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The purpose of this thesis is to discuss the fatigue
characteristics, microstructures and fracture modes of 35NCD16
steel under the control variable of strain and stress. The
material was quenched first, then it was tempered at 350℃,
550℃ and 750℃ to produce the different tempering maternsite
structure of precipitate carbide. In order to understand the
effect which are made by tempering temperature and
microstructure on these mechanical properties, a MTS810
dynamic material testing system is used to test tensile and
fatigue property. The strain amplitude of low cycle fatigue are
between 0.4% to 1.4%. The stress amplitudes of high cycle
fatigue are between 450 to 900 MPa. Tensile specimens are
deformed at the constant strain rate of 10-3S-1. After testing
, the fracture mode and microstructure are analyed with SEM and
TEM, the results are combined with that of macroscopic. The
experimental results indicate that the martensite structure and
precipitate carbide of 35NCD16 steel change as the tmpering
temperature. If the tensile behaviour is taken into
consideration, it is found that the more the tempering is low,
the more the strength hradness and work hardening cofficient
are high, but higher tempering produce brittle easily, and that
sample show the best combination of strength and toughness at
550℃.After tempering at three various temperature, low cycle
and high cyclefatigue life decrease as the increase of strain
and stress amplitude. Under the same strain amplitude, those
temperied at 750℃ have the best low cycle fatigue property.
Under the same stress amplitude, those tempered at 350℃ have
the best high cycle fatigue property. The fatigue striation
shows apparently on the fracture surface of samples under all
of the tested stress and strain amplitudes . The dislocation
cell structure ususally appears on the condition of bigger
strain and stress amplitude and higher work hardening
coefficient of the samples tempered at 350℃ and 550℃.
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