U-drawing of Fortiform 1050 third generation steels. Numerical and experimental results

Elasto–plastic behavior of the third generation Fortiform 1050 steel has been analysed using cyclic tension–compression tests. At the same time, the pseudo elastic modulus evolution with plastic strain was analysed using cyclic loading and unloading tests. From the experiments, it was found that the cyclic behavior of the steel is strongly kinematic and elastic modulus decrease with plastic strain is relevant for numerical modelling. In order to numerically analyse a U-Drawing process, strip drawing tests have been carried out at different contact pressures and Filzek model has been used to fit the experimental data and implement a pressure dependent friction law in Autoform software. Finally, numerical predictions of springback have been compared with the experimentally ones obtained using a sensorized UDrawing tooling. Different material and contact models have been examined and most influencing parameters have been identified to model the forming of these new steels

Strain Hardening Dependence on the Structure in Dual‐Phase Steels

Herein, an extensive study is presented on the microstructure–tensile properties relationship in dual-phase (DP) steels. A series of ferrite-martensite DP steels with varied martensite volume fractions ( V m) from 0.17 to 0.86, microstructure morphologies (globular and elongated) and structure finenesses (ferrite grain sizes from 1.9 to 10.7 μm) are produced applying appropriate heat treatments. The tensile properties are studied, and the strain hardening behavior is analyzed in terms of Holloman, Crussard–Jaoul (C–J) and modified C–J approaches. The tensile curves reveal up to three strain hardening stages with the highest strain hardening exponent at the beginning of straining. Increasing V m and refining the structure raises the number of strain hardening stages and improves the strain hardening capacity in the first stage (n1). For the DP steels with similar morphologies, the mean free path in ferrite (λf) is proposed to be the most significant microstructure factor affecting n 1 -value. The n 1 of the elongated morphology shows stronger dependence on λf than the globular one. Finally, the DP steels are subjected to aging treatments, which lead to improved yield strength and total elongation, however, the strain hardening exponent decreases significantly