Altering can also change the properties of steel without applying a lot of heat. For example, cold-worked steel is made stronger through a work-hardening process. Work hardening occurs when metals undergo plastic deformation. This can be done intentionally by hammering, rolling or drawing the metal. Work hardening can also occur unintentionally during machining if the cutting tool or work piece becomes too hot. Cold working can also improve the machine ability of steel. Mild steel is very suitable for cold working.