Rc. Reed et al., LASER-PULSE HEAT-TREATMENT - APPLICATION TO REAUSTENITIZATION FROM FERRITE CEMENTITE MIXTURES/, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 232(1-2), 1997, pp. 140-149
A technique capable of monitoring microstructural changes under condit
ions of rapid heating and cooling is presented. It involves the applic
ation of a high-powered 1 kW CO2 laser beam to thin-foil specimens. Th
e thermal cycle at the reverse face of the specimens is recorded durin
g irradiation using thermocouples and a purpose-built data acquisition
system. The method has been used to study the formation of austenite
from a mixture of ferrite and cementite in a high purity Fe-0.4C (wt%)
steel, in the heavily spheroidised condition. For foils of 3 mm diame
ter, it is found that the heating rates observed are between 10(4) and
10(5) degrees C/s for laser beam radii between 2.9 and 0.9 mm. Pulse
lengths necessary to reach austenitisation temperatures are then betwe
en 100 and 10 ms. These numerical results are consistent with the pred
ictions of a very simple numerical model which assumes one-dimensional
heat conduction. Consistent with the literature, it is found that nuc
leation of austenite occurs preferentially at ferrite/cementite interf
aces; however, the incubation period appears to be undetectable, even
on the timescale of the present experiment. (C) 1997 Elsevier Science
S.A.