on microstructure formation features of 9 % nickel … · its content in ferrite nickel steels is...

Pavel P. Poletskov, Olga A. Nikitenko, Dmitry M. Chukin, Marina S. Gushchina, Sergey А. Fedoseev

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ON MICROSTRUCTURE FORMATION FEATURES OF 9 % NICKEL COLD-RESISTANT STEEL AND ITS PROPERTIES

BROUGHT ABOUT BY DIFFERENT HEATING TREATMENT PROCEDURES


ABSTRACT

The communication presents results on microstructure integrated analysis of nickel cold-resistant steel «0Н9А» (9 % Ni) and its properties brought about by various heat treatment procedures: single, double hardening and fol-lowing high-temperature tempering at 500°С, 550°С, 600°С. It is shown that a structure consisting of tempered martensite, residual austenite, α-phase, and carbide particles, plating out mostly on grain boundaries is formed after single hardening and subsequent tempering in the investigated temperature range. This results in steel embrittlement. Verification is obtained by fractographic analyses and Charpy V-notch impact toughness at cryogenic temperature –196°С (49 J/cm2 - 58 J/cm2). A dsperse plastic duplex structure is formed upon double hardening in the intercritical temperature range (ITR, lamellarizing process) and subsequent high-temperature tempering. It consists of α-phase, “new” strips martensite, tempered martensite structure areas and residual stable austenite of a volume fraction of ca 4 % providing fracture resistance under cryogenic temperatures. Top-of-the-line properties combinations are also observed: hardness HV1 of 2826-2875 MPa, tensile strength of 850-860 MPa and impact toughness under cryogenic temperatures – 196°С of 105 - 107 J/cm2. They exceed twice the international standards requirements.

Keywords: rolled steel, cryogenic constructional steel, 9%Ni Steel, LNG tanks, single hardening, double harden-ing, heat treatment, tempering, impact toughness, cold-resistance, strength, hardness.

Received 17 April 2018Accepted 15 June 2018

Journal of Chemical Technology and Metallurgy, 53, 5, 2018, 967-976

Nosov Magnitogorsk State Technical University Lenin Street, 38, Magnitogorsk city, Chelyabinsk RegionRussian Federation, 455000E-mail: [email protected].

INTRODUCTION

The alloys used in machinery and equipment for producing, storage and transportation of liquefied natural gas (LNG) of a boiling temperature of – 80°С belong to cryogenic (cold-resistance) steels. They have complex features set defined by their duty – they have to provide the strength required but in combination with high toughness and plasticity. Moreover, such alloys must have a small sensitivity to stress concentration and low susceptibility to brittle fracture under extremely cold temperatures [1 - 4]. The technology of manufacturing pressure-tight facilities, tubes, and thin-wall construc-tions under low temperatures requires satisfactory

weldability of the corresponding steels under low tem-peratures. The steel high corrosion resistance is one of its most important characteristics [5 - 7].

Aluminum, austenite Cr-Ni, Cr-Mn, Cr-Ni-Mn steels and ferrite steels alloyed with nickel are widely used [8-10]. They are expected to ensure deficiency of con-struction brittle fractures under cryogenic temperature (– 164°C) specific for LNG. According to the analysis, the steel containing 9% of Ni is the most advanced material in terms of a low content of expensive alloy elements, high strength, cold-resistance and suitable weldability, which is used in Russian iron and steel works. The use of this steel has started in 1952 and ever since it is widely used for manufacturing cryogenic tanks inwalls. The

Journal of Chemical Technology and Metallurgy, 53, 5, 2018

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cryogenic steel containing 9% of Ni is included in the international standards: ASTM A 353, ASTM A 553, EN 10028-4, ISO 9328-4:2011, JIS G3127. It is also in-cluded in the technical regulations of the Russian works [12 - 13]. This ferrite steel high cold-resistance, which is comparable to that of austenite class steels, is obtained in the course of a heat treatment of stable austenite areas of a volume fraction of ca 4 %. This provides resistance to breakage at cryogenic temperatures [11, 14-17, 18-23]. A great quantity of retained austenite can be produced by additional steel hardening in ITR in correspondence with refs. [11, 14, 15, 18, 19, 25 - 28].

The heat in ITR low part is provided by austenite formation in alloyed nickel steels. The austenite, in that case, is enriched not only in carbon but also in alloy elements. Depending on the heat treatment conditions, different types of structures and significant changes of the volume fractions are observed in the two-phase (α + γ) field of mild nickel steels. Such heat treatment finds a practical use in increasing the strength properties of steels used for cryogenic equipment [11, 14, 18, 19] as well as for cold-resistance improvement of some steels. But suitable properties and structures can be achieved only in the course of a correct heat treatment.

The aim of this work is to analyze the heat treatment effect on microstructure formation of 9 % nickel cold-resistance rolled steel and a complex of its properties.

EXPERIMENTAL

Nickel containing cryogenic constructional steel 0H9A was chosen. Its chemical composition and the heat treatment conditions are presented in Table 1.

It is worth adding that nickel is the basic alloy ele-ment of this steel. Its function consists in stabilization of austenite produced in process of heat treatment. Austen-ite must be enriched with alloy elements as much as to stay stable under temperatures to – 196°C. That is why the nickel quantity in such steels is standardized in the range from 8,5 % to 9,5 %. The manganese additive in-creases austenite stability, but as it provides an extension of steel temper embrittlement, its content is not higher than 0,6 %. The carbon present in the constructional steel decreases its cold-resistance [8, 10] and which is its content in ferrite nickel steels is limited up to 0,06 %. Silicon provides additional strength but it can also have a negative effect, either on the toughness or the heat-affected zone during hardening. That is why its content is less than 0,37 %. The impurity elements such as sulfur and phosphorus, decrease the constructional steel tough-ness. This limits the sulfur and phosphorus content to less than 0,003 % and 0,010 %, correspondingly.

The analysis presented in this investigation was carried out in the scientific manufacturing complex „Engineering center Termodeform – NMSTU“. There,

Table 1. Chemical composition of 0Н9А steel and heat treatment conditions of ultracold-resistance rolled steel.

Content of chemical element (wt %), less or in range

HT temperature, °С

C Si Mn S P Ni First

hardening (from γ range)

Second hardening (from IRT

temperatures)

Tempering

0,06 0,17-0,37

0,6 0,003 0,010 8,5-9,5

830

- - - 500 - 550 - 600

670 - 670 550 670 600


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the actual steel and rolled metal production process was imitated by using:

– an induction vacuum furnace ZG-0.06L smelting less than 60 kg of steel;

– a chamber furnace PKM 3.6.2/12.5 for heating prior to the deformation treatment;

– a flued-actuated press P6334 of 250 t force for imitation hot roughing-down processes;

– a reversing hot rolling 500 „DUO“ mill combined with a control quenching plant (laminar supply, a sepa-rate control, a quenching speed 80°С/sec) for accelerated quenching processes imitation after rolling and also different types of heat treatment [29].

The metallographic analysis of the steel testing prototypes was carried out at „Nanosteel“ research in-stitute, Nosov Magnitogorsk State Technical University (Magnitogorsk, Russian Federation).

Prototypes of a diameter of 10 mm and a length of 80 mm were changed over to austenite condition aiming an undercooled austenite decomposition analysis of a given steel using Gleeble 3500 complex. Heating in a vacuum to 800°С with a speed 1°С/s was followed by holding within 15 min. Then cooling with a speed rang-ing from 0,025°С/s to 40°С/s was applied. The critical steel points were found by dilatometric tests carried out with a module Pocket Jaw complex.

Prototypes micro slices were prepared by pressing into «Transoptic» resin on Simplimet 1000 automatic press from Buеchler. A standard procedure was applied. Aiming microstructure defining the micro-slice surface was polished through immersing in a bath containing 4 % solution of nitric acid in ethanol. The metallographic analysis was made using Meiji Techno optical micro-scope with 200 to 1000 times magnifications. A picture computer analysis was done by using Thixomet PRO system [20]. The microstructure was studied with JSM 6490 LV scanning electron microscope in case of higher magnifications higher. The electron microprobe analysis was carried out with INCA Energy system.

The microhardness was determined by Buchler Mikromet hardness meter using the pressing-in method of a diamond pyramid with 136° angle between opposite planes. This was in accordance with GOST 9450-60. The force was 1 kg, while the pressing duration was 10 sec.

Differential-scanning calorimetry was carried out using the simultaneous thermal analysis device STA (Iupiter 449 F3) from «NETZSCH» (Germany). The sample was heated to 900°С in an alumina crucible with a speed of 20°С/min. A rare gas (argon) environment was provided. The samples weight was ca 79 mg.

The amount of the retained austenite was defined using a x-ray diffractometer Shimadzu XRD-7000. It had Cr anode tube, the voltage was 40 kV, while the current was 30 mA. The angle 2θ ranged between 66° and 71°, the shooting speed was 0,1 °/min. The quanti-tative characterization was made on the ground of the proportion of the diffraction maximum integral intensity of plane system (111): austenite (2θ = 67,1°) and (110) martensite (2θ = 68,7°) phase.

RESULTS AND DISCUSSION

The study shows that a structure of a packet-reed (or so-called dislocation) low-carbon martensite is formed (Fig. 1a) in course of single hardening. It refers to heating to the γ -area and subsequent cooling in water. It is also seen that the strips α-crystal parallel rows are extended in <111> α || <011> γ direction while grouping into pack-ages. The thickness of the plates in the bag is 0.2-2 μm, the length – 30 μm. The structure of such martensite, as well recognized, is formed by the sliding mechanism. The elementary volume of transformation has the form of a strip, each of which is a homogeneous shift result Sequential shifts form layers and then a package of par-allel rails. The slats are separated by thin interlayers of residual austenite with a thickness of ca 10 nm -20 nm [23 - 24]. The hardness of the sample is 3744 MPa. This high value is due to the small transverse dimensions of the martensitic crystals and the high density of disloca-tions in this steel after the rapid cooling (in water).

The subsequent heating of the hardened steel leads to a diffusion decay of the quenched structure. The microstructure of the sample after quenching at 830°C and subsequent tempering at 500°C consists of α-crystals and small cementite particles, which are released both along the needle boundaries of the α-phase and the primary austenite grains, but predominantly inside the grains (Fig. 1b). The inclusions identification by a mi-


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croprobe analysis shows the presence of nickel, carbon, manganese, molybdenum, titanium and niobium in addition to iron. Thus, the inclusions can be identified as complex carbides (carbonitrides) of molybdenum, titanium and niobium. Due to the low diffusion rate at these temperatures (500°C - 550°C), the process of formation of alloying elements special carbides is very slow. The shape of the α-phase crystals is determined by the initial structure of the lath martensite. The hardness of the sample is 2972 MPa.

The microstructure of the sample after quenching at 830°C and subsequent tempering at 550°C consists also of α-phase crystals and fine cementite particles, but the separation of the latter along the grain boundaries is

better expressed due to the diffusion rate increase (Fig. 1c). The shape of α-phase crystals is still determined by the original lath structure of the martensite, but the signs of its destruction become more obvious. The hardness of the sample is 2955 MPa.

The microstructure of the sample after quenching at 830°C and subsequent tempering at 600°C is shown in Fig. 1d. The diffusion mobility of the atoms is quite high at this temperature. The formation of carbides proceeds faster and in a greater amount than that at 550°C. Their spheroidization takes place. Besides, their size increases up to 0.1 μm.

However, the precipitation of the carbide phase pro-ceeds predominantly along the grain boundaries, where

a b

c d

Fig. 1. Samples microstructure after single hardening at 830°С (a) 10 J/cm2 and tempering at 500°C (b) 49 J/cm2, 550°С (c) 52 J/cm2 and 600°С (d) 58 J/cm2.


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the greatest depletion of the alloying elements occurs (Fig. 1d). Lath crystals partially lose their shape, but there is a small amount of residual austenite between the remaining slats. According to the X-ray diffractometer data, its amount is 1.6 %. The hardness of the sample is 2856 MPa.

The release of carbides at these tempering tem-peratures proceeds mainly along the grain boundaries, which leads to embrittlement of the steel. This fact is confirmed by the readings of the toughness at – 196°C (49 J/cm2 - 58 J/cm2). They refer to the lower limit of the

foreign quantities admissible values (Table 2), and the corresponding nature of the failure (Fig. 4a-b).

The microstructure after double quenching (at 830°C and 670°C with cooling in water) is shown in the Fig. 2а.

The temperature of heating in case of the second quenching - 670°C is in the temperatures ITR – it ex-ceeds Ac1 point (624°C), but is below Ac3 point (720°C) (Fig. 3). Therefore, a new austenite appears on repeated heating along with α phase, the „former“ martensite. The latter is initially present but undergoes decomposition on heating. When cooled, this austenite turns into a „new

Fig. 2. A microstructure obtained upon double quenching at 830°C and 670°C (a, b) (toughness of 20 J/cm2 at –196°C) and subsequent tempering at 550°C (c) (toughness of 105 J/cm2 at – 196°C) and 600°C (d) (toughness of 107 J/cm2 at – 196°C).

a b

c d


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portion“ of martensite along with the „old“ one. Thus, the structure after double quenching at 830°C and 670°C consists of an α phase and a „new“ martensitic phase. The latter is characterized by the presence of carbide par-ticles and residual austenite located along the boundaries of the martensitic crystals. The presence of the α phase upon double quenching from ITR explains the lower

value of hardness (3319 MPa) than that obtained in the course of a single hardening (3744 MPa).

In case of double quenching from the ITR, austenite is formed at the boundaries of the preceding austenite grains. Moreover, the heating to the lower part of ITR is accompanied by the formation of austenite enriched not only with carbon, but also with doping elements [16].

Table 2. Summarization of the results obtained.

Temperature, °С The amount of residual austenite at – 196 С, %

Impact strength

Charpy V (transv.)

at – 196 С, J/cm2

Tensile strength,

MPa

Hardness, НV1, MPa

Grain size, µ

The first hardening

(From γ-area)

The second

hardening (from ITR)

Tempering

830

- - - 10 1270 3744 - - 500 1,3 49 910 2972 11-14 - 550 1,4 52 890 2955 11-12 - 600 1,6 58 860 2856 8,9-11

670 - - 20 1120 3319 - 670 550 3,6 105 860 2875 6,8-9 670 600 3,8 107 850 2826 9

Requirements: ASTM А 553 ≥ 43 690-825 - - EN 10028-4 ≥ 50 640-840 - -

Fig. 3. Differential scanning calorimetry results obtained in case of heating after single quenching (at 830°C) (line 1) and double quenching (at 830°C and at 670°C) (line 2).


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This austenite becomes a „new“ martensite enriched with stabilizing elements in the course of a subsequent cool-ing. In this case, the „new“ martensite has a lower Ac1 point than the martensite undergoing a single quenching. This is confirmed by the results obtained by differential scanning calorimetry (DSC) (Fig. 3): Ac1 decreases by 20°C and amounts to 604°C, while Ac3 does not change.

Thus, the ITR of the temperature of the steel under study after a single hardening is ca 624°С -720°С, while the double it is ca 604°С - 720°С.

The microstructure of the samples after double quenching and subsequent tempering at 550°C and

600°C is shown in Fig. 2c-d. During the tempering process, the martensite also diffusively decomposes, but if the temperature is 500°C the martensite keeps its lath structure (orientation). A disruption of orientation proceeds at 600°C. Thus, the microstructure consists of an α-phase, a „new“ martensite, a martensite and a residual stable austenite with a volume fraction of about 4 % after tempering (550°C and 600°C). An increase in the residual austenite proportion in this treatment leads to a twofold increase of the toughness to 105 J/cm2 -107 J/cm2 (at – 196 °C), which provides resistance to fracture along a viscous mechanism (Fig. 4c-d).

Fig. 4. Fractografic studies of samples after single hardening at 830°C (10 J/cm2) and subsequent tempering at 600°C (a-b) (58 J/cm2) and after double quenching at 830°C and 670°C (20 J/cm2) and a subsequent tempering at 550°C (105 J/cm2) and 600°C (c-d) (107 J/cm2).

a b

c d


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The fractographic studies of the steel samples provide to establish the features of their destruction at cryogenic temperatures (Fig. 4). The fracture surface after single hardening and subsequent tempering at 600°C is shown in Fig. 4 (a-b). The electron microscopy shows predominantly “river patterns” or a “streamline structure” of the fracture (shown by arrows) (Fig. 4b) of the sample under investigation. This results from the interaction of a moving crack with the crystal defects, and the presence of preferred crystallographic facet ori-entations cleavage. There are areas of a pitched structure of the fracture (Fig. 4b) only at some places.

Thus, two different mechanisms of destruction are ob-served: a brittle one (or a fracture by cleavage) and a viscous one (occurring through nucleation, growth and fusion of micropores), but with a predominantly brittle component.

The fracture surface after double quenching and subsequent tempering at 550°C and 600°C is shown in Fig. 4c. The SEM examination reveals the presence of dimples, a characteristic “cup” structure of the fracture. As is known that the viscous fracture usually begins with the formation of microcracks in or near the second phase or the nonmetallic inclusions particles. Due to the weak cohesive strength of the interphase boundary, the inclusion-matrix already at an early stage produces pores

that grow and appear as pits at the break (Fig. 4c). Thus, this kind of a fracture can be as a viscous one (Fig. 4c-d).

The general results of the research refer to the meas-urements of the amount of residual austenite, values of toughness (cold resistance), hardness, temporary tear resistance and grain size (Table 2).

The CCT diagram of «0H9A» (9% Ni) cryogenic steel is presented in Fig. 5. It shows that austenite under-goes a transformation with the formation of martensitic and bainitic type structures during continuous cooling.

Martensite-austenite sections together with bainite are observed in the structure in the range of cooling rates from 0.025 °C/s to 1°C/s. The further cooling rate increase from 1 °C/s to 20°C/s results in martensite con-tent increase. This is accompanied by hardness increase from 2960 MPa to 3600 MPa. Martensitic transformation only takes place at cooling rates higher than 20°C/s. The obtained data is confirmed by the results of the study, obtained by means of optical and electron microscopy.

CONCLUSIONSThe investigations carried out provide to determine

the effect of thermal treatment (single, double quench-ing and subsequent high tempering at temperatures of 500°C, 550°C, 600°C) on the microstructure formation

Fig. 5. CCT diagram of «0H9A» cryogenic steel.


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and the complex properties of cold-resistant 0H9A (9 % Ni) steel. It is found that upon single hardening and subsequent tempering, a structure is formed in the inves-tigated temperature range consisting of release temper-ing martensite, residual austenite, α-phase and carbide particles, which are predominantly distributed along the grain boundaries, leading to steel embrittlement. After double quenching, a disperse plate-like duplex structure consisting of an α-phase, a „new“ martensite, a section with a tempered martensite structure and a residual stable austenite with a volume fraction of ca 4 %, is formed from the ITR and subsequent high tempering. This pro-vides fracture resistance at cryogenic temperatures by a viscous mechanism. After this treatment, the toughness at cryogenic temperatures (– 196°C) exceeds twice the values obtained by single hardening and high tempering regime without significant loss of strength characteris-tics. Thus, the best combination of properties is obtained: HV1 hardness of 2826 MPa - 2875 MPa, tensile strength of 850 MPa - 860 MPa, impact strength of 105 J/cm2 - 107 J/cm2 at –196°C. The mechanical properties deter-mined fully meet the requirements of ASTM A 553 and EN 10028-4 standards valid for production, transporta-tion and storage of liquefied natural gas.

AcknowledgementsThe study was financially supported by Ministry

of Education and Science of the Russian Federation within the scope of accomplishment of multiple-purpose projects of creating modern high-tech production with the participation of higher education institutions (Con-tract 03.G25.31.0235).

REFERENCES

1. P. Poletskov, K. Khakimullin, D. Nabatchikov, Pur-pose and scope of cold-resistant nanostructured sheet metal, Vestnik of Nosov Magnitogorsk State Technical University, 11, 2017, 85-88, (in Russian).

2. Seok Su Sohn, Seokmin Hong, Junghoon Lee, Effects of Mn and Al contents on cryogenic-temperature tensile and Charpy impact properties in four aus-tenitic high-Mn steels, Acta Materialia, 100, 2015, 39-52.

3. Lu Y.Q., Hui H. Investigation on Mechanical Be-haviors of Cold Stretched and Cryogenic Stretched Austenitic Stainless Steel Pressure Vessels, Procedia Engineering, 130, 2015, 628-637.

4. E.N. Kablov, M.P. Lebedev, O.V. Startsev, Climatic testing of materials, structural elements, machin-ery and equipment in extremely low temperatures, Proceedings of the VI Eurasian Symposium on the Strength of Materials and Machines for Cold Re-gions Eurastrencold, Yakutsk, 2013, 5-7.

5. M.V. Chukin, P.P. Poletskov, D.G. Nabatchikov, Analysis of technical requirements for ultra-cold-resistant sheet metal, Bulletin of the South Ural State University. Series «Metallurgy», 2, 2017, 52-60, (in Russian).

6. I.V. Crismaru, D. Dragomir-Stanciu, M.V. Atanasiu, The Behavior of a 1.4301 Stainless Steel Subjected to Cryogenic Temperatures, Procedia Technology, 19, 2015, 247-253.

7. Lu Y.Q., Investigation on Mechanical Behaviors of Cold Stretched and Cryogenic Stretched Austenitic Stainless Steel Pressure Vessels, Procedia Engineer-ing, 130, 2015, 628-637.

8. M.Yu. Matrosov, V.N. Zikeev, P.G. Martynov, Devel-opment of promising samples of cryogenic steels for gas carriers and stationary storage tanks for liquefied natural gas intended for use in the Arctic, Arctic: Ecology and Economy, 4, 2016, 80-89, (in Russian).

9. I.V. Gorinin, Yu. L. Legostaev, E.P. Osokin, Problems of marine transportation of liquefied natural gas: Materials for tank vessels of gas carriers, Shipbuild-ing, 5, 2009, 32-40, (in Russian).

10. G.K. Lavrenchenko, A.V. Kopytin, Cryogenic com-plexes for the production and shipment of LNG, its reception, storage and regasification in the inter-national trading system, Technical gases, 3, 2010, 2-19, (in Russian).

11. L. Smith, B. Craig, Properties of Metallic Materials for LNG Service, Presented at 9th MECC, Bahrain, 2001.

12. A.S. Zubchenko, M.M. Koloskov, Yu.V. Kashirsky, Marochnik of steels and alloys, Mechanical engi-neering, 2003, p. 784, (in Russian).

13. ASTM A553/A553M/ Standard Specification for Pressure Vessel Plates. Alloy Steel Quenched and


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Tempered 7, 8 and 9% Ni, STANDARD by ASTM International, 2014.

14. BS EN 10028-4:2017 Flat products made of steels for pressure purposes. Nickel alloy steels with specified low temperature properties.

15. S.A. Golovanenko, N.M. Fontstein, Two-phase low-alloy steels, Moscow, Metallurgy, 1984. P 206.

16. I.V. Gorynin, E.I. Khlusova, Nanostructured steels for the development of deposits of the shelf of the Arctic Ocean, Bulletin of the Russian Academy of Sciences, 12, 2010, 1069-1075.

17. F.B. Pickering, Physical metallurgy and develop-ment of steels, Moscow, Metallurgy, 1982, p. 183, (in Russian).

18. B.P. Sharov, V.N. Zikeev, L.I. Gladshtein, Proper-ties of 0H9 steel for cryogenic equipment, Steel, 3, 1988, 76-78.

19. E.V. Konopleva, R.I. Entie, V.M. Bayazitov, Thermo-cyclic treatment of low-carbon steels with quenching from the intercritical temperature range, Metallurgy and heat treatment of metals, 8, 1988, (in Russian).

20. V.M. Salganik, P.P. Poletskov, M.O. Artamonova, Scientific and production complex “Thermodeform” for the creation of new technologies, Steel, 4, 2014, 104-107, (in Russian).

21. Kogan, E.F. Matrokhina, R.I. Entin, Effect of aus-tenitization in the intercritical temperature range on the structure and properties of low-carbon steels, Physics of Metals and Metallurgy, 1981.

22. N.V. Koptseva, M.V.Chukin, O.A. Nikitenko, Use of the Thixomet pro software for quantitative analysis of the ultrafine-grain structure of low-and medium-

carbon steels subjected to equal channel angular pressing, Metal Science and Heat Treatment, 7-8, 2012, 387-392, (in Russian).

23. V.M. Schastlivtsev, N.V. Koptseva, T.V. Artemova, Electron-microscopic study of the structure of mar-tensite in low-carbon alloys of iron, Physics of met-als and metallurgy, 6, 1976, 1251-1260, (in Russian).

24. V.D. Sadovsky, N.P. Chuprakova, The effect of heat treatment on the amount of residual austenite and its decay during tempering in structural chromium-nickel steels, 10, 1941, 139-151.

25. A.Yu. Kaletin, Effect of residual austenite on the structure and properties of structural steels after a high tempering, PhD thesis, Sverdlovsk, 1985, p. 199.

26. Zhang J.M., H. Li, F. Yang, Q. Chi, L.K. Ji, Y.R. Feng, Effect of Heat Treatment Process on Me-chanical Properties and Microstructure of a 9% Ni Steel for Large LNG Storage Tanks, Journal of Materials Engineering and Performance, 22, 12, 2013, 3867-3871.

27. P. Stratman, E. Hornbogen, Mechanical properties of two-phase duplex and dispersed structures of nickel steels, Black metals, 12, 1979, 35-40.

28. E. F. Nippes, J. P. Balaguer, A Study of the Weld Heat-Affected Zone Toughness of 9 % Nickel Steel, Welding research supplement, 1986, 237-243.

29. Erin Barrick, Fundamental Studies of Phase Trans-formations and Mechanical Properties in the Heat Affected Zone of 10 wt% Nickel Steel, A Thesis Presented to the Graduate and Research Committee of Lehigh University in Candidacy for the Degree of Master of Science, 2016, p. 134.

on microstructure formation features of 9 % nickel … · its content in ferrite nickel steels is...

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