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US-20260125781-A1 - FE-CR-NI ALLOYS WITH EXCELLENT SURFACE PROPERTIES AND THEIR PRODUCTION METHODS

US20260125781A1US 20260125781 A1US20260125781 A1US 20260125781A1US-20260125781-A1

Abstract

A composition of non-metallic inclusions influence surface properties is controlled providing Fe—Cr—Ni alloys having surface properties and production methods. The Fe—Cr—Ni alloy having surface properties including, in mass %, C: 0.020 to 0.150%, Si: 0.05 to 0.80%, Mn: 0.10 to 1.50%, P: not greater than 0.035%, S, 0.0050%, Ni: 34.0 to 48.0%, Cr: 22.0 to 29.0%, Mo: 0.20 to 1.20%, Al: 0.005 to 0.180%, B: 0.0001 to 0.0080%, Mg: 0.0001 to 0.0100%, Ca: 0.0001 to 0.0100%, Nb: 0.20 to 0.80%, N: 0.050 to 0.500%, O: 0.0001 to 0.0060%, Cu, than 0.80%, Ti, 0.100%, Co, 0.50%, and Fe and inevitable impurities as the remainder, wherein non-metallic inclusions contain at least one of MgO, CaO, CaO—MgO type oxide, CaO—Al 2 O 3 —MgO type oxide and MgO·Al 2 O 3 , in which number ratio of the MgO·Al 2 O 3 with respect to the total oxide type non-metallic inclusions is not greater than 50%.

Inventors

  • Daiki Ogasawara
  • Kenji Mizuno

Assignees

  • NIPPON YAKIN KOGYO CO., LTD.

Dates

Publication Date
20260507
Application Date
20231006
Priority Date
20221021

Claims (8)

  1. 1 . A Fe—Cr—Ni alloy having excellent surface properties consisting of: in mass %, C: 0.020 to 0.150%, Si: 0.05 to 0.80%, Mn: 0.10 to 1.50%, P: not greater than 0.035%, S: not greater than 0.0050%, Ni: 34.0 to 48.0%, Cr: 22.0 to 29.0%, Mo: 0.20 to 1.20%, Al: 0.005 to 0.180%, Mg: 0.0001 to 0.0100%, Ca: 0.0001 to 0.0100%, Nb: 0.20 to 0.80%, N: 0.050 to 0.500%, O: 0.0001 to 0.0060%, Cu: not greater than 0.80%, Ti: not greater than 0.100%, Co: not greater than 0.50%, and Fe and inevitable impurities as the remainder, wherein non-metallic inclusions contain at least one of MgO and CaO—Al 2 O 3 —MgO type oxide as an essential component and contain optionally selected from CaO, CaO—MgO type oxide and MgO·Al 2 O 3 as an optional component, number ratio of the MgO·Al 2 O 3 with respect to the total oxide type non-metallic inclusions is not greater than 50%, and number ratio of total of the CaO and CaO—MgO type oxide with respect to the total oxide type non-metallic inclusions is not greater than 50%.
  2. 2 . The Fe—Cr—Ni alloy having excellent surface properties according to claim 1 , wherein the CaO—Al 2 O 3 —MgO type oxide contains 0.01 to 0.60 mass % of NbO.
  3. 3 . The Fe—Cr—Ni alloy having excellent surface properties according to claim 1 , wherein the CaO—MgO type oxide contains, in mass %, CaO: 20 to 80% and MgO: 20 to 80%, the CaO—Al 2 O 3 —MgO type oxide contains CaO: 10 to 60%, Al 2 O 3 : 5 to 60%, MgO: 10 to 80% and SiO 2 : not greater than 10%, and the MgO·Al 2 O 3 contains MgO: 10 to 40% and Al 2 O 3 : 60 to 90%.
  4. 4 . A method for producing the Fe—Cr—Ni alloy having excellent surface properties according to claim 1 , comprising steps of: melting raw materials in an electric furnace, decarburizing in AOD and/or VOD, adding lime and fluorite, adding one or both of ferrosilicon alloy and pure silicon, and Al, as primary deoxidation, adding Nb at a timing O concentration gets 0.0070 to 0.0120%, performing Cr reduction, secondary deoxidation and desulfurization by adding one or both of ferrosilicon alloy and pure silicon, and Al, after using CaO—SiO 2 —MgO—Al 2 O 3 —F type slag consisting of CaO: 45 to 75%, SiO 2 : 1 to 15%, Al 2 O 3 : 10 to 30%, MgO: 5 to 20%, F: 1 to 15%, forming slab or ingot by continuous casing apparatus or conventional ingot casting, performing hot forging in a case in which the ingot is formed, and performing only hot rolling or both of hot rolling and cold rolling.
  5. 5 . A method for producing the Fe—Cr—Ni alloy having excellent surface properties according to claim 3 , comprising steps of: melting raw materials in an electric furnace, decarburizing in AOD and/or VOD, adding lime and fluorite, adding one or both of ferrosilicon alloy and pure silicon, and Al, as primary deoxidation, adding Nb at a timing O concentration gets 0.0070 to 0.0120%, performing Cr reduction, secondary deoxidation and desulfurization by adding one or both of ferrosilicon alloy and pure silicon, and Al, using CaO—SiO 2 —MgO—Al 2 O 3 —F type slag consisting of CaO: 45 to 75%, SiO 2 : 1 to 15%, Al 2 O 3 : 10 to 30%, MgO: 5 to 20%, F: 1 to 15%, forming slab or ingot by continuous casing apparatus or conventional ingot casting, performing hot forging in a case in which the ingot is formed, and performing only hot rolling or both of hot rolling and cold rolling.
  6. 6 . The Fe—Cr—Ni alloy having excellent surface properties according to claim 2 , wherein the CaO—MgO type oxide contains, in mass %, CaO: 20 to 80% and MgO: 20 to 80%, the CaO—Al 2 O 3 —MgO type oxide contains CaO: 10 to 60%, Al 2 O 3 : 5 to 60%, MgO: 10 to 80% and SiO 2 : not greater than 10%, and the MgO·Al 2 O 3 contains MgO: 10 to 40% and Al 2 O 3 : 60 to 90%.
  7. 7 . A method for producing the Fe—Cr—Ni alloy having excellent surface properties according to claim 2 , comprising steps of: melting raw materials in an electric furnace, decarburizing in AOD and/or VOD, adding lime and fluorite, adding one or both of ferrosilicon alloy and pure silicon, and Al, as primary deoxidation, adding Nb at a timing O concentration gets 0.0070 to 0.0120%, performing Cr reduction, secondary deoxidation and desulfurization by adding one or both of ferrosilicon alloy and pure silicon, and Al, after using CaO—SiO 2 —MgO—Al 2 O 3 —F type slag consisting of CaO: 45 to 75%, SiO 2 : 1 to 15%, Al 2 O 3 : 10 to 30%, MgO: 5 to 20%, F: 1 to 15%, forming slab or ingot by continuous casing apparatus or conventional ingot casting, performing hot forging in a case in which the ingot is formed, and performing only hot rolling or both of hot rolling and cold rolling.
  8. 8 . A method for producing the Fe—Cr—Ni alloy having excellent surface properties according to claim 6 , comprising steps of: melting raw materials in an electric furnace, decarburizing in AOD and/or VOD, adding lime and fluorite, adding one or both of ferrosilicon alloy and pure silicon, and Al, as primary deoxidation, adding Nb at a timing O concentration gets 0.0070 to 0.0120%, performing Cr reduction, secondary deoxidation and desulfurization by adding one or both of ferrosilicon alloy and pure silicon, and Al, after using CaO—SiO 2 —MgO—Al 2 O 3 —F type slag consisting of CaO: 45 to 75%, SiO 2 : 1 to 15%, Al 2 O 3 : 10 to 30%, MgO: 5 to 20%, F: 1 to 15%, forming slab or ingot by continuous casing apparatus or conventional ingot casting, performing hot forging in a case in which the ingot is formed, and performing only hot rolling or both of hot rolling and cold rolling.

Description

TECHNICAL FIELDS The present invention relates to Fe—Cr—Ni alloys having excellent surface properties and their production methods, and in particular, relates to Fe—Cr—Ni alloys having excellent surface properties and their production methods, in which slag composition and Si, Al, Mg, Ca and O in molten metal are controlled thereby control non-metallic inclusions in molten metal to be harmless composition and reduce number of inclusions on the surface, and furthermore, relates to Fe—Cr—Ni alloys for which corrosion resistance and high temperature strength are highly required as a structural material such as for reactors. BACKGROUND ART During production of solar power installations, as material of reactors which are used for purifying polysilicon which is to be raw material for power generating elements, Fe—Cr—Ni alloy plate is often used. The reactor is used under high temperature and high pressure, that is, very severe environment from the viewpoints of high temperature strength and corrosion resistance. Since service life of the reactor may be shortened if high temperature strength and corrosion resistance are not sufficient, there is a demand for Fe—Cr—Ni alloys which satisfy such properties. Since Fe—Cr—Ni alloys having superior high temperature strength and corrosion resistance contain Cr, Ni and Mo in addition to Fe which is a main component and such metals are very expensive compared to iron, it is very important to improve yields and reduce production costs. Here, if surface defects such as linear damage occur on the surface of Fe—Cr—Ni alloy, since the surface defects should be removed by grinding or cutting thereby greatly deteriorate yields, Fe—Cr—Ni alloys having superior surface properties are demanded. Patent Document 1 discloses a technique in which size and number of nitrides or carbides of Nb and Ti are controlled in Fe—Cr—Ni alloy having superior high temperature strength thereby suppress crystal grains from being coarsened at annealing temperature of products and high creep rapture property is realized. However, the nitrides or carbides of Nb and Ti do not cause occurring damage of the surface of products. The invention according to the Patent Document 1 cannot be applied to the problem of surface properties due to oxide type non-metallic inclusions which are generated during refining which is a target in the present invention, and the problem of surface defects due to oxide type non-metallic inclusions still remains. Patent Document 2 discloses a technique in which mass ratio Ca/Al in oxide type inclusions is set to be in a range of 1.0 to 1.5 in high Ni alloys containing Al and Ti for high temperature and their production methods so that composition of the oxide type inclusions is controlled to be CaO—Al2O3 type having low melting point, an immerse nozzle of continuous casting apparatus is prevented from being blocked and surface damage on products is prevented. However, since 0.15 to 1.5% of Ti is contained in the Patent Document 2, it is considered that CaO—Al2O3—TiO2 is generated as oxide type inclusions thereby occur blocking in nozzle. Since Ti content in the present invention is not greater than 0.10%, blocking in nozzle by CaO—Al2O3—TiO2 does not occur. Surface properties of Fe—Cr—Ni alloys of the present invention is not sufficiently improved according to the technique disclosed in the Patent Document 2. Patent Document 3 discloses a technique in which, in high Ni alloys, composition of non-metallic inclusions in alloy is controlled to generate low melting point inclusions having good stretching-dividing property during hot or cold rolling, so that surface defects are reduced. However, target of the Patent Document 3 is for high Ni alloy containing Cr: not greater than 0.5% or containing Cr: 3 to 10%, it is different from the Fe—Cr—Ni alloy containing Cr: 22.0 to 29.0% of the present invention. Cr content has a great influence on control of inclusion composition, composition of oxide type non-metallic inclusions may differ greatly even if minor components such as Ca, Mg, Al, Si, O and the like are the same. That is, surface properties of the Fe—Cr—Ni alloy of the present invention cannot be improved sufficiently according to the method to control non-metallic inclusion composition disclosed in the Patent Document 3. Patent Document 4 discloses a technique in which in stainless steel plate, inclusions are controlled to be harmless MgO, CaO—Al2O3—MgO type oxides so as to reduce surface defects. Nb that is contained in the Fe—Cr—Ni alloy of the present invention at 0.20 to 0.80% has oxidation ability almost as same as that of Si and Mn. That is, Nb is an important element to control surface defects, since Nb oxides are contained in inclusions although in small amount, and stretching-dividing property during hot or cold rolling is improved by decreasing melting point of inclusions. However, since the stainless steel plate which is disclosed in the Patent Document 4 does not contain