The microstructure of cast iron

The microstructure of cast iron ABSTRACT THE MICROSTRUCTURE OF CAST IRON: In the experiment, the microstructures of five samples of different cast iron forms were observed and investigated under the optical microscope and an iron-carbide phase was studied. The suitable drawings were made under different magnification of 100 and 200. Each constituent of the microstructure was identified and also other structural features of the sample provided were identified. The samples areBlackheart malleable cast iron, Ferritic spheroidal graphite iron, Pearlitic spheroidal graphite iron, White cast iron and Phosphoric grey cast iron. The differences in the microstructure were due to the difference in heat treatment, process of cooling and additives present. COPPER SILVER EUTECTIC ALLOY: The eutectic alloy formed between silver and copper was observed. The microstructure of all the four samples was drawn using 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 alloy system, the features of interest as well as the constituent of the structure was identified for all the samples. INTRODUCTION THE MICROSTRUCTURE OF CAST IRON Cast irons are a class of ferrous alloys with a carbon content of between 2.0 4.5%; they contain sufficient carbon so that the eutectic reaction occurs during solidification. They are the most economical in terms of foundry cost which makes the useful even though they are quite brittle; they are fine for low stressed components like cylinder block. Their versatility makes them a high demand in the market. Cast iron contain contrasting amount of manganese, sulphur and phosphorus. They have varying strength and can resist wear and abrasion and corrosion and they can be easily machined. They are easily melted and cast making the good casting impression. The carbon in a cast iron exists in two forms, as a free form of graphite or in a combination as a cementite which is unstable iron carbide. Iron is hard and difficult to machine due to how brittle the cementite is while graphite is soft making the iron softer and easy to machine. Graphite weakens metal due to its occurrence in flakes by breaking up its continuity. Because of the characteristics of these two carbon form, the relative amount, the shape and distribution in the cast iron produces different cast irons variety of properties. Grey cast iron contains tiny interconnected flakes of graphite that allow low strength and ductility. Its the mostly used cast iron and named after its grey colour on fracture surfaces. White cast iron produces more cementite than graphite during solidification, it is a hard brittle alloy containing massive amount of fe3c. Alloyed white cast iron is used due to their hardness and wear resistance for abrasive wear. The name was given due to white fractured surface. Malleable cast iron is formed by the heat treatment of white cast iron, it has better ductility and they produce rounded clumps of graphite. It is very machinable and is made by heat treating unalloyed 3% carbon. A spherodite are micro constituent of coarse spheroidal graphite particles in a matrix of pearlite or ferrite, permitting excellent machining characteristics in high carbon steel. The structure of cast iron is affected by a number of factors. The type of iron form is determined by the rate of solidification as slow cooling will produce grey iron and the rapid one will produce white iron structure. Whether graphite or cementite is formed and by what quantity is determined by the carbon content of the melt and presence of other element. For example nickel and silicon promote the formation of graphite in the iron structure. The structure is affected by the type of heat treatment, cementite will decompose to ferrite and graphite will produce a completely different structure. COPPER-SILVER EUTECTIC ALLOYS: There are three single phase regions on the phase diagram of binary alloys of silver and copper. The phase is a solid solution rich in copper which has silver as the solute and an FCC structure it also include pure copper and is considered to include pure copper. An eutectic region can be defined as a three phase invariant reaction in which one liquid phase solidifies to form two solid phases. Copper and silver form an eutectic at 72%Ag and 28%Cu at a temperature of 780oC.The temperature at which an alloy become totally liquid decreases as silver is added to copper which is also the same as the addition of copper to silver. A microstructure may be defined as the structural feature of an alloy, its grain and phase structure that are subject to observation under microscope. Copper is a face centred cubic structured metal possessing good ductility, good thermal and electrical conductivity. It is often used as a constituent of various metal alloys. The melting point of pure copper is 1083oC while that of pure silver is 961oC. Silver possesses one of the highest electrical and thermal conductivity of any metal. It has FCC structure and is sometimes produced as a by-product of copper. When the full liquid solubility is possible with complete solid insolubility or very limited solid solubility then an eutectic relationship exist. This exists in copper and silver but they are fully soluble in liquid state. EXPERIMENTAL THE MICROSTRUCTURE OF CAST IRON Five prepared micro specimens were provided and the microstructure of each studied and drawn using a microscope. The specimens provided were Blackheart malleable cast iron at magnification 100 Ferritic spheroidal graphite iron at magnification 100 Pearlitic spheroidal graphite iron at magnification 200 White cast iron at magnification 100 Phosphoric grey cast iron at magnification 200 Each constituent and other structural feature of importance in the microstructure of white cast iron was labelled on the drawing. The procedure was performed to all specimens. COPPER-SILVER EUTECTIC ALLOYS Four polished and etched micro sections of copper silver alloys were provided. 30% Ag 70% Cu 72%Ag 28% Cu 50% Ag 50% Cu 90%Ag 10% Cu These alloys have already been melted in a gas fired furnace, deoxidised by polling with graphite rod and then cast in refractory moulds preheated to 500oC. I placed the samples under the microscope at a magnification of 200; my observation was drawn with the help of the microscope. The constituent and structural features are drawn and labelled, I repeated the steps for the entire specimen and the equilibrium diagram was drawn from the data. RESULTS The results are compiled in the couple of pages attached to the next pages. DISCUSSION THE MICROSTRUCTURE OF CAST IRON The way a metal is cooled produces the different structures of cast iron. Two of these structures are white and grey cast iron. As the metal is cooled, the amount of austenite in the matrix increases. At the eutectic temperature of 1130Â °C the remaining liquid solidifies producing austenite in a eutectic matrix. A structure consisting of cementite, Fe3C and eutectoid iron starts to form as structure starts to decompose. The eutectoid contains area of pearlite and cementite and its also a mixture of cementite and ferrite. The pearlite is formed as a result of the decomposition of the austenite on cooling. This structure is that of white cast iron which is formed due to the rapid rate of cooling. The cooling rate of white and grey cast iron affects the structure; fast cooling rate promotes white cast iron while slower cooling rate promotes grey cast iron. The carbide composition can have effect on the structure of the iron produced; high amount of chromium promotes white cast iron while low amount promotes grey cast iron. Section size can also determine iron structure obtained. Cool section cool faster and produce white cast iron while thick sections will cool slower promoting formation of grey cats iron. A number of variables must be controlled in order to produce grey cast iron instead of white cast iron. For a grey cast iron to form, the rate of cooling must be made as slow as possible. High silicon content will also promote the formation of grey cast iron as silicon has strong graphitising tendencies. Phosphoric grey iron is stronger, has a lower melting point and better fluidity than normal grey cast iron. The Blackheart malleablising process is the packing of white iron castings into pots with a neutral packing, such as sand or crushed slag, and heating them to 900Â °C for three days. After the three days they are cooled very slowly. The cementite in the white iron is being decomposed into ferrite and graphite is being precipitated in a smoothly dispersed form. The structure is composed entirely of ferrite and graphite. The graphite present in the structure is shown as ‘rosettes of carbon in the ferrite. After the process, the small amount of pearlite left has no effect on the properties of the casting. The steel produced in this process has good wear resistance and strength and reasonable toughness. Additives are used to produce spheroidal graphite iron rather than flake graphite iron. Magnesium amounting to 1-2% of the weight of the iron is added in the form of a nickel magnesium alloy of 10-20% magnesium. The alloy is used to prevent an extremely violent reaction from occurring. The presence of silicon also assists the formation of the nodules therefore Ferro-silicon is added. The sulphur level needs to be kept low in order to avoid removing the Mg as sulphide. In the production of a ferritic graphite iron, spheroids of graphite in pearlite matrix are heat treated to form spheroids of graphite in ferrite matrix. This is time dependent process and doesnt go into completion therefore causing pearlite area to still be seen. COPPER-SILVER EUTECTIC ALLOYS On drawing of the 30%Ag70%Cu, alpha particles can be seen and dark patches show primary dendrites outside eutectic. The 50%Ag50%Cu alloy sample also shows primary alpha dendrites outside eutectics. In the 90%Ag10%Cu sample there is small amount of eutectic and light areas show beta particles while the dark areas show alpha particle. On the equilibrium diagram ADB is the liquidus and ACDEB is the solidus. The area ACF represents the alpha phase of the silver in copper while BEG represent the condition of limited solid solution of copper in silver which is the beta phase. Below FCDEG the two phases alpha and beta exist side by side. The 72%Ag28%Cu micro section has an all eutectic composition with dark areas also representing alpha particles and light areas showing beta particles the centre of the microstructure is the first to solidify then the outside area. Composition of solid and liquid phases will vary with the temperature along the solidus and liquidus lines. The final liquid between composition C and E will always end at eutectic regardless of what the initial composition may be. As a result the solid will be composed of masses of A and B. At eutectic CW parts liquidus composition Y while WY parts composition C. During casting its virtually impossible to achieve equilibrium conditions. Coring is the non equilibrium cooling on microstructures. Coring explains how the varying primary dendrites allow lighter areas in the centre than in the outside. The properties of a cored structure are less than optimal, as a casting having a cored structure is reheated causing grain boundaries regions will meet first as long as they are richer in low melting components. The liquid film that separate the grain gives an outcome of sudden loss of mechanical integrity. The melting may begin at a temperature below the equilibrium solidus temperature of the alloys. Homogeneous heat treatment can be used to remove coring at a temperature below the solidus point of the alloy composition. During the process, atomic diffusion occur producing compositionally homogeneous grain. CONCLUSION Cast irons have many different structures each one caused by a different cooling rate, additives and different heat treatments. Formation of grey cast iron over white cast iron is promote by slow cooling rate and enormous silicon content Coring can be eliminated by a homogenising heat treatment. Magnesium and silicon help to produce spheroidal graphite iron rather than flake graphite iron To produce a ferritic spheroidal graphite iron from pearlitic spheroidal graphite iron the steel must be heated to just below the lower critical temperature. Phosphoric iron will enable to cast very fine details and in blackheart malleablising process, rosettes from graphite in ferrite matrix are produced from white cast iron. The composition of the copper silver eutectic alloys has a very large effect on the microstructure of the alloy, with different amounts of the phases being produced on cooling.

Summary Response of the Earth Is Full

In his article, The Earth Is Full, Friedman (2011) begins by stating that in recent years, first decade of 21st century, humanity encounters dangers that threaten humanity and the nature because of their unconcerned behaviors. Economic problems, high growing population rate and natural disasters compel humans to question about those recent years. The writer then moves on to the veteran Australian environmentalist-entrepreneur Paul Gilding and his book, Gilding, P. (2011) The Great Disruption: Why the climate crisis will bring on the end of shopping and the birth of a new world. More Summary of Devil at My HeelsNew York: Bloomsbury Press. Gilding (2011) discusses how much land and water area humanity needs to produce the resources they consume and absorb their waste. According to Gilding (2011), earth is growing at a dangerous rate and points out that over-used resources and worsening ecologic environment damage to social and economic system. Friedman reports the current growth rate is 150 percent of earth’s sustainable capacity and states that excessive use of resources and too much waste that creates the problem, â€Å"The Earth Is Full. He mentions about two loops; first, population growth and global warming push up food prices, which leads to political instability, which leads to higher oil prices, which leads to higher food prices, and so on in a insurmountable circle. Second, higher productivity means fewer jobs, which requires humans to produce more sources to create jobs. The more sources create global warming. Afterwards, the writer turns hi s attention to possible solutions. The solutions are discussed by giving Gilding’s eco-optimist view. In the article, also it is stated that economic systems are not changed without a crisis.Friedman (2011) states that â€Å"But don’t worry, we’re getting there. † Finally, Friedman prefers to use quotations from Gilding who say nations are heading for a crisis-driven choice and develop a new sustainable economic model slowly. Global warming, starvation, worsening ecological environment, exhaustion of resources, too much waste and the conflict between humanity and nature are very current and serious problems of the entire world. In the article these problems are discussed based on the fundamental source of the problems, high population rate. Also, based on Sullivan, M. 1999) Population control: How many are too many? , she states â€Å" Global warming, the thinning of the ozone layer, increasing crime rates, toxic chemicals in our food, and starvation in developing nations, each of which is at least partially due to growing world population† (Sullivan, 1999). According to that paper, there are now 5. 8 billion human beings on the planet now, and according to the United Nations, the population of earth is expected to grow to around 7. 9 billion by 2050. According to statistics, it is clear that growth rate is too much for the earth and causes a huge instability.In the article, Friedman, T. (2011) The Earth Is Full, some economic models are taken in hand as a basis for the solution. However, the damages that high population brings cannot be dispelled only with economic systems. Also, political systems must be developed and humans must be made conscious about all of those problems. †¢Friedman, T. (2011) The earth is full. NYT †¢Gilding, P. (2011) The Great Disruption: Why the climate crisis will bring on the end of shopping and the birth of a new world. New York: Bloomsbury Press. †¢Sullivan, M. (1999) Population c ontrol: How many are

Character Analysis of Mrs Foster Essay

The short story â€Å"The Way up to Heaven† is written by Roald Dahl, who is a British novelist and a short story author. He was born in Wales in 1916. â€Å"The Way up to Heaven† is a story about Mr. and Mrs. Foster â€Å"sad† life. The story takes place on a January of 1950’ in New York City, on East Sixty- second Street. It also takes place on the New York Airport and in Paris. Mrs Foster herself, is an old-fashioned woman who has a fear of missing a train, a plane, a boat etc. If she is in the situation, her eyes will begin to twitch. She likes to wear a fur coat with a black hat on the top of her head. Mrs Foster wants everything to be fast. Her man, Mr Foster, doesn’t likes to be early, but she would never dare to tell him to hurry. The story became complicated when Mrs. Foster’s flight was delayed until eleven o’clock on the next day due to the fog. Mrs. Foster had to go back home again and come back to the airport the next day. In the second conflict Mr. Foster tried to slow her journey to the airport again. Read more: This is water David foster Wallace summary  essay It started when Mr. Foster asked Mrs. Foster to wait in the taxi while he went inside the house again to find the present that he wanted to give to his daughter in Paris. He claimed that he left the present inside the house, whilst he actually had wedged the present down under the seat, which Mrs. Foster had noticed at last when Mr. Foster went looking for it in the house. Mrs. and Mr. Foster have a frigid relationship. It does not look like they love each other. At some point in the story, she changes. Mrs.Foster stopped to listen for the repetition of some sound at the house door. This happened when Mr.Foster pretended to look for the gift and yet left it in the car on purpose. She left the place without waiting for Mr.Foster. As the reader of the story, I sympathize with her. Mr. Foster knew that his wife couldn’t bare the imagination to miss the flight she was going to take to Paris. In one way, he tortures Mrs. Foster. The climax, or the main turning point, of the story is the moment when Mrs Foster freezes at the front door to listen to a sound. She is a completely changed person after that. When she was in Paris she knew her husband is in danger but pretended not to know. Towards the ending of the story, Mrs.Foster will go to check out the elevator and when she returns, she’ll have a glimmer of satisfaction on her face. This shows that she’s happy that her torturous husband, Mr.Foster is no more and she  can return to Paris with her daughter. Even after what she has done, I sympathize with her because she devoted all her life on him but he couldn’t keep her happy.

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