DOI 10.1007/s11015-017-0533-6 Metallurgist, Vol. 61, Nos. 7–8, November, 2017 (Russian Original Nos. 7–8, July–August, 2017)

DEVELOPMENT OF SUPERALLOY PRODUCTION AT THE ELECTROSTAL METALLURGICAL PLANT I. V. Kabanov,1 B. S. Lomberg,2 and T. N. Sidorina1

UDC 669.14.018.44

Stages of superalloy production development at the Electrostal Metallurgical Plant are reviewed. Dynamics of the increase in stress-rupture strength indices, and also areas for improvement of manufacturing technology providing the requirements for superalloys are reviewed. Keywords: stress-rupture strength, superalloys, carbide strengthening, intermetallic strengthening.

The Electrostal Metallurgical Plant, producing the first melt in 1917, was considered by the founders as the first plant in Russia for high quality metallurgy. In fact, for this reason the first electrometallurgical furnaces in the country were installed, i.e., advanced not yet assimilated but most promising from the point of view of preparing especially high quality metal. In fact for this reason all subsequent destiny of the plant was put together in order that within Russia industrial technology for manufacture of almost all steels and alloys was developed, proven, and obtained a “pass into life” in the plant. Over many years, the plant in fact had the unofficial status of a plant-laboratory, The first steels produced in the plant were structural low-alloy, tool, and ball bearing. Then the grade range was modified and subsequently stainless steel of type 18-8, and materials with controlled magnetic properties were produced. Therefore, at the time of assimilation of high-temperature steels the plant had specific experience for manufacture of complexly alloyed steels [1]. The history of development for superalloy production may be separated into three large stages [2]. The first stage is a search for obtaining the required level of stress-rupture strength by expanding alloying of existing steels. The second stage (started about 1945) is connected with creation overseas of the first “nimonic” alloy and a suggestion of using nickel as a base for superalloys. In fact at this time the active phase started of creating superalloys capable of providing the set of properties required for aero engines. The third stage (start related to the middle of the 1960s) was connected with introduction into industrial production of methods of special metallurgy, i.e., processes of vacuum induction melting (VI), vacuum arc (VA), and electroslag (ES) remelting. In 1948, the plant was given the task of creating technology for melting superalloys and organizing their industrial production. At the same time, at the end of the 1940s VIAM began research on superalloys for gas turbine engines (GTE). A difficult task was set of creating superalloys operating for quite a long time at 1000°C. It should be noted that in 1945 at VIAM there was development and at the Electrostal Plant there was industrial approval of steel EI388 containing up to 36% of alloying elements having 100 h stress-rupture strength of 43 kgf/mm2 (~422 MPa) at 600°C. However, at 800°C the steel weakened to 13 kgf/mm2 (127.5 MPa) which was inadequate. A further increase in the level of heat resistance occurred due to an increase in the proportion of alloying elements in the complexly alloyed steels: following this path were steels EI395, EI787, and EP105 containing up to 50% alloying 1 2

Electrostal Metallurgical Plant, Electrostal, Moscow Region, Russia; e-mail: [email protected]. State Research Center of the Russian Federation – All-Russia Research Institute of Aviation Materials (VIAM), Moscow, Russia; e-mail: [email protected].

Translated from Metallurg, No. 7, pp. 53–56, July, 2017. Original article submitted July 5, 2017.

0026-0894/17/0708-0565 ©2017 Springer Science+Business Media New York

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TABLE 1. Stress-Rupture Strength of GTE Alloys Stress-rupture strength σ100 (kgf/mm2/MPa) at temperature, °C

Alloy 500

600

700

800

900

1000

EI437

73/716

58/569

36/353

15/147

–

–

EI617

–

–

57 /559

32/314

–

–

EI826

–

–

65/637

38/373

16/157

–

EI867

–

–

76/745

47/461

22/216

–

EI929

–

–

74/726

45/441

22/216

7/69

EP220

–

–

80/785

49/481

28/275

10/98

TABLE 2. Stress-Rupture Strength of First Disk Nickel Alloys Alloy

Stress-rupture strength σ100 (MPa) at temperature, °C 650

750

EI437B

620

300

EI698

720

420

components. Similar alloying made it possible to raise the level of the 100 h stress-rupture strength at 800°C to 22 kgf/mm2 (~216 MPa), but at 900°C they weakened to an unacceptable level [3]. For development and industrial technology of manufacturing these alloys, the plant specialists together with workers of the aviation industry were awarded a USSR state prize. Therefore, development of superalloys based on complexly alloyed steels as a result of increasing the amount of alloying components made it possible to achieve a certain level of stress-rupture strength, but did not provide the results required and they almost came to an end. It became clear that in order to achieve the stated aim another fundamental approach was necessary. The second stage of producing superalloys in the plant was connected with development and introduction of industrial technology for producing superalloys based on nickel. Taking account of experience of development abroad the first alloy of the nimonic type, VIAM specialists started in 1947 extensive research on nickel-base superalloys and studies the field of superalloy strengthening theory. The aim at this stage was creation of alloys with a working temperature of 900°C and a test life 25–50 h. Research and development of superalloys for GTE components showed that alloys should be differentiated with respect to their purpose since turbine disk and compressor blades, and combustion chamber components operate under different conditions from the point of view loading, stressed state, and thermal regime. Therefore, for each group of materials it was necessary to develop special technology for their manufacture. The first domestic alloy for blades based on nickel was alloy EI437 [2, 3]. Subsequently, in view of the requirements of GTE builders a group of heat-resistant wrought alloys was created for blades with better properties. Creation of industrial technology for alloy manufacture in the plant was completed in the 1950s. The level of stress-rupture strength is given in Table 1. Turbine disks operate at considerably lower temperatures than rotor blades. However, the stressed state for them is much more complicated. The first material used for disks was the steel mentioned previously EI388. Then, production was assimilated for iron-nickel alloys EI696 (58% iron) and EI787 (41% iron). The stress-rupture strength for 100 h of loading at 600°C for alloy EI787 reached the level of 70 kgf/mm2 (686 MPa) and 45 kgf/mm2 (441 MPa) at 700°C. Currently, these materials are still in demand and are mass produced by the plant for disks of small and medium sizes. These alloys were the predecessors of disk nickel superalloys. In this period, the plant developed and proved a technology for production of the first 566

TABLE 3. Stress-Rupture Strength of Contemporary Superalloys Produced by Plant Stress-rupture strength σ100 (MPa) at temperature, °C

Alloy

650

750

EP742

830

520

EK79

900

600

EK151

1050

650

EP975

1080

750

TABLE 4. Mechanical Properties of Contemporary Superalloys Produced by Plant Alloy

σu, MPa

σ02, MPa

δ, %

EP742

1300

800

20

EK79

1350

950

18

EK151

1450

1050

16

EP975

1400

1050

14

nickel alloys as disks: EI437B (modification of an alloy developed previously for blades EI437) and alloy EI698 whose composition ad properties (Table 2) appeared to be so successful that they are used extensively in GTE at the current time [4, 5]. Alloys for combustion chambers should exhibit good gas corrosion resistance, have good thermal shock resistance indices, and also adaptability during forging, rolling, and welding. In this case, a lower level of stress-rupture strength is acceptable [2, 3]. Among nickel alloys of this generation at the plant alloys EI435, EI602, and EI703 were assimilated, and somewhat later alloy EI868. All these alloys are in extensive demand and are currently mass produced by the plant. Towards the start of the 1960s, it became evident that a further increase in superalloy material properties depended on their structure, nonmetallic inclusion, gases, and harmful impurity content. At the Electrostal Plant, at this time vacuum induction and also vacuum arc and electroslag furnaces were installed and operated. This determined to a significant extent the possibility of producing new materials exhibiting good mechanical property indices, stress-rupture strength, but displaying low production ductility. The presence in the plant of special equipment for deformation (4000 Ts press, 3600 MN press) made this problem fundamentally resolvable. With close cooperation of VIAM specialists and the plant industrial technology for producing metallurgical semiproducts was developed and introduced in the plant (forgings, washers, extruded bars) of a new generation of superalloys. These alloys with respect to operating and mechanical properties are at the level of overseas analogs and with respect to stress-rupture strength surpass them (Tables 3 and 4) [4, 6–8]. In the last decade, in the plant industrial technology has been developed and introduced for producing highly heat-resistant wrought nickel alloys of a new generation (VZh175, VZh172, and EI171). With respect to properties, these alloys are no worse than overseas analogs and significantly surpass those produced previously for a similar purpose. Alloy VZh175 is highly alloyed disk superalloy of a new generation and contains ~50% strengthening γʹ-phase. It surpasses existing domestic and overseas analogs with respect to stress-rupture strength, and also fatigue properties with identical values of short-term strength limits. Highly heat-resistant alloy VZh172 is a very strong weldable alloy with a working temperature up to 900°C, it exhibits good process ductility, and this significantly expands the possibility of its application for engine components. Alloy EK171 is a structurally stable alloy with a working temperature up to 1000°C prepared from bars, forgings, strip, sheet and rings, and has good strength, heat resistance and creep properties. In 2014, at the plant a contemporary set of equipment was put into operation making it possible to manufacture stampings, rings, and other complete conversion objects. In view of this, production of superalloys is at a new level. The plant 567

manufactures billets for customer plants and supplies final product (disks, rings) for aviation plants. The first favorable results have been obtained. Currently, the Electrostal Metallurgical Plant is the main base for special metallurgy supplying a broad range of objects made from highly heat-resistant materials for aviation, space, atomic, and other branches of industry.

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