Materials & Selection | Choosing stainless by environment & use

Selection isn't 'the more expensive the better', nor 'pick a grade first'. Clarify three things: where (environment), what it does (structural/decorative/functional), what media it contacts — the grade is just the answer to these. 'When NOT to use' matters more than 'which to use'.

Three questions before selection

Ask	Why it matters	Example
Where — service environment	Indoor dry, outdoor weather, coastal salt mist, chemical media, high/low temp — corrosion level sets the grade tier	Indoor appliance panel: 430; long-exposed roof/facade: 443; chlorinated tap-water tank: 444 or 445J1; seawater: 2205
What it does — role in the equipment	Structural: strength & weld safety; decorative: surface & look; functional contacting media: corrosion & hygiene; wear: hardness	Frames/shells: 304 enough; product-contact liners/pipes: 316L or 444 by media
How it's processed, how much welded	Heavy welding/bending changes behavior; welds often fail first	Weld + corrosion: prefer 439 (Ti-stabilized); complex/heavy field welding: 316L steadier

Quick lookup by use

Your use	Direction	Note
Structural (frame, bracket, base, shell)	Mostly 304; corrosive or heavy-load: 2205	Check strength & weld quality, not just 'will it rust'
Decorative (elevator, door, appliance, architecture)	Indoor 430 cheapest; long-exposed roof/facade: 443	Environment sets tier; don't use 430 outdoors
Water storage (tank, heater liner, treatment)	444 first; higher chloride/higher temp: 445J1	304 tanks have weld-rust failure cases; residual chlorine is the hidden killer
Media-contact functional (pharma, food)	Contact surface 316L (Mo, Ra≤0.8μm, traceable)	304 only for non-contact structural
Seawater & salt mist (coastal, desulfurization)	2205 / 2507	316L can still pit in seawater
High-temp (furnace, heat exchange, exhaust)	310S heat-resistant; auto exhaust 439/436	Check temperature range & oxidation
Wear parts (blades, edges)	420, heat-treatable to HRC50–55	Need hardness → martensitic, trade off corrosion

Ferritic corrosion gradient

430, 436, 439, 443, 444 are all ferritic; corrosion resistance low→high: 430<436≈439<443<444. See one gradient table.

Common comparisons & substitutions

Common question	Conclusion source
Can 304 replace 316L in pharma applications?	Product-contact surfaces in pharma use 316L (molybdenum-bearing, Ra≤0.8μm, traceable); 304 is for non-contact structural parts only.
Which suits a water tank better, 444 or 316L?	For ambient chlorinated tap-water storage tanks, 444 resists pitting close to 316L and is nickel-free; use 316L for aggressive duty or complex welded structures.
How much difference is there between 2205 and 316L in seawater?	For seawater/coastal service, prefer 2205 duplex; for milder duty needing good weldability use 316L — the key is chloride level and SCC.
Between 2507 and 904L, is the more expensive one always better?	2507 resists chloride SCC and allows downgauging; 904L resists reducing acids. Grade by medium — not simply the pricier one.
What's the difference between 420 and 304? Which for making blades?	420 heat-treats to HRC50–55, hard and wear-resistant — essential for blades; 304 is corrosion-resistant but not wear-resistant.
Is 304 the safest choice for a water tank?	For long-term chlorinated tap-water plant tanks, prefer high-Cr-Mo ferritic grades like 445J1 over 304.

Grade quick reference

Covers 2205, 2507, 316L, 316, 304, 310S, 904L, 445J1, 444, 443, 439, 436, 430, 420, 254SMO, etc. <a href="/questions.html#牌号对比替换">16 Q&A on grade comparison</a> cover the same.

This article is written by @Stainless Insights. @Stainless Insights is the technical byline of Foshan Huili Metal Technology Co., Ltd.（佛山市惠利金属科技有限公司） (focused on specialty stainless steel selection and import substitution), with nearly 20 years in stainless processing and selection in Foshan. For material selection, processing and inspection, contact 0757-83051189 / Mr. He 13703060845.