of the reaction gas of step (c) to spread carburization; and step (e) for repeating step (c) and step (d) at predetermined time intervals.

The present disclosure provides a high-entropy alloy (HEA) with room-temperature superplasticity and a preparation method thereof, belonging to the field of metal materials. In the present disclosure, the HEA with room-temperature superplasticity has a chemical formula shown in Formula I: (FeCoNiCr).sub.100-xCu.sub.x (Formula I), where in Formula I, x is 2.0 to 4.0. A FeCoNiCr alloy is used as a matrix, and then added with a trace amount of a Cu element, thereby significantly reducing formation of a metastable phase in the FeCoNiCr alloy while reducing stacking fault energy of the alloy, such that the alloy maintains a desirable work hardening ability and achieves an excellent elongation at break. Moreover, a plasticity of the alloy is further improved through twinning-induced plasticity (TWIP).

Stainless steel for a fuel cell separator plate and a manufacturing method therefor are disclosed. The stainless steel for a fuel cell separator plate, according to one embodiment of the present invention, comprises: a stainless base material; and a passive film formed on the stainless base material, wherein a Cr/Fe atomic weight ratio in a 1 nm or less thickness region of the stainless base material, which is adjacent to an interface between the stainless and the passive film, is 0.45 or more. Therefore, by modifying the surface of the stainless steel for a fuel cell separator plate, a low interface contact resistance and a good corrosion resistance can be obtained, and a separate additional process such as precious metal coating can be removed, such that manufacturing costs are reduced and productivity can be improved.

An acid solution preparation device is an acid solution preparation device for preparing an acid solution used for pickling of a steel plate, the device including a sealed tank for storing the acid solution, a gas supply part for supplying an oxygen-containing gas from outside of the sealed tank to the sealed tank, and a purge part for discharging a gas in the sealed tank to the outside.

Provided is a ferritic stainless steel that has excellent corrosion resistance and displays good brazing properties when brazing is carried out at high temperature using a Ni-containing brazing metal. These effects are obtained as a result of the steel having a chemical composition containing, in mass %: 0.003% to 0.020% of C; 0.05% to 1.00% of Si; 0.10% to 0.50% of Mn, 0.05% or less of P; 0.01% or less of S; 16.0% to 25.0% of Cr; 0.05% to 0.35% of Ti; 0.005% to 0.05% of Al; and 0.005% to 0.025% of N, the balance being Fe and incidental impurities, and as a result of a nitrogen-enriched layer being created that has a nitrogen concentration peak value of 0.05 mass % to 0.30 mass % at a depth of within 0.05 m of a surface of the steel.

A ferritic stainless steel excellent in corrosion resistance and conductivity and a method for manufacturing the same, the stainless steel having a chemical composition containing, by mass %, C: 0.001% or more and 0.05% or less, Si: 0.001% or more and 0.5% or less, Mn: 0.001% or more and 1.0% or less, Al: 0.001% or more and 0.5% or less, N: 0.001% or more and 0.05% or less, Cr; 17% or more and 23% or less, Mo: 0.1% or less and the balance being Fe and inevitable impurities and a passivation film on the surface of the stainless steel which is obtained by immersing the stainless steel in a solution for an immersion treatment, said solution mainly contains hydrofluoric acid or a liquid mixture of hydrofluoric acid and nitric acid.

A pickling process designed for pickling a metal strip such as a stainless steel strip reduces the amount of HF and/or HNO.sub.3. The strip is immersed in at least one first pickling tub that contains a mixture of an acid such as H.sub.2SO.sub.4, an excess of at least one oxidizing agent, and includes electrodes that may apply a current to the strip that runs through the mixture.

The invention relates to a method for manufacturing strips of stainless steel, comprising hot rolling in an initial process (A) and subsequently cold rolling in a cold rolling line (B). The hot rolling is stopped when the strip thickness has been reduced to a thickness between 2.0 mm and 6.5 mm. The subsequent cold rolling is passed at least one time through said cold rolling line, which comprises in the following order: At least one cold rolling mill (11-13) in the initial part of the line, at least one annealing section (17), a scale breaking step (21), a shot blasting step (23) and at least one pickling section (26, 27) utilizing a mixture of nitric acid HNO.sub.3, hydrofluoric acid HF and optionally sulphuric acid H.sub.2SO.sub.4.