Lead-free alloys usually have higher solidus and liquidus temperatures than does tin-lead solder. This means one must solder at higher temperatures; the exact temperature, of course, depends upon the alloy chosen but in general the operating temperature will be higher than that used with tin/lead - as much as 30°C. in some cases. Also, lead-free alloys do not wet as well as tin/lead, and thus require the use of more active, or corrosive, fluxes. Because of these characteristics, the time required to form a good joint may be slightly longer than with tin-lead solder.
Note that the better thermal recovery your station has, the lower you can set the soldering temperature; and the larger the tip, the less will be the heat loss. These are always true, of course, and I do not mean always use a big huge tip, but do use the largest tip commensurate with the size of the joint being soldered.