Applications · Austenitic, Duplex and Martensitic Stainless
Stainless Steel Machining: Tooling and Cutting Data for Austenitic, Duplex and Martensitic Grades
Stainless steel is the material that punishes a light pass. It work-hardens under the cutting edge, so a tool that rubs instead of cutting leaves a skin harder than the material below it, and the next pass then has to cut that skin. It also conducts heat poorly, so the edge takes most of the temperature the cut produces, and it galls, so a chip that is not thrown clear welds to the edge and smears the finish. The grade family decides how much of each you get: austenitic 300-series is the work-hardening and galling case, the ferritic and martensitic 400-series cuts more like a low-alloy steel, and duplex sits between them with more strength than either. The cutting speeds published for stainless turning, milling and drilling are given below, with why the feed matters more than the speed here.
Failure Modes
Three failure modes that decide how you cut stainless steel
Stainless steel fails by changing the workpiece rather than by wearing the tool in a straight line. The material under the cut gets harder, the heat stays at the edge instead of leaving with the chip, and the chip welds itself to whatever surface it touches. Reading which of the three below dominates your operation settles the feed, the geometry and the coolant before the grade is chosen.
Failure mode 01
Work hardening — the material gets harder while you cut it
What actually fails
Austenitic stainless does not have, at the start of the cut, the hardness it will have during it. The surface work-hardens under the cutting edge, so a light pass, a slow feed or a moment of dwelling leaves a layer harder than the material beneath. The next revolution then cuts that harder layer, which work-hardens again, and the edge ends up riding on a surface it can no longer cut cleanly. What the operator sees is an insert that fails early on a material that is not particularly hard.
What to look for in the tool
Look for an edge that cuts rather than rubs: sharp, positive, and tough enough to take a real chip load, with a cutting material that resists the notch wear this produces at the depth-of-cut line. Set a feed high enough to keep the edge under the hardened layer rather than riding on top of it, and never dwell in the cut, because a pause work-hardens the surface under the tool and the next revolution cuts the harder skin.
Failure mode 02
Heat concentration and the edge that absorbs it
What actually fails
Stainless steel carries heat away from the cut poorly, so much less of the cutting temperature leaves with the chip than it does on carbon steel. The edge therefore runs hotter, its coating breaks down sooner, and the failure arrives as cratering behind the edge and notching at the depth-of-cut line rather than as even flank wear. Adding coolant badly makes it worse: coolant that reaches a hot edge intermittently thermally cracks it instead of cooling it.
What to look for in the tool
Look for a substrate and coating that hold hardness at temperature, and settle the coolant strategy deliberately rather than by habit: a full, continuous flow aimed at the cut, or a considered dry operation, and never a flow that arrives in bursts. A depth of cut that is generous enough to carry heat away with the chip does more for edge life here than a slower speed does.
Failure mode 03
Galling — the chip welds to the edge and smears the finish
What actually fails
Stainless steel is prone to welding to whatever it touches under pressure, and the cutting edge is under pressure by definition. A built-up edge forms, tears away and takes coating and edge material with it, leaving a torn finish and an insert that appears to have failed for no reason. The problem compounds in a hole or a deep pocket, where the chip cannot leave and is recut until it welds.
What to look for in the tool
Look for a coating and substrate combination chosen to resist adhesion rather than one chosen only for abrasion resistance, and for a geometry with enough rake to keep the cut ahead of the weld. Surface speed within the published window helps, but so does anything that gets the chip away from the cut: through-tool coolant on a deep hole, a thread mill instead of a tap where the chip has nowhere to go, and a climb cut on a finish pass where the machine supports it.
One boundary is worth stating plainly. Stainless steel in the ISO M group — austenitic, duplex, ferritic and martensitic grades — is what the figures below cover. Hardened stainless above roughly 45 HRC is cut against the hardened steel data rather than with these figures, and titanium and nickel alloys sit in a different group entirely and are quoted on request.
The 300-series and 400-series rows in the table below are not interchangeable. Austenitic grades work-harden and gall, and they are the reason the rules here exist; ferritic and martensitic grades machine much closer to a low-alloy steel. Tell us the grade rather than just the word stainless and the answer will be specific.
Tool Matrix
Which tool family for which stainless steel operation
Turning leads the matrix because it removes most of the material and because the depth-of-cut line is where stainless notches an insert. Milling and then the hole and the thread follow, and the same rule runs through all three: this is a material that rewards toughness and a sharp edge over wear resistance.
Every card stops at the level of tool family, geometry and cutting material. The specific grade and edge preparation are decided against the grade of stainless, the operation and the tolerance on the drawing, and they come back with a quotation.
Turning
Turning stainless is where the choice of edge preparation shows up fastest. The insert has to be sharp enough to cut under the work-hardened skin and tough enough to survive the notch that forms at the depth-of-cut line.
Turning inserts for stainless steel
Tough coated carbide grades for austenitic and duplex work, pairing a strong substrate with a sharp, positive edge. Toughness and sharpness together are what stainless asks for, where carbon steel would be answered with wear resistance instead.
Inserts for finishing and slender stainless parts
Low-force positive geometry for the finishing passes on thin-wall and slender stainless parts, where keeping the cutting force down matters more than edge strength and where a built-up edge has to be kept off the finish.
All turning shapes and groups
The ISO turning shapes available in stainless grades, with the note that belongs to each, so a shape can be settled before the grade and edge preparation are chosen.
Milling
Milling stainless puts the edge in and out of the cut on every tooth, which is exactly the condition that work-hardens a surface fastest. Geometry that controls chatter matters here, because a vibrating cutter rubs as much as it cuts.
Milling inserts for stainless steel
Tough coated grades for face and shoulder milling, chosen for edge strength rather than maximum wear resistance, with positive geometry that keeps the cut ahead of the work-hardened layer on an interrupted pass.
Solid carbide end mills for stainless steel
Coated solid carbide geometry with a strengthened edge for slotting, profiling and pocketing, where chatter control and chip clearance decide the result more than the coating does.
All milling and holemaking ranges
Insert milling, solid end mills, drills and threading tools in one place, grouped by the operation they are bought for, so a stainless part can be planned as a whole.
Drilling, threading and workholding
The hole is where stainless breaks tools, because the chip cannot leave and the surface work-hardens around the drill. Threading is the operation most likely to end a part outright, and workholding decides whether the cutter can run at the speed the material asks for.
Drill bits for stainless steel
HSS-Co and HSS-E-PM drills for general work, and solid carbide drills with internal coolant where the depth or the tolerance demands it. In stainless the drill sets the surface the tap then has to cut, so a dull drill costs more than its own price.
Threading tools for stainless steel
Thread milling and taps suited to austenitic and duplex grades, where the thread is the operation most likely to break a tool. Thread milling in particular keeps the chip clear of a cut that has nowhere to put it.
Tool holders for stainless turning and milling
Holders that keep the tool square and rigid at the speeds and feeds stainless needs, because the work hardening this material is known for starts the moment the tool rubs instead of cutting.
Cutting Data
Published cutting speeds for turning, milling and drilling stainless steel
The table gives the surface speed published for stainless steel in each operation, drawn from the same source data as the cutting speed reference so the two cannot disagree. Read it as a window rather than a setting: within the window, the feed and the depth of cut decide whether the edge stays under the work-hardened layer.
The rows separate the grade families on purpose. An austenitic 304 and a martensitic 410 are both called stainless and neither is cut like the other, and the difference between them is wider than the difference between two operations on the same grade.
| Stainless condition | Operation | Tool family | Cutting speed (m/min) | Cutting speed (SFM) | Basis of the range | Source (as recorded) |
|---|---|---|---|---|---|---|
| Austenitic stainless steel, 304 and 316 | Turning | coated indexable carbide | 25-180 | 80-590 | two published grade families; the range spans both | KCSM25S & KCPM25S 30-180; KCU25S 25-140 |
| Austenitic stainless steel, 304 and 316, around 180 HB | Turning | coated indexable carbide | 120-215 | 395-705 | lowest to highest value published across the grades listed | range across grades |
| Duplex and ferritic-martensitic stainless steel, around 200 HB | Turning | coated indexable carbide | 105-200 | 345-655 | lowest to highest value published across the grades listed | range across grades |
| Martensitic stainless steel, 240 HB | Turning | coated indexable carbide | 90-185 | 295-605 | lowest to highest value published across the grades listed | range across grades |
| Stainless steel, 300 series | Milling | coated solid carbide | 61-107 | 200-350 | published as a column range, converted from surface feet per minute | OSG VG446 col.3 = 200-350 SFM; column mapping verified by x-coordinate; SFM converted |
| Stainless steel, 400 series | Milling | coated solid carbide | 91-122 | 300-400 | published as a column range, converted from surface feet per minute | OSG VG446 col.2 = 300-400 SFM; SFM converted |
| Stainless steel, 304 | Milling | coated solid carbide, variable geometry | 46-107 | 150-350 | published as a column range with the column mapping verified against the source | OSG VGM7 col.3 = 150-350 SFM; column mapping verified by x-coordinate; SFM converted |
| Stainless steel, general | Milling | coated indexable carbide | 80-180 | 262-590 | published as a wet window and a dry window; the range spans both | p.10/p.11 (wet 80-130 / dry 120-180); SFM converted |
| Austenitic stainless steel, 304 and 316 | Drilling | HSS-Co and HSS-E-PM drills | 13-20 | 43-66 | two published grades; the range spans both | 820902 · 810434 |
| Ferritic and martensitic stainless steel | Drilling | HSS and HSS-E-PM drills | 15-20 | 49-66 | two published grades, both landing on the same window | 811505 · 810434 |
Sources: recommended cutting speeds are taken from the published application data of tool makers — Kennametal TopSwiss MBS and inserts application data, Ingersoll IMC Cutting Data and Parameters handbook, OSG VGM7 / VG446 / HSS-Co datasheets, Guhring RF 100 series, Uddeholm Unimax cutting data and Dormer Pramet workpiece material groups. The reference recorded for every row — as it is logged in our data, which is a document page, a column, a document number, or the grade breakdown the document itself prints — is carried in the last column of the table, so each figure can be taken back to what it came from without asking us for it. Values published only as surface feet per minute were converted at 1 m/min = 3.28084 SFM and are marked as converted. The rows in the table are the extremes of the published range for each stainless grade condition and operation, with no interpolation between them. ISO P / M / K / N / S / H group letters follow ISO 513:2012.
Read the row that matches your grade family and operation, then treat the feed as the variable that matters most. A stainless insert run at a correct surface speed with too light a feed work-hardens the surface in front of it; the same insert at the same speed with a real chip load cuts cleanly. When a job is failing on tool life, the feed is the first thing to check and the speed is the second.
The table gives surface speed only. Feed and depth of cut depend on the insert geometry and the machine, and a figure printed here would be wrong for most readers. Thread cutting follows the same rule: the figure that governs a thread in stainless comes with the specific tap or thread mill, and it is well below the drilling figures above, because a tap has far less space to clear a chip that welds. Send us the grade and the thread callout and we come back with that figure rather than a general one.
From surface speed to spindle speed
- Spindle speed in metric: n = (vc x 1000) / (pi x D), with vc in m/min and D the diameter in millimetres.
- Spindle speed in imperial: n = (SFM x 3.82) / D, with D the diameter in inches.
Worked from the table above
- Turning a 50 mm 304 bar: at 150 m/min, n = (150 x 1000) / (3.14159 x 50) = 955 rpm.
- The same surface speed on a 200 mm flange: n = (150 x 1000) / (3.14159 x 200) = 239 rpm, which is why a large stainless part is often limited by the machine rather than by the insert.
- Milling 304 at 250 SFM: with a 12 mm cutter, n = (250 x 3.82) / 0.472 = 2,021 rpm.
- Drilling 304 with a 10 mm HSS-Co drill: at 18 m/min, n = (18 x 1000) / (3.14159 x 10) = 573 rpm, which is the low-speed, high-feed picture that keeps the drill under the work-hardened skin.
Put it on the machine
The same arithmetic is on the cutting speed reference, with drill and tap diameters from every series rather than the stainless rows above, so a figure read here can be turned into a spindle setting for any tool in the job without leaving the site.
Where the table gives a window rather than a figure, start at the bottom of it on an unfamiliar setup and move up while the chip breaks cleanly and the finish holds. The machine, the holder and the part decide how far up the window you can go; the table only says where the window is.
Data and Service
Where the figures come from
Every figure here carries its origin, and the three kinds of source are kept apart: published standards named by number and year, industry figures named by the document they were read from, and customer feedback written up as what it is.
Published standards
The ISO P / M / K / N / S / H application groups used to describe the tooling come from ISO 513:2012, which fixes what each letter covers. Where a figure comes from a standard, it is named with the standard and the year it was issued, per row.
Tool makers and industry data
The cutting-speed ranges in the table above are the values printed by the tool makers our data is taken from. They are used as published, at the extremes of the published window, and every row carries its document and page or column reference in our source file so any figure can be checked before it is used on a job.
Trial feedback
Where a customer tells us what a grade actually did on their machine, it is recorded as an attributed note rather than reworked into an illustrative story. We do not publish references we cannot point to.
What comes with a quotation
Two things we do go beyond the table. Both are actions rather than figures, and both are visible in a quotation before anything is ordered.
A starting cutting speed with the quotation
Send the stainless grade or its designation, the operation, and the machine it runs on. The quotation comes back with a starting surface speed and a feed range for the insert family we propose. Treat it as the first setting rather than a guarantee of the result: the figure is decided by your setup, the holder and the part, and it is meant to be adjusted from the chip and the finish.
Trial quantities to prove it on the machine
The honest answer to "will this grade run on my stainless" is a trial order, not a data sheet. Small quantities and mixed orders are welcome, and charges and freight are confirmed against the actual enquiry rather than published as a fixed number.
How we handle a tooling enquiry from first question to delivery
Questions Buyers Ask
Stainless steel questions we are asked before quoting
The published windows in the table above run from 25 to 215 m/min for austenitic grades, and the width of that window is the honest answer: the number depends on the grade, the insert and the rigidity of the setup more than on the material alone. Start in the lower half on an unfamiliar setup and move up while the chip breaks cleanly. On a 50 mm bar, 150 m/min is 955 rpm. If the job is failing, check the feed before you change the speed.
That notch is where the material meets the part of the edge that is not cutting, and on stainless it is aggravated by the work-hardened layer the previous pass left at exactly that depth. Removing that layer rather than skimming it, keeping the depth of cut out of the hardened band, and choosing a grade with a strong edge and a geometry that resists notching are the three levers. Where depth is fixed by the drawing, say so when you order and we will quote for the notch rather than against it.
Because a tap has almost no space to clear a chip that is inclined to weld, and it is doing it in a hole that work-hardens around it. The usual failure chain starts with a dull or oversize drill, which leaves a harder surface for the tap to cut. Thread milling removes most of the problem by interrupting the cut and letting the chip fall clear, and where a tap is unavoidable the drill condition and a slightly larger hole matter more than the tap itself.
The surface of austenitic stainless hardens as it is deformed, and cutting deforms it. A light pass, a slow feed or a pause with the tool still in contact leaves a layer harder than the material below, and the next revolution cuts that harder layer and hardens it again. The way out is to cut rather than rub: a sharp, positive edge, a feed high enough to keep the edge below the hardened skin, and no dwelling anywhere in the cut.
No, and the difference is large. Austenitic 300-series grades work-harden strongly and gall, and they are the reason the rules here exist. Ferritic and martensitic 400-series grades cut much closer to a low-alloy steel, and duplex grades sit between the two with higher strength than either. Give us the grade rather than the word stainless and the answer will be specific to it.
Usually yes, and continuously rather than intermittently. Stainless carries heat away from the cut poorly, so the edge runs hot, and coolant that reaches a hot edge in bursts thermally cracks it. The useful strategies are a full flow aimed at the cut, or through-tool coolant on a deep hole, rather than a general flood over the whole part. If the operation is being run dry, that should be a decision made for a reason rather than a habit.
Not well. Stainless is in the ISO M group and carbon steel is in ISO P, and the two groups ask for opposite things: P grades are built around wear resistance and heat, M grades around edge strength and toughness, because stainless work-hardens and notches the edge instead of wearing it evenly. An insert that performs on carbon steel will usually chip or notch on stainless, and the reverse wastes the tool life the M grade was bought for.
Yes. Send the grade designation, the operation and the machine, and we come back with the insert family, the grade and a starting surface speed for it. Where the grade is one we have not quoted before, we confirm which family it belongs to — austenitic, duplex, ferritic or martensitic — before naming an insert, because that single question decides whether the answer is built around toughness or around wear resistance.
Send the grade and the operation — get the insert family and a starting speed
Tell us the stainless grade rather than the word stainless, what the part is and which machine it runs on. You get the insert family and grade we would quote for it, the holder that suits the setup, and a starting surface speed and feed for the combination.