ABSTRACT THE EFFECT OF CRYOGENIC TREATMENT ON THE ...

ABSTRACT

THE EFFECT OF CRYOGENIC TREATMENT ON THE FATIGUE LIFE OF CHROME
SILICON STEEL COMPRESSION SPRINGS


Debra Lynn Smith, B.S., M.S.

Marquette University, 2011


The purpose of this dissertation is to explore the effect of cryogenic treatment on
the fat
igue life of compression springs. Product manufacturers are constantly searching
for ways to make their products last longer. This dissertation addresses three
questions: (1) What is the effect of cryogenic treatment on the fatigue life of chrome
silicon

steel compression springs? That is, does the life increase, decrease, or remain
the same? (2) What is the effect of cryogenic treatment on the Stress Relaxation
(Percent Load Loss) of chrome silicon steel compression springs? (3) What are the
possible
changes in the material that cause these effects?

The following tests were carried out; wire tensile test, hardness test, chemical
analysis, residual stress, retained austenite, lattice dimensions of atomic spacing, force
vs. deflection, stress relaxatio
n (percent load loss), fatigue, microstructures, and eta
carbides.

This research produced a number of key findings: (1) The cryogenically treated
springs had a longer cycle life and a higher endurance limit than the untreated springs.
(2) The stress rel
axation (percent load loss) of the cryogenically treated springs was
similar to the untreated springs. (3) The cryogenically treated springs had a higher
compressive residual stress at the surface than the untreated springs. (4) The
cryogenically treated

springs were slightly harder than the untreated springs and had a
narrower range of values.

The conclusions of this research are that the cryogenic treatment of chrome
silicon steel compression springs led to an increase in compressive residual stress o
n
the wire surface, which in turn led to an increase in fatigue life and a higher endurance
limit. A recommended future study would be to compare cryogenically treated springs
to shot peened springs.