At around 775 degree C the crystal structure of steel undergoes a transformation

Question

At around 775 degree C the crystal structure of steel undergoes a transformation on heating from a body centred cubic structure (atom packing density, 68.02% of available space filled) to a face centred cubic structure (atom packing density, 74.05% of available space filled). From the following list, choose the correct observation and reason for that observation as the metal is heated through the transformation temperature. Which of the following is true: Work Hardening increases the elastic modulus of a metal. Which of these features of a material has the greatest influence on its elastic modulus?

Explanation / Answer

1 (e) it decreses with increase in temperature.

2(b) if you have smaller grain boundary then there is lesser movement of dislocation.

3(b) False , because hardening changes the shape of the stress strain curve by increasing the elastic region and decreasing the plastic region. The slope in the elastic region (Young's modulus) remains the same in both cases. To generate a strain hardened stress-strain diagram you essentially draw a line parallel to the elastic region

4(d) Elastic modulus is an intrinsic material property and fundamentally related to atomic bonding.

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