Hastelloy is Haynes International's trademarked family of nickel-based corrosion-resistant superalloys, developed to withstand chemical environments aggressive enough to eat through standard stainless steels — strong acids, chloride-bearing solutions, and both oxidizing and reducing media found in chemical processing, pollution-control equipment, and pharmaceutical manufacturing. Hastelloy B was the original member of the molybdenum-rich B-family, built around a nickel-molybdenum composition (roughly 26-30% Mo, with the balance nickel) that gives it exceptional resistance to hydrochloric acid and other strongly reducing acids across a wide concentration and temperature range, an environment where chromium-bearing alloys actually perform worse because the passive oxide layer that protects them elsewhere breaks down.

Unlike the chromium-containing C-family grades, Hastelloy B carries almost no chromium at all — that's intentional, since chromium adds little value against reducing acids and can even promote localized attack in this specific service. The tradeoff is that Hastelloy B is not well suited to oxidizing conditions (nitric acid, oxidizing salts, or aerated solutions), where it's outperformed by the C-family alloys. Original-composition Hastelloy B has largely been superseded in new construction by the lower-carbon, more weld-stable Hastelloy B-2, but B-composition stock still appears in legacy piping, valves, and reactor components that shops are asked to service or replace.

Hastelloy B is one of the more demanding materials a shop will put through a spindle. Its very low thermal conductivity means the heat generated in the cut has nowhere to go except into the tool's cutting edge instead of spreading through the chip and workpiece, so edge temperatures climb fast even at modest cutting speeds. The alloy also work-hardens aggressively under the tool — any rubbing, dwelling, or light finishing pass leaves a hardened skin that makes the next pass harder to start cleanly, which is why feed rates need to stay high enough to consistently cut beneath the layer worked by the previous pass rather than riding on top of it.

On top of the heat and work-hardening, this alloy has a strong tendency to gall and weld itself to the tool surface, building up on the cutting edge and tearing rather than shearing cleanly. That combination calls for rigid setups with minimal deflection, sharp positive-rake carbide geometries that keep cutting forces down, and coatings selected for hot hardness and resistance to adhesion rather than raw abrasion resistance. Cutting speeds need to stay low to moderate compared with steel or stainless, and tool paths that favor a steady chip load over light skimming cuts will get noticeably better tool life and surface finish.