It is quite remarkable that only 16, plus a few rare earth elements (REE), of the hundred or so elements in the periodic table can be combined in many subtle ways to produce the common steel alloys (carbon steels, stainless steels and low alloy steels).
A glance at the periodic table shows that these elements fall into two main groups.
The light nonmetallic (B, C and N) and semi metallic elements (Al and Si) are in periods 2 and 3 of the table.
The remaining heavier alloying metallic are all close together in periods 4, 5 and 6.
Ref. (with minor changes), The alloy tree, J. C. M. Farrar
