First of all, you need to install and enable a driver that will allow you to hold the ALT key.

The macro itself works as follows. First, we move the character to the melting point and activate the hotkey that will launch the macro. 

The script itself starts by holding down the ALT key, then right-click to open the melting menu. The next step is to move the mouse to the right to select the desired item, and left–click to start melting. Next, we place the mouse cursor on individual fragments of iron and make a click.

After that, the macro is briefly suspended (the time is set according to the duration of the melting), and then begins its work again, repeating all the above actions. The whole process is repeated until the macro is stopped manually.