Cast iron remains one of the most widely machined materials across automotive, general engineering, and pump and valve industries. Despite its favorable machinability compared to steel or superalloys, achieving optimal tool life, surface finish, and process stability requires careful grade and geometry selection. Two manufacturers that dominate this segment are Korloy and Seco, each offering dedicated CVD-coated carbide portfolios engineered specifically for gray cast iron (GJL/ISO 250-350), ductile cast iron (GJS/ISO 400-700), and compacted graphite iron (CGI) applications.
This article delivers a comprehensive technical comparison of Korloy and Seco cast iron turning insert grades, examining substrate design, CVD coating architecture, recommended cutting parameters, and real-world application boundaries.
Cast Iron Machining: Key Metallurgical and Thermal Challenges
Before comparing grades, it is essential to understand the material-specific demands cast iron places on cutting tools:
- Abrasive pearlite and carbide phases accelerate flank wear, demanding hard, wear-resistant coatings.
- Discontinuous chip formation in gray cast iron generates cyclic mechanical and thermal loading, promoting edge chipping and thermal fatigue cracks.
- Nodular graphite in ductile iron creates a more ductile chip that is harder to break, increasing cutting forces and built-up edge (BUE) tendency.
- CGI exhibits tensile strength 40-75% higher than gray iron with lower thermal conductivity, concentrating heat at the cutting edge.
These factors make substrate toughness, coating adhesion, and edge preparation equally important as coating hardness when selecting a grade for cast iron turning.
Korloy Cast Iron Turning Portfolio
Korloy addresses cast iron machining through its PC series CVD-coated grades, built on a gradient-substrate technology platform that increases cobalt content near the coating interface for improved adhesion and crack resistance.
PC3500 / PC3510: Medium-to-High Speed Gray Cast Iron
The PC3500 grade utilizes a medium-coarse WC-Co substrate with a TiCN-Al2O3 multilayer CVD stack. The Al2O3 outer layer provides thermal barrier protection during high-speed continuous cutting, while the TiCN base layer offers abrasion resistance against hard carbide inclusions. PC3510 is a post-treated variant with polished rake faces and edge honing optimized for semi-finishing to light roughing where surface quality is critical.
Typical parameters:
- Cutting speed (Vc): 250-450 m/min (gray cast iron, continuous)
- Feed rate (f): 0.20-0.45 mm/rev
- Depth of cut (ap): 1.0-5.0 mm
- Applications: Brake disc facing, pump housing boring, general-purpose turning
PC3600: Ductile and Compacted Graphite Iron
PC3600 is engineered for the higher cutting forces and adhesive wear mechanisms associated with nodular graphite structures. Its substrate features a finer grain size and higher cobalt percentage than PC3500, improving fracture toughness. The CVD coating includes a thicker TiCN layer to withstand the abrasive action of ferrite-pearlite matrices in GJS-500 and GJS-700 grades.
Typical parameters:
- Cutting speed (Vc): 150-280 m/min (ductile iron, continuous to light interrupted)
- Feed rate (f): 0.15-0.35 mm/rev
- Depth of cut (ap): 1.5-6.0 mm
- Applications: Crankshaft roughing, camshaft turning, gearbox housing machining
PC3700: Heavy Interruption and Scale-Cutting
For castings with sand inclusions, hard scale, or heavy interrupted cuts, PC3700 employs a high-toughness substrate with a reduced coating thickness to minimize edge brittleness. The grade sacrifices some wear resistance for mechanical reliability, making it the preferred choice for as-cast surfaces and foundry-facing operations.
Typical parameters:
- Cutting speed (Vc): 120-220 m/min
- Feed rate (f): 0.25-0.60 mm/rev
- Depth of cut (ap): 2.0-8.0 mm
Seco Cast Iron Turning Portfolio
Seco’s approach centers on the TK grade family, developed with a dual-layer CVD platform and a cobalt-enriched substrate zone immediately beneath the coating. Seco emphasizes edge-line integrity and consistent coating thickness across complex insert geometries.
TK1000 / TK1500: High-Productivity Gray and Ductile Iron
TK1000 is Seco’s primary CVD grade for gray cast iron, featuring a thick Al2O3 layer engineered for high-speed, continuous cutting. TK1500 adapts the same coating system to a slightly tougher substrate for ductile iron and mixed-mode machining where the cut transitions between gray and nodular sections.
Typical parameters (TK1000, gray iron):
- Cutting speed (Vc): 300-500 m/min
- Feed rate (f): 0.20-0.50 mm/rev
- Depth of cut (ap): 1.0-6.0 mm
Typical parameters (TK1500, ductile iron):
- Cutting speed (Vc): 180-320 m/min
- Feed rate (f): 0.15-0.40 mm/rev
- Depth of cut (ap): 1.5-7.0 mm
TK2000: Interrupted Cutting and CGI
TK2000 is positioned as Seco’s heavy-duty cast iron grade. Its substrate contains a higher binder fraction and a medium tungsten carbide grain size, delivering the shock resistance needed for scale-covered surfaces, casting skin, and CGI. The CVD coating is optimized for thermal shock resistance rather than pure abrasion resistance, extending tool life in cyclic thermal conditions.
Typical parameters:
- Cutting speed (Vc): 140-260 m/min
- Feed rate (f): 0.20-0.55 mm/rev
- Depth of cut (ap): 2.0-10.0 mm
- Applications: CGI cylinder block roughing, foundry scale removal, heavy rough turning
Coating Technology Comparison
| Attribute | Korloy PC Series | Seco TK Series |
|---|---|---|
| Coating method | Medium-temperature CVD (MT-CVD) | Medium-temperature CVD (MT-CVD) |
| Primary layers | TiCN + Al2O3 (+ optional TiN top) | TiCN + Al2O3 (+ TiN surface) |
| Al2O3 thickness | ~6-8 μm (PC3500/3600) | ~7-9 μm (TK1000/1500) |
| Substrate gradient | Cobalt-enriched zone near coating | Cobalt-enriched zone near coating |
| Post-treatment | Rake face polish (PC3510), edge conditioning | Rake face polish (TK1000/1500), brushed flank |
| Thermal barrier efficiency | High; optimized for Vc > 350 m/min | Very high; optimized for Vc > 400 m/min |
| Coating adhesion strategy | Controlled ETA-phase suppression | Smooth interface transition, stress-relief layer |
Both manufacturers employ MT-CVD to deposit TiCN at temperatures below 900°C, preserving substrate toughness while achieving dense, columnar coating structures. The primary differentiator lies in Al2O3 deposition uniformity and post-coat edge conditioning, where Seco tends to prioritize high-speed thermal protection and Korloy emphasizes balanced wear and chipping resistance.
Cutting Parameters and Performance Data
The following table summarizes recommended starting parameters for continuous turning of common cast iron grades under stable, rigid setups with internal coolant delivery.
| Workpiece Material | Grade | Vc (m/min) | f (mm/rev) | ap (mm) | Tool Life Target |
|---|---|---|---|---|---|
| Gray cast iron GJL-250 | Korloy PC3500 | 280-420 | 0.25-0.40 | 2.0-5.0 | 20-30 min |
| Gray cast iron GJL-250 | Seco TK1000 | 320-480 | 0.25-0.45 | 2.0-6.0 | 20-30 min |
| Gray cast iron GJL-300 | Korloy PC3500 | 250-380 | 0.22-0.38 | 1.5-4.5 | 18-25 min |
| Gray cast iron GJL-300 | Seco TK1000 | 280-420 | 0.22-0.40 | 1.5-5.0 | 18-25 min |
| Ductile iron GJS-500 | Korloy PC3600 | 160-260 | 0.18-0.30 | 2.0-5.0 | 15-22 min |
| Ductile iron GJS-500 | Seco TK1500 | 180-300 | 0.18-0.32 | 2.0-6.0 | 15-22 min |
| Ductile iron GJS-700 | Korloy PC3600 | 140-220 | 0.15-0.28 | 1.5-4.0 | 12-18 min |
| Ductile iron GJS-700 | Seco TK1500 | 160-250 | 0.15-0.30 | 1.5-5.0 | 12-18 min |
| CGI GJV-450 | Korloy PC3700 | 120-200 | 0.20-0.35 | 2.0-5.0 | 10-15 min |
| CGI GJV-450 | Seco TK2000 | 140-240 | 0.20-0.40 | 2.0-6.0 | 10-15 min |
Parameter notes: Reduce Vc by 15-25% for interrupted cuts, cast skin, or setups with L/D > 4. Increase feed rate slightly in roughing to promote chip breakage in ductile iron. When using high-pressure coolant (>70 bar), both Korloy and Seco grades can tolerate Vc values at the upper end of the stated ranges without premature thermal cracking.
Insert Geometry and Chip Control
Beyond grade, chip breaker geometry significantly influences process security in cast iron turning.
Korloy Chip Breakers
- FP geometry: Finishing to medium machining, positive rake, low cutting forces, excellent surface finish on gray iron.
- MP geometry: General-purpose roughing, neutral rake with reinforced edge, designed for GJL and GJS continuous cuts.
- RP geometry: Heavy roughing, strong negative land, wide chip pocket, optimized for scale and interruption.
Seco Chip Breakers
- -M geometry: Medium machining, balanced edge strength and chip curling, suitable for both gray and ductile iron.
- -R geometry: Roughing with reinforced cutting edge, open chip groove to accommodate high feed rates and deep cuts.
- -F geometry: Finishing and semi-finishing, sharp edge with positive rake for minimal burr formation and tight tolerances.
For ductile iron in particular, Korloy’s RP geometry and Seco’s -R geometry provide the edge strength and chip space needed to handle the longer, more ductile chips. In gray iron finishing, Seco’s -F geometry and Korloy’s FP geometry deliver comparable Ra values in the 1.6-3.2 μm range under standard parameters.
Application Recommendations
| Application Scenario | Recommended Korloy Grade | Recommended Seco Grade | Selection Guidance |
|---|---|---|---|
| High-volume brake disc turning | PC3510 (FP) | TK1000 (-F) | Seco TK1000 allows higher Vc; Korloy PC3510 offers better cost efficiency per edge. |
| Crankshaft roughing (GJS-700) | PC3600 (MP) | TK1500 (-R) | Both suitable; Seco -R geometry handles higher feed rates with lower risk of edge fracture. |
| CGI engine block facing | PC3700 (RP) | TK2000 (-R) | TK2000 provides superior thermal shock resistance in CGI; PC3700 is a cost-effective alternative. |
| Pump housing boring (GJL-300) | PC3500 (MP) | TK1000 (-M) | Either grade performs well; select based on insert geometry preference and toolholder availability. |
| Foundry skin/scale removal | PC3700 (RP) | TK2000 (-R) | Both grades designed for impact; reduce Vc by 20% and use robust geometry. |
Conclusion
Korloy and Seco both deliver mature, high-performance CVD-coated carbide solutions for cast iron turning, but their portfolios reflect slightly different design philosophies. Seco TK1000 and TK1500 push the envelope on cutting speed and thermal protection, making them ideal for high-volume, stable continuous cutting where throughput dominates cost-per-part calculations. Korloy PC3500 and PC3600 offer a balanced combination of wear resistance and chipping resistance, often providing superior value in mixed-mode machining where conditions vary between continuous and lightly interrupted cuts.
For heavy interruption, CGI, and as-cast scale machining, Seco TK2000 demonstrates marginally better thermal shock behavior, while Korloy PC3700 remains a highly capable and economically attractive alternative. The final selection should consider not only the grade but also the available chip breaker geometries, toolholder compatibility, and local supply chain factors.
Engineers evaluating a grade change from one manufacturer to the other should begin at the midpoint of the recommended parameter ranges, monitor flank wear and notch wear progression over a statistically meaningful batch size (minimum 20 parts), and adjust Vc in 10% increments to identify the true process optimum for their specific machine tool, workpiece material batch, and coolant conditions.
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