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If a low-carbon steel is only stressed to some point between the upper and lower yield point then the surface develops Lüder bands. [7] Low-carbon steels contain less carbon than other steels and are easier to cold-form, making them easier to handle. [3] Typical applications of low carbon steel are car parts, pipes, construction, and food cans ...
[1]: 58 For example, low-carbon steel generally exhibits a very linear stress–strain relationship up to a well-defined yield point. The linear portion of the curve is the elastic region, and the slope of this region is the modulus of elasticity or Young's modulus .
In one study, strain hardening exponent values extracted from tensile data from 58 steel pipes from natural gas pipelines were found to range from 0.08 to 0.25, [1] with the lower end of the range dominated by high-strength low alloy steels and the upper end of the range mostly normalized steels.
Steel may be work hardened by deformation at low temperature, called cold working. Typically, an increase in cold work results in a decrease in the strain hardening exponent [citation needed]. Similarly, high strength steels tend to exhibit a lower strain hardening exponent [citation needed].
This causes carbon to diffuse into the surface of the steel. The depth of this high carbon layer depends on the exposure time, but 0.5mm is a typical case depth. Once this has been done the steel must be heated and quenched to harden this higher carbon 'skin'. Below this skin, the steel core will remain soft due to its low carbon content.
Steel with a high carbon content will reach a much harder state than steel with a low carbon content. Likewise, tempering high-carbon steel to a certain temperature will produce steel that is considerably harder than low-carbon steel that is tempered at the same temperature. The amount of time held at the tempering temperature also has an effect.
In this state, the crack will propagate by successive cleavage of the grains. At these low temperatures, the yield strength is high, but the fracture strain and crack tip radius of curvature are low, leading to a low toughness. [8] At higher temperatures, the yield strength decreases, and leads to the formation of the plastic zone.
Lüders bands are a type of plastic bands, slip band or stretcher-strain mark which are formed due to localized bands of plastic deformation in metals experiencing tensile stresses, common to low-carbon steels and certain Al-Mg alloys. [1]