Kyocera vs Mitsubishi Inserts: Best Choice for Stainless Steel?

Stainless steel is one of the most challenging materials in CNC machining. Its high work-hardening rate, low thermal conductivity, and strong tendency for built-up edge (BUE) formation demand inserts with specific coating and substrate properties. Kyocera and Mitsubishi Materials are two Japanese manufacturers with deep expertise in stainless steel machining, each offering grades and chipbreakers designed to overcome the unique difficulties of turning austenitic (304, 316L), martensitic (410, 420), and duplex (2205) stainless steels. This article compares their offerings head to head.

Understanding Stainless Steel Machining Challenges

Austenitic stainless steels like SUS304 and SUS316L work-harden rapidly during cutting, with surface hardness increasing by 50-200% after the first pass. The low thermal conductivity (approximately 16 W/mK for 304 vs 45 W/mK for carbon steel) means that heat concentrates at the cutting edge rather than dissipating into the chip. Combined with the material’s high ductility and strong affinity for carbide, this creates conditions for notch wear at the depth-of-cut line, BUE on the rake face, and premature chipping. Selecting the right insert grade is critical to managing these failure modes.

Kyocera’s Stainless Steel Grades

Kyocera’s flagship stainless steel grade is PR1535, a PVD-coated micro-grain carbide designed specifically for ISO M-class applications. The coating consists of a TiAlN layer with Kyocera’s proprietary MEgA (Multi-Eutectic Gradient Architecture) treatment, which reduces the coefficient of friction at the chip-tool interface by approximately 20% compared to standard PVD coatings. This directly addresses the BUE problem common in austenitic stainless turning. For heavier cuts, PR1220 provides a tougher substrate with a CVD TiCN/Al2O3 coating for roughing operations where edge security takes priority over surface finish.

The PR1725 grade bridges the gap between finishing and roughing, offering a medium-grain substrate with a PVD TiAlSiN coating that provides both oxidation resistance at high temperatures and good chipping resistance in interrupted cuts. Kyocera’s chipbreaker lineup for stainless includes the ML (medium-light), MZ (medium), and MH (medium-heavy) geometries, with the ML being the preferred choice for finishing 304 and 316L at feed rates of 0.08-0.25 mm/rev.

Mitsubishi Materials’ Stainless Steel Grades

Mitsubishi’s stainless steel specialist is the MP9005 grade, featuring their Miracle coating technology, a PVD (Ti,Al)N layer deposited via a high-ionization sputtering process that achieves exceptional coating adhesion. The MP9005 grade covers the M10-M25 application range and is optimized for finishing to light roughing of austenitic stainless steels at cutting speeds of 120-220 m/min. Its sharp cutting edge geometry minimizes work hardening by shearing the material cleanly rather than ploughing through it.

For roughing, Mitsubishi offers the MP9015 grade (M15-M35) with a tougher substrate and slightly thicker coating for interrupted cuts and heavy depth-of-cut operations. The MC5020 grade, a CVD-coated option, targets martensitic stainless steels like 410 and 420, where higher cutting speeds of 200-350 m/min are achievable due to the material’s lower ductility and better chip formation.

Detailed Grade Comparison

Performance in Real-World Applications

In production turning of SUS304 shafts at Vc = 160 m/min, f = 0.2 mm/rev, and ap = 1.5 mm, Kyocera PR1535 inserts with ML chipbreaker typically achieve 150-180 parts per edge before notch wear reaches the 0.2 mm criterion. Under the same conditions, Mitsubishi MP9005 delivers 130-160 parts per edge. The advantage for Kyocera comes primarily from its MEgA coating’s superior friction reduction, which keeps the cutting zone cooler and delays notch wear onset at the depth-of-cut line.

For interrupted cuts on stainless steel flanges with bolt holes, Mitsubishi MP9015 shows better edge security than Kyocera PR1220. The Miracle coating’s high adhesion strength prevents coating delamination at the cutting edge during entry and exit impacts, resulting in fewer chipped edges and more predictable tool life. This makes Mitsubishi the preferred choice for components with frequent interruptions.

Duplex Stainless Steel Considerations

Duplex stainless steels like SAF2205 present an even greater challenge due to their mixed austenite-ferrite microstructure, high strength (yield strength approximately 450 MPa vs 205 MPa for 304), and severe work-hardening tendency. Both manufacturers recommend their toughest stainless grades for this material: Kyocera PR1220 at conservative speeds of 80-130 m/min, and Mitsubishi MP9015 at 80-120 m/min. Feed rates should be kept above 0.15 mm/rev to ensure the cutting edge engages below the work-hardened layer from the previous pass.

Budget-Friendly Options

For shops seeking cost-effective stainless steel inserts, Korloy’s PC2510 grade offers solid performance in general turning of austenitic stainless steels. With a PVD TiAlN coating and a sharp cutting edge, the PC2510 handles SUS304 and SUS316L at speeds up to 180 m/min. While it may not match Kyocera or Mitsubishi in BUE resistance or notch wear life, the lower cost per edge makes it viable for less critical operations or shorter production runs.

When to Choose Which

Choose Kyocera when you need maximum tool life in continuous or near-continuous turning of austenitic stainless steel, especially when notch wear at the depth-of-cut line is your primary failure mode. The PR1535 grade’s MEgA coating technology provides measurable advantages in friction reduction and heat management.

Choose Mitsubishi when your stainless steel machining involves frequent interruptions, when edge chipping is a recurring problem, or when you machine a mix of austenitic and martensitic stainless steels and want a single supplier with dedicated grades for each. The MP9015 grade’s edge toughness in interrupted cuts is a genuine advantage on the shop floor.

Conclusion

Both Kyocera and Mitsubishi offer excellent solutions for stainless steel machining, with Kyocera leading in continuous-cut tool life and Mitsubishi excelling in interrupted-cut reliability. The optimal choice depends on your specific part geometry, production volume, and dominant failure mode. Both brands, along with value alternatives from Korloy, are available at hooguu.com with fast shipping and competitive pricing for CNC shops worldwide.