What makes stainless steel non-magnetic whereas ordinary steel and iron are magnetic?
S.P.S. JAIN
Greater Noida, Uttar Pradesh
We have to first understand how magnetic fields are generated around
magnetic metals to answer this question. We know that within each atom,
electrons spin on their axis that, in turn, causes magnetic field around
them. Some electrons spin clockwise, some counter-clockwise. Generally
they are paired so that the magnetic fields are cancelled. Iron which is
a magnetic substance has three unpaired electrons. Each electron
generates a magnetic field of its own.
If all the fields pull in the same direction then you have a magnet. In
other words, the magnetic fields are aligned in a magnet. In the case of
stainless steel, there are several types of them. In general they are
made of iron (Fe), carbon (C), and about 10 per cent chromium (Cr). Some
contain Nickel (Ni).
But other metals are added to obtain different properties. As stainless
steel contains iron, a magnetic metal, one it would seem that it would
be magnetic. However, when nickel (Ni) is added to stainless steel the
result is a non-magnetic form of stainless steel, called austenitic
stainless steel. At the atomic level, all the iron atoms act as mini
magnets that are aligned in the same direction.
The net effect of this is that collectively the magnetic properties of
all the iron atoms add up to produce the overall magnetisation of the
material. This is known as ferromagnetism. But the addition of other
elements to iron changes the properties. For instance, when chromium and
nickel are added, the arrangement of atoms changes completely and this,
in turn, affects the magnetic properties of iron. The nickel and
chromium that are added to iron tend to cancel the magnetic fields and
the net outcome is that stainless steel becomes a non-magnetic
substance.
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