Cast Iron
Iron-carbon-silicon alloys with carbon content generally between 2% and 4%, featuring high compressive strength and vibration damping.
Subfamily Classifications (2)
| UNS • Canonical Grade | Subfamily | Standard Identifiers | Conductivity (% IACS) | Yield & Context | Status | Actions |
|---|---|---|---|---|---|---|
| ASTM A48 Class 20 Gray Cast IronClass 20 Gray Iron | Gray Cast Iron | ASTM: A48 Class 20UNS: F11401SAE: J431 G2000 | — | — | VERIFIED | |
| ASTM A48 Class 25 Gray Cast IronClass 25 Gray Iron | Gray Cast Iron | ASTM: A48 Class 25UNS: F11701SAE: J431 G2500 | — | — | VERIFIED | |
| ASTM A48 Class 30 Gray Cast IronClass 30 Gray Iron | Gray Cast Iron | ASTM: A48 Class 30UNS: F12101SAE: J431 G3000 | — | — | VERIFIED | |
| ASTM A48 Class 35 Gray Cast IronClass 35 Gray Iron | Gray Cast Iron | ASTM: A48 Class 35UNS: F12401SAE: J431 G3500 | — | — | VERIFIED | |
| ASTM A48 Class 40 Gray Cast IronClass 40 Gray Iron | Gray Cast Iron | ASTM: A48 Class 40UNS: F12801SAE: J431 G4000 | — | — | VERIFIED | |
| ASTM A48 Class 50 Gray Cast IronClass 50 Gray Iron | Gray Cast Iron | ASTM: A48 Class 50UNS: F13501SAE: J431 G5000 | — | — | VERIFIED | |
| EN-GJL-150 Gray Cast IronGG-15 | Gray Cast Iron | EN: EN-GJL-150W-Nr: EN-JL1020DIN: GG-15 | — | — | VERIFIED | |
| EN-GJL-200 Gray Cast IronGG-20 | Gray Cast Iron | EN: EN-GJL-200W-Nr: EN-JL1030DIN: GG-20 | — | — | VERIFIED | |
| EN-GJL-250 Gray Cast IronGG-25 | Gray Cast Iron | EN: EN-GJL-250W-Nr: EN-JL1040DIN: GG-25 | — | — | VERIFIED | |
| EN-GJL-300 Gray Cast IronGG-30 | Gray Cast Iron | EN: EN-GJL-300W-Nr: EN-JL1050DIN: GG-30 | — | — | VERIFIED | |
| ASTM A536 Grade 60-40-18 Ductile Cast IronDuctile Iron 60-40-18 | Ductile (Nodular) Iron | ASTM: A536 Grade 60-40-18UNS: F32800SAE: J434 D4018 | — | ≥ 276 MPaMINIMUM · Annealed or As-Cast · Governing minimum 0.2% offset yield strength per ASTM A536 (40 ksi = 276 MPa). | VERIFIED | |
| ASTM A536 Grade 65-45-12 Ductile Cast IronDuctile Iron 65-45-12 | Ductile (Nodular) Iron | ASTM: A536 Grade 65-45-12UNS: F33100SAE: J434 D4512 | — | ≥ 310 MPaMINIMUM · As-Cast · Governing minimum 0.2% offset yield strength per ASTM A536 (45 ksi = 310 MPa). | VERIFIED | |
| ASTM A536 Grade 80-55-06 Ductile Cast IronDuctile Iron 80-55-06 | Ductile (Nodular) Iron | ASTM: A536 Grade 80-55-06UNS: F33800SAE: J434 D5506 | — | ≥ 379 MPaMINIMUM · As-Cast or Normalized · Governing minimum 0.2% offset yield strength per ASTM A536 (55 ksi = 379 MPa). | VERIFIED | |
| ASTM A536 Grade 100-70-03 Ductile Cast IronDuctile Iron 100-70-03 | Ductile (Nodular) Iron | ASTM: A536 Grade 100-70-03UNS: F34800SAE: J434 D7003 | — | ≥ 483 MPaMINIMUM · Normalized or Q&T · Governing minimum 0.2% offset yield strength per ASTM A536 (70 ksi = 483 MPa). | VERIFIED | |
| ASTM A536 Grade 120-90-02 Ductile Cast IronDuctile Iron 120-90-02 | Ductile (Nodular) Iron | ASTM: A536 Grade 120-90-02UNS: F36200SAE: J434 D9002 | — | ≥ 621 MPaMINIMUM · Quenched and Tempered · Governing minimum 0.2% offset yield strength per ASTM A536 (90 ksi = 621 MPa). | VERIFIED | |
| EN-GJS-400-18 Ductile Cast IronGGG-40 | Ductile (Nodular) Iron | EN: EN-GJS-400-18W-Nr: EN-JS1020DIN: GGG-40 | — | ≥ 250 MPaMINIMUM · Ferritic · Governing minimum 0.2% proof stress (Rp0.2) per EN 1563. | VERIFIED | |
| EN-GJS-400-15 Ductile Cast IronEN-JS1030 | Ductile (Nodular) Iron | EN: EN-GJS-400-15W-Nr: EN-JS1030ISO: 1083/JS/400-15 | — | ≥ 250 MPaMINIMUM · Ferritic | VERIFIED | |
| EN-GJS-500-7 Ductile Cast IronGGG-50 | Ductile (Nodular) Iron | EN: EN-GJS-500-7W-Nr: EN-JS1050DIN: GGG-50 | — | ≥ 320 MPaMINIMUM · Ferritic-Pearlitic · Governing minimum 0.2% proof stress (Rp0.2) per EN 1563. | VERIFIED | |
| EN-GJS-600-3 Ductile Cast IronGGG-60 | Ductile (Nodular) Iron | EN: EN-GJS-600-3W-Nr: EN-JS1060DIN: GGG-60 | — | ≥ 370 MPaMINIMUM · Pearlitic-Ferritic · Governing minimum 0.2% proof stress (Rp0.2) per EN 1563. | VERIFIED | |
| EN-GJS-700-2 Ductile Cast IronGGG-70 | Ductile (Nodular) Iron | EN: EN-GJS-700-2W-Nr: EN-JS1070DIN: GGG-70 | — | ≥ 420 MPaMINIMUM · Pearlitic · Governing minimum 0.2% proof stress (Rp0.2) per EN 1563. | VERIFIED |
Verified Cast Iron Comparison Pairs (1)
Open Compare Engine →How to Remove Rust from Cast Iron: Restoration Protocol →
Comprehensive metallurgical protocol for safely remediating surface iron oxide without degrading graphite matrix integrity. Covers chemical chelation, electrolysis, vinegar conversion, seasoning chemistry, and long-term corrosion prevention.
Gray Cast Iron vs Ductile Iron: Mechanical & Damping Comparison →
Direct benchmark comparing ASTM A48 Class 30 flake iron against ASTM A536 65-45-12 nodular iron. Explores tensile vs compressive ratios, vibration damping physics, machinability, impact toughness, and cost tradeoffs.
Cast Iron Physical Metallurgy & Classification Principles
Graphite Morphology & Mechanics
Cast irons are multicomponent ferrous alloys containing 2.0 to 4.0 wt% carbon and 1.0 to 3.0 wt% silicon. The fundamental engineering divide is governed by graphite shape: flake graphite in gray iron produces zero plastic yield and peak acoustic damping, while nodular (spheroidal) graphite in ductile iron yields high ductility, toughness, and true 0.2% yield strength.
Matrix Structure: Ferrite vs Pearlite
The metallic matrix determines base hardness and yield strength. Annealed ferritic grades (e.g. 60-40-18, EN-GJS-400-18) offer maximum elongation and low-temperature impact energy. Pearlitic grades (Class 40, Class 50, 80-55-06, EN-GJS-600-3) provide superior wear resistance, high hardness (up to 270 HBW), and high fatigue thresholds.
Section Sensitivity & Standard Testing
Standard tensile ratings reflect separately cast standard test bars (e.g., ASTM Test Bar B: 30.5 mm / 1.2 in. diameter). In production castings, thick sections cool slower and exhibit lower strength, while thin sections cool faster and risk chilling. ASTM and EN standards are comparable in target strength but are not identical metallurgical equivalents.
Gray Cast Iron Catalog Matrix (10 Verified Grades)
Flake graphite gray irons standardized under ASTM A48 / SAE J431 and EN 1561 / ISO 185. Note: Gray iron exhibits non-linear stress-strain behavior with no yield point.
| Grade | Standard Designation | Tensile UTS (Min) | 0.2% Yield Strength | Elastic Modulus | Hardness (HBW) | Matrix Structure |
|---|---|---|---|---|---|---|
| ASTM A48 Class 20 Gray Cast Iron | A48 Class 20 | 138 MPa | None (Continuous) | 80 GPa | 155 | Pearlitic |
| ASTM A48 Class 25 Gray Cast Iron | A48 Class 25 | 172 MPa | None (Continuous) | 90 GPa | 175 | Pearlitic |
| ASTM A48 Class 30 Gray Cast Iron | A48 Class 30 | 207 MPa | None (Continuous) | 100 GPa | 200 | Pearlitic |
| ASTM A48 Class 35 Gray Cast Iron | A48 Class 35 | 241 MPa | None (Continuous) | 105 GPa | 215 | Pearlitic |
| ASTM A48 Class 40 Gray Cast Iron | A48 Class 40 | 276 MPa | None (Continuous) | 120 GPa | 235 | Pearlitic |
| ASTM A48 Class 50 Gray Cast Iron | A48 Class 50 | 345 MPa | None (Continuous) | 130 GPa | 265 | Pearlitic |
| EN-GJL-150 Gray Cast Iron | EN-GJL-150 | 150 MPa | None (Continuous) | 85 GPa | 155 | Pearlitic |
| EN-GJL-200 Gray Cast Iron | EN-GJL-200 | 200 MPa | None (Continuous) | 95 GPa | 185 | Pearlitic |
| EN-GJL-250 Gray Cast Iron | EN-GJL-250 | 250 MPa | None (Continuous) | 105 GPa | 205 | Pearlitic |
| EN-GJL-300 Gray Cast Iron | EN-GJL-300 | 300 MPa | None (Continuous) | 115 GPa | 225 | Pearlitic |
Ductile (Nodular) Iron Catalog Matrix (10 Verified Grades)
Spheroidal graphite cast irons standardized under ASTM A536 / SAE J434 and EN 1563 / ISO 1083. Formulated with magnesium inoculation for high yield strength and tensile ductility.
| Grade | Standard Designation | Tensile UTS (Min) | 0.2% Yield (Min) | Elongation (Min) | Hardness (HBW) | Typical Microstructure |
|---|---|---|---|---|---|---|
| ASTM A536 Grade 60-40-18 Ductile Cast Iron | A536 Grade 60-40-18 | 414 MPa | 276 MPa | 18% | 160 | Ferritic |
| ASTM A536 Grade 65-45-12 Ductile Cast Iron | A536 Grade 65-45-12 | 448 MPa | 310 MPa | 12% | 185 | Pearlitic |
| ASTM A536 Grade 80-55-06 Ductile Cast Iron | A536 Grade 80-55-06 | 552 MPa | 379 MPa | 6% | 220 | Ferritic |
| ASTM A536 Grade 100-70-03 Ductile Cast Iron | A536 Grade 100-70-03 | 689 MPa | 483 MPa | 3% | 270 | Pearlitic |
| ASTM A536 Grade 120-90-02 Ductile Cast Iron | A536 Grade 120-90-02 | 827 MPa | 621 MPa | 2% | 310 | Tempered Martensite |
| EN-GJS-400-18 Ductile Cast Iron | EN-GJS-400-18 | 400 MPa | 250 MPa | 18% | 155 | Ferritic |
| EN-GJS-400-15 Ductile Cast Iron | EN-GJS-400-15 | 400 MPa | 250 MPa | 15% | 160 | Ferritic |
| EN-GJS-500-7 Ductile Cast Iron | EN-GJS-500-7 | 500 MPa | 320 MPa | 7% | 200 | Ferritic |
| EN-GJS-600-3 Ductile Cast Iron | EN-GJS-600-3 | 600 MPa | 370 MPa | 3% | 230 | Pearlitic |
| EN-GJS-700-2 Ductile Cast Iron | EN-GJS-700-2 | 700 MPa | 420 MPa | 2% | 265 | Pearlitic |
Cast Iron Engineering Trade-Off Evaluations
Evaluate quantitative property differences across gray cast iron classes, ductile iron grades, and structural steels. Explore why gray iron provides optimal damping and compressive strength for machine beds, whereas ductile iron offers fatigue and tensile resistance for crankshafts and pressurized valves.
Cast Iron Metallurgy & Engineering Frequently Asked Questions
Why does gray cast iron have no defined yield strength?
Gray cast iron contains interconnected flake graphite with sharp, notch-like tips that create severe localized stress concentrations under tensile load. Plastic deformation initiates locally at flake edges at very low macro-stresses, producing continuous, non-linear stress-strain curvature from the onset of loading. Because there is no proportional elastic limit or sudden yield plateau, standard engineering specifications (ASTM A48, EN 1561, ISO 185) specify only minimum ultimate tensile strength (UTS) and strictly prohibit defining a 0.2% offset yield strength.
How does graphite morphology differentiate gray iron from ductile iron?
In gray cast iron, graphite crystallizes during eutectic solidification as sharp-edged interconnected flakes (ASTM A247 Type VII). In ductile (nodular) cast iron, minute additions of magnesium or cerium (~0.035–0.060 wt% residual Mg) alter the interfacial graphite-melt surface energy, causing graphite to grow as isolated spheroids or nodules (ASTM A247 Type I). Eliminating sharp flake tips removes stress-concentration planes, transforming a brittle material into a ductile alloy with true yield strength (276–620 MPa) and significant plastic elongation (2% to 18%+).
Why is cast iron prone to surface rusting, and how can it be restored?
Cast iron contains high carbon (>2 wt%) and silicon (>1.5 wt%) but virtually no chromium or nickel to form a passive oxide film. When exposed to ambient oxygen and moisture, electrochemical oxidation forms hydrated ferric oxides (rust, Fe₂O₃·nH₂O). Flake graphite exposes porous micro-voids that can harbor electrolytes. Surface rust should be treated using controlled chemical chelation, vinegar immersion, or mechanical abrading followed by thorough desiccation and seasoning or protective coatings.
Why are gray cast irons preferred for machine tool bases and engine blocks?
Gray iron has unmatched specific damping capacity—approximately 10 to 25 times greater than structural carbon steels. Flake graphite absorbs dynamic vibrational energy via internal shear deformation across the flake interfaces. This damps resonant chatter during heavy machining, enhances cutting precision, dampens acoustic noise in engine blocks, and provides high compressive strength (3 to 4 times its tensile strength) for supporting static machine loads.
What is section sensitivity in cast iron components?
Gray iron is highly sensitive to casting section thickness and local cooling rates. Slower cooling in heavy sections produces coarse eutectic cells, coarser graphite flakes, and a predominantly ferritic matrix, lowering tensile strength significantly below the standard 30.5 mm (1.2 in) Test Bar B value. Conversely, rapid cooling in thin sections can induce chilling (formation of hard, unmachinable white iron / iron carbide), requiring careful foundry inoculation.