About 400|Monel 400 (67% nickel, 30% copper). One of the few alloys resistant to both hydrofluoric acid and seawater. Tough, corrosion-resistant, and difficult to machine. Work-hardens aggressively. Produces long, stringy chips that wrap around everything. Use sharp coated carbide, rigid setups, aggressive feeds, and flood coolant at 10%+ concentration. Don't let the tool dwell or rub. Used for marine hardware, chemical processing, oil and gas components, and anywhere you need to handle both acids and seawater. Expensive. Compare to 316 stainless (much cheaper, adequate for mild marine environments) and Inconel
625 (better at high temperatures).