FAKULTI TEKNOLOGI DAN KEJURUTERAAN MEKANIKAL
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
BMKU 2511
MECHANICAL ENGINEERING LABORATORY 1
TITLE:
HEAT TREATMENT OF STEEL
DATE OF LAB:
11/12/2024
LECTURER’S NAME:
PROGRAM:
NO
DATE OF REPORT:
DR. RAFIDAH BINTI HASAN
BMKK
STUDENT’S NAME
SECTION:
MATRIX
NUMBER
1
AMIRUL QARAZI BIN MOHD NAWI
B132410180
2
HAZIQ HAFIZUDIN
B132410171
3
LEONG ZI QING
B132410197
4
MUAMMAR ANIQ BIN ADAM
B132410202
LECTURER’S REMARK
14/01/2024
S1
CONTRIBUTION
- Assist on experiment
procedures
- Experimental Result
- Question 1 & 3
- Discussion Question 1 & 2
- Assist on experiment
procedures
- Experimental Result
- Theory & Question 2
- Edit and finalize report
- Assist on experiment
procedures
- Discussion Question 3 & 4
- Question 5
- Write conclusion
- Assist on experiment
procedures
- Recording Data
- Plotting Graph
- Question 4
UNIVERSITI TEKNIKAL
MALAYSIA MELAKA
MECHANICAL ENGINEERING LABORATORY I
Heat Treatment of Steel
No. Dokumen:
BMCG1011
No. Isu./Tarikh:
3/11-10-2022
No. Semakan/Tarikh:
3/11-10-2022
Jum. Mukasurat 5
OBJECTIVES
1. To learn and conduct the methods of heat treatment for plain carbon steel.
2. To familiarize the quenching process of steel in different quenching mediums.
3. To determine the hardness properties of quenched steel.
4. To analyze the effect of quenching medium on the hardness properties.
LEARNING OUTCOMES
At the end of laboratory session, student should be able:
1. Familiarize quenching as one of the common heat treatment process done on
steels.
2. Understand the relation between hardness properties and quenching media.
THEORY
Heat treatment of steel
Steels are among our most important engineering materials. Without them, the
machinery and tools required to establish any industrial activity would be difficult
to imagine. A very important property of steel is the ability to alter its hardness
by simple heat treatments. Hardened steel is capable of cutting and shaping
other softer materials such as other steels, nonferrous materials, plastics, wood
and stone.
Heat treatment of steels is a heat-treating process whereby the steels are
exposed to an elevated temperature for a period of time and cooled, which alters
the mechanical properties without changing the product shape. There are many
different ways to heat treat steel, one of the most popular ways is through a
method known as quenching.
Quenching or hardening involves the rapid cooling of a steel. To perform the
quenching process, a steel is heated to a temperature greater than that of normal
conditions, typically somewhere above its recrystallization temperature but below
its melting temperature. Figure 1 shows the temperature ranges for quenching
(hardening) and other heat treatments of plain carbon steels. The steel may be
held at this temperature for a set time in order for the heat to “soak” the material.
Once the steel has been held at the desired temperature, it is quenched in a
medium until it returns to room temperature.
There are a variety of quenching media available that can perform the quenching
process. Each media has its own unique quenching properties. The main types
of quenching media are air, water and oil.
Figure 1 Temperature ranges for hardening and other heat treatments plain carbon steels
(Foundations of Materials Science and Engineering, Fifth Edition in SI Units, The McGraw-Hill
Companies, 2004)
The Iron-carbon phase diagram of steel
Figure 2 shows the equilibrium diagram for combinations of carbon in a solid
solution of iron. The diagram shows iron and carbons combined to form Fe-Fe3C
at the 6.67%C end of the diagram. The left side of the diagram is pure iron
combined with carbon, resulting in steel alloys. Three significant regions can be
made relative to the steel portion of the diagram. They are the eutectoid E, the
hypoeutectoid A, and the hypereutectoid B. The right side of the pure iron line is
carbon in combination with various forms of iron called alpha iron (ferrite),
gamma iron (austenite), and delta iron.
Figure 2 Iron-Carbon Phase Diagram (Materials Science and Metallurgy, 4th ed.,
Pollack, Prentice-Hall, 1988)
Hardness properties
Hardness is defined as a material's ability to resist permanent indentation (that
is plastic deformation). Typically, the harder the material, the better it resists wear
or deformation. The term hardness, thus, also refers to local surface stiffness of
a material or its resistance to scratching, abrasion, or cutting.
EQUIPMENTS
Plain Carbon Steel (0.18 wt% C), Electric Furnace, Fire Resistant Jacket, Heat
Resistant Glove, Heat Resistant Face Shield, Furnace Tongs, Tins with Water
and Oil, Grinding and Polishing Apparatus, Sand Paper and Rockwell Hardness
Tester.
PROCEDURES
I. Sample preparation
1. Four specimens of plain carbon steel were prepared with a dimension of
20 cm x 20 cm x 20 cm.
2. All the specimens were treated according to the specified parameters.
Refer to Table 1.
Quenched
specimen
Austenitizatio
n temperature
Soaking time
(min)
Quenching
medium
850
60
Air
(°C)
Air quenched
Water
quenched
Oil quenched
850
60
Water
850
60
Oil
As-received*
-
-
-
Table 1 Heat treatment process for each specimen
*This specimen will not go through the quenching process and it is used as a reference.
II. Quenching process
1.
The specimen was placed into the electric furnace.
2.
The specimen was heated to 850oC (austenization temperature) and hold
for 60 minutes (soaking time).
3.
The specimen was removed from the furnace with the tongs as quickly as
possible.
4.
The specimen was immersed into the specified quenching medium for rapid
cooling process. For air quenched, the specimen was left to cool normally
to the room temperature in sand bucket.
(Safety precaution: Student must wear a fire-resistant jacket, heat resistant
glove and face shield when performing heat treating operation and always
use tongs to handle hot metal.)
III. Grinding process
1.
The surface, if possible, was ground using grinding-polishing apparatus or
sand paper.
2.
The surface was ensured to be flat and smooth.
3.
The surface was carefully cleaned to remove any oil, grease or rust.
IV. Rockwell Hardness Test
1.
The specimen was placed on the test stage (anvil) of the Rockwell
hardness tester. The surface to be tested must be parallel to the opposite
one.
2.
A suitable indenter was selected for the specimen. Make sure that the
indenter to be used for the test is correctly assembled.
3.
A Rockwell hardness scale C (HRC scale) was chosen for the specimen.
4. The specimen was positioned in such way as to avoid the sleeve coming out
more than 50 mm. The distance between specimen and indenter must be at least
2 or 3 mm.
5. A minor load of 10 kg was applied to the specimen and set the gauge to be zero.
6. A start button at 6 dx 6 sx was pressed, which is located at the base of device
and it was continuously pressed until the beginning of the countdown for the
predefined time of permanent load.
7. The major load was applied by tripping a lever. After 15 seconds the major load
was removed.
8. The specimen was allowed to recover for 15 seconds by waiting the indenter to
return to its initial position.
9. The Rockwell hardness value appears at the LCD display was recorded.
10. The hardness values were measured at least at three different points of each
specimen. The average data was used for Experimental Results.
EXPERIMENTAL DATA
Record the hardness of all the specimens in Table format.
Quenched
specimen
Rockwell Hardness (HRC) value
HRC #1
HRC #2
HRC #3
Air quenched
34.4
17.5
24.1
Water quenched
50.4
39.3
44.5
Oil quenched
20.7
29.3
30.1
As-received
21.6
30.4
28.6
EXPERIMENTAL RESULTS
1. Plot the graph of temperature vs. time of overall heat treatment process for each
quenched specimen. The graph also must include the cooling process (in terms
of cooling rates) in three quenching media.
2. Measure the average values of HRC for each specimen.
Quenched
specimen
Rockwell Hardness (HRC) value
HRC #1
HRC #2
HRC #3
HRC Average
Air quenched
34.4
17.5
24.1
(34.4+17.5+24.1)÷3=25.33
Water quenched
50.4
39.3
44.5
(50.4+39.3+44.5)÷3=44.73
Oil quenched
20.7
29.3
30.1
(20.7+29.3+30.1)÷3=26.70
As-received
21.6
30.4
28.6
(21.6+30.4+28.6)÷3=26.87
1.
Plot the Histogram chart of HRC value vs. quenching medium for each specimen
DISCUSSIONS
1.
Discuss the HRC value for as-received and quenched plain carbon steels.
The HRC value for as-received is higher than the HRC value of air quenched
carbon steels, but is lower than the HRC value of water and oil quenched carbon
steels. This might be due to the air quenched carbon steel still cooling down on the
inside, thus making the true hardness of the carbon steel not forming up enough to
match the as-received carbon steel.
2.
Which quenching media has the highest and lowest cooling rates? Please
give your reason.
Oil quenched has the highest cooling rate followed by water quenched and air
quenched carbon steels. This is due to the great heat conducting abilities of
oil, compared to water or air. This allows the treating carbon steel in oil cools
down rapidly and forms the treated final product much faster than other
mediums.
3.
Discuss the relationship between the resulting hardness and quenching
process (quenching media).
The relationship between the resulting hardness of a material and the
quenching process is rooted in the transformation of the material's
microstructure. Quenching is a heat treatment process in which a material,
typically metal, is rapidly cooled from a high temperature (above its critical
temperature) to lock in certain microstructural changes. This rapid cooling
significantly impacts the hardness and other mechanical properties of the
material.
4.
Define the relationship between hardness, quenching media and cooling rates.
Different quenching media will affect the hardness of the carbon steels undergoing
heat treatments.The higher the heat conduction rate of the quenching media, the
faster the cooling rate of the treating carbon steels. The faster the cooling rates of
the treating carbon steels, the harder the strength of the treated carbon steels.
QUESTIONS
1.
Explain the heat treatment terms below:
a. Annealing.
Annealing is a type of heat treatment that is primarily used to make materials
more ductile and less hard. The reduction of dislocations in the annealed
material's crystal structure causes this shift in hardness and ductility. After a
material has gone through a cold working or hardening process, annealing is
frequently done to keep it from breaking easily or to make it more pliable for
further processes.There are three main stages to an annealing process which
are recovery stage,recrystallization stage and grain growth stage.
b. Normalizing.
A metal is heated to a certain temperature, held there for a while, and then cooled
to room temperature as part of the normalizing heat treatment process. The
mechanical qualities of metals, including their ductility, toughness, and hardness,
are enhanced by this technique. After undergoing mechanical or thermal
hardening procedures, normalizing is used to enhance the mechanical
characteristics of metals.
c. Tempering.
The heat treatment technique known as tempering, or drawing, involves heating
the components and maintaining them at a specific temperature below the critical
point for a predetermined amount of time. After that, the parts are allowed to cool
in still air to room temperature. The tempering process modifies the metal's
undesired mechanical properties to better suit the intended use, much as other
heat treatment procedures like annealing and normalizing.
2.
What are applications and relative usage of heat-treated plain carbon steel?
Why are they often utilized in such an area?
Heat-treated plain carbon steels are widely used in various applications due to
their enhanced mechanical properties achieved through heat treatment. Here
are the applications and relative usage:
Applications:
1. Automotive Industry: Components like gears, crankshafts, and axles utilize
heat-treated plain carbon steels for strength, wear resistance, and durability.
2. Construction: Tools, reinforcement bars, and structural components benefit
from their high strength and toughness.
3. Cutting Tools: Heat-treated carbon steels are used in manufacturing blades,
drill bits, and chisels due to their hardness and edge retention.
4. Industrial Machinery: Shafts, springs, and fasteners employ these steels for
their ability to withstand high stress and fatigue.
Relative Usage:
Heat-treated plain carbon steels are frequently utilized in applications requiring
a balance between cost-effectiveness and specific mechanical properties.
Their availability, ease of processing, and adaptability make them a preferred
choice for medium- to high-strength applications.
Reasons for Utilization:
1. Cost-Effectiveness: Plain carbon steels are relatively inexpensive compared to
alloy steels while providing satisfactory performance.
2. Customizable Properties: Heat treatment processes like annealing, quenching,
and tempering allow precise control over hardness, toughness, and ductility.
3. Versatility: They can be tailored to suit a wide range of applications, making
them an all-purpose material.
4. Good Strength-to-Weight Ratio: They offer sufficient strength without excessive
material usage, making them efficient for various industries.
This combination of properties and affordability explains their frequent use in
industrial and commercial applications.
3.
How are steels classified according to:
a. Carbon content?
Based on its carbon content, steel is divided into four classes. With a carbon
content of 0.05% to 0.25%, low carbon steel is renowned for its exceptional
weldability, high ductility, and comparatively low strength. It is frequently found
in pipelines, car body panels, and structural elements. With 0.25% to 0.60%
carbon, medium carbon steel offers a compromise between ductility and
strength. It is frequently utilized in railway tracks, axles, shafts, and gears and
can be heat treated for better mechanical qualities. High carbon steel is perfect
for cutting tools, springs, and high-strength wires since it has a high strength and
hardness but a low ductility due to its 0.60% to 1.25% carbon content. Last but
not least, ultra-high carbon steel has a carbon concentration of more than 1.25%,
making it extremely hard and brittle and ideal for specialized uses such as dies,
punches, and blades.
b. Alloy content?
Steel is categorized as plain carbon, low-alloy, high-alloy, and tool steels
according to the alloying components. Plain carbon steel is appropriate for
general-purpose structural and engineering applications because it has few
alloying elements and primarily depends on its carbon content for its qualities.
Low-alloy steel, which has a total alloy percentage of less than 8%, is frequently
used in pressure tanks, pipelines, and automobile parts because it provides
improved strength, toughness, and corrosion resistance. High-alloy steel, on the
other hand, is distinguished by its remarkable resistance to corrosion, heat, and
wear and contains more than 8% alloying elements. One prominent example is
stainless steel, which is utilized in high-temperature applications and medical
devices. Tool steel offers remarkable hardness and wear resistance by
combining a high carbon content with several alloying metals including tungsten,
chromium, and vanadium. These are frequently used to cut dies, molds, and
tools.
4.
Distinguish between proeutectoid ferrite and eutectoid ferrite.
Proeutectoid Ferrite
Eutectoid Ferrite
Composition
Made up of alpha-ferrite,
which has an extremely poor
solubility in carbon.
Found in pearlite, which
alternates in a lamellar
structure with cementite.
Formation
Forms in hypoeutectoid steels
when austenite cools to a
temperature greater than
eutectoid (727°C).
When austenite passes
through the eutectoid
transition, it forms at the
eutectoid temperature.
Microstructure
Before eutectoid transition, it
manifests as networks or
patches
along austenite grain
boundaries.
Exists in the structure as
cementite layers that alternate
with pearlite.
Characteristics Soft and ductile, it increases
hypoeutectoid steels'
hardness.
Contributes strength and
robustness to the pearlite's
microstructure.
Function
Reduces the carbon content
of austenite to get it ready for
the eutectoid transition.
Improves steel's mechanical
properties by forming pearlite
through a combination with
cementite.
Occurrence
Found in hypoeutectoid steels
Found in eutectoid steel or
structures containing pearlite.
5.
Name two thermal properties of a liquid that will influence its quenching
effectiveness?
Good heat conductors, which increase the cooling rate by promoting quick heat
dissipation from the quenched material, are thermal characteristics of a liquid that
have a major impact on its quenching effectiveness.The quantity of heat energy
needed to increase a unit mass of liquid's temperature by 1°C is known as its specific
heat capacity.Because it can absorb more heat before its temperature increases
substantially, a liquid with a high specific heat capacity can cool down during
quenching more efficiently.
CONCLUSION
The carbon steel treated in oil as the quenching medium achieves the highest HRC
value and hardness compared to the carbon steel treated in water, and followed
by carbon steel treated in air. Overall, the HRC value of oil and water quenched
carbon steels are higher than the HRC value of air quenched and as-received
carbon steels.The difference in the HRC value determines the mechanical strength
of the carbon steels.
REFERENCES
https://www.wisoven.com/support/technical-information/heat-treating-definitions
Classification & Types of Steel: The Ultimate Guide | MachineMFG
https://www.jswonemsme.com/blogs/blogs-articles/importance-of-carbon-content-insteel-for-industrial-applications