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Title

INFLUENCE OF TEMPERATURE ON THE FINAL MICROSTRUCTURE OF MICRO-ALLOYED STEEL SUBJECTED TO SEVERE PLASTIC DEFORMATION

Authorship

Ramos, Leandro Rigo; Machado, Marcelo Lucas Pereira; Barcelos, Mariana Valinhos; Nunes, Lumena Gloria de Souza

Ramos, Leandro Rigo

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Machado, Marcelo Lucas Pereira

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Barcelos, Mariana Valinhos

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Nunes, Lumena Gloria de Souza

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DOI

10.5151/9785-9785-32409

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Abstract

The aim of the present work was to study the influence of temperature in the grain refining process from severe plastic deformations through the simulation of Accumulative Roll Bonding (ARB) by torsion tests at temperatures lower than the end of the austenite-ferrite transformation in micro-alloyed steel. The assays were performed to simulate the ARB at three different temperatures of 550 ° C, 625 ° C and 700 ° C with 5 torsion cycles with equivalent deformation of 0.8 per cycle at a rate of 0.1s^(-1), totalizing an accumulated deformation of 4.0. Samples of the annealed steel and of each deformation temperature were analyzed by optical and scanning electron microscopy to measure the final grain size of the process. Thus, after 5 cycles of deformation, grain refining was achieved in the material. The analysis of the stress and strain graphs revealed the occurrence of dynamic recrystallization during the deformation stages, which resulted in grain refining at three temperatures reaching the mean size of 2*10^(-6)m in the 550 ° C test. At the temperature of 625 ° C there was the grain refining of the material for the average size of 5*10^(-6)m and at the temperature of 700 ° C for the average size of approximately 6*10^(-6)m. Vickers hardness tests were also performed on the annealed test specimens and those obtained at the end of the process. In addition to grain refining, the Vickers hardness increased by 68% from 119HV in the annealed sample to 175HV in the deformed sample at 550 ° C. In the deformations at 625 ° C and 700 ° C the value of 130HV E and 150HV respectively was obtained. Based on the obtained results, it can be affirmed that the severe plastic deformations in microliged steel, carried out at temperatures lower than the end of the austenite-ferrite transformation, produce refined grains of the order of 2*10^(-6)m and consequently the increase of the mechanical strength of the material.

Keywords

Microalloyed steel; severe plastic deformation; torsion test; grain refining.