Hastelloy is Haynes International's trademarked family of nickel-based corrosion-resistant superalloys, developed for chemical environments aggressive enough to attack standard stainless steels — strong acids, chlorides, and both oxidizing and reducing media used across chemical processing, pollution control, and pharmaceutical equipment. Hastelloy G takes a different chemistry path than the B and C families: it's built on a nickel-iron-chromium base — roughly 46% nickel, 22% chromium, and a substantial 20% iron — with molybdenum and a deliberate copper addition rather than the very high molybdenum content that defines the B-family.

That copper addition is the key to G's specialty: it gives the alloy strong resistance to sulfuric acid across a wide range of concentrations, along with good performance in phosphoric acid service — two of the most corrosive, widely handled process acids in fertilizer production and chemical manufacturing. The high iron content also makes G more cost-effective than the leaner, higher-nickel B and C grades while still holding up to hot, contaminated acid mixtures containing chlorides and oxidizing agents that would attack straight stainless steel. It's a common choice for pickling equipment, sulfuric acid piping, and fertilizer processing components.

Hastelloy G is demanding to machine, though its higher iron content makes it marginally more forgiving than the leaner, higher-nickel B and C grades. Thermal conductivity is still very low compared with steel, so heat generated in the cut concentrates at the cutting edge rather than clearing out in the chip, driving up tool temperatures even at modest cutting speeds. The alloy work-hardens under light or dwelling cuts, leaving a hardened layer behind the tool that resists the next pass — feed rates need to stay generous enough to consistently cut beneath that layer rather than skate across it.

G also tends to gall and adhere to the tool surface rather than shearing cleanly, producing built-up edge and accelerated flank wear when the tooling isn't well matched to the material. Rigid, low-deflection setups, sharp positive-rake carbide geometry to minimize cutting forces, and coatings selected for hot hardness and resistance to adhesion all pay off in tool life. Cutting speeds should stay low to moderate relative to steel, and a steady, adequate feed — rather than light finishing passes — keeps the cut productive and reduces work-hardening between passes.