The microstructure of cast iron



In the experiment, the microstructures of five samples of different dramatis personae Fe signifiers were observed and investigated under the optical microscope and an iron-carbide stage was studied. The suited drawings were made under different magnification of 100 and 200. Each component of the microstructure was identified and besides other structural characteristics of the sample provided were identified. The samples areBlackheart ductile dramatis personae Fe, Ferritic spheroidal graphite Fe, Pearlitic spheroidal graphite Fe, White cast Fe and Phosphoric grey dramatis personae Fe. The differences in the microstructure were due to the difference in heat intervention, procedure of chilling and additives present.


The eutectic metal formed between Ag and Cu was observed. The microstructure of all the four samples was drawn utilizing the optical microscope with 200 magnifications. 90 % Ag 10 % Cu, 72 % Ag 28 % Cu, 50 % Ag 50 % Cu, 30 % Ag 70 % Cu are the samples provided. An equilibrium diagram was constructed for the copper-silver metal system, the characteristics of involvement every bit good as the component of the construction was identified for all the samples.



Cast chainss are a category of ferric metals with a C content of between 2.0 – 4.5 % ; they contain sufficient C so that the eutectic reaction occurs during hardening. They are the most economical in footings of metalworks cost which makes the utile even though they are rather brickle ; they are all right for low stressed constituents like cylinder block. Their versatility makes them a high demand in the market. Cast Fe contain contrasting sum of manganese, sulphur and P. They have changing strength and can defy wear and scratch and corrosion and they can be easy machined. They are easy melted and cast doing the good casting feeling.

The C in a dramatis personae Fe exists in two signifiers, as a free signifier of black lead or in a combination as a iron carbide which is unstable Fe carbide. Iron is difficult and hard to machine due to how brittle the iron carbide is while black lead is soft doing the Fe softer and easy to machine. Graphite weakens metal due to its happening in flakes by interrupting up its continuity. Because of the features of these two C signifier, the comparative sum, the form and distribution in the dramatis personae Fe produces different dramatis personae chainss assortment of belongingss.

Grey cast Fe contains bantam interrelated flakes of black lead that allow low strength and ductileness. It ‘s the largely used dramatis personae Fe and named after its gray coloring material on break surfaces. White cast Fe produces more cementite than black lead during hardening, it is a difficult brickle metal incorporating monolithic sum of fe3c. Alloyed white dramatis personae Fe is used due to their hardness and wear opposition for scratchy wear. The name was given due to white fractured surface.

Ductile dramatis personae Fe is formed by the heat intervention of white dramatis personae Fe, it has better ductileness and they produce rounded bunchs of black lead. It is really machinable and is made by heat handling unalloyed 3 % C. A spherodite are micro component of coarse spheroidal black lead atoms in a matrix of pearlite or ferrite, allowing first-class machining features in high C steel.

The construction of dramatis personae Fe is affected by a figure of factors. The type of Fe signifier is determined by the rate of hardening as slow chilling will bring forth gray Fe and the rapid one will bring forth white Fe construction. Whether black lead or iron carbide is formed and by what measure is determined by the C content of the thaw and presence of other component. For illustration Ni and Si promote the formation of black lead in the Fe construction. The construction is affected by the type of heat intervention, iron carbide will break up to ferrite and graphite will bring forth a wholly different construction.


There are three individual stage parts on the stage diagram of binary metals of Ag and Cu. The stage is a solid solution rich in Cu which has Ag as the solute and an FCC construction it besides include pure Cu and is considered to include pure Cu. An eutectic part can be defined as a three stage invariant reaction in which one liquid stage solidifies to organize two solid stages. Copper and silver organize an eutectic at 72 % Ag and 28 % Cu at a temperature of 780oC.The temperature at which an metal become wholly liquid lessenings as Ag is added to copper which is besides the same as the add-on of Cu to silver.

A microstructure may be defined as the structural characteristic of an metal, its grain and stage construction that are capable to observation under microscope. Copper is a face centred three-dimensional structured metal possessing good ductileness, good thermal and electrical conduction. It is frequently used as a component of assorted metal metals. The runing point of pure Cu is 1083oC while that of pure Ag is 961oC.

Silver possesses one of the highest electrical and thermic conduction of any metal. It has FCC construction and is sometimes produced as a byproduct of Cu. When the full liquid solubility is possible with complete solid unsolvability or really limited solid solubility so an eutectic relationship exist. This exists in Cu and Ag but they are to the full soluble in liquid province.



Five prepared micro specimens were provided and the microstructure of each studied and drawn utilizing a microscope.

The specimens provided were

  • Blackheart ductile dramatis personae Fe at magnification 100
  • Ferritic spheroidal black lead Fe at magnification 100
  • Pearlitic spheroidal black lead Fe at magnification 200
  • White cast Fe at magnification 100
  • Phosphoric Grey cast Fe at magnification 200

Each component and other structural characteristic of importance in the microstructure of white dramatis personae Fe was labelled on the drawing. The process was performed to all specimens.


Four polished and engraved micro subdivisions of Cu Ag metals were provided.

  • 30 % Ag 70 % Cu
  • 72 % Ag 28 % Cu
  • 50 % Ag 50 % Cu
  • 90 % Ag 10 % Cu

These metals have already been melted in a gas fired furnace, deoxidised by canvassing with graphite rod and so cast in furnace lining molds preheated to 500oC.

I placed the samples under the microscope at a magnification of 200 ; my observation was drawn with the aid of the microscope. The component and structural characteristics are drawn and labelled, I repeated the stairss for the full specimen and the equilibrium diagram was drawn from the informations.


The consequences are compiled in the twosome of pages attached to the following pages.



  • The manner a metal is cooled produces the different constructions of dramatis personae Fe. Two of these constructions are white and gray dramatis personae Fe. As the metal is cooled, the sum of austenite in the matrix additions. At the eutectic temperature of 1130 & A ; deg ; C the staying liquid solidifies bring forthing austenite in a eutectic matrix. A construction dwelling of iron carbide, Fe3C and eutectoid Fe starts to organize as construction starts to break up. The eutectoid contains country of pearlite and iron carbide and it ‘s besides a mixture of iron carbide and ferrite. The pearlite is formed as a consequence of the decomposition of the austenite on chilling. This construction is that of white dramatis personae Fe which is formed due to the rapid rate of chilling.
  • The chilling rate of white and gray dramatis personae Fe affects the construction ; fast chilling rate promotes white cast Fe while slower chilling rate promotes grey cast Fe. The carbide composing can hold consequence on the construction of the Fe produced ; high sum of Cr promotes white cast Fe while low sum promotes grey cast Fe. Section size can besides find Fe construction obtained. Cool subdivision cool faster and bring forth white dramatis personae Fe while thick subdivisions will chill slower advancing formation of Grey cats iron.

    A figure of variables must be controlled in order to bring forth gray dramatis personae Fe alternatively of white dramatis personae Fe. For a gray dramatis personae Fe to organize, the rate of chilling must be made every bit slow as possible. High Si content will besides advance the formation of gray dramatis personae Fe as Si has strong graphitising inclinations. Phosphoric Grey Fe is stronger, has a lower thaw point and better fluidness than normal gray dramatis personae Fe.

  • The Blackheart malleablising procedure is the wadding of white Fe castings into pots with a impersonal wadding, such as sand or crushed scoria, and heating them to 900 & A ; deg ; C for three yearss. After the three yearss they are cooled really easy. The iron carbide in the white Fe is being decomposed into ferrite and black lead is being precipitated in a smoothly dispersed signifier. The construction is composed wholly of ferrite and black lead. The graphite nowadays in the construction is shown as & A ; lsquo ; rosettes ‘ of C in the ferrite. After the procedure, the little sum of pearlite left has no consequence on the belongingss of the casting. The steel produced in this procedure has good wear opposition and strength and sensible stamina.
  • Additives are used to bring forth ellipsoid black lead Fe instead than flake graphite Fe. Magnesium amounting to 1-2 % of the weight of the Fe is added in the signifier of a nickel Mg metal of 10-20 % Mg. The metal is used to forestall an highly violent reaction from happening. The presence of Si besides assists the formation of the nodules hence Ferro-silicon is added. The sulphur degree demands to be kept low in order to avoid taking the Mg as sulfide.
  • In the production of a ferritic black lead Fe, ellipsoid of revolutions of black lead in pearlite matrix are heat treated to organize ellipsoid of revolutions of black lead in ferrite matrix. This is clip dependent procedure and does n’t travel into completion therefore doing pearlite country to still be seen.


  • On drawing of the 30 % Ag70 % Cu, alpha atoms can be seen and dark spots show primary dendrites outside eutectic.
  • The 50 % Ag50 % Cu metal sample besides shows primary alpha dendrites outside eutectics. In the 90 % Ag10 % Cu sample there is little sum of eutectic and light countries show beta atoms while the dark countries show alpha atom.

    On the equilibrium diagram ADB is the liquidus and ACDEB is the bezant. The country ACF represents the alpha stage of the Ag in Cu while BEG represent the status of limited solid solution of Cu in Ag which is the beta stage. Below FCDEG the two stage ‘s alpha and beta exist side by side.

    The 72 % Ag28 % Cu micro subdivision has an all eutectic composing with dark countries besides stand foring alpha atoms and light countries demoing beta particles the Centre of the microstructure is the first to solidify so the outside country.

    Composition of solid and liquid stages will change with the temperature along the bezant and liquidus lines. The concluding liquid between composing C and E will ever stop at eutectic regardless of what the initial composing may be. As a consequence the solid will be composed of multitudes of A and B. At eutectic CW parts liquidus composing Y while WY parts composing C.

  • During projecting it ‘s virtually impossible to accomplish equilibrium conditions. Coring is the non equilibrium chilling on microstructures. Coring explains how the varying primary dendrites allow lighter countries in the Centre than in the exterior. The belongingss of a cored construction are less than optimum, as a casting holding a cored construction is reheated doing grain boundaries parts will run into foremost every bit long as they are richer in low thaw constituents.
  • The liquid movie that separate the grain gives an result of sudden loss of mechanical unity. The thaw may get down at a temperature below the equilibrium solidus temperature of the metals. Homogeneous heat intervention can be used to take coring at a temperature below the solidus point of the metal composing. During the procedure, atomic diffusion occur bring forthing compositionally homogenous grain.


  • Cast chainss have many different constructions each one caused by a different chilling rate, additives and different heat interventions.
  • Formation of gray dramatis personae Fe over white dramatis personae Fe is promote by slow chilling rate and tremendous Si content
  • Coring can be eliminated by a homogenising heat intervention.
  • Magnesium and Si aid to bring forth ellipsoid black lead Fe instead than flake graphite Fe
  • To bring forth a ferritic spheroidal black lead Fe from pearlitic spheroidal black lead iron the steel must be heated to merely below the lower critical temperature.
  • Phosphoric Fe will enable to project really all right inside informations and in blackheart malleablising procedure, rosettes from black lead in ferrite matrix are produced from white dramatis personae Fe.
  • The composing of the Cu Ag eutectic metal has a really big consequence on the microstructure of the metal, with different sums of the stages being produced on chilling.