ASTM A638 grade 660 is the canonical industrial spec for A286 (UNS S66286) forgings, covers the alloy in forged condition for high-temperature pressure-bearing service. Two types: Type 1 (sol 1650 °F + aged, higher room-temperature tensile) and Type 2 (sol 1800 °F + aged, higher stress-rupture strength). The spec is referenced in ASME Section III Subsection NB for nuclear pressure-vessel components, and in petrochemical / refinery forgings for high-temperature service. Distinguished from ASTM A453 grade 660 by scope: A453 is bolting; A638 is forgings. See parent A286 AMS specifications hub, related A286 forged bar, A286 forgings, flanges.
Spec Scope & Coverage
ASTM A638 grade 660 covers A286 forgings for high-temperature pressure-bearing service. Material is VIM-VAR melted ingot, hot-forged in open-die or closed-die operation at 1095-1150 °C, then heat-treated per Type 1 or Type 2. Type 1: sol 1650 °F + aged 1325 °F × 16 h, hardness 29-32 HRC, higher room-temperature yield. Type 2: sol 1800 °F + aged 1325 °F × 16 h, hardness 24-30 HRC, higher stress-rupture strength at 1100-1300 °F. Used for nuclear pressure-vessel internals, petrochemical forgings, and gas-turbine casing forgings.
Higher RT tensile + yield. Lower stress-rupture vs Type 2.
Type 2
Sol 1800 °F + aged 1325 °F × 16 h
≥ 895
≥ 585
24-30
Higher stress-rupture strength at 1100-1300 °F.
When to Specify ASTM A638 Grade 660, A286 Forgings
Nuclear pressure-vessel forgings: ASTM A638 grade 660 Type 1, accepted in ASME Section III Subsection NB. Used for control-rod-drive housings, primary-coolant-pump casings.
Aerospace forgings (alternate): AMS 5731 / 5732 typically cited for aerospace; ASTM A638 acceptable as alternate.
Petrochemical / refinery forgings: ASTM A638 grade 660 Type 2 for hot-section refinery forgings (1100-1300 °F service). Higher stress-rupture strength.
Gas-turbine casing forgings: Type 1 or Type 2, Type 1 for casing-split bolted joints; Type 2 for hot-section structural forgings.
Forged flange manufacture:A286 flanges per ASME B16.5 are typically forged from ASTM A638 grade 660 Type 1 stock.
ASTM industrial spec for A286 (UNS S66286) forgings for high-temperature pressure-bearing service. Type 1: sol 1650 °F + aged (higher RT tensile). Type 2: sol 1800 °F + aged (higher stress-rupture strength). Nuclear and petrochemical pressure-vessel forgings.
Type 1 vs Type 2, which to specify?
Type 1: higher room-temperature yield (655 MPa vs 585 MPa Type 2). Type 2: higher stress-rupture strength at 1100-1300 °F. Choose Type 1 for room-temperature high-load service; Type 2 for hot-section stress-rupture-critical.
Is ASTM A638 grade 660 the same as ASTM A453 grade 660?
Different scope: A638 is forgings; A453 is bolting. Chemistry identical (UNS S66286). Heat-treatment requirements similar but the spec applies to different forms, pressure-bearing forgings vs bolted-joint fasteners.
Is ASTM A638 grade 660 ASME III nuclear-acceptable?
Yes, Type 1 is accepted in ASME Section III Subsection NB for primary-pressure-bearing nuclear forgings. Used for control-rod-drive housings, primary-coolant-pump casings, pressuriser bolted-flange forgings.
What forging route is used for ASTM A638?
Open-die forging from VIM-VAR ingot at 1095-1150 °C, provides superior grain-flow continuity and isotropic mechanical properties vs hot-rolled. Closed-die for higher-volume standard sizes.
Can ASTM A638 grade 660 forgings be NACE MR0175 compliant?
Yes, when supplied with hardness ≤ HRC 35 per NACE MR0175 / ISO 15156-3. Specify on PO; each heat receives Vickers traverse before release.
What's the lead time on ASTM A638 forgings?
Standard sizes 75-150 mm: 12-16 weeks from heat release. Larger sizes 150-300 mm: 16-24 weeks. ASME III certified with EN 10204 3.2 third-party witness: 16-24 weeks. Custom sizes > 300 mm: 20-32 weeks.
Is ASTM A638 grade 660 ultrasonically inspected?
Yes, 100 % UT per ASTM A388 with Class 1 acceptance for nuclear and aerospace lots. Internal flaw detection critical for forging-grade applications. Class 2 acceptance for industrial.
Is ASTM A638 magnetic?
No. Magnetic permeability < 1.005 verified per ASTM A342. Compatible with non-magnetic pressure-vessel and aerospace forging applications.
Mechanical Properties per This Spec
Type
Tensile (MPa)
Yield (MPa)
Hardness HRC
Type 1 (Sol 1650 °F + aged)
≥ 895
≥ 655
29-32
Type 2 (Sol 1800 °F + aged)
≥ 895
≥ 585
24-30
A286 Products Manufactured per This Spec
TorqBolt manufactures the following A286 products to this specification:
A286 forged bar, ASTM A638 grade 660 Type 1, sol-treated and aged, ⌀ 150 mm × 3000 mm length, +5/-0 mm OD tolerance, ASTM A388 ultrasonic Class 1, EN 10204 3.2.
