Effect of Fine Grained Dual Phase Steel on Bake Hardening Properties

Abstract

High strength dual phase (DP) steels have been increasingly used in car body structure for reducing weight and increasing safety performance. Bake hardening process is widely applied for improving final mechanical properties of formed components by means of carbide precipitation and occurred Cottrell cloud. In this work, effects of bake hardening on mechanical behavior of coarse and fine grain DP steels are investigated. Initially, fine grain ferritic-pearlitic structure is produced from a low carbon steel by constrained groove pressing (CGP) based on severe plastic deformation. Ferrite grains with a submicro size of 470 nm can be hereby achieved. DP microstructures are generated afterward by intercritical annealing. Finally, bake hardening at the temperature of 160 8C for 20 min is performed under consideration of various pre-strains between 0 and 10%. It is found that bake hardenability of the DP steels can be significantly increased due to the fine grain structure induced by the CGP, which provide enhanced heterogeneous nucleation sites for precipitates and accelerated carbon diffusion.[ Ã ] Prof.

Refinement of Banded Structure via Thermal Cycling and Its Effects on Mechanical Properties of Dual Phase Steel

“…Different techniques have been used for grain refinement of DP steels. The intercritical annealing of cold‐worked martensite or ultrafine grained (UFG) ferrite‐carbide aggregate, fast and ultrafast heating, ultrafast cooling (UFC), Deformation‐induced ferrite transformation (DIFT), and severe plastic deformation have been recently practiced. Most of these techniques are based on prior deformation and need rolling facilities or more complicated and expensive deformation routes.…”

Effect of Intercritical Annealing on Mechanical Properties and Work‐Hardening Response of High Formability Dual Phase Steel

“…In this regard, Cai et al, Das et al, Ahmad et al, Kalhor and Mirzadeh, Seyedrezai et al, and Schemmann et al showed that changing the initial microstructure can significantly affect the attributes of the DP microstructure. Moreover, the effect of tempering has also been noted . On another front, Calcagnotto et al and Papa Rao et al focused on warm deformation and intercritical annealing, where the importance of bimodal ferrite grain structure was also discussed .…”

“…Moreover, the effect of tempering has also been noted. [17][18][19] On another front, Calcagnotto et al [20] and Papa Rao et al [21] focused on warm deformation and intercritical annealing, where the importance of bimodal ferrite grain structure was also discussed. [11] Azizi-Alizamini et al [22] studied the effects of cold rolling of tempered martensite, subsequent tempering step, and heating rate to intercritical annealing temperature.…”

Microstructure and Mechanical Properties of Dual‐Phase Steels by Combining Adjusted Initial Microstructures and Severe Plastic Deformation

“…On the other hand, severe plastic deformation (SPD) in combination with intercritical annealing has been a particular technique in the category of thermomechanical processing which could be employed to produce UFG DP steels, as shown in previous studies. [ 27–31 ] Among all variously available SPD techniques, [ 32,33 ] constrained groove pressing (CGP) has become one of the effective methods for generating severe plastic deformation on sheet metals, in which the initial dimensions of sample were not altered. During the CGP process, the workpiece was subjected to a repetitive corrugating and straightening under the plane strain deformation condition by using alternate pressing with the asymmetrically grooved and flat dies.…”