What is the difference between ASTM A48 Class 30 and Class 40?

Class 40 has a higher minimum tensile strength (40 ksi vs. 30 ksi) and a higher typical Brinell hardness than Class 30. This translates into better load-carrying capacity and wear resistance but somewhat lower machinability and potentially higher casting cost. Class 40 also requires tighter process control to achieve consistent properties, especially in thicker sections.

What does the number in "Class 30" gray iron mean?

The number in the ASTM A48 class designation corresponds to the minimum tensile strength, in ksi, measured on a separately cast test bar. For Class 30, the specification requires at least 30 ksi (207 MPa) tensile strength. Actual castings may exhibit slightly different tensile values depending on section thickness and cooling rate.

Can gray iron Class 50 be welded?

Welding high-strength gray iron such as Class 50 is generally not recommended as a routine fabrication method due to the risk of cracking and property degradation. If welding is unavoidable, it should be treated as a repair operation with specialized procedures: preheat, controlled heat input, compatible filler, and slow post-cooling. For designs that require extensive welding, ductile iron or steel is typically a better choice.

Which ASTM A48 grade is most machinable?

Lower-strength grades such as Class 20 and Class 25 offer the best machinability due to their softer, more ferritic matrices. Class 30 still machines very well and is often considered the best compromise between machinability and strength. As you move to Classes 35–60, increasing hardness and pearlite content reduce machinability and increase tool wear.

Is higher class gray iron always better?

No. Higher classes provide higher strength and hardness, but they also increase cost, reduce machinability, and can make casting more demanding. The optimal grade is the lowest class that safely meets the mechanical, wear, and service requirements of the part. Over-specifying strength often adds cost without delivering proportional benefit.

What is the hardness range for Class 35 gray iron?

Class 35 gray iron typically falls in the 207–255 HB Brinell hardness range. The exact hardness will depend on section thickness, cooling rate, and foundry processing, but this range is representative for most Class 35 applications. ---

Cast Iron Weight & Cost Calculator

Estimate the weight and cost of a gray iron and ductile iron part: pick the alloy grade (density is filled automatically), enter the part volume, and get the weight in kg and lb. Plus a full ASTM ↔ EN ↔ GB ↔ JIS grade cross-reference below.

Alloy / grade Density (g/cm³) Part volume

Tip: get the exact volume from your 3D/CAD model (mass properties).

Material price (optional, per kg)

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Weight (lb)—

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Estimate only (material + grade). Final cast weight includes gating/risers & machining stock — send your drawing for an exact quote.

Cast Iron alloy grade chart — ASTM ↔ EN ↔ GB ↔ JIS

Density and minimum properties per ASTM specification. Cross-standard equivalents are by composition/class for reference — confirm exact interchange for critical parts.

Grade	Density (g/cm³)	Tensile (per ASTM)	Cross-standard equivalent	Typical use
Gray Iron — ASTM A48 Class 30	7.15	207 MPa (30 ksi) tensile	EN-GJL-200 / GB HT200	General machinery, housings
Gray Iron — ASTM A48 Class 40	7.2	276 MPa (40 ksi) tensile	EN-GJL-250 / GB HT250	Gears, machine bases, wear parts
Gray Iron — ASTM A48 Class 50	7.25	345 MPa (50 ksi) tensile	EN-GJL-350 / GB HT350	High-strength gray iron
Ductile Iron — ASTM A536 60-40-18	7.1	414/276 MPa, 18% elong	EN-GJS-400-18 / GB QT400-18	Pressure parts, high ductility
Ductile Iron — ASTM A536 65-45-12	7.1	448/310 MPa, 12% elong	EN-GJS-450-10 / GB QT450-10	Valves & pump bodies (general)
Ductile Iron — ASTM A536 80-55-06	7.1	552/379 MPa, 6% elong	EN-GJS-550-5 / GB QT550-5	Gears, crankshafts
Ductile Iron — ASTM A536 100-70-03	7.15	689/483 MPa, 3% elong	EN-GJS-700-2 / GB QT700-2	Heavy-duty, wear-resistant

Frequently Asked Questions

How do you calculate the weight of a casting?

Casting weight = part volume × material density. Get the volume from your 3D/CAD model, select the alloy for its density (cast iron grades shown above), multiply to get grams, then divide by 1000 for kilograms. Add gating, risers and machining allowance for the as-cast weight.

What is the GB and EN equivalent of ASTM A536 65-45-12 ductile iron?

ASTM A536 65-45-12 is broadly equivalent to EN-GJS-450-10 and GB/T 1348 QT450-10 (ductile/nodular iron, ~450 MPa tensile, ~10% elongation). Composition and minimum properties are comparable; always confirm the exact controlling standard for critical parts.