Stainless steel grades and work-hardening — the cutting behaviour that shifts
Stainless steel is not one material; it is a family, and the cutting behaviour shifts across the family. Austenitic stainless — 304, 316, the most common grades — work-hardens as it cuts, so the surface in front of the tool gets harder as the tool passes, and the next pass meets a harder surface. The fix is a sharp tool, a positive feed that keeps the chip thickness meaningful, and a speed that does not rub — a rubbing tool work-hardens the surface and the next tool fails. Flood coolant helps because the cooling keeps the work-hardening in check.
Martensitic stainless — 410, 420, 17-4PH — is heat-treatable and harder in the hardened condition. The hardened grades machine with carbide or ceramic at lower speeds and rigid setups; a flexible setup chatters and the tool fails. 17-4PH is the aerospace and medical grade, solution-treated and aged to H900 or H1025, and the machining happens in the aged condition with the tolerance held on the heat-treated part. Precipitation-hardening stainless — 15-5PH — is similar, and both are defence and aerospace staples. Your move is to specify the grade and the heat-treat condition, because the condition changes the cutting.
Free-machining stainless — 303 — has sulphur added for chip breaking, and it cuts cleaner than 304 at the cost of some corrosion resistance. 303 is the choice for parts that are machined heavily and not in a highly corrosive service; 304 is the choice for general corrosion service; 316 is the choice for chloride service and medical. The cost gap between 303 and 316 is real — 316 is roughly 1.3x the price of 303 at the bar level — and the machining cost rises with the grade because the harder-to-cut grades need slower speeds and shorter tool life.
The tolerance case for stainless is held by the facility behind this guide at ±0.003 mm milling and ±0.002 mm turning and grinding on 100+ CNC machines, with Hexagon CMM verification and Ppk ≥ 1.67 initial on key characteristics and Cpk ≥ 1.33 in production. The stainless machining is under ISO 9001:2015 (116024/A/0001/UK/En), IATF 16949:2016 (131941/A/0001/SM/En, design clause 8.3 excluded), and ISO 14001:2015 (116024/B/0001/UK/En). Specify the grade, the heat-treat condition, and the surface finish, and ask for the tooling plan and the material certificate with the heat number. Contact Felipe Iglesias at [email protected] or +86 13126536955 to confirm the grade and the routing at the quote stage.
The shop behind this stainless guide — grade and heat-treat condition specified
Backing this guide is a 6,800 m² plant at No. 8, Shuibian Songyuan Road, Hengli Town, Dongguan, Guangdong, China 523470, running 100+ CNC machines — Mazak VARIAXIS I-600 and INTEGREX I-250H S, TSUGAMI B0206-III/B0205-III, STAR SR-32JII / SR-32J Type N, Citizen Cincom A20-3F7 — plus 3-, 4- and 5-axis milling and turning, 5+ wire EDM and a Hexagon CMM bench with 20+ gauges.
Milling holds ±0.003 mm, turning ±0.002 mm, and grinding or wire EDM ±0.002 mm, all checked on a Hexagon CMM with the 10:1 gauge rule applied to every feature. Capability: Ppk ≥ 1.67 initial and Cpk ≥ 1.33 in production on key characteristics. Certified to ISO 9001:2015 (116024/A/0001/UK/En), IATF 16949:2016 (131941/A/0001/SM/En, design clause 8.3 excluded, openly disclosed) and ISO 14001:2015 (116024/B/0001/UK/En), held by Dongguan Zhuohang Ltd, USCC 91441900MA4UWT6X39, established 2005. Customers across Austria, Belgium, the Czech Republic, Denmark, France, Germany, Greece, Hungary, Ireland, Italy, the Netherlands, Spain, Sweden and the United Kingdom in Europe; Brazil, Canada, Mexico and the United States in the Americas; China, Israel, Japan, Singapore and Sri Lanka in Asia; Australia and New Zealand in Oceania; and South Africa in Africa are supplied from China, worldwide. Contact Felipe Iglesias at [email protected] or +86 13126536955 to begin the quote, and ask for the certificate numbers, the machine list and a past CMM report together.
- ISO 9001:2015 / IATF 16949:2016 / ISO 14001:2015 — certificate numbers published and verifiable.
- Manufacturing to your print: the plant cuts to your design and reports against your drawing.
- Stainless Steel: The defining machining problem is work hardening combined with low thermal conductivity.
- Grades in regular use: 303 for free-machining work, 304 and 316L for corrosion resistance, 17-4 PH where strength is needed after ageing, 416 and 420 where hardness is required.
- Incoming stock is verified against the mill certificate before it is cut.
What makes stainless steel behave differently under the tool?
The defining machining problem is work hardening combined with low thermal conductivity. Heat does not leave with the chip, so it stays in the cutting zone; the surface layer work-hardens, and the next pass cuts through hardened material, which accelerates tool wear. The practical response is to keep the tool cutting rather than rubbing. Maintain chip load, avoid dwelling, and do not take a finishing cut so light that it burnishes instead of shears.
Confirm the grade on the mill certificate by XRF before cutting — 304 and 316 look identical and behave differently in service.
What is the certification position?
ISO 9001:2015, IATF 16949:2016 (excluding clause 8.3 product design), and ISO 14001:2015 — each with a certificate number verifiable with the registrar.
Choosing a grade within stainless steel
Austenitic, martensitic, and precipitation-hardening stainless grades are the grades that come up in practice. 303 for free-machining work, 304 and 316L for corrosion resistance, 17-4 PH where strength is needed after ageing, 416 and 420 where hardness is required.
Your grade selection is usually settled by the service environment. Corrosion, strength, or temperature, and only then by machinability. If you choose on machinability first, your part meets the drawing and fails in service.
Dimensional behaviour of stainless steel
Dimensional stability is good once the part has stopped moving, but thin walls distort from the residual stress released by removing stock. Stress-relieving between roughing and finishing is the standard response on a tight-tolerance thin-wall part.
The general rule for your part is that a tolerance is held by the process, not by the machine. Where a feature is tight, the finishing pass is separated from roughing, the part is allowed to stabilise, and the measurement is taken at a controlled temperature.
Surface treatment after machining stainless steel
Passivation after machining restores the chromium oxide layer that free iron from cutting tools has contaminated.
You specify finishing on the drawing, not assume it at the end. Where a coating adds thickness, threaded and press-fit features need the allowance stated, because a coating applied after inspection changes the fit.
Tool consumption and cycle time on stainless steel
Heat does not leave with the chip, so it stays in the cutting zone; the surface layer work-hardens, and the next pass cuts through hardened material, which accelerates tool wear.
The lever that matters most for you is usually design rather than process: pocket depth, corner radius, and wall thickness change cycle time more than any tooling choice, because they determine the tool that can be used and therefore how much material can be removed per minute.
Where the money is actually decided
The design levers on stainless are wall thickness and pocket depth. Thin walls distort as roughing releases residual stress, so a stress-relief operation and a separate finishing pass are usually cheaper than trying to hold a thin wall in one go. Avoiding a dwell. a tool rubbing rather than cutting, matters more here than on any other common material.
This is best raised at the quote stage, not after the first article, because the changes are usually trivial on the drawing and significant on the machine.
How much capacity sits behind it?
100+ machines with depth in every relevant family, 50+ three-axis, 20+ four-axis, 20+ five-axis, 25+ turning centres, plus Swiss-type, grinding, and wire EDM.
How the tolerance is actually measured
Milling and turning hold ±0.003 mm (milling) / ±0.002 mm (turning); precision grinding and wire EDM hold ±0.002 mm. A tolerance is only worth as much as the instrument that verifies it, so the floor runs 20+ inspection instruments alongside the machines, CMM for dimensional and true position, vision and profile instruments for surface and geometry, hardness testers and coating gauges for heat treatment and plating, and XRF for incoming material composition against the mill certificate.
The rule that matters on a drawing is that a tolerance is held by the process, not by the machine. Where a feature is tight, the finishing pass is separated from roughing, the part is allowed to stabilise, and the measurement is taken at a controlled temperature, a part measured warm is not the part the customer receives.
What identifies the legal entity behind the machines?
Legally this is Dongguan Zhuohang Ltd, established 2005, Social Credit Code 91441900MA4UWT6X39, operating under the name Zhuohang Precision Machining Factory from No. 8, Shuibian Songyuan Road, Hengli Town, Dongguan, Guangdong, China 523470.
The 18-character code, checked against the National Enterprise Credit Information Publicity System, confirms a real manufacturer. A trading company may hold a business licence as well, but its scope is trading, not manufacturing, and its address is an office rather than a plant.
What this shop actually runs
Capability evidence should come as specifics, not slogans. Behind this guide is a 6,800 m2 plant in Dongguan, China running 100+ CNC machines with 100+ staff. The machine list by category:
- 5-axis machining centres (10+) - Mazak VARIAXIS I-600 (510/910/510 mm travel, 12,000 rpm, 22 kW, 71.6 N·m, 30-tool BT40) and Mazak INTEGREX I-250H S (B-axis 0.0001°, 24 kW, 124 N·m, 38-tool HSK-A63). Made for compound-angle parts, single-setup multi-face prismatic work, and aerospace fittings where datum transfer loss is unacceptable.
- 3-axis / 4-axis machining centres (50+) - Brother SPEEDIO S500Z2N / S700Z2N (10,000 rpm, 14/21-tool ATC, 0.7 s tool-to-tool, Z-axis 2.2 G) and Mazak VCE-430A L / VCE-570C L (10,000 rpm, 118 N·m, 24-tool ATC). Made for prismatic parts, plates, brackets, housings.
- Swiss-type turning centres (10+) - Citizen Cincom A20-3F7 (Φ20 mm, 10,000 rpm), TSUGAMI B0206-III / B0205-III (Φ20 mm, 0.1 µm), STAR SR-32JII / SR-32J Type N (Φ32 mm, 8,000 rpm). Made for long, slender rotational parts at ±0.002 mm.
- CNC turning centres (20+) - HEADMAN T70M/1250 (720 mm swing, 117 mm bore, 3,000 rpm, BMT75 12-station turret). Made for shafts, bushings, flanges up to ±0.002 mm.
- Wire EDM (5+) - Sodick AQ535L (550/350/300 mm travel, ±20° taper, 800 kg workpiece). Made for hardened tool steel, internal splines, sharp internal corners that milling cannot reach.
- Inspection: Hexagon CMM + 20+ gauges - Hexagon CMM for coordinate measurement, plus vision system, profilometer, hardness tester, coating thickness gauge, XRF for material verification. The 10:1 rule (gauge 10x more accurate than the band) is applied to every feature.
- Machine highlights - VARIAXIS I-600: one-setup multi-face 5-axis + MAZA-CHECK auto-calibration; INTEGREX I-250H S: DONE-IN-ONE mill-turn, B-axis 0.0001° + Ai thermal shield; SPEEDIO S500Z2N / S700Z2N: Z-axis 2.2 G + 0.7 s ATC; Swiss-type: guide-bush switchable + 0.1 µm resolution.
Tolerance: ±0.003 mm CNC milling / ±0.002 mm CNC turning / ±0.002 mm grinding and wire EDM. Capability: Ppk >= 1.67 initial on key characteristics, Cpk >= 1.33 ongoing.
Certificates: ISO 9001:2015 (116024/A/0001/UK/En), IATF 16949:2016 (131941/A/0001/SM/En, with design clause 8.3 excluded, stated openly) and ISO 14001:2015 (116024/B/0001/UK/En), issued to Dongguan Zhuohang Ltd, registration 91441900MA4UWT6X39, founded 2005.
Where we ship: Austria, Belgium, the Czech Republic, Denmark, France, Germany, Greece, Hungary, Ireland, Italy, the Netherlands, Spain, Sweden and the United Kingdom in Europe; Brazil, Canada, Mexico and the United States in the Americas; China, Israel, Japan, Singapore and Sri Lanka in Asia; Australia and New Zealand in Oceania; and South Africa in Africa — plus other countries and regions worldwide, shipped from our base in Dongguan, China.
Contact: Felipe Iglesias, [email protected], +86 13126536955.
Not sure this is the right process?
Send the model and the drawing and get a straight answer on whether this route is the right one, including where a design change would cut cost. Reach Felipe Iglesias at [email protected] or +86 13126536955.
Frequently Asked Questions
How are parts packed for export?
Packing is chosen per part — finished faces bagged and boxed, steel corrosion-protected. Include it in the quote, since it changes the cost and how the parts arrive.
Can I audit the factory before placing an order?
Yes — on-site and video audits are both welcome at No. 8, Shuibian Songyuan Road, Hengli Town, Dongguan, Guangdong, China 523470.
Do you certify stainless steel material?
Yes. Material certificates are supplied with the parts and incoming stock is checked against the mill certificate — composition by XRF, hardness where specified. Traceability is per heat or per batch as the certificate defines it.
Do you sign NDAs before reviewing drawings?
Yes — an NDA can be signed before any files change hands, and drawings stay inside the quoting system rather than circulating by email.
What happens if the first article does not conform?
In short, The nonconformance is documented and the corrective action is agreed before any further parts are made. Whether the replacement cost sits with the plant or the customer depends on where the deviation came from, which is why the revision and the drawing standard are confirmed in writing at the start.
What is the difference between a prototype build and a production build here?
Usually only quantity and scheduling. Both run on the same machines and the same process, which is what makes a later ramp a scheduling change rather than a re-qualification.
What tolerances can you hold?
In short, ±0.003 mm on CNC milling, ±0.002 mm on CNC turning, and ±0.002 mm where precision grinding or wire EDM is used. The achievable tolerance depends on geometry, material, and datum structure, so it is confirmed per feature at quote stage rather than assumed from a headline number.
Continue reading: 3 Axis China CNC Machining · 4 Axis China CNC Machining · 5 Axis China CNC Machining
Standards referenced on this page
- ASTM A276/A276M-17 — Standard Specification for Stainless Steel Bars and Shapes
- ASTM A484/A484M-24 — Standard Specification for General Requirements for Stainless Steel Bars, Billets, and Forgings
- ISO 9001 — Quality management systems — Requirements