The present invention provides a hot-rolled and annealed ferritic stainless steel sheet which has sufficient corrosion resistance and in which cracks can be prevented during blanking into a thick flange, and a method for manufacturing the same. A hot-rolled and annealed ferritic stainless steel sheet has a chemical composition containing, in percent by mass, C: 0.001% to 0.020%, Si: 0.05% to 1.00%, Mn: 0.05% to 1.00%, P: 0.04% or less, S: 0.01% or less, Al: 0.001% to 0.100%, Cr: 10.0% to 19.0%, Ni: 0.65% to 1.50%, Ti: 0.10% to 0.40%, and N: 0.001% to 0.020%, with the balance being Fe and unavoidable impurities, and has a threshold stress intensity factor K.sub.IC of 35 MPa.Math.m.sup.1/2 or more.

Provided is a cold-rolled steel plate for hot forming, which is excellent in corrosion-resistance and spot-weldability, contains, by weight %, C: 0.1-0.4%, Si: 0.5-2.0%, Mn: 0.01-4.0%, Al: 0.001-0.4%, P: 0.001-0.05%, S: 0.0001-0.02%, Cr: 0.5% to less than 3.0%, N: 0.001-0.02%, and a balance of Fe and inevitable impurities, satisfying formula (1) below, and includes an Si amorphous oxidation layer continuously or discontinuously formed at a thickness of 1 nm-100 nm on the surface thereof. Formula (1): 1.40.4*Cr+Si3.2 (wherein element symbols denote measurements of respective element contents by weight %).

Provided is a cold-rolled steel plate for hot forming, which is excellent in corrosion-resistance and spot-weldability, contains, by weight %, C: 0.1-0.4%, Si: 0.5-2.0%, Mn: 0.01-4.0%, Al: 0.001-0.4%, P: 0.001-0.05%, S: 0.0001-0.02%, Cr: 0.5% to less than 3.0%, N: 0.001-0.02%, and a balance of Fe and inevitable impurities, satisfying formula (1) below, and includes an Si amorphous oxidation layer continuously or discontinuously formed at a thickness of 1 nm-100 nm on the surface thereof. Formula (1): 1.40.4*Cr+Si3.2 (wherein element symbols denote measurements of respective element contents by weight %).

A dual hardness steel article comprises a first air hardenable steel alloy having a first hardness metallurgically bonded to a second air hardenable steel alloy having a second hardness. A method of manufacturing a dual hard steel article comprises providing a first air hardenable steel alloy part comprising a first mating surface and having a first part hardness, and providing a second air hardenable steel alloy part comprising a second mating surface and having a second part hardness. The first air hardenable steel alloy part is metallurgically secured to the second air hardenable steel alloy part to form a metallurgically secured assembly, and the metallurgically secured assembly is hot rolled to provide a metallurgical bond between the first mating surface and the second mating surface.

A dual hardness steel article comprises a first air hardenable steel alloy having a first hardness metallurgically bonded to a second air hardenable steel alloy having a second hardness. A method of manufacturing a dual hard steel article comprises providing a first air hardenable steel alloy part comprising a first mating surface and having a first part hardness, and providing a second air hardenable steel alloy part comprising a second mating surface and having a second part hardness. The first air hardenable steel alloy part is metallurgically secured to the second air hardenable steel alloy part to form a metallurgically secured assembly, and the metallurgically secured assembly is hot rolled to provide a metallurgical bond between the first mating surface and the second mating surface.

Oxides formed during annealing of stainless steel strip are removed with abrasive brushes, in lieu of acid or molten salt based pickling. In some embodiments, the stainless steel strip is treated with a rare earth element or a related transition metal before annealing, and then brushed after annealing to remove any oxides. The selection of brushes can impart a finished appearance to conventionally polished stainless steel.

A rolled stainless steel object has surface with a raised and indented pattern including a random juxtaposition of at least two types of polygons. Each of the polygons has at least three sides, and is made up of substantially parallel rectilinear scratches, having a depth of from 5 to 30 m separated by ridge lines, the axes of which are from 0.1 to 0.3 mm from each other, and a Fourier transform spectral analysis of which, carried out on a square of at least 100 mm.sup.2, shows that they have an isotropy of at least 40% between the rolling direction and the sideways direction, and two adjacent preferred angular orientations of which scratches, from among the three main preferred angular orientations thereof, are spaced apart by a minimum of 20 and a maximum of 60.

A rolled stainless steel object has surface with a raised and indented pattern including a random juxtaposition of at least two types of polygons. Each of the polygons has at least three sides, and is made up of substantially parallel rectilinear scratches, having a depth of from 5 to 30 m separated by ridge lines, the axes of which are from 0.1 to 0.3 mm from each other, and a Fourier transform spectral analysis of which, carried out on a square of at least 100 mm.sup.2, shows that they have an isotropy of at least 40% between the rolling direction and the sideways direction, and two adjacent preferred angular orientations of which scratches, from among the three main preferred angular orientations thereof, are spaced apart by a minimum of 20 and a maximum of 60.

The hot-rolled Nb-containing ferritic stainless steel sheet of the present invention has a composition containing C: 0.030 mass % or less, Si: 2.00 mass % or less, Mn: 2.00 mass % or less, P: 0.050 mass % or less, S: 0.040 mass % or less, Cr: 10.00 mass % to 25.00 mass %, N: 0.030 mass % or less and Nb: 0.01 mass % to 0.80 mass %, with the balance being made up of Fe and unavoidable impurities. In this hot-rolled Nb-containing ferritic stainless steel sheet, the precipitation amount of Nb carbonitrides is 0.2 mass % or more, and the number of Laves phases having a grain size of 0.1 m or less is 10 or fewer per 10 m.sup.2 of surface area.

The hot-rolled Nb-containing ferritic stainless steel sheet of the present invention has a composition containing C: 0.030 mass % or less, Si: 2.00 mass % or less, Mn: 2.00 mass % or less, P: 0.050 mass % or less, S: 0.040 mass % or less, Cr: 10.00 mass % to 25.00 mass %, N: 0.030 mass % or less and Nb: 0.01 mass % to 0.80 mass %, with the balance being made up of Fe and unavoidable impurities. In this hot-rolled Nb-containing ferritic stainless steel sheet, the precipitation amount of Nb carbonitrides is 0.2 mass % or more, and the number of Laves phases having a grain size of 0.1 m or less is 10 or fewer per 10 m.sup.2 of surface area.