ASTM A1014/A1014M Bolting Specification
ASTM A1014 / A1014M covers Precipitation Hardening Bolting (UNS
N07718)
for High Temperature Service. AS 7467 Bolts And Screws is also reffered for Nickel
Alloy, UNS N07718
Tensile Strength 185 KSI [1275 MPa] Stress Rupture Rated Procurement Specification.
Bolting material
alloy shall be multiple-melted using consumable electrode practice in the remelt
cycle or shall be
induction melted under vacuum. If consumable electrode re-melting is not performed
in vacuum,
electrodes produced by vacuum induction melting shall be used. Fully heat treated
bolting material
shall meet the dimensional requirements of Specification B637
for UNS N07718. Headed
bolting
components such as bolts, studs, or screws with a body length three times the
diameter of the
component or longer shall be subjected to full size tensile test and shall conform
to the tensile
strength as per this specification. The microstructure of the bolting material shall
be free of
freckles, white spots, and Laves phases. Threads of bolting components may show
evidence of cold
working as a result of rolling. The average grain size shall be determined in
accordance with Test
Methods E112 and found to be ASTM No. 5 or finer. Up to 20 % of the structure may
have a grain size
as large as a No. 3 due to the presence of non-crystallized grains. Bolting
components produced from
forgings shall exhibit continuous flow lines in the threads and in any shank to head
or fillet
and/or bearing surface areas.
Heat treatment for high-temperature fasteners must be performed
under a suitable protective atmosphere, such as a vacuum or inert gas environment, to
maintain surface integrity. This requirement prevents the formation of heavy oxidation
scales and avoids the depletion of reactive elements like chromium, aluminum, and
titanium at the fastener's surface. By eliminating "denuded zones," S1 ensures the
material retains its full precipitation-hardening potential and corrosion resistance
across the entire cross-section.
Supplementary requirement S2 mandates advanced precision
cleaning of all bolting materials to remove industrial lubricants, oils, and metallic
residues prior to heat treatment. In nickel-based superalloys like Inconel 718, surface
contaminants can cause liquid metal embrittlement or severe intergranular attack when
exposed to solution treatment temperatures as high as 1850°F(1010°C).
Implementing S2 is essential for ensuring long-term structural
reliability and preventing premature stress-rupture failure in aggressive service
environments.
S3 specifies the cold-working of the underhead fillet radius to
significantly enhance the fatigue life of bolts and screws. By applying high pressure
to the radius, this process induces beneficial residual compressive stresses that
effectively delay the initiation and propagation of fatigue cracks. Fillet rolling is a
critical quality enhancement for fasteners subjected to high-frequency vibration,
cyclic thermal loading, and mechanical stress concentrations in aerospace and turbine
systems.
Under supplementary requirement S4, fastener heads must be
formed using a forging process rather than being machined from bar stock. Forging
ensures a continuous internal grain flow that follows the geometric contour of the
head-to-shank transition, providing superior shear strength and resistance to
"head-popping" failures. This metallurgical reinforcement is vital for safety-critical
components used in high-vibration and high-impact industrial applications.
S5 provides stringent protocols for the permanent marking and
traceability of bolting components throughout the supply chain. Fasteners must be
marked with manufacturer identification and grade symbols on the head or stud ends to
allow for rapid verification of material and heat lot data. Standardized marking is a
fundamental safety measure that ensures high-strength superalloys are correctly
identified and never interchanged with lower-grade materials in critical
high-temperature service.
Supplementary requirement S6 governs the parameters for thread
rolling, requiring that threads be cold-formed specifically before the final
precipitation heat treatment. Cold rolling displaces material to create a high-strength
thread profile with improved grain density and superior surface finishes in the thread
roots. By performing rolling prior to aging, the fastener benefits from the full
strength development of the subsequent precipitation cycle while maintaining the
structural advantages of the cold-formed threads.
