Steel is a major construction material and has various application. Its properties and laboratory tests are discussed in brief.

1. CVL3211 : Civil Engineering Materials
Department of Civil Engineering
Abhipsa Kar
Pranjal Mandhaniya
Rashmisikha Behera
ITER, SoA University
November 7, 2016
1 / 7

2. CVL3211 : Civil Engineering Materials
Steel
Steel
This chapter will cover under given topics.
Properties of steel
Carbon equivalent
Iron-Carbon Phase diagram
Heat treatment
2 / 7

3. CVL3211 : Civil Engineering Materials
Properties and application of steel
Properties and application of steel
Steel is an alloy of iron and carbon, where maximum carbon
percentage is less than 2.
Steel is manufactured by adding manganese or/and silicon to molten
iron that reduce excess carbon as slag.
Carbon content in steel is directly proportional to hardness,
brittleness, melting point, corrosion resistance and inversely
proportional to toughness, softness, ductility, weldability.
Steel can be divided in three categories based on its carbon content:
Low carbon steel (0-0.4% carbon)
Medium carbon steel (0.4-0.8% carbon)
High carbon steel (0.8-1.2% carbon)
Another form of iron-carbon alloy is cast iron (2-4% carbon). It is
called so because it can be casted in any form easily but its brittleness
induced due to high carbon content cause it difficult in cold forming.
3 / 7

4. CVL3211 : Civil Engineering Materials
Physical behavior of steel
Physical behavior of steel
Steel shows strain-hardening behavior.
Stress-strain diagram of a cylindrical steel rod is given below based on
its testing in universal testing machine (UTM).
Elastic/proportional
limit
Yeild/necking
point
Rupture
point
Ultimate
strength
Stress
Strain
Ultrasonic testing is performed
on welds to check their
uniformity.
Other tests like torsion and
V-notch tests are also performed
to find out shear and hardness of
steel.
4 / 7

5. CVL3211 : Civil Engineering Materials
Carbon equivalent and weldability
Carbon equivalent and weldability
Effect of varying carbon content in steel effects its strength as shown in
figure below. It was also mentioned previously.
0 0.1
Strain
Stress,MPa
1,000
0
0.64%
0.49%
0.19%
Carbon 0.90%
800
600
400
200
0.2 0.3
Carbon equivalent is percentage
of alloyed metals equivalent to
the percent of carbon.
Ceq = %C + %Mn/6 + (%Cr +
%Mo + %V)/5+(%Ni +
%Cu)/15
Ceq is inversely proportional to
weldability of steel. As higher
carbon cause more hardness and
that affect ability to melt when
being welded.
5 / 7

6. CVL3211 : Civil Engineering Materials
Iron-Carbon phase diagram
Iron-Carbon phase diagram
Its study is useful for treatment of steel and to metallurgy of steel. It
critical to look and understand all transitions in this diagrams.
0
400
Percent weight of carbon
6.7
Liquid
Temperature,C
Upper critical
temperature
lines
Lower critical temperature line
2.11% 4.3%1148 C
0.77% 727 C
Liquid g
Liquid Fe3C
d Liquid
a Fe3C
g Fe3C
a, Ferrite
g, Austenite
d
g d
a g
100% Fe3C600
1 2 3 4 5 6
800
1000
1200
1400
1600
1539
1394
912
Maximum carbon content here
is 6.7%, at this point pure
cementite (Fe3C) exists in mix.
Critical temperature lines are
defined for transition from
phases of iron (α(BCC), γ(FCC)
and δ(BCC))
Maximum carbon content for
pure α is 0.022% and for pure γ
is 2.11%.
6 / 7

7. CVL3211 : Civil Engineering Materials
Heat treatment and cold formed shapes
Heat treatment and cold formed shapes
Four basic heat operation are used on steel to reform it for various
applications:
Annealing: Heating 500C above austenite line and cooling at
200C/hour till 6800C then air cooling/natural convection.
Normalizing: Heating 600C above austenite line and cooling by
natural convection.
Hardening/Quenching: Heating 500C above austenite line and rapid
cooling by quenching in water.
Tempering: Cooling hardened steel to 400C then reheating it by
immersion in oil. Natural air convection is used to cool later.
Controlled heating or cooling require more industrious setup and hence all
processes but annealing can be used by simple blacksmith.
7 / 7