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
  • C21C1/00—Refining of pig-iron; Cast iron
  • C21C1/10—Making spheroidal graphite cast-iron
• • 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
  • C21C1/00—Refining of pig-iron; Cast iron

Definitions

• This invention relates to the production of nodular cast iron and, more particularly, to an improved process for the production of as-cast nodular iron.
• magnesium has generally been considered to be the most suitable spheroidizing agent, there are numerous disadvantages associated with the use of magnesium.
• the boiling point of magnesium (2025 F.) is considerably lower than the temperature of the molten iron bath at the time magnesium must be added to cause spheroidization of the graphite. Consequently, a violent reaction accompanies introduction of magnesium to molten iron.
• Many methods of subduing this reaction have been devised. These include alloying the magnesium with nickel or silicon prior to introducing the element or alloy into a ladle of molten iron, introducing the magnesium 3,492,118 Patented Jan.
• cerium to effect graphite spheroidization rather than magnesium.
• the mechanical properties of cast iron improve nearly linearly with increasing cerium contents up to a cerium level between .02 percent and .06 percent.
• residual elements which inhibit spheroid formation can be tolerated at higher levels in cerium-treated nodular iron than in magnesium-treated nodular iron.
• cerium and the other rare earth elements generally found with cerium boil at temperatures greatly in excess of the temperature of the molten iron bath. Thus, negligible volatilization losses are encountered, the process is less sensitive to iron temperature, and the hazards involved in introducing cerium to the bath are far less than when magnesium is added as a spheroidizing agent.
• cerium has been limited to research for several important reasons. Cerium is believed to be effective in causing only hypereutectic graphite to spheroidize. Magnesium, on the other hand, imparts nodular structure to both hypoeutectic and hypereutectic graphite.
• Mischmetal which is an alloy composed of about 48 percent cerium, 25 percent lanthanum, 15 percent neodymium, 9 percent other rare earths, and up to about 5 percent iron, is ductile and must be sawed, cut, or cast into pieces of convenient size for adding to the iron. Therefore, it is difiicult to size mischmetal into small particles which permit the addition of exact amounts of cerium to the bath.
• cerium-treated cast iron is extremely sensitive to both the rate of cooling and the number of spheroids present per unit volume of iron. It is generally believed that the graphite spheroids formed in hypereutectic cast iron treated with cerium according to present practices are enveloped in an austenite coating above the eutectic temperature. As the temperature of the melt is lowered and the eutectic transformation proceeds, carbon migrates through the coating of austenite and deposits on the spheroid. The extent to which this migration and deposition occurs depends upon the cooling rate and the number of spheroids present per unit volume of iron.
• the iron contains a sufficient number of spheroids and if the cooling rate is slOW enough to permit carbon diffusion to proceed, all of the carbon liberated during the eutectic transformation will deposit on the initial hypereutectic graphite spheroids. However, if the diffusion path is too long because of relatively too few hypereutectic graphite spheroids or if the rate of cooling through the eutectic region is too rapid, some of the eutectic graphite will fail to reach its destination and will precipitate as short flakes known as vermicular graphite. Very rapid cooling through the eutectic region also results in the formation of iron carbide which, if it decomposes, liberates vermicular graphite. Vermicular graphite forms frequently by these mechanisms in cerium-treated nodular iron. The mechanical properties of nodular iron are adversely affected by the presence of vermicular graphite.
• My invention provides a method of manufacturing nodular iron which yields iron
• the rare earth-silicon-iron alloy may be added to the molten bath of cast iron in a gas-fired or electric melting furance just prior to tapping. However, I prefer to add the alloy to a ladle being filled with the molten iron.
• Carbon or graphite ladle linings insure the highest reof a uniform structure, consistent properties, with an 5 covery of cerium but either acid or basic linings can be outstanding efficient use of the nodulizing agent.
• the alloy particles should be of a size that will process is not dependent upon the iron temperature and pass through a b. inch or smaller screen. Subsequent to is not adverse affected by the presence of deleterious rethe addition of the rare earth-silicon-iron alloy, the bah sidual elements in amounts which previously had been conmay be inoculated with a silicon base alloy such as 75 sidered prohibitive. Finally, it provides a means of utilpercent ferrosilicon, although this addition is not necesizing cerium to produce nodular iron essentially free sary. from vermicular graphite.
• my invention comprises the steps of prepared heats of cast iron in a l00-pound induction furforming a molten bath of cast iron composition, adding nace.
• the furnace charge consisted of low sulfur pig to the molten iron bath an alloy of rare earth, silicon iron, Armco iron, and ferrosilicon.
• the iron was tapped and iron in an amount suflicient to introduce about 0.03 from the furnace into a 100-pound ladle and during the percent to 0.15 percent cerium in the bath, pouring tapping operation, a rare earth-silicon-iron alloy sized castings from the bath and allowing the castings to solidiminus inch or smaller was added to the ladle.
• the fy The furnace charge consisted of low sulfur pig to the molten iron bath an alloy of rare earth, silicon iron, Armco iron, and ferrosilicon.
• the rare earth-silicon-iron alloy should contain up to rare earth-silicon-iron alloys utilized were prepared by 50 percent rare earths, at least half of which is cerium, reducing silica and concentrated rare earth ore with carand at least percent silicon. bon in a submerged arc smelting furnace. Iron was in- Although the exact mechanism by which my novel troduced by adding steel scrap to the furnace charge. method provides a superior nodular cast iron is not Following the tap, one pound of 75 percent ferrosilicon known, it is believed that the high degree of nodularity 25 was stirred into the iron bath.
• cerium is the only essential spheroidizing element.
• most of the rare earth-silicon-iron alloys that were used contained about 0.6 part of lanthanum, 0.2 part of neodymium and 0.1 part of other rare earth for each unit of cerium.
• Rare earth elements other than cerium apparently serve to a small extent in deoxidizing and desulfurizing the iron and thereby may improve the cerium efiiciency.
• cerium generally improves as the weight percentage ratio of silicon to cerium is increased.
• the silicon content of the cerium alloy should be greater than about 25 percent and preferably greater than 30 percent.
• the practical minimum cerium content of the alloy is approximately 2 percent.
• a third test series was conducted in the same manner as Test Series No. 1 and No. 2 using a rare earth-siliconiron alloy having a composition of 22 percent cerium, 45 percent silicon, 19 percent other rare earths, one-half percent calcium, one-half percent aluminum, and the balance iron and incidental impurities.
• the composition of the iron in this test series was the same as the composition of the iron in the second test series.
• the castings were performed using the same procedures utilized in Test Series No. 1 and No. 2 as described above. Additional data pertaining to Test Series No.
• said rare earth-silicon-iron alloy contains from 10 to 25 percent cerium and from 35 to 50 percent silicon.
• said rare earth-silicon-iron alloy has a composition of 10 percent cerium; 39 percent silicon; 7 percent other rare earhts; and the balance iron and incidental impurities.
• said rare earth-silicon-iron alloy has a composition of 10 to 25 percent cerium; 35 to 50 percent silicon; 5 to 20 percent other rare earths; 0 to 1 percent calcium; 0 to 1 percent aluminum; and the balance iron and incidental impurities.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)

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Cited By (16)

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Citations (3)

• 0
  • FR FR48709A patent/FR1525645A/fr not_active Expired
• 1966
  • 1966-05-24 US US552438A patent/US3492118A/en not_active Expired - Lifetime
• 1967
  • 1967-05-10 GB GB21812/67A patent/GB1126013A/en not_active Expired
  • 1967-05-24 DE DE19671583305 patent/DE1583305A1/de active Pending
  • 1967-05-24 SE SE7303/67A patent/SE317397B/xx unknown

Patent Citations (3)

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