Low carbon steel is a ductile material. The stress-strain curve during stretching is mainly divided into four stages: elastic stage, yield stage, strengthening stage, and local deformation stage. There are obvious yielding and necking phenomena in the local deformation stage. At the beginning, it is the elastic stage, fully following Hooke's law and rising in a straight line. After the proportional limit, the deformation accelerates, but there is no obvious yield stage.