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28XV International Symposium on Self-Propagating High-Temperature Synthesis
APPLICATION OF SHS-ELECTRODE MATERIALS IN METALLURGY
A. E. Kudryashov*", A. V. MakarovA, N. I. Repnikovfi, and E. M. MartynovA
aNational University of Science and Technology MISiS, Moscow, 119049 Russia bA.A. Ugarov Stary Oskol Technological University, Branch of the National University of Science and Technology MISiS, Stary Oskol, 309516 Russia *e-mail: [email protected]
DOI: 10.24411/9999-0014A-2019-10074
Electrospark deposition is one of efficient technologies for enhancing the durability of forming rollers. VK (WC-Co) and TK (WC-TiC-Co) hard alloys, ferrochrome, high-chromium and high-carbon (1.0-2.0 % C) steels and alloys are used as electrode materials to strengthen the rollers [1]. Electrode materials of STIM grade (a Russian acronym for synthetic hard tool material) fabricated using the self-propagating high-temperature synthesis (SHS) are the most promising materials to strengthen forming rollers. Performance characteristics (hardness, heat and wear resistance) of coatings made of these materials are superior to those made of VK6 and T15K6 alloys [2].
Further enhancement of performance properties of the coatings deposited using the electrospark technology involves the application of SHS electrode materials modified with a nanodispersed component [3] and conduction of electrospark deposition via two stages. A barrier sublayer and a multifunctional protective coating are formed at the first and second stages, respectively.
This study aimed to demonstrate how SHS-electrode materials and the electrospark deposition technology are applied in metallurgy (forming rollers, rollers of a continuous billet casting machine).
When elaborating the technology for strengthening forming rollers, SPKhN-60 white cast iron samples were used as cathodes (substrates). STIM-40NAOKn (TiC-NiAl-ZrO2nano) and STIM-11OKn (TiB2-NiAl + ZrO2nano) alloys modified with a nanodispersed component were employed as electrode materials for production of the multi-functional layers.
Electrospark coatings were deposited in air on an Alier-Metal G53 setup.
Calculation of the Palatnik's criterion showed that the electrodes made of chromium and nickel are the optimal ones for sublayer deposition. The energy regime for treatment with metal electrodes was determined (0.175 J). The energy regime of 0.4 J was used for treatment using hard-alloy electrodes [2].
The cathode weight was increasing throughout the entire coating deposition duration (7 min) when the electrodes made of nickel and chromium were applied. Treatment of the samples without a sublayer and with a chromium sublayer with STIM-40NAOKn alloy led to cathode weight loss during 10 min. For the sample strengthened using a nickel sublayer, the cathode weight was increasing during the first 5 min. Application of the STIM-11OKn electrode caused cathode weight loss.
Electrospark treatment in the optimal energy regime gives rise to coatings characterized by high continuity (up to 100%), thickness up to 100 |im, and hardness up to 10.5 GPa.
Transmission electron microscopy examination revealed that grain size of the wear-resistant phases in the resulting layers was 10 nm.
Adhesion strength between the two-layer electrospark coatings and the white cast iron substrate is higher than 100 N.
It was found that preliminary deposition of a sublayer increases the content of refractory phases in the deposited coatings (TiC, Fe3(B,C), Fe23B6, Fe2B, Ti B2). The maximum content
ISHS 2019 Moscow, Russia
of the refractory phases is observed in the coatings containing a nickel sublayer.
The coatings formed by the electrodes based on titanium diboride have higher heat resistance (T = 500°C) as compared to the coatings made of titanium carbide. Deposition of a nickel sublayer increases the heat resistance of STIM-11OKn coatings more than eightfold.
The application of two-layer coatings reduced wear rate fourfold as compared to that in non-strengthened white cast iron samples.
It was decided to test application of the electrospark deposition technology and STIM-11OKn and STIM-40NAOKn SHS-electrode materials for strengthening rollers of the continuous billet casting machine (CBCM).
Application of the electrode material based on titanium carbide (E = 0.4 J) was found to result in cathode weight gain, while treatment with an electrode based on titanium diboride caused cathode weight loss.
A set of studies of the structure, composition, and properties of the coatings deposited onto 20X13 steel was carried out.
No surface cracks were found after the coated samples had undergone 10 thermocycling rounds (exposure to T = 900°C for 30 min, cooling at a rate of 3°C/s).
The findings obtained in this study were used to elaborate the technology process for strengthening forming rollers.
The developed technology process was tested for forming rollers of a finisher stand no. 24 (roller diameter, 376.5 mm) using the facilities of the Oskol Electrometallurgical Plant JSC. The results of the tests showed that durability of the strengthened roll pass was eightfold higher than that of the uncoated roll pass.
1. A.E. Kudryashov, E.I. Zamulaeva, E.A. Levashov, O.S. Manakova, M.I. Petrzhik, Application of the electrospark deposition technology and modified SHS-electrode materials to enhance durability of forming rolls in a hot-rolling mill. Part 1. The features of coating formation on substrates made of SPKhN-60 white cast iron. Electron-assisted treatment of materials. Elektron. Obrab. Mater., 2018, vol. 54, no. 5, pp. 43-55. (In Russ)
2. A.E. Kudryashov, O.N. Doronin, E.I. Zamulaeva, E.A. Levashov, N.V. Shvyndina, The prospects of application of electrode SHS materials and the electrospark deposition technology to strengthen forming rollers. ChernyeMet., 2013, no 10, p. 61-68. (In Russ)
3. A.E. Kudryashov, Yu.S. Pogozhev, E.A. Levashov, Electrodes. Concise Encyclopedia of Self-Propagating High-Temperature Synthesis History, Theory, Technology, and Products, Eds I. Borovinskaya, A. Gromov, E. Levashov, Yu. Maksimov, A. Mukasyan, A. Rogachev, Elsevier, 2017, pp. 103-104.
