AL 29-4C is a superferritic stainless steel, UNS S44735, built around an unusually high 29% chromium and 4% molybdenum content with iron making up the balance. Because it solidifies and stays ferritic (body-centered cubic) rather than austenitic, it does not work-harden the way 300-series stainless does and it is mildly magnetic. What makes the "superferritic" family possible at all is an extremely tight limit on carbon and nitrogen — the interstitial elements that otherwise make high-chromium ferritic stainless brittle and prone to sensitization at the grain boundaries, especially near a weld. By keeping carbon and nitrogen very low, AL 29-4C retains enough toughness and weldability to be used as mill-annealed sheet, tube, and plate rather than just a cast or coarse-grained product.

The payoff for that alloy content is corrosion resistance that rivals or exceeds many high-nickel austenitic and superaustenitic grades, particularly against chloride pitting and crevice attack, without the nickel cost. That combination makes AL 29-4C a standard choice for seawater-cooled condenser and heat exchanger tubing, brackish and salt water piping, and other chloride-heavy service in power generation and chemical processing where 316 or even 6-Mo superaustenitics would eventually pit.

Only the UNS designation could be verified against current standards; other cross-references were not confirmed and are omitted rather than guessed.

Carbon and nitrogen are held to very low "low-interstitial" limits by design — this is what gives the alloy its weldability and toughness despite the very high chromium and molybdenum content.

Because AL 29-4C is ferritic rather than austenitic, it does not work-harden as aggressively as 304, 316, or the 6-Mo superaustenitics, and its chip tends to be somewhat more manageable. That said, this is still a very high-alloy stainless — nearly 30% chromium plus 4% molybdenum — and high total alloy content drives up cutting forces and abrasive tool wear regardless of crystal structure. Expect gummy chip flow and a tendency to smear rather than shear cleanly if the edge is dull or the feed is too light, similar to what you'd see machining a high-alloy austenitic grade.

Low thermal conductivity is also a factor here, as it is with most stainless: heat concentrates at the cutting edge instead of dissipating into the chip, so coolant and a sharp, positive-rake geometry matter more than they would on a plain carbon or low-alloy steel. Keep feeds firm enough to cut underneath any work-hardened or smeared skin left by the previous pass, and favor a wear-resistant coated grade to handle the abrasive wear from the high chromium-molybdenum content.

Values assume favorable conditions: a well-matched insert grade, rigid tool and workpiece clamping, good raw material quality, short tool overhang, and adequate coolant.

Turning

Parting / Grooving

Milling