The tensile curve of mild steel is: first, an inclined straight line (proportionality limit), then a section of the curve to the top (yield limit) after a downward inflection, followed by an upward curve and cut-off (strength limit, at which time the material breaks open). That is, first, according to the law of elastic deformation, to the yield limit after the material has strengthened (metamorphic hardening), and ultimately fracture.
The cast iron tensile curve is an inclined straight line in the first part and a curve with a larger slope in the second part, and there is no inflection point.
From the tensile test analysis, mild steel has a better plasticity, there is a significant yield point, high elongation and section shrinkage, material fracture before the occurrence of large plastic deformation. Cast iron, on the other hand, does not have these advantages.
From the compression side, similar to the tensile side, mild steel compression stress is too large will also occur first yield, stress and then increase, will start from the edge of the crack, but still with the center part of the connection; and cast iron compression stress is too large, it will be the whole broken, and there is no plastic deformation between the existence of.
Mild steel is mostly used in the need for deformation, machining, welding, such as pipe, plate, bar manufacturing important machine parts; cast iron is mostly used in machine seats, lower pressure pipelines, etc..
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