Update:
Some heavy googling determined this is a proprietary grade, with a duplex structure. Composition is 11.5Cr-1.4Mn-0.8Ni-0.13Ti-0.1Nb-MCN(350ppm). Also, several complex stipulations about Ti and Nb minima. No idea what MCN means (My brain reached acronym saturation back about 2005.)
In the case of 410UF, UF apparently indicates for 'utility ferritic'. [I hope my quest is not 'ultimately futile'.] It appears to be designed for improved weldability and low temperature toughness.
The goal is to weld this with good low temperature impact properties.
Any suggestions for a filler metal and process? Since it is proprietary we are going from first principles (see composition above). Any experience/advice is welcome; this corner of the stainless universe has avoided me and my career until now.