MANUFACTURING LAB-1 (ME-207)
TITLE: Heat treatment of mild steel.
OBJECTIVE:
1. To understand various heat treatment processes.
2. Performing certain amount of cold work to investigate effect of different heat treatment
processes on mechanical properties of material.
3. Heat treatments to be performed are: Annealing, Normalizing and Quenching.
4. Demonstration of hardness measurement.
MATERIAL REQUIRED:
1. Mild Steel
2. Electric furnace
5. Hardness testing machine
3. Cutoff machine
4. Other tools
4. Anvil and Hammer
EXPERIMENTAL PROCEDURE:
1. Mild steel rod is cut into 6 pieces using chop saw machine.
2. Fix amount of cold work is done on each specimens using hammer and anvil.
3. Keep one sample for the reference and the others will go through different heat
treatment processes (based on their type of cooling and soaking time).
Heat Treatment Processes:


Each specimen (5) is heated to 950˚C in the furnace with different soaking time
(30min and 60min).
Take out the specimens and cool it with different cooling methods (very slow,
normal and fast).
Cooling method
Cooling rate
Procedure
Annealing
very slow
Specimen is cooled in the furnace.
Normalizing
slow
Specimen is cooled in open air.
Quenching
Fast
Specimen is cooled in cold water.
4. After cooling down, specimens will undergo hardness measurement (including the
reference specimen).
Hardness Measurement:
Indentation Hardness is measured using Rockwell Hardness method (macro-hardness)
Indenter used is diamond cone and scale used is A-scale.

Specimen is put on the hardness testing machine and a minor force is applied on
it through the indenter.



Major force is applied and indentation depth is measured after removing the
major load but keeping the minor force.
Using the indentation depth, Rockwell hardness (HRA) is calculated and shown
on the screen of the machine.
These steps are done multiple times at different locations of the specimen and
average of these HRAs is noted down for each specimen.
RESULTS AND DISCUSSION:
Initial thickness of specimens = 16mm
Thickness after cold work
= 12.8mm
S.No.
Cold
work
Heat
Temperature
(˚C)
Soaking
Time
(minute)
Type of
Cooling
Process Type
Average HRA
calculated
1.
Yes
950
--
--
Cold work
70.4
2.
Yes
950
30
Furnace
Annealing
61.16
3.
Yes
950
30
Air
Normalizing
55.18
4.
Yes
950
60
Air
Normalizing
63.36
5.
Yes
950
30
Water
Quenching
56.78
6.
Yes
950
60
Water
Quenching
67.20
As we can see here, all these processes have reduced the hardness of the steel to a particular
point compared to the cold work specimen.




When we increase the soak time of the specimen, the hardness of it has increased as
well which indicates the relation between these factors.
Hardness is decreased in annealing as this process refines the grain sizes and eliminate
the non-uniformity & gas contents.
The results have shown that the hardness of annealed specimen is higher than that of
quenched or normalized specimen. But as we know that quenching and normalizing
usually increases the hardness of the material, this proves that our result is not
accurate.
The reason for the error is that the composition of the material is not known to us, the
machine was not calibrated properly due to the covid lockdown and also the cold work
was done manual which doesn’t provided us uniformity to our specimen.
LEARNINGS FROM THE EXPERIMENT:


We have learned that choosing different cooling method can significantly change certain
factors in the material i.e.
1. Hardness and toughness
2. Internal stresses
3. Microstructure and composition of the material
Hardness testing of the material can be done on a microscopic level as well as
macroscopic level. Both of these have different methods and approaches.