Gas-metal interactions
Gases other than hydrogen in iron and steel

In this article, when writing chemical reactions, the state of a constituent will be indicated using the following symbols:

< > : solid state.

The allotropic variety can be indicated as an index.

For example, _α represents α-iron, cubic-centered. Under these conditions, the standard state of iron is pure iron in its α structure.

( ): liquid state.

The standard state is then the pure liquid element.

[ ]: state dissolved in a solvent which, unless otherwise indicated, is the iron whose state is indicated in the subscript.

For example, [N] _γ represents nitrogen dissolved in γ-iron,...