Y. SONG et al.: EFFECT OF NITROGEN ON THE THERMAL DEFORMATION BEHA VIOR OF MARTENSITIC STAINLESS ...
809–818
EFFECT OF NITROGEN ON THE THERMAL DEFORMATION
BEHA VIOR OF MARTENSITIC STAINLESS BEARING STEEL
VPLIV DU[IKA NA TOPLOTNO DEFORMACIJO
MARTENZITNEGA NERJA VNEGA LE@AJNEGA JEKLA
Yaohui Song
1
, Yibo Lu
2
, Yugui Li
2*
, Haosong Sun
3
, Huaying Li
3
, Hui Xu
3
,
Yihang Wang
2
1
Heavy Machinery Education Engineering Department Research Center, Taiyuan University of Science and Technology,
Taiyuan, 030024, Shanxi, China
2
School of Mechanical Engineering, Taiyuan University of Science and Technology, Taiyuan 030024, Shanxi, China
3
School of Materials Science and Engineering, Taiyuan University of Science and Technology, Taiyuan 030024, Shanxi, China
Prejem rokopisa – received: 2024-05-16; sprejem za objavo – accepted for publication: 2024-10-24
doi:10.17222/mit.2024.1194
The thermal deformation behaviors of martensitic stainless bearing steels (0.16N, 0N) in the temperature range 850–1150 °C,
strain rate 0.01–10 s
–1
, and deformation of 60 % were studied using a single-pass compression experiment. After adding 0.16 %
nitrogen, the peak stress of the martensitic stainless bearing steel increased under all thermal forming conditions, and the aver-
age peak stress increased by about 33.724 MPa. The strain-rate sensitivity diagram, power dissipation diagram, instability factor
diagram, and thermal processing diagram under different strains were constructed based on the stress-strain curve. The thermal
deformation activation energy under different strains was constructed and combined with a metallographic structure analysis.
The results show that under the same conditions, the occurrence of DRX in 0.16N bearing steel is less than that of 0N bearing
steel, but the grains are finer than those of 0N bearing steel.
Keywords: martensitic stainless bearing steel, thermal deformation behavior, power dissipation diagram, thermal deformation
activation energy, thermal processing diagram
Avtorji v ~lanku opisujejo {tudijo obna{anja dveh martenzitnih le`ajnih jekel; enega brez du{ika in drugega legiranega
z 0,16 w/% N (ozna~enih kot 0N in 0.16N), med toplotno (termi~no) tla~no deformacijo v temperaturnem obmo~ju med 850 °C
in 1150 °C, pri hitrosti deformacije med 0,01 s
–1
in 10 s
–1
ter 60 % deformacijo. Po legiranju jekla z 0,16 w/% du{ika se je
maksimalna tla~na napetost martenzitnega nerjavnega le`ajnega jekla znatno pove~ala pri vseh izbranih pogojih termi~ne
deformacije. V povpre~ju je ta napetost zna{ala pribli`no 33,724 GPa. Avtorji so na osnovi izvedenih eksperimentov in
dobljenih diagramov napetost- deformacija konstruirali diagram ob~utljivosti na hitrost deformacije, disipacijski diagram mo~i,
diagram faktorja nestabilnosti in diagram termi~nega procesiranja. Avtorji so konstruirali tudi diagrame termi~ne aktivacijske
energije za deformacijo pri razli~nih deformacijah in ga kombinirali z metalografskimi analizami mikrostrukture. Rezultati
analiz so nadalje pokazali, da je pri enakih pogojih termi~ne deformacije obseg dinami~ne rekristalizacije (DRX) pri le`ajnem
jeklu 0.16N manj{i kot pri le`ajnem jeklu 0N, toda z du{ikom legirano jeklo ima finej{a kristalna zrna.
Klju~ne besede: martenzitno nerjavno le`ajno jeklo, termi~na deformacija, diagram raztrosa mo~i, aktivacijska energija toplotne
deformacije, diagram toplotnega procesiranja
1 INTRODUCTION
Bearings are essential components in modern indus-
trial systems, affecting the stability and longevity of me-
chanical equipment. Selecting the right bearing steel is
critical, as high-quality materials provide superior me-
chanical properties, including strength, hardness, and re-
sistance to wear and shock.
1
However, traditional, high-
carbon, chromium martensitic stainless steels, such as
9Cr18 and 9Cr18Mo, are limited by the presence of
coarse eutectic carbides.
2
Nitrogen alloying has been
shown to refine carbides and grains, enhancing the
steel’s strength without sacrificing toughness, making ni-
trogen-containing martensitic stainless steel a promising
candidate for high-performance bearings.
3
Research has
predominantly focused on optimizing thermal treatment
processes and improving the material’s corrosion, fa-
tigue, and impact resistance.
4
For effective production of
nitrogen-alloyed bearing forgings, it is crucial to explore
the material’s plastic deformation behavior, micro-
structural evolution, and thermal processing properties at
elevated temperatures. This study aims to establish a
solid theoretical basis and practical guidelines for opti-
mizing the thermal forging parameters, ensuring that
stainless-steel bearings achieve the desired micro-
structure and mechanical properties during manufac -
ture.
5–8
In recent years, researchers have made the following
studies on stainless bearing steel. Zhang et al.
9
studied
the effects of forming temperature and strain rate on the
austenitizing and dynamic recrystallization of
30CrMnSiNi2A steel. According to the experimental re-
sults, the constitutive equation and machining diagram of
30CrMnSiNi2A steel are established. The unsafe zone of
30CrMnSiNi2A steel is not only distributed in the region
with low temperature and low strain rate but also in the
Materiali in tehnologije / Materials and technology 58 (2024) 6, 809–818 809
UDK 669.14.018.8:537.226.86 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek Mater. Tehnol.
*Corresponding author's e-mail:
lygtykd@163.com (Yugui Li)

region with high temperature and high strain rate.
30CrMnSiNi2A steel exhibits ideal thermoplastic
formability when heat treated at 1050 °C at a strain rate
of 0.1–1 s
–1
. Feng et al.
10
developed a machining diagram
of a 20CrMnTiH steel using a dynamic material model in
the temperature range 850–1150 °C and a strain variabil-
ity of 0.01–1 s
–1
. According to the developed machining
diagram, the thermal working characteristics of
20CrMnTiH steel are analyzed, and the optimal thermal
working parameter values of 20CrMnTiH steel are found
to obtain good thermal working properties and a small
grain size in the process parameter range of
1036–1070 °C, 0.1–1 s
–1
. Lin et al.
11
studied the dynamic
recrystallization mechanism of bearing steel
G13Cr4Mo4Ni4V . The results show that because the de-
formation ability of ferrite and carbide is different from
that of the matrix, their dissolution, precipitation behav-
ior, and interaction with dislocation during deformation
are the main reasons for inducing steel recrystallization.
Despite numerous studies on the properties of
martensitic stainless steel, research focusing on the influ-
ence of nitrogen content on its thermal deformation be-
havior under high-temperature conditions is relatively
scarce, limiting the material’s further development and
application. To address this gap, we systematically inves-
tigated two types of bearing steels: nitrogen-containing
martensitic stainless bearing steel (0.16N) and nitro-
gen-free martensitic stainless bearing steel (0N).
Through single-pass compression experiments conducted
at temperatures ranging from 850 °C to 1150 °C, strain
rates of 0.01 s
–1
to 10 s
–1
, and 60 % deformation, we es-
tablished comprehensive thermal processing maps based
on stress-strain curves. These maps include strain-rate
sensitivity diagrams, power-dissipation diagrams, insta-
bility-factor diagrams, and thermal processing diagrams
under different strains, providing a new theoretical foun-
dation for optimizing hot-working processes. Addi-
tionally, we calculated the thermal deformation activa-
tion energy and combined it with metallographic
structure analyses to reveal the mechanisms by which ni-
trogen addition influences dynamic recrystallization and
grain refinement. This study seeks to contribute to the
understanding of how nitrogen affects the thermal defor-
mation behavior of martensitic stainless bearing steel, of-
fering insights that might assist in enhancing its perfor-
mance through controlled hot-working practices.
2 EXPERIMENTAL PART
The alloys used in this study are bearing steel with a
nitrogen content of 0.16 % (from now on referred to as
0.16N) and nitrogen-free bearing steel (from now on re-
ferred to as 0N), both of which are cut in to incompletely
forged ingots with a forging ratio of 1:2. The primary
chemical constituents are shown in Table 1. The cylin-
drical compression specimens of 0.16N and 0N were
prepared, with a height of 15 mm and a diameter of
10 mm. A Gleeble-3800 thermal simulation testing ma-
chine conducted the thermal compression test in a vac-
uum. In order to reduce the influence of friction and pre-
vent adhesion between the sample and the equipment,
graphite lubricant was coated on both ends of the sam-
ple, and a tantalum sheet and graphite sheet were added.
The thermal compression process is shown in Fig-
ure 1a. The test strain rates are 0.01–10 s
–1,
respectively;
Y. SONG et al.: EFFECT OF NITROGEN ON THE THERMAL DEFORMATION BEHA VIOR OF MARTENSITIC STAINLESS ...
810 Materiali in tehnologije / Materials and technology 58 (2024) 6, 809–818
Figure 1: a) Schematic of the thermal deformation process; Original microstructure: b) 0.16N, c) 0N
Table 1: Chemical composition of 0.16N and 0N (w/%)
Materials C Si Mn P Cr Mo N Fe
0.16N 0.3 0.51 0.42 0.002 15.16 0.83 0.16 Bal.
0N 0.3 0.51 0.42 0.002 15.16 0.83 0.00 Bal.

the temperature range is 850–1150 °C, the deformation
rate is 60 %, and the true strain is 0.916. The specific
process is heating at 10 °C/s to 1200 °C for 2 min and
then cooling at 5 °C/s to the deformation temperature,
compression after 30 s, and water cooling immediately
after compression to retain the high-temperature tissue.
The compressed sample was cut along the compression
direction and heated in a water bath with 2g KMnO
4
+
6mLH
2
SO
4
+94mLH
2
O etchant for 40 min. Then, OM
was used to observe the metallographic structure. The
original microstructure is shown in Figures 1b and 1c.
3 RESULTS
3.1 Stress-strain curve
The stress-strain curves obtained by thermal com-
pression of 0.16N and 0N stainless bearing steels are
shown in Figure 2. The trend of experimental curves of
the two kinds of steel is generally the same, and the flow
stress of the material increases with the increase of strain
rate under the condition of keeping the deformation tem-
perature unchanged. Under the same strain-rate condi-
tion, the flow stress of the material shows a decreasing
trend with an increase in temperature. This indicates that
both steels are positively sensitive to strain rate and neg-
atively sensitive to temperature. In addition, under the
same conditions, the flow stress of 0.16N bearing steel is
higher than that of 0N bearing steel. It can be seen from
Figure 2i that after adding 0.16 % nitrogen, the peak
stress under all thermal forming conditions is increased,
and about 33.724 MPa increases the average peak stress.
This data indicates that the addition of nitrogen has a
positive effect on improving the deformation resistance
of the material. Especially when the deformation is car-
ried out at 850 °C and the low strain rate of 0.1 s
–1
, the
increase in the stress value is particularly prominent,
which indicates that the solid solution strengthening of
nitrogen and the nailing effect of carbides and nitrides
are the most significant under this condition. The consis-
tent trend in the overall increment ratio shown in Figure
2i indicates that the increase in deformation resistance is
uniform and steady, which helps to ensure that the mate-
rial maintains high-performance stability over a wide
range of application conditions.
Y. SONG et al.: EFFECT OF NITROGEN ON THE THERMAL DEFORMATION BEHA VIOR OF MARTENSITIC STAINLESS ...
Materiali in tehnologije / Materials and technology 58 (2024) 6, 809–818 811
Figure 2: Stress-strain curves of 0.16N at different rates: a) 0.01s
–1
,b )0 . 1s
–1
,c )1s
–1
,d )1s
–1
; stress-strain curves of 0N at different rates:
e) 0.01 s
–1
,f )0 . 1s
–1
,g )1s
–1
,h )1 0s
–1
; i) comparison diagram of peak-stress difference and increment between 0.16N and 0N

3.2 Comparison of thermal processing properties
3.2.1 Strain-rate sensitivity index
Generally speaking, the strain rate affects the high-
temperature deformation characteristics of steel. In order
to understand the effect of strain rate on material behav-
ior deeply, many researchers have introduced the
strain-rate sensitivity index to conduct in-depth studies
of various materials. The specific mathematical expres-
sion of the index is as follows:
12
m =
∂
∂
(ln )
(ln )
$
$
(1)
Figure 3 shows the strain-rate sensitivity diagram of
0.16N and 0N martensitic stainless bearing steel at
strains of 0.3, 0.6, and 0.9. In the process of thermal de-
formation, m represents the sensitivity of the flow stress
to the strain rate, and the greater m is, the more sensitive
the flow stress of the material is to the strain rate. Ac-
cording to the value of m, it can be divided into three
grades:
13
low m value (m<0.15), high m value
(0.2<m<0.3), and superplastic region (m>0.3). By ob-
serving the strain-rate sensitivity graphs of the two mate-
rials under each strain, we see that the low m-value re-
gion decreases gradually. In contrast, the high m-value
and superplastic regions increase first and then decrease.
Taking 0N bearing steel as an example, when the strain
is 0.3, the low m value zone is 950–1075 °C and
(1075–1200 °C, 0.13–10 s
–1
); when the strain is in-
creased to 0.7, the main low m value zone is
950–1000 °C, 0.01–0.05 s
–1
and 950–1000 °C,
2.71–10 s
–1
). When the strain is 0.3, the high m-value re-
gion is located at 1100–1150 °C, 0.01–0.05 s
–1
. With the
increase of the strain, the high m value region first in-
creases and is located at 1025–1150 °C, 0.01–0.08 s
–1
and 1100–1150 °C, 2.71–10 s
–1
. After the area is re-
duced, located at 1100–1150 °C, 0.01–0.08 s
–1
. The
superplastic region of the two materials is slightly differ-
ent. The superplastic region of the 0N bearing steel is
mainly concentrated in 1125–1150 °C,
#<– 4s
–1
(under
different strains), while the superplastic region of the
0.16N bearing steel is first concentrated in
1100–1150 °C,
#<0.02 s
–1
. Then, with the increase of
strain, the superplastic region of the two materials be-
comes slightly different. It was gradually transferred to
the low-temperature and low-rate region 875–975 °C,
#<0.02 s
–1
. Note that the superplastic phenomenon of 0N
bearing steel usually occurs at high temperature and low
speed, while the superplastic phenomenon of 0.16N
bearing steel tends to shift to low temperature and high
speed with increased strain. In addition, it is not difficult
to see from the figure that the area of high m region and
superplastic region of 0.16N bearing steel under different
strains is larger than that of 0N bearing steel, indicating
that the flow stress of 0.16N bearing steel is more sensi-
tive to the strain rate.
3.2.2 Power dissipation efficiency
In thermal processing engineering, different power-
dissipation efficiency ( ) values correspond to different
microstructure-evolution mechanisms, and the three-di-
mensional contours consisting of power-dissipation
value, temperature, and strain rate are called power-dissi-
pation diagrams. The higher the  value, the better the
thermal processability of the region in which it is lo-
cated, indicating the better microstructure evolution
mechanism, while the negative value indicates the possi-
ble unstable microstructure.
When the m value is constant and non-linear with
temperature or strain rate, the power-dissipation effi-
ciency ( ) can be expressed as:
14
h
J
J
m
m
==
+
max
2
1
(2)
Figure 4 shows the power-dissipation efficiency of
0.16N and 0N martensitic stainless bearing steel when
the strain is 0.3, 0.6, and 0.9. It is not difficult to see that
the change in power-dissipation efficiency is very similar
to that of the strain-rate sensitivity coefficient: regions
Y. SONG et al.: EFFECT OF NITROGEN ON THE THERMAL DEFORMATION BEHA VIOR OF MARTENSITIC STAINLESS ...
812 Materiali in tehnologije / Materials and technology 58 (2024) 6, 809–818
Figure 3: Comparison of strain-rate sensitivity index: a) 0.16N bearing steel, b) 0N bearing steel

with low  value ( <15 %) gradually decrease, while re-
gions with high m value increase first and then decrease.
The three dynamic evolution processes of work harden-
ing, DRV , and DRX are closely related to the power-dis-
sipation values, and the  value represents different mi-
croscopic transformations.  generally reflects the
microstructure-deformation mechanism;
13
0.2< <0.3 is
DRV , and 0.2< <0.3 is DRX. Taking 0.9 strain as an ex-
ample, the high  value ( >35 %) of 0N bearing steel is
mainly concentrated in the high-temperature and
low-strain-rate zone (1100–1150 °C,
#< 0.05 s
–1
), and the
high-temperature and high-strain-rate zone
(1125–1150 °C,
#>4.5 s
–1
). The high  value ( >35 %) of
0.16N bearing steel is mainly concentrated in the
low-strain-rate zone (850–1150 °C,
#<0.05s
–1
). In the
evolution process,  varies from 6.4 % to 49.4 %. Both
steel sheets’ high  region occurs at high temperatures
and low rates (1100–1150 °C,
#<0.05 s
–1
) because a
higher deformation temperature is conducive to
grain-boundary migration. In contrast, a lower strain rate
provides a longer deformation time and increases the
time for recrystallization. The dynamic recrystallization
occurs entirely.
3.2.3 Instability factor
The power-dissipation-efficiency diagram is estab-
lished to clearly distinguish the distribution of
power-dissipation efficiency during the thermal deforma-
tion. However, the region of material instability cannot
be known from this figure. Therefore, Prasad et al. pro-
posed the evaluation criterion of plastic deformation and
rheological instability based on Ziegler’s criterion of
continuous large plastic deformation, and its primary ex-
pression is as follows:
14
#
#
(
 )
ln
ln
 =
+
+<
∂
∂
m
m
m
1
0 (3)
Figure 5 shows the instability diagram of 0N and
0.16N martensitic stainless bearing steel under 0.3, 0.6,
and 0.9 strains. The figure shows the relationship be-
tween the instability factor and the temperature and
strain rate. The yellow region is the unstable region
Y. SONG et al.: EFFECT OF NITROGEN ON THE THERMAL DEFORMATION BEHA VIOR OF MARTENSITIC STAINLESS ...
Materiali in tehnologije / Materials and technology 58 (2024) 6, 809–818 813
Figure 5: Comparison of instability factors: a) 0.16N bearing steel, b) 0N bearing steel
Figure 4: Comparison of power-dissipation values: a) 0.16N bearing steel, b) 0N bearing steel

( <0), and the blue region is the stable region (% 0). The
instability zone of 0N bearing steel is mainly concen-
trated in (875–1000 °C, 0.37–10 s
–1
), and a small part of
the instability zone is at low temperature and low strain
rate (T < 875°C, 0.01–1 s
–1
). With the increase of strain,
the instability zone decreases and then increases. For
0.16N bearing steel, the instability zone is concentrated
at 850–1050 °C, 0.01–0.6 s
–1
, and the instability zone de-
creases first and then increases with the increase of
strain. Generally speaking, the low deformation tempera-
ture and high strain rate in thermal working lead to many
dislocation proliferation and inter-delivery entanglement,
resulting in an unstable flow.
15
3.2.4 Thermal working diagram
Based on the Kumar Prasad criterion, the thermal
working diagram of 0.16N and 0N bearing steels can be
obtained by superimposing the power-dissipation-effi-
ciency diagram and the instability diagram. The thermal
working diagram of the two steels under the conditions
of 0.3, 0.6, and 0.9 strains is shown in Figure 6.
The optimal processing region should be selected to
be as large as possible  under no instability
16
. As shown
in Figures 6a to 6c, 0.16N, the instability region has lit-
tle change with the increase of strain, and the essential
characteristics of the thermal processing diagram are
similar. The instability range under different strains is
approximately 850–1025 °C, 0.01–0.6 s
–1
). The thermal
working of the 0.16N bearing steel should avoid the low
temperature and low strain rate area at 1050–1200 °C,
0.01–0.08 s
–1
suitable for processing. 0N With the in-
crease of strain, the instability region always has two
parts, and the essential characteristics of the thermal
working diagram are similar. Under different strains,
there are instability regions of T < 875 °C, 0.01–1 s
–1
,
875–1000 °C, 0.37–10 s
–1
. The optimal processing re-
gion of 0N and 0.16N is also suitable for processing
(1050–1200 °C, 0.01–0.08 s
–1
).
3.3 Microstructure analysis
Metal plastic deformation is a thermal activation pro-
cess; at this time the crystal atoms will migrate to a new
equilibrium or non-equilibrium position, which requires
the atoms’ energy to cross a “threshold value,” and the
energy required is called the deformation activation. The
smaller the activation energy, the easier the deformation
is to perform. The formula for calculating the activation
energy is as follows:
17
{}
{}
QR
T
T
=
⎡ ⎣ ⎢ ⎢ ⎤ ⎦ ⎥ ⎥ ⎡ ⎣ ⎢ ∂
∂
∂
∂
ln(
 ln sinh( )
ln sinh( )
(/ )
#
$
$
1
⎢ ⎤ ⎦ ⎥ ⎥ #
(4)
The activation energy distributions of 0.16N and 0N
under different strains are shown in Figures 7a and 7b.
For both 0.16N and 0N, Q decreases with the increase of
temperature and strain rate under the same strain. With
the increase of strain, the area of the high Q value region
(red region, 0.16N: greater than 580 kJ/mol; 0N: greater
than 510 kJ/mol) shows a decreasing trend. It is not diffi-
cult to see that from 0.3 strain to 0.6 strain, the Q value
Y. SONG et al.: EFFECT OF NITROGEN ON THE THERMAL DEFORMATION BEHA VIOR OF MARTENSITIC STAINLESS ...
814 Materiali in tehnologije / Materials and technology 58 (2024) 6, 809–818
Figure 6: Thermal working diagram of 0.16N bearing steel under different strain: a) 0.3, b) 0.6, c) 0.9; Thermal working diagram of 0N bearing
steel under different strain: d) 0.3, e) 0.6, f) 0.9

decreases sharply (taking 0.16N as an example, 587.65
to 511.58 kJ/mol) because the flow stress corresponding
to 0.3 strain is close to the peak stress, and the work
hardening is the most serious at this time. From 0.6
strain to 0.9 strain, Q value slowly decreases (taking
0.16N as an example, 511.58 kJ/mol to 494.13 kJ/mol),
which is because DRV and DRX phenomena will occur
with the increase of strain variable, which can play a
softening effect and reduce the degree of work
hardening
18
. After 0.6 strain, as shown in Figure 2b, the
stress-strain curve will enter a relatively smooth phase
where deformation is more likely to occur. Compared
with the activation-energy-distribution diagram of 0.16N
and 0N, the thermal deformation activation energy of
0.16N bearing steel (531.12 kJ/mol(average)) is higher
than that of 0N bearing steel (457.99 kJ/mol(average)),
indicating that the deformation resistance of 0.16N bear-
ing steel is better than that of 0N bearing steel. This is
mainly due to the solid-solution strengthening effect of
nitrogen in steel. The existence of nitrogen atoms effec-
tively enhances the deformation resistance of the mate-
rial.
The temperature distribution and strain rate inside the
compressed sample vary greatly, so the region where the
temperature and strain rate are consistent with the exper-
imental setting conditions is first determined according
to the results. The metallographic diagrams in Figure 8
were taken after the thermal compression was com-
pleted; the strain was 0.916. The diagram of deformation
activation energy at 0.9 strain can be analyzed, as shown
in Figure 7a. Q decreases with the increase of tempera-
ture and strain rate, which is precisely corresponding to
Figure 8, as shown in Figure 8b, 8f, 8j and 8n. When
the strain rate is constant at 0.1 s
–1
, the microstructure at
850 °C is deformed grains caused by the elongation of
the original grains, fibrous structures formed at some
grain boundaries, and small recrystallized grains. The
elongation direction is perpendicular to the compression
direction (CD), indicating that dynamic recrystallization
will begin to occur. At 950 °C, the original grains are
surrounded by many dynamically recrystallized grains
formed near the grain boundaries. The presence of a typ-
ical chain structure is formed by bowing out the nucleus
at a high-angle boundary (HAB), which is characteristic
of discontinuous recrystallization (DDRX) behavior.
19
The results show that grain-boundary expansion induced
by strain-induced grain-boundary migration is the pri-
mary mechanism of DRX nucleation, and high deforma-
tion temperature promotes the DRX process. At 1050 °C
there are a large number of small uniform particles. At
1150 °C the recrystallized grains grew uniformly. It
shows that the growth of recrystallized grains is the main
reason for the microstructure change with increased de-
formation temperature at high temperatures. In combina-
tion with Figure 7a, DRX grain growth behavior at
1050–1150 °C is more likely to occur and requires less Q
than DDRX at 850–950 °C.
Figure 9 compares the microstructure change behav-
ior of 0.16N and 0N at 1050 °C and the upper and lower
metallography. Firstly, it can be seen that the
recrystallization of 0.16N bearing steel is less than that
of 0N bearing steel under the same conditions, but the
grains are finer than that of 0N bearing steel. In combi-
nation with Figure 7a and 7b, it can be found that Q of
0.16N is significantly larger than that of 0N, indicating
that DRX of 0.16N under the same conditions requires
more deformation energy than that of 0N. This is be-
cause, with the increase of nitrogen content when the
austenite region is experienced in the cooling process of
smelting, nitrogen has a more vital refining ability for
austenite structure; nitrogen contributes to the short-
range ordering of atoms so that it can be pinning disloca-
tion and the interstitial nitrogen atoms have an ability to
hinder grain-boundary migration.
20
They can delay grain
growth, so the material with a high nitrogen content has
finer grains. In addition, by comparing the deforma-
tion-activation-energy diagram of 0.16N and 0N (Figure
7a and 7b), at 1050 °C the strain rate of 0N varies from
Y. SONG et al.: EFFECT OF NITROGEN ON THE THERMAL DEFORMATION BEHA VIOR OF MARTENSITIC STAINLESS ...
Materiali in tehnologije / Materials and technology 58 (2024) 6, 809–818 815
Figure 7: Distribution of deformation activation energy under 0.3, 0.6, and 0.9 strains: a) 0.16N, b) 0N

Y. SONG et al.: EFFECT OF NITROGEN ON THE THERMAL DEFORMATION BEHA VIOR OF MARTENSITIC STAINLESS ...
816 Materiali in tehnologije / Materials and technology 58 (2024) 6, 809–818
Figure 8: metallographic diagram of 0.16N bearing steel: a) 850-0.01 s
–1
, b) 850-0.1 s
–1
, c) 850-1 s
–1
, d) 850-10 s
–1
, e) 950-0.01 s
–1
,
f) 950-0.1 s
–1
, g) 950-1 s
–1
, h) 950-10 s
–1
, i) 1050-0.01 s
–1
, j) 1050-0.1 s
–1
, k) 1050-1 s
–1
, l) 1050-10 s
–1
, m) 1150-0.01 s
–1
, n) 1150-0.1 s
–1
,
o) 1150-1 s
–1
, p) 1150-10 s
–1
Figure 9: Comparison of 0.16N bearing steel and 0N bearing steel metallographic diagram: 0.16N: a) 1050-0.01 s
–1
, b) 1050-0.1 s
–1
,
c) 1050-1 s
–1
, d) 1050-1 s
–1
; 0N: e) 1050-0.01 s
–1
, f) 1050-0.1 s
–1
, g) 1050-1 s
–1
, h) 1050-10 s
–1

0.01–10 s
–1
, and the value of Q does not change much.
However, for 0.16N, the color of Q changes from
0.01–0.1 s
–1
(1050 °C), the value of Q changes a little
from 0.1–1 s
–1
, and the value of Q also changes signifi-
cantly from 1 to 10 s
–1
, which is precisely consistent with
the change of metallographic diagram. It shows that 0.16
is sensitive to 0.01 s
–1
and 10 s
–1
. Combined with Fig-
ure 9, at 1050 °C the dynamic recrystallization behavior
of 0N has fully occurred, and the strain-rate effect on
DRX is less evident than that of 0.16N.
4 CONCLUSIONS
Based on the stress-strain curve, strain-rate-sensitiv-
ity diagram, power-dissipation diagram, instability-factor
diagram, and thermal working diagram under different
strains are constructed. The activation energy of the ther-
mal deformation under different strains was constructed
and combined with microstructure analysis.
(1) 0.16N and 0N are both positively sensitive to
strain rate and negatively sensitive to temperature. In ad-
dition, under the same conditions, the flow stress of
0.16N bearing steel is higher than that of 0N bearing
steel, and about 33.724 MPa increases the average peak
stress.
(2) The superplasticity of 0N bearing steel usually
occurs at high temperature and low speed, while the
superplasticity of 0.16N bearing steel tends to shift to
low temperature and high speed with the increase of
strain. The high  value ( >35 %) of 0N bearing steel is
mainly concentrated in 1100–1150 °C,
#<0.05 s
–1
,
1125–1150 °C,
#>4.5 s
–1
. The high  value ( >35 %) of
0.16N bearing steel is mainly concentrated in
850–1150 °C,
#<0.05 s
–1
. Both 0.16N and 0N are suitable
for processing at high temperatures and low rates.
(3) Under the same conditions, the occurrence of
DRX in 0.16N bearing steel is less than that in 0N bear-
ing steel, but the grains are finer than those in 0N bear-
ing steel. DRX grain growth at 1050–1150 °C is more
likely to occur and requires less Q than DDRX at
850–950 °C, regardless of 0.16 or 0N. At 1050 °C, 0.16
is more sensitive to 0.01 s
–1
and 10 s
–1
, while dynamic
recrystallization behavior of 0N has fully occurred, and
the effect of strain rate on DRX is not apparent.
Acknowledgements
This project is supported by the Central Guiding Lo-
cal Science and Technology Development Fund Project
(YDZJSX2021A036), the Graduate Education Innova-
tion Project of Taiyuan University of Science and Tech-
nology (SY2023036), the National Natural Science
Foundation of China (52375364), the Basic Research
Program of Shanxi Province (TZLH20230818001), and
Shanxi Province’s Key Core Technology and Common
Technology Research and Development Project
(20201102017).
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