Sandvik vs Iscar Stainless Steel Turning Inserts Compared: Coating Technology, Chipbreakers, and Cutting Parameters

Introduction

Stainless steel turning remains one of the most demanding operations in metalworking. The combination of high-temperature strength, work-hardening tendency, and poor thermal conductivity places exceptional stress on cutting inserts. Choosing the right insert grade and geometry directly impacts tool life, surface finish, and machining economics.

Sandvik Coromant and Iscar are two industry leaders that have invested heavily in stainless steel turning solutions. Sandvik’s GC2015 and GC2025 grades, paired with their SM and MM chipbreaker geometries, compete directly against Iscar’s IC806 and IC807 grades with their respective F3P/M3P chipformers. This article provides an in-depth technical comparison of these product families, examining substrate composition, coating architecture, chipbreaker design, and real-world cutting performance across a range of stainless steel materials (ISO M).

Stainless Steel Machining Challenges

Before comparing the products, it is essential to understand why stainless steel (ISO M group) is uniquely challenging:

• High hot hardness: Stainless steels, particularly austenitic and duplex grades, retain significant strength at elevated temperatures, increasing cutting forces and heat generation at the tool-chip interface.
• Work hardening: Austenitic grades like 304 and 316 work-harden rapidly during machining, leading to depth-of-cut notching and accelerated flank wear on the secondary cutting edge.
• Low thermal conductivity: Approximately 50% lower thermal conductivity than carbon steel means more heat concentrates at the cutting edge rather than dissipating through the workpiece.
• Built-up edge (BUE): The affinity between stainless steel and tool material promotes BUE formation, degrading surface finish and causing unpredictable chipping.
• Long, stringy chips: Ductile austenitic stainless steels produce continuous chips that are difficult to break, increasing the risk of chip entanglement and poor surface quality.

Both Sandvik and Iscar address these challenges through targeted grade development, but their technical approaches differ in meaningful ways.

Substrate Technology: Sandvik vs Iscar

Sandvik GC2015 / GC2025 Substrate

Sandvik’s GC2015 and GC2025 grades use a fine-grained WC-Co cemented carbide substrate specifically engineered for ISO M applications. The substrate features a graded cobalt structure — a higher cobalt content at the surface for increased toughness, combined with a harder bulk composition for wear resistance.

• WC grain size: 0.8–1.2 μm (fine to medium-fine grain)
• Cobalt content: 8–10 wt% (GC2015 leans toward the lower end for higher hardness; GC2025 uses higher cobalt for toughness)
• Hardness (HV30): ~1650 for GC2015, ~1550 for GC2025
• Transverse rupture strength: ~3200 MPa for GC2025

The graded cobalt structure — often referred to as a “cobalt gradient” or “duplex structure” — is produced through a controlled sintering process that migrates cobalt toward the surface. This creates a tougher surface layer (approx. 15–20 μm deep) that resists plastic deformation and crack propagation, while the harder substrate bulk maintains dimensional stability at high cutting speeds.

Iscar IC806 / IC807 Substrate

Iscar’s IC806 and IC807 grades employ a submicron-grain carbide substrate with a uniform cobalt distribution, optimized for high hot hardness and thermal fatigue resistance.

• WC grain size: 0.6–0.9 μm (submicron grain)
• Cobalt content: 7–9 wt%
• Hardness (HV30): ~1700 for IC806, ~1600 for IC807
• Transverse rupture strength: ~3400 MPa for IC807

Iscar’s approach prioritizes finer grain size for inherently higher hardness and wear resistance. The trade-off is slightly lower fracture toughness compared to Sandvik’s cobalt-gradient approach, particularly in interrupted cuts. However, Iscar compensates through coating design and geometry optimization, as discussed in the following sections.

Substrate Comparison Summary

Coating Architecture

Sandvik Inveio™ Coating Technology

Sandvik’s GC2015 and GC2025 grades use their proprietary Inveio™ CVD coating technology. The key innovation of Inveio is the controlled crystal orientation of the Al2O3 layer, where columnar alpha-Al2O3 crystals grow with their basal planes (0001) parallel to the cutting edge surface.

The coating stack typically consists of:

1. TiCN base layer (3–5 μm): Provides wear resistance and adhesion to the substrate. Deposited via MT-CVD (medium-temperature CVD) for fine-grained structure.
2. α-Al2O3 layer (4–6 μm): The thermal barrier layer. Inveio technology aligns crystals for maximum thermal conductivity along the cutting direction, efficiently drawing heat away from the edge.
3. TiN top layer (0.5–1 μm): Reduces friction and serves as a wear indicator. The gold color makes wear visible to operators.

The total coating thickness ranges from 8–12 μm depending on the specific grade variant. The Inveio crystal orientation reportedly improves crater wear resistance by 30–50% compared to conventional randomly-oriented Al2O3 coatings.

Iscar Sumo Tec® Coating Technology

Iscar’s IC806 and IC807 grades feature their Sumo Tec® post-treatment applied to a PVD TiAlN-based coating system. Unlike Sandvik’s CVD approach, Iscar uses PVD (Physical Vapor Deposition) for stainless steel grades, which produces thinner, smoother coatings with higher compressive residual stress.

The coating architecture includes:

1. TiAlN base layer (2–3 μm): Deposited via arc evaporation with controlled Al/Ti ratio (~60/40) for high hot hardness and oxidation resistance up to ~900°C.
2. Sumo Tec® post-treatment: A proprietary surface treatment that smoothes the coating surface, reduces droplet formation typical of arc PVD, and introduces beneficial compressive stress. This reduces friction, BUE formation, and chipping tendency.
3. Total coating thickness: 3–5 μm

The Sumo Tec® treatment is Iscar’s signature differentiator. By reducing surface roughness and introducing controlled compressive stress, it significantly improves chip flow and reduces the tendency for built-up edge — a critical benefit in stainless steel machining.

CVD vs PVD for Stainless Steel: The Fundamental Trade-off

The choice between CVD (Sandvik) and PVD (Iscar) represents a fundamental engineering trade-off:

In practical terms, Sandvik’s CVD grades excel at higher cutting speeds where thermal load is dominant, while Iscar’s PVD grades perform better at lower to medium speeds where edge integrity and BUE resistance are more critical. The crossover point depends heavily on the specific stainless steel grade, cutting depth, and machine stability.

Chipbreaker Geometry Comparison

Sandvik SM and MM Chipbreakers

Sandvik offers two primary chipbreaker families for stainless steel turning:

SM Geometry (Semi-finishing):

• Positive rake design with a narrow, controlled land width
• Optimized for finishing and semi-finishing operations at low to medium feed rates (fn 0.1–0.3 mm/rev)
• Small chip gullet for tight chip curling and short chip breaking
• Particularly effective on austenitic stainless steels where BUE is a concern

MM Geometry (Medium / Roughing):

• Wider land and deeper chip gullet for higher feed rates (fn 0.2–0.5 mm/rev)
• Reinforced cutting edge for interrupted cuts and roughing operations
• 3D chipformer design that varies rake angle along the cutting edge for optimal chip control across different depths of cut
• Recommended for duplex and super duplex stainless steels where higher cutting forces are encountered

Iscar F3P and M3P Chipbreakers

Iscar’s chipbreaker portfolio for stainless steel includes:

F3P Geometry (Finishing):

• Sharp, positive cutting edge with hone-free preparation for minimum cutting force
• Designed for fine finishing at feed rates from 0.05–0.25 mm/rev
• Narrow chip groove that produces short, C-shaped chips even at shallow depths of cut
• Excellent surface finish capability — regularly achieves Ra 0.8–1.6 μm in good conditions

M3P Geometry (Medium):

• Versatile all-around geometry for general turning at feeds of 0.15–0.4 mm/rev
• Modulated edge preparation (small hone) for improved edge strength without sacrificing sharpness
• Asymmetric chipformer design optimized for both longitudinal and facing operations
• Broad application range covering austenitic, ferritic, and martensitic stainless steels

Geometry Comparison Summary

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Cutting Performance Comparison

Austenitic Stainless Steel (AISI 304 / 316)

Austenitic stainless steels are the most commonly machined ISO M materials. They are characterized by high ductility, strong work-hardening tendency, and poor chip control.

Recommended Cutting Parameters — Continuous Turning, Finishing:

Analysis: In continuous finishing of 304/316, Sandvik’s GC2015 with Inveio coating holds a speed advantage of approximately 25–30%, thanks to the superior thermal barrier of Al2O3. However, Iscar’s IC806 with Sumo Tec delivers better surface finish at comparable feeds and shows excellent BUE resistance, which can be critical for applications requiring tight surface quality specifications. At the upper end of Iscar’s speed range (~200 m/min), crater wear accelerates rapidly due to the absence of an Al2O3 layer.

Duplex Stainless Steel (2205 / 2507)

Duplex stainless steels present a higher level of difficulty due to their higher strength, greater work-hardening rate, and abrasive nitride precipitates.

Recommended Cutting Parameters — Rough Turning:

Analysis: In duplex stainless steel roughing, the performance gap narrows. Sandvik’s GC2025 with its tougher cobalt-gradient substrate and reinforced MM geometry handles the higher cutting forces and abrasive nature of duplex slightly better, particularly at depths of cut above 3 mm. Iscar’s IC807 is competitive at the lower to middle end of the parameter range, where the sharp M3P edge reduces cutting forces and the Sumo Tec surface helps manage BUE. However, at higher speeds and depths, the thinner PVD coating and finer substrate grain of IC807 become limiting factors, with notch wear developing more rapidly at the depth-of-cut line.

Interrupted Cutting (e.g., Slotted Bars, Castings with Scale)

Interrupted cutting conditions impose mechanical shock loads that test the toughness of both the substrate and the coating-substrate interface.

Analysis: Sandvik’s GC2025 with MM geometry has a slight advantage in interrupted cuts due to the cobalt-gradient substrate’s higher surface toughness and the thicker CVD coating’s ability to distribute impact loads. Iscar’s IC807, while having a higher TRS value on paper, is more susceptible to coating delamination under impact loading because the PVD coating is thinner and the substrate’s finer grain structure, though harder, is somewhat more brittle. In practice, both grades handle light to moderate interruptions well; the difference becomes noticeable only in severe interrupted conditions with heavy engagement.

Coolant and Application Considerations

Both manufacturers emphasize the importance of proper coolant application in stainless steel turning:

• Coolant concentration: 8–12% for water-soluble coolants; neat cutting oil for severe operations
• Coolant pressure: Minimum 10 bar for conventional applications; 70+ bar for high-pressure coolant (HPC) systems
• Nozzle placement: Direct coolant at the cutting zone, with one nozzle aimed at the rake face and a secondary nozzle at the flank face
• High-pressure coolant benefit: HPC can increase tool life by 30–50% and/or allow 20–40% higher cutting speeds by effectively breaking the vapor barrier and penetrating the tool-chip interface

Sandvik offers dedicated HPC toolholders (Coromant Capto with integrated coolant channels) optimized for their insert geometries, while Iscar provides similar solutions through their Jet-Cut and Turn-Jet systems. Both manufacturers recommend HPC particularly for duplex and super duplex stainless steels, where the temperature at the cutting edge is highest.

Practical Selection Guide

Based on the technical comparison above, here are practical recommendations for different scenarios:

Choose Sandvik When:

• You need to run at higher cutting speeds (Vc > 200 m/min in austenitic stainless)
• Thermal load and crater wear are the dominant failure modes
• You have a stable, rigid setup with good coolant supply
• You are machining duplex or super duplex stainless steels at moderate to heavy depths of cut
• Production volume is high and tool change downtime must be minimized

Choose Iscar When:

• Surface finish quality is a critical requirement (especially in finishing operations)
• You are running at lower to medium cutting speeds (Vc < 180 m/min)
• Built-up edge is a persistent problem with your current setup
• Your machine has limited rigidity or spindle power
• You require sharper cutting edges for thin-walled or delicate components

Conclusion

The comparison between Sandvik and Iscar stainless steel turning inserts reveals two fundamentally different engineering approaches, each with distinct advantages. Sandvik’s CVD-coated GC2015/GC2025 grades with Inveio technology excel in higher-speed applications where thermal management is paramount, delivering superior crater wear resistance and longer tool life at elevated cutting speeds. The cobalt-gradient substrate provides an excellent balance of surface toughness and bulk hardness.

Iscar’s PVD-coated IC806/IC807 grades with Sumo Tec® shine in applications requiring sharp edges, excellent surface finish, and superior BUE resistance. The thinner, smoother PVD coating with compressive residual stress makes these grades particularly well-suited for finishing operations and for machines with limited rigidity.

Neither brand is universally superior — the optimal choice depends on your specific application parameters, material, machine capability, and quality requirements. In many shops, having both brands available for different operation types is the most cost-effective strategy, leveraging each manufacturer’s strengths where they provide the greatest benefit.

As always, we recommend conducting in-house tool trials under your actual production conditions to validate performance, as factors like machine rigidity, coolant quality, operator skill, and workpiece material variation can significantly influence real-world results.