Specifying a corrosion resistant alloy without matching it to the environment your part will see is one of the most common, and most expensive, material selection mistakes. Corrosion resistance covers a whole category of behavior, and the alloy that holds up in a humid warehouse will fail fast in a marine or chemical environment. This guide breaks down the corrosion resistant alloys engineers reach for most often for CNC machined and fabricated parts, what each one resists, and where each one falls short.
Stainless steel, 300 series
304 stainless is the default for a reason. It resists general atmospheric corrosion and most everyday chemical exposure at a reasonable cost. It is not chloride-resistant. Coastal environments, de-icing salt, or chlorinated water will pit 304 over time. 316 stainless adds molybdenum specifically to resist chloride pitting, making it the standard upgrade for marine hardware, medical devices, and food processing equipment that sees regular washdown. For fabricated parts, our comparison of mild steel vs. stainless steel covers when stainless is worth the upgrade at all.
Duplex stainless steel
Duplex grades combine austenitic and ferritic microstructures, giving them higher strength than standard 300 series stainless along with strong resistance to chloride stress corrosion cracking. They cost more and machine harder, so duplex earns its place on parts where 316 isn’t holding up rather than as a default upgrade.
Nickel alloys
Inconel and Hastelloy sit at the top of the corrosion resistance range, built for high temperature, high pressure, or aggressive chemical environments: aerospace exhaust components, chemical processing equipment, and applications where standard stainless doesn’t survive. They also cost significantly more and machine slower, so specifying a nickel alloy where 316 would do is an expensive mistake in the other direction. Our guide to Inconel 718 machining covers what drives that cost.
Aluminum
Aluminum resists corrosion through a natural oxide layer, and anodizing thickens that layer for additional protection. It’s a strong, lightweight option for general atmospheric exposure, but it needs the right alloy and coating before it goes into chloride-heavy, strongly acidic, or alkaline environments.
Titanium
Titanium resists corrosion across an unusually wide range of environments, including seawater and many acids, at roughly half the density of stainless steel. The tradeoff is cost and machinability. Titanium is the right call when weight and corrosion resistance both matter enough to justify the price, with medical implants and aerospace fittings as the clearest examples. See aluminum vs. titanium for machined parts for a side-by-side.
Matching the alloy to the environment
The short version: general atmospheric exposure rarely needs more than 304. Anything touching saltwater, chlorine, or regular washdown should move to 316 as the floor. High-temperature or aggressive chemical environments call for nickel alloys. Weight-critical, corrosion-critical applications point toward titanium. Defaulting to whatever the last part used is how buyers end up overpaying for capability they don’t need or under-speccing a part that fails in the field. The CNC machining materials guide covers the full range of grades.
Send us the drawings with your application details and we’ll help you land on the alloy that fits the environment, rather than the one that’s easiest to quote.
Frequently asked questions
It depends on the environment. Nickel alloys like Hastelloy handle the most aggressive chemical and high-temperature conditions. Titanium resists seawater and many acids across a wide range. For most atmospheric and washdown applications, 316 stainless is enough.
316 adds molybdenum, which improves resistance to chloride pitting. Use 316 for saltwater, chlorine, and regular washdown. 304 is fine for general atmospheric exposure at a lower cost.
Yes, in general atmospheric conditions, thanks to its natural oxide layer. Anodizing adds protection. In chloride-heavy, acidic, or alkaline environments it needs the right alloy and coating.
When weight and corrosion resistance both matter, often yes. When only corrosion resistance matters, 316 stainless or a nickel alloy is usually the more economical choice.
