Laser welding of hardenable steel

Abstract: In the present work a novel idea based on nucleation and growth applied to
an induction heat treatment of a laser welded component is presented. With
this new concept, the microstructure and hardness of hardenable steel
SS142225 with a thickness of 12 mm are believed to be improved by
prolonging the cooling time after laser-welding and decreasing the preheat
temperature. Initially, a simple analytical model was used to calculate
thermal cycles. This knowledge then was used to programme a weld thermal
simulator. A number of Gleeble tests were then performed in order to study
the resulting microstructure. In these tests, important parameters such as
pre-heating temperature, cooling time after welding, post weld heat
treatment temperature were varied. After that and in order to compare the
results obtained from the simulated specimens, real weldments were produced
at Ferruform with the same parameters. After welding, the samples were
prepared for microscopy and hardness examinations. The metallurgical phases
are analyzed and described. A comparison between Gleeble samples and
Ferruform samples is made. Both Gleeble and Ferruform results show that, it
is possible to get microstructures that do not contain any untempered
martensite in the heat affected zone. A reduction in the hardness values of
the SS142225 hardenable steel was achieved in most of the experiments. A
microstructure consisted of a mixture of bainite, tempered martensite and
some ferrite and a duplex microstructure constituted by tempered martensite
and bainite were obtained as two of the most promising results.