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
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D27/00—Treating the metal in the mould while it is molten or ductile ; Pressure or vacuum casting
  • B22D27/20—Measures not previously mentioned for influencing the grain structure or texture; Selection of compositions therefor
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C28/00—Alloys based on a metal not provided for in groups C22C5/00 - C22C27/00

Definitions

• the invention relates to the field of metallurgy, in particular to the creation of a refining and modifying alloy for treating cast iron and improving the quality of castings.
• the proposed alloy can be used in metallurgical, engineering and foundries.
• the disadvantage of the alloy is the low spheroidizing and unstable graphitizing ability in the processing of structural gray cast iron in the production of castings with a wall thickness of less than 3 mm, which leads to a decrease in mechanical properties and the appearance of bleach in castings.
• the lack of stability of the graphitizing ability is due to the strong dependence of the graphitizing effect of the active element of strontium even with slight fluctuations in the content in the alloy aluminum and calcium.
• the presence of rare earth metals in the indicated range without the main spheroidizing element - magnesium does not allow to obtain graphite of a globular shape.
• the disadvantage of the modifier is the lack of reproducibility of the modifying effect when processing cast iron.
• the modifier contains less than 0.1% calcium, at a lower level of silicon (15%) and any combination within the indicated limits of zirconium and / or titanium, the maximum solubility of strontium will be less than 0.1% (Yu. A. Ageev, S. A Archugov, Investigation of the solubility of alkaline earth metals in liquid iron and alloys based on it / Journal of Physical Chemistry (T. LIX. JVs 4, 1985, pp. 838 - 841).
• the modifier of this composition does not ensure the absence of bleach in castings from structural gray cast irons with a wall thickness of less than 3 mm.
• the aim of the invention is to create an alloy, the composition of which provides high strength and ductility characteristics of the alloy guna in the absence of bleached in sections of castings less than 3 mm, as well as the necessary reproducibility of the modifying effect.
• the alloy additionally contains magnesium and rare earth metals in the following ratio of components, May. %:
• the ratio of the components in the proposed alloy is selected in such a way that, due to the mutual influence of these elements, reliable reproducibility of the modification results is ensured. This effect is achieved even if up to 1.0% of industrial slag consisting of metal oxides and sulfides gets into the alloy, and up to 1.0% in the amount of inactive metals that are impurities in charge materials.
• the lower and upper limits of the content of alloy components are selected based on the achievement of the goal, as well as economic considerations.
• the lower limit of the silicon content in the alloy is due to the fact that when the content in it is less than 45%, the modifying properties of this element are weakly manifested.
• silicon is a solvent for other alloy components.
• An increase in the silicon content in the alloy of more than 78% is impractical, since it does not lead to a further increase in the modifying ability of this element, but only to an increase in the cost of the alloy.
• Rare earth metals are introduced into the alloy to stabilize the results of spheroidizing modification due to the neutralization of non-ferrous metal impurities of deglobulinizers (Pb, Sn, Sb, etc.) by binding them to finely dispersed compounds, which, moreover, are additional centers of graphitization.
• REM sulphides and oxysulphides having a high density comparable with the density of molten iron, also serve as centers of graphite crystallization, enhancing the graphitizing effect.
• the REM content in the alloy is less than 0.1%, their effect on the properties of cast iron is hardly noticeable, the content of REMs above 2.2% is impractical due to the attenuation of the increase in the graphitizing ability of these metals and the rise in price of fame.
• lanthanum and neodymium are most effective.
• strontium in the alloy leads to an improvement in the shape of graphite and a sharp increase in its graphitizing ability.
• the graphitizing potential of strontium is significantly reduced in the presence of calcium and aluminum.
• the lower limit of the strontium content in the alloy is due to the fact that when the content in it is less than 0.1% Sr, the addition of the alloy to cast iron is ineffective.
• the upper limit of the strontium content in the alloy is limited by the capabilities of the technological process for its production.
• the presence of calcium in the presence of magnesium in the alloy improves the conditions for the formation of graphite nuclei during the crystallization of cast iron, and the higher the calcium content, the greater the magnesium content in the alloy.
• the magnesium content is sufficient no more than 0.15%.
• the upper limit of calcium content (1.5%) also corresponds to the upper limit of magnesium content (7.0%) in the alloy.
• the calcium content in the alloy of more than 1.5% causes a decrease in the rate of dissolution of the alloy in molten iron due to the blocking of the reaction surface by the formed silicates.
• the aluminum content in the alloy should not exceed 2.0%, since aluminum reduces the graphitizing ability of strontium.
• the lower limit of the aluminum content in the alloy is due to the high costs associated with the refining of ferrosilicon from aluminum, since industrial varieties of ferrosilicon contain up to 2.5% aluminum.
• magnesium in the alloy of less than 0.1% does not allow to stabilize its composition and provide the necessary ratio of the content of strontium, calcium and aluminum in a narrow range.
• Magnesium increases the solubility of strontium in the iron-silicon melt and allows you to stably maintain the content of this element at the upper limit (2.0%) even with a minimum silicon content in it (45%).
• magnesium is the main spheroidizing element.
• the magnesium content in the alloy of more than 7% leads to its increased waste and pyroelectric effect when the modifier is introduced into molten iron. Therefore, such a content of it in the alloy is not economically and environmentally sound.
• Zirconium was introduced into the composition of the alloy to level the harmful effects of aluminum on the graphitizing effect of strontium. Moreover, the lower limit of the zirconium content corresponds to the lower aluminum content in the alloy, and the upper limit of the zirconium content corresponds to the highest aluminum content in the alloy. It is known that strontium in in the presence of aluminum in iron-silicon modifiers, it exhibits its graphitizing properties not stable and the use of these modifiers does not always lead to the complete elimination of bleach in castings. Zirconium introduced into the composition of the alloy within the indicated limits stabilizes the powerful graphitizing ability of strontium due to the formation of strong compounds ZrAl 2 , ZrAl 3 and others and helps to prevent bleaching in thin-walled castings.
• a zirconium content of less than 0.1% does not provide stable operation of strontium with an aluminum content of 0.3% in the alloy.
• the content of zirconium in the alloy in an amount of 2.0% allows you to completely suppress the harmful effects of aluminum even with an aluminum content of 2.0%.
• Example 1 Obtaining an alloy for modifying cast iron.
• the alloy (Table 1) is obtained in the induction furnace IST-1.0 by fusing silicon, steel scrap, mischmetal or oxide of lanthanum, magnesium, silicicirconium and strontium carbonate. The melt is released into the mold. After cooling, the alloy is separated from the slag and it is crushed on a DLShch-80 jaw crusher with the separation of a fraction of 1-5 mm.
• Table 2 presents the results of the modification of cast iron by alloys of compositions 1 to 7. Mechanical tests were carried out on 10 mm samples according to GOST 1497-84, the bleach value was measured in a casting with a wall thickness of 3 mm. Table 1.
• the alloy contains industrial slag and impurities in an amount of 1% each.

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

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