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The Characterization of Structural Materials
Marek Kovár,1), Tomáš Peták,2), Jirí
Švancara, Školitelé Tomáš Skiba, Štepán
Válek
High school Karla Sladkovského, Sladkovského
námestí 8, Praha 3, 130 00 Department of
Materials, Faculty of Nuclear Sciences and
Physical Engineering, CTU, Trojanova 13, Praha 2,
120 00 Corresponding authors 1)
kovar.ma_at_seznam.cz 2) t.petak_at_seznam.cz
Abstract
The miniproject The Characterization of
Structural Materials consists of complete
metallographic study of the steel 11 373
(according to the CSN). The different heat
treatments were applied. The metallographic
samples were prepared and these studied by means
of optical microscopy with subsequent application
of the quantitative stereologic analysis. The
hardness tests as well as the Charpy notch impact
toughness tests were performed. The transition
temperature was then evaluated.

• 7 steel 11 373 specimens with different heat
  treatment applied were prepared
• Combined heat treatment 30 minutes / 900C air
  cooled at room temperature given to the furnace
  heated to 900C and then very slow cooled in the
  furnace down to the room temperature.
• Annealed 4 hours / 900C air cooled at room
  temperature.
• Water quenched 30 minutes / 900C water
  quenched.
• Oil quenched 30 minutes / 900C oil quenched.

1) Taking of Samples The specimens were taken
from the all three directions (x, y, z ) to
ensure having the 3D representation of the
material. Very often the grains are not
completely symmetrical but deformed in some
direction caused by different phenomenon.

• At 800C 30 minutes / 900C. Charpy impact
  toughness test performed at approximately 800C.
  (100C loss was estimated during transport from
  the furnace to the Charpy test equipment)
• Air cooled 30 minutes / 900C air cooled at
  room temperature.
• As cast without any heat treatment applied.

The experimental set-up consists of the Charpy
punch (see figure on the right). The punch has
defined potential energy at its starting position
E1 (300J in this case). The specimen, having the
dimensions of 10x10x55 mm according to the CSN EN
10 045 1 (420381), has a 2 mm notch. The
specimen is then put on a support, having the
notch directly at the place where the punch hit
the sample. The tests were carried out on 7
specimens subjected to different heat treatments
The cross-sections of the specimens were studied
by means of optical microscopy (using NEOPHOT
32). The microstructure evaluation was then
carried out. Three circles of known radius were
put on each micrograph. All micrographs exhibit
the same nominal magnification 300x. Along the
circle, the distances between the grain
boundaries was measured (for each phase). Overall
distances were then summed and divided by the
number of the grains. After the calculation
according to the magnification, the result show
the average grain size.
Cross-section 3 Water quenched Cross-section 4 Oil quenched

Average ferrite grain size 9,92 ?m Average pearlite grain size 27,23 ?m Due to quenching, the grains are not clearly visible - some areas (gray) of martensite. Average ferrite grain size 8,23 ?m Average pearlite grain size 5,8 ?m Due to quenching, the grains are not clearly visible - see typical martensite structure (the gray areas).
Cross-section 7 As cast condition

Average ferrite grain size 23,09 ?m Average pearlite grain size 11,77 ?m
Cross-section 1 Combined heat treatment Cross-section 2 Annealed

Average ferrite grain size 16,88 ?m Average pearlite grain size 8,45 ?m Average ferrite grain size 19,29 ?m Average pearlite grain size 7,38 ?m

1. Combined heat treatment ? 202 J
2. Annealed ? 168 J
3. Water quenched ? 188 J
4. Oil quenched ? 198 J
5. At 800C ? 135 J
6. Air cooled ? 228 J
7. As cast ? 20 J

From the results it can be clearly seen that the
heat treatment applied has a fundamental impact
on mechanical properties.
Note Specimen 5 At 800C was taken from the
furnace having 900C but during the manipulation,
the loss of 100C was taken into account.
Few specimens were heated in the furnace up to
the different temperatures where the Charpy notch
impact toughness test was performed. At certain
temperature region, the rapid change of energy
(needed for breaking the specimen) is observed.
This region is called transition region and its
mean temperature the transition temperature. In
this region the brittle fracture changes into the
ductile fracture.
The Vickers hardness test is a static test. The
experimental set-up is prescribed by the Czech
State Norm CSN 42 0374. It is the most often used
hardness test. The test is based on the
indentation of the diamond tip into the material
and subsequent evaluation of the deformation of
the material (measurements of the sizes of
indents)
The Vickers hardness test were performed on 7
steel specimens using the loading of 30 kg. On
each specimen 10 indents were carried out. These
average values were evaluated

• Combined heat treatment HV 30 127,9
• Annealed HV 30 110,2
• Water quenched HV 30 192,9
• Oil quenched HV 30 164,5
• At 800C HV 30 140,9
• Air cooled HV 30 132,6
• As cast HV 30 195,7

Energy (J)
It can be seen that the highest value of the
Vickers hardness HV30 were measured at the as
cast condition of the material. Very high values
were also measured on water and oil quenched
specimens. The smallest hardnesses were found on
annealed material. The standard deviations has
also be taken into account.
Temperature (C)
T0 50C
Using the least square method, the function (1)
was smoothed by experimental data. The parameter
evaluated were A0 78J B0 70J C0 11,56C
T0 48,01C. The transition temperature is then
approximately 50C. In fact, it is an inflex
point of the curve, the boundary between the
lower and the higher plateau. The values of the
lower and higher plateau were estimated as 10 and
150J, respectively.
The work within the miniproject Characterization
of the Structural Materials involved complex
metallographic investigation of the steel CSN
11 373. The work was carried out at the
Department of Materials, FNSPE, CTU in Prague.
The authors had the opportunity to get experience
with an applied research and after being trained
perform mechanical tests by themselves (namely
Vickers hardness tests, tensile tests or Charpy
impact toughness tests). The heat treatment of
the material was applied, the cross-sections were
prepared for metallographic study using optical
microscope. The results from the Charpy impact
toughness tests were than used for evaluation of
the transition temperature. It was investigated,
that the impact of the heat treatment on a
material is of great importance. For example, due
to the different heat treatment, the values of
the notch impact toughness were increased ten
times. The huge differences were observed in the
microstructure where the impact on the grain size
was reported. All measured and evaluated values
were in a good agreement with the literature.