A method for manufacturing a low-carbon nitrogen-containing austenitic stainless steel bar sequentially includes smelting, electroslag remelting, and forging. During electroslag remelting, the steel ingot obtained in the smelting process is used as an electrode bar of the electroslag furnace and is remelted with specific slag and crystallized. The specific slag comprises CaF.sub.2 (65-70%), Al.sub.2O.sub.3 (15-20%), CaO (5-10%) and MgO (2-5%) in percentage by weight. Specific forging methods, including upsetting-and-drawing and radial forging, are used. In upsetting-and-drawing, the pass deformation is less than 35%, the pass reduction is 50-80 mm, the pass heating temperature is 1130-1150? C., and the pass deformation method is ellipse-ellipse-circle. The method can obtain the low-carbon high-strength nitrogen-containing austenitic stainless steel with uniformly distributed chemical composition, high purity and high strength.

Martensitic stainless steel, characterized in that its composition consists of, in percentages by weight: 0.10%C0.45%; tracesMn1.0%; tracesSi1.0%; tracesS0.01%; tracesP0.04%; 15.0%Cr18.%; tracesNi0.50%; tracesMo0.50%; tracesCu0.50%; tracesV0.50%; tracesNb0.03%; tracesTi0.03%; tracesZr0.03%; tracesAl0.010%; tracesO0.0080%; tracesPb0.02%; tracesBi0.02%; tracesSn0.02%; 0.10%N0.20%; C+N0.25%; Cr+16N5C16.0%; preferably 17Cr+500C+500N570%;

the rest being iron and impurities resulting from the development.

A method for the production of a semi-finished product from this martensitic stainless steel, and cutting tool produced from this semi-finished product.

A corrosion resistant alloy suitable for use as a seamless tubular is described. The corrosion resistant alloy includes 13-15 wt. % chromium, 5-7 wt. % nickel, and 2.5-4.5 wt. % molybdenum. The balance of the corrosion resistant alloy is iron.

A charged material containing a metal raw material of at least one of ferrochromium containing metal Si or ferrosilicon and unreduced slag containing Cr oxide generated by oxidation refining is charged into an AC electric furnace including three electrodes, a mass ratio of a metal Si amount to a Cr oxide amount being from 0.30 to 0.40, and a C concentration being from 2.0% by mass to a saturation concentration.

There is provided a method for manufacturing a duplex stainless steel sheet having reduced inclusions through argon oxygen decarburization (AOD), ladle treatment (LT), and twin roll strip casting. The method includes deoxidizing molten steel using silicon (Si) during the AOD, wherein the molten steel has a silicon (Si) content of 0.55 wt % to 0.75 wt % at the end of the AOD.

A duplex stainless steel material that has excellent general corrosion resistance and pitting resistance in a supercritical corrosive environment in which SO.sub.X gas and O.sub.2 gas are contained in a supercritical CO.sub.2 gas is provided. A duplex stainless steel material of the present disclosure has the chemical composition described in the description, and in the duplex stainless steel material, on a precondition that the content of each element is within a range described in the description, Fn defined by Formula (1) is 57.0 or more, and a total number per 1 mm.sup.2 of Mn sulfides having an equivalent circular diameter of 1.0 m or more and Ca sulfides having an equivalent circular diameter of 2.0 m or more is 0.50/mm.sup.2 or less.

[00001]$\begin{array}{cc}\mathrm{Fn}=\mathrm{Cr}+3.3\left(Mo+0.5W\right)+16N+2Ni+Cu+2Co+10\mathrm{Sn}& \left(1\right)\end{array}$

Where, the content in mass % of a corresponding element is substituted for each symbol of an element in Formula (1).

A martensitic stainless steel pipe according to the present disclosure consists of, in mass %, C: less than 0.030%, Si: 1.00% or less, Mn: 1.00% or less, P: 0.030% or less, S: 0.0010 to 0.0050%, Cr: 10.00 to 14.00%, Ni: 5.00 to 7.50%, Mo: 1.10 to 3.50%, Cu: 1.00 to 3.50%, Al: 0.005 to 0.050%, N: 0.0030 to 0.0500%, V: 0.01 to 0.30%, Ti: 0.020 to 0.150%, Co: 0.01 to 0.50%, Ca: 0.0010 to 0.0050%, and the balance: Fe and impurities. The yield strength is 758 MPa or more. A number density of Ca sulfides having an equivalent circular diameter of 1.0 m or more is 3/mm.sup.2 or more.

An argon oxygen decarburization (AOD) refining method for molten austenitic stainless steel includes, preparing molten austenitic stainless steel in an electric arc furnace, pouring the molten austenitic stainless steel into an AOD refining furnace by adjusting a carbon concentration of the molten austenitic stainless steel to 2.0 wt % to 2.5 wt %, decarburizing the poured molten austenitic stainless steel by blowing oxygen (O.sub.2) and argon (Ar) thereinto, and reduction-decarburizing the decarburized molten austenitic stainless steel by blowing argon (Ar) thereinto.

After molten metal has been poured from a ladle 6 into a converter, metal 6b adhering to the ladle 6 is dropped into the ladle 6 on-line, and molten metal is poured from an electric furnace into the ladle 6 into which the metal 6b has been dropped. As a result, the metal 6b is melted and is recovered as a material.

Heat exchange tubes of a heat exchanger are formed of an alloy containing Mn (0.2 to 0.3 mass %), Cu (0.1 mass % or less), and Fe (0.2 mass % or less), the balance being Al and unavoidable impurities. A Zn diffused layer is formed in an outer surface layer portion of the peripheral wall of each heat exchange tube. T200, 0.57A1.5, D/T0.55, and 0.0055A/D0.025 are satisfied, where T is the thickness [m] of the peripheral wall of the heat exchange tube, A is the Zn concentration [mass %] at the outermost surface of the outer surface layer portion, and D is the maximum depth [m] of the Zn diffused layer. The spontaneous potential of the Zn diffused layer is lower than that of a portion of the peripheral wall located on the inner side of the Zn diffused layer.