Question

Cast iron just like steel has wide applications. It is an alloy with carbon content in excess of about 2%C (usually between 2.5 and 4.3%C) and Si content in excess of 0.5%. The microstructure of cast iron after solidification influences the final properties of the casting From the iron carbon phase diagram above answer the following questions: a) Calculate the volume fraction of ledeburite (eutectic component) present in the alloy containing 3%C after solidification under: i) equilibrium conditions ii) fully non-equilibrium conditions b) What is the average composition of liquid and solid under both conditions in 1(a) above in a 3%C alloy at 1 148°C + T c) The strength of an eutectic alloy depends on the interlamellar spacing between the two phases. Can you reduce the interlamellar spacing to increase the strength of eutectic alloy by adding grain refiners? d) Distinguish between the thermal dendrites and dendrites formed during constitutional supercooling?

Answer 1

Ledeburite is cutectic component in which generally > 43% of carbon contain at eutectic condition. at more than 43 % c cementite and tedeburite and more than 24% carbon contains Austenitr + ledeburite commutative volume fraction of ledebunite equilibrium condition: = 6.7 - 3/6.7 - 2 = 0.7872 Fully non - equilibrium conditions: = 6.7 - 3/6.7 - 0.8 = 0.6271 Grain refinement gives better homogeneity, susceptibility to hot cracking is reduced and mechanical properties are improved significantly. By reducing the size primarily grain grain refiner to cutectic alloy significantly refine coarse dendrites to fine equated dendrites Thermal dedrite constitutive It involves nucleation state where creation of surface or interface of surface bet embryo and liquid environment involve activation energy barner constitutive supercoding arists because of the segregation on alloying elements ahead the solid - liquid front