MFET 3451 -Materials Engineering
Lab # 5 Surface Hardening( Flame)
BRITTLE-DUCTILE TRANSITION IN STEEL
Instructions:
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You will be given five steel samples
Austenize 5 samples
Perform hardness and impact testing on all the steel samples
Part 1: Quenching process of austenized samples
Sample 1: Quench the austenized sample in RT water
Sample2: Remove a Second specimen and place it on a ceramic brick and allow it to
cool in air (Normalized).
Sample 3: Anneal the 3rd sample inside the furnace
Sample 4: Tempering 4th sample
Sample 5: Quench the austenized sample in hot oil
Part 2: Hardness testing
Perform hardness testing using Rockwell hardness tester and determine the hardness value of the
samples.
Part 3: Fracture Analysis
Analyze the fractured surface for each specimen to identify the type of fracture. Evaluate the
resulting microstructures, fracture mode, and fracture strength as they relate to the
heat treatment of the steels.
Results must include the comparison of mechanical properties of untreated and treated steel samples.
Explain ductile-brittle transition in the samples.
1
Some definitions (Figure 1):
1. Heat treating is a process in which steel is subjected to high temperatures to
modify its properties.
2. 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 1400° F. The austenizing temperature is also called critical
temperature.
3. 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.
4. 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 or oil.
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.
Report (Due on
):Please submit a report which can follow format of the
lab. Report guidelines. One report per student will be submitted.
Steel samples:
2
3