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INTERNATIONAL JOURNAL OF LATEST TECHNOLOGY IN ENGINEERING,
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ISSN 2278-2540 | DOI: 10.51583/IJLTEMAS | Volume XV, Issue III, March 2026
“Study of Heat Treatment Variables on Microstructure and Mechanical
Properties of Aisi 4130 Low Alloy Steel’’
Jignasha Parmar
1
*, Dr. Vandana J Rao
2
1
Assistant Professor, Department of Metallurgical and materials Engineering, [The maharaja Sayajirao
university], Baroda, India
2
Associate Professor, Department of Metallurgical and materials Engineering, [The maharaja Sayajirao
university], Baroda, India
DOI:
https://doi.org/10.51583/IJLTEMAS.2026.150300101
Received: 27 March 2026; March: 02 April 2026; Published: 21 April 2026
ABSTRACT
The present study investigates the effect of heat treatment on the microstructure and mechanical properties of
AISI 4130 steel. The material was subjected to a sequence of normalizing, hardening, and tempering treatments
to evaluate the influence of tempering temperature on performance characteristics. Normalizing was carried out
at 890°C followed by air cooling, resulting in a refined ferrite–pearlite microstructure. Subsequently, hardening
was performed at 860°C and followed by quenching to obtain a martensitic structure.
Tempering was conducted at two different temperatures, 565°C (Sample A) and 655°C (Sample B), to study the
variation in mechanical behavior.
The results highlight that tempering temperature plays a critical role in tailoring the balance between strength
and toughness in AISI 4130 steel. This study provides useful insights for optimizing heat treatment parameters
for engineering applications requiring a combination of mechanical performance and structural reliability.
Keywords: Heat treatment, Normalizing, Hardening, Tempering
INTRODUCTION
In this modern world we come across various engineering materials, but when these materials are scrutinized,
we find that steel remains predominant. Steel has provided modern engineer the leverage to tailor engineering
components ranging from a small nut to huge skyscrapers. Amongst various classes of steel, medium carbon
steels stands apart and are considered to be the backbone of modern industry. Steel can briefly be divided into
three types; one of them is medium carbon steel. A medium carbon steel having 0.80-1.10% Cr, 1% Ni and 0.28-
0.33 C with Tempered Martensite structure can be considered as a medium carbon steel. Medium carbon steels
occupy a unique status as engineering materials by virtue of their excellent combination of properties such as
high strength, adequate ductility, toughness and good corrosion resistance. These steels find extensive
application in chemical plants, power generation equipment’s, in gas turbines as turbine and compressor blades
and discs, aircraft engine components and fittings and in marine components.
These steels can be heat treated to obtain a wide range of mechanical properties to meet the requirements of
specific application AISI 4130 is one of the most potentially attractive steels in this medium carbon steel class
used extensively for parts requiring a combination of high tensile strength, good toughness and corrosion
resistance. 4130 is a high chromium-low nickel low hardenability Medium carbon steel and generally used as
hardened and tempered in the tensile range 655 min MPa, Brinell range 204-244 BHN. Characterised by very
good corrosion resistance in general atmospheric corrosive environments, good resistance to mild marine and
industrial atmospheres, resistant to many organic materials, nitric acid and petroleum products coupled with high
tensile and high yield strength plus excellent toughness in the hardened and tempered condition. So AISI 4130
is used in highly-stressed aircraft components, pump shafts and valve stems etc.
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Generally heavy components of AISI 4130 steel like shaft, axle etc can be manufactured by open die hot forging
(heavy forging). The forging of type AISI 4130 steel is carried out between the ranges of 900 to 1200 °C followed
by slow cooling up to room temperature. The slow cooling of materials shall be done by either furnace or
insulating materials. Normalizing process (after cooling of heavy forged part) immediately required for forged
products to make them machinable after normalizing followed hardening and tempering.
EXPERIMENTAL METHODOLOGY
26 specimens were prepared for microstructural characterization and mechanical testing, including hardness,
tensile, and impact tests. Metallographic preparation was carried out in accordance with ASTM E3, followed by
etching as per ASTM E407 to reveal the microstructure. Brinell hardness measurements were performed
according to ASTM E10 using a standard ball indenter, and the reported values represent the average of three
readings. Tensile testing was conducted in accordance with ASTM E8/E8M using a universal testing machine to
determine strength and ductility parameters. Impact toughness was evaluated using the Charpy impact test as per
ASTM E23. The Specimens (Sample A and Sample B) were normalized at 890°C with a holding time of 10hr,
followed by air cooling
After normalizing, hardness is 184-191 BHN,
Figure 1: Microstructure of normalized Steel Specimen (Ferrite-pearlite),2% Nital
100 X
200 X
400 X
1000 X
Table 1: Parametric- variables
Object dimension (mm)
Normalizing Temp
Tempering Temp
(0
C)
Sample A (390 Ø x 210 L)
860
o
C
518+ 47 =565
Sample B (390 Ø x 265 L)
860
o
C
565 + 90 = 655
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Experiment 1 For Sample A
Hardening.
Figure 2: Heat Treatment Cycle showing hardened Sample A at 860
o
C(Holding time 8Hrs) and water
Quenched, Resulting in Approximately cooling rate (1.18 °C/s, ).
Tempering
Figure 3: The hardened sample A Was Tempered at 565
o
C, for 13 hr and air cooled.
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Experiment 2 for Sample B
Hardening
Figure 4: Heat Treatment Cycle showing hardened Sample B at 860
o
C (Holding time 8Hrs) and water
Quenched, Resulting in Approximately cooling rate (0.64 °C/s ).
Tempering
Figure5: The hardened sample B Was Tempered at 655
o
C, for 13 hr and air cooled.
RESULTS AND DISCUSSION
Table 2: Result of Tensile Testing, Impact & Hardness for Sample A
Hardness after hardening at 860 ֯C
(BHN)
Hardness after tempering
at 565 ֯C (BHN)
Yield
strength
(MPa)
312,312,312
232,223,232
L = 627
T = 597
R= 621
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Tensile
Strength
(MPa)
Elongation
(%)
Reduction
Area (%)
Impact (Charpy V notch)
Temp – 45 ֯C (J)
Avg
788
24.50
63.148
84,55,54
64.33
776
25.14
59.290
50,48,34
44
757
24.94
53.912
52,39,58
49.67
Where L = Longitudinal Direction, T = Transverse Direction, R=Radial Direction
Table 3: Result of Tensile Testing, Impact & Hardness for Sample B
Sample
(Ø390 X 265 Lmm )
Hardness after hardening
at 860 ֯ C (BHN)
Hardness after tempering
at 655 ֯ C
(BHN)
Yield strength
(MPa)
B
326,331,311
197,212,204
L = 488
T = 503
R= 463
Tensile
Strength
(MPa)
Elongation
(%)
Reduction
Area (%)
Impact (Charpy V notch)
Temp – 45 ֯C (J)
Avg
693
29.08
69.038
105,58,78
80.33
684
29.02
60.068
12,83,38
44.33
665
25.14
59.375
32,84,29
48.33
Where L = Longitudinal Direction, T = Transverse Direction, R=Radial Direction
Microstructure Analysis after tempering
Figure 6: Microstructure of Tempered Sample A (tempered martensite & Ferrite, Etchant 2%Nital.
100 X
400 X
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Micro analysis after tempering as below of Sample B:
Figure 7: Microstructure of Tempered Sample B (tempered martensite & Ferrite), Etchant 2% Nital
100 X
400 X
DISCUSSIONS
The mechanical properties of Samples A and B are strongly influenced by their respective cooling rates during
quenching. Sample A, with a higher cooling rate of 1.18 °C/s, exhibited higher hardness (~232 BHN) and
superior strength, with yield strength up to 627 MPa and tensile strength up to 788 MPa. In contrast, Sample B,
with a lower cooling rate of 0.64 °C/s, showed reduced hardness (~204 BHN) and lower strength values.
However, Sample B demonstrated relatively higher ductility, as indicated by increased elongation and reduction
in area.
Microstructural examination of both samples revealed the presence of tempered martensite along with ferrite.
The higher cooling rate in Sample A restricted diffusion and retained a finer tempered martensitic structure,
resulting in improved strength and hardness. Conversely, the lower cooling rate in Sample B promoted greater
ferrite formation and coarsening of the microstructure during tempering, leading to reduced hardness and
enhanced ductility.
Furthermore, variations in impact toughness along longitudinal, transverse, and radial directions can be attributed
to non-uniform cooling and section thickness effects. These results highlight that cooling rate plays a crucial role
in controlling microstructural evolution and consequently governs the balance between strength and ductility in
the material.
CONCLUSIONS
Hardening at 860°C followed by tempering significantly influences the balance between strength and toughness
of the material.
Tempering temperature significantly affects the mechanical properties of AISI 4130 steel, where lower tempering
(565 °C) provides higher strength and hardness, while higher tempering (655 °C) improves ductility and softens
the microstructure.
Both conditions exhibit tempered martensite with ferrite, confirming a strength–ductility trade-off governed by
tempering temperature.
REFRENCES
1. ASM Handbook volume 1 Properties & selection Irons steels & High performance alloys
2. ASM Handbook Volume 14 – Forming & Forging.
3. Poloprudský, J., Chlupová, A., Šulák, I., & Obrtlík, K. (2023). Effect of heat treatment on the
microstructure and fatigue behaviour of AISI 4130 steel. Metallic Materials/Kovove Materialy, 61(6).
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4. Heidary, O., Mirzaee, O., Raouf, A. H., & Borhani, E. (2020). UP-quenched SAE 4130 steel: Mechanical
properties assessment and bainite formation. Materials Science and Engineering: A, 787, 139479.
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