A method for desulfurizing molten steel comprising taking a sample out from molten steel after tapping from a converter or during secondary refining and analyzing the sample rapidly with high accuracy by a method comprising a high frequency induction heating step wherein the sample is combusted and oxidized under the high frequency induction heating in an oxygen atmosphere having an oxygen purity of 99.5 vol % or more to convert S in the sample into SO.sub.2 and an analyzing step wherein SO.sub.2-containing gas produced in the high frequency induction heating step is analyzed through an ultraviolet fluorescence method to quantify S concentration of the sample.

Provided in the present application are a rare-earth microalloyed steel and a control process. The steel has a special microstructure, and the microstructure comprises a rare earth-rich nanocluster having a diameter of 1-50 nm. The nanocluster has the same crystal structure type as a matrix. The rare earth-rich nanocluster inhibits the segregation of the elements S, P and As on a grain boundary, and obviously improves the fatigue life of the steel. In addition, a rare-earth solid solution also directly affects a phase change dynamics process so that the diffusion-type phase change starting temperature in the steel changes at least to 2° C., and even changes to 40-60° C. in some kinds of steel, thereby greatly improving the mechanical properties thereof, and providing a foundation for the development of more kinds of high-performance steel.

A calcium, aluminum, and silicon alloy is provided. The alloy includes about 15 to 45% calcium, 20 to 40% aluminum, and 20 to 40% silicon.

A bearing steel includes, as a metallographic structure, inclusions which contain complex oxysulfides including Rare Earth Metal, Ca, O, S, and Al, TiN, MnS, Al.sub.2O.sub.3, and complex oxides including Al and Ca, wherein, a number fraction of the complex oxysulfides in a total number of the inclusions is 50% to less than 100% and a number of complex oxysulfides having a major axis of 5 μm or more is 0.001 pieces to 2 pieces in an observed section of 1 mm.sup.2, and a number of TiN existing independently from the complex oxysulfides and having a major axis of 5 μm or more is 0.001 pieces to less than 1.0 piece in an observed section of 1 mm.sup.2.

A bearing steel includes, as a metallographic structure, inclusions which contain complex oxysulfides including Rare Earth Metal, Ca, O, S, and Al, TiN, MnS, Al.sub.2O.sub.3, and complex oxides including Al and Ca, wherein, a number fraction of the complex oxysulfides in a total number of the inclusions is 50% to less than 100% and a number of complex oxysulfides having a major axis of 5 μm or more is 0.001 pieces to 2 pieces in an observed section of 1 mm.sup.2, and a number of TiN existing independently from the complex oxysulfides and having a major axis of 5 μm or more is 0.001 pieces to less than 1.0 piece in an observed section of 1 mm.sup.2.

Disclosed is a method for controlling a Ti concentration in a steel when manufacturing a silicon-deoxidized steel comprising 0.1 to 3% by mass of Si and 0.0001 to 0.005% by mass of Al by ladle refining of a molten steel, the method including the step of: adding an oxide including TiO.sub.2 to a slag in a ladle during the ladle refining, wherein the slag produced at end of the ladle refining satisfies formulas (1) to (7) below:

0.5≦CaO/SiO.sub.2≦1.8  (1)

4% by mass≦Al.sub.2O.sub.3≦20% by mass  (2)

MgO≦15% by mass  (3)

1.5% by mass≦TiO.sub.2≦10% by mass  (4)

CaO+SiO.sub.2+Al.sub.2O.sub.3+MgO+TiO.sub.2≧90% by mass  (5)

0.4≦TiO.sub.2/MnO≦5  (6)

1≦TiO.sub.2/T.Fe≦10  (7)

where a compound represented by a chemical formula represents the content of the compound in percent by mass; and T.Fe represents the total concentration, in mass ratio, of Fe contained in Fe oxides in the slag.

Disclosed is a method for controlling a Ti concentration in a steel when manufacturing a silicon-deoxidized steel comprising 0.1 to 3% by mass of Si and 0.0001 to 0.005% by mass of Al by ladle refining of a molten steel, the method including the step of: adding an oxide including TiO.sub.2 to a slag in a ladle during the ladle refining, wherein the slag produced at end of the ladle refining satisfies formulas (1) to (7) below:

0.5≦CaO/SiO.sub.2≦1.8  (1)

4% by mass≦Al.sub.2O.sub.3≦20% by mass  (2)

MgO≦15% by mass  (3)

1.5% by mass≦TiO.sub.2≦10% by mass  (4)

CaO+SiO.sub.2+Al.sub.2O.sub.3+MgO+TiO.sub.2≧90% by mass  (5)

0.4≦TiO.sub.2/MnO≦5  (6)

1≦TiO.sub.2/T.Fe≦10  (7)

where a compound represented by a chemical formula represents the content of the compound in percent by mass; and T.Fe represents the total concentration, in mass ratio, of Fe contained in Fe oxides in the slag.

A Si-killed steel wire rod for obtaining a spring excellent in fatigue properties and a spring excellent in fatigue properties obtained from such steel wire rod are provided. In the Si-killed steel wire rod of the present invention, oxide-based inclusions present in the wire rod contain SiO.sub.2: 30-90%, Al.sub.2O.sub.3: 2-35%, MgO: 35% or below (not inclusive of 0%), CaO: 50% or below (not inclusive of 0%), MnO: 20% or below (not inclusive of 0%) and BaO: 0.2-20% respectively, and total content of (CaO+MgO) is 3% or above.

A Si-killed steel wire rod for obtaining a spring excellent in fatigue properties and a spring excellent in fatigue properties obtained from such steel wire rod are provided. In the Si-killed steel wire rod of the present invention, oxide-based inclusions present in the wire rod contain SiO.sub.2: 30-90%, Al.sub.2O.sub.3: 2-35%, MgO: 35% or below (not inclusive of 0%), CaO: 50% or below (not inclusive of 0%), MnO: 20% or below (not inclusive of 0%) and BaO: 0.2-20% respectively, and total content of (CaO+MgO) is 3% or above.

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: 0.25 to 0.50%, Si: 0.01 to 0.40%, Mn: 0.3 to 1.5%, P: 0.010% or less, S: 0.001% or less, O: 0.0015% or less, Al: 0.015 to 0.080%, Cu: 0.02 to 0.09%, Cr: 0.5 to 0.8%, Mo: 0.5 to 1.3%, Nb: 0.005 to 0.05%, B: 0.0005 to 0.0040%, Ca: 0.0010 to 0.0020%, 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 10 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 30 or less per 100 mm.sup.2.