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The stress-strain behaviour of stainless steel differs from that of carbon steels in a number of respects. The most important difference is in the shape of the stress-strain curve. Whereas carbon steel typically exhibits linear elastic behaviour up to the yield stress and a plateau before strain hardening, stainless steel has a more rounded response with no well-defined yield stress (see Figure).
Stainless steel ‘yield’ strengths are generally quoted in terms of the 0.2% proof strength, i.e. the proof strength at an offset permanent strain of 0.2%.
|Grade||Design strength (N/mm2)||Ultimate tensile strength (N/mm2)||Young’s Modulus (N/mm2)||Elongation (%)|
|304 (1.4301)||210||520||200 000||45|
|316 (1.4401)||220||520||200 000||40|
No limitations on thickness in relation to brittle fracture apply to stainless steel; the limitations for carbon steel are not applicable due to the superior toughness of stainless steel. The austenitic stainless steel grades do not show a ductile-brittle impact strength transition as temperatures are lowered.
Stainless steels can absorb considerable impact without fracturing due to their excellent ductility and their strain-hardening characteristics.
The main reasons for the difference in structural behaviour between carbon and stainless steel members are:
As a result of this, different buckling curves are required from those of carbon steel. This applies to:
Design guidance for structural stainless steel is available (see References).
As the stiffness of stainless steel decreases as the stress level increases, deflections are greater that those for carbon steel members. It is therefore necessary to use a reduced modulus to predict the behaviour of members in which high stresses occur. This is explained in the article Calculating the deflections of stainless steel beams