Project 6
MFET 3451 -Materials Engineering
EVALUATING THE EFFECT OF HEAT TREATMENT ON THE
MECHANICAL PROPERTIES OF STEEL
Instructions:
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Perform heat treatment on given steel samples
Perform quenching and normalizing treatments and …. on steel
Perform Hardness testing on the above samples
Perform Impact testing
Part I: Heat Treatment of steel
Some definitions (Figure 1):
1. Austenizing process is heating the steel to a temperature at which it forms
austenite (a mixture of cementite (carbon) and ferrite (iron)), which is
approximately 1600° F. The austenizing temperature is also called critical
temperature.
2. Annealing is a process heating the steel above upper critical temperature
and holding it until the composition is uniform. Then the steel is cooled very
slowly in the furnace below the lower critical temperature. This process
produces soft, low strength form of the material, free of internal stresses.
3. Normalizing is similar to annealing, but the steel is heated to a temperature
above the transformation range where austenite is formed approximately
(1600° F or 870°C).
This process results in a uniform internal structure in the steel and higher
strength steel compared to annealed steel.
5. Quenching is a process of heating steel to high temperatures and rapidly
cooling in a quenching medium like water and Liquid Nitrogen
The rapid cooling causes the formation of martensite, the hard strong form
of steel.
6. Tempering involves reheating the quenched steel to a temperature of 400°F
to 1300°F (200°C - 700°C) and then slowly cooling it in air back to room
temperature. Tensile strength and yield strength decrease with increase of
tempering temperature but ductility improves.
Part II: Mechanical Testing of steel
A) Hardness testing
Perform hardness testing using Rockwell hardness tester and determine the hardness value of the
samples.
B) Impact testing
Perform impact testing using Charpy’s impact tester and determine the impact values of the
samples.
I. OBJECTIVES:
The objectives of this activity are:
(1) to study, observe, and experiment with impact testing of various common materials;
(2) to develop skills in performing commercially accepted impact tests on various materials;
(3) to interpret data and prepare a technical report.
II. BACKGROUND INFORMATION:
Impact tests are made on materials, particularly metals, because it is recognized that the resistance of some
materials to shock is dependent upon factors other than those which control its resistance to a steady or
slowly applied load. Resistance to a slowly applied load may be measured in terms of stress.
Tests of this sort find use as control tests of steels for special types of service. The impact values must be
judged, however, in relation to a given type of steel and not by themselves. Impact tests are sensitive to
variations in heat treatment, to alloy content, to sulfur or phosphorus content, and to environmental
conditions. They are used considerably in some industries. Some materials such as glass and sealing wax
are sensitive to the pendulum speed.
III.
PROCEDURES:
1. Measure and record the dimensions of the specimens.
2. Zero the friction pointer.
Note: This is done with the pendulum freely suspended.
3. Place the specimen accurately in position according to the type of test. (Charpy or Izod test)
4. Break the specimen by releasing the suspended load. Record the energy value required to break
5. The specimen and the type of surface at the break.
IV. RESULTS:
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The report of this activity should include the following:
Type and capacity of machine used.
Type and size of specimen used, including type of notch.
Energy absorbed by the specimen and energy lost to friction, in foot-pounds.
Striking velocity.
Shape of fractured surface and its texture.
Temperature of the specimen or of the room conditions if both are alike.
Number of specimens failing to break and causes of non fracture.
Results must include the comparison of mechanical properties of untreated and treated steel
samples.