Sounds like you got hold of some no-lead solder. Your iron goes to about 450C, which is right at the edge of the melting points for some lead-free solders. Look for some 60/40 or 63/37 (tin/lead ratio) solder and you should be back in business.
You may be getting your Fahrenheit and Celsius temperatures mixed up.
The lead free solder we all use here in Europe has a melting point of around 220C. The 63/37 leaded solder has a melting point of 183C which is about the lowest you will ever get.
I use lead free solder all the time and have been doing so for at least the last 10 years like many electronics builders in Europe.
Most of the time my iron is set to around 360C which is commonly the default temperature setting of a lot of temperature controlled irons such as the Hakko FX888 and is quite suitable for soldering with any normal type of flux cored solder designed for electronic use.
The lead-free solder I have and what many in Europe and elsewhere use is quite capable of being used perfectly well at an iron temperature of 300C.
Here is a quote from Wikipedia regarding some lead free alloys:
Tin-silver-copper (Sn-Ag-Cu, or SAC) solders are used by two-thirds of Japanese manufacturers for reflow and wave soldering, and by about 75% of companies for hand soldering. The widespread use of this popular lead-free solder alloy family is based on the reduced melting point of the Sn-Ag-Cu ternary eutectic behavior (217 °C, 423 °F), which is below the 22/78 Sn-Ag (wt.%) eutectic of 221 °C (430 °F) and the 59/41 Sn-Cu eutectic of 227 °C (441 °F).[19] The ternary eutectic behavior of Sn-Ag-Cu and its application for electronics assembly was discovered (and patented) by a team of researchers from Ames Laboratory, Iowa State University, and from Sandia National Laboratories-Albuquerque.
Much recent research has focused on the addition of a fourth element to Sn-Ag-Cu solder, in order to provide compatibility for the reduced cooling rate of solder sphere reflow for assembly of ball grid arrays. Examples of these four-element compositions are 18/64/14/4 tin-silver-copper-zinc (Sn-Ag-Cu-Zn) (melting range 217–220 °C) and 18/64/16/2 tin-silver-copper-manganese (Sn-Ag-Cu-Mn; melting range of 211–215 °C).