Stainless steel is usually chosen for corrosion resistance, cleanliness or strength. The machining reality is work hardening, heat, burrs and finish expectations that need to be managed from the first toolpath.
Best fit
medical parts, food hardware, fittings, shafts, manifolds and corrosion-resistant assemblies
Common grades
303, 304, 316L, 17-4PH, 410 and 420
Watch point
work hardening, passivation, burr control and chloride exposure
Typical route
milling, turning, drilling, tapping, passivation and electropolishing
303 machines well but gives up some corrosion resistance. 316L handles harsher environments. 17-4PH is the strength option when heat treatment is part of the plan.
| Grade | Yield Strength | Tensile Strength | Hardness |
|---|---|---|---|
| 303 Free-Machining | ~ 240 MPa | ~ 600 MPa | ~ 85 HRB |
| 304 Stainless Steel | ~ 205 MPa | ~ 515 MPa | ~ 80 HRB |
| 316L Stainless Steel | ~ 170 MPa | ~ 485 MPa | ~ 79 HRB |
| 17-4PH Stainless Steel | ~ 725-1100 MPa | ~ 930-1310 MPa | ~ 35-44 HRC |
Stainless grade selection should be tied to the environment. "Stainless" does not mean immune to chlorides, cleaning chemicals or embedded iron.
| ASTM / AISI / UNS | DIN / EN | GB | Engineer Note |
|---|---|---|---|
| 303 | 1.4305 / X8CrNiS18-9 | Y1Cr18Ni9 | Best machinability in the common austenitic grades, but lower corrosion resistance than 304. |
| 304 | 1.4301 / X5CrNi18-10 | 06Cr19Ni10 | General-purpose stainless for equipment, enclosures and industrial hardware. |
| 316 / 316L | 1.4404 / X2CrNiMo17-12-2 | 022Cr17Ni12Mo2 | Molybdenum-bearing grade for marine, medical, pharmaceutical and chloride-adjacent service. |
| 17-4PH | 1.4542 / X5CrNiCuNb16-4 | 05Cr17Ni4Cu4Nb | Precipitation-hardening stainless when strength and corrosion resistance must work together. |
Stainless steel balances corrosion resistance, cleanliness, strength, and surface finish in machined components.
| Application | Recommended Material | Why This Material Works | Typical CNC Process | Finish / Risk Note |
|---|---|---|---|---|
| Medical Instruments & Device Parts | 316L or 17-4 PH | Sterilization compatibility and high strength for reusable hardware. | 5-axis milling, turning, polishing | Passivation or electropolishing may be required. |
| Food & Beverage Equipment | 304 or 316 Stainless | Clean surface and washdown corrosion resistance. | Milling, turning, sanitary radii | Avoid crevices and specify product-contact finish. |
| Marine Hardware | 316 Stainless | Better chloride resistance than 304. | Turning, milling, threading | Design for drainage; severe chloride exposure can still pit. |
| Fluid Fittings & Manifolds | 316L or 304 Stainless | Strong threads and corrosion resistance. | Turning, drilling, port milling | Deburr intersecting holes to protect seals and flow paths. |
| Sensor Housings & Enclosures | 304, 316, or 17-4 PH | Durable body material with good sealing surfaces. | Turning, milling, engraving | Use 17-4 for strength, 316 for corrosion. |
Match the grade to the part's real job first: strength, heat, wear, corrosion, insulation, transparency, or cosmetic finish.
Material choice changes tolerance risk, burr control, wall thickness, thread strategy, and finishing route.
Share the operating environment, mating parts, finish expectations, and inspection requirements with the drawing.
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With stainless, the cutter must cut. Rubbing creates work-hardened skin, extra heat and a bad day for the next tool.
Dwelling is the fastest way to harden the surface. We keep the tool engaged and avoid timid finishing passes that only polish the material.
303 is attractive for machining cost, but it is the wrong shortcut for harsh corrosion. 316L or passivated 304 may be the better answer.
Cutting and handling can leave free iron on the surface. For clean or corrosion-sensitive parts, passivation should be specified, not assumed.
Stainless finishing is about cleanliness, corrosion resistance and controlled appearance.
Removes free iron and supports the chromium oxide layer. Important after machining and before service in clean or wet environments.
Improves microscopic smoothness for medical, pharmaceutical and cleanability-driven parts.
Used for a controlled matte or bright appearance. Define cosmetic surfaces and acceptable tool marks.
Send grade, finish, passivation requirement, chloride or cleaning exposure, tolerance notes and inspection requirements.
Name the exact grade, stock condition and certificate requirement. The same alloy can machine and perform differently after heat treatment, aging or cold work.
Flag threads, bearing bores, sealing faces and mating materials. These features determine the machining sequence, surface requirement and inspection plan.
Include coating, masking, cosmetic zones and report needs in the controlled RFQ so finished dimensions and acceptance criteria are aligned before production.