ASTM A48 Class 30: Standard Gray Cast Iron for Machine Tool Frames
ASTM A48 · Published: 2026-06-03 · Updated: July 2026
ASTM A48 Class 30 gray cast iron is the most widely specified gray iron grade — the standard material for machine tool beds, engine blocks, brake rotors, and pump housings. Its graphite flake microstructure provides excellent vibration damping...
ASTM A48 Class 30 gray cast iron is the most widely specified gray iron grade — the standard material for machine tool beds, engine blocks, brake rotors, and pump housings. Its graphite flake microstructure provides excellent vibration damping (~20× better than steel), good thermal conductivity, and natural lubricity for sliding wear applications.
Quick Facts
| Category | Cast Iron |
| Standard | ASTM A48 |
| Density | 7.20 g/cm³ |
| Yield Strength | N/A (brittle) |
| Tensile Strength | 207 MPa (30 ksi) |
Global Equivalents & Cross-Reference
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Frequently Asked Questions
Why are machine tool bases made of gray cast iron?
Gray iron's graphite flake structure converts vibrational energy into heat through internal friction at the graphite-matrix interface — providing damping capacity 10-20× higher than steel. This directly improves machining accuracy by reducing chatter. Additionally, gray iron's low melting point (1,150-1,250°C) and excellent fluidity enable casting of complex ribbed structures at lower cost than steel weldments.
References & International Standards
- ASTM International. Standard Specifications for Steel & Metal Alloys. astm.org
- International Organization for Standardization (ISO). Metallic Materials — Cross-Reference Database. iso.org
- American Iron and Steel Institute (AISI). Steel Grade Designations & Equivalents. steel.org
- European Committee for Standardization (CEN). EN Steel Standards & Numbering System. cencenelec.eu