Effect of Carbon on the Physical Properties of Steel

In general, as the carbon content increases the hardness of the steel also increases. The tensile strength and the yield strength also increase to about 0.83 % carbon. Thereafter, they level out. This is shown in Figure1.

Figure 1. Effect of carbon on hardness, tensile strength and yield strength of steels.

The tensile strength and hardness are affected as the ratio of ferrite to cementite in the structure of steel changes. As the percentage of pearlite increases in the hypoeutectoid steels, the tensile strength increases. The hardness does not increase dramatically. The hypereutectoid steels show only a slight increase in strength as the cementite-to-ferrite ratio increases.

The elongation and the reduction in area represent how ductile or brittle a material is. Figure 2 indicates the effect of carbon on the ductility and impact resistance (toughness) of steels. The elongation and the reduction in area drop sharply with increase in carbon content, going almost to zero at about 1.5 % carbon. This indicates that the carbon content of 1.5 % or more will cause high brittleness. The impact resistance also decreases very sharply up to about 0.83 % carbon and then levels out.

Figure 2. Effect of carbon on the impact resistance and ductility of steels.


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Last update: March 15, 1999

By: Serdar Z. Elgun