The influence of temperatures and strain rates on the mechanical behavior of dual phase steel in different conditions

Abstract

j m a t e r r e s t e c h n o l . 2 0 1 5;4(1):68-74 w w w . j m r t . c o m . b r Dual phase steel Tensile properties Ductility Strain rate sensitivity Strain hardening a b s t r a c tThis study deals with the mechanical behavior of DP steel. A commercial dual phase steel (DP 800) was strained to 3.5% followed by annealing at 180 • C for 30 min to simulate the pressing of the plates and the paint-bake cycle involved in the manufacturing process of automobile body structures. The effect of temperature and strain rate on the mechanical behavior of this material was investigated by uniaxial tensile tests, covering applicable temperatures (−60 • C to 100 • C) and strain rates (1 × 10 −4 to 1 × 10 2 s −1 ) experienced in automotive crash situations. Yield and ultimate tensile strength, ductility, temperature effects and strain rate sensitivity as well as strain hardening rate have been determined and discussed.

Influence of Temperature on Mechanical Properties, Fracture Morphology and Strain Hardening Behavior of a 304 Stainless Steel

“…This phenomena could perhaps be related to one of the following: 1) necking occurring at lower stress than tensile strength, dynamic formation of martensite and local strengthening happening within the neck, resulting in an post-uniform strain 8 ; 2) the activation of strain hardening mechanisms involving a high dislocation density or possibly a complex stress state. Such increase in SHR at higher strains was also observed in previous publications 34,35 . It is evident that the average strain hardening exponent poorly represents the strain hardening exponent of the distinct strain hardening stages, as it contrasts with n i for most of the presented deformation temperatures and stages.…”

Thermographic analysis of dual-phase steel under quasi-static and dynamic tension

“…5, 6). An analysis of the results of investigations performed by Cao et al [11] on the DP 800 steel has proved that an increase oḟ ε from 10 −4 to 10 2 s −1 leads to an increase of UTS by about 10 % and a drop of deformation by about 34 %. The Docol 1200 steel under investigation displays a similar dependence of the indices of mechanical properties, whereby, in the course of impact stretching of this steel atε 2 , the obtained values of plastic deformation were nearly equal to those of the DP 800 steel.…”

“…This may be caused by the fact, that the largest local deformations in DP steels are being observed in ferrite, particularly in the zones of ferrite-martensite interfaces [12,13], which are the fracture initiation zones [12,14]. In the course of stretching with the rateε 1 , the temperature rise of the tested sample can intensify the diffusion of carbon to dislocations and phase boundaries, causing the effect of dynamic ageing [11]. The local depletion of carbon in ferrite and martensite may also lead to their plasticization and deformation.…”

New Insights into the Microstructural Changes During the Processing of Dual-Phase Steels from Multiresolution Spherical Indentation Stress–Strain Protocols

“…These processing steps typically include intercritical annealing at 730-830 • C for a few minutes up to an hour, quenching at different cooling rates, cold working to different deformation levels, and aging at 100-250 • C up to few hours. The last two steps are typically referred to as bake hardening [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. During the intercritical annealing treatment, the material is heated up to a temperature where the austenite and the ferrite phases are stable.…”

“…Furthermore, the relevant section of the phase diagram (see Figure 1) suggests that intercritical annealing at lower temperatures results in a smaller volume fraction of martensite but with a higher carbon content. As already mentioned, another important component in the processing of DP steels is the bake hardening (BH) [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] step, which includes cold working followed by aging heat treatment. This step is known to impart DP steels with a characteristic property known as continuous yielding, which is generally attributed to the production and pinning of dislocations in the ferrite component, especially in the vicinity of ferrite/martensite interfaces [1,[7][8][9][10][11][12][13][14]16,18,19,22,28,[30][31][32][33][34].…”