Quality of Surfaced Running Wheels Kvaliteta navarjenih tekalnih koles R. Kejžar*, ZRMK Ljubljana, Slovenia L. Kosec, FNT - Montanistika (Metalurgija), Ljubljana, Slovenia Results of tribologlc testing of samples of running orane wheels as well as of orane rails shovv that vvear resistanee of running vvheels can be considerably improved by surfacing. The vvear of the vvheels coated vvith higher-alloyed claddings is insignificant. It is only the vvear of crane rails vvhich becomes significant, and vvhich increases vvith the increase of hardness of the running vvheel surface (it depends only on alloying of the surfaced cladding). Hard running vvheel surfaces are interestmg mostly in the čase of greater stresses because they permit operation vvith lovver frietion moment, and consequently lovver heating of contact surfaces in sliding as well as m rolling frietion. Key vvords: vvear of running crane vvheels, submerged-arc surfacing, alloyed agglomerated fluxes, tribologic testing of vvear resistanee of surfacings. Rezultati tribološkega testiranja vzorcev tekalnih koles žerjavov in tirnice so pokazali, da lahko z navarjanjem znatno izboljšamo obrabno ostojnost tekalnih koles. Obraba koles, kijih platiramp z močneje legiranimi prevlekami, je neznatna. Pomembna postane samo obraba tirnice, ki pa se s trdoto tekalne površine kolesa (odvisna je od legiranja navarjene prevleke) povečuje. Trde tekalne površine koles so zanimive predvsem pri večjih obremenitvah, ker zagotavljajo obratovanje z nižjim momentom trenja in s tem manjše segrevanje stičnih površin tako pri drsnem kot tudi kotalnem trenju. Ključne besede: Obraba tekalnih koles žerjavov, navarjanje pod praškom, legirani aglomerirani praški, tribološke preiskave obrabne odpornosti navarov. 1. Introduction Wear mechanisms are simulated by tribologic testing. The state of stress of a material depends on the load applied, number of revolutions. and slip. Stresses generated in a material due to the operation of a machine element exert a decisive influence on its applicability'h. Quality of the surfaces subject ti) vvear is of extreme impor-tance. Life of the machine element depends on the steel or allov applied. Its making of high-alloy steels or special alloys, vvhich vvould result in its high vvear resistanee, hovvever, vvould be very expensive. It is surfacing processes vvhich make it possible that soleh the surfaces and edges subject to vvear during operation need to be made of special vvear-resistant steels or alloys7The verv submerged-arc surfacing of vvheels vvith alloved vvire "EPP Cr 6" and vvith fused llux somevvhat improves their vvear resistanee vv ith regard to that of unsurfaced vvheels. An even more distinet improvement of vvear resistanee of the vvheels can be achieved if running vvheel surfaces are submerged-arc surfaced vvith alloyed agglomerated fluxes or high-effieiencv alloyed thick-coated eleetrodes to obtain higher-alloved and harder claddings. These filler materials permit ns to surface structural unalloved steels in one laver vvith high-alloyed claddings1"1 2. Qualitv of samples for tribologic testing Multi-laver submerged-arc surfacing of vvorn-out running ' Dr. Rajko Kt J/AR. ilipl. in/ . ZRMK Ljubljana. Dimičcva 12. 0100(1 Ljubljana vvheels vvith vvire "EPP Cr 6" and fused flux provides quite an ac-ceptable quality of the repaired running vvheels. The running vvheels repaired in this way are even a little more vvear-resistant than the unsurfaced ones. This vvas proved also by tribologic testing" s Surfacing of the vvorn-out running vvheels vvith alloyed vv ire "EPP Cr 6" can be replaeed by submerged-arc surfacing vvith unalloved vvire "EPP 2" and alloyed agglomerated flux. The surfacing is alloved vvith chromium and other selected elements coming from the alloved agglomerated flux. The compositions of one-layerand multi-layer surfacings, i.e. deposited metals. obtained in submerged-arc surfacing vvith unalloyed vvire "EPP 2" and vvith the nevv alloyed agglomerated IIux "0—7 SIVI" corre-spond verv vvell to those of the surfacings obtained in submerged-arc surfacing vvith vv ire "EPP Cr 6" and fused flux (see Table 1). Testing of vvear resistanee of the surfacings has shovvn that the alloyed agglomerated vvelding flux "0-7 SM" in eombination vvith the unalloyed vvire "EPP 2" is quite a suitable substitute to be applied for submerged-arc surfacing of the running vvheels vvith alloyed vvire "F.PP Cr 6" and fused flux. For surfacing of higher-alloyed vvear-resistant claddings, high-alloyed agglomerated vvelding flu.xcs "U-Mo 1" and "BM-2" have been developed in addition lo the alloved agglomerated vvelding flux "0-7 SM". Samples for tribologic testing (Fig.l) have been made of steel C.4732. They have been atilomalicallv submerged-arc sur- Table 1: Chemical analyses of one-layer and multi-layer submerged-arc surfacings (deposited metals) made vvith wires - EPP Cr 6 and fused fhix and - EPP 2 and alloyed agglomerated flux "0-7 SM" respectively. Tabela 1: Kemične analize enoslojnega in večslojnega navara (čistega vara) z žico - EPP Cr 6 pod taljenim praškom in - EPP 2 pod legiranim aglomeriranim praškom "0-7 SM" Surfacing C Si Mn Cr Mo (%) (%) (%) (%) (%) EPP Cr 6/fused flux - one-layer 0,20 0.24 0,65 4,53 - multi-layer 0,10 0,25 0,7(1 7,00 HPP 2/alloyed flux "0-7 SM" - one-layer 0,32 0,35 0.87 3,56 - multi-layer 0,11 0,55 1,21 9,12 0,31 0,48 running contact surfaces of the rollers surfaced and of the rail samples have been ground and polished to Ra = about 0.3 mm before being tested on a tribometer "Amsler". 3. Results of tribologic testing of the surfacings and of the rail Parameters for tribologic testing of the running erane wheels and of the rail have been chosen in such a manner that Hertz's pressure in the čase of our test carried out betvveen tvvo rollers (Amsler) is the same as that in aetual condition e\istinii the running vvheel and the erane rail1'. Testing conditions in rolling frietion are as follovvs: P = 600 N/cm, 1200 N/cm, and 2000 N/cm v = 200 r.p.m. (0.42 m/s), and 400 r.p.m. (0.84 m/s) t = 24 min Diagrams of frietion moment are given in Fig. 2. faced vvith vvire "VAC 60" 01.2 mm (I = 140 A, U = 21 V, and vweld. = 30cm/min; q = 5 KJ/cm) and alloyed agglomerated fluxes "0-7 SM". "U-Mo 1". and "BM-2" vvhich. during surfacing, heated up to the temperature of 350°C. Cooling rates of the surfacing and of the heataffected zone correspond to those in surfacing of preheated running vvheels carried out in practicc1'1 Chemical compositions and hardness valucs for the surfacings and the heat-affected zones are given in Table 2. Table 2: Chemical compositions and hardness values of the samples surfaced for tribologic testing (50 % overlapping of runs) Tabela 2: Kemične sestave in trdote navarjenih vzorcev za tri-bološke preiskave (50%-no prekrivanje varkov) Surfacing C" Cr Mo W V (%) (%■) (%) (%) (%) _Hardness in HV _ Final Weld HAZ layer centre VAC 60/0-7SM 0,31 5,3 0,3 - - 410 366 183 VAC 60/U-Mo 1 0,55 9,8 2,3 - 0,9 6S7 556 172 VAC 60/BM-2 0,85 5,1 4,2 5,0 1,9 707 586 163 I. Pr. 23 10 P„= 600 N/cm 11/1-10 PN =1200 N/cm Pr 24 11/2-11 PN =2000 N/cm Pr 25 7 1 6 5 5 ž 4 3 2 1 f 5 °r f J 0 4 8 1 2 16 20 24 11/3-12 63°c / I Mmin) 21/1-30 4 8 12 16 20 24 Mmin) 21/2-31 0 4 8 12 16 20 24 t (min) Pr.19 21/3-26 fcc l 4- t S 0 4 8 12 16 20 24 t (min) Pr. 22 9 8 _ 7 e 6 ^ r 5 ^ 4 3 2 ■ 1U \ e 6 r55 - 5 5°r r v ^ C 5 0 C £4 I 4 7° c / J I 0 4 8 12 16 20 24 t-(min) 0 4 8 12 16 20 24 t(min) 0 4 8 12 16 20 24 t (min) Figure 2: Diagrams of frietion moment vvhen testing vvear resistance of unsurfaced (I.) and surfaced vvheels vvith flux "U-Mo 1" (II.) and 'BM 2" (III.): v = 400 r.p.m. or 0.84 m/s. Slika 2: Diagrami momenta trenja pri testiranju obrabne obstojnosti nenavarjenih (I.) ter navarjenih koles pod praškom "U-Mo I" (II.) in "BM 2" (III.): v = 400 obr./min. oz. 0.84 m/s Wear of the vvheels surfaced vvith higher-alloved claddings is insignificant. It is only vvear of the rail vvhich becomes impor-tant and vvhich inereases vvith the incrcased hardness of the running vvheel surface (vvhich itself depends on alloving of the cladding surfaced). Hard running vvheel surfaces are of interesi most of ali vvith higher stresses because they make possible op- Figure 1: Scheme of surfacing and preparation of a hard running surface bv specimens for tribologic testing (1 - first surfacing, 2 - second surfacing). Slika I: Skica navarjanja in priprave trde tekalne površine pri vzorcih za tribološke preiskave (I - prvi navar. 2 - drugi navar) Quality running surfaces of the surfaced rollers are obtained if the surfacings are broached at an angle of 45 (Fig. 1). The samples of the rail not being broached, it is the surfaced samples vvhich determine the gap vvidth in tribologic testing (5 mm). The 590 Figure 3: Microstructure of a rail section a) Pr. 10 - high friction moment; more than 10 Nm bi Pr. 5 - lov, friction moment; about 6 Nm Slika 3: Mikrostruktura preseka tirnice a) Pr. 10 - visok moment trenja; preko 10 Nm b) Pr. 5 - nizek moment trenja; okoli 6 Nm Figure 5: Damaged running surface - parts of oxides, stickers of metals... (unsurfaced running wheel) Slika 5: Poškodovana tekalna površina - delci oksidov, nalepi kovine., (nenavarjeno tekalno kolo) Figure 4: Appearance of an unsurfaced running wheel section and its microstructure Slika 4: Izgled preseka nenavarjenega tekalnega kolesa in njegova mikrostruktura eration vvith a lovver friction moment, and consequently result in a vveaker heating of the contact surfaces in sliding friction as vvell as in rolling friction. Heating ofthe contact surfaces, vvhich is particularly strong vvith high friction moments, results, in the čase of strong loads, in a considerable deformation of the surface layers of the rail (Fig.3) and of the running vvheels (Fig.4) if they have not been Figure 6: Appearance of a surfaced (0-7 SM) running vvheel section and its microstructure. Slika 6: Izgled preseka navarjenega (0-7 SM) tekalnega kolesa in njegova mikrostruktura surfaced, i.e. refined vvith a hard cladding. Plastic deformation is accompanied also by crystalline modification of the surface lay-er if the latter heats above 555°C due to rolling friction15. If heating during rolling, vvhich strongly depends on friction moment, is very intensive, the crystalline modification zone can extend also beyond the deformation zone (Fig.3). The deformation zone in rails goes approximately 0.4 mm deep, vvhile the crystalline modification zone, in the čase of high friction moments, goes even 2 mm deep (Fig.3). Figure 7: Damaged running surface - parls of oxides, stickers of metals... (surfaced running wheel; 0-7 SM). Slika 7: Poškodovana tekalna površina - delci oksidov, nalepi kovine... (navarjeno tekalno kolo; 0-7 SM) Figure 9: Damaged rolling surface - parts ot ovides. stickers of metalls... (surfaced rolling wheel; BM-2) Slika9: Poškodovana tekalna površina - delci oksidov, nalepi kovine (navarjeno tekalno kolo; BM-2) the deformation depth vvith the surfaced sample is onlv 80 to 100 um (see Fig. 6). vvhieh is easy to understand since the surfaced-laver has martensitic-bainitic strueture vvhile vv ith the unsurfaced sample (Fig. 4, deformation depth 200-250 um), the surface laver has ferritic strueture. With the surfaced samples of the running vvheels. deformation and oxidation cause damages to the contact surface. i.e. fold-ed metal and stickers of metals and oxides (Fig. 7). These are. hovvever, esscntiallv vveaker than thosc to the unsurfaced samples (cf. Figs. 5 and 7). Even vveaker deformation and lesser damages of the running surface occurred vvith the samples vvhieh vvere submerged-arc surfaced vvith high-alloved vvelding fluxes "Ll-Mo 1" and "BM-2" (see Fig. 9). After tribologic testing, the surface laver has been very little deformed (Fig. 81. Increase of the contact surface duc to deformation and oxidation of the surface (Fig. 8i is insignifi-cant too (around 5 c/c). 4. Conclusion Wear resistance of running vvheels can bc improved bv surfacing. The very submerged-arc surfacing of the vvheels vvith alloved vvire "EPP Cr 6" and vvith fused flux somevvhat improves their vvear resistance vvith regard to that of unsurfaced vvheels. An even more distinet improvement of vvear resistance of the vvheels can bc achieved if running vvheel surfaces are submerged-arc surfaced vvith alloved agglomerated fluxes or high-efficicncy alloved thick-coated electrodes to obtain higher-al-loyed and harder claddings. These filler materials permit tis to surface struetural unallovcd steels in one laver vvith high-alloved claddings. Testing ol' vvear resistance of the surfacings has shovvn that the alloyed agglomerated vvelding flu\ "0-7 SM" in combination vvith the unallovcd vvire "EPP 2" is quite a suitable substitute to bc applied for submerged-arc surfacing of the running vvheels vvith alloved vvire "EPP Cr 6" and fused flux. A distinet deformation and oxidation of the surface dne to in-tensive heating of the contact surfaces during rolling results in damages to the running vvheel surface (Fig. 5). Submerged-arc surfacing itself vvith alloyed agglomerated flux "0-7 SM" highly improves vvear resistance of the running vvheel. Deformation of the surface laver is considerablv vveaker. The contact surface inereases, due to vvear and plastic deformation, only by 15 % (see Fig. 6). With the unsurfaced sample. the contact surface has inereased by even 30 during testing. Also Figure S: Appearance of a surfaced (BM-2) running vvheel seetion and its microstructure. Slika S: Izgled preseka navarjenega (BM-2) tekalnega kolesa in njegova mikrostruktura 800- 700- A A A AA A * BM 2 D • 1 \ 0 Ao \« □ % \ \ --M A A A • ______ UMo1 i 600-> 500- 3= ul i 400- "O A D Legeni A and A,- BM 2 (first and second surfacinq) 0 and • UMo1 ( u □ and 0-7SM( " X and X, unsurfaced specimens (Č 4732 and rail ) 0-7SM n: X □ □ 0 □ □ 300- —S-212L Rail 200- 1 0 100 2 00 3 00 400 500 600 700 800 Running surface Disfance from surface (^j.m) - — Figure 10: Hardness of sections of unsurfaced and surfaced specimens Slika 10: Trdote na prerezu nenavarjenega in navarjenih tekalnih koles High wear-resistance of the claddings which were sub-merged-arc surfaced on the running wheel vvith alloyed-agglom-erated t"lux "(1-7 SM" is resulting from surface hardening (600-700 HV: Fig. 10) due to deformation of the surface laycr. The claddings which were submerged-arc surfaced w i t h high-alloyed agglomerated fluxes "U-Mo 1" and "BM-2", however, are hard (around 700 H V: Table 2) right after surfacing; therefore, thcv practically neither deform nor harden during tribologic testing. In the čase when the wear resistant cladding vvas made by submerged-arc surfacing \vith high-alloyed agglomerated flux "BM-2". stress and heating of the running surface resulted even in stress relieving and insignificant decrease of hardness imme-diatelv upon the surface (Fig. 10, upper curve). Wear of the wheels surfaced with higher-alloyed claddings is insignificant. It is onlv the vvearof the rail which becomes im-portant and which increases with the increased hardness of the running wheel surface (which itself depends 011 alloying of the cladding surfaced). Hard running wheel surfaces are of interest most of ali vvith highcr stresses because tliev make possible op-eration with a lower friction moment; and consequent!y result in a weaker heating of the contact surfaces in sliding friction as vvell us 111 rolling friction. Wear resistance of the running crane wheels can be considerablv improved by surfacing and by appropriate selection of filler materials without essentially influencing the wear of the rail. References L. Foppl: lieanspruehung von Scliiene und Rad beim Anfahren und Bremsen. Munchen 1963. •' K. H. Kloos, F. Broszeit. M. Koch: Eigenspamuingesdnderungen Mm Uberrollen von gehdrtetem Wdlzlagerstahl 100 Cr 6". Institut fiir Werkstoffkunde. Darmstadt. ' II. Poritsky, N. Y. Schenectady: Stresses and defletions ofevlin-drieal bodies, New York 1949. ' Dr. Marko Kos: Raziskava trajnostne meje tekalnih koles in tirnice. Ljubljana 1972. J. Vižintin, A. Vesel: Popis napetostnega stanja na tekalnem kolesu in tirnici. 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