Faculty of Engineering

University of Kragujevac

Seminar work

Theme:

Carbon Steel

Professor: Student:

Dr Sandra Stefanovic Tomica Mutavdzic 11/2015

Kragujevac, 2015

1

Contents

1. Foreword ........................................................................................................... 2

2. Carbon steel ....................................................................................................... 3

3. Material Properties ............................................................................................ 5

4. Heat treatment of carbon steel .......................................................................... 7

5. Modern steel making ......................................................................................... 9

5.1. Wootz steel and domascus way .................................................................. 9

5.2. Bessemer converter ................................................................................... 10

5.3. Siemens-Martin steel ................................................................................ 11

6. Conclusion ...................................................................................................... 12

7. Literature ......................................................................................................... 13

2

Foreword

In this seminar work I choose theme ,,Carbon steel”. Reason beacuse I

choose this theme is this:

Carbon steel is one of the most important steel in The World. Of course there is

much more steels, but I choose this one.

In introduction of “Carbon steel” you will see what is carbon steel, in which

five classes is broken down based on carbon content.

Then you will see material properties of carbon steel, and one phase diagram

that describe the conditions necessary to form different phases, and you will see

some methods of modern steel making.

At the end of this seminar, you will see what literature I used.

3

Carbon steel

Carbon steel, also called plain-carbon steel, is steel where the main interstitial

alloying constituent is carbon. We can define carbon steel as: Steel that is considered to be

carbon steel when no minimum content is specified or required for chromium, cobalt,

molibdenum, nickl, niobium, titanium, tungsten, vanadium or zirconium, or any other

element to be added to obtain a desired alloying effect. When the specified minimum for

copper does not exceed 0.40 percent or when the maximum content specified for any of the

following elements does not exceed the percentages noted: manganese 1.65, silicon 0.60,

copper 0.60 (Amsterdam University, 2010).

The term „carbon steel― may also be used in reference to steel which is not stainless steel, in

this use carbon steel may include alloy papers (Amsterdam University, 2010).

As the carbon content rises, steel has the ability to become harder and stronger throught heat

treating and this also makes it less ductile. Regardless of the heat treatment, a higher carbon

content reduces weldability. In carbon steels, the higher carbon content lowers the melting

point (Amsterdam University, 2010).

Carbon steel is broken down in to five classes based on carbon content:

Low carbon steel:

Low carbon steels suffer from yield-point runout where the material has two yield

points. The first yield point (or upper yield point) is higher than the second and the yield

drops dramatically after the upper yield point. If a low carbon steel is only stressed to some

point between the upper and lower yield point then the surface may develop Luder bands

(Amsterdam University, 2010).

Mild carbon steel:

Mild carbon steel is the most common form of steel because its price is relatively low

while it provides material properties that are acceptable for many applications. Low carbon

steel contains approximately 0.05–0.25% carbon and mild carbon steel contains 0.16–0.29%

carbon; there fore, it is neither brittle nor ductile. Mild steel has a relatively low tensile

strength, but it is cheap and malleable; surface hardness can be increased through carburizing.

It is often used when large quantities of steel are needed, for example as structural steel

(Amsterdam University, 2010).

4

Higher carbon steels:

Carbon steels which can successfully undergo heat-treatment have a carbon content in

the range of 0.30–1.70% by weight. Trace impurities of various other elements can have a

significant effect on the quality of the resulting steel. Trace amounts of sulfur in particular

make the steel red-short. Low alloy carbon steel, such as A36 grade, contains about 0.05%

sulfur and melts around 1426–1538°C. Manganese is often added to improve the

hardenability of low carbon steels. These additions turn the material into a low alloy steel by

some definitions, but main definition of carbon steel allows up to 1.65% manganese by

weight (Amsterdam University 2010).

Medium carbon steel:

Approximately 0.3–0.6% carbon content. Balances ductility and strength and has

good wear resistance, used for large parts, forging and automotive components (Amsterdam

University, 2010).

High carbon steel:

Approximately 0.6–1% carbon content. Very strong, used for springs and high-

strength wires (Amsterdam University, 2010).

Ultra-high carbon steel:

Approximately 1–2 % carbon content. Steels that can be tempered to great hardness.

Used for special purposes like knives, axles or punches. Most steels with more than 1.2%

carbon content are made using powder metallurgy. Note that steel with a carbon content

above 2.1% is considered cast iron (Amsterdam University, 2010).

5

Material Properties

Iron is found in the Earth's crust only in the form of an ore, i.e., combined with other

elements such as oxygen or sulfur (Amsterdam University, 2010). Typical iron-containing

minerals include Fe2O3—the form of iron oxide found as the mineral hematite, and FeS2—

pyrite (Amsterdam University, 2010). Iron is extracted from ore by removing oxygen and

combining the ore with a preferred chemical partner such as carbon. This process, known as

smelting, was first applied to metals with lower melting points, such as tin, which melts at

approximately 250 °C and copper, which melts at approximately 1,100 °C (Amsterdam

University, 2010). In comparison, cast iron melts at approximately 1,375 °C. All of these

temperatures could be reached with ancient methods that have been used since the Bronze

Age (Amsterdam University, 2010). Since the oxidation rate itself increases rapidly beyond

800 °C , it is important that smelting take place in a low-oxygen environment. Unlike copper

and tin, liquid iron dissolves carbon quite readily. Smelting results in an alloy containing too

much carbon to be called steel. The excess carbon and other impurities are removed in a

subsequent step (Amsterdam University, 2010).

Iron-carbon phase diagram (Amsterdam University, 2010), showing the conditions necessary

to form different phases:

Nickel and manganese in steel add to its tensile strength and make austenite more chemically

stable, chromium increases hardness and melting temperature, and vanadium also increases

hardness while reducing the effects of metal fatigue (Amsterdam University, 2010). To

prevent corrosion, at least 11% chromium is added to steel so that a hard oxide forms on the

6

metal surface; this is known as stainless steel. Tungsten interferes with the formation of

cementite, allowing martensite to form with slower quench rates, resulting in high speed

steel. On the other hand, sulfur, nitrogen, and phosphorus make steel more brittle, so these

commonly found elements must be removed from the ore during processing. Even in the

narrow range of concentrations which make up steel, mixtures of carbon and iron can form a

number of different structures, with very different properties (Amsterdam University, 2010).

Understanding such properties is essential to making quality steel. At room temperature, the

most stable form of iron is the body-centered cubic (BCC) structure a-ferrite. It is a fairly soft

metallic material that can dissolve only a small concentration of carbon, no more than 0.021

% at 723 °C , and only 0.005% at 0 °C (Amsterdam University, 2010).

When steels with less than 0.8% carbon, known as a hypoeutectoid steel, are cooled from an

austenitic phase the mixture attempts to revert to the ferrite phase, resulting in an excess of

carbon (Amsterdam University, 2010). One way for carbon to leave the austenite is for

cementite to precipitate out of the mix, leaving behind iron that is pure enough to take the

form of ferrite, resulting in a cementite-ferrite mixture. Cementite is a hard and brittle

intermetallic compound with the chemical formula of Fe3C (Amsterdam University, 2010).

At the eutectoid, 0.8% carbon, the cooled structure takes the form of pearlite, named after its

resemblance to mother of pearl. For steels that have more than 0.8% carbon the cooled

structure takes the form of pearlite and cementite (Amsterdam University, 2010).

Perhaps the most important polymorphic form is martensite, a metastable phase which is

significantly stronger than other steel phases (Amsterdam University, 2010). When the steel

is in an austenitic phase and then quenched it forms into martensite, because the atoms

"freeze" in place when the cell structure changes from FCC to BCC. Depending on the

carbon content the martensitic phase takes different forms. Below approximately 0.2%

carbon it takes an a ferrite BCC crystal form, but higher carbon contents take a body-centered

tetragonal (BCT) structure (Amsterdam University, 2010).

7

Heat treatment of carbon steel

The purpose of heat treating carbon steel is to change the mechanical properties of

steel and his copability to be more usefull, usually ductility, hardness, yield strength, or

impact resistance (Bowman B. and Lefrank P. 1998). Note that the electrical and thermal

conductivity are slightly altered. As with most strengthening techniques for steel, Young's

modulus is unaffected. Steel has a higher solid solubility for carbon in the austenite phase.

There fore all heat treatments, except spheroidizing and process annealing, start by heating to

an austenitic phase (Bowman B. and Lefrank P. 1998). The rate at which the steel is cooled

through the eutectoid reaction affects the rate at which carbon diffuses out of austenite.

Generally speaking, cooling swiftly will give a finer pearlite (until the martensite critical

temperature is reached) and cooling slowly will give a coarser pearlite.

Here is a list of the types of heat treatments possible:

Spheroidite:

Spheroidite forms when carbon steel is heated to approximately 700 °C for over 30

hours. Spheroidite can form at lower temperatures but the time needed drastically increases,

as this is a diffusion-controlled process. The result is a structure of rods or spheres of

cementite within primary structure (ferrite or pearlite, depending on which side of the

eutectoid you are on) (Bowman B. and Lefrank P. 1998).

Full annealing:

Carbon steel is heated to approximately 40 °C above Ac3 or Ac1 for 1 hour; this

assures all the ferrite transforms into austenite (although cementite might still exist if the

carbon content is greater than the eutectoid). The steel must then be cooled slowly, in the

realm of 38°C per hour. Usually it is just furnace cooled, where the furnace is turned off with

the steel still inside. This results in a coarse pearlitic structure, which means the bands of

pearlite are thick (Bowman B. and Lefrank P. 1998).

Process annealing:

A process used to relieve stress in a cold-worked carbon steel with less than 0.3 % C.

The steel is usually heated up to 550–650 °C for 1 hour, but sometimes temperatures as high

as 700 °C (Bowman B. and Lefrank P. 1998).

8

Isothermal annealing:

It is a process in which hypoeutectoid steel is heated above the upper critical

temperature and this temperature is maintained for a time and then the temperature is brought

down below lower critical temperature and is again maintained. Then finally it is cooled at

room temperature. This method rids any temperature gradient (Bowman B. and Lefrank P.

1998).

Normalizing:

Carbon steel is heated to approximately 55 °C above Ac3 or Acm for 1 hour; this

assures the steel completely transforms to austenite. The steel is then air-cooled, which is a

cooling rate of approximately 38 °C per minute. This results in a fine pearlitic structure, and a

more-uniform structure. Normalized steel has a higher strength than annealed steel; it has a

relatively high strength and ductility (Bowman B. and Lefrank P. 1998).

Quenching:

Carbon steel with at least 0.4 wt% C is heated to normalizing temperatures and then

rapidly cooled (quenched) in water, brine, or oil to the critical temperature. The critical

temperature is dependent on the carbon content, but as a general rule is lower as the carbon

content increases. This results in a martensitic structure (Bowman B. and Lefrank P. 1998).

Martempering:

Martempering (Marquenching): Martempering is not actually a tempering procedure,

hence the term "marquenching". It is a form of isothermal heat treatment applied after an

initial quench of typically in a molten salt bath at a temperature right above the "martensite

start temperature". At this temperature, residual stresses within the material are relieved and

some bainite may be formed from the retained austenite which did not have time to transform

into anything else (Bowman B. and Lefrank P. 1998).

Quench and tempering:

This is the most common heat treatment encountered, because the final properties can

be precisely determined by the temperature and time of the tempering. Tempering involves

reheating quenched steel to a temperature below the eutectoid temperature then cooling

(Bowman B. and Lefrank P. 1998).

9

Modern steel making

There is a several ways to make a steel:

1. Wootz steel and domascus way

2. Besemers way

3. Simmens-Martins way

Wootz steel and domascus way

Evidence of the earliest production of high carbon steel in the Indian Subcontinent

was found in Samanalawewa area in Sri Lanka. Wootz steel was produced in India by about

300 BC. Along with their original methods of forging steel, the Chinese had also adopted the

production methods of creating Wootz steel, an idea imported into China from India by the

5th century AD (Encyclopedia Britannica, 2005). In Sri Lanka, this early steel-making

method employed the unique use of a wind furnace, blown by the monsoon winds, that was

capable of producing high-carbon steel. Also known as Damascus steel, wootz is famous for

its durability and ability to hold an edge. It was originally created from a number of different

materials including various trace elements. It was essentially a complicated alloy with iron as

its main component. Recent studies have suggested that carbon nanotubes were included in

its structure (Encyclopedia Britannica, 2005), which might explain some of its legendary

qualities, though given the technology available at that time, they were produced by chance

rather than by design. Natural wind was used where the soil containing iron was heated up

with the use of wood. The ancient Sinhalese managed to extract a ton of steel for every 2 tons

of soil[citation needed], a remarkable feat at the time. One such furnace was found in

Samanalawewa and archaeologists were able to produce steel as the ancients did long ago

(Encyclopedia Britannica, 2005).

Crucible steel, formed by slowly heating and cooling pure iron and carbon (typically in the

form of charcoal) in a crucible, was produced in Merv by the 9th to 10th century AD. In the

11th century, there is evidence of the production of steel in Song China using two techniques:

a "berganesque" method that produced inferior, inhomogeneous steel and a precursor to the

modern Bessemer process that utilized partial decarbonization via repeated forging under a

cold blast (Encyclopedia Britannica, 2005).

10

Bessemer converter

Since the 17th century the first step in European steel production has been the

smelting of iron ore into pig iron in a blast furnace. Originally using charcoal, modern

methods use coke, which has proven to be a great deal cheaper (Encyclopedia Britannica,

2005).

In these processes pig iron was "fined" in a finery forge to produce bar iron (wrought iron),

which was then used in steel-making. The production of steel by the cementation process was

described in a treatise published in Prague in 1574 and was in use in Nuremberg from 1601.

A similar process for case hardening armour and files was described in a book published in

Naples in 1589 (Encyclopedia Britannica, 2005).

The process was introduced to England in about 1614. It was produced by Sir Basil Brooke at

Coalbrookdale during the 1610s. The raw material for this were bars of wrought iron

(Encyclopedia Britannica, 2005).

During the 17th century it was realised that the best steel came from oregrounds iron from a

region of Sweden, north of Stockholm. This was still the usual raw material in the 19th

century, almost as long as the process was used. Crucible steel is steel that has been melted in

a crucible rather than being forged, with the result that it is more homogeneous. Most

previous furnaces could not reach high enough temperatures to melt the steel. The early

modern crucible steel industry resulted from the invention of Benjamin Huntsman in the

1740s. Blister steel (made as above) was melted in a crucible or in a furnace, and cast

(usually) into ingots (Encyclopedia Britannica, 2005).

Picture 1. (Encyclopedia Britannica, 2005) Picture 2. (Encyclopedia Britannica, 2005)

11

Siemens-Martin steel

White-hot steel pouring out of an electric arc furnace. The modern era in steelmaking

began with the introduction of Henry Bessemer's Bessemer process in 1858 (Encyclopedia

Britannica, 2005). His raw material was pig iron. This enabled steel to be produced in large

quantities cheaply, thus mild steel is now used for most purposes for which wrought iron was

formerly used. The Gilchrist-Thomas process (or basic Bessemer process) was an

improvement to the Bessemer process, lining the converter with a basic material to remove

phosphorus (Encyclopedia Britannica, 2005). Another improvement in steelmaking was the

Siemens-Martin process, which complemented the Bessemer process.

These were rendered obsolete by the Linz-Donawitz process of basic oxygen steelmaking

(BOS), developed in the 1950s, and other oxygen steelmaking processes. Basic oxygen

steelmaking is superior to previous steelmaking methods because the oxygen pumped into the

furnace limits impurities (Encyclopedia Britannica, 2005). Now, electric arc furnaces (EAF)

are a common method of reprocessing scrap metal to create new steel. They can also be used

for converting pig iron to steel, but they use a lot of electricity (about 440 kWh per metric

ton), and are thus generally only economical when there is a plentiful supply of cheap

electricity (Encyclopedia Britannica, 2005).

Picture 3. (Encyclopedia Britannica, 2005)

12

Conclusion

Well, at the end of this seminar work I will tell you that I choose this theme because it’s very

common in mechanical engineering and we learned some things about Carbon steel, like :

Carbon steel is one of the most important steel in The World.

Carbon steel is: Steel that is considered to be carbon steel when no minimum content is

specified or required for chromium, cobalt, molibdenum, nickl, niobium, titanium, tungsten,

vanadium or zirconium, or any other element to be added to obtain a desired alloying effect.

This steel is broken down in to five classes based on carbon content, and there is a several

ways to make a steel, etc.

13

Literature:

- Amsterdam University (2010), Huge archive of steels, Amsterdam

- Bowman B. and Lefrank P. (1998), Electric Furnace Steelmaking,

The AISE Steel Foundation, Pittsburgh

- Encyclopedia Britannica (2005), Simmens-Martins process 2,

Encyclopedia Britannica Inc. , Chicago

- Encyclopedia Britannica (2005), Bessemer process 2,

Encyclopedia Britannica Inc. , Chicago