This technique
is not widely known, but it allows detection of residual stress and the measurement
of austenite remaining in metal samples.
Residual stress is due to thermal treatment, mechanical processes, welding and
surface treatment that the pieces undergo during the manufacturing process.
This type of stress permanently influences the piece's resistance, especially
under strain, and often the cause
of breaks that have no metallurgical justification. One example is given by
the alterations in the surface tension induced by heat in grinding, easily detected
with X Ray diffraction or with the Barkhausen
Noise method.
Even a small percentage of residual austenite (5%) can cause deformations that
make the piece unusable. An example can be given with ball bearing tracks and
injector pins for diesel motors. Detection of their presence can optimise thermal
treatment.
2 Effe Engineering uses special equipment to measure residual stress and residual
austenite, providing a thorough non-destructive analysis of samples of any dimension,
so detection can be made directly.
Eng. Marconi, for example, has analysed the stress caused by casting and mechanical
operations on the Stîrebealt Bridge in Denmark.
Main
application of x-ray are:
-
definition
of the quantity of residual austenite on bearings and parts
of diesel motor injectorsl
-
detection
of residual stress on sprocket wheels
-
detection
of residual stress on car motor parts (cam axles, connecting
rods, engine shafts, equalisers)
-
detection
of residual stress induced by deep drawing (household appliances,
structural parts)
-
detection
of existing operational stress on gas conducts
-
detection
of operational stress on large tensioned structures
-
measurement
of efficiency of shot-peening and rolling of components subjected
to stress
-
detection
of residual stress in castings (cast iron parts of tool machines
and aluminium automotive components)
-
detection
of stress induced by (laser and electron) welding
-
search
for a correlation between residual stress and stress resistance
of aluminium alloy car rims
-
optimisation
of working parameters for swarf removal to improve the stress
resistance of mechanical components
-
detection
of residual stress on helicoidal and leaf springs
-
search
for critical zones after applying work loads (arms and aeronautics)
A particular application of XRD technology permits to quantitatively analyze the presence of different crystalline phases of the materials; this is possible by analysing a large spectrum. In some cases it's very important to know the real phases because they could have a big influence on the functional characteristics of the material. It also possible to check the composition of the powders for the HVOF plant.
