SUS630 (martensitic precipitation-hardening stainless steel) and 304 (austenitic stainless steel) differ mainly in material type, performance focus, and application scenarios. SUS630 emphasizes high strength, while 304 emphasizes corrosion resistance and versatility.
Performance differences
1. Material Type and Strengthening Method
* SUS630: Martensitic precipitation-hardening type, contains copper and niobium, requires “solution + aging” heat treatment to precisely control strength.
* 304: Austenitic type, balanced chromium and nickel content (Cr 18–20%, Ni 8–12%), cannot be strengthened by heat treatment, only minor strengthening via cold working.

2. Mechanical properties
* Strength and Hardness: SUS630 aged tensile strength 1000–1400 MPa, hardness 30–45 HRC; 304 annealed tensile strength ~515 MPa, hardness ≤201 HB. SUS630 is much stronger and harder.
* Plasticity and Formability: 304 has excellent ductility and cold-forming ability, easily bent or stretched into complex shapes; SUS630 has moderate plasticity after aging, better in solution-treated state but still less than 304.

3. Corrosion resistance
* SUS630: Resistant to atmosphere, freshwater, neutral salt solutions; moderate chloride pitting resistance, suitable for high-strength applications without strong corrosive exposure.
* 304: Superior corrosion resistance overall, excellent against organic acids, weak alkalis, and chlorides; representative of general-purpose corrosion-resistant stainless steel.

4. Other key features
* Cost: 304 is widely used and mature in production, cheaper than SUS630, offering higher cost-effectiveness.
* Magnetism: SUS630 is magnetic; 304 is non-magnetic or weakly magnetic.
* Machining and Welding: 304 has better welding and cutting performance, no post-treatment needed; SUS630 is machinable in solution-treated state, welding requires post-weld aging to restore strength.

Application scenario comparison
* SUS630: Aerospace components, high-strength bolts, high-pressure valves, mechanical shafts, medical implants—applications prioritizing strength.
* 304: Food processing equipment, chemical containers, architectural decoration, household appliances, pipelines, outdoor facilities—applications prioritizing corrosion resistance and versatility.