Unionmelt 80 is a flux

For 1-1/4 Chrome / 1/2 moly I would use ESAb's Spoolarc U515 with either  Unionmelt 80, 709-5 or 429 flux depending on what the requirements are; price, mechanicals and joint configuration. For example if a High Toughnes is required use the Unionmelt 709-5 flux.