Non-contact ultrasonic measurements have been made on ferritic and aus
tenitic steel specimens as a function of temperature from ambient to 1
200-degrees-C, using a pulsed laser to generate and a reference beam l
aser interferometer to receive the ultrasound. The. generation efficie
ncy is found to remain surprisingly constant in both thermoelastic and
ablation regimes over a wide temperature range. The sensitivity of th
e laser interferometer is also found to be temperature independent to
a first approximation. However, it is typically reduced by 3-6 dB by c
onvection currents above approximately 900-degrees-C. Both the compres
sion and shear velocities decrease with rising temperature. The former
is measured with a precision of 1 in 10(3), the latter rather less ac
curately with the present configuration. Compression wave attenuation
increases steadily below 600-degrees-C in both materials. There is a p
eak in attenuation in ferritic steel between 600 and 750-degrees-C, wh
ich is absent in austenitic steel. It coincides with a steeper decreas
e in ultrasonic velocity and is believed to be due to the martensitic
structural phase transformation. The attenuation rose more rapidly in
both materials as 1000-degrees-C was approached. The material attenuat
ion varied with heat treatment, a value in the range 1-1.5 dB cm-1 bei
ng recorded at 1000-degrees-C. Complicated effects were observed durin
g heat treatments at 1000-degrees-C and above. Both attenuation and fo
rward scattering data were consistent with some annealing out of sub-s
tructure, in addition to austenitic grain growth. Finally, there was e
vidence of lattice softening at the highest temperatures investigated.
The data suggest that thicknesses of steel in the range 100-250 mm sh
ould be inspectable with a scaled-up system, depending upon various fa
ctors such as the presence of oxide scale, provided high power lasers
are employed for generation and reception and an optimum bandwidth is
chosen.