ASTM A48 Class 35 Castings: Properties, Tolerances & Best Uses

Table of contents

What Class 35 means (and doesn’t)

Definition: In ASTM A48, “Class 35” means minimum tensile strength 35 ksi (≈241 MPa) measured on a separately cast test bar. The standard subordinates chemistry to tensile strength, i.e., composition is not fixed—meeting tensile is the requirement. ASTM International | ASTM+1

Implication: You can see different matrix balances (pearlite/ferrite) from different foundries and still meet Class 35. For wear, machining or hardness consistency, you may need to specify additional controls (e.g., Brinell range) or use EN/ISO grades that include hardness.

Leak-tightness: Flake graphite is not pressure-tight by nature. Class 35 is not a pressure-part material; consider ductile iron or impregnation + leak test if you must hold pressure (see internal links below).

Typical properties & microstructure (for designers)

Acceptance is by tensile per A48; values below are typical, for design context—not acceptance criteria.

Design cue: For NVH-sensitive housings, gray iron’s internal damping reduces ringing vs steel/ductile iron. See: Cast Iron for Noise & Vibration Damping

Standards cross-reference: ASTM ⇆ EN ⇆ ISO

Cross-reference is approximate—confirm details in the target standard.
Standards referenced: ASTM A48 (gray iron, tensile-based classes) and EN 1561 / ISO 185 (grey cast irons by tensile grade; many users treat EN-GJL-250 as the closest peer to Class 35).

Where Class 35 works best (and where it struggles)

Best-fit parts (non-pressure, structural-light):

• Machine bases, motor/gear housings, pump frames (non-pressure)
• Brake drums, pulleys, flywheels, counterweights
• Compressor feet, general brackets with low impact risk

Use with caution / upgrade if:

• Pressure-tight is needed → shift to ductile iron (ASTM A536); see Selecting Iron for Pressure Parts
• High impact/shock → consider ductile iron or cast steel
• High wear at low sliding speed → consider pearlitic/harder gray (EN-GJL-300 / ASTM Class 40) or surface treatments
• High corrosion → use coatings or material upgrade (see §6)

Casting route, ISO 8062 CT & machinability notes

Process choice by geometry & surface:

• Green Sand Casting
• Resin vs Green Sand (accuracy/finish)
• Shell Molding for Thin-Wall

Dimensional control: call ISO 8062 CT per size band; see ISO 8062 Casting Tolerances

Machining: Gray iron machines easily, but mind graphite dust and edge crumble:

• Tooling & coolant strategy: Machinability: Gray vs Ductile Iron
• Surface targets by process: Surface Finish by Process (Ra)

Corrosion & NVH: coatings and damping advantages

• Corrosion: Gray iron rusts in outdoor/splash service—solve with coating stacks (zinc-rich epoxy + epoxy mid + PU top for C3/C4), prep Ra 6–12 µm after blast; see Coatings vs Material Choices
• Damping (why gray wins): Flake graphite breaks up vibration energy—great for NVH-sensitive housings; see Why Gray Iron Still Wins

Alternatives: when to pick Class 40 / ductile / CGI / steel

(CGI reference: ISO 16112 classification.)

What to put on the drawing

Material call-out

Material: ASTM A48 Class 35 (gray iron). Acceptance by tensile on separately cast test bars per A48.
Optional: Brinell hardness (HBW) informational range 170–220, measured on casting.

Casting & dimensional

Process: [Green sand / Resin sand / Shell], supplier to propose for geometry.
Tolerances: ISO 8062 CT [grade] per size band; maintain machining stock on all critical faces.
Soundness: Supplier to design gating/risering to avoid shrinkage at T/Y/X junctions; provide plan at PPAP.

Coating (if outdoor/C3–C4)

• Prep: shot-blast to clean metal; blast profile Ra 6–12 µm (240–475 µin).
• Primer: zinc-rich epoxy 60–80 µm; Mid: high-build epoxy 80–120 µm; Top: aliphatic PU 40–60 µm.
• Mask: fits/threads/sealing faces (see view).

QA & documentation

Provide tensile test (Rm) per A48, metallographic graphite form/type snapshot on pilot, and CMM FAI on datum stack. If pressure-tested: shift to ductile iron or specify impregnation + leak test (method/limit) on drawing.

What YB Metal delivers

YBmetal Solution quotes with a material plan attached:

• Class 35 vs alternatives decision backed by section map, NVH and duty.
• Recommended process route (green/resin/shell), CT grade and machining stock.
• Coating stack (if outdoor) with DFT/cure & adhesion checks.
• Pilot evidence pack: tensile logs, hardness snapshots (if used), micrographs (graphite type), and CMM FAI.

Need a part-specific plan? Upload your drawing at /rfq—we’ll return recommendations and a quote.