SUS630 (martensitic precipitation-hardening stainless steel) and 201 (austenitic stainless steel) differ significantly in material type, properties, and application scenarios. SUS630 focuses on high strength, while 201 emphasizes low cost and basic corrosion resistance.
1. Material and Strengthening Method
* SUS630: Martensitic precipitation-hardening type, contains copper and niobium, requires “solution + aging” heat treatment to achieve high strength.
* 201: Austenitic type, manganese substitutes for nickel (Ni 3.5–5.5%), cannot be strengthened by heat treatment, only by cold working.

2. Mechanical Properties
* Strength and Hardness: SUS630 aged tensile strength 1000–1400 MPa, hardness 30–45 HRC; 201 annealed tensile strength ≥520 MPa, hardness ≤201 HB. SUS630 is far stronger.
* Toughness and Plasticity: 201 has excellent ductility and cold forming performance; SUS630 has moderate plasticity after aging, better in solution-treated state but still less than 201.

3. Corrosion Resistance
* SUS630: Resistant to atmosphere, freshwater, neutral salt corrosion; moderate chloride pitting resistance, better than 201.
* 201: High manganese and low nickel content make it relatively less corrosion-resistant, prone to pitting; suitable for dry or mildly corrosive environments only.

4. Other Key Features
* Cost: 201 is cheaper due to low nickel/high manganese.
* Magnetism: SUS630 is magnetic; 201 is non-magnetic.
* Machining and Welding: 201 has better welding and cold-working performance; SUS630 is machinable in solution-treated state, welding requires post-weld aging to restore strength.

Application Scenario Comparison
* SUS630: High-strength bolts, aerospace components, high-pressure valves, mechanical shafts—situations requiring high strength.
* 201: Decorative hardware, low-cost appliance shells, supports in dry environments, non-load-bearing structures—scenarios sensitive to cost with no strict corrosion requirements.