ASTM A536-84(2019)e1 covers both Grade 60-40-18 and Grade 80-55-06, with castings required to meet the named tensile, yield, and elongation values written into the grade code itself [S1]. In round numbers: 60-40-18 = 60,000 psi UTS / 40,000 psi YS / 18% min elongation, and 80-55-06 = 80,000 psi UTS / 55,000 psi YS / 6% min elongation [S1][S2].
Those three digits are the spec: the first is minimum tensile strength, the second is minimum yield strength, and the third is minimum elongation in 50 mm, so the difference is not a chemistry tweak but a 33% jump in tensile and a tripling-to-cutting of ductility [S1][S4]. Choosing between them is therefore a question of whether your part needs to deform or carry load, not which one has more "strength" in a marketing sense.
Mechanical Properties Side by Side
60-40-18 has a UTS of 60,000 psi (414 MPa), yield of 40,000 psi (276 MPa), and 18% minimum elongation, and its as-cast density is 0.256 lb/in³ (7.1 g/cm³) with a melting point around 2,100 °F [S2]. 80-55-06 raises UTS to 80,000 psi and yield to 55,000 psi but drops elongation to 6%, with fatigue strength at both grades landing around 40,000 psi in continuous-cast bar stock [S3][S9].
Compression behaviour diverges sharply: 60-40-18 carries about 429 ksi (2,960 MPa) compressive strength, which is what makes it attractive for housings and frames that see crushing rather than tensile loads [S2]. Thermal expansion for the ferritic 60-40-18 matrix is 6.4 × 10⁻⁶ /°F (11.5 × 10⁻⁶ /°C) between 68 and 212 °F, and thermal conductivity is 250 Btu/hr·ft·°F (36 W/m·K), falling about 20% as pearlite content rises [S2].
Microstructure and How the Properties Are Reached
60-40-18 is a mostly ferritic nodular iron; minimizing pearlitising elements (Mn, Cu, Ni) and using clean steel scrap plus quality pig iron lets foundries hit it as-cast, while a full ferritising anneal is the alternative route when the pour trends toward pearlite [S2][S5]. Full ferritising anneal also keeps mechanical properties essentially unchanged through subsequent stress relief, so 60-40-18 castings are dimensionally stable after heat treat [S5].
80-55-06 sits in a ferrite-plus-pearlite matrix: UTS comes from a meaningful pearlite fraction, and the grade is typically produced as-cast or by normalising, with quenching-and-tempering reserved for higher-strength grades like 100-70-03 [S4][S8]. The same graphite-nodule metallurgy underlies both grades, so castability, machinability, and corrosion resistance of ductile iron carry over from the 60-40-18 family to the 80-55-06 family [S7].
Chemistry Envelope (Typical, Not Specified)
ASTM A536 does not mandate chemistry, so the numbers below are foundry targets used to land 60-40-18: C 3.4-3.8%, Mn max 0.3%, Si 2.00-2.50%, Cr max 0.08%, Ni max 0.5%, Cu max 0.2%, Mg min 0.025% max 0.055% [S2]. The same Mg window applies to 80-55-06, with Mn and Cu pushed up to grow pearlite and the lower Si end used to avoid over-ferritising [S9].
Because Mg is the noduliser that turns flake graphite into spheroids, holding Mg in the 0.025-0.055% band is what keeps the graphite morphology correct for both grades; the difference between 60-40-18 and 80-55-06 lives in the matrix around those nodules, not in the nodules themselves [S4][S9].
Impact and Low-Temperature Behaviour
ASTM A536 itself does not call out impact values for 60-40-18; ISO 1083 is the spec engineers switch to for that, with a benchmark of 12 J at -20 °C achievable when pearlite is held below 15% of the microstructure [S2]. Going after that 12 J number usually means specifying a fully ferritic 60-40-18 rather than an 80-55-06, because the higher pearlite fraction in 80-55-06 eats into Charpy transition-temperature margin [S2][S4].
For Sour Service (NACE MR0175 / ISO 15156), annealed 60-40-18 is the NACE-compliant choice, with Dura-Bar's 60-40-18 stock also meeting ASTM A395 in addition to A536 [S6]. In a side-by-side decision, 60-40-18 is the impact and sour-service grade, 80-55-06 is the higher-load grade with less documented low-temperature margin.
Decision Matrix: When to Pick Each
Use this short comparison to anchor the choice on engineering criteria rather than habit. 60-40-18 wins on elongation (18% vs 6%), impact (12 J at -20 °C achievable, NACE-compliant when annealed), compressive strength (429 ksi / 2,960 MPa), and weldability/repairability; 80-55-06 wins on tensile (+33%), yield (+37.5%), wear resistance under sliding contact, and elevated-temperature dimensional stability [S2][S3][S4][S6].
For pumping and valve body castings in mild service, 60-40-18 is the default and matches the matrix most water and process flow meter bodies are designed around [S2]. For gearbox housings, brake components, and high-load hubs where stiffness and wear dominate, 80-55-06 is the right call, especially on continuous-cast bar where it also offers good free-machining behaviour from the high nodule count [S3][S4].
Applications Pull-Through
60-40-18 shows up across industrial brakes (actuator housings, frames, toggle levers), winches, wind energy hubs, nacelles and gearboxes, automotive brake components, pump side liners, frames and valve bodies, oil-and-gas motor housings and compressor bodies, lumber sheaves, transportation pulleys, and mining housings [S2]. 80-55-06 sits in the higher-load subset of the same family: brakes, pumps, gearboxes, wind energy parts, and transmission components where the 6% elongation is still adequate for the geometry [S4][S9].
Where the two converge: a single plant often stocks both, with 60-40-18 reserved for impact- or compliance-sensitive parts and 80-55-06 specified on the drawing whenever a part's stress report needs the extra 20,000 psi of UTS and 15,000 psi of yield. A useful sanity check is to map the part's dominant failure mode to one number: tensile overload pushes you to 80-55-06, brittle or impact failure pushes you back to 60-40-18.
Heat Treatment, Cost, and Lead-Time Notes
60-40-18 reached by full anneal costs more per pound than the same chemistry poured to an 80-55-06 spec, because the anneal furnace cycle is a real shop-hour adder; this is one reason continuous-cast bar producers list 60-40-18 as a non-stock grade while 80-55-06 stays in stock [S3]. On the casting side, foundries with in-house heat treat can hit 60-40-18 by anneal when chemistry control alone does not deliver sub-15% pearlite, which is the standard route to the 12 J impact number [S2][S3].
For sourcing, the practical rule is: if the drawing allows either 65-45-12, 60-40-18, or 80-55-06, the lowest-cost ductile iron is usually 65-45-12 or 80-55-06 because they can be poured as-cast, while 60-40-18 only gets cheap when the foundry can hit ferrite from chemistry alone without a separate anneal step [S2][S3]. Specifications written for foundries that don't run a separate anneal furnace should therefore consider accepting 65-45-12, which per ASTM A536 has 65,000 psi tensile strength, 45,000 psi yield strength, and 12 elongation [S3].
Spec-Writing Checklist and Common Pitfalls
Write the grade on the drawing as "ASTM A536 Grade 60-40-18" or "ASTM A536 Grade 80-55-06", not by chemistry; A536 deliberately does not fix chemistry, so a chemistry callout only invites disputes with the foundry [S1][S2]. If the part needs ISO 1083 impact, add "ISO 1083, 12 J min at -20 °C" as a separate line, and call out the sub-15% pearlite limit if the foundry is new to the part [S2].
For sour service, write "annealed, NACE MR0175 / ISO 15156" rather than just naming the grade, because the anneal state is what makes 60-40-18 compliant rather than the grade code itself [S6]. Finally, do not request 80-55-06 where the part's true requirement is impact or low-temperature ductility, because 6% elongation is the structural warning sign, not just a number on a certificate [S4].
Watch also for foundry disclosures on continuous-cast 60-40-18 availability, which is currently non-stock at the major US bar producers and shapes lead-time more than the grade choice itself [S3].
The underlying component specifications are covered under cast iron.
This topic is covered further in End-to-end automated assembly for smart devices: the seven-stage line architecture.