Sp. Gadag et al., EFFECT OF LASER PROCESSING PARAMETERS ON THE STRUCTURE OF DUCTILE IRON, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 196(1-2), 1995, pp. 145-154
Laser processing of structure sensitive hypereutectic ductile iron, a
cast alloy employed for dynamically loaded automative components, was
experimentally investigated over a wide range of process parameters: f
rom power (0.5-2.5 kW) and scan rate (7.5-25 mm s(-1)) leading to soli
d state transformation, all the way through to melting followed by rap
id quenching. Superfine dendritic (at 10(5) degrees C s(-1)) or feathe
ry (at 10(4) degrees C s(-1)) ledeburite of 0.2-0.25 mu m lamellar spa
ce, gamma-austenite and carbide in the laser melted and martensite in
the transformed zone or heat-affected zone were observed, depending on
the process parameters. Depth of geometric profiles of laser transfor
med or melt zone structures, parameters such as dendrile arm spacing,
volume fraction of carbide and surface hardness bear a direct relation
ship with the energy intensity P/UDb2, (10-100 J mm(-3)). There is a m
inimum energy intensity threshold for solid state transformation harde
ning (0.2 J mm(-3)) and similarly for the initiation of superficial me
lting (9 J mm(-3)) and full melting (15 J mm(-3)) in the case of ducti
le iron. Simulation, modeling and thermal analysis of laser processing
as a three-dimensional quasi-steady moving heat source problem by a f
inite difference method, considering temperature dependent energy abso
rptivity of the material to laser radiation, thermal and physical prop
erties (kappa, rho, c(p)) and freezing under non-equilibrium condition
s employing Scheil's equation to compute the proportion of the solid e
nabled determination of the thermal history of the laser treated zone.
This includes assessment of the peak temperature attained at the surf
ace, temperature gradients, the freezing time and rates as well as the
geometric profile of the melted, transformed or heat-affected zone. C
omputed geometric profiles or depth are in close agreement with the ex
perimental data, validating the numerical scheme.