Material Selection8–10 min read
Gray, Ductile and Malleable Cast Iron: Grade Selection Explained
Graphite structure, casting section and test-coupon scope matter more than a familiar class number.
Author: Mat Grades Editorial DeskRead Guide →
ASTM A48 Class 40 Gray Cast Iron
Primary Designation:ASTM A48 Class 40
Aliases:
Class 40 Gray IronSAE G4000 Gray Iron
Mat Grades internal verification confirms source-backed fidelity and data integrity. It does not constitute external certification or guaranteed lot conformity. Read engineering disclaimer →
Data Completeness:6 composition elements and 9 condition-specific property values cataloged.
Omitted fields represent unverified properties. "Missing is better than invented."
Key Engineering Properties
Representative source rows, qualified by their reported conditions. Inspect the tables below for all values, limits, and source notes.
Density
7.25 g/cm³TYPICAL · temperature not stated
Thermal Conductivity
44 W/(m·K)TYPICAL · temperature not stated
Specific Heat Capacity
490 J/(kg·K)TYPICAL · temperature not stated
Composition Excerpt
C 2.9–3.2 wt%Carbon (range)
Standard Elemental Basis: RANGETensile Strength
≥ 276 MPaMINIMUM · As-Cast · temperature not stated
Engineering Summary
ASTM A48 Class 40 is a high-strength, premium engineering gray cast iron. Featuring a minimum tensile strength of 40 ksi (276 MPa) on standard Test Bar B, it possesses a completely pearlitic microstructure with fine Type A graphite flakes. It is frequently inoculated or microalloyed with chromium, copper, or molybdenum to maintain uniform pearlite and prevent chilling in variable casting sections. Widely used for diesel engine cylinder heads, heavy gears, and hydraulic manifolds.
ASTM A48 Class 40 Gray Cast Iron Documented Applications
- ›Heavy-duty diesel engine cylinder heads and exhaust manifolds
- ›Precision machine tool spindles, gear blanks, and heavy frames
- ›High-pressure hydraulic manifolds, valve bodies, and pump components
- ›Locomotive brake shoes and industrial crushing machinery liners
Recognized Aliases
Source-backed commercial trade name and short designations cataloged in canonical data.
Class 40 Gray IronSAE G4000 Gray Iron
ASTM A48 Class 40 Gray Cast Iron Specifications & Designations
Standard Designations & Applicable Specifications — Semantically classified designations distinguishing primary standard identifiers, commercial trade names, and applicable specification references.
Direct Standard DesignationsDIRECT DESIGNATION
3 Primary IdentifiersScroll horizontally for full designation data
| System | Identifier | Standard System Name | Classification Notes & Provenance |
|---|---|---|---|
| ASTMPRIMARY | A48 Class 40 | ASTM International | —Ref: Standard Specifications for Gray and Ductile Cast Iron (ASTM A48/A48M, ASTM A536, EN 1561, EN 1563, ISO 185, ISO 1083, SAE J431, SAE J434, ASM Handbook Vol 1) |
| UNS | F12801 | Unified Numbering System | —Ref: Standard Specifications for Gray and Ductile Cast Iron (ASTM A48/A48M, ASTM A536, EN 1561, EN 1563, ISO 185, ISO 1083, SAE J431, SAE J434, ASM Handbook Vol 1) |
| SAE | J431 G4000 | SAE International | —Ref: Standard Specifications for Gray and Ductile Cast Iron (ASTM A48/A48M, ASTM A536, EN 1561, EN 1563, ISO 185, ISO 1083, SAE J431, SAE J434, ASM Handbook Vol 1) |
Recognized Commercial Aliases & Trade NamesCOMMON ALIAS
2 ListedScroll horizontally for full alias classifications
| Recognized Name / Alias | Classification | Technical Usage & Context |
|---|---|---|
| Class 40 Gray Iron | Commercial Alias | Colloquial or commercial industry synonym |
| SAE G4000 Gray Iron | Historical Alias | Colloquial or commercial industry synonym |
Applicable Specifications & Product Form ReferencesSPECIFICATION REFERENCE
3 Applicable StandardsScroll horizontally for full standard specifications
| Standards Body | Specification Code | Specification Title / Scope | Relationship Type |
|---|---|---|---|
| ASTM | ASTM A48 / A48M | Standard Specification for Gray Iron Castings | Specification Reference |
| SAE | SAE J431 | Automotive Gray Iron Castings (Grade G4000) | Specification Reference |
| ISO | ISO 185 | Grey cast irons — Classification | Specification Reference |
Engineering Notice: Applicable specifications establish manufacturing requirements, dimensional tolerances, and test criteria for specific product forms (e.g. bus bar, wire, plate, pipe). They represent applicable technical standards, not alternative or equivalent alloy grades.
ASTM A48 Class 40 Gray Cast Iron Chemical Composition
Chemical Composition (Weight %) — Elemental limits and values from the cited source. Preserves exact semantic limits (minimums, maximums, and ranges).
Scroll horizontally for full elemental limits
| Element | Symbol | Atomic No. | Semantic Basis | Specified Value | Unit | Metallurgical Notes & Qualification | Data Status |
|---|---|---|---|---|---|---|---|
| Carbon | C | 0 | RANGE | 2.90 – 3.20 | wt% | Ref: ASTM International, CEN, ISO & ASM International Standards Technical Committees | VERIFIED |
| Silicon | Si | 0 | RANGE | 1.60 – 2.00 | wt% | Ref: ASTM International, CEN, ISO & ASM International Standards Technical Committees | VERIFIED |
| Manganese | Mn | 0 | RANGE | 0.70 – 1.00 | wt% | Ref: ASTM International, CEN, ISO & ASM International Standards Technical Committees | VERIFIED |
| Phosphorus | P | 0 | MAXIMUM | ≤ 0.08 | wt% | Ref: ASTM International, CEN, ISO & ASM International Standards Technical Committees | VERIFIED |
| Sulfur | S | 0 | MAXIMUM | ≤ 0.12 | wt% | Ref: ASTM International, CEN, ISO & ASM International Standards Technical Committees | VERIFIED |
| Iron | Fe | 0 | REMAINDER | Remainder | wt% | Ref: ASTM International, CEN, ISO & ASM International Standards Technical Committees | VERIFIED |
* Elemental percentages are expressed in weight percent (wt%). Values represent applicable specification limits. Unspecified trace elements are not fabricated or assumed.Preserves exact semantic basis
Property Display UnitsSwitch between Canonical SI and Source / US Customary units:
ASTM A48 Class 40 Gray Cast Iron Physical Properties
Source-specific physical properties. Test temperatures are shown only where reported.
Scroll horizontally for full property parameters
| Property Parameter | Canonical SI Value | Semantic Basis | Test Temperature / Context Range | Source Raw Reference | Source Reference | Status |
|---|---|---|---|---|---|---|
| Density | 7.25 g/cm³ | TYPICAL | 7.25 g/cm³ | ASTM International, CEN & ISO Technical Committees | VERIFIED |
ASTM A48 Class 40 Gray Cast Iron Thermal & Thermodynamic Properties
Phase change temperatures, thermal conductivity, specific heat, mean coefficients of thermal expansion across standardized temperature ranges, and recommended thermal processing windows.
Scroll horizontally for full property parameters
| Property Parameter | Canonical SI Value | Semantic Basis | Test Temperature / Context Range | Source Raw Reference | Source Reference | Status |
|---|---|---|---|---|---|---|
| Thermal Conductivity | 44 W/(m·K) | TYPICAL | 44 W/(m·K) | ASTM International, CEN & ISO Technical Committees | VERIFIED | |
| Specific Heat Capacity | 490 J/(kg·K) | TYPICAL | 490 J/(kg·K) | ASTM International, CEN & ISO Technical Committees | VERIFIED | |
| Coefficient of Thermal Expansion | 10.8 µm/(m·K) | TYPICAL | 10.8 µm/(m·K) | ASTM International, CEN & ISO Technical Committees | VERIFIED |
ASTM A48 Class 40 Gray Cast Iron Electrical Properties
Electrical conductivity and resistivity in their reported units and conditions.
Scroll horizontally for full property parameters
| Property Parameter | Canonical SI Value | Semantic Basis | Test Temperature / Context Range | Source Raw Reference | Source Reference | Status |
|---|---|---|---|---|---|---|
| Electrical Resistivity | 620 nΩ·m | TYPICAL | 620 nΩ·m | ASTM International, CEN & ISO Technical Committees | VERIFIED |
ASTM A48 Class 40 Gray Cast Iron Mechanical Properties
Contextual Mechanical Properties & Tempers: Engineering strength, ductility, and hardness values grouped by product form, temper, and section thickness. Mechanical properties are contextual and not isotropic averages.
Elastic & Baseline Mechanical ConstantsSource-specific measurement conditions
Poisson Ratio
0.27 dimensionless
Showing 3 of 3 conditions
Scroll horizontally for all conditions & tempers
| Product Form | Temper / Condition | Section Size | Tensile (UTS) | Yield Strength | Elongation | Shear Strength | Fatigue Strength | Hardness (Scales Preserved) | Status |
|---|---|---|---|---|---|---|---|---|---|
| Standard Product Form | As-CastSource values and qualifiersUltimate Tensile Strength: ≥ 276 MPa (MINIMUM)Governing minimum tensile strength per ASTM A48 Class 40 (40 ksi = 276 MPa). Gray iron exhibits no distinct yield point.ASTM International, CEN, ISO & ASM International Standards Technical Committees — ASTM A48, ASTM A536, EN 1561, EN 1563, ISO 185, ISO 1083, SAE J431, SAE J434, ASM Handbook Vol 1 | 30.5 mm Test Bar B | ≥ 276 MPa | — | — | — | — | — | VERIFIED |
| Standard Product Form | As-CastSource values and qualifiers | — | — | — | — | — | — | — | VERIFIED |
| Standard Product Form | As-CastSource values and qualifiers | — | — | — | — | — | — | 210–260 HBW | VERIFIED |
Hardness Integrity Notice: Rockwell B (HRB), Rockwell F (HRF), and Superficial 30T (HR30T) scales are reported on their measured scales without cross-scale mathematical conversion.
Source: See fact-level citations
ASTM A48 Class 40 Gray Cast Iron Processing & Fabrication
Machining, joining, forming, and thermal processing ratings cataloged from the cited authoritative technical reference.
Machinability
Good machinability (~70% relative to C36000 baseline). Fully pearlitic matrix requires rigid machine tool setups, coated carbide tooling, and positive rake geometries.
Weldability & Joining
Extremely difficult to weld. Fusion welding creates high susceptibility to cracking due to high carbon equivalent. Recommended strictly for casting salvage using qualified hot-box procedures (350°C–400°C preheat).
Heat Treatment & Working Ranges
Stress relief at 565°C–620°C for 2 hours. Induction surface hardening achieves 54–58 HRC for heavy wear surfaces.
Forming & Cold Working
Non-deformable. Cannot be rolled or cold formed.
Practical Engineering & Fabrication Notes
By Mat Grades Editorial Desk · Updated 2026-11-14. Use alongside the specified product standard and supplier certificate.
Machining & shop-floor behavior
The cataloged machining note for ASTM A48 Class 40 Gray Cast Iron states: Good machinability (~70% relative to C36000 baseline). Fully pearlitic matrix requires rigid machine tool setups, coated carbide tooling, and positive rake geometries. A relevant hardness example is HBW Hardness: 210–260 HBW (range; As-Cast). Use that supplied condition for a trial of the difficult feature. Record tool changes, burr removal, unclamped dimensions and accepted parts per hour. Relative machinability ratings from different reference scales should not be compared as if they were one common test.
Weldability, brazing & joining
The available joining assessment states: Extremely difficult to weld. Fusion welding creates high susceptibility to cracking due to high carbon equivalent. Recommended strictly for casting salvage using qualified hot-box procedures (350°C–400°C preheat). The first cataloged strength example is Ultimate Tensile Strength: minimum 276 MPa (minimum; As-Cast, 30.5 mm Test Bar B). Assess the final part after joining or thermal processing. Include distortion, cleanup and inspection in the quotation. A material designation or favorable process rating is a starting point for qualification, not evidence that an untested joint meets the drawing.
Corrosion & service environment
Consider moisture, coating, local tensile stress and impact as well as the cast-iron family. Surface protection does not repair porosity or a highly stressed transition. Casting section and sampling arrangement affect how coupon evidence relates to the finished component; keep those limits visible in the approval. The recorded thermal example is Thermal Conductivity: 44 W/(m·K) (typical; additional condition not stated). State the exposure and inspection access in the design record so that a change of installation or cleaning method triggers a review. The selected composition entries are C 2.9–3.2 wt%, Si 1.6–2 wt%, Mn 0.7–1 wt%. Chemistry documents identity; it does not establish fluid compatibility.
Selection trade-offs & applications
Use ASTM A48 Class 40, UNS F12801, SAE J431 G4000 to identify the candidate, then specify the product form and delivered condition separately. The catalog lists Heavy-duty diesel engine cylinder heads and exhaust manifolds as an application example. The related candidate ASTM A48 Class 30 Gray Cast Iron is linked for comparison; its commonly compared relationship must be checked before substitution. Compare the complete route through machining, joining, finish and inspection. Keep the certificate, required test location and acceptance criteria with the first-article record. A later change of grade, condition or source should be assessed against that same requirement.
Technical references: ASTM International, CEN, ISO & ASM International Standards Technical Committees
ASTM A48 Class 40 Gray Cast Iron Equivalent & Comparable Grades
Comparable Grades & Cross-References: Carefully classified cross-reference relationships for ASTM A48 Class 40 Gray Cast Iron. Comparable does not mean equivalent.
Scroll horizontally for relationship classifications & comparisons
| Related Material | Family | Relationship Classification | Metallurgical Notes & Differences | Status | Action |
|---|---|---|---|---|---|
| ASTM A48 Class 30 Gray Cast Iron | Cast Iron | Commonly Compared | Class 40 provides 33% higher minimum tensile strength (276 vs 207 MPa) and greater wear resistance, but Class 30 is easier to cast without chilled edges and offers higher thermal conductivity (48 vs 44 W/(m·K)).Materials serve different design priorities (e.g. higher strength vs superior corrosion resistance or cost). | VERIFIED | |
| EN-GJL-250 Gray Cast Iron | Cast Iron | Approximate Equivalent | EN-GJL-250 (min 250 MPa tensile on 15–30 mm wall) provides similar structural duty to ASTM A48 Class 40 (min 276 MPa on 30.5 mm Test Bar B), but differing standard test specimen dimensions require careful engineering comparison.Engineering substitution review required. Design calculations must verify temper, formability, and corrosion limits before specifying as a direct replacement. | VERIFIED |
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Sources
Sources & Provenance Trail: Authoritative reference publications, standards specifications, and data registers cited across this material record.
ASTM International, CEN & ISO Technical CommitteesStandard Specifications for Gray and Ductile Cast Iron (ASTM A48/A48M, ASTM A536, EN 1561, EN 1563, ISO 185, ISO 1083, SAE J431, SAE J434, ASM Handbook Vol 1)
STANDARDS ORG
Authoritative foundry data harmonized across ASTM A48, ASTM A536, EN 1561, EN 1563, ISO 185, ISO 1083, SAE J431, SAE J434, and ASM International Handbook Volume 1 (Properties and Selection: Irons, Steels, and High-Performance Alloys).
Issuing Body: ASTM International, CEN, ISO & ASM International Standards Technical CommitteesRevision: ASTM A48/A48M-22 / ASTM A536-84(2024) / EN 1561:2020 / EN 1563:2018 / ISO 185:2020 / ISO 1083:2018View Source Record ↗
Intellectual Property & Provenance Notice: Mat Grades cites technical literature from recognized industry associations and standards organizations. Underlying technical standards and publication data remain the intellectual property of their respective issuing organizations.