De. Bray et al., IDENTIFICATION OF ULTRASONIC ECHO SOURCE IN 4140 STEEL BARS USED FOR AN OIL-FIELD TOOL, Materials evaluation, 55(8), 1997, pp. 897-902
Ultrasonic reflections obtained in inspections of 4140 round steel bar
s being manufactured into oilfield tools were not associated by the ma
nufacturer with any easily identified anomaly within the material. One
of the bars was selected for more detailed analysis. A detailed secti
oning procedure was initiated in order to isolate the source of the re
flections. Using both angle beam and longitudinal beam probes, reflect
ions were confirmed in smaller pieces cut from the bar. An attempt to
correlate the reflections with cracks in the material was unsuccessful
. It became clear in the course of the investigation that the indicati
ons were originating within a region where the attenuation was higher
than expected. After the presence of significant cracking in the mater
ial was eliminated, extensive metallurgical investigations showed that
the region of the material which exhibited the high attenuation, and
was the source of the reflections, also possessed a higher than expect
ed density of nonmetallic inclusions in the form of manganese sulfide
stringers. Comparisons with other regions in the bar showed the densit
y of the inclusions to be higher in the region that was the source of
the reflections. While the correlation of the reflections and the incl
usions is only circumstantial, the association is felt to be quite str
ong.