This document discusses notch wear mechanisms during the machining of high austenitic stainless steels. Special step-turning tests were conducted on four stainless steel alloys to study the degree of work hardening ahead of the tool and the side flow of work material at the depth of cut line. Microhardness measurements and SEM analysis showed severe localized shear and chip side flow interacting strongly with the tool, leading to notch wear initiation. Notch wear was found to be most sensitive to cutting parameters for the alloy with the highest nickel content, and increased with feed and depth of cut. Hardness was highest in the side flow region, indicating work hardening affects notch wear progression.

1. Chip Flow and Notch Wear Mechanisms
during the Machining of High Austenitic StainlessSteels
prtosmu-
. .Alloy
Cr Ni Mo Si C Mn N, Fe
SS 2378 20.3 17.8 6.0 0.45 0.012 0.51 0.21 rest
SS2584 26.8 30.2 3.3 .0.39 0.016 1.69 0.05 rest
SS2375 17.3 13.2 2.58 0.67 0.016 1.60 0.18 rest
SS2375. 18.0 12.2 2.56 0.67 0.016 1.20 0.13 rest
.............................................................................................. 1..-.._"...
H. Chandrasekaran (2),J. 0.Johansson,
Swedish Institutefor Metals Research, Drottning Kristinas Vag 48,114 28 Stockholm
Receivedon January 15,1994
aterial
Notch wear at the depth of cut line is a serious problem during the machining of high-austenitic stainless
steels. The mechanism of such notch wear was investigated through special step-turning tests involving four
high austenitic stainless steels with cemented carbide tool. Chip studies and micro-hardness measurement of
work material at the chip flow region, along with SEM studies were c m i d out to elucidate the role of work
hardening and chip flow upon wear. These clearly showed severe locnlisedshear and chip sideflow and its
strong adhesive interaction with the tool material in the notch region.The critical initiation of the notch
seems to be related to factors such as,transverse stress and temperature distribution and chemical interaction.
Subsequent progress of notch was often through the interaction of the localised shear region of the chip and
the exposed binder phase of the tool. Direct evidence between the strain hardening index of the work
materialsand the level of notch wear was also observed.
Key words: turning, wear, stainless steel
Mechanical Propenies Hardness Machinabiliv
RpO.2 Rm A5 HB "10,. 0.3
(MPa) (MPa) % mlmm
1INTRODUCTION
In view of the ever greater demand for environmentally favourableand
maintenance free materials,the application potential for high austenitic
stainless steels are increasing.The very propertiesthat are essential from the
above context, such as high temperaturecorrosion and oxidation resistance,as
well as good forming properties are,on the other hand, not fwourable from the
view point of good machinability. which often could be very critical in terms of
machining economics. The poor machinability of austenitic stainless steel in
terms of different tool wear modes such as flank,crater, and notch wear, as
well as plastic deformation and micro-chipping,is often regardedasa
consequence of poor thermal propertiesof these materials and the resulting
high cutting temperatures. Severeadhesion to tool materials and propensity to
built-up edge formation along with small tool-chip contact length are the other
features associated with these materials.
In the course of the investigations reported in this paper and devoted to the
turning machinability of commercial variantsof austenitic stainless steels with
high alloy content (30 %to 62 %) using cementedcarbide inserts it was shown
that, while the machinability grading based upon differentcriteria were
comparable, the notch wear of the cutting edge often limited the practical tool
life (I). Such wear is also observedduring the machining of nickel based
superalloys (2,3,4). Here, Shaw et al(2)and Lee et al(3) have identified
seizure and pull out of tool material as possible wear mechanisms, while
d i f i i o n is identified by Tan and Zhang(5) in this context.The primary
interest in most of the referred studies has been towardsthe tool geometry and
tool material aspects (coated, un-coated and superhard type) during the
machining of superalloys.
Thus, a real need was felt for understandingthe material related aspects of
notch wear, and the basic mechanismsassociatedwith it, in the context of high
austenitic stainless steel materials.Such informationcould be useful in the
development of better materials with sufficientmachinability,but with intact OK
even improved primary end properties.Accordingly,keeping the tool geometry
and tool material constant, a systematic investigation using turning tests was
carried out to identify the role of cutting parameters such as speed, feed and
depth of cut upon the prevailing notch wear. In some of these special turning
tests, attention was focused upon the degree of work hardeningof the material
ahead of the tool-tip as well asthe influenceof the side flow of the work/ chip
material at the depth of cut line @CL) during machiningand their role on the
development of notch wear vis a vis the alloy typemachined. The observed
morphology of the region at the DCL and the measured high temperature
mechanical properties of these steels were used to provide qualitative
explanation for the notch or grooving wear phenomenon.These results will be
presented now.
2 STAINLESS STEEL WORK MATERIALS
2.1 Chemical composition
Fourhigh austenitic steels were used in our notch wear studies. The first high
alloyed variant SS2378 (20 Cr-18 Ni-6 Mo steel) is intended for severe
corrosive application, while variant SS 2584 (27 Cr-30Ni-3.3 Mo steel)
exhibits goodresistance to corrosion and especially pitting and crevice
corrosion.
Both have very small S content, while SS 2378 is in addition N alloyed
(021%). The austenitic steel SS 2375 containssmall amount of S but up to
0.18% ofN. The ESR steel is an dectro-slagrefined variantwith low inclusion
content. The mechanical propertiesof the of the four stainless materials are
shown in Table I.
Table la Room temperature mechanical properties and machinability
..........................................
):z1:; 500
650
590
Table I b Results from high temperatures tensile tests
ernp.0C) 1 2 1 2 1
............
* 1-3000~: 2 - 9 0 0 0 ~
Annals of the ClRP Vol.43/1/1994 101
2.2 Mechanical properties and machinability
The standard room temperature tensile strengthproperties for the steels used in
our machinability tests, based upon specificationsare shown in Table 2a, while
Table 2b shows results from elevated temperature(3000 and 900OC)tensile
tests. The intention was to correlate the basic deformationpropertiesof the
steels from standard tests with the deformationprocessduring chip formation
and hence to tool wear and machinability.Since tool temperatureover 1OOOo C
was indicated from ourearlier tests (l), 3000 and 9000 C were chosen for the
tensile rests. The machinability results ( ~ ~ 0 .o,3)arebased uponlongihldinal
turning (I) using un-coated cemented carbidetips. The room temperature
properties indicate that the high alloyed variantwith maximumN content (SS
2378) to be the strongest, while the two SS2375 variants,as may be expected,
have practically the same mechanicalproperties.

2. The high temperature behaviour is also similar in general,the highest alloyed
variants retaining their strength (about 25 Oh greater than the low alloyed
variants) even at 9000 C. The most remarkabledifferencecould be seen in the
ductility parameter 2 (percentage contractionof area). Here, while for the two
SS 2375 alloys the value of 2 increases from low to high temperature. the
highest alloyed variant SS 2584 indicates a maximum in Z around 300° C.and
at 9000C it decreases appreciably. The two SS 2375 variants in particular
show a very large deformability at 9OOOC (> 90 O h ) . Both alloys SS 2378 and
SS 2584 display similar maximum in A5 around 3000 C. As will be shown
later this peculiarity of steel SS 2584 is manifestedduring machining through
its enhanced propensity to wear the tool at the DCL.
Cuning conditions C u h g time
..............................
3 EXPERIMENTAL STUDIES
3.1 Xotch wear studies
For a given tool geometry, it was proposedto identifythe role of the following
conditions upon the origin and propagationof notch wear namely,
* the cutting conditions speed, feed and depth of cut
..................... ............................................... ..................."..
V S a
d m i n mmlrev mm
150 0.15 4.0 and 0.5
I50 0.3 and 0.08 1.5
60and240 0.15 ' I .5
..............................................................................................
................................ I.. .........................................................
Table 2 Turning tertr for notch wear studies
Tool grade: Cementedcarbide IS0 P 15
Coolant: None
bark
..... ......
* the degree of strain hardening associated with the layer of work material
ahead of the tool from previous machiningoperation, and
" the degree of side flow of the work materialespecially at DCL.
In order to verify these features, two test series were carried out involving
a) conventional longitudinal turning with cleaning cuts in between and
b) special turning teststo monitor the side flow of work /chip material at the
DCL for two limiting conditions of cutting.
Cutting conditions corresponding to test a) areshown in Table 2. Thecarbide
grade (PI 5 ) and tool geometry (60 rake and 750 approach angles) used earlier
for machinability studies were also used here. A specific machining time of 4
min. was used and the resulting notch wear length (NL) was monitored. In
order to keep the mechanical state of the material coming into the cutting zone
invariant, the work material was machined with a cleaning pass with a new
cutting insert and mild cutting conditions (V=150 dmin, S=O.lmdrev and
a = 1.O mm) between each test pass. Such intermediatecleaning passwas not
carried out when the influence of the cutting speed was investigated. Further,
chip hammering and consequent damage to the cutting edge outside the DCL
was also observed frequently.Typical tool with notch wear as seen in a low-
power stereo-microscope is shown in Fig. I. High alloyed variants displayed
greater notch wear aswell assticking metal.
3.2 Notch wear results
The quantitative influence of the cutting parameters upon notch wear is shown
in Figs. 2 and 3. Two of the high alloyed variantsdisplay differing sensitivity
to the cutting parameters namely feed and depth of cut, while the notch wem of
the other two variants SS 2375 and SS2375 ESR changes very little with feed
or depth of cut. Both these features are rather special when we compare the
flank or crater wear of these alloys. As a rule unlike the feed, the influence of
depth of cut upon notch wear appears to be marginal.
I,,oc v = 100m/min 0 552315 ESR
a i1.0nnn A 552375
s s m
Y 23%
s s m
Y 23%
I I I I
0 0.1 0 2 0 3
5 nrn/rev -
Fig. 2 Variation of notch wear NL with feed S for a cutting time T=4 min.
s z 0.6 rnrn/rev
E
n
,+-
0
0 0 s 1 1.5 2
--
a rnm -Fig. 3 Variation of notch wear NL with depth of cut a. All other conditions are
the same as in Fig. 2.
The notch wear of the alloy SS2584 exhibits the highest sensitivity,the wear
length NL increasing almost linearly with feed Sand depth of cut a. This
means that, while in all the other alloys (including the highest alloyed SS 2378)
notch wear appears to stabilise after a short while, it continues to progress in
the case of alloy SS 2584, although the magnitudeof notch wearat the lowest
feed of 0.08 is greater for the high alloy variant SS 2378. However,the results
of notch studies could be more useful in relative terms rather than in the
absolutesense, as these are based on well controlled, but limited number of
tests. The wom tools were examined in low power stereo- microscope for
measuring the notch wear, and some of these were also examined subsequently
in a scanning electron microscope (SEW.
3.3 Deformation of work material and notch wear
The previous test series indicated the total effect of the cutting parameters such
as speed, feed and depth of cut upon the generatednotch wear. The next test
was to observe the rolddegree of side spread of the work material/chip just
ahead of the toolppon notch wear. These testswere carriedout for two levels
of speed,feed and depth of cut. For each cutting condition a length of about 20
mrn was tumed and then the turning process was terminatedsuddenly so as to
retain the build-up of work material ("collar") ahead of the tool. Corresponding
test conditions are shown in Table 3.
Fig.1 Tool with notch wear; steel SS 2375,V=IOO m/..niti S= 0.32 mm/rev
102

3. The three surfaces of interest in this context are
I. Surface resulting from the cutting conditions of rhe previous smge.
2. Inremediare surface containing the side flow region.
3. Surface produced under the current cutting conditions.
The state of the work material (hardnessand stateof deformation) as a function
of cutting conditions (current and the previous) could now be investigated.The
remnant deformation or side flow correspondingto the width of cut could also
be studied in the transition mne. The parameten measured here are.
* the micro-hardness (Vicken's micro-hardnesswith a load of 200 gmj in the
three regions. namely incoming, transition and resultant:
* the extentof metal flow (normal to the machined surface) in the transitional
region between the incoming and resultant surfaces and
* the incoming and resultant surface finish.
-.- -
f y - Fig. 4 Schematic view of the primary
cuningedge and thework material
showing the side flow.
1,2,3and 4- Position for hardness
measurement; I-incoming surface;
11-machinedsurface; f-side tlow
2 Tronsitim wrloce
__. * _ _ I
nvl
i I I I1 z 3 b
POSlllOU ALONG T K 7RANSlENT ZQNE
Fig. 5 Variation of micro-hardness (HV0.2) from step turning tests (a=I.O and
4.0 mm) for the four stainless steels; V-150 m/min,S=O.lSd r e v .
The last two measurements were carriedout using noti-cnntactLaser surface
finish measuring system (LSM) facility.Fig. 5 shows the variation of micro
hardness(HV,,) along points I. 2.3 and 4 in the side flow region resulting
from the turning test with a large depth of cut (a =4 mm). Similar distribution
was observed forother tests involving two levels of feed and sped
Irrespective of the type of steel, the region of maximum side flow of the work-
material w i n 12 in Fig. 4)displayed the highest hardness,while poinr 1
corresponding 10the in-coming work material displayed the lowest hardness.
Moreover, the hardness at point 4 located in the vicinity of the machined
surface,was greater (Fig. 5 ) than thehardnessof the in-coming material from
the previous stnge (point 1) for all conditions of Table 3, indicating thereby.that
point 1 had undergone some softening asit was about to enter the chip
formation zone.
3.4Side flow of work material
Some of the results from the measurementof side flow fof work material
(normal to the in-corningsurface) are shown in Fig. 6.The influenceof feed S
was rather linle. Bothdepth of cut and cutting speed seems to have a greater
effect (inverse) upon side flow f than the feed. Moreover,the low alloyed ESR
variant seems to display the largest side flow f. Interpretationof the absolute
value of the side flowlevel is difficult (noquick- stop was used), and the
results from experimentation at high cutting speedsare thus questionable. Our
results could however, be used for the qualitative understanding of the
influence of work material upon side flow and notch wear.
4 CHIP STUDIESAND XOTCIIWEAR
4.1 Chip deformation
The chips from the notch wear tests here evaluated in terms of geomemc
parameters such as thickness, lameIra formationand featuresassociatedwith
chip width and side tlow using both optical and scanning electron microscopy
(SEM). Machining ofaustenitic stainless steels is characterisedby severe shear
Iocalisation resulting in both farceandtemperature fluctuations.
0 *m -
b
Fig. 6 Side flow f as a function of cutting speed V (Fig. 6a) and depth of cut a
(Fig. 6b) for the four stainless steels.
The variants with poor machinability (in terms of flankor crater wear), also
displayed severe notch wear as already observed earlier (53.2). Thus,it IS
meaningful to look for common factors in termsof chip strain and im
distribution across the width,as well as the interactionbetween the chip/
workpiece material and the cutting tool in the notch region. Some of these
features were covered by us through the detailedstudy of chips and the tool in
a SEM,and these results will be presented now.
In view of the variation in the thicknessof cut along the cutting edge and the
angle of approach near the tool nose, the normal conditions fulfilling two
dimensional deformation of chip (constancy of chip thickness ratio
the chip width) is far from true, especially when the work materialdisplays
severe strain and strain rate hardening tendencies.
across
b) SS2375 ESRa) SS 2584
Fig. 7 Cross section of chips; V=lOO dmin; a=I .5 mm and S-0.308 d r e v
CHIP WIDTH h, mm -
Fig. 8 Variation in the chip thickness ratio <b(=hh / hb) across the width of
cut for the 2 steel variants shown in Fig.7.
These effectsare readily seen in the appreciabledifference in the cross section
of a chip from identical machining conditionsshown in Fig. 7 comparing steels
SS 2584 and SS 2375 ESR These steels alsodisplay largedifference in terms
of tool notch wear (Fig. 2). As the thickness of cut h increases from tool nose
to DCL, the chip thickness along the width of cut hbc also increases. The
variation in the chip thickness ratio across chip width <b (= h h /hb ) is shown
In Fig. 8. Wecan see that the variation in <b is more severe for steel SS 2584
than for the other work matenal. The severe non-uniformityin <b observed by
us in the chip secdon, irowver, means that duringthe machining of thesetype
of steelstheir three-dimens~onaldefermation behaviouraffect the outcome, and
the classical metal cutting parameterssuch as shear plane angle cp and <, often
103

4. measured in the plane normal to the main cutting edge. could only he
considered as mean values for a given instant correspondingto a specific cross
section of the chip. Using the results of Fig. 8 ,the shear plane angle across the
width of cut qb ( = arctan Cos y / &- sin y. where y is the rake angle) for the
above two steel variants was calculated (see Table. 4). While the average value
of rp varies very little for the whole range of these steels (between 230 and
26.40). across the chip width this varies from 180 near tool nose to 21" for
most of the width, rising almost upto 65O near the notch region for the steel
SS2584. In the case of steel SS 2375 ESR the correspondingvalues of cp are
respectively 240.300 and 320.
hb bbf <b 'Pb
mm mm d q .
0.06 0.14 2.33 24
0.13 0.42 3.23 17.6
0.18 0 5 2 2,89 19.6
0.26 0.66 2.54 12.2
0.30 0.82 2.73 20.7
0.30 0.80 2.67 21.2
0.29 0.16 0.55 65.5
........................ "...............".A
Table 4 Chip thickness ratio and shear plane angle across the chip
V = 100dmin: a = 1.5 mm; S = 0.308 mdrev
hc <b 'Pb
mm d q .
............................................................................................
0.08 1.33 38.9
0.30 2.31 24.3
0.32 1.78 30.7
0.95 1.92 28.7
0.54 1.80 30.4
0.50 1.67 32.4
.............................................
..............................
Position across the
chip from tool nos1
1mm
0.12
0.20
0.40
0.80
1.20
1.40
I.6
..............................
..............................
...........................................................................................
SS2584 [ SS2375ESR
The most relevant difference between the material variantsin this context is the
fact,that cp for the region corresponding to the uniform thickness of cut (the
rectilinear portionof cutting edge) now differsby almost 50% (20.70 and 30.4O
respectively) for the steels SS 2584 and SS 2375 ESR.The implicationsof
such variations in shear plane angle across the width are conducive to severe
discontinuities in terms of plane strain and plane stressconditions at the DCL.
The chip material close to the rake surface at the DCL may be expected to
undergo severe outward deformation in the direction of width of cut.
4.2 SEM studies of chip
Inorder to verify the above hypothesisoptical and scanningelectron
microscopy (SEM)of the chip was carried out. From the appearanceof the
outer surface of chips for a stainless steel (Fig. 9), showinggreater influence of
feed S(indirectly the thickness of cut h) upon segmentation,thanthe depth of
cut a could be seen. The lamella from segmentationwerenot contiguous across
the width of the chip (depth of cut),and showed severe changes at the depth of
cut line. The behaviour of the high alloyed variants werecomparableto each
other, but more complex than that of steel SS 2375.
Fig. 10A view (SEW of chip showinglamella formationand severe side flow
at the notch region; work material SS 2375; V = 100mimin, S =0.308 mmirev;
a) general view of chip; b) detail from (a) showing the extent of side
deformation and evidence of its detachment (arrow);c) under side of (b)
displaying traces of intermittentadhesion.
Fig. 9 Typical chips showing lamella formation and its variationswith feed
(a and b) and depth of cut (c and d) for the steel SS2375, V=lOOdmin.
a) S = 0.308 mdrev, b) S = 0.08 d r e v ; (a = 1.5 mm for both)
c) a = 0.5 mm, d) a = 4.0 mm; (S = 0.15 d r e v for both)
Special attention was paid to the study of the notch region of the tools as well
as the chip material and its movement in the notch region in the SEM studies.
This region of interest h h e chip for steel SS 2375 is shown in Fig. 10.The
Severe side deformation of the chip material close to the rake surface at the end
of the strain localisedregion could be clearly seenin Fig. lob. Actually what
we see is a tongue of chip material after it had been severely pulled away from
the rake (notch) surface due to the chip movement. A view of the underside of
the chip corresponding to thispull-out zone is shown in Fig. IOc, indicatingthe
intermittent making and breaking of contact between these deformation
"tongues" and the tool surface.
Fig. 11a A view of the rake side of notch wear region (SEM);work material
-SS 2375, V = 100 mimin, S =0.I5mdrev and a = 1.5 mm,
b) detail from (a) showing the "etched"appearanceof the wear region.
The region of notch wear often displayed severe adhesion of work material.
The type of tool material damage at the notch itself as seen from the flank
surface indicated no abrasive wear tracks. With ceramic tool materials notch
wear from abrasive action of the chip at DCL has been reported (4). The
appearance resembling brittle-fracture in the damagedregion of notch wear did
not differ significantly between the tools used with the different steel variants.
The case of a tool after machining steel SS2375 is shown in Fig. 11. It is
noteworthy that, the damaged region here displayedan "etched" appearance in
high magnification (Fig. 11b), indicating probablythe preferential loss of the
binder phase from this 55.5 WC-35(TiC+TaNbC)-9.5 Co hardmetal insert,
through metallurgical interaction between the side flow regions of chip material
and the tool material. In this context Tan and Zhang (5) have suggested
104

5. diffusion 3s an important factor in the case ofpure nickel work material. In the
present situation it was not possible to ascertain the type of interaction (such as
oxidation, diffusion etc.) controlling this featureleading to the local depletion
of binder phase and consequent weakeningof the tool material.
The chip form and flow as described earlier are very specific in our case, and it
is worth considering how conducive are these factors for notch wear. For
exaniple. some correlation between the tensile strength and the specificcutting
load has been reported for carbon steels with comparable percentageelongation
by Konig (6). However, no general and simple correlationexists between
mechanical behaviour and rnachinability,as both these cover a range of
properties. Similarly the critical role of chip shape upon notch wear is indicated
in (4). while the occurrence of rake notch wear in CBN tools machining
standard stainless (304) alloy and the role of chip shape therein, have been
reported by Oishi et a1(7). Thus, severe non-uniformityof contact loads at the
notch region could well be expected in our case too: especially in view of the
large chip thickness here.
- 1 3 I
E
4.3 Possible notch wear mechanisms
From the results so far we observe,that the severe lateral deformationof chip
material in the notch region has a significant role upon notch wear. The type
and extent of deformation occurs in conjunction with the shear localisation
process (asshown in Fig. 10b), and results in the exposure of nascent work
material surface capable of high metallurgicalreactivity and adhesive
tendencies. The large shear plan angle at the depth of cut line (vicinity of
notch) is indicative of the fact that,
* the actual line of chip separation h m the work material occurs well inside
the chip rather than the work material; and
* the chip separation that is predominantlyshear is more of a "tearing"
process at the DCL resulting in ragged surface.
This is a recurring process resulting in makingand breakingof adhesive
contacts at the depth ofcut line.The resulting damage (notch wear) would
depend upon the following factors:
I. the extent of area available for adhesion (lateral deformation of chip)
2. adhesive affinity between the tool and work material,
3. the hot strength of the adhesivejunction,
4. frequency of interruption in the adhesive contact.
Of these influences,on the basis of our test results on side flow (Fig. 6) and
lamella frequency, the factors I and 4 do not seem to differ all too much for the
family of alloys under consideration. Factors2 and 3 may be expected to differ
for these alloyson the basis of their high temperaturedeformation properties
(Table. 2b). The material exhibiting high hot strength (SS 2584 and SS 2378)
and hence high resistance after adhesion, could also be associated with severe
notch wear. Further, the hot strength of thejunction would depend upon the
temperature distribution across the chip, where the poor thermal conductivity
of ihese materials and the role of plane st& to plane stress transition at DCL
are additional negative factors(2). Expressingthe stress strain relationshipof
the work materials intheform 0 = A E 0. (0-stress and z-plastic strain for
Rp 1 <o < Rm), the key role of the strain hardening index n upon notch wear
(KL)in this context is self evident from Fig. 12.
i
STRAIN HAROCNING INDIX n A
Fig. 12The relation between the strain hardening index n calculatedfrom
tensile test results at 3000 C and the machinability (criterion V,%,, )as well as
notch wear NL (4 min. with V=IOO,S=0.15 and a=1.5) from cutting tests for
the four stainless steels.
Thus.high strain hardenabilityalong with high hot strength appear to be
important conditions for initiating and continuing notch wear. Once a finite
volume of tool damage has occurred, the exposed phases of the tool material
undergo degradation due to metallurgical interaction,where the environment
(oxygen potential ) h& a prominent role. Evidencefrom other research(2,3)
also support this hypothesis. Thus, a good pictureof the temperature
distribution across the width of contact (hardly any informationto-day) and the
identification of the selective role of atmosphere during machining,along with
the fundamental information ahout adhesive affinity between the alloying
elements of the work material and the phases of tool material, are some of the
critical information required for understandingthe phenomenonof notch wear.
5 CONCLUSIONS
The results of the technological tests and the later chip and notch wear studies
allow us to make some conclusions concerning the phenomenon of notch wear.
1. In characterising the deformation of the high austenitic work material during
machining and correlate it to their machinability, it is fruitfulto use the concept
of variations in the chip ratio and shear plane angle acrossthe widthojcut.
2. In un-coated carbide of the type used here, flank notchappears to limit the
tool life for most of the high austenitic steels consideredhere.
3. The segmentation in the direction of chip flow due to strain localisation in
the chip formation process is not contiguous across chip width, and this
phenomenon varies with the thickness ofcut.
4. Loss of tool material from'the notch region is initiateddue to the
deformation and sideflow ofa highly reactive nascentchip/workmaterial
exhibiting the highest hardnessclose to the rake surface at the depth of cut line
and its repeated local adhesive welding to and breakingfrornthe tool.
5. The damage to the tool material in the notch region resemblesa brittle
fracture, and the apparent loss of binder phase indicatesadditional interactions
between the work and tool materials.
6.The observed notch wear appears to increase in proportion (Fig. 12)to the
strain hardening index estimated from high temperaturetensile tests.
ACKNOWLEDGEMENTS
This research project was funded by Swedish National Board for Technical
Development WTEK), Sandvik Steel AB,AvestaStainless AB and
Uddeholm AB.Our sincere thanks are due to StaffanGunnanson and Maths
Svensson (Uddeholm AB) for the machining testsas well the high temperature
tensile tests. Further. the dynamic interest shown by the project research
committee headed by Bela Leffler,(Avesta-Shefeld AB) and useful comments
Gom Carl-Gustav Carlborg and Per-Ake Franklind,(AB Sandvik Steel),
Andea Lenander (Sandvik Coromant AB) and Thomas Mainert(Seco Tools
AB) are also gratefully acknowledged.
REFERENCES
I. J.O. Johansson, H.Chandrasekaran,S. Gunnarssonand M. Svensson,(1990).
Machinability of high austenitic stainless steels -results fromturning tests (in
Swedish), Swedish Institute for Metals Report IM -2676,Sept.
2. M.C. Shaw, A.L. Thurman and H.J.Ahlgren, (1966), Plasticity problems
involving plane strain and plane stress simultaneously-Grooveformation in the
machining of high temperature alloys, Trans. of ASME, Ser. B,J. Engr. for
Industry., 88, pp.142-146
3.1M.Lee, J.G.Home and D.Tabor, (1979). The mechanismof notch formation
at the depth of cut line of ceramic tools machiningnickel base super alloys,
Wear of Materials, Proc.of Int. Conference on Wear, USA, pp460-469
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