The paper presents the data of studying the characteristics of graphite inclusions in various samples of AChS-2 cast iron. The metallographic analysis was carried out using the Thixomet Pro software, the length of the graphite inclusions, their shape and the occupied area were estimated. The slip coefficient and hardness were measured on the same samples. It was found that the characteristics of the graphite phase affect the antifriction properties of the alloy

Aubakirov, D. R.

Chsherbakova, Ye. P.

Dostaeva, A. M.

Kvon, Sv. S.

English

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200  METALURGIJA 61 (2022) 1, 200-202YE. P. CHSHERBAKOVA, SV. S. KVON, A. M. DOSTAEVA, D. R. AUBAKIROVSTUDYING THE GRAPHITE PHASE IN ANTIFRICTION AChS-2 CAST IRONReceived – Primljeno: 2021-04-25Accepted – Prihvaćeno: 2021-07-25Preliminary Note – Prethodno priopćenjeYe. P. Chsherbakova, Sv. S. Kvon, V. Yu. Kulikov, A. M. Dostaeva, S. K. Arinova (e-mail: sherbakova_1984@mail.ru, KTU), Karaganda Technical University, Karaganda, KazakhstanThe paper presents the data of studying the characteristics of graphite inclusions in various samples of AChS-2 cast iron. The metallographic analysis was carried out using the Thixomet Pro software, the length of the graphite inclu-sions, their shape and the occupied area were estimated. The slip coefficient and hardness were measured on the same samples. It was found that the characteristics of the graphite phase affect the antifriction properties of the alloy.Keywords: cast iron, graphite inclusions, properties, slip coefficient, hardnessINTRODUCTIONFor manufacturing the parts operating under condi-tions of friction with lubrication, there are used materi-als with sufficiently high hardness, wear resistance, and good antifriction properties: the friction coefficient should be no higher than 0,12 - 0,5 in the absence of lubrication and 0,001 - 0,02 with lubrication [1]. In a number of cases, bronzes are used for manufacturing castings that operate under friction conditions, but they are quite expensive; therefore, other antifriction materi-als, in particular, gray cast irons of the AChS 1 - 6 grades, are widely used.Cast irons of this group have the pearlite or pearlite-ferrite base without free cementite and necessarily con-tain free lamellar graphite in the structure.The shape, the size and the quantity of free graphite in fact determine the coefficient of friction (or slip coef-ficient), since graphite acts as a lubricant. It should be noted that hardness and wear resistance of antifriction cast irons, all other things being equal, are mainly deter-mined by the structure of pearlite: the less dispersion of pearlite, the higher the material hardness and strength.A lot of parts of mining equipment (sleeve bearings, bushings, bushing inserts, etc.) are made of AChS-2 an-tifriction cast iron. Table 1 shows the chemical compo-sition of AChS-2 cast iron, Table 2 shows the require-ments to AChS-2 graphite inclusions [2].RESEARCH METHODOLOGYAChS-2 grade cast iron is used in conjunction with steel hardened or normalized surfaces, i.e. they must have sufficient hardness. According to [1], its hardness ISSN 0543-5846METABK 61(1) 200-202 (2022)UDC / UDK 621.741:661.666.002.61:621-31/621.317.6:620.178.1=111is 180-229 HB. In order to increase hardness and resist-ance to wear, chromium is introduced into cast iron that also promotes chilling, which is undesirable in antifric-tion cast iron [2-6]. Titanium contributes to the produc-tion of small inclusions of graphite and also increases the metal base strength, silicon provides good casting properties of the alloy and the course of the graphitiza-tion process at a certain Cr:Si ratio. Nickel promotes graphitization and formation of small inclusions of graphite, prevents chilling and improves machinability of cast iron [2, 7-12].Thus, AChS-2 cast iron has a balanced composition, which provides fairly good performance properties. Ac-cording to [1], the variation of the shape and the size of graphite inclusions is quite wide: from 15 μm to 250 μm. It is obvious that such a wide range of shapes and sizes of graphite leads to instability of the properties of cast iron and consequently, the uncertainty of the ser-vice life of the same batch of castings [12-15].Table 1 Chemical composition of AChS-2 cast iron / wt. %C Si Cr Mn Ni Cu Ti P S3,0-3,81,4-2,20,2-0,50,3-1,00,2-0,50,2-0,50,03-0,10,15-0,4≤ 0,12Таble 2 Requirements to AChS-2 graphite inclusionsShape of graphite inclusionsSize of graphite inclusionsDistribution of graphite inclusionsPGf14 PGd15, PGd180 PGr1-PGr3rectilinear, winding, nest-shapedup to 15 µm120-250 µmuniform, uneven, in coloniesEXPERIMENTAL STUDIESEquipment and toolsThe purpose of this study was to establish the relation-ship between the graphite phase characteristics and some properties (slip coefficient and hardness) of the alloy.201YE. P. CHSHERBAKOVA et al.: STUDYING THE GRAPHITE PHASE IN ANTIFRICTION AChS-2 CAST IRONMETALURGIJA 61 (2022) 1, 200-202The samples of AChS-2 cast iron from different batches were used as the object of research. The sam-ples were cut from various retired castings. On the basis of the prepared samples, thin sections were prepared to study the graphite phase; the metal base was not etched and was not studied.When studying the graphite phase, the length of the graphite inclusions, the characteristics of the shape of the inclusions, and the area occupied by the graphite phase were estimated. The Thixomet Pro software was used for the analysis, the studies were carried out in at least 3 fields of view. An example of using the program is shown in Figure 1.The shape factor was calculated using the formula: where А is the inclusion area; D is the inclusion diameter.The shape factor is one of the inclusion parameters and characterizes the tendency of the inclusion shape to develop towards spherical. In other words, the higher the value of the shape factor, the closer to the sphere the shape of this inclusion.The slip coefficient was determined on the COF - P01(M) instrument with the following characteristics: dry friction (without lubrication), the angle of inclina-tion 150; the angular velocity 10 0/s. The measurements were performed with  three doubles. The results are pre-sented in Table 3.If it compare the data in Table 3 with the require-ments for the AChS-2 graphite inclusions (Table 2), it is obvious that in all the samples under study the parame-ters of the graphite inclusions meet the required charac-teristics. It can be seen from the data in Table 3 that the variation of the data of the alloy hardness is about 10 %, the variation of the data of the slip coefficient is more than  70 %, while all the characteristics of the graphite inclusions of the samples under study meet the require-ments. It should be expected that with such a variation of the data, the service life and wear resistance of the materials certified as AChS-2 will definitely be differ-ent despite their full compliance with the GOST.The analysis of Figure 2 shows that increasing the length of graphite inclusions has a negative effect on the value of the slip coefficient (Figure 2a). The distribu-tion of graphite inclusions also has a negative effect on the antifriction properties: the distribution of graphite in the form of colonies is the least favorable from the point of view of the slip coefficient value. Increasing the area of graphite inclusions leads to decreasing the alloy hardness as a whole (Figure 2b).A number of studies [3-5] have shown that addition-al alloying of the basic composition of gray cast irons has a positive effect on the shape and content of the graphite phase and thus, on the properties of cast iron as a whole. The introduction of such alloying agents as nickel, vanadium, molybdenum, and others contribute to increasing the metal phase hardness by increasing the dispersion of pearlite and refining the graphite phase and increasing the uniformity of distribution.Figure 1  Example of using the Thixomet Pro: а) analysis of the graphite inclusions shape; b) analysis of the graphite inclusions lengtha)b)Таble 3 The results of studies Sample No. Graphite inclusions length / µmDistribution Shape factor Area occupied by graphiteSlip coeffi  cient Hardness / НВ1 18 PGr1 0,048 4,12 0,49 2032 126 PGr3 0,066 6,46 0,33 1763 84 PGr3 0,072 3,78 0,65 2204 65 PGr2 0,05 5,02 0,51 1905 202 Pgr3 0,039 6,13 0,27 183202  METALURGIJA 61 (2022) 1, 200-202YE. P. CHSHERBAKOVA et al.: STUDYING THE GRAPHITE PHASE IN ANTIFRICTION AChS-2 CAST IRONAdjusting the AChS-2 basic composition with such elements can be considered as one of the ways to affect the parameters of the graphite phase and consequently, the slip coefficient and increasing antifriction properties.CONCLUSIONBased on the results obtained, it can be unambigu-ously asserted that from the point of view of the slip coefficient and therefore, the efficiency of the AChS-2 alloy as an antifriction material, it is necessary to obtain sufficiently small graphite inclusions of the order of 65-80 microns, which corresponds to PGd45, PGd90 grades. Reducing the length of graphite inclusions be-low these values do not make sense, because with de-creasing the length of the graphite inclusions the slip coefficient does not practically change.AcknowledgmentsThese studies were carried out in the framework of the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan grant AP09058350 «Developing and implementing the tech-nology of producing chrome antifriction cast iron for parts of mining equipment».REFERENCES[1]  GOST 1585-85 «Antifriction iron for casting. Grades»[2]  Gabets D. A., Markov A. M., Gabets A. V., Chertovskikh E. O. Assessment of the effect of alloying additives on the structure and mechanical properties of gray cast irons, Polzunovskiy Vestnik (2018) 4, 189-195.[3]  K. Sertucha, J. Lacaze, J. Serrallach, J. Suarez, R. Osuna. Effect of alloying on mechanical properties of as cast ferri-tic nodular cast irons, Materials Science and Technology 28 (2012) 2, 184-191.[4]  M. Górny, E. Tyrała, H. Lopez. Effect of Copper and Ni-ckel on the Transformation Kinetics of Austempered Duc-tile Iron, Journal of Materials Engineering and Performan-ce 23 (2014), 3505-3510.[5]  M. Rezvani, R. A. Harding &J. Campbell // The effect of vanadium in as-cast ductile iron//International J. of Cast Metals Research 10 (1997) 1, 1-15.[6]  Y. Jing; L. Yanchuan; S. Bo. Microstructure and Properties of Fe-Based Alloy Coating on Gray Cast Iron Fabricated Using Induction Cladding, Coatings (2020) 9, 89-94.[7]  A. Mari, W. Kentaro, M. Hisao. The influence of interac-ting small defects on the fatigue limits of a pure iron and a bearing steel, International journal of fatigue 135 (2020) 2050-2054.[8]  Hossain Md. Sojib S., Rashid, A. K. M. Bazlur B. Precon-ditiong and Inoculation of Low Sulphur Grey Iron, Archi-ves of foundry engineering 1 (2020) 20, 61-66.[9]  R. Iulian; S. Stelian; Chisamera, Mihai. Simultaneous ther-mal and contraction / expansion curves analysis for solidi-fication control of cast irons // China foundry 2 (2020) 17, 96-110.[10]  Wojciechowski, S., Talar, R., Zawadzki, P. Evaluation of physical indicators and tool wear during grooving of sphe-roidal cast iron with a novel WCCo/cBN (BNDCC) in-serts, Wear (2020) 4102-4106.[11]  Vodolazskaya N., Sharaya O., 2020. Modifying of the Sur-face of Products from Cast Iron as the Element of Produc-tion Modernization, Solid State Phenomena 299 (2020), 588-593. https://doi.org/10.4028/www.scientific.net/ssp.299.588[12]  Vodolazskaya N. V. Wear resistance of cast iron parts due to modification of surface layer / N. V. Vodolazskaya, O.А. Sharaya, Journal of Advanced Research in Technical Science. – Seattle, USA: SRC MS, Amazon KDP, 18 (2020), 33-36.[13]  Kvon, S. S., Kulikov, V. Y., Shcherbakova, Y. P., Arinova, S.K. Effect of inoculant introducing on improving ingot structure, Metalurgija 58(2019)3-4, 315-318.[14]  Kovalev, P., Riaboshuk, S., Issagulov, A., Kvon, S., Ku-likov, V. Improving shipbuilding steel grade quality at sta-ges of smelting, secondary refining, and continuous ca-sting, Metals 9(2019)2, 203.[15]  Kvon, S. S., Kulikov, V. Y., Issagulov, A. Z., Dostayeva, A. M., Kovalyova, T. V. Studying structure and properties of shaped ingots obtained in various conditions of crystalliza-tion, Metalurgija 57 (2018) 4, 313-316.Note:  Responsible for the English language is Natalya Drak, Karagan-da, KazakhstanFigure 2  Graphite inclusions characteristicsimpact on the alloy properties: a) the graphite inclusions area effect on hardness; b) the graphite inclusions length effect on the slip coefficient

Studying the graphite phase in antifriction AChS-2 cast iron

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