A control process of inclusions in ultra-clean rare earth steel, wherein the content of rare earth elements REM in the ultra-clean rare earth steel, the total oxygen content T[O]m, the total sulfur content T[S]m in the steel, and the total oxygen content T[O]r in a rare earth metal or alloy added to the steel are controlled to satisfy the following formula: ?500<REM?(m*T[O]m+n*T[O]r+k*T[S]m)<?30, where REM is the content of rare earth elements in the steel, in ppm; T[O]m is the total oxygen content in the steel, in ppm; T[O]r is the total oxygen content in a rare earth metal or alloy added to the steel, in ppm; T[S]m is the total sulfur content in the steel, in ppm; m is a first correction coefficient, with a value of 2-4.5;n is a second correction coefficient; and k is a third correction coefficient.

A method of producing a steel material includes a step of adding Ca to molten steel with an amount of Ca adjusted within a range satisfying the formula (1) below: $\begin{array}{c}0.5\frac{\{\mathrm{Ca}.Math.y\text{/}100-\left(\left[S.Math.W\text{/}100\right).Math.40.08\text{/}32.07\right\}\frac{56.08}{40.08}}{(\left[{\mathrm{Al}}_2{O}_3\right].Math.W\text{/}100}\end{array}$

A method of producing a steel material includes a step of adding Ca to molten steel with an amount of Ca adjusted within a range satisfying the formula (1) below: $\begin{array}{c}0.5\frac{\{\mathrm{Ca}.Math.y\text{/}100-\left(\left[S.Math.W\text{/}100\right).Math.40.08\text{/}32.07\right\}\frac{56.08}{40.08}}{(\left[{\mathrm{Al}}_2{O}_3\right].Math.W\text{/}100}\end{array}$

Provided is a stainless steel product having a chemical composition consisting of C: less than 0.05%, Si: 4.0 to 7.0%, Mn: 1.50% or less, P: 0.030% or less, S: 0.030% or less, Cr: 10.0 to 20.0%, Ni: 11.0 to 17.0%, Cu: 0.15 to 1.5%, Mo: 0.15 to 1.5%, Nb: 0.5 to 1.2%, Sol. Al: 0 to 0.10%, Mg: 0 to 0.01%, and balance Fe and impurities, wherein MgO.Al.sub.2O.sub.3 inclusions constitute an area fraction of 0.02% or less. This stainless steel product has excellent corrosion resistance to hot concentrated sulfuric acid of approximately 93 to 99% concentration, for example, and also is economically advantageous.

A steel material which is excellent in machinability, in which occurrence of cracks during hot working and melting cracks during induction hardening can be suppressed, and which has excellent fatigue strength when formed into a component for machine structural use is provided. A steel material of the present embodiment contains, in percent by mass, C: 0.05 to 0.30%, Si: 0.05 to 0.45%, Mn: 0.30 to 2.00%, P: 0.030% or less, S: 0.010 to 0.095%, Cr: 0.01 to 2.00%, Bi: 0.0051 to 0.1500%, and N: 0.0030 to 0.0250%, and satisfies the following Formula (1). In the steel material, a number density of fine Bi particles is 80 to 8000 pieces/mm.sup.2 and a number density of coarse Bi particles is 10 pieces/mm.sup.2 or less.

[00001]$\begin{array}{cc}0.25C+\left(\mathrm{Si}/10\right)+\left(\mathrm{Mn}/5\right)-\left(5S/7\right)+\left(5\mathrm{Cr}/22\right)+1.65V1.& \left(1\right)\end{array}$

A non-oriented electrical steel sheet having a high magnetic flux density and a low iron loss at not only a commercial frequency but also a high frequency zone, which has a chemical composition including C: not more than 0.0050 mass %, Si: more than 1.5 mass % but not more than 5.0 mass %, Mn: not more than 0.10 mass %, sol. Al: not more than 0.0050 mass, P: more than 0.040 mass % but not more than 0.2 mass %, S: not more than 0.0050 mass %, N: not more than 0.0040 mass % and Ca: 0.001-0.01 mass % and the remainder being Fe and inevitable impurities and a compositional ratio of CaO in oxide-based inclusions existing in a steel sheet of not less than 0.4 and/or a compositional ratio of Al.sub.2O.sub.3 of not less than 0.3, and a hot rolled steel sheet used as a raw steel material thereof.

Provided is a non-oriented electrical steel sheet having such a low Al concentration so that it is excellent in terms of the recycling efficiency of scrap iron and having a high magnetic flux density and low iron loss. The non-oriented electrical steel sheet according to the present invention has a chemical composition containing C; 0.0050 mass % or less, Si; 1.5 mass % to 5.0 mass %, Mn; 0.2 mass % to 3.0 mass %, sol.Al; 0.0030 mass % or less, P; 0.2 mass % or less, S; 0.0050 mass % or less, N; 0.0040 mass % or less, T.Ca; 0.0010 mass % to 0.0080 mass %, T.O; 0.0100 mass % or less, REM; 0.0001 mass % to 0.0050 mass %, and a balance of Fe and inevitable impurities, in which a value of a mass-related fractional expression ((T.Ca+REM)/(T.O+S)), which is a relational expression for the masses of the four constituents described above, that is, T.Ca, REM, T.O, and S, is 0.4 or more.

An operation method of ladle refining treatment by which ladle refining treatment of a molten steel is performed while continuously measuring a molten steel temperature during operation of the ladle refining treatment of the molten steel is provided. The operation method includes setting a time earlier than a scheduled ending time of the ladle refining treatment in a continuous measurement period of the molten steel temperature as a determination timing, and estimating the molten steel temperature at the scheduled ending time on the basis of a change with time of the molten steel temperature in continuous measured data of the molten steel temperature from a start of continuous measurement of the molten steel temperature to the determination timing.

The invention provides a maraging steel production method in which an oxide is added during an Mg oxide formation step, the production method including: the Mg oxide formation step in which Mg is added to molten steel and MgO is formed in the molten steel, during primary melting; a consumable electrode production step in which, after the Mg oxide formation step, the molten steel is solidified and a consumable electrode having residual MgO is obtained; and a vacuum arc re-melting step in which the consumable electrode is used and vacuum arc re-melting is performed.

A molten steel denitrification method, wherein an extremely low nitrogen concentration range is stably reached in a short time without use of a top-blown gas, is a denitrification process wherein CaOandAl.sub.2O.sub.3-containing slag formed by a combination of an Al addition step of adding a metalAl-containing substance to molten steel to deoxidize and turn the molten steel into Al-containing molten steel and a CaO addition step of adding a CaO-containing substance to the molten steel is brought into contact with the Al-containing molten steel to remove nitrogen in the molten steel, in which the molten steel is stirred at a stirring power density of 60 W/t or higher. In the denitrification process, a surface of the molten steel or the slag is subjected to an atmosphere of 1.010.sup.5 Pa or lower. In a steel production method, the obtained molten steel is cast after the components are adjusted.