The ASTM A-890 Grade 1B (CD4MCuN) is a duplex stainless steel alloy  that is similar to the Grade 1A, but has a controlled nitrogen level 

C - 0.04 max,       Cr - 24.5-26.5,        Ni  - 4.75-6.00, 
Cu - 2.75-3.25,      Mo - 1.7-2.3,          N - 0.10-0.25, 
Mn - 1.00 max,     P -  .040 max,       S - 0.040 max, 
Si - 1.00 max

Controlled nitrogen in the 1B increases the fracture  toughness of the alloy.  But the ultimate tensile strength and yield strength of the baseline grade 1B are too low.

Spuncast  engineers modified the 1B alloy with a proprietary composition change which increased the ultimate strength, yield strength, and % elongation, so that all the mechanical requirements were met.