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Fig. 6. Optical micrograph of the En32 steel immediately adjacent to the weld showing cracks that originated after the
nitriding (etchant: 2% Nital).

Fig. 7. SEM fractograph of the fracture surface as received. The intergranular nature of the fracture and secondary cracks
can be seen.

4. DISCUSSION

The absence of evidence of fatigue and the short operational life of the actuators indicated that
the components entered service flawed or contained such high residual stresses in the weld that
operational loading resulted in cracking and fracture.
Table 2 shows the nickel and chromium equivalents of the various steels used. The exact extent
of dilution of the weld metal was not determined, but the combination of the parent metals and
E3 12 filler metal places the resultant weld metal composition into the A + F or A + M + F zone on
the Schaeffler diagram. Since the welds were very wide and a large degree of dilution had taken