Surface transformation hardening
of Class 40 Gray Cast Iron was also performed
without the use of an absorptive coating or
inert gas shielding using a HPDDL. The beam
was defocused 4 to 8 mm and moved at various
speeds over the workpiece. The gray cast iron
was much more sensitive than the 4140 due
to a very narrow process widow between melting,
producing surface carbides, and desirable
hardening. It was determined that at a 6 mm
defocus a case would be produced with a higher
hardness value than the case produced at 8
mm defocus. The 4 mm defocus produced surface
melting and carbides. At a higher degree of
defocusing the case depth would increase at
the expense of hardness. This will occur up
to a critical amount of defocusing. This application
will benefit greatly from temperature control,
which is completely within the means of the
HPDDL.
