How to Choose the Right Carbide Insert Grade: ISO P/M/K/N/S/H Classification Explained
Walk into any machine shop and you will see drawers full of carbide inserts — each with a unique grade code stamped on the box. Selecting the wrong grade can mean premature tool failure, poor surface finish, or wasted cycle time. This guide explains the ISO 513 classification system that every machinist needs to know, and maps the most popular Korloy grades to their ISO groups and competitor equivalents.
The ISO 513 Classification System
The ISO 513 standard divides workpiece materials into six main groups, each identified by a letter and color code:
| ISO Letter | Color Code | Material Group | Typical Materials | Chip Type |
|---|---|---|---|---|
| P | Blue | Steel | Carbon steel, alloy steel, tool steel, cast steel | Long continuous chips |
| M | Yellow | Stainless Steel | Austenitic, ferritic, martensitic, duplex stainless | Segmented / tangled chips |
| K | Red | Cast Iron | Gray iron, nodular iron, CGI, malleable iron | Short discontinuous chips |
| N | Green | Non-Ferrous | Aluminum, copper, brass, bronze, plastics | Long chips (Al), short (brass) |
| S | Brown | Super Alloys | Inconel, titanium, Hastelloy, Waspaloy, Co-Cr alloys | Short, segmented chips |
| H | Gray | Hard Materials | Hardened steel (>45 HRC), chilled cast iron, hard ceramics | Dust-like, powdery chips |
Understanding Sub-Groups (P10 vs. P20 vs. P30)
Each main group is further divided into sub-groups numbered 01–50. Lower numbers indicate harder, more wear-resistant grades for stable, continuous cutting. Higher numbers indicate tougher, more shock-resistant grades for interrupted cuts.
| Sub-Group | Hardness (HV30) | Transverse Rupture Strength | Best For |
|---|---|---|---|
| 01–10 | 1700–1900 | Low–Medium | Finishing of stable, continuous cuts. High speed, low feed. |
| 10–20 | 1550–1750 | Medium | Semi-finishing. General purpose for stable conditions. |
| 20–30 | 1400–1600 | Medium–High | Medium roughing. Moderate interruptions. |
| 30–40 | 1250–1450 | High | Heavy roughing, interrupted cuts, unstable setups. |
| 40–50 | 1100–1300 | Very High | Severe interruptions, milling of hard steels, scale removal. |
Grade Selection Matrix by Material and Operation
| Workpiece Material | ISO Group | Operation | Korloy Grade | Coating | Sandvik / Kennametal / Sumitomo |
|---|---|---|---|---|---|
| Low Carbon Steel (C ≤ 0.25%) | P10–P20 | Finishing | PC5300 | CVD TiCN/Al₂O₃ | 4225 / KCP25 / AC8025P |
| Medium Carbon Steel (0.25–0.55% C) | P20–P30 | General Turning | PC5335 | CVD TiCN/Al₂O₃ | 4325 / KCP35 / AC8035P |
| Alloy Steel (hardened to 38–48 HRC) | P30–P50 | Roughing | PC5400 | CVD TiCN/Al₂O₃ | 4425 / KCP40 / AC8045P |
| Austenitic Stainless (304, 316L) | M10–M20 | Finishing | PC215K | PVD TiAlN | 2220 / KCU25 / AC6020P |
| Austenitic Stainless (interrupted) | M20–M30 | Roughing | PC2507 | CVD Al₂O₃/TiCN | 2325 / KCU30 / AC6030P |
| Duplex Stainless (2205) | M30–M40 | Heavy Roughing | PC2507 | CVD Al₂O₃/TiCN | 2330 / KCU30 / AC6040P |
| Gray Cast Iron (GJL-200) | K10–K20 | Finishing / General | KC5305 | CVD Al₂O₃/TiCN | 3210 / KCK15 / AC410K |
| Nodular Iron (GJS-500) | K20–K30 | Roughing | KC5335 | CVD Al₂O₃/TiCN | 3225 / KCK25 / AC420K |
| Aluminum Alloy (6061-T6) | N10–N20 | High-Speed Machining | NCM325 | PVD TiB₂ / Uncoated | H10F / K313 / ACP200 |
| Inconel 718 | S10–S30 | Turning | PC3545 | PVD AlTiN | 2235 / KCS10B / AC6030P |
| Titanium Ti-6Al-4V | S20–S30 | Turning | PC3545 | PVD AlTiN | 2235 / KCU30 / ACP300 |
| Hardened Steel (>55 HRC) | H10–H20 | Hard Turning | NC3225 | PVD AlTiN / CBN | 7015 / KB5625 / BNC200 |
PVD vs. CVD Coating: When Does Each Win?
| Factor | CVD Coating | PVD Coating |
|---|---|---|
| Coating thickness | 8–20 µm (thick) | 2–6 µm (thin) |
| Edge sharpness | Slightly rounded (edge prep required) | Very sharp (near-zero hone) |
| Wear resistance | Excellent (Al₂O₃ thermal barrier) | Good |
| Toughness | Moderate | Excellent |
| Best for | Steel & cast iron, stable continuous cuts, high speed | Stainless, super alloys, interrupted cuts, low speed |
| Recommended Korloy series | PC53xx, KC53xx, KC54xx | PC215K, PC3545, NC3225 |
Decision Flowchart: Choosing Your Grade in 4 Steps
Step 1: Identify your ISO material group. Check your material cert or spark test. Steel = P, Stainless = M, Cast Iron = K, Aluminum = N, Superalloy = S, Hardened = H.
Step 2: Determine the operation type. Roughing = higher sub-group number (tougher). Finishing = lower sub-group number (harder/wear-resistant).
Step 3: Assess cutting conditions. Stable setup with good clamping? Use harder grade. Interrupted cuts, long overhang, or poor fixturing? Step up to tougher grade.
Step 4: Select coating type. Continuous cuts on steel/iron = CVD. Stainless, super alloys, or interrupted = PVD. Aluminum/non-ferrous = PVD TiB₂ or uncoated polished carbide.
Common Mistakes to Avoid
- Using P-grade on stainless steel: P-grade lacks the toughness and heat resistance for work-hardening austenitic stainless. Switch to M-grade immediately.
- Using finishing grade for roughing: A P10 grade in interrupted roughing will chip within seconds. Always match sub-group to severity.
- Ignoring chipbreaker selection: Even the perfect grade will fail if the chipbreaker does not match the feed rate and depth of cut. See our chipbreaker guide for details.
- Running too fast with PVD: PVD coatings have lower thermal limits than CVD. Keep Vc 10–20% lower than CVD recommendations for steel.
Ready to find your optimal grade? Browse Korloy inserts by ISO group at hooguu.com — our catalog includes cross-references to Sandvik, Kennametal, Sumitomo, and Tungaloy equivalents. Contact us for a free grade recommendation based on your specific application.
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