As noted earlier, only the outer 25 mm or so in
the near surface of the treated component is
affected by the process. It is interesting to see
the effect that this surface treatment has on tensile
properties. Figure 8 shows stress-strain curves for
treated and nontreated 316 stainless steel specimens,
using a standard flat dog-bone specimen
with a cross section of 0.635 mm (0.025 in.). For
the low-temperature carburized specimen, there
is a small increase in yield stress—from 650 to
670 MPa (94 to 97 ksi)—and a more noticeable
increase in ultimate tensile stress, from 690 to
750 MPa (100 to 109 ksi). A minor decrease in
strain-to-failure, from 45 to 40%, also is evidenced,
indicating the treated material is still ductile.
In combination with the increased surface
hardness and compressive surface stresses, these
minor changes in tensile properties have profound
effects on performance characteristics, in particular
fatigue, wear, and erosion.