Citation: Nikulin, S.A.; Rogachev,
S.O.; Belov, V.A.; Zadorozhnyy, M.Y.;
Shplis, N.V.; Skripalenko, M.M. Effect
of Prolonged Thermal Exposure on
Low-Cycle Bending Fatigue
Resistance of Low-Carbon Steel.
Metals 2022, 12, 281. https://doi.org/
10.3390/met12020281
Academic Editor: Alberto Campagnolo
Received: 30 December 2021
Accepted: 31 January 2022
Published: 4 February 2022
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Article
Effect of Prolonged Thermal Exposure on Low-Cycle Bending
Fatigue Resistance of Low-Carbon Steel
Sergey A. Nikulin
1
, Stanislav O. Rogachev
1,2,
* , Vladislav A. Belov
1
, Mikhail Y. Zadorozhnyy
3
,
Nikolay V. Shplis
1
and Mikhail M. Skripalenko
4
1
Department of Physical Metallurgy and Physics of Strength, National University of Science and Technology
MISIS, 119049 Moscow, Russia; nikulin@misis.ru (S.A.N.); vbelov@ymail.com (V.A.B.);
shplisnikolay@mail.ru (N.V.S.)
2
Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences, 119334 Moscow, Russia
3
Centre of Composite Materials, National University of Science and Technology MISIS, 119049 Moscow, Russia;
zadorozhnyy.my@misis.ru
4
Department of Metal Forming, National University of Science and Technology MISIS, 119049 Moscow, Russia;
mms@misis.ru
* Correspondence: csaap@mail.ru
Abstract:
Using a dynamic mechanical analyzer, the comparative studies of a low-cycle bending
fatigue were carried out for AISI 1022 low-carbon steel after extreme thermal exposure, simulating the
severe beyond-design-basis accident at nuclear power plants. In the as-delivered state, the steel has a
high resistance to low-cycle fatigue (the fatigue strength at N = 3.5
×
10
4
cycles (
σ
Nf
) was 360 MPa).
Long-term thermal exposure led to a slight decrease in the resistance to low-cycle fatigue of steel:
σ
Nf
is decreased by 9%. The influence of AISI 1022 steel structure on the characteristics of fatigue
strength and fracture mechanisms is analyzed.
Keywords:
low-carbon steels; low-cycle fatigue; dynamic mechanical analyzer; fatigue crack; thermal
exposure; microstructure
1. Introduction
Currently, low-carbon steels remain the most popular structural material for civil
and industrial construction of buildings and structures [
1
–
3
]. This is due to the good
combination of satisfactory mechanical properties, good weldability and the low cost of
these steels. Therefore, as a rule, large-sized products and structures are made of such steels.
In particular, low-carbon steels of the AISI 1022 type (22 K—Russian standard) are used
for the manufacture of core catcher vessels (CC-vessel) with a wall thickness of 60 mm for
nuclear power plants with new VVER reactors [
4
]. The permissible operating temperatures
of products made of AISI 1022 steel do not exceed 450
◦
C [
5
–
7
]. At the same time, with
the development of a severe beyond-design-basis accident, when the corium falls outside
the reactor core, the CC-vessel, according to calculations, heats up to 1000–1200
◦
C with
subsequent long-term cooling [
8
,
9
]. Under such conditions, a significant change in the
steel structure can occur and, as a consequence, cause the degradation of the mechanical
properties of steel (due to the growth of austenitic grain and the development of reversible
temper embrittlement), leading to a loss of strength in the CC-vessel and an increase in the
risk of its fracture.
Recently, data on the study and clarification of the high-temperature properties of
low-carbon steels under static loading have appeared in the literature [
10
,
11
]. At the same
time, the problem of the resistance of the material for the CC-vessel to low-frequency,
low-cycle fatigue is urgent, primarily for nuclear power plants operating in seismically
active regions.
The low-cycle fatigue and high-cycle fatigue of low-carbon steels have been widely
studied [
12
–
20
]. However, detailed studies of the effect of the steel structure after extreme
Metals 2022, 12, 281. https://doi.org/10.3390/met12020281 https://www.mdpi.com/journal/metals
