Applications · Carbon and Alloy Steel
Steel Turning: Choosing the Insert Family and Cutting Data for Carbon and Alloy Steel
Steel is the material most turning work is quoted in, and it is not one material. Free-cutting and low-carbon grades machine easily but tear the finish and build an edge up on the insert; medium and high-carbon grades wear the flank and dig a crater behind it; alloyed, forged and scaled stock loads the edge unevenly and sets up vibration before the insert is anywhere near worn out. What actually changes the choice is the ISO P group, the coated carbide grade behind it, and the geometry that suits a continuous or an interrupted cut; the cutting speeds published for steel turning, milling and drilling by the tool makers our data comes from are set out below. It is written for the buyer or process engineer who has a steel part, a machine and a delivery date, and needs to know which insert family to order and what to start it at.
Failure Modes
Three failure modes that decide how you cut steel
Almost every steel turning problem we are asked about lands in one of three places, and they pull the choice of grade and geometry in different directions. Reading which one applies before ordering is what stops a grade being changed twice for the wrong reason.
Failure mode 01
Built-up edge and a torn finish
What actually fails
Free-cutting and low-carbon steel is soft enough that the chip welds to the cutting edge under pressure instead of flowing away from it. The built-up edge grows until it breaks off, taking coating and edge material with it. What the operator sees is a finish that looks torn rather than turned, a diameter that drifts across the batch, and an insert that appears to have failed long before its wear land says it should have.
What to look for in the tool
Look for a grade whose coating resists adhesion rather than one that only resists abrasion, and for a geometry with a sharp, positive cutting edge that keeps the cut ahead of the built-up edge. Surface speed suppresses it as well, which is why the free-machining rows in the table below sit so much higher than the alloy steel rows.
Failure mode 02
Crater and notch wear on higher-carbon steel
What actually fails
As carbon content and hardness rise, the chip leaves hot and stays hot. That heat sits on the rake face and digs a crater behind the cutting edge, while the depth-of-cut line notches away at the flank. Both progress faster on dry, continuous turning of medium and high-carbon steel than a plain flank-wear calculation expects, so the insert looks like it failed early even though it was never overloaded.
What to look for in the tool
Look for a coating that acts as a thermal barrier and a substrate with enough hot hardness to hold the edge under the crater. Keep the next pass out of the skin the previous one hardened, and use coolant only if the machine can deliver it continuously rather than in bursts. This is the reason the carbon and alloy steel rows below are slower than the free-machining rows.
Failure mode 03
Deflection, chatter and a hard or scaled surface
What actually fails
Long shafts, thin walls and unsupported overhangs bend under the cut long before the insert reaches its wear limit, so the failure arrives as chatter and a tapered shaft rather than as a worn edge. Hot-rolled, forged and flame-cut stock adds a hard, uneven skin on top: the insert enters it intermittently and is loaded harder by the first pass than by everything that follows.
What to look for in the tool
Look for a tougher geometry and a coating that tolerates interrupted cutting, take the first pass under any scale or skin rather than through it, and support the part with a steady or a tailstock before blaming the grade. Where the part cannot be supported, the answer is usually a lighter depth of cut at a higher speed rather than a harder insert.
One boundary is worth stating plainly. Carbon, alloy and free-machining steel cut in the normalised or annealed condition is the ISO P group, and it is what the figures below cover. Steel that has been through-hardened above roughly 45 HRC behaves differently: it is machined by a different family of cutting materials, against the hardened steel data, together with CBN and PCD inserts. Three figures sit near each other and mean different things — 45 HRC is the line between the two sets of data, the ISO H group spans 40 to 60 HRC, and a vendor row is published at the hardness that row was tested at. If the drawing carries a hardness callout rather than a grade, that callout decides which figures apply.
Tool Matrix
Which tool family for which steel operation
Steel turning is where most of the cost sits, but it is rarely the only operation on the part. The blocks below follow the order a job is usually quoted in — turning first, then milling, then the hole and the thread — and every card stops at the level of the tool family, its coating or material group and its ISO application group.
Grade designations, edge preparations and sizes are decided against the actual operation, the holder and the tolerance on the drawing, and they belong to the product range rather than to a material overview. Tell us the operation and we will name the specific inserts; the cards here tell you which range you are choosing between.
Turning
Turning removes most of the material and sets up every dimension that follows. The choice inside the range is between coating systems and edge geometry, and both are decided by whether the cut runs continuously or enters and leaves the steel on every revolution.
Turning inserts for steel
Coated carbide indexable inserts in the P group. CVD-coated grades for continuous cuts from roughing through medium turning, PVD-coated grades where the cut is interrupted or the edge has to stay sharp. Negative-rake double-sided shapes for the heavier passes, positive-rake for light finishing and slender parts.
Inserts for finishing and slender steel parts
Sharp, low-force positive-rake inserts for the last passes on shaft work and thin-wall steel parts, where reducing cutting force matters more than edge strength and where a built-up edge has to be kept off the finish.
All turning insert shapes and groups
The ISO turning shapes we quote and the application groups they cover, with the note that belongs to each, so a shape can be matched to the operation before a grade is picked.
Milling
Milling steel is where the grade is chosen for the cut as much as for the material. A continuous dry face-milling pass and an interrupted shoulder cut in scaled stock ask for opposite properties from the same ISO P group.
Milling inserts for steel
Coated carbide inserts for face and shoulder milling of carbon and alloy steel. Tougher grades where the cut is interrupted or the surface carries scale, harder and more wear-resistant grades for continuous dry milling of unalloyed and mild steel.
Solid carbide end mills for steel
Coated solid carbide end mills in 4- and 6-flute geometry for slotting, side milling and profiling steel, with HSS-Co options for lower-speed machines and longer reach.
All milling and holemaking ranges
The full range the figures here draw from — insert milling, solid end mills, drills and threading tools in one place, grouped by the operation they are bought for.
Drilling, threading and workholding
The hole and the thread are where a correct choice is cheapest and a wrong one is most expensive, because both fail by breaking the tool inside the part. Workholding is the third block for the same reason: it decides whether the insert you chose actually runs at the parameters it was bought for.
Drill bits for steel
HSS, HSS-Co and HSS-E-PM twist drills for general steel drilling, plus indexable carbide drills and U-drills for larger holes and higher production. In steel, the drill is usually the first tool into the material and sets up what the rest of the job inherits.
Threading tools for steel
Thread turning inserts and thread mills in P-group grades for external and internal threads, plus taps for through and blind holes where a milled or turned thread is not the practical answer.
Tool holders for steel turning and milling
Turning holders, boring bars and milling arbors that hold the insert square to the workpiece and match the shape you have chosen. A holder that flexes costs more in insert life than the insert choice does.
Cutting Data
Published cutting speeds for turning, milling and drilling steel
The table gives the surface speed published for steel in each operation, drawn from the same source data as the cutting speed reference so the two sets of figures cannot disagree. Ranges are used exactly as the tool makers print them: the lower figure is where a cautious setup starts and the upper figure assumes a rigid machine, stable support and a first-choice grade.
Turning steel spans the widest range of any operation here, because the difference between free-machining steel and alloy steel is a difference in how the chip behaves rather than a difference in hardness. Drilling is the slowest operation in the table for the same reason that it is the hardest to recover from: the speeds are low because the cutting edge sits in a hole with no way for the heat to leave.
| Steel condition | Operation | Tool family | Cutting speed (m/min) | Cutting speed (SFM) | Basis of the range | Source (as recorded) |
|---|---|---|---|---|---|---|
| Free-cutting and low-carbon steel (under 0.3% C) | Turning | coated indexable carbide | 50-395 | 165-1295 | lowest to highest value published across the coated carbide grades the source lists for this material | range = min-max across HT-series grades · KCP20S 50-274; KTP25S 122-351 |
| Medium and high-carbon steel (over 0.3% C) | Turning | coated indexable carbide | 50-312 | 165-1025 | same basis as the row above: the extremes of the published grade range | range across grades · KCP20S 50-250; KTP25S 122-312 |
| Unalloyed and mild steel | Milling | coated indexable carbide, dry | 250-290 | 820-951 | published as one dry-milling window for wear-resistant grades | p.10/p.11; SFM converted |
| Alloy steel 800 to 1,100 N/mm2 | Milling | coated indexable carbide | 110-250 | 361-820 | the two strength bands are published as separate rows; the range shown spans both | p.10/p.11; SFM converted |
| Mild steel, brass, bronze | Milling | HSS-Co, 4 and 6 flute | 24-46 | 80-150 | one published column covers the three materials together | OSG p.1410 col.1, 80-150 SFM; column mapping verified by x-coordinate |
| Non-alloy carbon steel | Drilling | HSS and HSS-Co jobber drills | 22-28 | 72-92 | two published grades; the range spans both | vc 25 (23-28) m/min, 811505 · vc 25 (22-27) m/min, 820902 |
| Non-alloy carbon steel | Drilling | HSS-E-PM drills | 30-40 | 98-131 | published as a single recommended figure with a working window around it | vc 35 (30-40) m/min, 810434 |
| Low-alloy steel | Drilling | HSS worm-pattern drills | 15-20 | 49-66 | published range for the grade | 811505 |
Sources: recommended cutting speeds are taken from the published application data of tool makers — Ingersoll IMC Cutting Data and Parameters handbook, Kennametal TopSwiss MBS and turning inserts application data, Guhring RF 100 series, OSG VGM7 / VG446 / HSS-Co datasheets, Uddeholm Unimax cutting data, SSAB Hardox machining recommendations 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. Where a row combines several published values, the last column lists each of them. 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 steel 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 steel condition and operation, pick a figure inside the range, then adjust on the machine. If the finish is bright but the edge is notching, you are at the high end of the window; if the chip is tearing or the spindle is stalling, you are at the low end or the machine is the limit rather than the grade.
The table gives surface speed only. Feed and depth of cut are both are properties of the insert geometry and the machine rather than of the material, and a number printed here would be wrong for most of the readers who used it. Thread cutting follows the same rule. Thread turning and tapping run far slower than the speeds above, and the figure that governs is the one the tap or thread-turning insert is published with for the specific thread form and depth. Send us the thread callout with the material 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 steel shaft: at 200 m/min, n = (200 x 1000) / (3.14159 x 50) = 1,273 rpm.
- The same surface speed on a 100 mm shaft: n = (200 x 1000) / (3.14159 x 100) = 637 rpm — half the speed for twice the diameter.
- Milling with a 2 in cutter: at 650 SFM, n = (650 x 3.82) / 2 = 1,242 rpm.
- Free-machining steel at the top of the window: a 25 mm bar at 395 m/min gives n = (395 x 1000) / (3.14159 x 25) = 5,029 rpm, which is the point at which most manual machines run out of spindle rather than the grade running out of capability.
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 steel 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 steel grade or its hardness, 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 steel" 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
Steel turning questions we are asked before quoting
For general turning of mild and low-carbon steel, a coated carbide insert in the ISO P group with a positive cutting edge and a coating that resists adhesion is the sensible starting family. Mild steel is soft enough to weld onto the edge rather than wear it, so edge sharpness and coating choice matter more than substrate hardness. Tell us the operation, the machine and whether the part is slender, and we will name the specific insert we would quote rather than a general recommendation.
The published window for free-cutting and low-carbon steel in the table above runs from 50 to 395 m/min across the coated carbide grades it covers, which is a wide window because it spans roughing to finishing grades. Start low in the range if the setup is not rigid or the part is long, and move up while the chip and the finish stay good. Convert the figure to spindle speed with the formula above; on a 50 mm shaft, 200 m/min is 1,273 rpm.
Free-machining steel is designed to break the chip early, and the price of that is a soft, adhesive workpiece surface. The chip welds to the edge, the weld breaks off, and it takes coating with it — so the insert fails by chipping rather than by wearing out. A coating that resists adhesion, a sharper edge and a higher surface speed all push the failure point back. If the insert is chipping in the first minute rather than after a batch, the setup is usually entering the cut too heavily as well.
ISO 513:2012 sorts hard cutting materials into main application groups by the workpiece they suit, and P is the group for steel — carbon, alloy and free-machining. A grade printed with a P group is a grade whose coating and substrate were developed for steel chip formation and steel heat. Ordering a grade from another group for a steel job is the most common way to get an insert that wears out early or breaks, and it is also why the same insert shape can appear in several groups with different behaviour.
Coated, for almost every steel job. The coating is what holds the heat away from the substrate and lets the insert run at the surface speeds in the table; an uncoated carbide insert on steel usually has to be run slower and still wears faster. The useful distinction is between coating systems rather than between coated and uncoated: a chemically vapour deposited coating for continuous cuts and higher temperatures, a physically vapour deposited coating where the cut is interrupted or the edge must stay sharp.
Support first, then grade. Chatter on a slender steel shaft is usually a stiffness problem rather than an insert problem, so a steady or a tailstock removes more of it than any change of grade will. After that, reduce the depth of cut and raise the surface speed, which moves the cut away from the natural frequency of the part. If the insert is running at the top of its speed window and still chattering, a tougher geometry that tolerates the vibration is a better answer than a harder one.
Yes, at least for the first pass. Scale and the decarburised skin under it are hard and uneven, so the insert enters and leaves the material on every revolution instead of cutting continuously. Take the first pass under the scale rather than through it, and use a grade and geometry intended to tolerate interrupted cutting. Once the skin is off, the same part can be finished with the grade you would have chosen for clean stock — which is often where the second insert on the job earns its cost back.
Yes. The table covers the steel conditions that most enquiries fall into, not every grade in a standard. Send the material designation or its hardness and tensile strength, the operation, and the machine it will run on; we come back with the insert family, the grade we would quote and a starting surface speed for it. For a draw that specifies a grade we have not quoted before, we confirm the material group before naming an insert rather than working backwards from the grade we happen to stock.
Send the steel grade and the operation — get the insert family and a starting speed
Tell us the grade or its hardness, 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 it, and a starting surface speed for the combination, rather than a catalogue to search through.