Machinability Chart

A machinability rating compares the cutting speed a material allows, for a fixed tool life, with a reference material. The American Iron and Steel Institute (AISI) scale uses B1112 — a resulfurized Bessemer screw-machine steel — cold drawn, turned with a high-speed-steel tool at 180 surface feet per minute (about 55 m/min) for a 60-minute tool life, as 100 %. B1112 is no longer made; 1212 replaced it and rates the same. Higher ratings mean higher speeds, longer tool life or both.

Copper alloys are traditionally rated on their own scale with free-cutting brass C36000 = 100. Free-cutting brass runs at roughly 1.7 times the speed of B1112, so this chart lists copper alloys as the CDA rating × 1.7 and keeps the original CDA number in the row details.

Estimating a Cutting Speed

The rating scales a speed you already trust:

Example: your shop runs 1018 (78 %) at 400 sfm with a carbide insert. 304 stainless (45 %) starts at about 400 × 45 ÷ 78 ≈ 230 sfm. To do this in the chart, enter 400 × 100 ÷ 78 ≈ 513 as the B1112 speed and read the Est. speed column. Treat the result as a starting point; insert grade, coating, coolant, rigidity and depth of cut all move the real number.

ISO 513 Material Groups

Tooling catalogues group workpiece materials by ISO 513 letter and colour. The chart tags every row the same way.

Group	Materials	How they cut
P Blue	Carbon, alloy and tool steel; ferritic and martensitic stainless	Long continuous chips; chip control and crater wear dominate.
M Yellow	Austenitic, duplex and PH stainless	Work hardening, built-up edge and notch wear; keep a constant feed.
K Red	Grey, ductile, malleable and compacted graphite iron	Short chips, abrasive; flank wear dominates.
N Green	Aluminium, magnesium, copper alloys	Low forces and high speeds; built-up edge and long chips in soft grades.
S Orange	Fe, Ni and Co superalloys; titanium	Heat stays at the edge, high forces, work hardening; low speeds.
H Grey	Hardened steel (about 45–68 HRC), chilled and white iron	Hard turning and milling with CBN or ceramic, or grinding.

Rating Colour Bands

Band	Rating	Typical materials
Excellent	≥ 150 %	Magnesium, aluminium, free-cutting brass, 12L14, malleable iron
Very good	100–149 %	1212, 1215, soft grey iron, leaded bronze
Good	70–99 %	1018, 1117, 4130, 303, 416
Fair	50–69 %	1045, 4140, 4340, 410, H13
Poor	30–49 %	304, 316, 17-4 PH, A2, Monel 400, CP titanium
Difficult	15–29 %	D2, duplex 2205, Ti-6Al-4V, Inconel 625, Hastelloy
Very difficult	< 15 %	Inconel 718, Waspaloy, cast Stellite, hardened steel

Designation Systems in the Table

Column	System	How to read it
UNS	Unified Numbering System (SAE J1086 / ASTM E527)	Letter for the family + 5 digits. G10180 = 1018, S30400 = 304, A96061 = 6061, C36000 = free-cutting brass, N07718 = Inconel 718, R56400 = Ti-6Al-4V.
AISI / SAE / ASTM	US grade or governing spec	Steel grades (1018, 4140), stainless types (304, 17-4 = Type 630), Aluminum Association numbers, ASTM specifications for castings, pipe and plate.
AMS	SAE Aerospace Material Specification	Procurement specs for aerospace; one alloy has several (e.g. Ti-6Al-4V bar AMS 4928, sheet AMS 4911).
DIN (EN)	German / European short name (EN 10027-1)	Describes chemistry. C45 = 0.45 % C. 42CrMo4 = 0.42 % C, Cr×4 ≈ 1 %, Mo. X5CrNi18-10 = high-alloy, 0.05 % C, 18 % Cr, 10 % Ni. Older names (Ck45, GG-25, GGG-40) are listed as aliases.
WNR	Werkstoffnummer (EN 10027-2)	Number x.xxxx. 0 = cast iron, 1 = steel (1.4xxx stainless), 2 = Cu/Ni/Co alloys, 3 = Al/Mg/Ti alloys. 1.4301 = 304, 1.7225 = 4140, 3.7165 = Ti-6Al-4V.
JIS	Japanese Industrial Standard	SUS = stainless, SCM = Cr-Mo steel, SNCM = Ni-Cr-Mo, S45C = 0.45 % C, SKD/SKH = tool steels, A6061 = aluminium.

Cross-references are nearest equivalents. Chemistry ranges, heat treatments and test requirements differ between standards, so procurement must name the controlling specification.

Common Aliases You Can Search

• 18-8, 18/8, CRES, A2, V2A — 300-series austenitic stainless (302, 304, 304L). "CRES" (corrosion-resistant steel) is the aerospace term for any stainless.
• A4, V4A, marine grade — 316 / 316L.
• 630, 17-4 — 17-4 PH. XM-12 — 15-5 PH. XM-13 — 13-8 Mo.
• Chromoly / chrome-moly — 4130, 4140. Bearing steel — 52100 / 100Cr6 / SUJ2.
• Grade 5, Ti64, 6-4 — Ti-6Al-4V. Grade 23 — Ti-6Al-4V ELI.
• Alloy 718, IN718 — Inconel 718. Alloy 400 — Monel 400. Alloy 660 — A-286.
• FCB, Alloy 360 — C36000 free-cutting brass. BeCu — C17200. NAB — nickel-aluminium bronze.
• GG-25, GGG-40, GTS-35-10 — old DIN cast-iron names.

What Changes Machinability

• Hardness and strength. Within one alloy, harder almost always means slower. The Hardened Materials class shows how far 4340 and D2 drop once heat treated.
• Condition. Cold drawing improves chip breaking in low-carbon steel; spheroidize annealing helps high-carbon and tool steels; overaged PH stainless (H1150) cuts better than condition A.
• Free-machining additions. Sulfur, lead, bismuth, selenium and tellurium form inclusions that break chips (12L14, 303, 416, C36000, C14500, 2011).
• Work hardening. Austenitic stainless, nickel alloys and Hadfield-type steels harden ahead of the tool; light, rubbing cuts make it worse.
• Thermal conductivity. Titanium and nickel alloys keep heat at the edge instead of carrying it away in the chip.
• Abrasive phases. Primary carbides (D2), titanium carbonitrides (321), and silicon in cast aluminium wear tools quickly.

Limitations

Ratings are typical values compiled from widely published machinability tables, not test data for a specific heat or bar. Sources disagree by roughly ±10–25 %, more for cast iron, aluminium and superalloys, and the single-number rating says nothing about chip form, surface finish or burr formation. Rows marked * were estimated from similar alloys because no published rating was found. Use the chart to rank materials and to scale speeds you have already proven, and confirm cutting data with your tooling supplier.