No. 1, 1998 - Tribology in Industry

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30,0 FcL 25,0 t25 A. P= 01,/Po _,1 -e- P= 1900 MPc] _EF p- 3300l4pci _o,. p= 4700 t1p0 0,2 0,3 0,1, _* h (mnr) Fig.4. Depetdence of 8211 ott lr as relative residual austenite; this fact can explained by appearance of high temperatures inner surface layer which have various values at different depths; the correlation between the two sizes displays transformations of type Fea(TBC) - Fca(BCC) and Fey - Fea(BCC) or Fea(TBC); c) the size .8277 strongly varies up to 200 prre inside the surface Iayer and it follows a stabilization. In figure 5 is displayed the dependence of size 8226-oflh). From presented data results: the inner second order tensions have a peak between 100-200 pm depth, while the cuwes IJ2ao = Bzzo&) are alternately placed for the three values of the pressure P. This can be accounted for by changes of the prevailing mechanical and thermal effects at variorrs depths during pitting tests. Fig. 5. Dependcnce of B2x1 ort h In figure 6 it is presentecl the evolution on surface layer depth of the size (l,,rirlt,or)22a. The shapes of designed cun'es are similar for the three pressures. At P=0 MPa maximum of dislocations density is located at a depth of 3001.un inside the surtace layer. At pressure of 1900 MPa 8 ll, a l?i,, oq nfl 0,7 0,rl I f z\- p=rl j,4po C) '.f',.'1900 lt,lPa {.t P- 3300 I'll"ci l- P =1, i 0C lv1 Ptt | 0,1 | 0,2 - i-- 0,3 Fig" 6. Dt:ptndrnce af (l,rullrnut)220 ort lt is found a decrease of the general dislocations density level. The maximuln of this cun'e is situated near sut{ace of the sur{ace lrryer. For 1' = ,}300 tr[Pa zrnd I'>:4700 MPa the maxima of curyes remove inner of the surface layer, having the same values ancl are located in the sarne area approximately. This fact shorvs that the annealing thermal treatment is not enough or should be performed by an another diagram in orcler to reduce the level of the dislocations density. 6. CONCLUSIONS 1+-- _ J).,1:iii l. lr () /, al r, -t > Using the concepts of the tribosystem, tribomodel, triboelement and surface layer it was possible to prepare a pitting testing program in order to establish the tribological behavior of case-hardening steel 21 MoMnCrl2XS recommended for replacing the bearing-rolling steel RUL-1, > From the clistribution on the surfac:e layer depth of the structural changes IXS=XS&) andX5:y511't)] - distinguished by X-ray diffraction nrethod-the follorving conclusions can be drawn: a) the existence - in inner of the surface layer of the case-hardening steel - of the diference behveen mechanical and therrral effects which develop cluring pitting test; this fact is consiclered as a negative factor on the structural and dinrensionul .stabilities b) the existence on surflce layer depth of a nonhomogeneity fol inner secontl order tensious which, at ctepth of 100-2001trn, has a naximum value; this fact shows that it is possible that sorne microcracks appear in this area c) the existenc:e of a contact pressure limit which the case-hardening steel can be stressed; a higher pressure (over the nrentioned iimit) can Iead to appearance of -some phase transformations (e. g. Fea*Fey) which are not recr.rmrnencleci for case-hurdeninu steel. Ii'ibologt irt itultts'try, \blume 20, No. 1, 1998. )
The presenied nrethodoJr:gy ztlrr,l obtainecl cl:rta cart L,'c used in engineering design in order tL) repiace some expensive mat erials with other cheaper but with sirniiar performances. 7. REFERENCES 11.) Colins, L ,,1, Failure of Materials in N{echanical Design, Ltd. John Wiley. New York, 1981 [2.) Grudu. L, Palaghian, L., Ghectrghies;'C., Structural Modifications in the Superficial Layer of Metallic Materials in Wear and Fatigue Processes, Proceedings of International Tribologry Conference, Nitgoya 1990, Japan. vol. I, pp. 2M-214 13.) Czi c h o s,.I/., Systernanalyse und Physi k tribologische Vorgange, Teill, Grundlzrten, Schmirtechnik Tribologie, 32, 6.le1(t 14.) Djatnhmedov, A.11. F iziko stohasticeskoe tribomodelirovanie, Izd. Elm. Baku, 1988 15.) Ishlirurkii, A. 1., K'agelski, L V. c/. a/., Problenri iznashivanija tverdih tel i aspctirnehaniki, Trenie i iznos.4. 1986 [5.) Stcfntrcsctt, L, Gheorglties, C., 'l'he irrflrrence of 'I'hermornagnetic Treatment Applied to Rolling-tsearing Steel, Acta Tribologica, ),2,1994, pp. 13'l-146 17.] Ilabic, M", Jerenic, I]., Miiit:, iv"., 'frillological ['roperties of Crain Surfaces, Proceedings of BAI-KAN- -fRiB'96, Thessaloniki, Greece pp. 151-i58 18.)Gkeorylies, C., Structur:al Changes During Friction, Wear and Fatigue Procceses (in r
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No. 1, 1998 - Tribology in Industry

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