Grey Cast Iron GG25 Machining: Korloy PC8110 vs PC3545 Grade Selection

Grey cast iron GG25 (EN-GJL-250, ASTM Class 35-40) is one of the most commonly machined materials in the automotive, hydraulic, and general machinery industries. Its excellent castability, vibration damping, and moderate strength make it the go-to material for engine blocks, brake discs, pump housings, and machine tool bases. However, the graphite flake structure that gives grey iron its damping properties also creates unique challenges for tool selection. This guide examines the two dominant Korloy grade families for GG25 and provides cutting parameters for every common operation.

Material Properties of GG25

The pearlitic matrix provides reasonable hardness, while the graphite flakes act as internal chip breakers and provide self-lubrication at the cutting zone. This makes GG25 relatively free-machining compared to steel, but the abrasive graphite and occasional hard spots (cementite, sand inclusions from casting) demand wear-resistant coatings.

Korloy PC8110: The CVD Specialist for Grey Iron

Korloy PC8110 is a CVD-coated (Chemical Vapor Deposition) grade with a thick Al2O3 + TiCN multi-layer coating on a tough cobalt-enriched substrate. This combination provides excellent crater wear resistance and flank wear resistance in the abrasive environment created by graphite flakes.

PC8110 characteristics:

• Thick CVD coating provides maximum abrasion resistance
• Tough substrate absorbs the micro-shock from graphite flake interruptions
• Ideal for continuous and semi-continuous cuts at medium to high speeds
• Best suited for stable, rigid setups with good chip control

Korloy PC3545: The Versatile PVD Option

Korloy PC3545 uses a PVD (Physical Vapor Deposition) TiAlN coating on a fine-grained carbide substrate. The PVD process produces a thinner, smoother coating that maintains a sharper cutting edge compared to CVD grades. This makes PC3545 particularly effective in interrupted cuts, milling, and applications requiring sharp edges.

PC3545 characteristics:

• PVD TiAlN coating maintains edge sharpness
• Fine-grain substrate resists micro-chipping
• Excellent for interrupted cuts, milling, and light-to-medium turning
• Better surface finish capability than CVD grades
• Handles the variable hardness zones common in castings

Grade Selection Matrix

Alternative Grade Recommendations

Cutting Parameters: Turning GG25

Note on coolant: Grey cast iron is almost always machined dry. The graphite provides natural lubrication, and the chips are discontinuous (segmented), so chip evacuation is not an issue. Using flood coolant creates a slurry of fine graphite particles that contaminates machine ways and guideways. If cooling is needed, use compressed air blast or MQL.

Cutting Parameters: Milling GG25

Insert Geometry Recommendations

For GG25 turning, use the following insert geometry guidelines:

• Chipbreaker: Medium-duty chipbreaker (Iscar M3, Sandvik M-M geometry, Korloy GM) — grey iron produces short segmented chips, so aggressive chipbreakers are unnecessary and can cause edge chipping
• Nose radius: 0.8-1.2 mm for roughing, 0.4 mm for finishing — larger radii help distribute the abrasive wear from graphite
• Edge preparation: Light hone (0.02-0.04 mm) for CVD grades, sharp or very light hone for PVD grades
• Insert shape: CNMG, WNMG, or SNMG for roughing; CCMT, DCMT for finishing and boring

Dealing with Casting Skin and Hard Spots

The as-cast surface of GG25 often contains a hard skin layer (up to 350 HB) from rapid cooling at the mold interface, along with occasional sand inclusions. Strategies for managing these conditions:

• Use a depth of cut that penetrates below the casting skin on the first pass (minimum 1.5-2.0 mm)
• Reduce cutting speed by 20-30% for the first roughing pass
• If hard spots (white iron/cementite) are common, switch to PC3545 for its superior chipping resistance
• Consider CBN or ceramic inserts (Korloy KBN25) for heavily chilled castings with hardness above 280 HB

Drilling and Boring

Solid carbide drills with TiAlN coating are standard for GG25. Use cutting speeds of 80-150 m/min and feeds of 0.10-0.25 mm/rev depending on diameter. Indexable insert drills with PC3545 tips are economical for diameters above 20 mm. Boring bars with CCMT or DCMT inserts in PC3545 deliver excellent surface finish at 250-400 m/min.

Summary

GG25 grey cast iron is a forgiving material when matched with the right insert grade. Korloy PC8110 delivers maximum wear resistance for high-volume continuous turning, while PC3545 provides the edge toughness needed for interrupted cuts, milling, and variable casting conditions. Always machine dry, use medium-duty chipbreakers, and ensure the first roughing pass cuts below the casting skin.

hooguu.com is an authorized distributor of Korloy cutting tools and carries the full range of PC8110, PC3545, and other grades optimized for grey cast iron machining. Contact our technical team for grade selection support and volume pricing on your next GG25 production run.