1.   Steel is hardened by heating it to a very high temperature.

2.   These additives are designed to harden the steel.

3.   Cobalt production, a metal used to harden steel, also suffered from government neglect and looting.

4.   Cobalt production, a metal used to harden steel, has also suffered from government neglect and looting.

5.   The three companies also produce other minerals like zinc, silver, gold and molybdenum, which is used to harden steel.

6.   Molybdenum is a byproduct used for hardening steel, among other industrial uses.

7.   The chemical is a toxic byproduct of chromium, an element that hardens steel and is used in the manufacture of airplanes and other products.