Fatigue Crack Paths 2003

A

B

Figure 5. Position1, level-42µµm. Herethe visible crack fromA to B has disappeared. A nextension

of the crack is seen fromB and further right in the lower part of the right figure.

overlapping

A

B

Figure 6. Position 1, level–59 µµm. Thecracks are contained in the darkbandsobtained fromslight

over-etching dueto etch liquid soaked into the cracks. Novisible crack linkage betweenA andB is

seen. Theextension of the overlapping cracks is markedin the right figure.

The linking crack from A to B has disappeared at level -42μm. Twooverlapping cracks

have developed see Figure 5. Figure 6 shows level –59 μm.

Position 2

The crack walk in relation to Ni-rich austenite at position 2 reveals the same features

that have been found at position 1. One example from position 2 is shown in Figure 7

where micrographs from levels -20μm and -42μm are shown. Figure 7 also shows

typical interface crack walk between martensite and bainite.