1. Basic Composition

• Stainless Steel

• Primary Components: Iron (Fe) as the base, with chromium (Cr ≥ 10.5%), nickel (Ni), molybdenum (Mo), etc.

• Common Grades: 304 (18% Cr, 8% Ni), 316 (16% Cr, 10% Ni, 2% Mo), duplex steel 2205 (22% Cr, 5% Ni).

• Key Feature: Chromium forms a protective oxide layer for rust resistance; nickel enhances corrosion resistance in some grades.

• Nickel Alloys

• Primary Components: Nickel (Ni ≥ 50%) as the base, with chromium (Cr), molybdenum (Mo), cobalt (Co), etc.

• Common Grades: Inconel 625 (58% Ni, 22% Cr, 9% Mo), Hastelloy C276 (54% Ni, 16% Mo, 15% Cr).

• Key Feature: High nickel content ensures stability in extreme environments.

2. Corrosion Resistance

• Stainless Steel

• Suitable for mild corrosive environments (e.g., freshwater, atmosphere, weak acids).

• Prone to pitting corrosion in chloride-rich environments (e.g., 316 stainless steel in seawater).

• Nickel Alloys

• Resistant to strong acids, alkalis, and high-temperature/high-pressure corrosion (e.g., sulfuric acid, hydrochloric acid, hydrogen sulfide).

• Excellent resistance to chloride-induced stress corrosion cracking (e.g., Hastelloy in chemical reactors).

3. High-Temperature Performance

• Stainless Steel

• Austenitic grades (e.g., 310S) withstand temperatures up to 800–900°C but degrade over time due to oxidation and reduced strength.

• Martensitic grades (e.g., 410) perform poorly at high temperatures.

• Nickel Alloys

• Operate above 1000°C (e.g., Inconel 718 in jet engine turbine blades).

• Retain high strength, oxidation resistance, and creep resistance at elevated temperatures.

4. Mechanical Properties

• Stainless Steel

• Moderate strength: Austenitic grades yield ~200–300 MPa; duplex steels reach up to 500 MPa.

• Good low-temperature toughness (e.g., 304 in liquid nitrogen equipment).

• Nickel Alloys

• High strength and fatigue resistance (e.g., Inconel 625 with a yield strength of 500–800 MPa).

• Superior creep resistance under prolonged high-temperature stress.

5. Cost and Processability

• Stainless Steel

• Lower cost: Raw material prices are 1/3–1/5 of nickel alloys.

• Easier processing: Suitable for stamping, welding (e.g., 304 sheets for kitchenware).

• Nickel Alloys

• Higher cost: Expensive raw materials and energy-intensive processing (e.g., Hastelloy tubing costs 5–10× more than stainless steel).

• Difficult processing: Requires specialized tools and controlled welding (e.g., preheating, inert gas shielding).

6. Applications

• Stainless Steel

• Construction (structural components, façades), food processing (tanks, cutlery), medical tools.

• General corrosion resistance (e.g., water treatment pipelines).

• Nickel Alloys

• Aerospace (engine parts), nuclear power (reactor internals), deep-sea oil drilling (high-pressure corrosive environments).

• Critical components in extreme conditions (e.g., heating coils in chemical reactors).

Summary: How to Choose?

• Choose stainless steel for mild environments, budget constraints, or complex fabrication needs (e.g., kitchen sinks, railings).

• Choose nickel alloys for extreme temperatures/corrosion, high strength, or mission-critical longevity (e.g., rocket nozzles, chemical reactors).