How to Machine Stainless Steel — Grade-by-Grade Guide for Malaysian Engineers

Sep 8

4 min read

Stainless steel is machined across more Malaysian industries than almost any other material — Medical device components, Oil & Gas fittings, Food processing equipment, Semiconductor fixtures, and General Engineering parts all regularly involve stainless in one grade or another. It is also one of the materials most frequently machined incorrectly, leading to premature tool failure, poor surface finish, and frustrating scrap rates.

The root cause of most stainless machining problems is the same: work hardening. Stainless steel work-hardens rapidly when the cutting tool rubs rather than cuts. Once the surface work-hardens, tool life collapses within minutes. Understanding and preventing work hardening is the foundation of successful stainless machining.

The golden rule of stainless machining

Never allow the tool to rub on stainless steel. Always maintain a positive chip load — the tool must be cutting, not rubbing. This means:

Never reduce feed rate to improve surface finish in stainless — reduce cutting speed (Vc) instead.
Never dwell the tool in the cut — program smooth, continuous tool paths with no pauses.
Keep tools sharp — a dull tool rubs before it cuts, triggering immediate work hardening.
Never re-enter a work-hardened surface without a fresh, sharp cutting edge.

Grade 304 stainless steel

The most common austenitic stainless grade. Good general corrosion resistance, widely used in Food processing, Architecture, and General Engineering.

Tool recommendation: OSG EX-SUS series or Mitsubishi Materials solid carbide end mills and drills. AlTiN or TiAlN coating.
Cutting speed (turning): Vc 120–180 m/min with coated carbide inserts, positive rake chipbreaker.
Cutting speed (milling): Vc 80–120 m/min, fz 0.03–0.06mm per tooth, 4-flute end mill.
Coolant: Flood coolant mandatory. High pressure preferred — minimum 20 bar through spindle for drilling.
Common mistake: Using TiN-coated tools (gold colour). TiN coating has insufficient hardness for stainless — switch to AlTiN or TiAlN.

Grade 316L stainless steel

316L adds molybdenum for improved corrosion resistance. Standard for Medical devices, Marine, Chemical processing, and Oil & Gas applications. Slightly more difficult to machine than 304 due to higher work hardening tendency.

Tool recommendation: OSG EX-SUS series drills specifically designed for 316L — point geometry prevents work hardening on entry. MOLDINO or Mitsubishi Materials solid carbide end mills.
Cutting speed (turning): Vc 100–150 m/min. Reduce Vc versus 304 — 316L work-hardens faster.
Cutting speed (milling): Vc 60–100 m/min, fz 0.02–0.05mm per tooth.
Coolant: Flood coolant mandatory. Do NOT use chlorinated cutting fluids — causes stress corrosion cracking in 316L components for medical or marine applications.
Critical note: For surgical instrument or medical implant components in 316L — ensure your cutting fluid is chlorine-free and compatible with biomedical requirements.

17-4PH stainless steel (H900 condition)

Precipitation hardened stainless — 44–47 HRC in H900 condition. Used extensively in Aerospace fasteners, Oil & Gas valve components, and high-strength structural parts. Machines more like a hardened alloy steel than a standard stainless.

Tool recommendation: AlTiN-coated solid carbide end mills with positive rake geometry. Mitsubishi Materials or MOLDINO hard milling series.
Cutting speed (milling): Vc 60–90 m/min, fz 0.03–0.06mm. Conservative speeds prevent thermal shock at the cutting edge.
Coolant: Flood coolant for roughing and semi-finishing. MQL acceptable for finishing passes.
Common mistake: Treating 17-4PH like standard stainless and running at 304 cutting speeds — tool failure is rapid at incorrect parameters.

Duplex stainless steel (SAF 2205)

Two-phase (austenite + ferrite) microstructure. Higher strength than 304/316L, excellent corrosion resistance. Standard in Oil & Gas, Chemical processing, and Marine applications. The alternating hard and soft microstructure phases create uneven cutting resistance — the primary machining challenge.

Tool recommendation: Positive rake, sharp-edge carbide inserts (Mitsubishi Materials MC Series) for turning. OSG or Mitsubishi Materials solid carbide end mills for milling.
Cutting speed (turning): Vc 80–120 m/min, fz 0.10–0.18mm. Maintain positive chip load — work hardening in duplex is severe if feed drops too low.
Cutting speed (milling): Vc 60–90 m/min, fz 0.04–0.08mm.
Coolant: High-pressure flood coolant mandatory — minimum 40 bar for drilling, 20 bar for milling.
Critical: Do not reduce feed to improve finish in duplex stainless — reduce Vc instead. Reducing feed in duplex causes immediate work hardening.

Super Duplex stainless (SAF 2507)

Higher alloy content than standard duplex — more abrasive, faster edge wear, lower recommended Vc.
Vc: 60–90 m/min for turning, 50–75 m/min for milling. Expect shorter tool life than 2205 at equivalent parameters.
Insert indexing frequency must increase versus standard duplex — do not try to run super duplex inserts as long as duplex inserts.
Mandatory: through-spindle high-pressure coolant for all drilling operations.

Universal rules for all stainless grades

Always use sharp tools — never re-run a stainless job with a tool that showed wear signs on the previous run.
Always maintain positive chip load — the moment the tool starts rubbing, tool life collapses.
Use through-spindle or directed high-pressure coolant for drilling — chip evacuation in stainless is critical.
Choose positive rake insert geometries — negative rake geometries increase cutting forces and work hardening risk.
Monitor insert wear closely — stainless is unforgiving of worn tools. Change inserts more frequently than you think necessary until you establish your specific tool life baseline.

Get a stainless steel tooling recommendation

KS Precision Tools is the authorised distributor for OSG, Mitsubishi Materials, MOLDINO, and Rohm in Malaysia. Our technical specialists will recommend the right grade, geometry, coating, and cutting parameters for your specific stainless application.

Call 03-8941 7168 or email kokyong@ks-precision.com. Based in Seri Kembangan, Selangor. Local stock for standard stainless machining grades — same day or next day delivery.