Investigation on local mechanical properties in multiphase steels for designing local properties of constructional elements

Abstract

The investigation deals processes leading to
local strengthening in multiphase steels, being
characterized by a good formability,
continuous yielding, high strength and a
strong bake hardening and aging effect. Dual
phase (DP) and complex phase (CP) steels
have been investigated to examine the effect
of thermal and mechanical processing
parameters on local properties. For this
purpose, two methods have been used to
achieve local strengthening, namely local
deformation (LD) and local heat treatment
(LHT). The local deformation by means of
embossing with defined pre-strains leads to
enhanced hardness and strengthening. A
subsequent aging treatment results in a
further increase in mechanical properties.
Finally, a local laser heat treatment leads to
an increase of hardness and strength and to
local strengthening of the material. Local
aging on the adjusted strength could be
confirmed as well as the stability of the local
strengthening.
RIASSUNTO
La ricerca riguarda i processi che portano al
rafforzamento locale negli acciai a
multifase, che sono caratterizzati da buona
formabilità, snervamento continuo, elevata
resistenza e da un effetto pronunciato di
bake hardening e di invecchiamento. Sono
stati studiati gli acciai “dual phase” (DP) e
quelli a fase complessa (CP) per esaminare
l’effetto delle variabili termiche e
meccaniche di processo sulle proprietà
locali. A questo scopo, sono stati usati due
metodi per avere il rafforzamento locale,
cioè deformazione locale (LD) e trattamento
termico locale (LHT). La deformazione
locale, effettuata mediante intaglio con predeformazione
definita, porta all’aumento
della