Abstracts Book - IMRC 2018

• SD7-O002
ANALYSIS OF THE INFLUENCE OF THE AUSTEMPERING HEAT
TRATMENT OVER THE BEHAVIOR IN THERMAL FATIGUE OF GRAY
IRON AND COMPACTED GRAPHITE IRON
Luis Angel Aguirre Hernández 1 , María de Jesús Pérez 2 , Efraín Almanza 3 , Nelly Rodríguez 3
1 Instituto Tecnológico de Saltillo, División de Estudios de Posgrado, Mexico. 2 Instituto
Tecnológico de Saltillo, Metal-Mecáncia, Mexico. 3 Instituto Tecnológico de Saltillo, Metal-
Mecánica, Mexico.
One of the causes of the failure of parts such as brake discs, combustion engine
liners, among others, is associated with the phenomenon of thermal fatigue.
During the service life of the parts there are continuous heating and cooling that
generate residual stresses in the material. Although thermal fatigue is one
important cause of failure, it is a property that has not been studied in detail.
This may be due to the fact that there is no standardized test, as well as the
difference in sizes and geometries of the samples used.
The aim of this work is to contribute with experimental information about the
behavior in thermal fatigue of gray iron (GI) and compact graphite iron (CGI),
using a standardized sample, similar to use in the tension test. The samples of
both cast iron were subjected to austempering consisting of: austenitization at
900°C for 60 minutes, isothermal hold in a bath of molten salts at 320°C for 5,
30, 60 and 90 minutes, followed of cooling in a water bath. The thermal fatigue
cycle consisted of heating of samples room temperature to 400 ± 10°C, holding
at this temperature for 30 seconds followed by cooling to 50°C. The test
concludes upon completion of 30 cycles. The microstructural characterization of
the samples before and after the fatigue test was carried out by optical and
scanning electron microscopy.
The results showed that the initial maximum stress in thermal fatigue in both
irons are very similar (139 to 145 MPa), however, as the thermal cycles increase,
the stress decreases more quickly in the GI becoming of the order of 65%, while
in CGI the decrease in stress is less than 30%. The analysis of the microstructure
showed that the acicular nature of the ausferrite has little influence on the
previous behavior and that the relaxation of the stress is associated with the
nucleation of microcracks in the graphite particle. For the investigated irons, it
is found that the laminar morphology of the graphite present in the GI,