The invention discloses a method for preparing a stainless steel seamless tube with ultra-high cleanliness for an integrated circuit and an IC industry preparation device, and a stainless steel seamless tube with ultra-high cleanliness. The stainless steel seamless tube which comprises, by mass, C≤0.010%, P≤0.020%, S≤0.010%, Mn≤0.10%, Si≤0.30%, Se≤0.010%, Al≤0.010%, Cu≤0.20%, Cr16.50-17.00%, Ni14.50-15.00%, Mo2.20-2.50%, N≤0.010%, Ni≤0.010%, Ti≤0.010% and the balance Fe and impurities is prepared through a: a stainless steel refining process; b: a vacuum induction melting and vacuum consumable remelting process; c: a stainless steel forging process; d: a hot piercing process; e: a cold working process; f: an inner bore electrolytic polishing, pickling and passivation process; and g: a cleaning process. The stainless steel seamless tube with ultra-high cleanliness prepared through these processes meet the requirements for ultra-high cleanliness and high performance of 316L stainless steel tubes for a semiconductor preparation device.

Fe—Ni—Cr alloy contains, in mass, from 0.001% to 0.050% of C, from 0.18% to 1.00% of Si, from 0.20% to 0.80% of Mn, 0.030% or less of P, 0.0001% to 0.0020% of S, from 12% to 21% of Ni, from 18% to 24% of Cr, from 0.20% to 1.50% of Mo, 0.30% or less of Cu, from 0.10% to 0.70% of Al, from 0.10% to 0.70% of Ti, from 0.002% to 0.015% of N, from 0.0001% to 0.0010% of B, from 0.0002% to 0.0030% of O, 0.002% or less of Ca, and from 0.0010% to 0.0150% of REM in total, said REM being composed of one or more elements selected from among La, Ce and Y, with the balance being made up of Fe and unavoidable impurities, and which satisfies formulae 1 and 2. Formula 1: 0.575xNi+1.25xCr+3.43xMo-39xP-5.3xAl-641xREM-1018xO≥20.0 Formula 2: 1.5xMn+41.3xSi+1469xS-1.67xAl-1.34xTi-150xO-620xREM≥5.0.

The invention relates to a ferritic stainless steel having excellent corrosion and sheet forming properties. The steel consists of in weight percentages 0.003-0.035% carbon, 0.05-1.0% silicon, 0.1-0.8% manganese, 20-24% chromium, 0.05-0.8% nickel, 0.003-0.5% molybdenum, 0.2-0.8% copper, 0.003-0.05% nitrogen, 0.05-0.8% titanium, 0.05-0.8% niobium, 0.03-0.5% vanadium, less than 0.04% aluminium, and the sum C+N less than 0.06%, the remainder being iron and inevitable impurities in such conditions, that the ratio (Ti+Nb)/(C+N) is higher or equal to 8, and less than 40, and the ratio Ti.sub.eq/C.sub.eq=(Ti+0.5l5*Nb+0.940*V)/(C+0.858*N) is higher or equal to 6, and less than 40.

A process for manufacturing an iron-based alloy comprising forming targeted fine oxide and/or carbide dispersoids in a melt, and sequentially precipitating transition-metal nitrides on the dispersoids for heterogeneous nucleation of equiaxed grains. An iron-based cast alloy having a highly equiaxed fine grain structure.

A thin steel sheet contains, in terms of percentage by mass, from 0.010 to 0.200% of C, more than 2.00% and 4.00% or less of Si, from 0.01 to 3.00% of Mn, 3.00% or more and less than 10.00% of Ni, from 11.00 to 20.00% of Cr, from 0.010 to 0.200% of N, from 0 to 3.00% of Mo, from 0 to 1.00% of Cu, from 0 to 0.008% of Ti, from 0 to 0.008% of Al, and the balance of Fe, with unavoidable impurities; and having a number density of a non-metallic inclusion lining up with an interparticle distance in the rolling direction of 20 mm or less and an interparticle distance in the sheet thickness direction of 10 mm or less that has a length in the rolling direction of 40 mm or more of 3.0 or less per square millimeter on the L cross section.

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 process for manufacturing an iron-based alloy comprising forming targeted fine oxide and/or carbide dispersoids in a melt, and sequentially precipitating transition-metal nitrides on the dispersoids for heterogeneous nucleation of equiaxed grains. An iron-based cast alloy having a highly equiaxed fine grain structure.

[Summary]

[Assignment] A precipitation hardening martensitic stainless steel having superior strength and improved welding properties.

[Solution] In mass %, C: 0.030 to 0.065%, Si: 1.0 to 2.0%, Mn: 0.51 to 1.50%, P: not more than 0.04%, S: not more than 0.0020%, Ni: 4.0 to 10.0%, Cr: 11.0 to 18.0%, Mo: 0.1 to 1.50%, Cu: 0.30 to 6.0%, Al: 0.005 to 0.2%, Sn: 0.003 to 0.030%, N: 0.001 to 0.015%, Ti: 0.15 to 0.45%, Nb: 0.15 to 0.55%, Ca: not more than 0.0025%, Mg: 0.0001 to 0.0150%, O: not more than 0.01% and Fe and inevitable impurities as a remainder, and satisfying the following formula (1). and cal. (vol. %) defined by the formula (2) is in a range of 1.0 to 9.0.

Sn+0.009Cu0.06(1)

cal. (vol. %)=4.3(1.3Si+Cr+Mo+2.2Al+Ti+Nb)3.9(30C+30N+Ni+0.8Mn+0.3Cu)31.5(2)

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.

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.