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 30 Gray Cast Iron
Primary Designation:ASTM A48 Class 30
Aliases:
Class 30 Gray IronSAE G3000 Brake Rotor IronGrade 30 Gray Cast 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
7.2 g/cm³TYPICAL · temperature not stated
Thermal Conductivity
48 W/(m·K)TYPICAL · at 20 °C
Specific Heat Capacity
480 J/(kg·K)TYPICAL · temperature not stated
Composition Excerpt
C 3.1–3.4 wt%Carbon (range)
Standard Elemental Basis: RANGETensile Strength
≥ 207 MPaMINIMUM · As-Cast · temperature not stated
Engineering Summary
ASTM A48 Class 30 is the global reference standard for general-purpose engineering gray cast iron. Engineered with a predominantly pearlitic matrix containing finely dispersed Type A graphite flakes, it provides an outstanding combination of moderate tensile strength (min 30 ksi / 207 MPa), high compressive strength (~750 MPa), exceptional vibration damping, resistance to frictional wear, and dimensional stability. It is the premier alloy for engine cylinder blocks, machine tool structures, and automotive brake discs.
ASTM A48 Class 30 Gray Cast Iron Documented Applications
- ›Automotive ventilated brake rotors, discs, and heavy brake drums
- ›Internal combustion engine cylinder blocks, liners, and crankcases
- ›Machine tool structural frames, beds, ways, columns, and tables
- ›Compressor cylinders, gear housings, and heavy industrial pump bodies
- ›Flywheels, sheaves, bearing housings, and valve components
Recognized Aliases
Source-backed commercial trade name and short designations cataloged in canonical data.
Class 30 Gray IronSAE G3000 Brake Rotor IronGrade 30 Gray Cast Iron
ASTM A48 Class 30 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 30 | 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 | F12101 | 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 G3000 | 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
3 ListedScroll horizontally for full alias classifications
| Recognized Name / Alias | Classification | Technical Usage & Context |
|---|---|---|
| Class 30 Gray Iron | Commercial Alias | Colloquial or commercial industry synonym |
| SAE G3000 Brake Rotor Iron | Commercial Alias | Colloquial or commercial industry synonym |
| Grade 30 Gray Cast Iron | Colloquial 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 G3000) | 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 30 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 | 3.10 – 3.40 | wt% | Carbon adjusted for fully pearlitic matrix in standard section sizes.Ref: ASTM International, CEN, ISO & ASM International Standards Technical Committees | VERIFIED |
| Silicon | Si | 0 | RANGE | 1.90 – 2.30 | wt% | Controls graphitization without promoting free ferrite.Ref: ASTM International, CEN, ISO & ASM International Standards Technical Committees | VERIFIED |
| Manganese | Mn | 0 | RANGE | 0.60 – 0.90 | wt% | Stabilizes pearlite matrix structure.Ref: ASTM International, CEN, ISO & ASM International Standards Technical Committees | VERIFIED |
| Phosphorus | P | 0 | MAXIMUM | ≤ 0.12 | wt% | Ref: ASTM International, CEN, ISO & ASM International Standards Technical Committees | VERIFIED |
| Sulfur | S | 0 | MAXIMUM | ≤ 0.15 | 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 30 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 | 7.2 g/cm³ | TYPICAL | 7.2 g/cm³ | ASTM International, CEN & ISO Technical Committees | VERIFIED |
ASTM A48 Class 30 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 | 48 W/(m·K) | TYPICAL | Test Temp: 20 °C | 48 W/(m·K) | ASTM International, CEN & ISO Technical Committees | VERIFIED |
| Specific Heat Capacity | 480 J/(kg·K) | TYPICAL | 480 J/(kg·K) | ASTM International, CEN & ISO Technical Committees | VERIFIED | |
| Coefficient of Thermal Expansion | 11 µm/(m·K) | TYPICAL | 11 µm/(m·K) | ASTM International, CEN & ISO Technical Committees | VERIFIED |
ASTM A48 Class 30 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 | 680 nΩ·m | TYPICAL | 680 nΩ·m | ASTM International, CEN & ISO Technical Committees | VERIFIED |
ASTM A48 Class 30 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
0.26 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: ≥ 207 MPa (MINIMUM)Governing specification minimum per ASTM A48 Class 30 (30 ksi = 207 MPa). Gray iron exhibits non-linear stress-strain behavior with no 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 (1.2 in.) diameter Test Bar B | ≥ 207 MPa | — | — | — | — | — | VERIFIED |
| Standard Product Form | As-CastSource values and qualifiersModulus of Elasticity: 100 GPa (TYPICAL)Secant modulus at 25% tensile strength.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 | — | — | — | — | — | — | — | VERIFIED |
| Standard Product Form | As-CastSource values and qualifiers | — | — | — | — | — | — | 175–225 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 30 Gray Cast Iron Processing & Fabrication
Machining, joining, forming, and thermal processing ratings cataloged from the cited authoritative technical reference.
Machinability
Excellent machinability (~90% relative to C36000 free-cutting brass). Flake graphite acts as internal lubricant and natural chip breaker. Readily turned, milled, and drilled without burr formation.
Weldability & Joining
Poor weldability. Arc welding produces brittle martensitic heat-affected zones and crack risks. Recommended repair procedure requires 250°C–350°C (480°F–660°F) preheat, nickel-iron (ENiFe-CI) electrodes, short beads with peening, and slow insulation cooling.
Heat Treatment & Working Ranges
Stress relief annealing at 540°C–595°C (1000°F–1100°F) for 1–2 hours eliminates residual casting stresses and prevents distortion. Flame or induction surface hardening can achieve 50–55 HRC on slideways.
Forming & Cold Working
Non-deformable. Gray cast iron is inherently brittle in tension and cannot be cold or hot deformed.
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 30 Gray Cast Iron states: Excellent machinability (~90% relative to C36000 free-cutting brass). Flake graphite acts as internal lubricant and natural chip breaker. Readily turned, milled, and drilled without burr formation. A relevant hardness example is HBW Hardness: 175–225 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: Poor weldability. Arc welding produces brittle martensitic heat-affected zones and crack risks. Recommended repair procedure requires 250°C–350°C (480°F–660°F) preheat, nickel-iron (ENiFe-CI) electrodes, short beads with peening, and slow insulation cooling. The first cataloged strength example is Ultimate Tensile Strength: minimum 207 MPa (minimum; As-Cast, 30.5 mm (1.2 in.) diameter 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: 48 W/(m·K) (typical; ; test temperature 20 °C). 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 3.1–3.4 wt%, Si 1.9–2.3 wt%, Mn 0.6–0.9 wt%. Chemistry documents identity; it does not establish fluid compatibility.
Selection trade-offs & applications
Use ASTM A48 Class 30, UNS F12101, SAE J431 G3000 to identify the candidate, then specify the product form and delivered condition separately. The catalog lists Automotive ventilated brake rotors, discs, and heavy brake drums as an application example. The related candidate ASTM A536 Grade 65-45-12 Ductile 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 30 Gray Cast Iron Equivalent & Comparable Grades
Comparable Grades & Cross-References: Carefully classified cross-reference relationships for ASTM A48 Class 30 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 A536 Grade 65-45-12 Ductile Cast Iron | Cast Iron | Commonly Compared | Fundamental cast iron selection comparison: Class 30 Gray Iron provides 3x higher vibration damping, superior thermal conductivity (48 vs 35 W/(m·K)), and lower casting cost, but 65-45-12 Ductile Iron provides true tensile ductility (12% elongation), specified yield strength (310 MPa), and high impact shock resistance.Materials serve different design priorities (e.g. higher strength vs superior corrosion resistance or cost). | VERIFIED | |
| EN-GJL-200 Gray Cast Iron | Cast Iron | Approximate Equivalent | EN-GJL-200 specifies min 200 MPa tensile strength on 15–30 mm wall thickness, closely approximating ASTM A48 Class 30 (min 207 MPa on 30.5 mm Test Bar B). However, EN 1561 incorporates mandatory wall-thickness derating tables not present in ASTM A48.Engineering substitution review required. Design calculations must verify temper, formability, and corrosion limits before specifying as a direct replacement. | VERIFIED | |
| SAE 1018 Carbon Steel | Steel | Commonly Compared | Class 30 Gray Iron offers net-shape casting capability, superior vibration damping, higher compressive strength (~750 vs ~400 MPa), and better machinability for heavy machine bases, whereas SAE 1018 steel provides high tensile elongation (~25%), yield strength, and structural weldability.Materials serve different design priorities (e.g. higher strength vs superior corrosion resistance or cost). | VERIFIED |
Related Engineering & Metallurgy Guides
Contextual technical guides explaining degradation mechanisms, testing methodologies, and selection criteria relevant to ASTM A48 Class 30 Gray Cast Iron.
Corrosion & Surface Engineering15 min read
How to Remove Rust From Cast Iron: Methods, Science & Prevention
Cast iron is an indispensable alloy family renowned for superior vibration damping and castability, but its iron matrix and carbon microstructure make it susceptible to atmospheric rust. Restoring rusted cast iron requires understanding how mechanical and chemical methods interact with the underlying metal.
Author: Mat Grades Editorial DeskRead Guide →
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.