The influence of temperature and specimens undercut place on impact toughness of railway axle material in service is investigated. The obtained results show inversely proportional dependence of impact toughness on undercut radius of specimens. The decrease of test temperature from +20 to –40 ºC decreases significantly the impact toughness and portion of ductile fracture.U radu je istražen utjecaj temperature i mjesta zajeda uzorka na udarnu žilavost materijala tračničke osovine u eksploataciji. Dobiveni rezultati pokazuju obrnutu proporcionalnost ovisnosti udarne žilavosti o polumjeru zajeda na uzorcima. Smanjenjem temperature ispitivanja od +20 to –40 ºC značajno se smanjuje udarna žilavost i udio žilavog loma

Jasnìî, O.

Pindus, Ju. I.

Samardžić, Ivan

Sorochak, Andriy

Vuherer, Tomaž

Digital library of University of Maribor

1Introduction2Experimental techniqueUvodEksperimentalna tehnikaDuring exploitation the railway axle is subjected to thestatic and cyclic loading, corrosive action and environmenttemperatures. The tendency to the brittle fracture of materialcan be described by means of impact toughness. In thispaper the influence of temperature and the specimens'undercut radius on impact toughness of railway axlematerial is investigated.Material of electric locomotive railway axle – the OSLsteel – after 20 years of service was investigated. Since inthe process of exploitation of railway axle fatigue cracks areinitiated on its surface and grow in radial direction,specimens were cut in axial direction. Specimens fordetermination of impact toughness were cut out from anaxle's section with diameter 198 mm at different distancesfrom its center. The scheme of specimens cutting is shownin Fig. 1.The impact toughness was determined on 10×10×55mm Charpy specimens with V-notches, 0,25 0,025 mm inradius, that were tested by three-point bending. The RKP-300 type impact-testing machine with the impact energy of300 kJ was used. Load-displacement diagrams in thecoordinates "impact force versus time" and "impact forceversus displacement of the specimen" were recorded. Twoseries of tests were done – under temperature of +20 °C and–40 °C. Using the obtained diagrams, the force at whichplastic deformation begins, the total energy of fracture, theenergy of crack initiation and energy of crack propagationwere determined. The portion of ductile fracture was alsoassessed based on the results of fractography investigationsof the specimens' fracture surface.The impact toughness was calculated using the87O Yasniy, T  Vuherer, Y  Pyndus, A  Sorochak, I. . . . . SamardžićISSN 1330-3651UDC/UDK 625.143.2.042.2:620.17IN-SERVICE DAMAGE OF RAILWAY STEEL AXLESOleh Yasniy, Tomaž Vuherer, Yuriy Pyndus, Andriy Sorochak, Ivan SamardžićThe influence of temperature and specimens undercut place on impact toughness of railway axle material in service is investigated. The obtained results showinversely proportional dependence of impact toughness on undercut radius of specimens. The decrease of test temperature from +20 to –40 ºC decreasessignificantly the impact toughness and portion of ductile fracture.Key words: in-service demage, railway axle, undercutimpact toughness,Preliminary notesU radu je istražen utjecaj temperature i mjesta zajeda uzorkast ovisnosti udarne žilavosti o polumjeru zajeda na uzorcima. Smanjenjem temperature ispitivanja od +20 to –40 ºC znana udarnu žilavost materijala tračničke osovine u eksploataciji. Dobiveni rezultati pokazujuobrnutu proporcionalno čajno sesmanjuje udarna žilavost i udio žilavog loma.Ključne riječi: oštećenje u eksploataciji, tračnička osovina, udarna žilavost, zajedaPrethodno priopćenjeOštećenje na čeličnoj tračničkoj osovini u eksploatacijiOštećenje na čeličnoj tračničkoj osovini u eksploatacijiTechnical Gazette 18, (2011),1 87-90formula:Figure 1Slika 1.The scheme of specimens cuttingShema rezanja uzorakaEKCVA (1)where – the total energy of fracture; – cross-sectionalarea of specimen at V-notch place.The control program of the RKP-300 testing machineand record program of test information "VUHI-CHARPY"allows to determine the value of constituents of specimen'sfracture energy by converting the dependence "impact forceversus time" ( – ) into dependence "impact force versusdisplacement" ( – ). The change of impact hammer speed( ) during loading of Charpy specimen with known mass ofimpact hammer , initial velocity and dependence ( )was calculated using double successive integrationaccording to recommendations [1, 2]:E AFFFtsv tm v t088In-service damage of railway steel axlesTehni ki vjesnikč ,18, 1(2011)  87-90In this case the dependence of impact hammerdisplacement on time can be found as:s tO Yasniy, T  Vuherer, Y  Pyndus, A  Sorochak, I. . . . . Samardžićinversely proportional (Fig. 3). Particularly, with theincrease of undercut radius from 12 mm to 94 mm theimpact toughness decreases to 15,6 % at temperature +20ºC, and with the change of undercut radius from 66 mm to 94mm at –40 ºC this parameter decreases to 32,5 %. Thereasons of this phenomenon can be in the technology ofproducing railway axles, during which an axle is subjectedto the strengthening treatment by a roller on a full length forthe increase of high-cycle fatigue resistance [4].The decrease of test temperature from +20 to –40 Cdecreases significantly the impact toughness and portion ofductile fracture. For the subsurface layers of axle impacttoughness decreases by more than 3 times.The microstructure of OSL steel is depicted in Fig 4.This steel belongs to ferrite-pearlite class of materials. Thepresence of structurally free ferrit and pearlite colonies thatare located in different parts of ferrite grains was found byscanning electron microscope researches. On the basis ofSEM image analysis it was determined that ferrite grainsoccupy about 30 % of the observed specimen area. Theiristypical for sorbite microstructure.°.average size is about 10 μm. The average size of pearlitecolonies is 25 μm and the minimum pearlite interlamellarspacing 0,2 μm. This value of interlamellar spacing is001( ) ( )dttt v F t tm    (2)0( ) ( )dtts t v t t  (3)The ( ) dependence and portions of energy for fractureat partial stages were calculated using the above mentionedexpressions.The fractography investigations of the specimens'fracture surface were carried out on the scanning electronmicroscope Selmi REM-106I in the secondary electronsmode. The polished surface of specimens was etched in themixture of hydrochloric and nitric acids, then washed inacetone and dried out.The railway axles are made of medium-carbon steelOSL [3], obtained by an open-hearth, basic oxygen orelectroarc process. Chemical composition of steel meets thestandards and is shown in Tab. 1.F s3DiscussionRasprava0 0,5E-3 1E-3 1,5E-3 2E-3051015202598710654321E/Jt / sTable 1Tablica 1Chemical composition of OSL steel(mass concentration of elements, in %). Kemi%)jski sastav OSL čelika(masene koncentracije elemenata, uLoad-displacement diagrams of specimens incoordinates "expense of energy on destruction versus time"can be seen in Fig. 2.Results of experimental determination of impacttoughness for each specimen, total energy of fracture, energy of crack initiation and energy of crackpropagation are presented in Tab. 2.The dependences of impact toughness on the undercutradius of specimens from the locomotive wheelpair axle areKCVE EEipFigure 2Slika 2.Load-displacement diag. of specimens in coordinates,fracture energy versus time, at temperature +20–40Dijagram e-pomak uzoraka u koordinatama,energija loma u odnosu na vrijeme, pri temperaturi od +20°opterećenjС (1-6, 10)and С (7-9)С (1-6, 10)i –40 С (7-9)°°°P S Cr Ni CuС Mn Siless than0,42-0,45 0,60-0,90 0,15-0,35 0,040 0,040 0,30 0,30 0,25Sp. No.*Undercut radius,mmTesttemperature,ºCEi/J Еp/J E/JPortion of ductilefracture, %KCV/J/cm21 12 +20 15,8 9,3 25,2 28,1 32,02 26 +20 16,3 8,6 24,9 33,1 31,13 52 +20 15,0 9,2 24,2 31,9 30,34 66 +20 13,6 9,0 22,6 33,0 28,25 80 +20 13,6 8,5 22,1 21,1 27,76 94 +20 13,4 8,6 22,0 26,6 27,57 66 –40 8,1 2,1 10,2 4,1 12,78 80 –40 5,2 3,8 9,0 3,3 11,29 94 –40 4,2 2,7 6,9 5,1 8,610 94 +20 13,6 8,1 21,7 33,3 27,1Sp. No.* – Specimen numberTable 2Tablica 2.Results of experimental determination of impact toughnessRezultati eksperimentalnog određivanja udarne žilavosti89Technical Gazette ,18, 1(2011)  87-90O Yasniy, T  Vuherer, Y  Pyndus, A  Sorochak, I. . . . . Samardžić Oštećenje na čeličnoj tračničkoj osovini u eksploataciji°°Fracture surface of OSL steel at temperature +20 C(Fig. 5a) consists of successive areas of dimple ductiletransgranular fracture (Fig. 5b) and areas of cleavage (Fig.5c). The fracture is characterized by an insignificant plasticstrain, the fracture surface is formed by a net of combs, thatindicates the presence of brittle and separate ductilemicromechanisms of destruction [5]. With the decrease oftest temperature to –40 C the portion of ductile fracture isreduced to 3-5 %.4ConclusionsZaključciThe influence of temperature and undercut radius ofspecimens on impact toughness of the material of railwayaxle is investigated. It was determined that with the increaseof undercut radius of specimen from the axle, impacttoughness decreases linearly. Decreasing of testtemperature from +20 C to –40 C results in decreasing ofimpact toughness by 3 times.° °0 20 40 60 80 1001015202530KCV/J/cm2r /mm+20°C–40°CFigure 3Slika 3.Dependence of impact toughness on the undercut radiusof specimensOvisnost udarne žilavosti o radijusu podreza uzorakaFigure 4Slika 4.Microstructure of the OSL steelMikrostruktura OSL čelikaa)b)c)Figure 5Slika 5.Fracture surface of Charpy specimen (a) and areas of ductilefracture (b) and cleavage (c)Površina loma Charpyevog eduktilnog loma (b) i rascjepa (c)uzorka (a) i područj90 Tehni ki vjesnikč ,18, 1(2011)  87-90Scanning electron microscopy investigation shows that thematerial of locomotive axle – the OSL steel – belongs toferrite-pearlite class of materials. Fractography study offracture surfaces of specimens shows the presence ofsuccessive areas of dimple ductile fracture and areas ofcleavage. With the decrease of test temperature to –40 ºC theportion of ductile fracture is considerably reduced.The authors acknowledge the support of commonUkrainian-Slovenian project under the number of stateregistration of Ukraine 0109U005184.Acknowledgments5ReferencesZahvaleLit raturae[1] ISO 14556. Steel Charpy V-Notch Pendulum Impact Test –Instrumented Test Method. – 05.01.2005.[2] Kharchenko, V. V.; Kondryakov, E. A.; Zhmaka, V. N.Influence of temperature and loading rate on energy of crackinitiation and crack propagation of Charpy specimens fromcarbon steel // Strength of materials. 5 (2006), str. 120-127. (inRussian)[3] GOST 4728-96. Axle billets for 1520 mm gauge railwayrolling stock. Specifications. – 1997. (in Russian)[4] GOST 30272-96. Black collar axles (profile stock) for 1520mm gauge railways. Specifications. – 1997. (in Russian)[5] Strnadel, B. Haušild, P. Statistical scatter in fracturetoughness and Charpy impact energy of pearlitic steel //Material science and engineering. 486 1-2(2008), str 208-214....;,Authors' addressesAdrese autoraOleh YasniyTomaž VuhererYuriy PyndusAndriy SorochakTernopil Ivan Pul'uj State Technical UniversityRuska Str. 5646001 Ternopil, Ukrainee-mail: oljgen@gmail.comUniversity of MariborFaculty of Mechanical EngineeringSloveniae-mail: vuhi38@gmail.comTernopil Ivan Pul'uj State Technical UniversityRuska Str. 5646001 Ternopil, UkraineTernopil Ivan Pul'uj State Technical UniversityRuska Str. 5646001 Ternopil, UkraineMechanical Engineering Faculty in Slavonski BrodCroatiaIvan SamardžićJ. J. Strossmayer University of OsijekTrg Ivane Brlić-Mažuranić 235000 Slavonski Brod,In-service damage of railway steel axles O Yasniy, T  Vuherer, Y  Pyndus, A  Sorochak, I. . . . . Samardžić

Oštećenje na čeličnoj tračničkoj osovini u eksploataciji

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