An ultra-high phosphorus molten iron low-cost smelting method for polar steel includes successively deoxidizing and tapping alloying raw materials including molten iron; performing slag adjusting and refining on the molten steel obtained in the converter smelting step to obtain a refined molten steel; vacuum degassing the refined molten steel; and performing continuous casting on the molten steel obtained after the RH degassing step to obtain a cast billet.

An ultra-high phosphorus molten iron low-cost smelting method for polar steel includes successively deoxidizing and tapping alloying raw materials including molten iron; performing slag adjusting and refining on the molten steel obtained in the converter smelting step to obtain a refined molten steel; vacuum degassing the refined molten steel; and performing continuous casting on the molten steel obtained after the RH degassing step to obtain a cast billet.

Provides is a non-oriented electrical steel sheet suitable for use in a rotor of an IPM motor that has excellent magnetic flux density B.sub.50 and high-frequency iron loss properties, high tensile strength and fatigue strength, and little variation in tensile strength. The non-oriented electrical steel sheet has a predetermined steel sheet chemical composition and a microstructure in which a ratio of non-recrystallized microstructure is 5% or more and 70% or less and the number of inclusion having a diameter of 5 μm or more is not more than 5 counts/mm.sup.2.

Provides is a non-oriented electrical steel sheet suitable for use in a rotor of an IPM motor that has excellent magnetic flux density B.sub.50 and high-frequency iron loss properties, high tensile strength and fatigue strength, and little variation in tensile strength. The non-oriented electrical steel sheet has a predetermined steel sheet chemical composition and a microstructure in which a ratio of non-recrystallized microstructure is 5% or more and 70% or less and the number of inclusion having a diameter of 5 μm or more is not more than 5 counts/mm.sup.2.

Provided herein is a low-alloy high-strength seamless steel pipe. The steel pipe of the present invention has a composition that contains, in mass %, C: 0.20 to 0.50%, Si: 0.01 to 0.35%, Mn: 0.45 to 1.5%, P: 0.020% or less, S: 0.002% or less, 0: 0.003% or less, Al: 0.01 to 0.08%, Cu: 0.02 to 0.09%, Cr: 0.35 to 1.1%, Mo: 0.05 to 0.35%, B: 0.0010 to 0.0030%, Ca: 0.0010 to 0.0030%, Mg: 0.001% or less, and N: 0.005% or less, and in which the balance is Fe and incidental impurities. The steel pipe has a microstructure in which the number of oxide-base nonmetallic inclusions satisfying the composition ratios represented by predefined formulae is 20 or less per 100 mm.sup.2, and in which the number of oxide-base nonmetallic inclusions satisfying the composition ratios represented by other predefined formulae is 50 or less per 100 mm.sup.2.

Provided herein is a low-alloy high-strength seamless steel pipe. The steel pipe of the present invention has a composition that contains, in mass %, C: 0.20 to 0.50%, Si: 0.01 to 0.35%, Mn: 0.45 to 1.5%, P: 0.020% or less, S: 0.002% or less, 0: 0.003% or less, Al: 0.01 to 0.08%, Cu: 0.02 to 0.09%, Cr: 0.35 to 1.1%, Mo: 0.05 to 0.35%, B: 0.0010 to 0.0030%, Ca: 0.0010 to 0.0030%, Mg: 0.001% or less, and N: 0.005% or less, and in which the balance is Fe and incidental impurities. The steel pipe has a microstructure in which the number of oxide-base nonmetallic inclusions satisfying the composition ratios represented by predefined formulae is 20 or less per 100 mm.sup.2, and in which the number of oxide-base nonmetallic inclusions satisfying the composition ratios represented by other predefined formulae is 50 or less per 100 mm.sup.2.

Provided is steel for a wind power gear with improved purity and reliability. The chemical components thereof comprise, in percentages by mass: 0.15-0.19% of C, ≤0.4% of Si, 0.5-0.7% of Mn, ≤0.012% of P, ≤0.006% of S, 1.5-1.8% of Cr, 0.28-0.35% of Mo, 1.4-1.7% of Ni, and 0.02-0.04% of Al, with the balance being Fe and inevitable impurities. A smelting method therefor comprises adding raw materials to a converter for primary melting, transferring same to a refining furnace for refining, carrying out continuous casting after vacuum degassing, and transferring same to a gas protection furnace for electroslag remelting. According to the present invention, a pure electroslag master batch is obtained by continuous casting, and the purity of the material is further improved by means of an electroslag remelting procedure; and the prepared steel material is used in a wind power gear, such that the flaw detection pass rate is significantly increased, large-particle inclusions in the steel material are significantly reduced, and the inclusions are fine and dispersed.

A steel board for polar marine engineering and a preparation method therefor. According to weight percentage, the components of the steel board are: C: 0.06-0.09%, Si: 0.20-0.35%, Mn: 1.48-1.63%, Nb: 0.020%-0.035%, Ti: 0.010%-0.020%, V: 0.020%-0.035%, Ni: 0.08%-0.17%, Als: 0.015%-0.040%, P: ≤0.013% and S: ≤0.005%. The preparation method for the steel board comprises: pre-refining, refining and casting to obtain a cast billet, and the slowly cooling down same. The slowly cooled billet is heated and then rolled out to obtain the steel board; and the steel board is cooled down and ready. The steel has an excellent comprehensive performance in terms of having high strength and low temperature resistance, being easy to weld and corrosion proof, and the steel has good low-temperature aging impact toughness.

A steel board for polar marine engineering and a preparation method therefor. According to weight percentage, the components of the steel board are: C: 0.06-0.09%, Si: 0.20-0.35%, Mn: 1.48-1.63%, Nb: 0.020%-0.035%, Ti: 0.010%-0.020%, V: 0.020%-0.035%, Ni: 0.08%-0.17%, Als: 0.015%-0.040%, P: ≤0.013% and S: ≤0.005%. The preparation method for the steel board comprises: pre-refining, refining and casting to obtain a cast billet, and the slowly cooling down same. The slowly cooled billet is heated and then rolled out to obtain the steel board; and the steel board is cooled down and ready. The steel has an excellent comprehensive performance in terms of having high strength and low temperature resistance, being easy to weld and corrosion proof, and the steel has good low-temperature aging impact toughness.

A ferritic stainless steel with chemical composition includes, in mass %, Cr: 10.5 to 25.0%; Al: 0.01 to 0.20%; Ti: 0.15% to 0.35%; O: 0.0001 to 0.0030%; and Mg: 0.008×[% Al] or more, in which oxysulfide-containing inclusions are present in the steel, a number ratio of the oxysulfide-containing inclusions whose minor axis is 3 μm or more is 5 pieces/mm.sup.2 or less, and a number ratio of the oxysulfide-containing inclusions whose minor axis is 15 μm or more is 0.05 pieces/mm.sup.2 or less. 75% or more of the inclusions whose minor axis is 3 μm or more have an oxysulfide part whose composition satisfies formulae (1) and (2),

CaO+Al.sub.2O.sub.3+MgO≥90%  formula (1),

Al.sub.2O.sub.3/MgO≤1.25  formula (2).