In terms of physical properties, stainless steels show appreciable differences between the various steel types and may also be markedly different from carbon steels.
The austenitic steels generally have a higher density than the other stainless steel types. Within each steel category, density usually increases with an increasing level of alloying elements, particularly heavy elements such as molybdenum.
The elastic modulus is a measure of the stiffness of the steel and is an important parameter in structural design. The true elastic modulus is not obtained from tensile testing, where there are a number of extraneous factors that influence the apparent modulus, but by, for example, ultrasound measurements. The elastic modulus decreases with increasing temperature.
The two important physical properties that show greatest variation between the stainless steel types are thermal expansion and thermal conductivity. These thermal properties are very important considerations in high-temperature applications. Austenitic steels exhibit higher thermal expansion than ferritic grades. Duplex grades show intermediate values, while ferritic grades are similar to carbon steel. Thermal expansion can cause thermal stresses in applications with temperature fluctuations, heat treatment of complete structures, and on welding.
Thermal conductivity for stainless steels is generally lower than for carbon steels and decreases with increasing alloying level for each stainless steel type. A low thermal conductivity is important for retaining heat, for example in building components and food containers.
The electrical resistivity of steels increases with the content of alloying elements and is therefore higher for stainless steels than for carbon steels. The highest values are seen for super-austenitic grades and the lowest for the leanest ferritic grades.
All ferritic, martensitic, and duplex grades are ferromagnetic, while stable austenitic grades are not magnetizable. Even small amounts of ferrite or martensite in an austenitic structure can have an appreciable effect on its magnetic properties and so must be avoided in applications where this is critical, for example cyclotrons and submarines.
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Thermal expansion is the tendency of the stainless steel to change in length in response to a change in temperature.