Technical guide · 2026-08-14
Gray Cast Iron
Gray cast iron contains flake graphite that gives excellent vibration damping, machinability and heat flow but creates stress concentration and low tensile ductility, making section-aware strength selection essential.
01
Definition and boundary
Use gray iron where compressive capacity, damping, thermal behavior or machinability matter more than tensile elongation and impact resistance.
Reference information only: final acceptance is controlled by the ordered product specification, condition, dimensions and certified test results.
02
How the material system works
Graphite flakes interrupt the matrix and damp vibration.
Pearlitic matrices raise strength and wear resistance relative to ferritic matrices.
Cooling rate changes graphite and matrix across thin and heavy sections.
03
Representative grades and systems
| Grade or system | Selection focus | Qualification |
|---|---|---|
| ASTM A48 Class 30 | General engineering class based on separately cast tensile bars. | Confirm the governing product specification, delivery condition, section size and acceptance tests before treating designations as interchangeable. |
| ASTM A48 Class 40 | Higher tensile class with tighter section and foundry control. | Confirm the governing product specification, delivery condition, section size and acceptance tests before treating designations as interchangeable. |
| EN-GJL-250 | European flake-graphite designation; not an exact A48 substitute. | Confirm the governing product specification, delivery condition, section size and acceptance tests before treating designations as interchangeable. |
04
Properties and trade-offs
High damping capacity
Good machinability and thermal conductivity
Low tensile elongation
05
Product forms and supply conditions
06
Applications and selection
Applications and selection
- Machine-tool beds
- Brake discs and engine blocks
- Pump housings and covers
Properties and trade-offs
- Use actual wall thickness in foundry feasibility review.
- Select strength class without sacrificing required machinability.
- Add pressure testing for fluid-retaining castings.
07
Fabrication, durability and inspection
Design uniform sections and generous fillets.
Control chill and inoculation to avoid hard edges.
Support brittle castings during machining and transport.
08
Procurement checklist
- State class, casting mass and controlling wall.
- Define coupon size and hardness locations.
- Specify leak test, machining datum and visual acceptance.
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