A method of manufacturing a martensitic stainless steel sheet by allowing ingot steel to pass through two casting rolls rotating in opposing directions through a twin roll strip caster is provided. The method includes rolling a steel sheet cast between the casting rolls at a temperature of 1000 to 1200 C. and a draft percentage of 25 to 50% with a first roller, and rolling the steel sheet at a temperature of 800 to 1000 C. and a draft percentage of 5 to 15% with a second roller.

A cold-rolled and annealed ferritic steel sheet is provided. The steel has a composition comprising, expressed by weight: 0.001C0.15%; Mn1%; Si1.5%; 7.5%AI10%; 0.020%Ti0.5%; S0.050%; and P0.1%.

A balance of the composition includes iron and inevitable impurities resulting from the smelting. The structure includes kappa () precipitates and equiaxed ferrite, an average grain size d of the equiaxed ferrite is less than 50 microns, and a linear fraction f of intergranular precipitates is less than 30%. The linear fraction f is defined by

[00001]$f=\frac{{}_{\left(A\right)}.Math.\mathrm{di}}{{}_{\left(A\right)}.Math.\mathrm{Li}}.$

.sub.(A)di denotes the total length of grain boundaries containing precipitates relative to an area (A) and .sub.(A)Li denotes the total length of the grain boundaries relative to the area (A). A content of carbon in solid solution is less than 0.005% by weight, and the cold-rolled and annealed ferritic steel sheet has a thickness between 0.6 mm and 1.5 mm. A skin part or structural part for the automotive field is also provided.

The invention relates to a hot-rolled ferritic steel sheet, the composition of the steel of which comprises, the contents being expressed by weight: 0.001C0.15%, Mn1%, Si1.5%, 6%Al10%, 0.020%Ti0.5%, S0.050%, P0.1%, and, optionally, one or more elements chosen from: Cr1%, Mo1%, Ni1%, Nb0.1%, V0.2%, B0.010%, the balance of the composition consisting of iron and inevitable impurities resulting from the smelting, the average ferrite grain size d.sub.IV measured on a surface perpendicular to the transverse direction with respect to the rolling being less than 100 microns.

Disclosed are a hot-rolled steel plate/strip with sulfuric acid dew point corrosion resistance and a method for producing the same, wherein the hot-rolled steel plate/strip comprises the following chemical elements in weight percentages: C: 0.02-0.06%, Si: 0.10-0.55%, Mn: 1.5%, P0.03%, S0.007%, Ti: 0.03-0.15%, Cr: 0.50-1.20%, Ni: 0.10-0.30%, Sb: 0.04-0.30%, Cu: 0.20-0.60%, N: 0.004-0.010%, Als: <0.001%, one or both of Sn: 0.005-0.04% and B: 0.001-0.006%, Mn/S250, total oxygen [O].sub.T: 0.007-0.020%; and a balance of Fe and other unavoidable impurities. The steel can be widely applied to the fields of tobacco baking apparatuses, air preheater heat exchange elements in industries such as petroleum, chemical industry, electric power, and metallurgy, delivery pipe, flue, and stack manufacturing structural parts, and boiler preheater and economizer equipment, of which the use environments have requirements for sulfuric acid dew point corrosion resistance performance.

A process that produces a microalloyed steel in an integrated casting-rolling plant having a continuous casting machine with a mold, a single- or multi-stand prerolling train, a finish-rolling train having a first stand group with at least one first finish-rolling stand and a second stand group having at least one stand cooler. A metallic melt is cast in the mold to obtain a partly solidified thin-slab strand, which is supported, deflected and cooled. The solidified thin-slab strand is rolled by the prerolling train to obtain a prerolled strip that is finish-rolled in the first stand group to obtain the finish-rolled strip, which is fed to the second stand group and force-cooled in the second stand group, the finish-rolled strip having a thickness that results in a cooling rate of the core of the finish-rolled strip in the second stand group greater than 20 C./s and less than 200 C./s.