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INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,
MANAGEMENT & APPLIED SCIENCE (IJLTEMAS)
ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XV, Issue III, March 2026
Effect of Heat Treatment on Microstructure and Hardness of Low
Carbon Steel
Manashvi S. Ghagre¹, Aayushi J. Rana¹, Jignasha Parmar²*, Dr. Vandana J Rao
3
¹B.E. Students, Department of Metallurgical and materials Engineering, [The maharaja Sayajirao
university], Baroda, India
²Assistant Professor, Department of Metallurgical and materials Engineering, [The maharaja Sayajirao
university], Baroda, India
³Associate Professor, Department of Metallurgical and materials Engineering, [The maharaja Sayajirao
university], Baroda, India
*Corresponding Author
DOI:
https://doi.org/10.51583/IJLTEMAS.2026.150300066
Received: 30 March 2026; Accepted: 04 April 2026; Published: 16 April 2026
ABSTRACT
Low carbon steel is widely used in structural and engineering applications due to its excellent formability and
weldability; however, its mechanical properties are highly dependent on microstructure. In the present study, the
influence of different heat treatment processes on the microstructure and hardness of low carbon steel was
investigated. Different heat treatment conditions, namely annealing, normalizing, conventional hardening (water
quenching), Neem Bath ,Ice Bath,Salt Bath,brine Bath quenching were applied. Metallographic analysis was
carried out using optical microscopy at magnifications of 100Ă— and 500Ă—. The results reveal significant variations
in phase distribution, grain size, and morphology due to different cooling rates. Fine pearlitic structures were
observed in normalized samples, whereas martensitic structures were dominant in quenched specimens.
Hardness values increased with increasing cooling rate, with brine-quenched samples showing maximum
hardness. The study establishes a clear correlation between heat treatment, microstructure, and hardness of low
carbon steel.
Keywords: Heat treatment, Normalizing, Annealing
INTRODUCTION
Mechanical properties of steels are strongly dependent on their microstructure, which can be controlled through
heat treatment processes. Heat treatment involves controlled heating and cooling operations to modify the
internal structure of materials without altering their chemical composition.
Low carbon steel (≤0.25% C) is extensively used in construction, automotive, and manufacturing industries due
to its low cost and high ductility. However, its relatively low hardness and wear resistance limit its applications
in severe environments.
The transformation of austenite into ferrite, pearlite or martensite depends on cooling rate and heat treatment
conditions. By selecting appropriate heat treatment techniques such as annealing, normalizing, quenching. it is
possible to tailor the microstructure and thereby enhance mechanical properties.
The present work focuses on:
Studying microstructural evolution under different heat treatments Comparing hardness variations Establishing
structure-property relationships
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INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,
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EXPERIMENTAL METHODOLOGY
Material
Material: Low carbon steel (TMT bar)
Composition: Use Spectroscopy
Sample Preparation for Metallography
Specimens cut 1 inch in size & has diameter of 20mm.
Grinding using SiC papers (220–1000 grit)
Polishing using diamond paste
Etching using 2% Nital
Heat Treatment Conditions
Table 1. Heat Treatment Conditions with respect to Cooling Medium
Sample
No
Heat
Treatment
Temperature (°C)
Holding
Time (min)
Cooling Medium
1
Annealing
940
60
Furnace cool
2
Normalizing
940
60
Air cool
3
Hardening
940
60
Neem Bath (121 gm of neem in 1L of water)
4
Hardening
940
60
Ice Bath (300gm of ice in 250ml of water)
5
Hardening
940
60
Salt Bath (38gm of salt in 1L of water)
6
Hardening
940
60
Brine Solution (125gm of salt, 45gm of dish-
wash, & 12.5gm of laundry detergent in 1L of
water)
Microstructure Observation
Figure 1: Annealing Sample
100X
Figure 2: Normalizing Sample
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INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,
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100X
500X
Figure 3: Hardening (Neem Bath)
100X
500X
Figure 4: Hardening (Ice Bath)
100X
500X
Figure 5: Hardening (Salt Bath)
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INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,
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100X
500X
Figure 6: Hardening (Brine Solution)
100X
500X
RESULTS AND DISCUSSION
Table 2. Chemical analysis of low carbon steel by spectroscopy
Element
Observed Value (%)
Carbon
0.213
Silicon
0.238
Manganese
0.627
Phosphorus
0.0275
Sulphur
0.0171
Table 3. Hardness value of heat Treatment Condition
Heat Treatment & Quenching Media
Average Hardness (HRC)
Furnace Cooling (Annealing)
11
Air Cooling (Normalizing)
13-14
Neem Bath
11.16
Ice Bath
43
Salt Bath
39.33
Brine Solution
27.91
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Graph 1: Hardness vs Quenching media
CONCLUSION
Neem bath quenching resulted in a refined ferrite–pearlite structure with fragmented cementite, indicating the
initiation of a partially bainitic structure.
Annealing and normalizing produced a uniform distribution of ferrite and pearlite, leading to a stable and
homogeneous microstructure.
Grai size Generally in annealing is 4 -5 and Normalizing Grain Size 6-8.
Quenching in brine solution and ice bath led to the formation of fine martensitic laths, contributing to higher
hardness.
Salt bath quenching resulted in a mixed microstructure of martensite and retained austenite.
The highest hardness was observed in ice bath quenched samples, while the lowest hardness was obtained in
annealed and neem bath.
REFRENCES
1. ASM Handbook, Volume 4: Heat Treating
2. Hardening Characteristics of Plain Carbon Steel and Ductile Cast Iron Using Neem Oil as Quenchant,
DOI: 10.4236/jmmce.2011.102011,
https://www.scirp.org/journal/paperinformation?paperid=20838&utm_source=chatgpt.com
3. Heat treatment - Principles & Techniques by T.V. Rajan
4. Metallographic Handbook by George F. Vander Voort.
5. Microscale & Macroscale Techniques in the Organic Laboratory by Mayo et al.
6. Physical metallurgy by Vijendra Singh.
7. Steels: Heat Treatment & Processing Principles by George Krauss.
5
10
15
20
25
30
35
40
45
50
Neem bath Brine Salt Bath Ice bath
Hardness Vs quenching media