Question 10: The following figure shows some micrographs of various steels havin

Question

Question 10: The following figure shows some micrographs of various steels having the same composition that have been through different processing routes. For each micrograph: (i) Draw a sketch of each outlining the key features. (i) Identify the micrograph explaining your decision (iii) Explain the processing route required (iv) Explain how you think the micrograph developed during processing, and (v) The mechanical properties. (vi Suggest an application. Photo N"-1265 DétecteurSE Micrograph A Micrograph B

Explanation / Answer

The microstructure of crystalline materials is termed as its type, structure, shape and topological arrangement of phases with or without lattice defects.

Micrograph A: The key features are Layered structures formed. It seems to be a microstructure of  two phases: ferrite and cementite with dark regions as cementite and bright regions as ferrite. When an Iron Alloy having 0.77 % Carbon is cooled slowly, there is a transformation from single phase of austenite to pearlite structure as a result, such layered structure is formed. Hence, such layers are formed due to redistribution of Carbon atoms between ferrite and cementite by diffusion. The mechanical properties are between soft and brittle (Eutectoid steel).

Micrograph B:  Hypereutectoid steel (pearlite with network of cementite) is what it seems to be. It is because such tupe of microstructure is achieved when the carbon atoms are rejected in the form of ferrous carbide and the transfromation process of such a microstructure is not slow enough. It is near to hard steel.

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