Cutting speeds, feeds and grade selection for grey, ductile, malleable and compacted graphite iron, including the dust and edge-preparation issues cast iron brings.
Complete reference tables and engineering data for cast iron machining. All values verified against ISO, ANSI, and manufacturer standards.
Cast iron is not one material -- grey iron, ductile (nodular) iron, and compacted graphite iron (CGI) machine very differently. Understanding the difference is critical for selecting the right carbide grade, speeds, and feeds.
The graphite flakes in grey iron are a solid lubricant. Combined with the powder-like chips that don't stick to the tool, dry machining is practical for most grey iron turning and milling. Dry machining avoids the abrasive cast iron slurry created with coolant. Exception: drilling always needs coolant for chip evacuation.
Grey iron: tool life 2-3x longer than steel at the same speed because graphite lubricates the cut and chips don't adhere. Ductile iron: tool life similar to or slightly worse than 1045 steel due to the abrasive graphite nodules. CGI: tool life 50-70% shorter than grey iron -- the elongated graphite is highly abrasive and the material work-hardens at the chip-tool interface.
Grey iron: wear-resistant K-grade (6-8% cobalt) with CVD coating. Abrasion resistance matters most. Ductile iron: tougher grade (8-10% cobalt) to handle the more continuous chip and higher cutting forces. CGI: tough substrate with thick CVD coating or CBN-tipped inserts for volume production. Silicon-aluminium (SiAl) coatings work well for all cast irons.
Identify your cast iron type — grey, ductile, or CGI. Grey iron machines easily with standard carbide. Ductile iron requires tougher grades and lower speeds. CGI demands premium tooling (CVD-coated carbide or CBN) for acceptable tool life. Always verify the material certificate; many castings are misidentified by operators.
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MACHINING CAST IRON? Cast iron is abrasive and inconsistent, which makes the substrate choice decisive. Our checks are in how to confirm a supplier's grade before shipping.
We source carbide cutting tools from China for job shops. We do not own a factory, which is why we can quote your drawing against two or three plants that actually run your material.
Cutting formulas with the units worked through · Speed and feed starting points for all six ISO material groups · How to read a carbide grade past its ISO code. 12 pages.
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