Engineers requiring cost-effective casting solutions with reliable mechanical strength frequently specify ASTM A48 Class 35 for medium-to-high duty industrial components. This comprehensive guide examines the ASTM A48 Class 35 chemical composition, critical ASTM A48 Class 35 material properties, and international ASTM A48 Class 35 equivalent grades that make it a practical choice for applications demanding balanced strength with superior machinability. The ASTM A48/A48M standard provides the official specifications for gray iron castings used in general engineering applications.
Industry professionals value ASTM A48 Class 35 for several compelling technical advantages:
- Minimum 35,000 psi tensile strength delivers substantial load-bearing capacity for general engineering applications
- Excellent machinability from optimized graphite flake structure enables faster cutting speeds and extended tool life
- Superior damping capacity reduces vibration in rotating machinery and structural applications
- Balanced hardness (187-241 HB) provides adequate wear resistance while maintaining workability
- Proven reliability in pump housings, valve bodies, machine tool bases, and automotive components
- Cost-effective alternative to higher-strength cast irons offering 30-50% manufacturing cost savings
Engineers who understand ASTM A48 Class 35 material properties, chemical composition requirements, and ASTM A48 Class 35 equivalent standards can optimize component design and achieve reliable performance across diverse industrial applications.
Key Takeaways
- ASTM A48 Class 35 delivers minimum 35,000 psi (241 MPa) tensile strength for medium-duty applications
- The ASTM A48 Class 35 chemical composition includes 2.8-3.3% carbon, 1.2-1.7% silicon, and 0.8-1.2% manganese
- International ASTM A48 Class 35 equivalent grades include EN-GJL-250 (Europe), HT250 (China), and FC250 (Japan)
- ASTM A48 Class 35 material properties include hardness 187-241 HB with excellent machinability characteristics
- The flake graphite structure provides superior damping capacity and thermal conductivity
- Applications include machine tool components, pump housings, automotive brake components, and hydraulic valve bodies
- Selecting experienced gray iron casting foundries ensures consistent ASTM A48 Class 35 quality
What Is ASTM A48 Class 35?
ASTM A48 Class 35 is a medium-strength gray iron casting grade with minimum 35,000 psi tensile strength, featuring optimized flake graphite microstructure that delivers reliable mechanical properties with exceptional manufacturing efficiency.
Material Classification
ASTM A48 Class 35 follows the American designation system established by ASTM A48, the standard specification for gray iron castings. The classification number “35” directly represents minimum tensile strength of 35,000 pounds per square inch measured on standard test bars. This standardized designation eliminates confusion during component specification, with engineers referencing ASTM A48 Class 35 consistently regardless of supplier location.
The ASTM A48 standard encompasses Classes 20, 25, 30, 35, 40, 50, and 60, with Class 35 positioned in the medium-to-high strength range. This classification provides balanced mechanical properties suitable for applications requiring moderate load-bearing capacity without the brittleness associated with higher-strength grades.
Microstructure Characteristics
The performance characteristics of ASTM A48 Class 35 stem from its carefully controlled microstructure. Gray iron contains carbon in the form of flake graphite distributed throughout a pearlitic or ferritic-pearlitic metallic matrix. These graphite flakes create the distinctive gray fracture appearance and provide unique properties distinguishing gray iron from other cast materials.
The metallic matrix surrounding graphite flakes consists predominantly of pearlitic structure in ASTM A48 Class 35 material. This matrix composition provides the balanced 35,000 psi tensile strength with exceptional machinability. The typical matrix ranges from 80-95% pearlite with 5-20% ferrite, differentiating Class 35 from lower-strength grades containing higher ferrite content.
| Microstructure Component | Typical Content | Contribution to ASTM A48 Class 35 Properties |
|---|---|---|
| Flake Graphite | 8-11% by volume | Superior machinability, damping capacity, thermal conductivity |
| Pearlite | 80-95% | Adequate strength, moderate hardness, wear resistance |
| Ferrite | 5-20% | Improved machinability, ductility |
| Graphite Flake Size | Type A, Size 4-6 | Property uniformity, consistent performance |
The flake graphite acts as an internal lubricant during machining operations, explaining the material’s exceptional machinability advantage. The predominantly pearlitic matrix delivers reliable tensile strength while maximizing manufacturing efficiency through reduced cutting forces and extended tool life.
ASTM A48 Class 35 Chemical Composition
The ASTM A48 Class 35 chemical composition includes 2.8-3.3% carbon, 1.2-1.7% silicon, 0.8-1.2% manganese, with controlled phosphorus below 0.15% and sulfur below 0.12%, ensuring balanced flake graphite formation for reliable 35,000 psi strength with excellent machinability.
Understanding ASTM A48 Class 35 chemical composition provides critical insight into material properties and processing behavior. Each element serves specific purposes achieving the balanced pearlitic microstructure required for reliable performance.
Primary Alloying Elements
Carbon (C): 2.8-3.3%
Carbon content directly determines graphite quantity and distribution in ASTM A48 Class 35 material. This controlled range enables excellent casting fluidity while providing sufficient graphite volume for superior machinability and damping capacity. The carbon level influences the pearlite-to-ferrite ratio, with moderate-to-high carbon content supporting predominantly pearlitic matrix structure delivering 35,000 psi tensile strength.
The carbon equivalent (CE = %C + %Si/3 + %P/3) typically ranges from 3.9 to 4.3 for optimal ASTM A48 Class 35 properties. Foundries monitor carbon content precisely during melting to maintain consistent mechanical performance and machinability characteristics. Higher carbon content within the specified range promotes finer graphite flake distribution, improving strength uniformity.
Silicon (Si): 1.2-1.7%
Silicon acts as a graphitizing element promoting flake graphite formation during gray iron solidification. The silicon range in ASTM A48 Class 35 composition balances graphitization with matrix structure control. Controlled silicon content maintains predominantly pearlitic matrix structure, optimizing strength while ensuring excellent machinability.
Silicon also improves casting fluidity and reduces shrinkage tendencies during solidification. The silicon level directly influences final microstructure, affecting both ASTM A48 Class 35 material properties and manufacturing characteristics. Moderate silicon content promotes uniform flake distribution while maintaining balanced mechanical properties.
Manganese (Mn): 0.8-1.2%
Manganese contributes to pearlite formation and strength enhancement in ASTM A48 Class 35 composition. Controlled manganese addition provides adequate strength without excessive hardness that would compromise machinability. The manganese content balances strength requirements with manufacturing efficiency, promoting pearlitic matrix development essential for Class 35 performance.
Manganese also neutralizes sulfur by forming manganese sulfide inclusions, preventing iron sulfide formation that would reduce material quality. The controlled addition maintains the predominantly pearlitic structure characteristic of ASTM A48 Class 35 material.
Impurity Control
Phosphorus (P): <0.15%
Phosphorus creates brittleness by forming iron phosphide (steadite) at grain boundaries in gray iron. The phosphorus limit prevents excessive steadite formation that would reduce impact resistance and machinability. However, phosphorus in controlled amounts (0.05-0.12%) can slightly increase fluidity and hardness, beneficial for thin-section castings.
Raw material selection controls phosphorus input, ensuring specification compliance while maintaining balanced mechanical properties. Foundries producing ASTM A48 Class 35 carefully manage phosphorus levels to optimize castability without compromising performance.
Sulfur (S): <0.12%
Sulfur content requires control during ASTM A48 Class 35 production to prevent excessive carbide formation and reduced graphitization. While sulfur levels are less critical in gray iron compared to ductile iron, excessive sulfur can create processing difficulties and reduce mechanical properties. The controlled sulfur specification ensures consistent graphite formation and reliable material quality.
| Element | ASTM A48 Class 35 Range | Function |
|---|---|---|
| Carbon (C) | 2.8-3.3% | Graphite formation, machinability |
| Silicon (Si) | 1.2-1.7% | Graphitization, matrix control |
| Manganese (Mn) | 0.8-1.2% | Pearlite formation, strength |
| Phosphorus (P) | <0.15% | Controlled for brittleness management |
| Sulfur (S) | <0.12% | Controlled for graphitization |
ASTM A48 Class 35 Material Properties
ASTM A48 Class 35 material properties include minimum 35,000 psi (241 MPa) tensile strength, hardness 187-241 HB, compressive strength 109,000-130,000 psi, and excellent thermal conductivity, delivering balanced load-bearing capacity with superior manufacturing efficiency.
The mechanical and physical properties defined by ASTM A48 Class 35 specification determine suitability for medium-duty applications. Comprehensive understanding enables accurate design calculations and appropriate component specification.
Tensile Properties
Tensile Strength (Rm): ≥35,000 psi / 241 MPa (typical 35,000-40,000 psi)
Tensile strength represents the primary defining characteristic of ASTM A48 Class 35. The minimum value of 35,000 psi provides substantial load-bearing capability for general engineering applications. Typical production material achieves 35,000-40,000 psi when foundries maintain rigorous process control and optimize the pearlitic microstructure.
The tensile strength depends primarily on matrix structure, carbon content, and section thickness. The predominantly pearlitic matrix (80-95% pearlite) provides reliable strength suitable for moderate-duty applications. Testing procedures follow ASTM A48 standards using separately cast test bars (typically 1.2-inch diameter) ensuring consistent evaluation conditions.
Compressive Strength
Compressive Strength: 109,000-130,000 psi (752-896 MPa)
Gray iron exhibits significantly higher compressive strength compared to tensile strength, typically 3-4 times greater. ASTM A48 Class 35 demonstrates compressive strength of 109,000-130,000 psi, making it particularly suitable for applications involving compressive loading such as machine bases, structural supports, and pressure-containing components.
This characteristic explains gray iron’s widespread use in applications where compressive loads dominate. The flake graphite structure, which creates stress concentrations under tension, has minimal negative effect under compression, allowing the metallic matrix to carry loads effectively.
Hardness Characteristics
Brinell Hardness: 187-241 HB (typical 200-220 HB)
Hardness measurements provide rapid verification of ASTM A48 Class 35 material properties. The Brinell hardness range reflects the predominantly pearlitic microstructure distinguishing Class 35 from lower-strength grades. Values of 200-220 HB indicate optimally controlled material with balanced strength and machinability.
The moderate hardness range provides adequate wear resistance for general applications while maintaining excellent machinability. Components operating in moderate abrasive conditions benefit from this balance between workability and surface durability.
| Property | ASTM A48 Class 35 Value | Test Standard |
|---|---|---|
| Tensile Strength (Rm) | ≥35,000 psi / 241 MPa | ASTM A48 |
| Compressive Strength | 109,000-130,000 psi / 752-896 MPa | ASTM A48 |
| Brinell Hardness (HB) | 187-241 HB | ASTM A48 |
| Shear Strength | ~45,000 psi / 310 MPa | ASTM A48 |
Physical Properties
Density: 0.260 lb/in³ / 7.2 g/cm³
The density of ASTM A48 Class 35 remains consistent across composition variations, enabling accurate weight calculations during design. Class 35 density closely approximates higher-strength cast irons and steel (0.283 lb/in³), providing approximately 8% weight savings compared to steel for equivalent volumes.
Modulus of Elasticity: 14-17 million psi / 97-117 GPa
The elastic modulus of ASTM A48 Class 35 material properties is significantly lower than steel (29-30 million psi). This characteristic affects deflection calculations, with gray iron components showing approximately 50% greater deflection than equivalent steel parts under identical loading. Engineers must account for this lower modulus when calculating structural deflection and vibration response.
Thermal Properties
Thermal Conductivity: 46-52 W/(m·K)
ASTM A48 Class 35 demonstrates excellent thermal conductivity, approximately 50% higher than steel. This characteristic makes gray iron particularly suitable for applications requiring heat dissipation, such as brake components, engine blocks, and machinery housings subjected to thermal cycling. The flake graphite structure provides efficient heat transfer pathways throughout the material.
Coefficient of Thermal Expansion: 10.8-11.6 × 10⁻⁶/K
The thermal expansion coefficient closely matches carbon steel values. This compatibility minimizes thermal stress when assembling ASTM A48 Class 35 components with steel parts, preventing loosening or binding across temperature ranges encountered in service.
Performance Characteristics
Damping Capacity
ASTM A48 Class 35 exhibits superior damping capacity compared to steel and other engineering materials. The flake graphite structure absorbs vibration energy through internal friction at graphite-matrix interfaces. This characteristic makes Class 35 particularly valuable for machine tool bases, engine components, and structural applications requiring vibration control.
Damping capacity in gray iron typically exceeds steel by 10-20 times, significantly reducing vibration amplitude and noise transmission. This property contributes to smoother operation and extended service life in rotating machinery applications.
Machinability
ASTM A48 Class 35 demonstrates excellent machinability, with cutting speeds 30-50% faster than comparable-strength steels. The graphite flakes act as chip breakers and provide internal lubrication during cutting operations. Tool life typically extends 2-3 times compared to machining equivalent-strength steel, reducing manufacturing costs through decreased tool replacement frequency.
The material produces short, easily controlled chips that evacuate readily from cutting zones. Surface finishes of 63-125 Ra are readily achievable using conventional machining practices without excessive tool wear or work hardening.
ASTM A48 Class 35 Equivalent Grades
The ASTM A48 Class 35 equivalent includes EN-GJL-250 (European), HT250 (Chinese), FC250 (Japanese), and Grade 250 (Indian) standards, representing balanced medium-strength gray iron grades across international specifications.
Understanding international equivalent grades enables global sourcing and ensures design compatibility across markets. The ASTM A48 Class 35 equivalent system facilitates international procurement and technical communication.
European Standard
The European designation for ASTM A48 Class 35 equivalent is EN-GJL-250, where “GJL” indicates lamellar (flake) graphite iron and “250” represents minimum tensile strength in megapascals (approximately 36,250 psi). This standard harmonized earlier national standards including DIN 1691 (Germany) and BS 1452 Grade 260 (UK).
EN-GJL-250 specifications:
- Tensile strength minimum: 250 MPa (36,250 psi)
- Brinell hardness: typically 180-230 HB
- Predominantly pearlitic matrix
- Applications: pump housings, valve bodies, machine components
The European specification shows slightly higher tensile minimum compared to ASTM specification, though production material typically meets both standards simultaneously.
Chinese Standard
HT250 (GB/T 9439)
Chinese national standard GB/T 9439 designates equivalent material as HT250. The “HT” represents gray cast iron (Hui Tie in Chinese) and “250” indicates minimum tensile strength in MPa. Chinese foundries produce HT250 extensively for automotive components, machine tools, and general machinery applications.
HT250 specifications:
- Tensile strength minimum: 250 MPa (36,250 psi)
- Brinell hardness: 170-241 HB
- Predominantly pearlitic matrix structure
- Widely used in Chinese manufacturing industries
Japanese Standard
FC250 (JIS G 5501)
Japanese Industrial Standard JIS G 5501 classifies equivalent material as FC250. The “FC” designation represents flake graphite cast iron while “250” indicates minimum tensile strength in MPa. Japanese automotive and machinery manufacturers utilize FC250 for components requiring balanced strength with excellent machinability.
FC250 specifications:
- Tensile strength minimum: 250 MPa (36,250 psi)
- Brinell hardness: typically 187-241 HB
- Excellent machinability and damping capacity
- Common in automotive and industrial applications
International Equivalent Comparison
| Standard | Designation | Tensile Strength (Min) | Hardness (HB) | Primary Region |
|---|---|---|---|---|
| American (ASTM A48) | Class 35 | 241 MPa (35 ksi) | 187-241 | USA, Americas |
| European (EN 1561) | EN-GJL-250 | 250 MPa (36 ksi) | 180-230 | Europe |
| Chinese (GB/T 9439) | HT250 | 250 MPa (36 ksi) | 170-241 | China, Asia |
| Japanese (JIS G 5501) | FC250 | 250 MPa (36 ksi) | 187-241 | Japan, Asia |
| Indian (IS 210) | Grade 250 | 250 MPa (36 ksi) | 180-240 | India |
When specifying ASTM A48 Class 35 equivalent grades internationally, engineers should verify mechanical property alignment. Most standards specify similar tensile strength levels (241-250 MPa) with comparable hardness ranges, providing equivalent load-bearing characteristics with excellent machinability across all equivalent grades.
Primary Applications of ASTM A48 Class 35 Material
ASTM A48 Class 35 applications include machine tool bases, pump housings, automotive brake components, valve bodies, engine blocks, hydraulic cylinders, and structural supports requiring balanced strength with excellent vibration damping for cost-effective manufacturing.
The unique combination of reliable strength, superior machinability, excellent damping capacity, and thermal conductivity makes ASTM A48 Class 35 suitable for diverse industrial applications where manufacturing efficiency enhances economic competitiveness.
Machine Tool Components
Bases and Structural Supports
Machine tool manufacturers utilize ASTM A48 Class 35 for equipment bases, bed frames, and structural components requiring vibration damping. The 35,000 psi tensile strength withstands operational loads while the superior damping capacity (10-20 times greater than steel) reduces vibration transmission, improving machining precision and surface finish quality.
The excellent thermal stability maintains dimensional accuracy during temperature variations from cutting operations. Production volumes benefit significantly from the 30-50% faster machining speeds compared to steel alternatives, reducing manufacturing costs for large castings.
Automotive Components
Brake Components
Automotive manufacturers specify ASTM A48 Class 35 for brake drums, rotors, and calipers requiring thermal stability with wear resistance. The excellent thermal conductivity (46-52 W/m·K) efficiently dissipates frictional heat, preventing brake fade during repeated braking cycles. The balanced hardness (187-241 HB) provides adequate wear resistance for moderate-duty applications.
The superior damping capacity minimizes brake noise and vibration issues, improving vehicle comfort. Cost-effective manufacturing from excellent machinability reduces production expenses for high-volume automotive components.
Engine Components
Engine blocks and cylinder heads for moderate-performance applications employ ASTM A48 Class 35 for thermal management capability. The high thermal conductivity enables efficient heat dissipation, while the flake graphite structure provides excellent vibration damping reducing noise transmission.
Hydraulic System Components
Pump Housings and Valve Bodies
Hydraulic equipment manufacturers specify ASTM A48 Class 35 for pump housings and valve bodies requiring moderate pressure containment. The 35,000 psi tensile strength combined with superior compressive strength (109,000-130,000 psi) enables pressure ratings up to 1,500-2,000 psi with appropriate safety factors.
The material machines efficiently for precise internal passages and mounting features. Excellent dimensional stability maintains tight tolerances throughout extended service intervals. The superior damping capacity reduces hydraulic noise transmission in industrial systems.
Industrial Equipment
Gear Housings and Structural Brackets
Industrial gearboxes employ ASTM A48 Class 35 for housings and structural components in moderate-duty applications. The adequate hardness provides reasonable wear resistance while excellent machinability enables economical production of complex geometries. The superior damping capacity reduces noise transmission in machinery installations.
Manufacturing economy from excellent machinability enhances competitiveness for high-volume production. The material’s dimensional stability maintains alignment tolerances throughout equipment service life.
Selecting a Gray Iron Casting Foundry
Selecting a gray iron casting foundry for ASTM A48 Class 35 production requires evaluating metallurgical expertise in pearlitic gray iron control, comprehensive quality systems, and demonstrated capability manufacturing components meeting ASTM A48 specifications.
Component quality depends critically on foundry expertise and process control capabilities. Engineers should assess technical competence when selecting manufacturing partners for ASTM A48 Class 35 applications.
Technical Capability Requirements
Gray Iron Expertise
Foundries specializing in gray iron production demonstrate deep understanding of ASTM A48 Class 35 chemical composition control, inoculation practices, and pearlitic microstructure development. They maintain metallurgical laboratories equipped for chemical analysis, metallographic examination, and mechanical testing. Experienced metallurgists oversee production and address quality concerns specific to gray iron grades.
The foundry should provide detailed certifications including chemical composition, tensile test results, hardness measurements, and metallographic verification of graphite morphology and matrix structure. Technical support during design optimization helps engineers select appropriate specifications.
Quality System Certification
Professional foundries maintain ISO 9001:2015 quality management certification demonstrating systematic process control. Advanced facilities pursue additional certifications including IATF 16949 for automotive applications. Certification provides independent verification of quality management supporting consistent ASTM A48 Class 35 material properties.
Production Capability Assessment
Request sample castings demonstrating capability producing components meeting ASTM A48 Class 35 specification. Examine samples for surface quality, dimensional accuracy, and absence of casting defects such as blowholes, shrinkage porosity, or sand inclusions.
Review material certificates confirming mechanical properties and chemical composition meet requirements. Metallographic examination verifies appropriate graphite flake size and distribution (Type A, Size 4-6) with predominantly pearlitic matrix structure (80-95% pearlite). Hardness testing confirms appropriate values within 187-241 HB range.
For engineers seeking a reliable gray iron casting foundry with proven expertise in ASTM A48 Class 35 production, SHENRGONG delivers specialized capabilities in pearlitic gray iron manufacturing with comprehensive metallurgical control and quality assurance systems ensuring consistent material properties for diverse industrial applications.
Conclusion
ASTM A48 Class 35 represents an excellent engineering material choice for applications requiring balanced strength, superior damping capacity, and exceptional manufacturing efficiency. The predominantly pearlitic microstructure created through precise composition control and optimized casting practices provides reliable 35,000 psi tensile strength with excellent machinability exceeding comparable alternatives.
Understanding ASTM A48 Class 35 material properties, chemical composition requirements, and ASTM A48 Class 35 equivalent grades enables engineers to optimize component design while controlling manufacturing costs. The material’s superior thermal conductivity, damping capacity, and machinability characteristics make it particularly suitable for machine tool components, automotive applications, and hydraulic system housings.
Success depends on partnering with experienced gray iron casting foundries maintaining rigorous metallurgical control and comprehensive quality systems for consistent ASTM A48 Class 35 quality throughout production.
Frequently Asked Questions (FAQ)
What is ASTM A48 Class 35 used for?
ASTM A48 Class 35 is used for machine tool bases, pump housings, automotive brake components, valve bodies, engine blocks, and structural supports requiring balanced 35,000 psi tensile strength with excellent vibration damping and thermal conductivity for reliable performance.
What are ASTM A48 Class 35 material properties?
ASTM A48 Class 35 material properties include minimum 35,000 psi tensile strength, 109,000-130,000 psi compressive strength, hardness 187-241 HB, and predominantly pearlitic matrix providing reliable strength with superior machinability and damping capacity.
What is ASTM A48 Class 35 chemical composition?
ASTM A48 Class 35 chemical composition includes 3.1-3.4% carbon, 1.9-2.3% silicon, 0.5-0.9% manganese, with controlled phosphorus below 0.15% and sulfur below 0.12%, ensuring balanced flake graphite formation for consistent mechanical properties.
What are ASTM A48 Class 35 equivalent grades internationally?
ASTM A48 Class 35 equivalent grades include EN-GJL-250 (Europe), HT250 (China), FC250 (Japan), and Grade 250 (India), all providing comparable tensile strength (241-250 MPa) with excellent machinability and damping characteristics.
Why is ASTM A48 Class 35 machinability superior?
ASTM A48 Class 35 machinability exceeds steel by 30-50% in cutting speed with 2-3 times longer tool life due to flake graphite acting as internal lubricant and chip breaker, enabling faster production and reduced manufacturing costs.
