ASTM A536 Ductile Iron Grades: 60-40-18 to 120-90-02 Compared

Quick Answer

ASTM A536 grade numbers are the properties. A grade like 60-40-18 reads: 60 ksi minimum tensile strength, 40 ksi minimum yield, 18% minimum elongation. Lower-strength grades are ferritic, tough and machinable; higher-strength grades are pearlitic or alloyed, harder and more wear resistant. The most commonly cast grades are 60-40-18, 65-45-12, 80-55-06 and 100-70-03 — and picking between them is mostly a question of whether the part needs impact toughness or wear strength.

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Related Engineering References: Cross-reference ASTM A536 with EN 1563 (EN-GJS-400-15 / 450-10 / 500-7), DIN GGG40/GGG50, JIS FCD, and GB QT grades in our ASTM vs EN/DIN vs JIS vs GB Grade Cross-Reference Tool, or compare against flake-graphite iron in GG25 Cast Iron (EN-GJL-250 / ASTM A48 Class 35).

The Five Standard Grades

Grade	Tensile min	Yield min	Elongation min	Matrix / character
60-40-18	414 MPa	276 MPa	18%	Ferritic — maximum toughness, easy machining
65-45-12	448 MPa	310 MPa	12%	Mostly ferritic — general purpose
80-55-06	552 MPa	379 MPa	6%	Ferritic-pearlitic — strength with some ductility
100-70-03	689 MPa	483 MPa	3%	Pearlitic — wear resistance, gears and sprockets
120-90-02	827 MPa	621 MPa	2%	Quenched and tempered — highest strength

ASTM A536 Grade 65-45-12 vs 80-55-06 (GGG40 / EN-GJS-450-10 vs GGG50 / EN-GJS-500-7): Head-to-Head Comparison

In commercial B2B casting RFQs, over 75% of ductile iron drawings come down to a choice between Grade 65-45-12 and Grade 80-55-06 (or their European counterparts EN-GJS-450-10 / GGG40 and EN-GJS-500-7 / GGG50). The fundamental difference lies in the ferrite-to-pearlite ratio in the matrix around the graphite nodules:

Comparison Criterion	ASTM A536 Grade 65-45-12	ASTM A536 Grade 80-55-06
EN 1563 / DIN 1693 Equivalent	EN-GJS-450-10 (or EN-GJS-400-15 / GGG40)	EN-GJS-500-7 (DIN GGG50)
JIS G5502 / GB/T 1348 Equivalent	FCD450-10 / QT450-10	FCD500-7 / QT500-7
Minimum Tensile Strength	65,000 psi (448 MPa)	80,000 psi (552 MPa) — +23% higher
Minimum 0.2% Yield Strength	45,000 psi (310 MPa)	55,000 psi (379 MPa) — +22% higher
Minimum Elongation (in 50 mm)	12% (2× higher ductility)	6%
Typical Brinell Hardness	156 – 217 HB	187 – 255 HB
Predominant Matrix Structure	Mostly Ferritic + 15–30% Pearlite	Pearlitic-Ferritic (50–75% Pearlite, often Cu-alloyed)
CNC Machinability & Tool Life	Excellent — high cutting speeds, minimal insert wear	Moderate — abrasive pearlite requires coated carbide tooling
Best Component Applications	Automotive caliper brackets, steering knuckles, pressure valve bodies, shock-loaded mounts	Gearbox housings, differential carriers, agricultural hubs, wear rollers, hydraulic cylinders

What Makes Ductile Iron “Ductile”

A magnesium treatment just before pouring forces the graphite to form as spheres instead of the flakes found in gray iron. Flake graphite acts like thousands of internal notches — that is why gray iron snaps. Nodular graphite lets the metal stretch, giving cast iron elongation numbers once reserved for steel, while keeping iron’s castability, damping and lower cost. We covered the gray iron side of the family in our ductile iron sand casting guide.

How Buyers Should Choose a Grade

Shock and impact loads, or cold climates: 60-40-18. Its ferritic matrix keeps toughness at low temperatures — the reason it dominates wind-turbine hubs and municipal castings.
General machinery parts with no extreme requirement: 65-45-12. The default of the family.
Higher loads, moderate wear: 80-55-06 — brackets, housings, crankshafts and machine bases.
Sliding wear, gear teeth, sprockets: 100-70-03, often with induction-hardened surfaces.
Maximum strength in iron: 120-90-02, heat treated; at this point also compare price against cast steel.

Ductile Iron vs Cast Steel for the Same Part

Ductile iron pours at lower temperature, shrinks less, and machines faster — typically making it 20–40% cheaper than a cast steel equivalent. Cast steel keeps the advantage in weldability (iron welding is repair-only in practice), in impact toughness at the highest requirements, and in code-driven pressure applications that specify steel. For many housings, brackets and counterweights, 80-55-06 quietly replaces WCB steel at a better price.

Specification Checklist

Call out ASTM A536, grade — e.g., A536 65-45-12
State test-bar type if it matters to your code (separately cast Y-blocks are the default)
Add hardness window if machining lines are sensitive to it
Specify nodularity check (microstructure exam or ultrasonic velocity) for critical parts
For safety-critical or low-temperature parts, require Charpy impact tests — A536 itself does not mandate them

FAQ

What does 80-55-06 mean exactly?

80 ksi (552 MPa) minimum tensile, 55 ksi (379 MPa) minimum yield, 6% minimum elongation. The naming is the spec.

Is ductile iron weldable?

Only with difficulty — treat it as non-weldable at the design stage. If the assembly needs welding, use cast steel or design a bolted joint.

Which A536 grade is easiest to machine?

60-40-18 and 65-45-12. Machinability drops as the pearlite fraction rises through 80-55-06 to 100-70-03.

Can the same pattern produce different grades?

Yes. Grade is controlled by chemistry and cooling/heat treatment, not tooling — useful when one design serves several load cases.