No. 1, 1998 - Tribology in Industry

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.
)