Effects of Austenite Stability on Forming and Work Hardening Behavior of 1.2 GPa Gen3 AHSS

Chiriac, C. I.; Sohmshetty, Raj; Balzer, Jason; Mueller, Todd; Ju, Jong Doo

doi:10.1088/1757-899x/418/1/012004

Cited by 2 publications

(1 citation statement)

References 9 publications

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“…[24][25][26][27][28][29] Deformation factors such as strain state, strain rate, strain path, and temperature also affect the apparent stability of austenite, which affect formability. [30][31][32][33][34][35] For example, for a medium manganese TRIP steel, Wu et al showed that strain path changes during forming can be manipulated to achieve a desired retained austenite content and mechanical properties in stamped parts. [36] The deformation response of Q&P steels under nonlinear and dynamic loading conditions is of paramount interest to the sheet forming community.…”

Section: Introductionmentioning

confidence: 99%

Strain Rate Dependent Ductility and Strain Hardening in Q&P Steels

Finfrock

Thrun

Bhattacharya

et al. 2021

Metall Mater Trans A

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Due to their high strength, formability and affordable cost, quenched and partitioned (Q&P) steels have shown the potential to reduce the mass of vehicles, thereby decreasing fuel consumption during service. Furthermore, because a lower mass of steel is used in each vehicle, energy consumption associated with the steelmaking process is also reduced. Q&P steels utilize the deformation-induced martensitic transformation (DIMT) of metastable retained austenite to enhance ductility and strain hardening. Accordingly, improvement of mechanical performance is contingent on the ability to precisely control the chemical and mechanical stability of austenite. Considering the multitude of factors that influence austenite stability, optimizing microstructures to delay necking or fracture is challenging, particularly as temperature and strain rate increase. Tensile tests of an intercritically annealed C-Mn-Si Q&P steel were performed over a range of strain rates (10 À4 to 10 À1 s À1 ) to evaluate effects on the DIMT and sheet tensile properties. As strain rates increased from 10 À4 to 10 À1 s À1 , the uniform elongation decreased from approximately 19 to 14 pct. This reduction in uniform elongation is associated with a decrease in the strain hardening exponent near the onset of strain localization. Based on experimental data from this study and review of previous research, it is postulated that the strengthening contribution of DIMT is controlled by competing effects of: (i) a decreasing chemical driving force for DIMT caused by deformation-induced heat accumulation at higher strain rates and (ii) an increasing number of martensite nucleation sites. This suggests that tailoring austenite stability for specific deformation conditions could enable further optimization of formability and vehicle crash behavior.

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