Technical guide · 2026-08-14
Compacted Graphite Iron
Compacted graphite iron uses vermicular graphite to bridge the thermal behavior of gray iron and the strength of ductile iron, but its narrow acceptable graphite morphology demands close process and microstructure control.
01
Definition and boundary
CGI is not merely high-strength gray iron; its compacted graphite percentage and nodularity ceiling must be demonstrated for the represented casting section.
Reference information only: final acceptance is controlled by the ordered product specification, condition, dimensions and certified test results.
02
How the material system works
Vermicular graphite reduces flake stress concentration while retaining interconnected heat paths.
A narrow magnesium window controls compacted rather than spheroidal graphite.
Section cooling rate influences graphite form and matrix.
03
Representative grades and systems
| Grade or system | Selection focus | Qualification |
|---|---|---|
| ASTM A842 Grade 300 | Entry CGI strength level with specified graphite morphology. | Confirm the governing product specification, delivery condition, section size and acceptance tests before treating designations as interchangeable. |
| ASTM A842 Grade 400 | Higher-strength compacted graphite casting grade. | Confirm the governing product specification, delivery condition, section size and acceptance tests before treating designations as interchangeable. |
| ISO 16112 grade family | International CGI designations require exact grade and test basis. | Confirm the governing product specification, delivery condition, section size and acceptance tests before treating designations as interchangeable. |
04
Properties and trade-offs
Strength above typical gray iron
Thermal conductivity above typical ductile iron
Intermediate damping and machinability
05
Product forms and supply conditions
06
Applications and selection
Applications and selection
- Diesel engine blocks
- Exhaust manifolds
- High-output cylinder heads
Properties and trade-offs
- Verify thermal and mechanical simulation uses CGI data.
- Select grade with machining capacity and tool life in mind.
- Agree microstructure sampling locations before tooling release.
07
Fabrication, durability and inspection
Use rapid thermal or chemical process feedback.
Qualify cutting tools for reduced machinability.
Prevent local graphite-form drift in thick transitions.
08
Procurement checklist
- State minimum compacted graphite and nodularity limits.
- Define matrix, hardness and sampling map.
- Require process traceability and representative mechanical coupons.
09
Standards, sources and review
Standards and designation context
- Applicable ASTM A04 iron-casting specification
- Buyer drawing and foundry process qualification
- Agreed test-coupon and inspection standard