Abstract
The form of the stress-strain currve of grey cast iron is influenced by its microstructure. The relationship between stress and strain is given by
σ=bε/(ε+a)
where σ is stress in kg/mm2, ε strain in %, a and b proportional factors. The factors a and b can be experimentally obtained from the stress-strain curve. For example, if iron has A type graphite structuctre, both a and b are of large value and the stress increases proportionally with increasing the strain. The iron has a balanced property of elongation and tensile strength. In the case of iron having fine graphite structure, a becomes smaller, while b becomes larger. Hence, the stress is greatly increased with increasing the strain. This means that the iron is of low elongation and high strength.
If iron has ferritic matrix, both a and b are small. In this case, the stress-strain curve is not linear but remarkedly curyed. The iron is characterized by its low strength and high elongation.
