SPECIAL FEATURES OF FORMATION OF STRUCTURE AND PROPERTIES
OF STEELS WITH HETEROGENEOUS BAINITE-MARTENSITE
STRUCTURE FOR GAS AND OIL PIPELINES
S. V. Belikov,
K. I. Sergeeva,
O. Yu. Kornienko,
I. N. Ashikhmina,
and A. I. Stepanov
Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 12, pp. 9 – 14, December, 2010.
Processes of formation of heterogeneous bainite-martensite structure in steels used for making oil and gas
pipes are studied. It is shown that the type of the formed bainite (upper or lower) affects the impact toughness
and the corrosion resistance of the steels.
Key words: gas and oil pipelines, bainite-martensite structure, sparingly alloyed steel, corrosion.
Fabrication of low-alloy steels with about 2 wt.% alloy-
ing elements and a high level of mechanical properties is a
demand of today. However, creation of new steels should be
substantiated scientifically in order to obtain the required
structure and properties . For example, creation of a
martensitic structure leads not only to elevation of the
strength properties but also to a loss in the ductility, while the
cost of the alloying increases. Bainitic steels meet the re-
quirements mentioned better.
Novel bainitic steels contain a reduced amount of carbon
and alloying elements. These steels are heat treated with the
use of accelerated cooling that provides a bainitic structure.
They possess better weldability but higher strength due to a
finer bainitic structure [2, 3]. The range of commercial
bainitic steel includes
– low-carbon steels with high weldability;
– high-strength steels competing with hardened and
tempered martensitic alloys and steels and having a high
creep resistance; these grades have served for tens of years in
the power industry;
– forged steels preferred to martensitic alloys due to the
lower number of operations in the production process;
– inoculated steels, in which the intragrain formation of
bainite producing a random structure is stimulated by intro-
duction of particles of difficultly soluble compounds, which
elevates the resistance to crack propagation.
The structure of high-strength steels is represented by a
mixture of bainite, retained austenite, and martensite. The re-
quired hardenability is attained by introducing additives of
Mn, Cr, Ni and a considerable amount of Cr (about 2 wt.%)
in order to prevent formation of carbides [4 – 6].
It is important for the steel-intense gas and oil industry to
create martensite-bainite structures, which makes it possible
to alloy the metal more sparingly without deterioration of the
strength characteristics as compared to martensitic struc-
The aim of the present work
was to study the effect of
bainite on the fracture behavior, the impact toughness, and
the corrosion resistance of sparingly alloyed Cr – Mo – V
METHODS OF STUDY
We studied sparingly alloyed structural steels of grades
26Kh1MFA, 25Kh2M1FA, and 22Kh1MFA produced by the
“Seversky Pipe Plant” Company by a standard process. The
chemical composition of the steels is presented in Table 1.
Metallographic analysis was performed with the help of
an “Epiphot 200” light microscope with magnification of
´ 200 – 1000. Photographs of microstructure were obtained
using a “Nikon” digital camera and “Nis-Elements Basic Re-
The kinetics of the decomposition of supercooled austen-
ite under isothermal conditions in continuous cooling was
analyzed using a Linseis L78 R.I.T.A. dilatometer equipped
Metal Science and Heat Treatment, Vol. 52, Nos. 11 – 12, March, 2011 (Russian Original Nos. 11 – 12, November – December, 2010)
0026-0673/11/1112-0581 © 2011 Springer Science + Business Media, Inc.
Ural Federal University in the Name of the First President of Rus
sia B. N. Eltsyn, Ekaterinburg, Russia.
“Severskii Pipe Plant” Company, Polevskoi, Russia (e-mail:
We have used some results obtained at the Laboratory for Struc
tural Methods of Analysis and Properties of Materials and Nano
materials of the UGTU-UPI Collective Use Center.