Quick answer: these grades are not a simple strength ranking. 409 and 430 are ferritic stainless steels, 410/410S and 420 are martensitic families with different heat-treatment responses, 440 grades target higher hardness, and 446 is a high-chromium ferritic grade for elevated-temperature oxidation service. Choose by environment, heat treatment, fabrication and the governing plate specification.
Grade-Family Comparison
| Grade | Family / main direction | Selection caution |
| 409 | Ferritic; economical heat and exhaust service | Appearance and general corrosion resistance are below 430 in many environments |
| 410 | Martensitic; heat treatable for moderate strength/hardness | Properties depend strongly on hardening and tempering |
| 410S | Low-carbon 410 modification; limited hardenability | Do not substitute where hardened 410 properties are required |
| 420 | Martensitic; higher carbon for greater hardness | Grade variant and heat treatment must be defined |
| 430 | Ferritic; decorative and mild-corrosion applications | Lower weld toughness/formability than common austenitic grades in some conditions |
| 440 family | High-carbon martensitic grades for wear and hardness | 440A, 440B and 440C are different grades; heat treatment and section control are critical |
| 446 | High-chromium ferritic; elevated-temperature oxidation resistance | Not a general-purpose corrosion or high-toughness grade |
How to Narrow the Choice
Corrosion and temperature
Define the actual medium, chloride level, condensation, cleaning chemistry and temperature cycle. Oxidation resistance in hot gas does not guarantee resistance in wet acids or chloride-bearing water.
Strength, hardness and fabrication
Martensitic grades require a complete heat-treatment specification. Plate thickness affects achievable properties and distortion. Ferritic grades are not strengthened by conventional quench-and-temper treatment and need appropriate welding and forming controls.
RFQ Checklist
- Exact grade, including 440 variant
- Plate standard, thickness, width and length
- Annealed or heat-treated condition and hardness range
- Surface, flatness and machining allowance
- Testing, NDT, MTC and traceability
- Service temperature and corrosive medium
Review stainless steel plate options; final substitution should be approved against the design specification.
Post time: Jun-27-2023