403Cb+ is a further evolution of the niobium-stabilized 403Cb line, built for turbine components that need to hold their strength at higher operating temperatures and for longer service lives than plain 403Cb can manage. On top of the base 11% chromium martensitic structure, this grade adds molybdenum and vanadium for elevated-temperature strength and creep resistance, plus a small nitrogen addition that works alongside the niobium to refine and stabilize the carbide/nitride precipitates that carry the alloy's high-temperature performance.

That combination pushes the practical service temperature for this grade up toward 580°C (roughly 1075°F), which is well beyond what a plain 12% Cr martensitic stainless like 403 or 410 can sustain without excessive creep. It's a specification-driven material used almost exclusively for steam and gas turbine blading and closely related high-stress, high-temperature rotating components — not a general machine shop stock item — and it's typically supplied and machined in the quenched-and-tempered condition needed to develop its full strength.

403Cb+ machines noticeably harder than the base 403Cb grade — higher carbon, plus the vanadium and additional niobium content, add more fine carbide and carbonitride precipitate for the tool to work through, and this alloy is typically supplied at a higher strength level to suit its turbine-blading role. Cutting forces and heat generation both run higher, closer to what you'd see machining a mid-alloy martensitic stainless like 431 than a plain, softer 12% Cr grade.

A tough, wear-resistant carbide grade with a coating suited to elevated cutting temperatures generally outperforms a sharp, lightly honed edge on this material, since the priority is resisting abrasive flank wear rather than minimizing work hardening. Rigid setups, conservative feed rates, and adequate coolant for heat control matter more here than on the softer, lower-carbon stainless grades on this site.