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Study of the microstructural parameters controlling the twin Induced Plasticity (TWIP) effect in austenitic steels

Grant number: 19/07178-6
Support type:Regular Research Grants
Duration: October 01, 2019 - September 30, 2021
Field of knowledge:Engineering - Materials and Metallurgical Engineering - Physical Metallurgy
Principal Investigator:Andrea Madeira Kliauga
Grantee:Andrea Madeira Kliauga
Home Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil
Assoc. researchers:Carlos Alberto Della Rovere ; Ilana Timokhina ; Jose Benaque Rubert ; Maurizio Ferrante ; Raul Eduardo Bolmaro ; Vitor Luiz Sordi

Abstract

The occurrence of strain-induced martensitic transformation (TRIP effect) and mechanical twinning (TWIP effect) increases the strain hardening and the total elongation of CFC alloys with medium and low stacking fault energy (SFE) thus providing higher strength and tenacity to these materials. The technological advantages of these effects are: (i) the higher ductility allows the conformation of more complex parts in a smaller number of processing steps, (II) the increase in strength allows the design of smaller sections reducing weight, at the same time that the impact resistance is improved (III) the high strain hardening results in higher abrasion resistance. The objective of this project is to study the TWIP effect in austenitic steels, isolating the variables of this mechanism and to test mathematical models that describe the phenomenon. The future development is to implement a constitutive model in the numerical simulation for the mechanical processing of these materials. The TWIP effect in austenitic steels occurs when the SFE is between 15 and 40 mJ/m2. Some factors influence this deformation mechanism: chemical composition, temperature, strain rate, deformation mode and grain size. The objective of this project is to obtain systematic data that may assist in the theoretical description of this effect. The proposal considers the study of two materials CFC with EFE between 25 and 30 mJ/m2:316 LV and TWIP (POSCO composition) and a TRIP steel AISI 201L with SFE in the range of 10 to 15 mJ/m2. The approximate temperature gaps in which the twin mechanism is active for these steels are -200 to 200 oC and 200 to 600 °C respectively. The project will determine:1) Which are the transition temperatures for these materials 2) Whow temperature and strain rate affect the critical shear stress for twinning3) Which effect the deformation mode (tension, compression simple shear, and plane strain) and crystallographic orientation has on the volume fraction of twinned grains. 4) The effect of grain size will be studied in a SPRINT project that has been simultaneously proposed in cooperation with professors Dr. Ilana Timohkina e Dr. Rimma Lapovok from Deakin University - Australia Through mechanical tests imposing controlled stress states modes (tension, compression simple shear, and plane strain) at controlled temperature and strain rates and detailed microstructural characterization (x-ray diffraction analysis, EBSD, and TEM) the following data will be obtained: critical shear stress for twinning and the volume fraction of mechanical twins. The results will be used to test constitutive models of this mechanism. The research team will be composed by: *Andrea Madeira Kliauga, Materials Engineering Department UFSCar, *Vitor Luis Sordi, Materials Engineering Department - UFSCar, *José Benaque Rubert, Mechanical Engineering Department - UFSCar, *Raul Eduardo Bolmaro, Instituto de Fisica de Rosario- Conicet, Argentina, *Ilana Timohkina, Deakin University - Austrália. (AU)