ISO P M K N S H Carbide Grades: Complete Cross-Brand Parameter Reference

Understanding the ISO Carbide Classification System

The International Organization for Standardization (ISO) classifies cemented carbide grades into six major application categories based on the workpiece material they are designed to machine. Each category is designated by a letter — P, M, K, N, S, or H — and sub-divided by hardness/toughness performance bands numbered 01 through 50. Lower numbers indicate harder, more wear-resistant grades suited for finishing operations, while higher numbers represent tougher grades optimized for roughing.

This reference guide consolidates cutting parameters, grade equivalents, and application data for five major carbide manufacturers — Sandvik Coromant, Seco Tools, Kennametal, Mitsubishi Materials, and Sumitomo Electric Hardmetal — giving machinists a single-sheet comparison across the full ISO spectrum.

ISO Application Categories at a Glance

ISO P — Steel Turning: Grade Cross-Reference

Steel machining accounts for the largest share of indexable insert consumption globally. P-class grades must balance crater wear resistance (driven by high cutting temperatures during continuous cutting) with sufficient edge toughness to handle interrupted cuts and scale on forged surfaces.

Sandvik, Seco, Kennametal, Mitsubishi & Sumitomo — P-Class Equivalents

Recommended P-Class Cutting Parameters

ISO M — Stainless Steel: Grade Cross-Reference

Stainless steel presents a unique machining challenge because it work-hardens during cutting, generates high cutting forces, and tends to weld to the tool edge. M-class grades require a specialized balance of hot hardness, chemical stability, and edge sharpness.

Grade Equivalents for Stainless Steel

Recommended M-Class Cutting Parameters

ISO K — Cast Iron: Grade Cross-Reference

Cast iron machining demands exceptional abrasive wear resistance due to the hard graphite and carbide inclusions within the material. K-class grades typically feature high cubic boron nitride (CBN) content or thick Al₂O₃ coatings to combat the high-speed abrasive action encountered in gray and ductile iron turning.

Grade Equivalents for Cast Iron

Recommended K-Class Cutting Parameters

ISO S — Heat-Resistant Superalloys: Grade Cross-Reference

Nickel-based and titanium alloys used in aerospace, energy, and medical industries present the most demanding machining challenges. Low thermal conductivity concentrates heat at the cutting zone, while the material’s inherent strength at elevated temperatures causes rapid tool wear. S-class grades rely on advanced PVD coatings (TiAlN, AlTiN) with high hot hardness.

Grade Equivalents for Superalloys

Recommended S-Class Cutting Parameters

ISO N — Non-Ferrous Alloys: Grade Cross-Reference

Aluminum, copper, and their alloys are typically machined at very high cutting speeds. The primary challenges are built-up edge (BUE) formation and achieving the required surface finish. N-class grades use polished PVD coatings (diamond-like carbon, TiB₂) or uncoated micro-grain carbide to maintain sharp cutting edges.

Grade Equivalents for Non-Ferrous Materials

Recommended N-Class Cutting Parameters

ISO H — Hardened Materials: Grade Cross-Reference

Hard part machining (HPM) eliminates grinding operations by turning or milling materials at hardness levels above 45 HRC. This demands grades with exceptional hot hardness, typically using CBN or advanced ceramic substrates. PVD-coated carbide grades can handle up to approximately 55 HRC, while CBN is required for 55–68 HRC materials.

Grade Equivalents for Hardened Materials

Recommended H-Class Cutting Parameters

Coating Technology Comparison: CVD vs PVD

The choice between CVD (Chemical Vapor Deposition) and PVD (Physical Vapor Deposition) coatings significantly impacts insert performance. Most P and K class roughing grades use CVD for its thicker, more wear-resistant layers, while finishing and S-class grades favor PVD for sharper edges and lower residual stress.

Practical Selection Guidelines

• Always match ISO class to workpiece material. Using a P-class grade on stainless steel or a K-class grade on steel will result in dramatically shorter tool life due to incompatible coating chemistry and substrate toughness.
• When in doubt, go one grade tougher. Selecting a grade that is slightly tougher (higher number) than theoretically necessary usually provides more forgiving performance than choosing the hardest available grade.
• Check coating compatibility. Titanium alloys can react chemically with certain Ti-based coatings, accelerating wear. Use AlCrN or AlTiN coatings for titanium and nickel alloys.
• Consider the cutting operation. Finishing operations prioritize sharpness and wear resistance (lower band numbers), while roughing operations need toughness and thermal shock resistance (higher band numbers).
• Leverage cross-brand equivalents. If a preferred brand grade is unavailable, use this reference to find the equivalent grade from another manufacturer. Always verify with the manufacturer’s catalog, as formulations change between product generations.
• Account for coolant delivery. High-pressure coolant (70+ bar) can shift parameter windows significantly, particularly for stainless steel and superalloys. When HPC is available, upper-range Vc and f values become more achievable.

Conclusion

Selecting the right carbide grade is a foundational decision that impacts every downstream metric — surface finish, tool life, cycle time, and cost per part. By understanding the ISO classification system and how major manufacturers position their grades within it, machinists can make informed substitutions, optimize parameter selection, and avoid common mismatches that lead to premature tool failure. Keep this reference handy at the tool crib or CNC terminal for quick grade lookups during setup.