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Formation of structures in cavitation-resistent Cr-Mn-V-N steels*

Formation of structures in cavitation-resistent Cr-Mn-V-N steels*Formation of structures in cavitation-resistent Cr-Mn-V-N steels*Formation of structures in cavitation-resistent Cr-Mn-V-N steels*
Lyudmila Isaeva, преподаватель, кандидат химических наук, доцент

Лев Исаак Ефимович, профессор, доктор технических наук, профессор

Национальная Металлургическая академия Украины, Украина

Шипицин Сергей Яковлевич, заведующий отделом, доктор технических наук, профессор

Академия наук Украины - Физико-технологический институт металлов и сплавов, Украина

Участник первенства: Национальное первенство по научной аналитике - "Украина";

Открытое Европейско-Азиатское первенство по научной аналитике;

Efficiency of dispersion hardening of the new generation cavitation–resistent Cr–Mn–V–N steels with stable austenitehad been investigated. Phases and structures forming at the annealing of samples in the interval 700–1200ºC had been determined. It was showed that the general level of cavitation stability for a steel with instable austenite is considerably lower than in steels with stable austenite.

Keywords: austenitic steel, phase, structure, dispersion hardening, cavitation stability.

 

Research into efficiency and mechanism of dispersion hardening of the new generation cavitation-resistent  Cr-Mn-V-N steels with stable austenite for high-temperature heat power engineering showed [1] that besides nanodimension incoherent particles of the basic hardening phases VN in the steel 17X15Г19АФcarrying (mass %): 0.17C; 0.08Si; 18.97Mn; 14.89Cr; 0.223N; 0.32V; 0.045Al; 0.011S; 0.013P also other phases are formed depending on the ageing temperature. The quantity and chemical analysis of these phases had been determined by the way of electric chemical dissolution of metallic base [2] as well as by means of the chemical and X-ray phase analysis [3].

Withthe purpose of approaching the system to equilibrium, the time of isothermal heating had been determined on the basis of data as to the influence of the ageing temperature upon the rate of isolating the particles VN in Cr-Ni austenite in the paper [3]. The time of isothermal heating, hours (at the temperatures), was: 2(1200); 4(1100); 6(1000); 10(900): 20(800); 30(700).

The phase analysis of a steel in accordance with the ageing temperature (Fig.1) had been determined in terms of elements’ content in electrolytic precipi tates and by literary data from the paper [4] about forming the possible phases in austenitic Cr – Mn – V – N steels.

· Continuation of research published in the Collection of materials of the XXIV International scientific and practical conference and of the first stage of the Championship in scientific analytics in physical, mathematical and technical sciences. London, 3–13 May 2012, p.p.86–89.

Fig. 1. Influence of the ageing temperature on the quantity Q of non–metallic phase: Cr23C6 (1), VN (2), Cr2N (3), MnmNn (Mn4N, Mn2N, Mn3N4)(4), AlN (5), MnS(6) in the steel 17Х14Г19АФ

According to obtained data, two hours–homogenization at 1200?C with water hardening ensures practically homogenous state of matrix, what means only its solid solution hardening with C, N, V, Cr. Besides coarse oval inclusions on the base of Al2O3, inclusions of AlN and MnS are also present in the structure on the boundaries of initial grains. (Fig.2, a, b).

Ageing at 700?C ensures in the main intragranular dispersion hardening with vanadium nitrides measuring up to 40nm in the quantity 18%). In spite of the great mass quantity of Cr23C6 in this sample, their influence on the dispersion hardening is not efficient because of their dimensions to some micrometers and isolation of vanadium nitrides along the boundaries of austenitic grain also in twins (Fig.2, e, f).

Under ageing at 900–1000?C the mass fraction of particles VN accounts for ~50% of their quantity under ageing at 700?C what ensures the complex solid solution and dispersion hardening of austenite (Fig.2, c, d).

Fig.2.Microstructures of annealed samples: a – 2(1200), x500; b – 2(1200), x 3000; c – 10(900), x500; d – 10(900), x300; e – 30(700), x500; f – 30(700), x3000

Cavitation stability for samples of steels under investigation had been determined by means of magnetostrictional method in the installation УЗДН–2тin water–pipe water at the room temperature and oscillation frequency 22 kHz by the loss of mass ?P·102, kg/m2 (Fig. 3).

Fig.3. Mass loss ?P of samples depending on the time of cavitation stability tests: a – steel 17Х14Г14АФ; b – steel 17Х15Г19АФ. Austenite hardening: 1 – solid solution hardening (homogenization at 1200ºC); 2 – complex(ageing at 900ºC); 3 – dispersion hardening (hardening at 700ºC)

For comparison, cavitation stability had been also determined in austenitic steel with instable austenite (17X14Г14АФ) that is used at present. Mass loss after 20 hours of tests made (see table) accordingly at the solid solution /complex/ dispersion hardening of austenite 2.8/ 3.4/ 6.5 and 2.3/ 1.9/ 1.5 for steels 17X14Г14АФwith instable austenite and 17X15Г19АФ.

Table

Change in hardness of samples after deformation hardening and subsequent tempering at 300 C – 2 hours.

Steel

Heat treatment

Hardness,HB

Before tempering

After tempering

Hardness decrease

17Х14Г14АФ

Homogenization, 1200ºС

 

310

277

33

Ageing, 900º C

290

258

32

Ageing, 700º C

290

282

8

17Х15Г19АФ

Homogenigation,1200ºС

260

243

17

Ageing, 900º C

270

261

9

Ageing, 700º C

300

297

3

It is obvious that the general level of cavitation stability in the steel with instable austenite is considerably lower than in the steel with stable austenite; beside that the replacement of the solid solution austenite in the first steel by dispersion hardening leads to essential decrease of cavitation stability, whereas in the second steel this, on the contrary, increases it. This is in agreement with data about the influence of the mode of austenite hardening on the degree and mechanism of deformation hardening.

An important advantage of deformation hardening by dislocation mechanism this is  its increased heat stability what, indisputably, makes steels type 17X15Г19АФwith dispersion hardening more acceptable for heat power engineering.

 

References:

  1. Isayeva L., Shypitsyn S.Y., Lev I.Ye.  The formation of nitride and carbide phsesa under dispersion hardening of Cr-Mn-V-N austenic steels // Theory and practice in the physical, mathematical and technical sciences, 2012. P.86-89/
  2. Исаева Л.Е., Грещик А.М., Лев И.Е. Исследование процесса изолирования нитридов молибдена из сталей // Вопросы химии и химической технологии. Общегосударственный научно-технический журнал. Днепропетровск. 2005. № 1. С.163-167.
  3. Лев И.Е., Покидышев В.В., Лазарев Б.Г., Мицкевич Н.С. Анализ азотсодержащих соединений в сплавах железа. М.Металлургия. 1987. 120с.
  4. Бабаскин Ю.З., Шипицин С.Я., Кирчу И.Ф. Конструкционные и специальные стали с нитридной фазой. – Киев: Наукова думка, 2005. –  371с.
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Ваша оценка: Нет Средняя: 6.8 (6 голосов)
Комментарии: 3

Артамонова Елена Николаевна

Therefore, the present study is able assist in identifying whether the deformation-induced martensitic transformation varied as a function of carbon content and the resulting fracture behavior, thereby enabling us to understand the work-hardening behavior of these steels.

Выходец Александр Михайлович

Актуальная металловедческая работа - есть небольшая теория и проверка по классическим схемам проверки свойств. Глубокое изучение сложных структур имеет не просто методологическое значение. но может применено и в других направлениях - наррмер, при исследовании своств композитных материалов. Подходы авторов могут дать основу для исследования 6-8 составляющих в системе.

Руденко Нина Павловна

Данный доклад посвящен актуальной тематике. Исследования проведены на достаточно высоком научном уровне. Важным моментом работы является глубокое изучение структуры исследуемой системы. Результаты работы могут найти применение в различных областях технических приложений, в частности, в тепловой энергетике. Авторам доклада желаем успешного продолжения экспериментов и развития научного обоснования полученных новых результатов. Нина Руденко. Левко Елена.
Комментарии: 3

Артамонова Елена Николаевна

Therefore, the present study is able assist in identifying whether the deformation-induced martensitic transformation varied as a function of carbon content and the resulting fracture behavior, thereby enabling us to understand the work-hardening behavior of these steels.

Выходец Александр Михайлович

Актуальная металловедческая работа - есть небольшая теория и проверка по классическим схемам проверки свойств. Глубокое изучение сложных структур имеет не просто методологическое значение. но может применено и в других направлениях - наррмер, при исследовании своств композитных материалов. Подходы авторов могут дать основу для исследования 6-8 составляющих в системе.

Руденко Нина Павловна

Данный доклад посвящен актуальной тематике. Исследования проведены на достаточно высоком научном уровне. Важным моментом работы является глубокое изучение структуры исследуемой системы. Результаты работы могут найти применение в различных областях технических приложений, в частности, в тепловой энергетике. Авторам доклада желаем успешного продолжения экспериментов и развития научного обоснования полученных новых результатов. Нина Руденко. Левко Елена.
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