The American Journal of Interdisciplinary Innovations
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TYPE
Original Research
PAGE NO.
23-27
10.37547/tajiir/Volume07Issue03-05
OPEN ACCESS
SUBMITED
22 January 2025
ACCEPTED
20 February 2025
PUBLISHED
23 March 2025
VOLUME
Vol.07 Issue03 2025
CITATION
Khasanov Abdurashid Solievich, Utkir Mirzakamolovich Khalikulov, &
Djeparova Medine Narimanovna. (2025). Modern Trends in Heat
Treatment of Chromium-Molybdenum Steel. The American Journal of
Interdisciplinary Innovations and Research, 7(03), 23
–
27.
https://doi.org/10.37547/tajiir/Volume07Issue03-05
COPYRIGHT
© 2025 Original content from this work may be used under the terms
of the creative commons attributes 4.0 License.
Modern Trends in Heat
Treatment of Chromium-
Molybdenum Steel
Khasanov Abdurashid Solievich
Professor, Doctor of Technical Sciences, Almalyk Branch, National
University of Science and Technology "MISIS", Almalyk, Uzbekistan
Utkir Mirzakamolovich Khalikulov
Associate Professor, Almalyk Branch, National University of Science and
Technology "MISIS", Almalyk, Uzbekistan
Djeparova Medine Narimanovna
Student, Almalyk Branch National University of Science and Technology
"MISIS", Almalyk, Uzbekistan
Abstract:
This article discusses the heat treatment
temperature regimes of chromium-molybdenum steel
and their impact on the material's mechanical
properties. The main heat treatment methods, including
annealing, normalizing, quenching, and tempering
processes, are analyzed. The influence of various
processing regimes on the formation of the structure
and the operational characteristics of the steel is
studied. Optimal parameters that enhance strength,
ductility, and wear resistance are identified. The
obtained results enable the development of efficient
heat
treatment
technologies
that
meet
the
requirements of various operating conditions.
Keywords:
Heat treatment, chromium-molybdenum
steel,
modification,
crystallization,
phase
transformations, mechanical properties, quenching,
tempering, normalizing, annealing, thermokinetic
diagrams, microstructure, grain size, residual stresses,
strength,
ductility,
wear
resistance,
corrosion
resistance, heat resistance, computer modeling,
metallurgy, alloying, austenite, bainite, martensite.
Introduction:
Relevance of studying the heat
treatment process of chromium-molybdenum steel.
In the rapidly developing industrial economy of
Uzbekistan, particularly in machine engineering,
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The American Journal of Interdisciplinary Innovations and Research
chromium-molybdenum steel is one of the most
sought-after materials due to its properties:
•
high strength;
•
heat resistance;
•
corrosion resistance.
Chromium-molybdenum steel is widely used in the
energy and mechanical engineering sectors, where
there are high demands on the reliability and durability
of structures.
Heat treatment regimes play a crucial role in forming
the mechanical properties of chromium-molybdenum
steel, as they enhance the existing properties and
characteristics of these steels. Consequently, the
question of selecting optimal temperature regimes
arises for domestic scientists and engineers, which
would allow improving strength, ductility, wear
resistance, and reducing internal stresses in the
material.
Different heat treatment methods, such as annealing,
normalizing, quenching, and tempering, have a varying
impact on the steel's structure and properties.
In order to achieve optimal property values for
chromium-molybdenum steels, especially to enhance
their strength characteristics, the steel composition is
alloyed with carbide-forming elements. Carbide-
forming elements help stabilize the supercooled
austenite [1] and improve the hardenability of the
alloy.
Medium-carbon chromium-molybdenum steels have
gained particular popularity in machine engineering,
energy, and the mining and metallurgical industries due
to their combination of high strength, toughness, wear
resistance, and fatigue resistance. These properties
make them indispensable for manufacturing critical
components such as wheelbases for excavators,
excavator buckets, inner linings of drum mills at
beneficiation plants, gears, discs, turbine blades, and
other structural elements subjected to significant
mechanical and thermal loads.
It should be noted that the key factor determining the
operational properties of steel is heat treatment, the
parameters of which are selected based on special
diagrams
reflecting
the
kinetics
of
phase
transformations. Most often, thermokinetic and
isothermal diagrams are used for this purpose, which
predict the metal's structure depending on temperature
and holding time (Figure 1).
The kinetics of austenite decomposition, at high thermal
values, is easily determined by the chemical
composition of the steel, including iron, carbon,
manganese, chromium, molybdenum, silicon, and other
elements. Other factors, such as cooling rate, heating
conditions, and preliminary treatment, are also critical.
The initial grain size of the metal significantly influences
phase transformations, which, in turn, depends on the
austenitization temperature and the regimes of
preliminary heat treatment. Control of these
parameters allows for the correction of the steel
structure, achieving an optimal balance between
strength, ductility, and resistance to failure [3].
Figure 1. Isothermal transformation of austenite for chromium-molybdenum
steel grade 35KhML.
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The American Journal of Interdisciplinary Innovations and Research
Methodology of Heat Treatment Regimes for
Chromium-Molybdenum Steel
When developing heat treatment regimes for
chromium-molybdenum steel, the methodology of
preliminary studies should take into account the
impact of all main stages of production, as they directly
affect the process of decomposing supercooled
austenite and, consequently, the formation of the final
structure of the billet after heat treatment [2].
The following types of heat treatment were considered
during the study:
Annealing: Conducted within a temperature range of
850
–
900°C with slow cooling to relieve residual
stresses and improve machinability.
Normalizing:
The
35KhML
grade
chromium-
molybdenum steel sample was heated to 870
–
920°C,
followed by cooling in natural atmospheric conditions.
This regime promotes the formation of a
homogeneous structure and improves the material's
mechanical characteristics.
Quenching: After heating to 850
–
900°C, the
chromium-molybdenum steel was cooled in oil,
ensuring a high level of strength and hardness.
Tempering: Performed at 500
–
700°C to reduce
brittleness and increase toughness.
The equipment used included a muffle furnace with
temperature control (Nabiterm), Brinell and Rockwell
hardness
testers,
and
an
electron-optical
metallographic microscope (OEM ODM).
When selecting the optimal heat treatment regime for
chromium-molybdenum steels, several significant
factors must be considered:
Casting crystallization after pouring, which depends on
the billet's mass and production technology (use of
molds, continuous casting, etc.). These parameters
determine the size of the dendritic structure and the
primary austenitic grain.
Heating and cooling processes during pressure
treatment, which generally occur at temperatures
above the phase transformation point. As a result, the
primary dendritic structure is destroyed, and new
austenitic grains are formed depending on the
thermomechanical processing conditions.
Distribution and formation of austenitic grain and its
decomposition products in the transverse cross-section
of the billet during heating and cooling. These processes
affect the material's structural homogeneity.
Moreover,
several
problems
arise
during
thermomechanical
processing
of
chromium-
molybdenum steel. One of the most significant
challenges is the inability to precisely assess the impact
of the material's initial inhomogeneity on the
thermokinetic diagram of supercooled austenite
decomposition. This is due to uneven heating and
cooling, as well as complex deformation distribution
within the billet.
Even steels with identical chemical compositions can
demonstrate significant differences in thermokinetic
characteristics. The start time of supercooled austenite
transformation can vary considerably, as its
decomposition process involves a sequential transition
from a pearlitic structure to bainitic and then
martensitic structures. These changes result in a
dramatic alteration of the material's mechanical
properties.
The main reasons for such a range of values are related
to:
Complex and uncontrolled thermomechanical history of
the billet's structure formation at various stages of
metallurgical production.
Differences in sample selection points, which are
especially critical when working with large billets.
Given these features, it is clear that an individual
approach to heat treatment is necessary. At present, it
is impossible to apply standard quenching and
tempering regimes for critical components based solely
on the thermokinetic diagram obtained from trial bars
or similar billets. Each billet requires the construction of
an individual diagram with mandatory data verification
to achieve the required operational characteristics of
the material. For example, when cooling at a rate of 0.1
–
5 K/s for 35KhML chromium-molybdenum steel, the
following structural changes can be observed, as shown
in the diagram (Figure 2):
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The American Journal of Interdisciplinary Innovations and Research
Figure 2. Structural changes during dilatometric investigation.
Table 1. Kinetics of supercooled austenite transformation in 35KhML steel.
When developing heat treatment regimes for
chromium-molybdenum steel, it is necessary to
consider the probabilistic nature of the processes that
transform the cast structure of the ingot, which occur
under the influence of complex thermodynamic
conditions and previous stages of thermomechanical
processing. These changes are caused by thermal and
deformation effects that:
contribute to stabilizing the chemical micro-
heterogeneity of the alloyed steel in large billets;
form decomposition products of undercooled
austenite, which depend on its heterogeneous
composition at the level of the austenite grain.
Thus, the development of heat treatment regimes
requires a detailed consideration of all factors
influencing the evolution of the material's structure, as
well as the need to obtain data directly for each billet to
ensure predictable mechanical properties and
operational reliability of the chromium-molybdenum
steel.
Key objectives and goals of heat treatment
. Heat
treatment of chromium-molybdenum steel pursues
several key objectives:
Increasing strength and hardness
Heat treatment ensures the formation of a strong and
wear-resistant structure, which is especially important
for components operating under high loads. During
quenching, a martensitic or bainitic structure is formed,
and subsequent tempering allows for the optimal
combination of strength and ductility.
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The American Journal of Interdisciplinary Innovations and Research
Improving impact toughness and plasticity
To prevent brittle failure, it is important to achieve
sufficient
material
toughness.
Tempering
at
intermediate temperatures (350
–
500°C) helps relieve
internal stresses and increases resistance to failure
under dynamic loads.
Ensuring heat resistance and thermal stability
Chromium and molybdenum contribute to forming a
structure that is resistant to high temperatures. Special
aging and tempering regimes improve creep strength
and property stability during prolonged operation
under heat.
Improving corrosion resistance
With proper heat treatment, carbides are formed in
the structure of chromium-molybdenum steel, which
enhance resistance to oxidation and corrosion,
especially in aggressive environments.
Minimizing residual stresses
After casting, mechanical processing, or welding,
residual stresses remain in the metal, which can lead
to deformations and cracking. Heat treatment,
including
normalizing
and
high-temperature
tempering, reduces these stresses, improving the
durability of the components.
CONCLUSION
Heat treatment of chromium-molybdenum steel is a
key technological process that determines the
operational characteristics of the material. The study
has established that selecting optimal heat treatment
regimes significantly improves the strength, ductility,
heat resistance, and corrosion resistance of the steel,
which is particularly important for products operating
under high loads and in aggressive environments.
The results of the analysis of various heat treatment
methods, including annealing, normalizing, quenching,
and tempering, confirmed their significant impact on
the steel's microstructure. Quenching forms a
martensitic or bainitic structure, which increases
strength and hardness, while tempering helps reduce
residual stresses and increases toughness. Studies on
the kinetics of phase transformations have shown that
the chemical composition of the steel, cooling rate,
and initial grain size play a decisive role in the
formation of the final structure.
The need for an individual approach to developing heat
treatment regimes was identified, especially for critical
components, as the heterogeneity of the initial
structure of the ingot can lead to significant variation
in mechanical properties. To improve the accuracy of
predicting phase transformations, the use of
thermokinetic
and
isothermal
diagrams
is
recommended, taking into account the chemical
inhomogeneity and thermomechanical history of the
blanks.
Thus, the proposed heat treatment technologies allow
for the optimization of the properties of chromium-
molybdenum steels for specific operating conditions,
ensuring their reliability, durability, and high
performance in mechanical engineering, energy, and
the mining and metallurgical industries. A promising
direction for further research is the application of
modern computer modeling methods for predicting
structural changes during heat treatment, as well as the
development of new alloying compositions and
processing regimes that contribute to improving the
steel's characteristics.
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