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- New Alloy for Marine Bolts
A new alloy
developed for fasteners in critical marine applications has been
announced by the SPS Technologies Aerospace Fasteners Group, Jenkintown,
Pa. SPS Technologies supplies high-performance fasteners for commercial
and military aircraft, space vehicles, jet engines, racing cars,
marine use and other applications requiring reliability and consistent
quality. Working with raw material suppliers, the company has been
able to modify existing alloys for the manufacture of high performance
fasteners to meet ever-changing requirements.
marine fastener profile presented to SPS engineers was for a bolt
exhibiting 150 ksi yield strength, extremely high fracture toughness,
plus resistance to fatigue, corrosion and hydrogen embrittlement.
Bolt sizes from 3/8-in. up to 3-in. were required.
History in Brief
Over the years, SPS Technologies has developed a number of proprietary
superalloys to satisfy increasing demands for high technology fasteners.
Following are descriptions of two materials in the SPS® MULTIPHASE®
superalloy family. This family of superalloys was likely to help
engineers meet the marine application requirements.
- MP35N® superalloy: MP35N alloy was the first fastener
superalloy developed by SPS. It provides a combination of high
strength and superior corrosion resistance, with a high temperature
capability of 750°F as well as excellent cryogenic properties.
In fact, it was the first high strength CRES bolt alloy (AMS5844),
exhibiting 260 ksi ultimate tensile strength and 145 ksi shear
Due to its property matrix, MP35N alloy helped SPS establish a
fastener niche in the U.S. Space program. MP35N alloy has been
successfully applied outside of the aerospace industry as well.
For instance, it is the highest strength material approved for
structural components in aggressive, sour well environments.
- MP159® superalloy: In response to the more severe
operating demands of turbine engine manufacturers, the company
developed MP159 alloy, which boosted the high-end operating temperature
capability to 1100°F, while maintaining the high strength
and corrosion resistance advantages of MP35N alloy.
The ambient temperature fatigue properties of MP159 alloy also
led to its application in high performance racing car connecting-rod
bolts. Tension-, shear-, and fatigue-rated bolts up to 1.50 inch
diameter are manufactured from MP159 alloy, as attachment bolts
for airplane wings, and in landing gears.
SPS identified MP159 alloy as the likely candidate to help meet
the challenge of the new marine application. However, changes in
the metallurgy were required to achieve the performance specifications.
This new superalloy, designated MP98T alloy, would have the
same chemistry as MP159 (AMS 5842) alloy with different cold work
and age hardening parameters. Fastener tensile strength would be
reduced from its aerospace level of 260 ksi to meet the high fracture
toughness requirement. The new alloy would exhibit a combination
of strength, toughness and corrosion resistance not previously available
in a fastener material.
principle strengthening mechanism is the solid-state phase transformation
of part of the matrix from a face-centered cubic (fcc) crystal structure
to a hexagonal close-packed (hcp) structure by cold working. The
reason for this transformation is the high cobalt content in the
alloy, and it has been termed "the multiphase reaction."
of two distinct crystal structures creates a barrier to the motion
of dislocations and leads to pronounced strengthening while retaining
ductility. Subsequent age hardening acts to stabilize these two
phases through the process of solute partitioning, which contributes
to further strengthening.
strengthening mechanism involves the addition of elements to the
chemical composition to cause the precipitation of the gamma prime
(y') phase during age hardening. The gamma prime phase (Ni3Ti,
Al), which forms in many conventional nickel-base superalloys, promotes
cycle took SPS engineers less than a year. The anticipated size
range for MP98T bolts is 3/8-in. up to 3-1/2-in., with larger sizes
possible. A new 1-3/4-in. MP98T bolt was able to replace a 4-1/4-in.
bolt in one marine application because of its higher strength and
The new fastener alloy may also have selected applications in the
aerospace industry because of its incredibly high fracture toughness.
Interestingly, there are both engine and airframe applications that
would benefit from a fastener alloy with this strength level and
toughness. Finally, its resistance to hydrogen embrittlement in
high-pressure hydrogen environments make it attractive for rocket
motors using liquid hydrogen for fuel.
For more information:
Steven Buzolits, Manager-Product Engineering SPS Technologies, 301
Highland Avenue, Jenkintown, PA 19046-2692 phone (215) 572-3565
fax (215) 572-3133; E-mail: firstname.lastname@example.org;
web site: www.spstech.com/aero.
Table 1 - Raw
material minimum tensile properties
Table 2 - MP159 & MP98T Chemistry
Table 3 - Typical properties of MP 159 and MP98T
MP159, and MULTIPHASE are registered trademarks of SPS Technologies,