CAST IRON PDF
PDF | On Feb 1, , Doru M. Stefanescu and others published Classification and Basic Metallurgy of Cast Iron. 𝗣𝗗𝗙 | On Oct 15, , Doru M Stefanescu and others published A History of Cast Iron. PDF | Cast iron with 3 wt. % Cu was prepared by induction melting and casting in sand molds. The structure of the samples was studied using light microscopy.
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Cast Iron Microstructure specifically, the inoculant enhances graphite nucleation, preventing the formation of primary carbides. Anomalies and Their Using the. Cast iron production in Ancient Greece: myth or fact? Mediterranean Archaeology and Archaeometry, vol.6, No 2 (), Maria Kostoglou. Steel and cast iron Chapter 11 - 1 Chapter 11 - 2 1 Taxonomy of Metals Metal Alloys Adapted from Ferrous Nonferrous Fig. , Callister 7e. Steels Steels Cast.
Phosphorus and sulfur may be burnt out of the molten iron, but this also burns out the carbon, which must be replaced.
Depending on the application, carbon and silicon content are adjusted to the desired levels, which may be anywhere from 2—3. If desired, other elements are then added to the melt before the final form is produced by casting. Alloying elements[ edit ] Iron-cementite meta-stable diagram Cast iron's properties are changed by adding various alloying elements, or alloyants. Next to carbon , silicon is the most important alloyant because it forces carbon out of solution.
A low percentage of silicon allows carbon to remain in solution forming iron carbide and the production of white cast iron. A high percentage of silicon forces carbon out of solution forming graphite and the production of grey cast iron. Other alloying agents, manganese, chromium, molybdenum, titanium and vanadium counteracts silicon, promotes the retention of carbon, and the formation of those carbides.
Nickel and copper increase strength, and machinability, but do not change the amount of graphite formed. The carbon in the form of graphite results in a softer iron, reduces shrinkage, lowers strength, and decreases density. Sulfur , largely a contaminant when present, forms iron sulfide , which prevents the formation of graphite and increases hardness.
The problem with sulfur is that it makes molten cast iron viscous, which causes defects. To counter the effects of sulfur, manganese is added because the two form into manganese sulfide instead of iron sulfide. The manganese sulfide is lighter than the melt, so it tends to float out of the melt and into the slag. The amount of manganese required to neutralize sulfur is 1. Chromium is added in small amounts to reduce free graphite, produce chill, and because it is a powerful carbide stabilizer; nickel is often added in conjunction.
A small amount of tin can be added as a substitute for 0. Copper is added in the ladle or in the furnace, on the order of 0. The carbon present in the white cast iron precipitates and forms large particles that increase the hardness of the cast iron. It is abrasive resistant as well as cost-effective making them useful in various applications like lifter bars and shell liners in grinding mills, wear surfaces of pumps, balls and rings of coal pulverisers, etc.
Grey cast iron Grey is the most versatile and widely used cast iron. The presence of carbon leads to formation of graphite flakes that does not allow cracks to pass through, when the material breaks. Instead, as the material breaks the graphite initiates numerous new cracks. The fractured cast iron is greyish in colour, which also gives it the name. The graphite flakes make the grey cast iron exhibit low shock resistance.
They also lack elasticity and have low tensile strength. However, the graphite fakes gives the cast iron excellent machinability, damping features as well as good lubricating properties making them useful in many industrial applications. The graphite microstructure of the cast iron has a matrix that consists of ferrite, pearlite or a combination of two.
The molten grey iron has greater fluidity and they expand well during the solidification or freezing of cast iron. In ductile iron, chromium is particularly noted for the formation of stable primary carbides that are not easily removed with heat treatment and are not easily removed with proper inoculation. Hydrogen is also noted for causing primary carbides. In this instance, however, the primary carbides can occur in the last iron to solidify because of H segregation to the liquid during solidification.
When this occurs, a particular carbide form results, known as inverse chill. Figure 13 shows an example. Primary Carbides and Steadite in Gray Cast Iron Two microstructure constituents in gray cast iron can cause hard spots, which aggravate machinists. These two constituents are iron carbides and iron phosphides.
Figures 14 and 15 show a typical example of iron carbides, and Figs. Photomicrograph showing primary carbides white constituent in a predominantly pearlitic gray iron matrix; X, nital etch. Ductile iron microstructure illustrating inverse chill primary Fig. Photomicrograph showing steadite in a predominantly carbides in a pearlitic ductile iron. Needle-like carbides toward pearlitic gray cast iron; X, nital etch.
Photomicrograph showing primary carbides in gray cast iron with a predominantly ferrite matrix. Black constituent at right is Fig. Photomicrograph showing same area seen at lower graphite that appears to have precipitated after solidification; X, magnification in Fig. The would be found in the structure. Figures 20—23 show an example of machinists have appropriately applied several other unprintable the microscopic voids that form from drawing the liquid eutectic names. Iron phosphide is more commonly known as steadite.
Both of phases from thin sections. Because they are eutectic, they are the last to solidify. The solidification temperature for iron carbide is F C. For iron phosphide, the solidification temperature is F C. When these two eutectics combine, a tertiary iron-carbon-phos- phorus eutectic, with a still lower melting point, will occur in the microstructure. An example of this combined eutectic structure is shown in Figs. Although the melting point for this constituent is not published, it is believed to be lower than the melting points for the individual eutectics.
Since these eutectics are the last to solidify, they can be present in the cast iron structure as liquid surrounded by solid, and can be drawn from thin sections to feed thick sections. The consequence can be microscopic shrinkage voids in thin sections.
These voids have a shape that is similar to the carbide and steadite constituents that Fig. Photomicrograph showing same area seen unetched in Fig.
Photomicrograph showing same void seen at lower Fig. Note how void appears to be associated eutectic in a pearlite matrix gray cast iron; X, nital etch.
Introduction to Cast Iron: History, Types, Properties, and Uses
As with ductile iron, inoculation in gray cast iron is primarily used to control the occurrence of primary carbides. Ladle inoculation, mold inoculation, late stream inoculation or a combination of the various inoculation techniques have all proven effective.
Control of tramp elements that are known carbide stabilizers, such as chro- mium, vanadium and molybdenum, and other less common ele- ments in gray cast iron, such as antimony, tellurium and hydrogen, are also essential. Photograph showing same area seen at lower magnifi- cation in Figs. Ductile iron microstructure with a dross type defect. This dross defect results from a reaction between magnesium dissolved in iron and oxygen in surrounding air; X, unetched condition.
Spectrum of elements representing base metal in Fig. Photomicrograph illustrating a dross defect in ductile iron. Dark constituent is pearlite; white constituent is ferrite. Note that Fig. Spectrum of elements representing partially dissolved ferrite concentrates with dross structure; 50X, nital etch. Magnesium, however, is a very reactive can occur between the Mg in the iron and the oxygen in the element. As a consequence, ductile iron has a higher tendency to surrounding environment.
This reaction can form dross, even in the form slag than does gray iron or malleable iron. The reaction mold. Dross defects such as this can occur, for example, in castings products that result are often called dross.
The presence of Mg in with knife gates. Dross can also be generated in the runner system molten iron also causes the iron to generate slag, almost continu- when fluid dynamics causes turbulent flow conditions to exist. This dross is the result of the Mg too cold. As a consequence, a good slagging practice must be exercised when pouring ductile iron.
Sometimes, the dross is associated with undissolved or partially dissolved inoculant. Figure 26 shows an example. Figure 24 shows an ex- have a normal silicon level, whereas the structure on the opposite side ample of the graphite structure associated with dross that has oc- will have a high Si level.
Energy dispersive x-ray EDX spectro- curred in the casting. When etched, the area associated with the dross graphic analysis has been helpful in identifying this type of dross will often have a ferritic structure, as shown in Fig. The occur- defect. Figures 27 and 28 show a typical example of analysis in the rence of dross in a casting can be the consequence of poor slagging normal structure vs. When slag enters the mold cavity during pouring, the dross-type structure shown in Figs. Other elements are also known to cause this problem.
Lead levels as low as 0. If the condition becomes significant, the precipitation onto crystallographic planes can occur, aside from the primary graphite flakes, creating hatch marks in the structure. Photomicrograph showing same area seen at lower magnification in Figs. Also note graphite forms with thin graphite forms in note that other graphite forms have precipitated within regions between graphite flakes toward middle and middle top; X, between flakes; X, unetched condition.
Photomicrograph showing a pearlitic gray cast iron with Fig. Photomicrograph of ductile cast iron. Photomicrograph showing same area seen at lower Fig. Photomicrograph of same area shown at lower magnifica- magnification in Fig. Photomicrograph showing same area seen at lower austenitizing temperature reached, in three-phase region indicated magnification in Figs.
In the two examples, the austenitizing tem- rich steadite regions. Research1,2 has shown that this graphite type perature reached the three-phase region, indicated by the arrow in can be controlled with the addition of rare earth elements, primarily the phase diagram in Fig.
As a consequence, the condition does not often occur in As a consequence, the austenite that was present transformed to ductile cast iron because of the presence of rare earth elements in the the desired pearlite or ferrite constituent.
However, the ferrite or treatment alloy. If the condition is occurring in gray cast iron, it can pearlite that was present in the structure, but was not transformed, be controlled by eliminating the lead. However, inoculation with a remained intact as the sample was cooled. The structures shown in cerium-bearing inoculant can also reduce the effect. The untransformed constituents are properties of the resulting iron.
For example, a normal Class 30 gray the cause of the unusual shapes in the photomicrographs. Cast irons that are quenched and tempered to form martensite can have unusual microconstituents. In addition to the expected marten- site, an unexpected white constituent in the structure can occur.
Unusual Ferrite Microstructure in This white constituent is shown in Figs. The constituent is retained Analyzing microstructures can sometimes be confusing.Small angular white constituents martensitic ductile cast iron.
It can be reasons for these inconsistencies.
Effect of Trace Elements (Boron and Lead) on the Properties of Gray Cast Iron
It is often removed from the ferrite content was excessive. Nitrogen content in gray cast iron varies between 0. Therefore, inoculation is crucial to successfully cast ductile iron without carbides.
Lead levels as low as 0. However, the graphite fakes gives the cast iron excellent machinability, damping features as well as good lubricating properties making them useful in many industrial applications.
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