Stainless Steel CNC Machined Parts — SS 304 & 316 Precision Parts

Precision CNC machined stainless steel parts in SS 304 (1.4301) and SS 316 (1.4401) manufactured by Jamnagar Brass Components. Turned, milled, and ground components. Threads, bores, and complex profiles. Medical, pharmaceutical, and food processing industries. Tolerances to ±0.005mm. ISO 9001 certified, exporting to USA and Germany.

Frequently Asked Questions — Stainless Steel CNC Machined Parts

Q1: What stainless steel grades are most commonly CNC machined?

SS 303 (free-machining, sulfur-addition, best machinability in austenitic family), SS 304/304L (most common grade, general corrosion resistance), SS 316/316L (molybdenum-addition, pitting and crevice corrosion resistance for chemical/marine use), SS 430 (ferritic, magnetic, good corrosion resistance, lower cost), and SS 17-4 PH (precipitation hardening, high strength to 1,200 MPa, aerospace applications) are the principal CNC machining grades.

Q2: What CNC machining processes are available for stainless steel?

Stainless steel is processed by CNC turning (multi-axis lathes with live tooling), CNC milling (vertical and horizontal machining centres), Swiss-type CNC turning for small precision parts (below 32 mm diameter), CNC grinding for tight-tolerance bores and surfaces, electrical discharge machining (EDM) for complex features, and deep hole drilling for long, small-diameter bores in hydraulic and injection moulding components.

Q3: What tolerances are achievable for stainless steel CNC machined parts?

Standard CNC turned stainless: ±0.025 mm on diameters. Precision Swiss turned SS 303: ±0.005 mm. CNC milled stainless: ±0.025 mm on pockets and bores. Reamed bores in SS 316: H7 tolerance. Ground bores: H5/H6. Thread tolerances: 6H/6g ISO class. Surface finish: Ra 0.4–1.6 µm from turning; Ra 0.05–0.4 µm from grinding; Ra below 0.2 µm with electropolishing applied after machining.

Q4: Why is SS 303 preferred over SS 304 for turning?

SS 303 contains 0.15% minimum sulfur, which forms manganese sulphide (MnS) inclusions that act as chip breakers, dramatically improving machinability compared to SS 304. SS 303 has approximately 45% of the machinability of free-machining brass vs. only 25–30% for SS 304. The trade-off: SS 303 has slightly lower corrosion resistance than SS 304 and cannot be welded. For turned-only components, SS 303 gives lower cost and better surface finish.

Q5: What is passivation and is it required for stainless steel machined parts?

Passivation (ASTM A967, AMS 2700) is a chemical process (typically nitric acid or citric acid) that removes free iron from the stainless steel surface and reforms the protective chromium oxide passive layer, maximising corrosion resistance. It is required after machining whenever the stainless steel surface has been contaminated by iron from tooling, fixtures, or handling. Passivation is standard on all our stainless steel machined parts.

Q6: Can stainless steel CNC machined parts be electropolished?

Yes. Electropolishing (anodic dissolution in phosphoric/sulphuric acid) removes 5–20 µm of surface material, levelling micro-asperities and producing a bright mirror-like finish (Ra below 0.2 µm). It enhances corrosion resistance beyond passivation alone, reduces bacterial adhesion (important for food and pharmaceutical applications), and provides a smooth, cleanable surface. Electropolishing certificates per ASTM B912 are provided.

Q7: What stainless steel alloys are suitable for cryogenic applications?

Austenitic stainless steels (SS 304, 304L, 316, 316L) maintain ductility and toughness to cryogenic temperatures (down to -196°C / liquid nitrogen), making them ideal for cryogenic vessel components, liquid gas fittings, and cryogenic instrument housings. Ferritic and martensitic stainless steels become brittle below approximately -40°C and are not suitable for cryogenic service.

Q8: What is the difference between SS 316 and SS 316L?

SS 316L (low carbon, max 0.03% C) is specified where components will be welded, to prevent sensitisation (chromium carbide precipitation at grain boundaries, reducing corrosion resistance) in the heat affected zone during welding. For machined-only components that will not be welded, standard SS 316 (max 0.08% C) is acceptable and may have marginally higher strength than SS 316L. We supply 316L as standard for most applications to ensure maximum corrosion resistance.

Q9: What is the lead time for stainless steel CNC machined parts?

Prototype quantities (5–10 pieces): 2–4 weeks depending on complexity. Standard production orders (25–500 pieces): 3–5 weeks. Complex multi-axis parts with grinding and electropolishing: 4–6 weeks. Repeat orders on established programs: 2–3 weeks. Expedited prototypes for emergency requirements: 7–10 working days for simple turned parts from in-stock bar. Air freight to USA: 3–5 days; sea freight 18–25 days.

Q10: What documentation is provided with stainless steel CNC machined parts?

Standard documentation: Material Test Certificate (EN 10204 3.1) confirming grade, chemical composition (including carbon, molybdenum, and nickel content), and mechanical properties; Dimensional Inspection Report; Certificate of Conformance; passivation certificate. Additional: PPAP Level 3 for automotive, FAIR (AS9102) for aerospace, electropolishing certificate, hardness test records, and SPC data for high-volume production.