Comparison of structural design in stainless steel and carbon steel
Stress-strain behaviour of carbon steel and stainless steel
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%.
Comparison of mechanical properties for stainless steel and carbon steel
||Design strength (N/mm2)
||Ultimate tensile strength (N/mm2)
||Young’s Modulus (N/mm2)
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.
Comparison of structural behaviour of stainless steel and carbon steel members
The main reasons for the difference in structural behaviour between carbon and stainless steel members are:
- The stress-strain curve for stainless steel departs from linearity at a much lower stress than that for carbon steels
- Stainless steels have greater ductility and a greater capacity for work hardening than carbon steels
- The material modulus of stainless steels reduces with increasing stress, unlike that of carbon steels which is constant
- The residual stresses arising from fabrication are higher in stainless steel than in carbon steels.
As a result of this, different buckling curves are required from those of carbon steel. This applies to:
- local, (plate), buckling for elements in compression
- flexural, torsional, torsional-flexural buckling for members subject to axial compression
- lateral-torsional buckling for beams with unrestrained compression flanges
Design guidance for structural stainless steel is available (see References).
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Estimation of deflections
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
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