[pt] Esta pesquisa teve como objetivos promover variações
microestruturais em um ferro fundido nodular ferrítico tipo
ASTM A536 60-40-18, pelo do uso de resfriadores durante a
solidificação do material e pela adoção de tratamentos
térmicos pós-fundição, bem como avaliar a influência de
tais variações microestruturais sobre as propriedades
mecânicas e vida em fadiga do material.
Inicialmente, amostras do material foram fundidas em areia
com e sem o uso de resfriadores. Após a fundição, algumas
amostras de ambas as condições de resfriamento sofreram
normalização, enquanto outras foram recozidas, perfazendo
seis diferentes condições microestruturais: sem resfriador
bruta de fundição (SRB); sem resfriador normalizada (SRN);
sem resfriador recozida (SRR); com resfriador bruta de
fundição (CRB); com resfriador normalizada (CRN) e com
resfriador recozida (CRR).
Em seqüência, corpos de prova de todas as condições
mencionadas acima foram ensaiados em tração e,
posteriormente, sofreram análises metalográficas
qualitativas e quantitativas. Dando continuação a etapa
experimental, levantaramse as curvas tensão versus número
de ciclos para a falha das condições microestruturais SRB,
SRR, CRB e CRR, por meio de ensaios de fadiga em flexão
rotativa. A vida em fadiga do material também foi
relacionada com às características metalúrgicas de cada
condição. / [en] The objectives of the present work were to promote
microstructural variations in an ASTM A 536 60-40-18
ferritic nodular cast iron, making use of cast coolers
during and adopting heat treatments after casting, as well
as to evaluate the influence of the microstructural
variations on the mechanical properties and fatigue life of
the material.
Initially, samples of the material were cast in sand moulds
with and without internal coolers. After casting, a number
of samples in both cooling conditions were subjected to
normalizing and annealing heat treatments and, therefore,
six different microstructural conditions were obtained: as-
cast without cooler (SRB), normalized without cooler (SRN),
annealed without cooler (SRR), as-cast with cooler (CRB),
normalized with cooler (CRN) and annealed with cooler (CRR).
Tensile test were carried out on specimens representing the
above mentioned conditions and their microstructures were
analysed by qualitative and quantitative metallography. In
the sequence of the experimental procedure, rotating bend
fadigue test were performed in order to establish the
stress-life curves for the SRB, SRR, CRB and CRR
microstructural conditions. The fadigue life of the
material was also related to the metallurgical
characteristics of each condition.
The metallographic analysis has indicated that the use of
coolers increases the number of graphite nodules, reduces
the graphite nodule size and otimizes the spherical
morphology. However, these microstructural modifications
seam to have no significant influence on the mechanical
properties of the material.
As to the effect of normalizing annealing, boht treatments
not imply in significant changes in the mechanical
properties of the as-cast conditions. Regarding the fadigue
resistance of the material in the as-cast conditions,
the CRB sample showed a longer fatigue life than the SRB
samples and this performance under cyclic loading was
attributed to the fact that the CRB condition is
characterized by a higher number of graphite nodules of
class VI. A comparison between the as-cast and annealed
conditions indicated that the microstructural conditions
SRR and CRR presented a lower fatigue resistance
than the conditions SRB and CRB, respectively. This
behaviour was associated with the microstructural features
of the as-cast conditions, namely the smaller graphite
nodule size, the higher microhardness of the matrix and the
presence of the bull`s-eye structure. Finally, the
experimental stress-life curves were modelled by means of
Coffin-Manson law, which was considered efficient in the
fadigue life data of ferritic nodular cast iron.
| Identifer | oai:union.ndltd.org:puc-rio.br/oai:MAXWELL.puc-rio.br:3721 |
| Date | 16 July 2003 |
| Creators | CARLOS ALBERTO TORRES DE MELLO |
| Contributors | MARCOS VENICIUS SOARES PEREIRA |
| Publisher | MAXWELL |
| Source Sets | PUC Rio |
| Language | Portuguese |
| Detected Language | English |
| Type | TEXTO |
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