Inconel
718 is an alloy of nickel and chromium
with excellent resistance to postweld cracking. This alloy has high
creep-rupture strength at high temperatures to about 1300°F
and it is age-hardenable. It is readily fabricated into complex parts and can
be cold rolled to achieve the temper properties. Two types of heat treatments
are utilized for Inconel 718. One is the solution anneal at 1700-1850°F
followed by rapid cooling in water and precipitation hardening at 1325°F
for 8 hours, furnace cool to 1150°F,
hold at 1150°F for a total
aging time of 18 hours followed by air cooling. Another is solution anneal at
1900-1950°F followed by rapid cooling in water
and precipitation hardening at 1400°F
for 10 hours, furnace cool to 1200°F,
hold at 1200°F for a
total aging time of 20 hours followed by air cooling.
·
Seal rings
·
Gas turbine
components
·
Nuclear hold down
spring and other components
·
Springs
Springs are manufactured for use in
environments with high or low temperatures and aggressive conditions in
applications including
·
Space and aircraft
industry
·
Oil and gas
exploitation
·
Chemical processes
·
Heating processes
·
Power production
·
Petrochemical industry
·
Marine environments
Inconel
718 is used to produce various types of
springs such as Disc springs, Compression springs, Torsion springs, Leaf
springs and Tension springs. Inconel 718 has high strength and high corrosion
resistance for use from -250°C
to 700°C. It is
used in applications including liquid fueled rockets components, sheet metal
parts for turbine engines & fasteners and rings. It needs ageing treatment
to develop best spring properties for spring applications.
Leaf springs and coil springs are
widely used in the motor vehicle industry. Premature fatigue failure is common
and the reasons for these failures are complex such as heat treatment,
intergranular cracking, grain boundary embrittlement, design deficiencies,
steel alloy chemistry and presence of Fe-S inclusions. This study provides an
overview of spring steel including its heat treatment, fatigue failure,
chemistry, residual stress and failure analysis of leaf and coil springs.
A spring is a component that can
store energy temporarily and permanently. There is a need of improving fatigue
strength of spring materials due to cyclic loading that accompanies the use of
springs. Spring efficiency is related to its ability to store energy per unit
weight and steel strengths of greater than 1379 MPa are required. Spring steels
were developed to meet ever-increasing demands for improved mechanical
properties with lower weight suspension materials to facilitate the larger
effort of developing automotive vehicles with lower weights and lower cost.
High strength spring steels with improved sag strength, fatigue strength and
improved quench embrittlement properties in addition to other thermophysical
and mechanical properties were developed in this work.
The two types of springs
were discussed such as helical coil springs and leaf springs. Coil springs are
commonly used in the automotive industry and are constructed from a length of
round steel wire that is formed into loops which allow for movement. Coil
springs are classified as compression and extension springs. The objective of
this study was to provide an overview of the most important factors involved in
either coil spring or leaf spring failures. As per the conclusion of this
study, surface defects including decarburization but the presence of seams,
laps and other defects lead to premature spring failure. High quality outer
layer of spring wire is achieved by a grinding or a draw-peeling process to
address these problems. Emphasis on spring design innovations is increased
which can be used with higher loads at reduced spring weight and size with
substantial improvements in fatigue strength.
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