Dominic Waldorf (MSE 250 Term Paper)
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Transcript of Dominic Waldorf (MSE 250 Term Paper)
Increasing MaterialsPerformance to Increase
Sustainability
Dominic WaldorfDecember 4th, 2012
MSE 250Section 2
PID: A44658174
Carl Boehlert Maddalena Fanelli
Harsha Phukan
Abstract
Within the last couple centuries, steel has played a large role in our society. Made from iron, steel
is one of the most used materials in the world. However, there have been many issues with the
performance of steel and how long it lasts. Scientists have found many ways to treat steel so that it last
longer and has the right qualities for the job it is being used for. It is important to learn more about steel
because if more is discovered about steel, then companies will be able to find different applications with
steel and there is potential to conserve time and money in countless industry.
Introduction
It is important to have knowledge about steel and its various identities because it is what makes the
world function on an industrial scale. In every day life, societies encounter many different forms of steel.
The average person would never guess how many experiments and how much engineering was put into all
of the products of steel. Tools like hammers, saws, and wrenches have had their microstructure
manipulated in order to have the desired use of the tool. The steel used goes through many different
procedures in order to have the right amount of hardness, ductility, and strength.
Since the dawn of the Iron Age, steel has been analyzed and broken down in order to figure out
every little detail of its composition. There are even phase diagrams that have been made to help better
understand the properties of steel. As technology has significantly increased, so has the ability to learn
more about this amazing material. Because of the invention of the microscope and the electron
microscope, scientists have been able to analyze the microstructure of steel to obtain a better
understanding of the metal. Having the ability to change the microstructure of steel makes it so steel can
be used for many different applications rather than just basic uses centuries ago. The objective of this
paper is to give the reader a better understanding of the steel and how to increase the performance of steel
giving it better sustainability.
Background
Strength of Steel: Steel was discovered back in the 13th century BC. Scientists have come a long way
since then with the fundamentals of steel. Through many experiments, we have discovered that the higher
the composition of carbon in steel, the harder and less ductile the steel becomes. This was very helpful for
construction because if the architects were building a structure that needed very strong steel, they would
use steel that had a very high carbon composition. However, if the architect wanted to save money and
did not need very strong steel, then he would use a steel with a lower carbon composition. For example,
the architect would use 1018 steel instead of 1080 steel because the 1018 only has .18 % C instead of .8%
C.
Heat Treatment: In more recent years, scientist began to analyze the phase shifts of steel at different
compositions of carbon. They could then manipulate the microstructure to change the hardness and
ductility of the steel by changing the cooling rates of the steel. Being able to do this was ground breaking
because steel can have many different applications in different areas of use. This process is done by
heating above the austenitizing temperature then cooling it. Putting the steel through this phase is known
as a eutectoid reaction. Martensite is the hardest product that can be created during this process. It is
when the austenite is quenched very rapidly in water. The microstructure changes and consists of mostly
cementite. This form is used to make tools like hammers. If the steel of a hammer ever breaks a piece is
chipped off rather than bent and broken. The reason behind this is because the martensite is very brittle
and hard, and has low ductility and is not malleable. If the steel is desired to be a little less hard and more
ductile than the martensite, it can be tempered which is reheating and cooling the steel another time.
Bainite is another result that can be obtained from heat treatment. Instead of having a rapid cooling in
water, the austenite is cooled in oil. As the austenite cools, a mixture of ferrite and longer strands of
cementite form. The microstructure becomes more equiaxed (ferrite) and has needle like strands
(cementite) in between the grain boundaries of the ferrite. Bainite is used when making parts for cars in
the automotive industry. The process saves the industry lots of money. An example is when the industry
is making a part like the camshaft. The desired outcome of the camshaft is to have the steel used to make
it be less hard and more ductile then the martensite. Before they would temper the martensite that would
make them have to heat the steel twice. Now they just cool the austenitized steel slower in order to form
bainite. Therefore, the industry saves money because heating the steel twice cost makes them use more
time and energy to create the product desired. Another product that can be forms when putting the
austenitized steel through a eutectoid reaction is fine or coarse pearlite. Fine pearlite forms when air-
cooled. The fine pearlite mainly consists of ferrite, which is equiaxed. Coarse pearlite is cooled even
slower than the fine pearlite. The austenitized steel is cooled in a furnace. The microstructure is equiaxed
with fine fibers in between the grain boundaries. The coarse pearlite is more ductile and not as strong as
the fine pearlite. Steel that is heat treated into pearlite has many applications. For example, handsaws are
made with pearlite. Since the saw is more ductile, it has the ability to bend back and forth without
breaking. Nails are also one of the products of having the ability to form pearlite. There are many
different ways to go about changing the microstructure. One very effective method is by using heat
treatment. This process has been used for centuries, and is still used in our society today.
Method and Materials
In order to perform the austenitizing heat treatment, the steel must be heated to austenitizing
temperature (above 723 degrees C). Depending on what type of results desired, there are many different
ways to cool the austenite. If martensite is desired, the austenite must be cooled rapidly. Quenching the
austenite in water is the most efficient way to transform the austenite into martensite. After quenching,
the martensite will form and will have a needle like looking microstructure. The steel will now be very
hard but will be very brittle and no ductile.
Creating bainite is a different procedure. The austenite must be quenched at slower cooling rate.
Quenching the austenite in oil is the best way to form bainite. The resulting product is a mixture between
pearlite and martensite which ferrite with long cementite particles. This will be a even mix of strong and
ductile material.
Taking the austenite, and letting the hot metal air cool create fine pearlite. The pearlite is very
ductile but not very hard. It is a more malleable product of the austenite. The microstructure has an
equiaxed microstructure. Coarse pearlite is cooled in a furnace. This is more ductile and less hard than
the fine pearlite. The microstructure is equiaxed with needle like fibers inside.
Fine Pearlite
Coarse Pearlite
This is the desired microstructure of martensite. The martensite has a BCT crystal structure. The
martensite consists of mostly cementite. The cementite is what makes the steel so strong.
The image above is the microstructure of bainite. As you can see it has a mix between ferrite and
long chains of cementite. The mixed of the two give the product a good amount of strength and ductility.
The fine pearlite in the image above on the right is completely equiaxed. The product is ductile
but not very strong. It consists of ferrite and layer of cementite. The image on the left is the coarse
pearlite. It is more ductile but not as hard as the fine pearlite. They are both malleable which means it can
flex more without breaking.
Data From Lab 9:
Hardness (Rockwell C)Alloy WQ OQ AC WQ-temp
1018 33 7.5 0 11
1045 49 22.5 9 27
1070 64.5 39.25 26.5 39.5
1080 52 50 38 32.5
1095 60 60.5 40 30.5
The data from lab 9 is evidence that the faster the steel is cooled, the harder the material becomes.
Also the higher the composition of carbon leads to a higher hardness. Another point to add is how the
hardness and ductility are inversely related. As hardness increases, the ductility of the steel decreases.
Discussion
The manipulation of the microstructure in steel has helped make our society run more effective and
efficient. The ability to make steel harder or softer and more or less ductile has made many new
applications of steel. For example, when the austenite is quenched, it forms martensite. This is what
hammers are made of so the when they hit the nail, so the hammer strike doesn’t lose energy to
deformation of the material. There are also many other applications, which were already discussed in
earlier sections of the paper. The process of Austenitizing Heat Treatment is just one way to manipulate
the microstructure that changes the ductility and hardness of the material. Other processes are cold work
reduction, annealing, age hardening, etc. All of these effectively achieve the goal changing the
microstructure. If there processes were never thought of, the quality of steel in everything would be a
very poor. There would be many more mishaps and injuries because of the failure of the steel. Further
research still needs to be developed for steel. This is because the society still has incidence of disaster
because of the failure of steel. For example, when the twin towers were hit by the jet aircrafts on
September 11th, 2001, many lives were lost because of the failure of steel. Although the towers were built
with steel that had a very high composition of carbon, the steel melted because of the heat given off by the
jet fuel igniting. This is one of the reasons for the towers falling and why so many lives were lost on that
tragic day. If scientists discovered how to change the microstructure of steel in ways that make it so it
austenitized at a higher temperature, we would not have such significant problems with steel failures.
Works Cited
Materials Science and Engineering: An Introduction 8th Edition
by David G. Rethwisch, William D. Callister Jr.
"Use of Bainitic Steels." The Bainite Reaction. N.p., n.d. Web. 04 Dec. 2012.
<http://www.msm.cam.ac.uk/phase-trans/bainitek.html>.
"What Are Martensites?" What Are Martensites? N.p., n.d. Web. 04 Dec. 2012.
<http://www.lassp.cornell.edu/sethna/Tweed/What_Are_Martensites.html>.