l) the sitiing oftwo sizes of p~xticles(5~10andl0~30 u m) 2) after sifting evahmfion of each condition as follows ;
(a):lhe evaluation of the disln'bution oflhe lX~de size by the C.C.-M
(b):aiter acid solulion for particles, the evaluation of the dism~lion of the p~icle size by ltae C.C. M (C): after acid ~ad alkali solution for l:mliclee, , the evaluation of the distnTmition of the particle size by
the C.C. M
3) the comparison with the distn'bution of the particle size for a, b, and c.
F i g u r e 21-Evaluation offusion of Al20~ by E.4~1.S usingpure-AleO3particles.
Application of Ultrasonic Testing on Rolling Contact Fatigue Life Testing
In order to clearly relate nonmetallic inclusions with rolling contact fatigue life, the experiments were carried out under the condition that the relative positions between the nonmetallic inclusions in the test piece and the race way on its san'face were specified clearly.
Method
Experimentalproceeding- Figure 22 shows the experimental proceeding. At first, the test pieces were detected precisely by the U.T., and all defects were registered with their size and depth. The position of significant defects were marked with the dent mad~ of the Vickers tesaer. After that, the relative position between the defect and the dent marks was reconfirmed by the U.T.. Fig23 shows the recamfim~ image by the U.T.. Next, the depth of the defect tiom the surf~,_e was adjusted to the experimental condition by polishing the surface. In setting of the test piece on the fatigue life tester, the position of the significant defect was controlled just under the race way by the dent marks. O f course, it was possa'ble to set the significant defect a little bit out of the race way, and c~eful setting was needed to avoid another defects existing under the race way_ Finally, the rolling conlact fatigue life testing was carried out.
[ Des [ byU.T. [ ~djusan~ of dg)th of detect t, F i g ~ 2 z - ~ ~ g . Table 6- Test Type Moil
Hertzian stress 5.3Gpa
Cycle rate 1500cpm
Steel grade JIS-SUJ2
Ball
]' size 3/8inchX 3ball
Lubricating oil machining oil:~ 10
Ro//mg ~ Faffgue/~ Test- Figure
24 ~:lws the sdlealalic ilhlsllation of the life
Fibre 2 3 - ~ ~ g e by the U.T.
tester and Table 6 shows tmt ~ Table 7 F i g u r e ~ ~ o f l i f e t e s t e r .
shows ~o various t~st ~ of the defect's ~ depth, and th~ ~ e ~ between the
de~'t avd the racy way. U p ~ t ~ 8 ~ tho fl~ing occtmen~ was checked ~d, if no f l ~ g ~
o t ~ v ~ t ~ ch~,~ of the &fect images was ~ a l ~ t ~ ~f~ t ~ g by th~ U.T.
Fm~mno~ ~ ~ was mad~ around~ &fea.
Table 7- Test conditions of rolting omtact fatigue lif~
Test type
A
B
Defect characteristics Relative I x ~ o n b~-eea
Defect andra~ way
subsurface 75-250 ~zm 8-30/~m just undea/ little bit out
mafacela~ 0-37 ~m :>8 lzm justund~lilflebitout IASAW
N I m e t t ~
Case of the Sub~rfaee Defect (Type .4)
(1) Case 1 0~dng)- Figu~ 25 shows an exlm~le of tilting; trod Table 8 shows the defect
dmmOetim~ evaluated by the U.T. b e f ~ testing and the mmalxt of c~les when flaking
occun~ Figure 26 shows the ~ of the flaking ~ by tim dq~th mete. The collation of
th~ ~ v e l~ition ~ the d ~ ma~ and (he fl~ing v~th thin ~ the d ~ m ~ ~
the defer, and the dcplh of the flaklng with that of the defect, indicaled that the f l ~ E ~ by
NISHIKAWA ET AL. ON NON-METALLIC INCLUSIONS 157
Figure 25-Examp/e of the flaling. Table 8-Defect c ~ ana(fat/gue l~b.
Defect characteristics Fatigue life depth size position cycles
150 um 32 um just under 1.5 ;< 107 Figure 26-Shape offlaking. (2) Case 2 (Change of Defectlmage)- In this case, the life testing was fini.qhed atter lxl08 cycles with no flaking and alter that, the defect was o l r e t ~ by the UT and the microscopic tester. Figure 27 shows an example of ~ defect image change from before to after life testing, and Table 9 shows the defect elmractefislics evahmted by the U.T. before and after life testing and the total number of cycles. Compmed with the defect image before testing, the image atter testing was remmt~ly diffca~at and the defect size inthe image had grown to more than three ~nes. That means that the actual size of the defect had grown to alxmt twice in size. The image atter tes~._g had the white band at the defect position that looked like the Milky Way. That indicated the race way and aplcz~-,ed by the ~ of the dent shaped by the roKing balls.
Figure 28 shows the example of the m i ~ c observation of the actual r after life testing by SEM~ That defect had a nonmeta/lic inclusion and cracks and it was confirmed by SEM
analysis that the ~ c inclusion was A1203-CaO complex. The ~mmrlcOole point was that
the cracks weae connected to the nomnetallic inclusion and inclined at an angle of about 45 degrees against the staface. So, it was prestmaed that stafdng from the nonmetallic inclusion, the cracks
were generamt and grew by the shear stress dining the life testin~ The ehzn~ of the ~ ~
a i ~ life testing indica~d the g e m ~ o n of the erack~
(3) Case 3 (No change ofDef~'t/mage)- In this ease, as in case 2, the life lesting was fini.ched 1 • 10s cycles with no tlaking and after fl~t, the defect was observed by U.T. Figure 29 shows an example ofthe defect image ehan~ from before to after life lesting; and Table I0 shows the defect characteristics evaluated by the U.T. before life testing and the total number of cycles. There was
no ehzn~ of the defect image, and the m i ~ c observation found no cracks. Figure 30 shows
the defect image of mother case, in which the relative position between the defect and the race way was set a little bit out. In this case, there was also no change of the defect image.
Table 10-Defect character/s017s andfat/gue l/~. Defect characteristics
depth size position
Before 180/zm 27/zm justunder
Before 180 gm 38 gm little bit out
Fatigue life cycles 1 x 10 s
Figure 29-Defect 0nage change m testing. Figure 30-Defect
~aage after l~e testing
(4)
Relationship Between Fatigue L~e and Nonmetallic/nc/us/ons
3)-Figure 31 shows there~on.~l'fip, b~we~ the ~ c il~hl~ol~ ~ the flaking o11 the ~ steel ~ . The
size and depth ~om the .--~.k~,le staface of the n o n m e t a ~ i~lusions were evaluated ~ ~ e U.T. before life lesting; and the flr&ing behavior was observ~ by rolling contact fatigue life testing; which was p e r f o m ~ on the condition of adjusting the position of the evaluated nonmetallic
inclusions just under the race way. It was c o n ~ ~ nonmelallic inclusions whose size was
over20 ~m and whose depth was lO0 g m to150 , m
understuface(the~gestshears~ess
NISHIKAWA ET AL. ON NON-METALLIC INCLUSIONS 159 v 50 100 ~, 15o t ~ 200 A~
"o[
( O ( O O 250 l o ,_L-~_~_% I I,Dead
zone J Ii - T , , .... I-l
. -'- i F l a k i n g a r e a.
I [I-I
] No f l a k i n g area i~laking
A_: C r a c k i n gO:Durable)
Figure 31"Re/attbnsh/p bemzeen 50 1 oo n o a r a ~ h~clusions and t?aking Estimated inclusions size (#m) /nm11/ngeontactfatiguelife~ Case of the Surface Layer Defect (Type B)
(1) Case 4 (FlaYb'ng)- Figuxe 32 shows an example of the fl~d6ng; and Table I 1 shows the defect
charact~is~ evaluated by the U.T. before l~dng mad tlae m m a ~ of cycles when flaking
occurred. Figure 33 shows the ~ of the flaking m~mstn~ by the d ~ . meter. The same as Type A, the flaking point was presumed at the defect point, but the situation was r~tarkably differ~at The number of cycles at flaking was smaller thsn that of Type A, and the depth of tl~ t~ddngreachesthemaxinmmshearslresstmge~xmt 150 um beyondthe~'tsi~e.Ofcourse, it was befo~mnd con~,,ed that no defect existed in that range.
F i ~ e 32-~xampte offlaya.g.
Tablel l-Defect ~ andfat/gue l@C~ Defect characteristics Fatigue life depth size position cycles
- 3 7 xtm just under 4.1X 106 Figure 33-Shape offlaldng. Case 5 (Change of Defect Image)- Figure 34 shows an example of the defect image change. Table 12 shows the defect characteristics and the total number of cycles, and Figure 35 shows the microscopic observation. The change of the defect image and the defect type was the same as Type A, but the result of the microscopic observation was slightly different. In that observation, it was coals'reed that the cracks ran vertically below the surface with the nonmetallic inclusion. So, it was presumed that the stress ttmt geserated the cracks was the tmasile smms which ~ the maxinmm in the safac~ layer. To return to Case 4, which had flakin5 the mech~ni.,~a oflhe flaking by the defect exisling in the sa'face hyer was presumed as
follows. First, the crack was generated by the tensile stress mrdng from the nomnemUic inclusion e r d s ~ in ~ae ~ lay~ ~ x t the ~ and it g c w v e ~ below fl~e ~ with the mmmemUic i~usion. Wlx~ ~ae crack approactzxi the maximmn sheer s~ess r a n ~ the g r o ~ direction of the crock was dmnged to tl~ ~ by the shear s~res~ and lin~gly it made the fl.~cing.
Figure 34-Defect ~nage change in l~e testing. Figure 35-M~scop/c obs~at/on.
The results shown above suggested that the most l~rmfl~! inclusions to the he~ing ILfe was the A1203-CaO comple~ inchsions whose size was over abotn 20 gin,but the life oflhe bearing was strongly dependem on its position. So, the most impomm subject for ~he steel mdcer is how to decrease ~ AI203-CaO complex indusions.
Improvement o f Nonmetallic Inclusion
P,-ocess a , , d ~ g ~
Figure 36 shows the process flow of No.3 EAF-BI./CC line in Aichi Steel Co. The bearing steels
are mainly produced on this line.Table 13 shows the details of the ev~aled sample. One of the c o u n l e ~ - c s to f~rn fine nonmetallic inclusions is the slag I~sicity control Two types of refining a'~hods ~ a t ~ l for the ~ o n of s~ples, one was Itm conventional reCmin~ n~'1tmd ((~lled Mefl~od A), =ld the oth~, which was twio~ as high slag basid~ ~ ~ ~ ~ f i n g m ~ o d (~led Method B). The smnples were taken at each stage from refining to final rolling. Each sample was ~ for ti~e dis~'bufion and the composition of the nonme~lic inchsiom by the U.T., E~A.S/C.C.NL and EPMA. In addition to flaese, the fir~ rolled were evalu~i on the fa~,ue life by ~e rolling o0n~t fatigue life ~ n g .
INo. EA I
b-4
F q Bc:cc I BL,CC:B oo
NISHIKAWA ET AL. ON NON-METALLIC INCLUSIONS 161
Specmaen SUJ2
Table 13-Deta//s of the evaluated sample. Refinin$ MethodA MethodB (h~proved) Stag basicity CaO/S~Zh 5 CaO/Si02 >10 S~Ung metal dur~g RH ~,'ati~