US3615348A - Stainless steel melting practice - Google Patents

Stainless steel melting practice Download PDF

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Publication number
US3615348A
US3615348A US3615348DA US3615348A US 3615348 A US3615348 A US 3615348A US 3615348D A US3615348D A US 3615348DA US 3615348 A US3615348 A US 3615348A
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United States
Prior art keywords
chromium
carbon
stainless steel
melt
furnace
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Expired - Lifetime
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English (en)
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Harry Tanczyn
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Armco Advanced Materials Corp
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Armco Inc
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Assigned to ARMCO ADVANCED MATERIALS CORPORATION reassignment ARMCO ADVANCED MATERIALS CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: ARMCO, INC.
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C5/00—Manufacture of carbon-steel, e.g. plain mild steel, medium carbon steel or cast steel or stainless steel
    • C21C5/52—Manufacture of steel in electric furnaces
    • C21C5/5264—Manufacture of alloyed steels including ferro-alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • One of the objects of the invention is. the production of stainless steel of the chromium grades, as well as the chromium-nickel grades, employing such combination of raw materials as to enjoy the maximum use of available furnace capacity with minimum slag volumes, minimum furnace operating temperatures, and minimum attack of furnace refractories.
  • Another object is the provision of a stainless steel melting process requiring a minimum consumption of electric power and minimum time of complete melting cycle.
  • a further object is the provision of such a process wherein clean, high-quality stainless steel is had, and wherein losses of chromium and other oxidizable ingredients into the slag are obviated and wherein the requirement for irrecoverable alloying additions, such as ferrosilicon is minimized.
  • the stainless steels generally are viewed as alloy steels containing chromium from about on up to about 35% or more, with or without other alloying ingredients. Carbon commonly is present, this on the order of some 0.03% to 0.10% for certain grades, and up to some 1.0% or more for others. And, too, in some grades nickel is present either in such a large amount, say 7% to 35% or more, to assure an austenitic steel, or in lesser amount for other purposes. Manganese and silicon in small amounts customarily are present, and so, too, the ingredients phosphorus, sulfur and nitrogen. Where desired, one or more of copper, aluminum, molybdenum, titanium and columbium may be present for special purposes. The number of different grades of stainless steel in this art is legion. But, as noted above, chromium is an essential element in all grades.
  • the prealloy contains some 66% to 72% chromium, with a carbon content not exceeding 2.00%, usually some 0.06% to 0.50% depending upon the carbon content permitted in the steel to be produced, and remainder iron.
  • High melting temperatures that is, temperatures of about 3400 F.
  • temperatures of about 3400 F. are employed in order to preferentially oxidize the carbon present as compared to the chromium, although substantial quantities of chromium nevertheless are oxidized and migrate into the slag.
  • the high-operating temperatures not only cause some fuming of the metal but they accelerate the attack on the furnace refractories, this frequently taking the form of severe localized erosion.
  • An object of the present of the present invention is to overcome certain of the shortcomings of prior practices and produce clean, high-quality stainless steel to precise chemical analysis while effecting a savings in furnace time, in furnace refractories, in electric power, and in ferrosilicon or other reducing agent, while at the same time achieving maximum utilization of furnace capacity with minimum encumbrance of furnace slag, and effecting virtually complete recovery of chromium and other oxidizable elements involve.
  • the electric arc furnace is charged with stainless steel scrap and/or other alloy of iron and chromium, such as high-carbon ferrochrome and/or ferrochrome-silicon.
  • high-carbon ferrochrome is employed, there additionally is employed lowcarbon steel scrap in order to provide suflicient iron; where substantial amounts of ferrochrome-silicon are employed there may be added chrome ore, this to take advantage of the silicon available for ore reduction.
  • the ore is directly charged into the bath instead of being placed around the banks of the furnace as in certain prior practices.
  • Melting ordinarily is had at a temperature of about 2,900 E, yielding a bath of the desired high-chromium content, a chromium content of about that desired in the finished steel, but having a carbon content greatly in excess of that finally desired. If find that the metal at the end of the melting operation is clean and significantly free of oxide inclusions, especially the chromium oxide inclusions commonly found at the end of the melting periods in the processes of the prior art.
  • the sulfur content is at desired low-value.
  • the weight of metal tapped is at a maximum because I find that in my process the slag volumes encountered are at a minimum.
  • Much of the slag is withdrawn from the bath or melt and the furnace tapped into a suitable ladle for transfer to a vacuum induction furnace.
  • a furnace located within a compartment which is exhausted of its atmosphere, this being commonly referred to as a degasser.
  • the molten metal is streamed in to the vacuum furnace rather slowly, the molten stream breaking into droplets, thereby providing a maximum of metal surface.
  • a strong oxidizing agent, or decarburizer to effect removal of the objectionably large amounts of carbon present in he molten metal; the amount of oxidizing agent required is determined by making a carbon analysis immediately before teeming into the vacuum furnace.
  • iron oxide although for certain grades, as for example the copper-bearing grades of stainless steel, excellent results are had with copper oxide.
  • oxides of cobalt, molybdenum, chromium, manganese, silicon, or titanium there may be employed the oxides of cobalt, molybdenum, chromium, manganese, silicon, or titanium, the kind and quantity of oxide added of course depending upon the particular composition and analysis of the metal sought.
  • the vacuum furnace preferably is lined with alumina having sufficient silica present to serve as a binder.
  • the alumina lining is well calculated to withstand the temperatures encountered. At the same time any alumina picked up the metal is not retained as an objectionable inclusion, but rather rises to the surface and is readily eliminated.
  • the carbon present in the metal combines with the oxygen content of the oxidizing agent employed forming carbon monoxide, a gas. This comes out of the metal in the form of minute bubbles, where upon reaching the surface of the metal, the gas is exhausted into the atmosphere.
  • the pressure in the vacuum furnace ranges from atmospheric pressure on down to several millimeters of mercury. While this pressure rises to about 50 millimeters or-more during much of the degassing operation, following the conclusion of streaming the pressure drops back to several millimeters, or even less.
  • the temperature of the metal in the vacuum vacuum is maintained at about 2,900 F., or perhaps 2,950 F. During this period there are made additions for composition adjustment and/0r auxiliary deoxidation as desired.
  • the degassing or vacuum treatment is at an end.
  • the vacuum is broken and the furnace tapped into a suitable ladle for teeming.
  • the ladle, and even the ingot molds may be maintained within the degasser, in which event the vacuum is not broken until the metal is streamed into the ladle or teemed into the ingot molds, as the case may be, all as more particularly noted hereinafter.
  • Final deoxidation of the metal conveniently is had by adding aluminum to the ladle in teeming.
  • the tapped metal is clean, sound and of desired highchromium content and low carbon content.
  • a maximum weight of metal is had in minimum total melting and degassing time, with minimum consumption of electric power and maximum utilization of furnace capacity, all as more particularly pointed to above. Wear of refractories is minimized. And a certain flexibility nevertheless is enjoyed in the selection of raw materials.
  • the charge is melted down under the heat of the electric arc, the molten metal reaching a temperature of some 2,900 E.
  • the slag overlying the metal has a depth of about 2 inches. It is fluid and well protects the metal from oxidation during the melting period. Moreover, the slag effects desulfurization without necessity of other special additions.
  • the molten metal analyzes 1.54/1.55% carbon, 0.35% manganese, 0.018% phosphorus, 0.011% sulfur, less than 0.05% silicon, 18.53% chromium, 6.32% nickel, and remainder iron.
  • the molten bath is subjected to a series of four oxygen blows, each at the rate of about 500 cubic feet per minute and at a pressure of about 120 pounds per square inch for about 8 minutes time.
  • the carbon content during the blowing drops radically. There, however, is some loss of chromium through oxidation, with resultant stiffening of the slag.
  • a substantial part of the slag is then withdrawn and the oxygen blow continued with further loss of carbon.
  • the carbon content of the molten metal amounts to 0.1 10/0.1 14%.
  • the metal analyzes 0.19% manganese, 0.01% phosphorus, 0.011% sulfur, less than 0.05% silicon, 16.62%
  • the chromium analysis of the bath suggests a significant loss of chromium into the slag, a chromium content of 16.62% as against a chromium content of 18.53% in the initial bath.
  • High-carbon ferrochromium in the amount of 235 pounds is then charged into the bath, this effecting a substantial recovery of the chromium content of the slag, but at the same time adding some carbon to the bath.
  • the heat analyzes 0. 250%carbon, 0.017% phosphorus, 0.011% sulfur, less than 0.05% silicon, 17.48% chromium, 6.51% nickel, and remainder ironfi'lhe analysis shows a substantial recovery of the lost chromium.
  • the metal With the substantial chromium recovery the metal is ready for transfer to the vacuum furnace. And in this regard the temperature of the bath is brought to about 3,000 E, some lime is added to stiffen the slag, and the heat is tapped beneath the slag into a suitable ladle for transfer to the vacuum furnace or degasser. It is found that bringing the bath to the 3,000 F. temperature immediately before tapping, adequate compensation is had for the chilling effect of the ladle. Conveniently, lime is thrown on top of the metal in the ladle in order to prevent a in the ladle in of heat and, to some extent, protect the metal oxidation. oxidation The molten metal is streamed into the vacuum induction furnace under a pressure of one atmosphere. The vacuum pumps are then turned on.
  • Nickel oxide of commercial purity is added from time to time, this on total amount of about 520 pounds. With the nickel oxide addition there is an oxidation of carbon, this forming carbon monoxide which is exhausted into the atmosphere.
  • the temperature of the metal is on the order of 2,900 P. .And the furnace pressure ranges from about 50 millimeters down to about 2.5 millimeter of mercury. The carbon-oxygen reaction is facilitated by a stirring action had in the induction furnace operation.
  • the metal analyzes 0.022% carbon, 0.11% manganese, 16.93 chromium, 7.64% nickel, and remainder iron.
  • the composition of the steel is then adjusted, this through the additions of low-carbon ferrochromium and pig nickel.
  • the metal analyzes 0.483% carbon, 0.71% manganese, 0.015% phosphorus, 0.006% sulfur, 0.17% silicon, 18.23% chromium, 5.67% nickel, and remainder iron. Small amounts of ferrosilicon are added in batches, one of about pounds and another of about pounds, both ofa 75% silicon grade. At this stage the metal analyzes 0.460% carbon, 0.66% manganese, 0.013% phosphorus, 0.005% sulfur, 0.05% silicon, 17.80% chromium, 5.68% nickel, and remainder iron. With a final check on the carbon, chromium and nickel contents, the metal here analyzing 0.459% carbon, 17.89% chromium, 5.62% nickel, and remainder iron, the heat is readied for tapping into a suitable ladle, as before.
  • the molten steel from the ladle is streamed into the vacuum induction furnace under one-atmosphere pressure, and the vacuum pumps then turned on. Because of the significantly higher carbon content than before (0.459% carbon as compared to 0.250% carbon in the prior illustrative heat), a substantially larger quantity of nickel oxide is charged into the vacuum furnace, this in separate batches. The total quantity of nickel oxide amounts to 1,040 pounds.
  • the pressures range from some 20 millimeters down to 0.6 millimeters of mercury.
  • the carbon content of the metal falls rapidly as a result of the reaction with the nickel oxide and the stirring action had in the bath. At the end of the decarburization period, the carbon content amounts to 0.042%.
  • the heat is then adjusted for composition through additions of low-carbon ferrochromium and pig nickel and tapped into a suitable ladle for teeming. There are had 37,780 pounds of ingots analyzing 0.042% carbon, 0.82% manganese, 0.028% phosphorus, 0.025% sulfur, 0.62% silicon, 18.38% chromium, 8.45% nickel, and remainder iron.
  • the skull and butt scrap amount to 660 pounds, giving a total weight of 38,440 pounds.
  • the heat is tapped into a ladle for transfer to the vacuum furnace.
  • the metal analyzes 0.05% carbon, 0.67% manganese, 0.014% phosphorus, 0.039% sulphur, 0.10% silicon, 18.31% chromium, 6.04% nickel, and remainder iron.
  • the metal is streamed from the ladle into the vacuum induction furnace under one-atmosphere pressure. the vacuum pumps are activated and nickel oxide in the amount of 1,170 pounds added, this to effect decarburization.
  • the temperature of the metal is maintained about 2,900 F.
  • the furnace pressures ranging from some 80 millimeters down to 1.6 millimeters of mercury. Adjustments in chromium, nickel, manganese, silicon, and sulfur contents are conveniently made through additions of low-carbon ferrochromium, pig nickel, ferromanganese ferrosilicon and iron pyrites.
  • the heat is tapped into a ladle for teeming. The vacuum is broken, the ladle removed, the ingots are teerned.
  • the metal is found to be sound, clean, and significantly free of oxide inclusions. There are had 37,720 pounds of ingots analyzing 0.079% carbon, 1.33% manganese, 0.019% phosphorus, 0.18% sulfur, 0.70% silicon,17.86% chromium,
  • the art which comprises melting in an electric arc furnace a charge comprising at least one of the following two ingredients stainless steel scrap and high-carbon ferrochromium, to give a bath of undesirably high-carbon content but desirably low chromium oxide content; and treating the resulting melt in a vacuum induction furnace in the presence of the reducible oxide at temperatures of at least about 2,900 F. and at pressures brought to a value, not exceeding several millimeters of mercury to eliminate carbon in the presence of chromium.
  • the art which comprises melting in an electric arc furnace a charge comprising at least one of the following two ingredients stainless steel scrap and high-carbon ferrochromium, yielding a melt of desirably high chromium and low chromium oxide contents but undesirably high-carbon content; and thereafter treating the melt in a vacuum induction furnace with one or more of the oxides of nickel, cobalt, molybdenum, chromium, copper, iron, manganese, silicon and titanium at temperatures of at least about 2,900 P. and under pressures brought to a value not exceeding several millimeters of mercury to eliminate carbon.
  • melt of undesirably high-carbon content is treated with a reducible oxide under pressures brought to a value not exceeding several millimeters of mercury and temperatures of at least about 2,950 F.
  • a chromium-nickel stainless steel containing about 10% to 35% or more chromium and with nickel up to 35% or more which comprises melting in an electric arc furnace a charge comprising at least one of the following two ingredients stainless steel scrap and high-carbon ferrochromium, forming a melt of undesirably high-carbon content but desirably low chromium oxide content at temperatures not exceeding about 3,000 F maintaining the melt under a slag of lime and ferrosilicon at such temperatures to eliminate sulphur; and thereafter ridding the melt of carbon by treating the same, in a vacuum induction furnace, with nickel oxide under conditions of high-temperature and under pressure brought to a value not exceeding 1 millimeter of mercury.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Manufacture And Refinement Of Metals (AREA)
  • Treatment Of Steel In Its Molten State (AREA)
  • Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)
US3615348D 1968-07-31 1968-07-31 Stainless steel melting practice Expired - Lifetime US3615348A (en)

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US74896968A 1968-07-31 1968-07-31

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US3615348A true US3615348A (en) 1971-10-26

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US3615348D Expired - Lifetime US3615348A (en) 1968-07-31 1968-07-31 Stainless steel melting practice

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US (1) US3615348A (enrdf_load_stackoverflow)
DE (1) DE1939044A1 (enrdf_load_stackoverflow)
FR (1) FR2014069A1 (enrdf_load_stackoverflow)
GB (1) GB1282457A (enrdf_load_stackoverflow)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3816100A (en) * 1970-09-29 1974-06-11 Allegheny Ludlum Ind Inc Method for producing alloy steel
US4027095A (en) * 1974-02-21 1977-05-31 Nisshin Steel Co., Ltd. Hermetically sealed arc furnace
US4340420A (en) * 1980-06-10 1982-07-20 Skf Steel Engineering Aktiebolag Method of manufacturing stainless steel
US5395420A (en) * 1993-11-30 1995-03-07 Centro Sviluppo Materiali S.P.A. Process for using foamed slag in stainless steel production
CN113265509A (zh) * 2021-05-14 2021-08-17 山西太钢不锈钢股份有限公司 使用电炉以氢氧化镍为原料冶炼镍系不锈钢的生产方法

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2263488B1 (enrdf_load_stackoverflow) * 1974-03-07 1976-06-25 Pilorget Andre
FR2283415A1 (fr) * 1974-06-11 1976-03-26 Haut Rhin Manufacture Machines Barillet de revolver pour l'ejection des douilles sans collerette
SE405983B (sv) * 1977-06-09 1979-01-15 Asea Ab Sett for framstellning av kromhaltig legering i ljusbagsugn
US4212665A (en) * 1978-07-27 1980-07-15 Special Metals Corporation Decarburization of metallic alloys
GB8711192D0 (en) * 1987-05-12 1987-06-17 Consarc Eng Ltd Metal refining process

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3816100A (en) * 1970-09-29 1974-06-11 Allegheny Ludlum Ind Inc Method for producing alloy steel
US4027095A (en) * 1974-02-21 1977-05-31 Nisshin Steel Co., Ltd. Hermetically sealed arc furnace
US4340420A (en) * 1980-06-10 1982-07-20 Skf Steel Engineering Aktiebolag Method of manufacturing stainless steel
US5395420A (en) * 1993-11-30 1995-03-07 Centro Sviluppo Materiali S.P.A. Process for using foamed slag in stainless steel production
CN113265509A (zh) * 2021-05-14 2021-08-17 山西太钢不锈钢股份有限公司 使用电炉以氢氧化镍为原料冶炼镍系不锈钢的生产方法

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Publication number Publication date
FR2014069A1 (enrdf_load_stackoverflow) 1970-04-10
GB1282457A (en) 1972-07-19
DE1939044A1 (de) 1970-02-05

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AS Assignment

Owner name: ARMCO ADVANCED MATERIALS CORPORATION, STANDARD AVE

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST. , EFFECTIVE DEC. 31, 1987.;ASSIGNOR:ARMCO, INC.;REEL/FRAME:004850/0157

Effective date: 19871216

Owner name: ARMCO ADVANCED MATERIALS CORPORATION,PENNSYLVANIA

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:ARMCO, INC.;REEL/FRAME:004850/0157

Effective date: 19871216