(d) If reflected light optical microscopy were used to confirm the formation of martensite (e.g., lath type or plate typ

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D If Reflected Light Optical Microscopy Were Used To Confirm The Formation Of Martensite E G Lath Type Or Plate Typ 1 (53.81 KiB) Viewed 10 times

(d) If reflected light optical microscopy were used to confirm the formation of martensite (e.g., lath type or plate type or mixed) a sample of the steel in part (c) would be polished flat to a sub-micron surface finish, etched with sodium bisulfate solution and examined. (1) Explain the reason for the polishing and etching steps during sample preparation. [2 marks] (ii) Typically what type of objective lens would you need to use in terms both magnification and numerical aperture, in order to observe the fine martensitic microstructure? [2 marks] (iii) Depending on the exact martensitic microstructure, a variety of defects could be observed such as dislocations and twins. Describe the general form of both these defects and indicate how they might be formed. [3 marks] (iv) If not all the austenite had transformed to martensite, using an additional technique, how could you determine the crystallographic orientation relationship (i.e. the orientation of one crystal lattice relative to another) between the retained austenite and the martensite? [2 marks]