Lab Report 2
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School
Sacramento City College *
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Course
412
Subject
Aerospace Engineering
Date
Jan 9, 2024
Type
Pages
10
Uploaded by MinisterRatPerson203
Instructor:
Shaher Abdallah
Course:
MAE 361 Sec06 9822 Materials & Properties Lab
Experiment Name:
Heat Treatment of AISI 1018 & AISI 1045
Date Performed:
9/11/2023
Department of Mechanical & Aerospace Engineering
California State University, Long Beach
OBJECTIVE:
The objective of this lab was to measure and compare the hardness values for steel alloys before
and after various heat treatments to see the effects treatments have on them. The heat treatments
used in this experiment are quenching, normalizing, and tempering. To study the effect hardness,
tests were run on a Rockwell Hardness Tester. While conducting the experiment, it was observed
the alloys formed a crust due to the heat treatments. The materials measured in this experiment
are SAE 1018, and 1045 Steel. The 1018 alloy was heated to 900
and 1045 to 850
both for
℃
℃
50 minutes, then one piece of each alloy was quenched and another piece normalized. The
quenched alloys were then tempered for 5 minutes with a temperature of 450
three times.
℃
After, the process was repeated but the alloys were tempered for 10 minutes.
Group 3
Group Members:
Name:
ID #
Sean Vergara
028084704
Anthony Pimentel-Legaspi
025513421
Obehi Ehigie
017347939
Martin Tran
027088293
Tyler Kieffer
030214507
2. PROCEDURE:
A. Normalizing
1.
Air cool half the specimen taken from the oven/furnace
2.
Remove the decarburized surface by grinding both ends of the specimen. The
high temperatures of the furnace will burn some of the carbon, making the surface
carbon depleted
3.
Use Rockwell scale A hardness test to measure the hardness of one side of each
specimen. Make sure to use a diamond indenter and a load of 60 kg
B. Quenching and Tempering
1.
Use room temperature water to immediately quench the other half of the specimen
2.
Make sure to grind and polish both ends of the specimen. Check the hardness of
one side using the Rockwell scale A hardness test
3.
For 5 minutes at a temperature between 300 C to 650 C, then quench the
specimen immediately. Once done, each group will be assigned to a different
temperature, then results will be shared with the rest of the class
4.
Repeat step 3
5.
Repeat step 4, 3x
6.
After tempering the specimen for 10 minutes, immediately quench
7.
Repeat step 3
8.
Repeat step 7, 3x
C. List of Apparatus (brand and model):
1.
Furnace
2.
United Tru-Blue II Hardness Testing System
3.
Metal plates / containers
4.
Metal Tongs
5.
Carbon Steels AISI 1018 & AISI 1045
6.
Grinder
3. DATA & RESULTS:
Scale: HRA
Table 1: Steel Hardness Before and After Normalizing
Specimen
Treatment
AISI 1018
AISI 1045
No Heat Trial 1
58.43 HRA
59.25 HRA
No Heat Trial 2
55.29 HRA
59.63 HRA
Average Hardness
56.86 HRA
59.44 HRA
Heated (Normalizing)
*AISI 1018 Temp: 900
℃
*AISI 1045 Temp: 850
℃
42.14 HRA
46.62 HRA
Table 2: Steel Hardness Before and After Quenching
Specimen
Treatment
AISI 1018
AISI 1045
No Heat Trial 1
58.43 HRA
59.25 HRA
No Heat Trial 2
55.29 HRA
59.63 HRA
Average Hardness
56.86 HRA
59.44 HRA
Heated (Quenching)
*AISI 1018 Temp: 900
℃
*AISI 1045 Temp: 850
℃
67.31 HRA
73.24 HRA
Table 3: Steel Hardness Before and After Tempering (5 minutes)
Specimen
Treatment
AISI 1018
AISI 1045
No Heat Trial 1
58.43 HRA
59.25 HRA
No Heat Trial 2
55.29 HRA
59.63 HRA
Average Hardness
56.86 HRA
59.44 HRA
Tempering: 5 min #1
*Temp for both: 450
℃
65.49 HRA
70.68 HRA
Tempering: 5 min #2
64.25 HRA
67.88 HRA
Tempering: 5 min #3
66.06 HRA
70.96 HRA
Average Tempering (5 mins)
65.27 HRA
69.84 HRA
Table 4: Steel Hardness Before and After Tempering (10 minutes)
Specimen
Treatment
AISI 1018
AISI 1045
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No Heat Trial 1
58.43 HRA
59.25 HRA
No Heat Trial 2
55.29 HRA
59.63 HRA
Average Hardness
56.86 HRA
59.44 HRA
Tempering: 10 min #1
*Temp for both: 450
℃
59.96 HRA
69.43 HRA
Tempering: 10 min #2
64.61 HRA
68.16 HRA
Tempering: 10 min #3
63.84 HRA
68.32 HRA
Average Tempering (10 mins)
62.80 HRA
68.64 HRA
5. DISCUSSION:
The data fit within the frame of our expectations throughout the normalizing and
quenching procedures, however when the steel was tempered our expectations were subverted.
The original values averaged to 56.86 and 59.44 HRA for SAE 1018 and 1045 respectively, after
taking the hardness the alloys were then quenched in water where the hardness values rose to
67.31 HRA for 1018 and 73.24 HRA for 1045 steel. These values were in line with expectations
as heating a steel beyond its recrystallization temperature but below melting temperature allows
for grain restructuring within the material then quenching traps the carbon in our material
increasing its hardness. After completing the quench the same materials were then put into the
heating oven after being measured for 5 minutes at around 450
℃
, this process was repeated 3
times. The values for SAE 1018 were 65.49, 64.25, and 66.06 HRA the values for SAE 1045 had
similar changes at 70.68, 67.88, and 70.96. The increase in hardness was not expected at first,
based on the previous value decreasing in hardness it was believed the trend would continue but
our expectations were subverted when the true value rose by 3.08. The rise in HRA was
potentially caused by the material losing more carbon in the second quenchand the third quench
increased the martensite in the steel.
A published value of 1018 steel that was heated to 750
℃
then water quenched, and
tempered at 350
℃
had a hardness of 197 HB or 57 HRA which is similar to our initial hardness
of 1018 with no treatment. This is most likely due to 1018 having a minimum recrystallization
temperature of 900
℃
and since the published 1018 never reached that temperature before being
quenched it never reached its recrystallization temperature and this prevents the material from
structuring itself and becoming harder. The published hardness value for 1045 with a water
quench around 820°C - 850°C and tempered between 540
℃
- 680
℃
has a hardness range of 210
- 245 HB or 58.5 - 62.1 HRA. Once again the final published value was lower than the
experiment's final value, this is due to the tempering process in the published process having a
higher tempering temperature used alloying for more carbon to escape the material lowering the
hardness but increasing the ductility. The results from the performed experiment do differ from
published values but other reasons could lie in the process; it is not specified in the published
values how long the material was heated for before it was quenched.
During the experiment there were four groups that were all sharing the same heating
ovens, each group had 2 pieces of material. This led to the oven being opened and exposed to the
cool air, some material would be sat on the counter outside the open where it was hotter for
longer than others this could affect the hardness and make some of the steel weaker than it
normally would be. Other problems faced were the inconsistent heat oven temperatures. During
the tempering process the material would only stay in the heat oven for 5 minutes at 450
℃
, but
due to the amount of groups testing material loading the heating oven took time and allowed for
the temperature to fall below 450
℃
and since the time was so short for heating the actual
temperatures varied between quenches. This could have effects on the hardness, if an alloy didn't
get heated it wouldn't allow for restructuring or release of carbon preventing much change from
taking place. Another aspect of the experiment was sanding the metal alloys down after each
cooling process to get rid of the crust that formed. Improper sanding could lead to crust on the
alloy obstructing the hardness test and making the results inaccurate.
6. ANSWER TO INSTRUCTOR’S QUESTIONS:
1.) List the hardness of each specimen. You should include the original hardness together
with hardness after quenching and normalizing heat treatment. You should also show
results of tempering at different temperatures. Only give the average values of hardness.
If you refer to results section your points for the question will be zero. (10 points)
a.) AISI 1018:
■
Average Original Hardness: 56.86 HRA
■
Quenching Hardness: 67.31 HRA
■
Normalizing Hardness: 42.14 HRA
■
Average Tempering Hardness (5 minutes): 65.27 HRA
■
Average Tempering Hardness (10 minutes): 62.80 HRA
b.) AISI 1045:
■
Average Original Hardness: 59.44 HRA
■
Quenching Hardness: 73.24 HRA
■
Normalizing Hardness: 46.62 HRA
■
Average Tempering Hardness (5 minutes): 69.84 HRA
■
Average Tempering Hardness (10 minutes): 68.64 HRA
2.) Describe the microstructure of each specimen. What are the definition of following
microstructures and their properties: pearlite, ferrite, cementite, and proeutectoid ferrite.
(4 points)
Specimens used were Carbon Steels. Iron alloys are classified as “Carbon Steels” when
containing up to 2% Carbon in the specimen. Anything over this threshold will categorize
the alloy as “Cast Iron.” Different phases of iron alloy manifest themselves as Carbon
content levels increase within a specimen. Ferrite exists as a Body-Centered-Cubic
crystalline structure and normally contains around 0.008-0.022% Carbon. Cementite, also
known as “Iron Carbide”, can be found in alloys containing at least 6.70% Carbon. While
Ferrite is softer and more ductile, Cementite is hard and brittle. Ferrite will become
Austenite when heated above 727ºC. Once this Austenite cools back down to 727ºC, the
microstructure for the alloy contains alternating layers of both Ferrite and Cementite. The
microstructure for this state is known as “Pearlite”, which has varying qualities of both
soft ductility and hard brittleness.
3.) Why was it important to grind 1/32 inch off of the ends of the specimen? (3 points)
The reason why it is important to grind 1/32 inch off the ends of the specimen is to
remove the decarburized surface. This is because the temperature from the heat burns the
carbon from the surface and could lead to inaccurate readings.
4.) Why was the Rockwell hardness scale A used? (3 points)
Rockwell hardness scale A was used because scale A had a better accuracy for measuring
carburized steel, which was AISI 1018 and AISI 1045. Unlike scale A, Rockwell
hardness scale B was good for softer steel and scale C was used for harder steel.
5.) Why would you want to use a higher temperature for austenitizing the SAE 1018 steel
over the SAE 1045 steel? (4 points)
You want to use a higher temperature for austenitizing SAE 1018 steel because there are
fewer amounts of carbon compared to SAE 1045. SAE 1018 with carbon composition of
0.14-0.20% which is significantly lower compared to SAE 1045 with carbon composition
of 0.43-0.50%. The difference in carbon composition means that the SAE 1018 will need
a little higher temperature than SAE 1045 to austenite because it needs more heat to reach
the carbon. This is shown in both SAE for the normalizing temperature. The SAE 1045
requires the temperature to normalize at 870
o
C - 920
o
C and then let it cool, while SAE
1018 takes up to 890
o
C - 940
o
C.
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6.) Discuss the effects of tempering time and temperature on the hardness of specimens
during the tempering process. (6 points)
The goal of tempering a steel specimen is to increase its toughness and lower its
brittleness. The effects of varying tempering times are described when comparing Tables
1,3, and 4. Table 1 explains the initial tempering of the steel characterized by a high heat
(850-900ºC), larger time period being heated (50 minutes), and a normalizing process
which allowed the steel to cool naturally. Results show a considerable drop in hardness
levels, which indicates improved ductility. Tables 3 and 4 describe the specimens when
heated to 450ºC , but Table 4 was heated for twice the amount of time as Table 3. The
AISI 1015 and 1045 steel specimens had initial average hardness ratings of 56.86 HRA
and 59.44 HRA respectively. After three 5-minute tempering trials, average hardness
ratings 65.27 HRA and 69.84 HRA were produced. After three 10-minute tempering
trials, hardness levels were observed to be 62.80 HRA and 68.64 HRA. From this, it can
be determined that hardness levels are inversely proportional to tempering times. Higher
temperatures also yield better ductility as well.
7.) Plot the experimental results of hardness vs tempering time. For the graph, titles should
be given. Axes should be clearly labeled and points found during experiment should be
clearly shown on the graph. The graph should be in this section. Since you want to
compare the behavior of SAE 1018 and SAE 1045 scales for the two graphs should be the
same.
Do not show this graph in the results section!
(10 points)
8.) Which observed microstructure possessed the greatest hardness? Lowest hardness?
Maximum toughness? You should specify which steel and heat treatment gave the highest
and lowest hardness and toughness. (3 points)
The highest hardness levels were produced when tempering for 50 minutes at higher
temperatures, in which AISI 1018 reached 67.31 HRA and AISI 1045 reached 73.24
HRA. Heating iron alloys to temperatures above 757ºC will cause the BCC
microstructure to switch to FCC, known as the Austenite phase. However, quenching
alloys in this state will convert the FCC microstructures to BCT (Body Centered
Tetragonal), known as Martensite, known to have high hardness and brittleness.
The lowest hardness was indicated when allowing the specimens to air cool completely
after a 50 minute heat treatment, a process called “normalization”. Hardness values for
AISI 1018 and 1045 dropped to 42.14 HRA and 46.62 HRA respectively. This is because
the microstructures of these alloys change completely to that of Austenite with an FCC
structure. Normalized steel typically exhibits higher toughness than any other structural
conditions, shown by low HRA values.
9.) If the austenitizing temperature had been 760
℃
instead of 900
℃
or 850
℃
, how would
the microstructure and hardness have been different after normalizing? (4 points)
The reason the specimens had to reach temperatures above 850ºC was to completely
change the alloy to austenite, in order to maximize the removal of internal stresses. If that
upper transformation temperature is not reached, some of the specimen might remain
ferrite . As seen from the tables 3 and 4, low temperature heat treatments in the ferrite
range are subject to higher RHA readings. This means that higher ferrite content would
cause the specimen to be more brittle than it would be if it were pure austenite.
10.)
How do the quenching medium and the temperature before quenching affect the
microstructure and mechanical properties of the quenched steel? (4 points)
Typical quench mediums are water, oil, and air. Each medium has a different cooling rate,
which directly affects the hardness level of a steel specimen. Water is classified as having
the most severe quench, meaning it can result in more cracking and warping. Quicker
quenching techniques result in higher hardness readings. This is visible when comparing
readings for the water-quenched and normalized specimens. The steel alloy that was
allowed to air cool produced a much more ductile piece, with hardness levels in the 40s.
This is almost completely opposite when looking at the quenched steel hardness values,
67.31 HRA and 73.24 HRA. Excessive heating before quenching can cause a build of
martensite, which is very hard and very brittle, which is why it is important to consider
temperature before quenching.
7. RECOMMENDATIONS & CONCLUSIONS:
The objective of the experiment was to see the effects of heat treatment so a
recommendation to improve the accuracy of the experiment is to allow for more time in the
heating oven for each specimen. One problem encountered during the process was the short time
the specimens were in the heating oven for the tempering phase, the oven wasn't consistently
able to reach the desired 450
o
C before they were removed. Another recommendation to ensure
accurate results is to add heating ovens for each set of specimens so the time they are exposed to
the air is significantly reduced.
This experiment highlighted the importance of heat treatment on metal alloys, a treatment
can change the composition of a material and in turn its use. Heat treating can both lower or
increase a material's hardness through the reorganization of its microstructure. Heat treatment
can be used to increase an alloy's machinability or its use as tools and there are many procedures
to help achieve that altered form of an alloy. To lower a material's hardness and give it more
ductility and machinability, normalizing can be utilized as normalizing heats up a material to a
high temperature and cools it slowly by exposing it to room temperature air.
Normalizing is the heat treatment process of heating a material and letting it cool in air
allowing for the material to become more homogeneous. The results of Normalizing the SAE
1018 steel was a hardness of 42.14 HRA and for SAE 1045 46.62 HRA comparing that to the
original 56.86, and 59.44 HRa for 1018, and 1045 respectively it is clear to see the effect
normalizing has on lowering hardness. To achieve an increase in martial hardness there is
Quenching, where you heat a material to a desired temperature usually above its recrystallization
temperature, then rapidly cooling said material in a medium like water or oil. Water has a much
faster effect and as a result increases a materials hardness more than would have been achieved
with oil. This is seen in the results collected from the experiment, Quenching the 1018 achieved
67.31 HRA and 1045 reached 73.24 HRA. Quenching puts the material in a greater amount of
stress which is what causes the increase in hardness, this stress makes the material significantly
more brittle and prone to cracks. The increased brittleness makes using a material more
impractical and as a result a secondary treatment is usually applied; one such treatment is
tempering. Tempering is a process of heating a material below its eutectoid or lower critical
temperature, then it is allowed to cool in room temperature air. The lower critical temperature for
steel is the temperature of change and going beyond this temperature results in the formation of
austenite structures in the steel. By keeping the steel below the lower critical temperature we can
relieve some of the stress out of the steel without changing its material structures. Tempering
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allows for more machinable alloys that are still high in hardness, as evident in the experiment
with 1018 ending at 65.27 HRA and 1045 ending at 68.64 HRA
8. REFERENCES & ACKNOWLEDGEMENT:
1.
Materials Science and Engineering, Introduction, William D. Callister Jr. and David G.
Rethwisch. 9th Edition, Wiley 2014.
2.
The hardness data for AISI 1018 was retrieved from Group 1.
3.
Aisi 1018 Steel, Carburized at 925°C (1700°F), Box Cooled, 775°C (1430°F) Reheat,
Water Quenched, 175°C (350°F) Temper. 19-32 Mm (0.75-1.25 in) Round
,
https://www.matweb.com/search/DataSheet.aspx?MatGUID=06e57ce7a3a14861a328dde
305ec267d Accessed 24 Sept. 2023.
4.
AG, From Alemnis, et al. “Aisi 1018 Mild/Low Carbon Steel.”
AZoM.Com
, 7 Aug. 2019,
www.azom.com/article.aspx?ArticleID=6115.
5.
“1045 Carbon Steel Bar.”
Interlloy
,
www.interlloy.com.au/data_sheets/carbon_steels/1045.html#:~:text=1045%20is%20a%2
0medium%20tensile,170%20%2D%20210%20in%20either%20condition. Accessed 24
Sept. 2023.
6.
Virtual Labs
, https://sm-nitk.vlabs.ac.in/exp/rockwell-hardness-test/theory.html Accessed
24 Sept. 2023.