Avaliação do amaciamento em aço inoxidável ferrítico por ensaios de torção a quente

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

The softening behavior changes that occur during hot deformation of ABNT 430 ferritic stainless steels were analyzed by hot rolling simulation using torsion tests aiming at achieving better microstructure for drawing process. Torsion specimens were machined from hot rolled plates 28mm in thickness after roughing mill. Interrupted deformation torsion tests were performed during continuous cooling. Tests were carried out in an electro-mechanical Instron 1125 universal testing computer controlled machine. The specimens were heated in an induction heating system. They were protected from oxidation as well as loss of N2 by a gas mixture of Ar plus N2 in the ratio of 85/15. A cycle of general vision was made for the temperatures determination of change in softening behavior of the steel through the adjustment of the curve of torsional mean stress in function of the inverse of the temperature. Specimens were first heated up to 1200C with a rate of 2C/s and held at this temperature for 120s. The samples were then cooled down at a constant rate of 1C/s. During cooling, deformations of equivalent strain of 0.2 were applied to the specimens at a strain rate 0.3s-1. The first deformation was applied at 1170C and the others with an interval of 30C from each other. The last deformation was applied at 690C. The temperatures of change of softening behavior had been determined at approximately 850C and 1000C. Interrupted torsion tests were performed in temperatures in the interval of 1050C to 810C. At the end of each assay the sample was submitted to fast cooling with CO2 and its microstructure was analyzed by optic microscopy with polarized light and microhardness measurements. Torsion tests with same heating and cooling cycle were carried through applying the equivalent deformation of 1.0 in only one pass, in the temperatures of 1080, 930 and 840C. The micrographs of the samples of multiple passes, associated to the measurements of microhardness confirmed the existence of two temperatures of occurrence of distinct mechanisms of softening. In the single pass tests, recrystallization was observed in the samples deformed at 840 and 930C, and recovery and subgrain boundaries in the sample deformed at 1080C. The recrystallization of stainless steel ABNT 430 can occur approximately in the temperature range of 850 to 1000C. For temperatures above of these values recovery is the predominant softening mechanism.

ASSUNTO(S)

engenharias mecanismo de amaciamento simulação de laminação aço inoxidável ferrítico abnt 430 torção a quente

ACESSO AO ARTIGO

Documentos Relacionados