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ASTM A638

ASTM A638 Specification

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Scope

ASTM A638 specification covers hot-finished or cold-finished precipitation hardening iron base superalloy bars, forgings, and forging stock for high-temperature service. The mechanical properties of these alloys are developed by suitable solution treating and precipitation hardening treatments.
Two grades of iron base alloy are covered. Selection will depend upon design, service conditions, mechanical properties, and elevated temperature characteristics.

Chemical Requirements

ElementCMnSiPSCrNiMoTiCuAlVB
Grade 660
(UNS S 66286)A		Ladle Analysis Range, %0.08 max2.00 max1.00 max0.040 max0.030 max13.50-16.0024.00-27.001.00-1.501.90-2.35…0.35 max0.10-0.500.0010-0.010
Check Analysis Over or Under0.01 over0.04 over0.05 over0.005 over0.005 over0.200.200.050.05…0.05 over0.030.0004 under 0.001 over
Grade 662
(UNS S 66220)A		Ladle Analysis Range, %0.08 max1.50 max1.00 max0.040 max0.030 max12.00-15.0024.00-28.002.50-3.501.55-2.000.50 max0.35 max…0.0010-0.010
Check Analysis Over or Under0.01 over0.040.050.005 over0.005 over0.150.200.100.050.03 over0.05 over…0.0004 under 0.001 over
  • A New designation established in accordance with Practice E527 and SAE J 1086.

Mechanical Requirements

GradeHeat treatmentBTensile strength, psi[MPa] min:Yield strength (0.2 % offset), psi[MPa] min:Elongation in 4D min, %Reduction of area min, %Brinell hardness
ASTM A638 Grade 660solution + precipitation harden130 000[895]85 000[585]1518248 min
ASTM A638 Grade 662 (bars)solution + precipitation harden130 000[895]85 000[585]1518248 min
ASTM A638 Grade 662 (forgings)Asolution + precipitation harden125 000[860]80 000[550]1518248 min

Stress-Rupture Requirements

GradeHeat TreatmentATest TemperatureApplied Stress During
Stress Rupture Testing		Minimum HoursBMinimum Elongation, %
°F[°C]psi[MPa]
ASTM A638 Grade 660solution + precipitation harden1200[650]65 000[450]233
ASTM A638 Grade 662solution + precipitation harden1200[650]60 000[415]153
  • A The elongation of tensile specimens machined tangentially from near the center of large disk forgings over 50 in.2 [320 cm2] in cross section may be as low as 10 %.The reduction of area may be as low as 12 %.
    B Refer to Table 3 of heat treatment.

Heat Treatment

GradeSolution TreatmentPrecipitation Hardening TreatmentA
ASTM A638 Grade 660Type 1 1650 ± 25°F [900 ± 15°C], hold 2 hr, oil or water quench1300 to 1400°F [705 to 760°C], hold 16 h, air cool or furnace cool
ASTM A638 Grade 660Type 2 1800 ± 25°F [980 ± 15°C], hold 1 h, oil or water quench1300 to 1400°F [705 to 760°C], hold 16 h, air cool or furnace cool
ASTM A638 Grade 6621750 to 1900°F [955 to 1040°C] hold 1 h, min, oil or water quench1250 to 1400°F [675 to 760°C], hold 5 h, min, slow cooling in 5 h,
min to 1200 ± 15°F [650 ± 10°C], hold 20 h, min, air cool or furnace cool

Certifications

  • EN 10204 3.1
  • EN 10204 3.2
  • PED 2014/68/EC
  • MERKBLATT AD 2000 W2/W7/W10
  • API 20 E BSL 1/ BSL 2
  • NACE MR 0175
  • NACE MR 0103