Why Won't a Magnet Stick to a Stainless Steel

Source: NY Times

While some common kinds of stainless steel are not attracted to a magnet, a magnet will stick to some other kinds. The magnetic properties of stainless steel vary from alloy to alloy.

Stainless steel in general has significant amounts of chromium added to iron to improve its corrosion resistance. Depending on the intended use, some types also have varying amounts of nickel added, or other metals, like manganese or molybdenum. Different combinations yield different degrees of different properties, like hardness, stress resistance and malleability.

What is known as 18/8 stainless steel, commonly found in cutlery, has 18 percent chromium and 8 percent nickel added to the iron and does not show magnetic properties at room temperature.

Whether a particular kind of stainless steel can be magnetized by exposure to a magnetic field depends on its crystalline structure, and that structure varies according to the various metallic additions to iron and sometimes according to temperature.

In types of stainless classified as ferromagnetic, the structure allows tiny internal magnetic regions called domains to line up by polarity when exposed to a magnetic field. In types classified as austenitic, this does not happen. The underlying difference is the arrangement of electrons in the inner core of the iron ions.