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>.