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
  • C21C1/08—Manufacture of 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

• the invention relates to a process of making cast iron of improved strength and machining properties, and more specifically to the use of specific nucleating agents in such process.
• the properties of cast iron are determined, on one hand, by the graphite formation, and, on the other hand, by the structure of the metallic base. Both items depend largely on the composition and on the melting, casting, and cooling conditions. in order to understand the crystallization processes taking place in cast iron, it is important to bear in mind that the modifications of the iron-carbon phase diagram which are caused by the usual contents of cast iron in silicon and phosphorus cannot be disregarded as may be the case with carbon steel. It is, rather, necessary to rely on the corresponding three or more component-phase diagram, in particular the iron-carbon-silicon diagram and the iron-carbon-phosphorus phase diagram.
• the saturation degree S of the alloy can be numerically defined by the abridged formula used generally in industrial practice, which reads as follows:
• C is the carbon content and Si is the silicon contact of the alloy expressed in percentages, while the number 4.23 indicates the carbon content of the binary graphite eutecticum.
• S, l the cast iron is subeutectic, and with S, l it is supereutectic.
• the graphite In case of graphite formation by way of laminae or flakes, the graphite usually occurs in the form of more or less coarse irregularly curved flakes which are frequently arranged in pockets. With subeutectic alloys it is no longer possible to discern a clear limit between the primarily eliminated 'y-mixed crystals and the eutecticum in the solidified structure.
• the primary precipitate of refined foam graphite in case of a supereutectic composition, is clearly set off by its particularly coarse structure from the much finer structure of the graphite of the eutecticum.
• the graphite eutecticum shows the fine distribution of the two components which is characteristic for a eutecticum only if an increased cooling rate and a correspondingly stronger supercooling is effected.
• the reason. for the tendency to form coarse graphite flakes in the eutecticum is that the graphite as the dominating crystal structure in the eutecticum is strongly affected in its crystallization by nucleating forces.
• the composition of the cast iron has to be selected to secure a graphitic solidification under the cooling conditions employed as they result from wall thickness Cut the casting and the type of mold, such as sand mold or ingot mold, cold or preheated mold, etc. This is accomplished particularly by a predetermined selection of the silicon contents which favors the graphitic solidification.
• An increase of the carbon contents likewise acts in the same direction while, on the other hand, a greater increase of manganese contents has the opposite effeet.
• the metallurgical pretreatment of the metal prior to casting likewise has a substantial bearing on the graphite formation.
• the reason is that a superheating causes the crystallization nuclei to be put into solution to a greater extent. This, in turn, causes more undercooling and thus a finer graphite structure.
• a fine-grained solidification and fine dispersion of the graphite precipitation in the melt is therefore of greatest importance for high-grade cast iron types such as are required particularly for the thin-walled products which have come more and more into use in recent practice.
• the inoculating agents used are predominantly FeSi, CaSi or other silicon base mixed alloys. These agents can be added in the form of loose granulates or in prepacked form. These agents have a deoxidizing effect, partly also having desulfurizing action and furthermore improve the eutectic structure of the cast iron.
• the amounts of additive are, in general, for instance 4 kg. of CaSi per ton of iron.
• nucleating agent is added to the superimposed melt comprising a highly dispersed silica or an alumina-silica or titanium dioxide-silica mixed oxide containing at least percent of silica.
• the highly dispersed silica employed in this invention may be an amorphous silica obtained in the gas phase by a pyrogenic process or may be a wet precipitated silica.
• the highly dispersed SiO because of its fine subdivision meets the requirement that the nucleating agent should result in the formation of as many local crystallization centers as possible and should correspond to the lattice structure of the metal crystals.
• the inoculation with superfine SiO results in a structure having a finely dispersed graphite and in addition favors the graphite precipitation to an extent that the edge hardness which is caused by the preferential heat discharge at the edges of the casting is completely eliminated. It is this edge hardness which causes subseque t difficulties in machining the metal.
• a similar effect is obtainable by inoculation with mixed oxides. preferably containing from 90 to 98 percent SiO and from 2 to 10 percent A1 0 or TiO,
• mixed oxides preferably containing from 90 to 98 percent SiO and from 2 to 10 percent A1 0 or TiO.
• the following is offered as an explanation for the effects of the superfine amorphous silica or the mentioned mixed oxides without intention to restrict the inventors to this theory. It appears that the superfinely dispersed SiO, particles exert some kind of a directional force on the melt during cooling and that by wetting of the SiO: particles by the melt and by the presence of free surface forces, an increased activity of the nucleating agent is provoked.
• the silica or mixed oxides may be used in the form of a prepacked composition, for instance it may be prepacked in a tin can.
• the package may be weighted down by materials such as FeMn, dry iron filings, etc. The package will thus drop to the ground in the ladle.
• a propelling agent may also be added, for instance in the form of a nitrogen-generating mixture, in order to cause a whirling effect with consequent thorough mixing and distribution ofthe silica.
• the cast iron used in this example contained 3 percent carbon and 1.6 percent silicon and had a saturation degree (S of 0.89.
• EXAMPLE A highly dispersed silica in an amount of about 100 g./t. of melt was added to the melt in the form of a prepackage in a tin can.
• the tin can in addition included weighting agents and a propelling agent.
• the weighting agents were dry iron filings, and the propelling agent was a nitrogen-generating salt mixture.
• This type of prepackage was thrown into the ladle, where it immediately dropped to the bottom of the mold.
• the propelling agent had an intense whirling effect and thus provided a uniform distribution of the silica throughout the entire ladle.
• nucleating agent in a process of making cast iron of improved strength and machining properties wherein a nucleating agent is added to the preheated and superheated melt whereupon the melt solidifies, the use, as the nucleating agent, of a highly dispersed silica or an alumina-silica or titanium dioxde-silica mixed oxide, the mixed oxide containing at least percent silica.
• silica is a silica obtained in the gas phase by a pyrogenic process.

Landscapes

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

Applications Claiming Priority (1)

Publications (1)

Family

ID=5694799

Family Applications (1)

Country Status (9)

Cited By (3)

Families Citing this family (3)

Citations (6)

• 1968
  • 1968-03-20 DE DE19681758004 patent/DE1758004B1/de active Pending
• 1969
  • 1969-02-17 CH CH235269A patent/CH523325A/de not_active IP Right Cessation
  • 1969-02-28 SE SE02838/69A patent/SE365545B/xx unknown
  • 1969-03-11 NL NL6903748A patent/NL6903748A/xx unknown
  • 1969-03-14 GB GB03536/69A patent/GB1222798A/en not_active Expired
  • 1969-03-18 BE BE730051D patent/BE730051A/xx unknown
  • 1969-03-18 US US808301A patent/US3617259A/en not_active Expired - Lifetime
  • 1969-03-20 FR FR6908139A patent/FR2004340A1/fr active Granted
  • 1969-03-20 AT AT278069A patent/AT309489B/de not_active IP Right Cessation

Patent Citations (6)

Also Published As

Similar Documents