ASTM A48 Class 30 Gray Cast Iron: Standard Engineering Grade
ASTM A48/A48M · Updated: 2026-05-25
ASTM A48 Class 30 (G3000) is the standard flake-graphite gray cast iron grade with 207 MPa minimum tensile strength. The graphite flakes provide exceptional vibration damping capacity (10× better than steel), excellent thermal conductivity, and superior machinability—the graphite acts as a built-in chip breaker and lubricant. Class 30 is the workhorse for machine tool bases, engine blocks, brake rotors, pump housings, and manhole covers. Not weldable in practice due to brittle martensite formation in the HAZ. The as-cast surface contains a pearlitic skin with higher hardness than the core. Casting section sensitivity: thinner sections cool faster and produce higher strength/hardness.
Quick Facts
| Category | Cast Iron |
| Standard | ASTM A48/A48M |
| Density | 7.20 g/cm³ |
| Yield Strength | N/A (brittle) |
| Tensile Strength | 207 MPa (30 ksi) |
Global Equivalents & Cross-Reference
| Alternative Standard / Grade | Action |
|---|---|
| EN-GJL-200 | Compare |
| GG20 | Compare |
| FC200 | Compare |
| HT200 | Compare |
| ISO 185/JL/200 | Compare |
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Frequently Asked Questions
Why can't gray cast iron be welded?
The high carbon equivalent (3.0-4.5% CE) combined with rapid weld cooling produces brittle martensite and iron carbide (cementite) in the HAZ, resulting in severe cracking. Specialized nickel-based electrodes (ENi-CI, ENiFe-CI) with preheat to 300-600°C and very slow cooling can produce marginally acceptable repairs, but structural welding of gray iron is not recommended. Use mechanical repairs (metal stitching, threaded inserts) or replace the casting instead.