Stainless Steel Encyclopedia 201 202 304: Which Grade Belongs in Your Part

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  Five stainless grades side by side
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  Stainless steel encyclopedia 201 202 304: how the low-nickel grades behave
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  301 and 302: the high-strength and general-purpose grades
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  Why 304 is the default choice for machined stainless
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  What changes on the shop floor
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  How grade choice affects the quote

Grade 201 replaces most of the nickel with manganese and nitrogen. That keeps the austenitic structure at a much lower alloy cost. It still resists rust in dry indoor air, so it ends up in elevator panels, trim strips and appliance shells.

The trade-off is corrosion margin. In salt spray, 201 starts to pit far sooner than 304. If the part sees coastal air, road salt or cleaning chemicals, 201 is the wrong call even though the quote looks better.

Grade 202 sits one step up with 4–6% nickel. It handles a wet kitchen environment better than 201 while staying cheaper than 304. Sinks, shelving and food-service carts are common uses.

Both grades are austenitic, so both are only slightly magnetic. A magnet test will not separate them from 304. You need a mill certificate or an XRF reading.

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  Pick 201 whenthe part stays dry and indoors
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  Pick 202 whenthe part sees water but no chlorides
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  Avoid both whensalt, acid or marine air is in the picture

Grade 301 carries less nickel than 304 and gains strength from cold rolling. In the annealed state it is soft, but after rolling it can reach very high tensile and yield values. That is why it becomes springs, clips, retaining rings and thin formed brackets.

Machining 301 in a cold-rolled condition is not pleasant. The material work-hardens fast, so a light feed rubs the surface and hardens it further. Use a deeper cut, a rigid setup and keep the tool moving.

Grade 302 is close to 304 in chemistry with slightly lower chromium and a bit more carbon. It is drawn into wire, woven into screens and stamped into washers. Corrosion resistance is good in normal outdoor exposure but below 304 in chloride service.

Neither grade is a good choice for a heavy machined block. They earn their place in thin sections, wire and formed parts where strength per unit weight matters.

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  Pick 301 whenyou need spring temper or high yield in thin stock
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  Pick 302 whenyou need wire, mesh or a stamped washer
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  Avoid both whenthe part is a thick machined body

Grade 304 holds 18–20% chromium and 8–10.5% nickel. That combination gives a stable austenitic structure with enough chromium to build a passive oxide layer that repairs itself in air. It is the grade most engineers mean when they write stainless on a drawing.

In food, dairy and medical equipment, 304 is the baseline because it tolerates repeated cleaning with mild chemicals and does not shed corrosion products into the process stream. It is also weldable and formable, which matters when a design mixes machined and welded features.

For machining, 304 is not free-cutting. It work-hardens, galls on the tool and pulls heat into the cutting edge. Expect lower surface speed than 303 and more attention to coolant. Free-machining 303 is the practical alternative when corrosion demand is moderate.

Where 304 falls short is chloride. Coastal air, de-icing salt or chloride-rich process fluid will pit it over time. That is the point to step up to 316 or 316L rather than pushing 304 harder.

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  Chloride exposureswitch to 316 or 316L
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  Light loads, tight toleranceconsider 303 for machinability
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  Welded assembliesuse low-carbon 304L to limit sensitization

Stainless grades share a habit: they harden under the tool. A cut that rubs instead of shearing leaves a hard skin that wears the next insert faster. The fix is consistent feed per tooth. Never let the tool dwell in the cut.

Coolant matters more than on aluminum. Flood coolant carries heat away from the edge and flushes chips out of the pocket. For deep holes and long pockets, high-pressure through-tool coolant shortens the cycle and protects the finish.

Rigidity drives the result. On a 304 part with a thin wall, chatter shows up before the tool breaks. Reducing overhang and supporting the wall from behind often matters more than changing the insert grade.

Our 127 CNC machines cover 3-axis, 4-axis and 16 simultaneous 5-axis centers, so a stainless part can be moved to the machine that suits its geometry. Tolerances run to ±0.005 mm and finishes to Ra 0.2–0.8 μm when the drawing calls for it.

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  Feed per toothkeep it heavy enough to shear, not rub
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  Coolantflood or through-tool, not a mist
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  Tool overhangshorten it before you change speeds

Nickel drives the price. 201 and 202 cost less per kilogram than 304 because they carry less nickel. On a large part, that difference is visible in the quote even before machining starts.

Machining time often outweighs the material saving. If 201 cuts 15% faster but the part then fails a salt spray test, the second run costs more than the first. Buyers who weigh only the metal price usually come back to 304.

We quote and return a DFM analysis within 12 hours, and production can start within 24 hours once the drawing and material are locked. Runs ship in 3–5 days. There is no minimum order quantity, so one prototype and a 10,000-part run take the same path through the shop.

Stock availability swings this decision too. 304 is stocked in more sizes and shapes than 201 or 202, which means fewer surprises on a tight schedule.

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  201 / 202lower metal cost, narrower corrosion margin
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  304higher metal cost, wide stock and mill support
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  316 / 316Lstep up only when chlorides demand it