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.

Special usage steels, particularly those intended to be in contact with combustion fumes, are described. Tubular components produced based on such steels are also described. The steel both is resistant to the coking phenomenon and has improved mechanical performances. The steel contains in percentage by weight from 0.08 to 0.15% carbon, from 0.4 to 0.8% manganese, from 1.5 to 2.5% silicon, from 0.5 to 2% copper, from 8 to 10% chrome, from 0.5 to 3% nickel, from 0.01 to 0.07% nitrogen, from 0.8 to 1.1% molybdenum, with the remainder being iron and impurities.

Disclosed are a Nb microalloyed high strength high hole expansion steel and a production method therefor. The chemical ingredients of the steel in percentages by weight are as follows: 0.01-0.05% of C, 0.2-0.6% of Si, 0.8-1.5% of Mn, ≤0.02% of P, ≤0.005% of S, ≤0.008% of N, <0.001% of Als, ≤0.0050% of Ca, 0.01-0.08% of Nb, and optionally one or both of 0.1-0.6% of Cu and 0.005-0.04% of Sn, wherein Mn/S>250, total oxygen [O].sub.T is 0.007-0.020%, and the balance is Fe and inevitable impurities. In the present invention, microalloy elements such as Nb are selectively added, and the basicity of slag, the type and melting point of the inclusion in steel, the content of free oxygen in molten steel, and the content of acid-soluble aluminum Als during the smelting process are controlled, and then, a strip is cast by means of twin-roll thin strip continuous casting, and the strip directly enters a lower closed chamber in a non-oxidizing atmosphere and enters an online rolling mill for hot rolling in closed conditions, and after rolling, the strip steel is cooled by air atomization cooling, and finally, the produced steel coil can be used directly as a hot rolled plate or can be used after acid pickling and leveling.

This hot-rolled steel sheet has a predetermined chemical composition, in which a microstructure contains, by area %, less than 3.0% of residual austenite, 15.0% or more and less than 60.0% of ferrite, and less than 5.0% of pearlite, has a ratio L.sub.60/L.sub.7 of a length L.sub.60 of a grain boundary having a crystal misorientation of 60° to a length L.sub.7 of a grain boundary having a crystal misorientation of 7° about a<110> direction of less than 0.60, has a standard deviation of a Mn concentration of 0.60 mass % or less, and has a tensile strength of 980 MPa or more.

According to an exemplary embodiment of the present invention, a method for manufacturing a grain-oriented electrical steel sheet includes: a step of hot-rolling a slab to manufacture a hot-rolled steel sheet; a step of performing hot-rolled sheet annealing on the hot-rolled steel sheet; a step of performing primary cold-rolling on the hot-rolled sheet annealed hot-rolled steel sheet; a step of performing primary decarburization annealing on the primarily cold-rolled steel sheet; a step of performing secondary cold-rolling on the decarburization-annealed steel sheet; a step of performing secondary decarburization annealing on the secondarily cold-rolled steel sheet; and a step of performing continuous annealing on the secondarily decarburization-annealed steel sheet.

A steel sheet has a predetermined chemical composition, in which a microstructure in a ¼ width portion, a microstructure in a ½ width portion, and a microstructure in a ¾ width portion, include, by area %, ferrite: 80% or more, martensite: 2% or less, and residual austenite: 2% or less, in which a proportion of unrecrystallized ferrite in the ferrite is 5% to 60%, an average grain size of carbonitrides is 6.0 nm to 30.0 nm, and Expressions (2) to (5) are satisfied.

Δ.sub.SF/μ.sub.SF≤0.10  (2)

Δ.sub.dF/μ.sub.dF≤0.20  (3)

Δ.sub.SUF≤20  (4)

Δ.sub.dC/μ.sub.dC≤0.50  (5)

A method for manufacturing of steel tube from a long steel strip, including providing a length of steel strip material to the process, forming a tube of the steel strip material, welding the formed tube in longitudinal direction, giving the tube a heat treatment wherein the mentioned steps are performed in one continuous in-line manufacturing line and the heat treatment includes a heating regime such that in successive cross-sections of the tube a microstructure is achieved which holds at least 50 vol % austenite and a cooling trajectory to re-introduce ferrite, and/or bainite in desired volume fractions.

The invention relates to a method for producing a component from a medium manganese flat steel product having 4 to less than 10 wt. % Mn, 0.0005 to 0.9 wt. % C, 0.02 to 10 wt. % Al, the remainder iron, including unavoidable steel-accompanying elements, and having a TRIP effect at room temperature. In order to produce a component, which is distinguished by very high strengths and an increased residual strain and re-shaping capacity, the flat steel product, according to the invention, is re-shaped by at least one re-shaping step to form a component and, before and/or during and/or after the at least one re-shaping step, the flat steel product is cooled down to a temperature of the flat steel product of less than room temperature to −196° C. The invention further relates to a component produced by this method and to a use for said components.

A method of shaping an article from a zinc or zinc alloy coated steel blank, including the steps of: a) providing a blank of the zinc or zinc alloy coated steel; b) reheating of the blank obtained in step a) to a reheating temperature T.sub.RH in the range Ac3-200° C. of the steel; c) soaking the blank for a time up to 3 minutes at the reheating temperature T.sub.RH; d) shaping the article in a press; and e) cooling the article. The steel includes (in wt. %) C: 0.01-0.2; Mn: 3.1-9.0; Al: 0.5-3.0; and optionally further alloying elements selected from Si, Cr, V, Nb, Ti and Mo; inevitable impurities and the balance is Fe.

A high-strength steel having excellent low-yield-ratio characteristics, according to one embodiment of the present invention, comprises, by wt %, 0.06-0.12% of C, 0.2-0.5% of Si, 1.5-2.0% of Mn, 0.003-0.05% of Al, 0.01% or less of N, 0.02% or less of P, 0.003% or less of S, 0.05-0.5% of Cr, 0.05-0.5% of Mo, 0.01-0.05% of Nb, 0.0005-0.005% of Ca and the balance of Fe and other inevitable impurities, and comprises polygonal ferrite as a microstructure, wherein the area fraction of the polygonal ferrite is 10-30% and the average hardness of the polygonal ferrite can be 180 Hv or less.