What is replacement soldering iron for

This complete replacement iron assembly includes cord and conical soldering iron tip. The handpiece and tips are designed to enable rapid heat recovery required for Lead Free soldering
http://www.cross-mark.com/replacement-soldering-iron-p-1784.html

Some of the fluxes used for soldering are acid based. So they will eventually eat up the electrical element of the soldering iron. Many irons come with a replaceable heating element for when the original is no longer usable.