Dissertação
Avaliação do mecanismo de transformação do revestimento galvanizado GA no aço 22MnB5 durante o processo de estampagem a quente
Fecha
2019-03-05Autor
Henrique Lacerda Eleutério
Institución
Resumen
Galvannealed steel (GA) has been successfully applied in the hot stamping process
and their consumption is expected to increase in the coming years, mainly due to
their excellent surface quality and galvanic resistance in relation to other types of
coating. The main challenge for the galvanized steels consumption increase is to
ensure the structural integrity of the coating layer containing Zn, without loss of Zn
mass and to avoid the appearance of cracks induced by liquid metal (LME) during
the hot forming process.
In this study, the effect of the austenitizing heat treatment and hot stamping on the
microstructure of the coating and its surface quality, microstructural integrity and
crack formation of the steel were assessed in laboratory scale in order to obtain a
product without defects. It was also evaluated the influence of the induction heater
(IH) temperature on the surface quality and integrity of the coating and substrate
after the forming process, in order to obtain the best operating conditions and to
minimize the occurrence of defects in the coating surface and cracks mainly induced
by LME.
In this study, industrial samples will be processed using a muffle and a hot stamping
press manufactured at Usiminas Research and Development Center (R&D). The
samples will be analyzed using laboratory resources as scanning electron
microscopy with coupled energy dispersive X-ray spectrometer (SEM / EDS), X-ray
diffraction (XRD), glow discharge optical emission spectrometry (GDOES) and
spectrometry of inductively coupled plasma (ICP-OES).
The results showed that GA steels produced with IH temperature with 585ºC and
isothermal soaking less than 35 s presented good surface quality, without LME
cracks in the substrate, after hot stamping with austenitizing treatment with medium
and high heat parameters and final process temperatures 910ºC and 930ºC.