Laboratory Experiment. Number 6 & 7
Heat Treatment and Hardenability of Steels
Laboratory Experiment No. 6 & 7
Heat Treatment and Hardenability of Steels
Abstract
This experiment is attempted to measure the hardenability of the steel and understand the process of heat treatment of different materials at different cooling strategies. Cooling through different procedures will cause the materials to have different properties and different microstructures. Furthermore next stage of experiment relates the cooling rate and hardness of 1045 steel and 4143 steel. This also helps in determine how alloying a material permits it to be heat treated more homogeneously. Investigated results also proven to be close enough to expected results in obtaining higher brittleness with rapid cooling in and to improve ductility the process of tempering is proven to be very efficient with increase of tempering temperature the hardness of material must be decrease. Last but not least, after finishing experiment 6 the group found out that the lower the tempering temperature the lower the hardness. Also, the results that the group found from experiment 7 after finishing it proved being inconsistent from what it should be.
Introduction
The purpose of this experiment is to determine what effect heat treating and then cooling has on the hardness and grain structure of two different types of steel. The two different types of steels were utilized are 1045 steel samples and 4143 steel sample which is considered to be a low-alloy steel.
The heat-treating process is a method to alter physical and mechanical properties of the material. The heat-treating process is consists of three crucial steps of annealing, hardening, and tempering. Annealing is primarily used to soften and to induce the ductility of the specimens by heating and holding at suitable temperature and then cooling, by instantly quenching in the water, which produces the higher brittleness with low ductility and toughness in the specimens. Moreover, tempering is a process of heat-treating, which is used to increase the toughness of metal. Tempering is important because it used to achieve desired hardness. To restore some the toughness and impact properties is obtained by tempering where specimens are reheated to a temperature between 5000 F and 10000 F for certain time which removes the internal strain caused by sudden cooling in the quenching bath without a large decrease in hardness or strength.
In attempting the first phase of the experiment it cannot determined why some heat-treated materials don’t reach a high hardness when cooled at certain temperature. With the hardness test the hardness of a material can be determined. The Hardenability is a property that determines the depth and distribution of hardness when steel is heated to a given temperature and then quenched to reach martensitic structure, which is obtained by performing Jominy test, where an austenitized steel bar is quenched at one end only, thu ...
Call Girls in Dwarka Mor Delhi Contact Us 9654467111
Laboratory Experiment. Number 6 & 7Heat Treatment and Hardenabil.docx
1. Laboratory Experiment. Number 6 & 7
Heat Treatment and Hardenability of Steels
Laboratory Experiment No. 6 & 7
Heat Treatment and Hardenability of Steels
Abstract
This experiment is attempted to measure the hardenability of the
steel and understand the process of heat treatment of different
materials at different cooling strategies. Cooling through
different procedures will cause the materials to have different
properties and different microstructures. Furthermore next stage
of experiment relates the cooling rate and hardness of 1045
steel and 4143 steel. This also helps in determine how alloying
a material permits it to be heat treated more homogeneously.
Investigated results also proven to be close enough to expected
results in obtaining higher brittleness with rapid cooling in and
to improve ductility the process of tempering is proven to be
very efficient with increase of tempering temperature the
hardness of material must be decrease. Last but not least, after
finishing experiment 6 the group found out that the lower the
tempering temperature the lower the hardness. Also, the results
that the group found from experiment 7 after finishing it proved
being inconsistent from what it should be.
Introduction
The purpose of this experiment is to determine what effect heat
treating and then cooling has on the hardness and grain
structure of two different types of steel. The two different types
of steels were utilized are 1045 steel samples and 4143 steel
sample which is considered to be a low-alloy steel.
The heat-treating process is a method to alter physical and
mechanical properties of the material. The heat-treating process
is consists of three crucial steps of annealing, hardening, and
tempering. Annealing is primarily used to soften and to induce
the ductility of the specimens by heating and holding at suitable
temperature and then cooling, by instantly quenching in the
2. water, which produces the higher brittleness with low ductility
and toughness in the specimens. Moreover, tempering is a
process of heat-treating, which is used to increase the toughness
of metal. Tempering is important because it used to achieve
desired hardness. To restore some the toughness and impact
properties is obtained by tempering where specimens are
reheated to a temperature between 5000 F and 10000 F for
certain time which removes the internal strain caused by sudden
cooling in the quenching bath without a large decrease in
hardness or strength.
In attempting the first phase of the experiment it cannot
determined why some heat-treated materials don’t reach a high
hardness when cooled at certain temperature. With the hardness
test the hardness of a material can be determined. The
Hardenability is a property that determines the depth and
distribution of hardness when steel is heated to a given
temperature and then quenched to reach martensitic structure,
which is obtained by performing Jominy test, where an
austenitized steel bar is quenched at one end only, thus
producing a range of cooling rates along the bar.
Procedure
First of all, the experiment provided six 1045 steel specimens
were for heat treating process, and for the second were only two
steel rods of 1045 steel and 4143 steel respectively used to
perform the Jominy test. In order to go though the details read
the following: First the group begin with identifying all each
specimen by punching different letter on to them using hammer.
Second, the engineer students heated all specimens at 16000 F
for 1/2 hour after obtaining the Rockwell a scale hardness
measurement. Third, The four samples were quenched in water,
one sample is allowed for air cool, and the other sample is set
for furnace cool for one hour and quenched in water. Then, the
two steel rods of different properties also allowed for heated at
16000 F for 45 minutes after obtaining the Rockwell scale
hardness measurements. Also, the group measured the Rockwell
a scale hardness on all six quenched specimens after being heat
3. treated and tempered the three-quenched specimen at different
temperature of 6000 F, 8000 F, and 10000 F respectively for 30
minutes. After tempering specimens then quenched in water.
Moreover, obtained hardness measurements using Brinell (3000
kg) and Rockwell A scale on all six steel specimens. In order to
perform the Jominy test one steel rod is then removed from the
furnace and is placed in the cooling tower for 10 minutes before
quenching in water, repeated the same procedure for other steel
rod. Finally, measured the hardness 1/16 inch for the first inch
and every 1/8 for the next inch and 1/4 for the next 2 inches
using Rockwell a scale for both steel rods.
Results and Discussions
The experiments “Heat Treatment of Steel” and “Hardenability
of Steel” are two different experiments, which show the effects
of heat-treating, and quenching of specimen provides different
hardness and microstructure in the materials. During first phase
of experiment the two specimens are left to cool at room
temperature and furnace temperature, these specimens were
quenched after an hour. The reason for this quenching after an
hour is due to the fact that the grains in the material are given a
chance to form when cooling at room temperature and furnace
cooling temperature. If the grains are not given enough time to
form when cooling at room and oven temperature the grain
structure would not be accurate as if actually air cooled and
furnace cooled. From the Table 1 it can be clearly seen the
hardness obtained through furnace cooled is lesser than
hardness obtained by air cooled specimens because in furnace
cooling allow the grains to from due to its slow cooling process
where as during air cool specimens tends to cool much quicker
compare to furnace cool and specimens have less time to form
grains. Due to that specimens will have more boundaries, which
mean there will be more interference with dislocation motion.
Also, in Table 1 it shows the Rockwell measurement is 76.99
for the instant quench. On the other hand, the furnace cooled is
55.05. Moreover, in Table 2 represent the Ultimate Tensile
strength (psi) for all samples from the average Brinell Hardness
4. number obtained. In fact, the hardness of both of the measured
BNH and the measured Rockwell are decreasing. The Ultimate
Tensile Strength (psi) is also decreasing because the hardness is
going down. As we know the harder a material is the higher the
strength is. Furthermore, the instant quenched sample has the
highest hardness and the Ultimate Tensile strength results.
Finally, Table 3 represents the hardness of the Steel 1045
sample after it has been placed at different tempering
temperatures. Moreover, Table 4 shows the difference in
hardness between Steel 1045 and Steel 4143 that that was taken
at different distance from the quenched end.
Table 1 Comparison between performed Brinell hardness
numbers measurements with Brinell hardness numbers obtained
by conversion of Rockwell A scale measurements.
Specimens
Rockwell
A scale
measurements
RHA Conversion to BHN
Dimple Diameters (mm)
BHN from Dimple Diameters
S instant quench
76.99
500
2.50
601
H Tempered @540 0C
71.58
390
3.20
363
D Tempered @ 430 0C
69.19
353
2.90
5. 444
K Tempered @ 315 0C
70.89
381
2.81
417
M (air cooled)
53.39
172
4.29
197
E (Furnace cooled)
53.05
169
4.51
179
Table 2 Computed Ultimate Tensile strength (psi) based on the
average Brinell Hardness number obtained.
Specimens
Measured BHN
(3000)kg
Measured Rockwell A scale numbers (HRA )
Conversion BHN
Average BHN
Ultimate Tensile Strength (psi)
S
401
75.53
500
550.5
2.75E+05
D
429
71.71
7. and Rockwell a numbers were proportional to each other a
straight line would be seen. A graph like the one shown in
Figure 1 could be a result of an inaccurate machine or
inaccurate measurement taking strategies.
Figure 1 Brinell Hardness numbers vs. Rockwell A scale
numbers obtained after heat treating of the specimens.
Table 3 The hardness measurements obtained using Rockwell A
scale for three 1045 steel specimens that has been tempered at
different temperatures after being heat treated.
Specimens
Hardness Rockwell
A scale (HRA)
Tempering temperature ( c )
D
71.71
430
K
66.89
315
H
66.99
540
Figure 2 Hardness obtained using Rockwell A scale hardness
after tempering the specimens.
To obtain desired mechanical properties in steel specimens it is
necessary to process heat treating, quenching, and tempering of
the steel. Hardening is way of making steel harder, by first heat
treating the specimens to 8850 C for half hour and immediately
cools it by quenching the specimens in water, which increase
the brittleness of the substance at much higher rate with very
low ductility and toughness in the samples. The tempering is the
process through which brittleness is reduced to improve
8. ductility and toughness by heating the specimens at different
temperature for certain time.
Higher tempering temperature will yield a somewhat softer
material with higher toughness, whereas a lower tempering
temperature will produce a harder and somewhat more brittle
material, as shown by the Figure 2 where hardness increases
with the increase of tempering temperature.
The possible errors of not quenching the specimens in desired
time or factors of obtaining the hardness of the samples at
softer spot may have occurred in processing the tempering of
specimens, which resulted on the graphs for not obtaining
consistency.
The decline in hardness of tempered specimens once has been
heat treated and quenched in Table 3 proves the hypothesis of
decrease in brittleness by tempering the specimens.
The Ultimate tensile strength of materials is determined using
equation 1 by using data collected for Brinell hardness for all
the specimens mentioned in Table 2.
Equation 1 Calculating the Ultimate Tensile Strength of
materials.
In determining the strength, obtaining the hardness is great
ways of making comparison, which can be attain using
Rockwell A scale and Brinell hardness scale which is directly
proportional to the tensile strength. In using Brinell hardness
scale timing in maintaining the load on the specimens may have
been a factor of slight variation of results where as in Rockwell
A scale ha
From the Figure 4 the amount of carbide ((Fe3C) can be
calculated at temperature 1338 0F for 1045 steel using equation
2 where C1 is 45% because that is the weight percent of carbon
in 1045 steel. Ca and Cb calculated using the lever rule which
consists of drawing a line across to determine how much weight
percent of material there is in the steel, where “a” is alpha and
“b” is Iron Carbide (Fe3C). Using equation 2 is determined that
Iron carbide percent is about 0.68% and 99.32% is presumed to
be alpha phase.
9. Wb = (C1 – Ca)/(Cb – Ca) , Ca= 2.2%, and Cb= 65% are the
weight percent composition.
Equation 2 To find the Fe3C (carbide) content using weight
percent equation.
Figure 4 The iron-iron carbide phase diagram.
Different microstructures obtained when specimens processed
through differen cooling strategies that is why the TTT (Time,
Temperature, Transformation) chart in Figure 5 is proven to be
great tool in determining the microstructure. The TTT chart
shows the amount of time needed to quench a material to reach
a certain phase. The left part line represents the beginning of
the transformation and the right part line represents the
conclusion of the transformation. The TTT chart also explains
the need of quenching the specimens after an hour of cooling
due to after certain time the specimens does not require any
more transformation. The martensite structure which is one of
the hardest of all phases is obtained upon quenching instantly to
a low temperature. But the other samples that quenched were
temperd again to move higher up in the TTT chart where less
hardened materials are . To obtained a desired phase it is
neccsary to for rapid change in temperature with respect to time
when quenching the 1045 steel to reach a Bainite phase.
The specimens that were furnace cooled and cooled at room
temperature are most likely to fall in the pearlite phase where
the one cooled at room temperature is said to be fine pearlite
while the other one is more close to coarse pearlite due to slow
cooling process. The specimens tempered at 540°C falls
between pearlite and bainite phases. The specimens tempered at
430°C and 315°C fall under the Bainite phase, the one tempered
at a lower temperature could be classified as being of finer
Bainite.
Figure 5 The TTT (Time, Temperature, Transformation) chart
for 1045 steel.
10. Microstructure and hardness are closely correlated;
microstructure consists of grain size and crystal structure. When
the specimens were reached at austenite phase, the grains are
more uniform and homogeneously distributed; upon completion
of this process the specimens are ready to be cooled in order to
obtain different hardeneability in the material. During instant
quenching of the specimens the specimens with evenly
distributed grains are not given a chance to form and are then
solidified giving the material a fine grain structure in contrast
to a material slowly cooling which gives a material more coarse
grains making the material less hard and more ductile. The
Jominy test results illustrated in Figure 3 prove that how
cooling rate affects hardness data obtained on the attempt of
experiment. The greater distance of quenching the less hard the
material is because, as mentioned before, the grains are given
more time to form, and the bigger the grains the less hard the
material. The inconsistency among results obtained instead of
constantly moving downward may have caused due to
experimental errors such as not placing it fast enough on the
Jominy tester. The graph line obtained by the 4143steel and
1045 steel quickly goes up and down not opening the water
enough for quenching during the Jominy test. The overall graph
is also does not matches to the expected results where 1045
steel graph must lower than the graph line obtained by the 4061
steel rod specimen is considered to be an experimental error of
not transporting the specimen on the tester with in time
duration.
Table 4 The Jominy test results obtained on two steel rods.
Distance from quenched end (in)
1045 Steel
4143 Steel
0.0625
75.9
66.2
13. 2.5
47.5
49.7
2.75
46.9
45.5
3
44.2
45.8
3.25
38.6
45.1
3.5
40.1
22.9
3.75
42.7
32
4
36.4
26.3
Figure 3 Plot showing Hardness as a function of distance from
the quenched end for 1045 steel and 4061 steel specimens. The
dash line is the Steel 4061 and the solid line is the Steel 1045.
Conclusion
Materials that cool at slower cooling rates tend to be softer
materials while those that are cooled at faster cooling rates tend
to be harder. Tempering a material lowers its ultimate strength
but increases the amount of stress the material can absorb
(toughness), higher the tempering temperature the lower the
ultimate strength. Tempering also adds more ductile
characteristics to the material. High hardness in materials only
14. can be attain when there is a low toughness, in order to acquire
toughness in a material that has been quenched, The tempering
of the specimens is then processed to improve the toughness in
the material and lower the brittleness.Fine grain structures tend
to be hard material where as materials with coarse grain
structure has more ductile properties. Furthermore, the data
does not accurately show what should be happening. The data I
collected has error that is obviously shows in my graph. The
graph should show a straight line going down similar to the one
in experiment 6. For example, after heating the Steel and
quenched it the group had to measured it and probably by
mistake the engineer student measured the same point twice or
took similar points close to each other. Also, maybe the time it
took to move the Steel from furnace to be quenched was too
long which effected the measurements. Moreover, the water that
was used to quench could have been too strong hitting the
specimen, which leads to make a huge differences in
measurements.
References
D. Callister Jr, Fundamentals of Materials Science and
Engineering, J. Wiley & Sons, NY, 3rd Ed. 2008, Flinn and
Trojan, Engineering Materials and Their Application, Chapter 6
Dieter, Mechanical Metallurgy ASM Handbook on Heat
Treatment, Vol. 2
http://www.smt.sandvik.com/en/products/strip-steel-and-strip-
based-products/strip-products/knife-steel/hardening-
guide/purpose-of-hardening-and-tempering/
http://www.carbidedepot.com/formulas-hardness.htm
William D. Callister, Jr., David G. Rethwisch. Fundamentals of
materials science and engineering, third edition
www.csun.edu/~bavarian/Courses/MSE%20227/Labs/2-
Charpy_test.pdf
