Mykhaylo Romanyuk; Martina Avalos; Edgardo R. Benavidez; Elena Brandaleze
Abstract
The application of IF steels in the automotive industry has increased significantly due to their excellent deep drawability. The chemical composition, the microstructure, the precipitation phenomena and texture of the material determine the mechanical properties. This paper proposes, a more profound ...
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The application of IF steels in the automotive industry has increased significantly due to their excellent deep drawability. The chemical composition, the microstructure, the precipitation phenomena and texture of the material determine the mechanical properties. This paper proposes, a more profound study of some aspects related to the application of high plastic deformation, as well as its relation with the formation of fine grain structures, texture, precipitates and grain boundaries interaction. The structure of an IF steel plate with ultra-low carbon was characterized using optical microscopy and scanning electron microscopy (SEM). A ferritic structure with very fine and recrystallized grains containing high number of triple point was observed. The precipitation kinetic of the steel was simulated applying Fact Sage 7.1. The main precipitates predicted are: TiN and TiS, these types of second phases improve the drawability behaviour. The formability aptitude of the sheet was evaluated by different mechanical tests: Hole Expansion, Erichsen and n-r determination. Finally, yield strength, tensile strength, percentage elongation and average r-value results, are correlated with the structural information. A strong (111) <110> recrystallization texture confirms the high formability of the IF steel sheet. Copyright © 2018 VBRI Press.
Elena Brandaleze; Martina Avalos; Mykaylo Romanyuk
Abstract
Steel wires under severe cold drawing deformation, develop high strength (5-6 GPa) and ductility. For these reasons it is relevant to increase the knowledge on the structural evolution and deformation mechanisms involved during wire drawing process, due to their critical applications such as bridges, ...
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Steel wires under severe cold drawing deformation, develop high strength (5-6 GPa) and ductility. For these reasons it is relevant to increase the knowledge on the structural evolution and deformation mechanisms involved during wire drawing process, due to their critical applications such as bridges, cranes and tire cord. This paper presents a comparative study of steel wires (0.84%C) at different deformation stages. The product presents a normal behaviour under torsion test, the mentioned test is normally used to corroborate the wire aptitude. The main objective of the study is to increase the knowledge on the structural evolution after cold drawn considering the deformation mechanisms, cementite dissolution, and epsilon carbide precipitation. The microstructural study was carried out applying light and scanning electron microscopy (SEM-EBSD). The structural information was correlated with results of differential thermal analysis (DTA) and FactSage simulation. The structural study verified the presence of curling phenomenon in the wires. The interlaminar spacing (l) and the thickness of cementite lamellae in wires cold drawn from 8 mm up to 2 mm of diameter was determined. Finally, the dynamic strain aging, which is promoted by cementite destabilization and the precipitation of epsilon carbide was studied. Copyright © 2018 VBRI Press.
Elena Brandaleze; Mykhaylo Romanyuk; Martina Avalos
Abstract
The alloy design concepts of high performance steels, involve the knowledge on the stability of carbides associated with nanoscale phenomena present in the structure as result of the deformation suffered during the thermomechanical processes. The understanding of the nanoscale phenomena open new frontiers ...
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The alloy design concepts of high performance steels, involve the knowledge on the stability of carbides associated with nanoscale phenomena present in the structure as result of the deformation suffered during the thermomechanical processes. The understanding of the nanoscale phenomena open new frontiers to understand mechanical behaviours in the steel, not totally clarified until now. The paper discuss the structure evolution during wire drawing of pearlitic steels and the impact of cementite stability on different nanoscale structure phenomena, which explain the specific mechanical behaviour to achieve ultra-high strength. Results on the kinetic and stability of carbides predicted on the base of thermodynamic simulation are correlated with thermal analysis tests results (dilatometry and differential scanning calorimetry) carried out by different authors in order to understand the cementite (Fe3C) dissolution during plastic deformation. In addition, information obtained by traditional and no traditional microscopy techniques and X ray diffraction complete the study and allows to understand more deeply the structure evolution, including nanoscale phenomena that justify the mechanical behaviour during wiredrawing and the final strength level. The dislocation substructure evolution together with the cementite dissolution during sever plastic deformation which leads to a steadily increase of the strain hardening is clarified. Copyright © 2018 VBRI Press.
