Speaker
Description
In developing lightweight materials, damage that occurs during the forming process is very critical. Knowledge of the damage mechanism makes it possible to develop damage-tolerant materials. It includes occurring less damage during the forming process with minimizing negative influence on material properties in the forming process. This damage-tolerance is determined by a number of microstructural parameters, which are influenced by chemical compositions and thermodynamic process paths. In dual phase steel materials, intercritical annealing heat treatment process in the semi-finished state is very important. In the previous studies which studied a single change of thermodynamic parameters, only the influence derived from the coupling of two or more microstructural parameters could be revealed. In this study, however, material models for damage-tolerance are designed based on the optimal conditions for microstructure formation through thermodynamic simulations. Furthermore, by systemically uncoupling microstructural parameters such as martensite phase fractions, martensite hardness values, grain size and grain morphology of each phase, the individual effect of each parameter on the overall damage properties is studied to determine damage mechanisms in dual phase steel materials.
Thermodynamic calculations allow for different temperature variations of intercritical annealing heat treatment with various alloying elements (especially carbon, silicon, manganese and in some cases chromium and molybdenum). Based on the results from calculations, a small amount of test alloy (scale of less than 1 kg) is produced and evaluated with the high screening throughput technique. To evaluate the mechanical properties of the prototype materials produced through the steps above, tensile tests and bending tests are performed and metallographic properties are analysed for phase fractions and grain morphologies. For the specimens carefully selected based on the evaluation results, in-situ-tensile test and in-situ-bending test are performed inside SEM (Scanning electron microscope) to analyse damage tolerance characteristics of the materials. After acquiring the knowledge from all processes, alloy conditions with excellent damage tolerant properties can be finally selected and a larger-scale prototype material (less than 10kg) will be produced to check feasibility of the material for the industrial production process.
References
[1] Balbi, M. ; Alvarez-Armas, I. ; Armas, A.: Effect of holding time at an intercritical temperature on the microstructure and tensile properties of a ferrite-martensite dual phase steel. In: Materials Science and Engineering A Bd. 733, Elsevier B.V. (2018), S. 1–8
[2] Farshchi, Yasamin Khebreh ; Mirzadeh, Hamed ; Tavakoli, Mohammad ; Zamani, Mehran: Microstructure tailoring for property improvements of DP steel via cyclic intercritical annealing. In: Materials Research Express Bd. 6, IOP Publishing (2019), Nr. 12.
[3] Nouroozi, Mahsa ; Mirzadeh, Hamed ; Zamani, Mehran: Effect of microstructural refinement and intercritical annealing time on mechanical properties of high-formability dual phase steel. In: Materials Science and Engineering A Bd. 736, Elsevier B.V. (2018), S. 22–26 — ISBN 9821820840
| Keywords | Dual phase steel, microstructure, martensite, hardness, phase fraction, Thermocalc, EBSD, High throughput screening |
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