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 Grade Equivalent Chart & Converter

Match gray and ductile iron grades across ASTM, EN, GB and JIS standards. Pick a grade to see its equivalents and key properties.

Select a grade

⚠️ Equivalents are matched by grade class / nominal properties for reference. Exact chemistry, heat treatment and part-critical interchange (incl. GB↔ASTM↔EN) must be confirmed against the controlling spec — our engineering team verifies interchange for your part.

Full cross-standard equivalence matrix

ASTM	EN / ISO	GB	JIS	DIN (old)	Tensile	Elong.	Density	Typical use
Gray — A48 Class 30	EN-GJL-200	HT200	FC200	GG20	200 MPa	<1%	7.15	General machinery, housings
Gray — A48 Class 35	EN-GJL-250	HT250	FC250	GG25	250 MPa	<1%	7.2	Gears, machine bases
Gray — A48 Class 40	EN-GJL-300	HT300	FC300	GG30	300 MPa	<1%	7.2	High-load wear parts
Gray — A48 Class 50	EN-GJL-350	HT350	FC350	GG35	350 MPa	<1%	7.25	High-strength gray iron
Ductile — A536 60-40-18	EN-GJS-400-18	QT400-18	FCD400	GGG40	400/250 MPa	18%	7.1	Pressure parts, high ductility
Ductile — A536 65-45-12	EN-GJS-450-10	QT450-10	FCD450	GGG45	450/310 MPa	12%	7.1	Valves & pump bodies
Ductile — A536 80-55-06	EN-GJS-550-5	QT550-5	FCD550	GGG55	550/380 MPa	6%	7.1	Gears, crankshafts
Ductile — A536 100-70-03	EN-GJS-700-2	QT700-2	FCD700	GGG70	700/460 MPa	3%	7.15	Heavy-duty, wear-resistant

Properties per ASTM specification minimums. Density in g/cm³.

Common questions

What is the difference between gray iron and ductile iron?

Gray iron (ASTM A48) has flake graphite: it is hard, brittle and has excellent vibration damping, machinability and thermal conductivity, best under compressive loads. Ductile iron (ASTM A536) has spheroidal (nodular) graphite, giving far higher tensile strength and elongation (it is ductile and impact-tolerant) — used for pressure and dynamic loads such as valve and pump bodies.

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

ASTM A536 65-45-12 is broadly equivalent to GB QT450-10 and EN-GJS-450-10 (ductile/nodular iron, ~450 MPa tensile, ~10–12% elongation), and JIS FCD450. Confirm the exact controlling standard for critical or pressure parts.

What is the difference between ASTM A536 and A395?

A536 is the general ductile iron specification covering several grades (60-40-18 up to 120-90-02). A395 specifies a single ferritic ductile iron grade (60-40-18) with a controlled microstructure intended for pressure-retaining and elevated-temperature service.

What does ASTM A48 Class 40 mean?

ASTM A48 Class 40 is gray cast iron with a minimum tensile strength of 40,000 psi (about 276 MPa). In ASTM A48 the class number equals the minimum tensile strength in ksi.

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