Low carbon steel is a plastic material. The elastic modulus, proportional limit and yield limit in compression are almost the same as those in tension. After the yield limit, the specimens become flatter and flatter, and the compressive strength increases continuously until they are pressed into cakes.

The compression curve of low carbon steel also has obvious yield point, but the yield stage of the sample is much shorter than that of tension, and the plastic deformation becomes larger and larger after entering the strengthening stage, and the deformation near the end face is limited by the triaxial stress state, so the deformation of the sample is drum-shaped.

Cast iron is a brittle material. When compressed, the sample will be dislocated along the inclined section with an inclination angle of 50 ~ 55 degrees from the axis. This failure is caused by shear force.

When cast iron is compressed, there is no influence of tensile stress. With the increase of load, the maximum shear stress of 45 section can be continuously increased, resulting in obvious plastic deformation, which makes the compression curve more curved than the tensile curve.

Extended data:

The annealed structure of low carbon steel is ferrite and a little pearlite, with low strength and hardness and good plasticity and toughness. Therefore, it has good cold formability and can be cold formed by crimping, bending and stamping. This steel also has good weldability.

Low carbon steel has a great aging tendency, including quenching aging tendency and deformation aging tendency. When steel is rapidly cooled from high temperature, carbon and nitrogen in ferrite are in supersaturated state, and iron, carbon and nitrogen can be slowly formed at room temperature, so the strength and hardness of steel are improved, while plasticity and toughness are reduced.

Low carbon steel is limited in use because of its low strength. The strength of carbon steel can be greatly improved by appropriately increasing the manganese content in carbon steel and adding trace alloying elements such as vanadium, titanium and niobium. If the carbon content in steel is reduced and a small amount of aluminum, boron and carbide forming elements are added, ultra-low carbon bainite with high strength, good plasticity and toughness can be obtained.

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