Choosing the Right Stainless Steel
There are over 150 grades of stainless steel. In practice, you’ll use about five of them 90% of the time. This guide covers those five — when to use each, what to watch out for, and the trade-offs between them.
The Big Five — Quick Comparison
| Property | 304 | 316 | 303 | 410 | 17-4 PH |
|---|---|---|---|---|---|
| Family | Austenitic | Austenitic | Austenitic | Martensitic | Precipitation Hardened |
| Tensile (ksi) | 75 | 75 | 75 | 65 (annealed) / 145 (HT) | 190 (H900) |
| Hardness | ~80 HRB | ~79 HRB | ~96 HRB | ~41 HRC (HT) | ~44 HRC (H900) |
| Magnetic? | Slightly | Slightly | Slightly | Yes | Yes |
| Machinability | Poor | Poor | Excellent | Good | Fair |
| Weldability | Good | Good | Poor | Fair | Fair |
| Corrosion | Good | Excellent | Fair | Moderate | Good |
| Heat Treatable? | No | No | No | Yes | Yes |
| Cost | $$ | $$$ | $$ | $ | $$$$ |
304 — The Standard
Also called “18-8” (18% chromium, 8% nickel). The most widely used stainless steel in the world. If someone says “stainless” without specifying, they probably mean 304.
- Kitchen equipment, food processing, brewing
- Architectural trim, railings, enclosures
- Chemical containers (mild chemicals)
- General industrial applications
Watch out: Susceptible to chloride stress corrosion cracking. Don’t use near saltwater or pool chemicals without upgrading to 316.
304L = low carbon version. Better weldability (less carbide precipitation in the heat-affected zone). Specify 304L for anything that’ll be welded.
316 — Marine Grade
Same as 304 but with 2–3% molybdenum added. The moly dramatically improves resistance to chloride pitting and crevice corrosion.
- Marine hardware, boat fittings
- Medical implants and surgical instruments
- Pharmaceutical and chemical processing
- Coastal architecture (handrails, fasteners)
Rule of thumb: If there’s any chance of saltwater, chlorine, or aggressive chemicals → use 316. The price premium over 304 is small compared to replacing corroded parts.
303 — The Machinist’s Friend
Free-machining version of 304. Sulfur is added to create manganese sulfide inclusions that act as chip-breakers. Machines beautifully on a lathe or screw machine.
- Screw machine products (shafts, pins, fittings)
- High-volume CNC turned parts
- Any stainless part where machinability beats corrosion resistance
Trade-offs: The sulfur that makes it machinable also reduces corrosion resistance and makes it essentially unweldable. Never specify 303 for welded assemblies.
410 — Hard Stainless
Martensitic — meaning it can be heat-treated to high hardness like carbon steel, but with moderate corrosion resistance. It’s magnetic, unlike the 300 series.
- Pump shafts and valve components
- Cutlery and kitchen knives
- Turbine blades
- Fasteners that need both hardness and some corrosion resistance
Note: 420 is similar but with more carbon (higher hardness, less corrosion resistance). 440C goes even further — razor blades and high-end knives.
17-4 PH — Aerospace Strength
Precipitation-hardened stainless. Heat treat it at relatively low temperatures (900–1150°F) and it reaches tensile strengths up to 190 ksi — competitive with high-strength alloy steels, but with stainless corrosion resistance.
- Aerospace components
- Oil and gas equipment
- High-strength shafts and gears in corrosive environments
- Nuclear components
Condition H900 = highest strength (aged at 900°F). H1150 = best toughness (aged at 1150°F).
Stainless Steel Families
| Family | Series | Key Feature | Magnetic? | Heat Treatable? |
|---|---|---|---|---|
| Austenitic | 300 | Most corrosion resistant, most common | Slightly (after cold work) | No |
| Ferritic | 400 (some) | Cheaper, magnetic, good formability | Yes | No |
| Martensitic | 400 (some) | Hardenable, moderate corrosion | Yes | Yes |
| Precipitation Hardened | 17-4, 15-5, etc. | Highest strength stainless | Yes | Yes |
| Duplex | 2205, 2507 | Best of austenitic + ferritic | Yes | No |
Related: Galvanic Compatibility | Machinability Ratings | Steel Equivalent Grades