Question

Provide a sketch of how the tensile strength and the hardness of a simple Fe-C alloy changes as the carbon content is varied. Details the reasons behind the responses that you have sketched – ensuring you relate these to the relevant diagrams.

Answer 1

As the carbon content increases more and more atoms go into interstitial sites. Plastic deformation happens by mivement of sislocations. The strength of a material increases if it's resistance to dislocation movements is high. So interstitial carbon atoms act as barrier to dislocation movements and hence strength and hardness increases. Based on the carbon content steels are classified as low carbon steel (up to 0.3 wt%C), medium carbon steel with carbon content between 0.3 to 0.55 wt% and high carbon steel with 0.56 to 0.9 wt%C.

Please see the attached figures for understanding the trends of hardness and strength with carbon content