Cryogenic properties of some cutting tool materials.pdf

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C r y o g e n i c P r o p e r tie s o f S o m e C u t tin g T o o l M a t e ria lsZ . Z h a o a n d S . Y . H o n g

C u t t i n g t o o l m a t e r i a l s b e l o n g t o a g r o u p o f n o n d u c t i l e m a t e r i a l s . C h i p p i n g a n d b r e a k i n g o f t h e c u t ti n ge d g e a n d f r a c t u r i n g o f t h e to o l a r e c o m m o n t y p e s o f t o ol f ai l u re e v e n u n d e r c o n v e n t i o n a l m a c h i n i n g c o n -d i t i o n s . T h i s l e a d s t o a c o n c e r n a b o u t w h e t h e r c u t t i n g t o o l m a t e r i a l s a r e a b l e t o m a i n t a i n t h e i r s tr e n g t ha n d t o u g h n e s s a n d w i t h s t a n d t h e l o w - t e m p e r a t u r e t h e r m a l s h o c k d u r i n g c r y o g e n i c m a c h i n i n g . T h e o b -j e c t i v e o f t h is i n v e s t i g a ti o n w a s t o s t u d y t h e b e h a v i o r s o f t h e s e k i n d s o f m a t e r i a l s a t c r y o g e n i c t e m p e r a -t u r e s . T h e r e s u l t s w i l l a l s o s e r v e a s a b a s i s i n s e l e c t i n g t h e s u i t a b l e c u t t i n g t o o l m a t e r i a l s f o r c r y o g e n i cm a c h i n i n g a n d i n d e t e r m i n i n g t h e c r y o g e n i c s tr a t e g y a n d o p t i m u m c u t t in g c o n d i t i o n s . S e v e r a l r e p r e-s e n t a t i ve c u t t i n g t o o l m a t e r i a l s , s u c h a s f i v e g r ad e s o f c o m m e r c i a l c a r b i d e - c o b a l t a l l o y s a n d M 4 6 h i g h -s p e e d s t e e l , a re i n v e s t ig a t e d i n t e r m s o f m i c r o s t r u c t u r a l o b s e r v a t i o n , i m p a c t t e s t in g , t r a n s v e r s e r u p t u r es t r e n g th m e a s u r e m e n t , a n d i n d e n t a t io n t e s t in g . I t h a s b e e n s h o w n t h a t c a r b i d e t o o l m a t e r i a l s g e n e r a l l yr e t ai n t h e i r st r e n g t h a n d t o u g h n e s s a s t h e t e m p e r a t u r e d e c r e a s e s t o l i q u id n i t r o g e n t e m p e r a t u r e . T h e b e -h a v i o r s o f c a r b i d e t o o l m a t e r i a l s a t c r y o g e n i c t e m p e r a t u r e s c a n b e e x p l a in e d i n t e r m s o f th e t e m p e r a t u r ee f f e c t s o n t h e b i n d e r p h a s e .

1. In troduct ionW I T H th e r a p i d d e v e l o p m e n t a n d a p p l i c a t i o n o f n u m e r i c a l c o n -t r o l m a c h i n e t o o l s , r e li a b i l it y a n d p r e d i c t a b i li t y o f c u t ti n g t o o lp e r f o r m a n c e a r e m o r e s i g n i f i c a n t t h a n b e f o r e . T h e i n c r e a s e dd e m a n d f o r h i g h e r m e t a l r e m o v a l r a t e s r e q u i r e s m o r e r e f r a c -t o r y m a t e r i a l s . M o s t r e f r a c t o r y m a t e r i a l s , h o w e v e r , b e l o n g t o ac a t e g o r y o f b r it t le , n o n f r a g i l e m a t e r i a l s . I t i s w e l l k n o w n t h a tt h e c h i p p i n g o f c u t t in g e d g e s a n d t h e f r a c t u r i n g o f c a r b i d e c u t -t i n g t o o l s a r e t h e m o s t f r e q u e n t t y p e s o f t o o l f a i l u r e s . [ 1,2 ] G e n -e r a l ly , m o s t m a t e r i a ls b e c o m e b r i t tl e t o v a r i o u s d e g r e e s a s th e ya r e e x p o s e d t o l o w t e m p e r a t u r e s . T h e s e t e n d e n c i e s o f w o r k -p i e c e m a t e r i a l s a r e b e l i e v e d t o b e b e n e f i c i a l in c r y o g e n i c m a -c h i n i n g , b e c a u s e t h e b r i t t le n e s s o f t h e m a t e r i a l p r o m o t e s c h i pf o r m a t i o n . [ 3,4 ] W i t h r e g a r d t o c u t t i n g t o o l m a t e r i a l s , h o w e v e r ,d e g r a d a t i o n o f s t re n g t h a n d t o u g h n e s s a t lo w t e m p e r a t u r e s , i fa n y , w o u l d d i s c o u n t a n y p o s s i b l e g a i n f r o m c r y o g e n i c m a c h i n -i n g . T h e r e f o r e , a l o g i c a l c o n c e r n i s w h e t h e r c u t t i n g t o o l m a t e r i -a l s c a n m a i n t a i n e n o u g h t o u g h n e s s , w h i c h w o u l d a l l o w t h e m t ob e a p p l i c a b l e i n c r y o g e n i c m a c h i n i n g . B e c a u s e c u t t i n g t o o l su s u a l l y a r e s u b j e c t e d t o h i g h - t e m p e r a t u r e c o n d i t i o n s i n tr a d i -t i o n a l m a c h i n i n g , l it t le i s k n o w n a b o u t t h e c r y o g e n i c p r o p e r t i e so f c u t t i n g t o o l m a t e r i a ls .

T h i s w o r k i s a n e f f o r t b o t h t o f i ll t h e g a p a n d t o e s t a b l is h ab a s i s f o r c r y o g e n i c m a c h i n i n g i n t e r m s o f s t u d y i n g c u t t i n g t o o lm a t e r i a l s a t c r y o g e n i c t e m p e r a t u r e . T h e r e f o r e , t h e o b j e c t i v e so f th i s s t u d y i n c r y o g e n i c m a c h i n i n g a r e t o ( l ) d e f i n e t h e p r o p -e r t i e s , a p p l i c a t i o n s , a n d l i m i t s o f s e v e r a l r e p r e s e n t a t i v e c u t t i n gt o o l m a t e r ia l s ; ( 2 ) s e l e c t t h e s u i t a b l e g r a d e o f c u t t in g t o o l m a t e -r i a ls f o r c r y o g e n i c m a c h i n i n g ; a n d ( 3 ) e s ta b l i s h t h e c o n n e c t i o nb e t w e e n t h e p r o p e r t i e s o f t o o l m a t e r i a l s a n d t h e i r p e r f o r m a n c e .G e n e r a l l y , a n i d e a l c u t t i n g t o o l m a t e r i a l s h o u l d h a v e t h e f o l -l o w i n g c h a r a c t e r i s t i c s :9 H i g h h a r d n e s s a n d a b r a s i v e w e a r r e s i st a n c e9 H i g h s t r en g t h

Z . Zh a o , R e se a rc h A ss i s t a n t, a nd S . Y . H ong, A ssoc ia te Profe s sor ,D e pa r tm e nt o f Me c ha nic a l a nd Ma te r i a l s Engine e r ing , Wr igh t S ta teU nive r s i ty , D a yton , O hio .

9 A c c e p t a b l e t o u g h n e s s t o r e s i st v a r i o u s k i n d s o f f r a c tu r e s9 L o w c o e f f i c ie n t o f t h e r m a l e x p a n s i o n9 H i g h c h e m i c a l a n d p h y s i c a l s t a b il i ty

I t is e x p e c t e d t h a t c r y o g e n i c t e m p e r a t u r e s a f f e c t n o t o n l y t h em e c h a n i c a l p r o p e r t i e s o f t h e t o o l m a t e r i a l s, b u t a l s o t h e i r p h y s i -c a l / c h e m i c a l p r o p e r t i e s . T h e c o e f f i c i e n t o f t h e r m a l e x p a n s i o n ,f o r e x a m p l e , h a s b e e n p r o v e n t o d e c r e a s e a s t h e t e m p e r a t u r e d e -c r e a s e s . [ 5,6 ] I t is a l s o b e l i e v e d t h a t t h e c h e m i c a l a n d p h y s i c a ls t a b il i ty o f t o o l m a t e r i a l s c a n b e i n c r e a s e d b y l o w e r i n g t h e t e m -p e r a t u r e . T h o s e t o o l m a t e r i a l p r o p e r t i e s a r e d e f i n i t e ly p o s i t i v ef o r c r y o g e n i c m a c h i n i n g . T h u s , t h e s c o p e o f t h i s w o r k i s re -s t r ic t e d t o t h e e v a l u a t i o n o f t h e m e c h a n i c a l p r o p e r t i e s b y t h em i c r o s t r u c t u r a l o b s e r v a t i o n a n d t h e t es t i n g o f i m p a c t s t r e n g t h ,t r a n s v e r s e r u p t u r e s t r e n g t h , a n d h a r d n e s s a t c r y o g e n i c t e m p e r a -t u r e s. T h e t e s t e d m a t e r i a l s i n c l u d e a h i g h - s p e e d s t ee l , M 4 6 , a n df i v e g r a d e s o f c a r b id e - c o b a lt a l l o y s - - K 3 1 0 9 , K 3 1 3 , K 4 2 0 ,K 6 8 , a n d S P 2 7 4 .

2 . E xp er im en ta l S e tu p an d P r o ced u r e2 .1 Im pac t Testing of Carbide Tool Materials

T h e s p e c i m e n s o f c a r b i d e - c o b a l t a l l o y s f o r u s e i n i m p a c tt e s t in g a r e 2 . 1 9 0 b y 0 . 3 9 4 b y 0 . 3 9 4 i n . s q u a r e b a r s . B e c a u s ec a r b i d e t o o l m a t e r i a l s g e n e r a l l y h a v e l o w i m p a c t s t r e n g t h , am o r e s e n s i t iv e i n s t r u m e n t r a t h e r t h a n t h e c o n v e n t i o n a l C h a r p y( e s te r i s r e q u i r ed . T h e i m p a c t t e s t in g o f c a r b i d e t o o l m a t e r i a l s i sp e r f o r m e d w i t h a n i n s t r u m e n t i m p a c t t e s t e r , D y n a t u p M o d e lG R C 7 3 0 - 1 , w h i c h r e c o r d s b o t h t h e a b s o r b e d e n e r g y a n d t h em a x i m u m a p p l ie d l o a d s i m u l t an e o u s ly . F i g u r e 1 i s an e x a m p l ec u r v e r e c o r d e d d u r i n g i m p a c t t e st i n g .2 .2 Transverse Rupture Strength

D u e t o e x t r e m e h a r d n e s s a n d b r i t tl e n e s s, c a r b i d e t o o l m a t e -r i a l s d o n o t r e s p o n d w e l l t o t e n s i l e t e s t i n g . I n s t e a d , a t e s t t h a t i sw i d e l y u s e d t o c h a r a c t e r i z e t h e f r a c t u r e s t r e n g t h o f t u n g s t e nc a r b i d e t o o l m a t e r i a ls i s th e t h r e e - p o i n t b e n d i n g t e s t o n t h e b a r

J o u r n a l o f M a t e r ia l s E n g i n e e r in g a n d P e r f o r m a n c e V o l u m e 1 5 ) O c t o b e r 1 9 9 2 - - 7 0 5


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Fig. 1 Loa d-tim e and energy-time curv es recorded by an instru-mented impact tester.s p e c i m e n . T h e t r a n s v e r s e r u p tu r e s t r e n g t h ( T R S ) c a n b e d e -f i n e d a s :

3 F LT R S = 2 b h 2whe re F i s the app l ied load a t the f rac tu re , L is the d i s tance be -t w e e n t h e c y l i n d e r a x i s , h i s t h e t h ic k n e s s o f t h e s p e c i m e n , a n db i s it s w i d th . A l l s p e c i m e n s w e r e g r o u n d 0 .2 0 b y 0 .2 0 b y 0 .7 5i n . s q u a r e b a r s t h a t w e r e p r o v i d e d b y K e n n a m e t a l R e s e a r c hL a b o r a t o r y . F i g u r e 2 s h o w s t h e s e t u p u s e d d u r i n g t h e T R S t e s ta t l o w t e m p e r a t u r e s . T o c h a n g e t h e t e m p e r a t u r e s o f t h e s p e c i -m e n s , t h e p a r t s a r e c o m p l e t e l y s u b m e r g e d u n d e r a c o o l e dc h e m i c a l l i q u i d w h o s e t e m p e r a t u r e i s a d j u s t e d b y m i x i n g i tw i t h l i q u i d n i t r o g e n o r d r y i c e . A l o a d w i t h a s l o w , c o n s t a n t r a t ei s a p p l i ed b y a u n i v e r s a l t e n s i l e m a c h i n e o n a l l o f t h e s p e c i -m e n s . T h e h e a t e x c h a n g e b e t w e e n t h e s p e c i m e n a n d i n d e n t a -t i o n b a l l m a y g i v e r i s e t o a t e m p e r a t u r e g r a d i e n t n e a r t h e i ri n t e r f a c e d u e t o t h e i r r e l a t i v e l y l o n g , t i g h t c o n t a c t d u r i n g l o a d -i n g . T o a v o i d t h e t e m p e r a t u r e g r a d i e n t, t h e i n d e n t a t i o n b a l l w a sk e p t b e l o w t h e l i q u id l e v e l f o r a s u f fi c i e n t t im e b e f o r e a p p l y i n gt h e l o a d . T h e a v e r a g e o f f i v e t e s t in g s a t t h e s a m e t e m p e r a t u r ew a s a d o p t e d a s th e t r a n s v e r s e r u p t u r e s t r e n g t h a t t h is t e m p e r a -t u r e. S p e c i m e n p r e p a r a t i o n , s e t u p , t e s t in g p r o c e d u r e , a n d d a t aa n a l y s i s w e r e i n a c c o r d a n c e w i t h A S T M s t a n d a rd , B 4 0 6 - 7 6 , o ft ransverse rup tu re s t r eng th t e s t ing o f the ca rb id e mate r ia l s l [7]2 . 3 H a r d n e ss M e asu r em en t s

H a r d n e s s e s a t r o o m t e m p e r a tu r e a n d a b o v e w e r e m e a s u r e dw i t h a c o m m e r c i a l l y a v a i l a b l e V i c k e r s t e st e r. A R o c k w e l l B r a l e

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Fig. 2 Schematic setup for low-temperature transverse rupturestrength measurement. Both the tested specimen and the three-point bending part were submerged in the cooled chem ical liq-uid, whic h was in a thermally insulated bath container.

i n d e n t e r f o r m e d a p e r m a n e n t i n d e n t a t i o n i m p r e s s i o n u n d e r a6 0 - k g l o a d ; t h i s w a s u s e d a s t h e m e a s u r e o f t h e h a r d n e s s a tc r y o g e n i c t e m p e r a t u r e s . S i m i l a r t o V i c k e r s h a rd n e s s , h a r d n e s s( /a i s de f ined by :

1 .103PH - - -d Ew h e r e P i s t h e a p p l i e d l o a d i n k i l o g r a m s , a n d d i s t h e d i a m e t e ro f th e i n d e n t a t i o n i m p r e s s i o n m e a s u r e d b y a n o p t i c a l m i c r o -s c o p e . E x a m i n a t i o n o f c a r b i d e t o o l m a t e r i a l s a t r o o m t e m p e r a -t u r e i n d i c a t e s t h a t t h i s m e t h o d y i e l d s s i m i l a r r e s u l t s a s t h eVickers ha rdness t e s t .2 .4 " I m p a ct T e s ti n g o f H i g h - S p e e d S t e e l

I m p a c t t es t i n g o f C - n o t c h e d s p e c i m e n s ( f o r d e ta i l e d d i m e n -s i o n s s e e F i g . 3 ) w a s p e r f o r m e d o n a C h a r p y i m p a c t t es t er . T h es a m p l e s w e r e m a c h i n e d f r o m s q u a r e t o o l b it s m a n u f a c t u r e d b yC l e v e l a n d T w i s t D r i l l C o m p a n y . D u r i n g i m p a c t t e s t in g , l i q u i dm e d i a w e r e a l s o u s e d f o r c o o l i n g o r h e a t i n g t h e s a m p l e s .

3. Ge neral Features and C ryogen ic Propert ies3 .1 C e m e n t e d C a r b i d e s

C e m e n t e d c a r b i d e s a r e a g r o u p o f h a r d , w e a r - r e s is t a n t , r e -f r a c t o r y m a t e r i a l s i n w h i c h t h e h a r d c a r b i d e p a r t i c l e s a r eb o n d e d o r c e m e n t e d t o g e t h e r b y a d u c t i l e m e t a l b i n d e r ( u s u a l l yc o b a l t o r n i c k e l ). [8 ] T h u s , t h e m i c r o s t r u c t u r e o f c e m e n t e d c a r -b i d e s u s u a l l y c o n s i s t s o f t w o p h a s e s : a n g u l a r W C g r a i n s a n d ac o b a l t o r n i c k e l b i n d e r. T h e p e r f o r m a n c e o f t h e c e m e n t e d c a r -b i d e t o o l l i e s b e t w e e n h i g h - s p e e d s t ee l a n d c e r m e t . C o m p a r e dw i t h h i g h - s p e e d s t e e l , c e m e n t e d c a r b i d e s a r e n o t o n l y h a r d e r

7 0 6 - - V o l u m e 1 (5 ) O c t o b e r 1 9 9 2 J o u r n a l o f M a t e r ia l s E n g i n e e r in g a n d P e r f o r m a n c e


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and mor e wear resistant, but they also exhibit lower toughnes sand fracture strength. Although high -speed steel allows cuttingspeeds less than 200 ft/min, carbide tool materials allow cuttingspeeds as high as 1000 ft/min.[ 8]

3.1.1 Microstructures and General FeaturesCemented carbides are available in many different grades,

which differ in hardness, wea r resistance, toughness, etc. In thisinvestigation, five commerc ial grades of carbide-co balt toolmaterials were selected as the test materials. Their chemicalcompo sitions are listed in Table 1. Figures 4 to 8 are the typicalmicrost ruc tures of K3109, K313, K 420, K68, and SP274, re -spectively. As indicated by the microstructures, the typical car-bide grain sizes range from submicron to several microns indiameter, depending on the individual grade. Even within thesame grade, the gra in sizes sti ll have a certain distribution. Thisis partially due to the fabrication process.

Substant ial amounts of W C were d issolved in coba l t dur ingsintering and precipitated during cooling. They appear as theWC grains and as the finely dispersed WC particles in thebinder, thus creating a variance in carbide grain sizes. In the al-loyed carbide grades, K420 and SP274, the introduction of TaCand TiC produced a considerable amount o f round carbidegrains from their alloying effect on the WC grains. This gaverise to the significantly different microstructures of the unal-loyed grades, K 3109, K313, and K68.

The m icrostructural parameters that usually affect the prop-erties of carbide tool materials are binder volume, binder m eanpath, carbide chem istry, carbide grain size, grain size distribu-tion, and carbide phas e contiguity. The variations o f these in thedifferent grades o f carbide tool materials ac count for the differ-

ent combinations of their properties. Following are brief de-scriptions of the characteristics of each carbide too l materialtested.

K3109 is characte r ized by a la rge volume of b inder phaseand the coarse WC grain size. It is also identified by high im-pact strength, high transverse rupture strength, and relativelylow hardness. As expected, K 3109 is the toughest grade am ongall the tested carbide tool materials.

K313 is an una l loyed grade tha t has a low percentage of co-balt binder phase and has the finest W C grains in its microstruc-ture. Therefore, i t is characterized by high hardness, high edgewear resistance, relatively high transverse rupture strength, andmoderate impact strength.

K420 is an a l loyed grade of a WC/TaC/TiC-Co tha t has amodera te amount of coba l t b inder phase and coarse carbidegrains. Althou gh the introduction of other carbides such as TaCand TiC contributes to high hardness and high thermal defor-mation resistance, they also cause a decrease in hardness. A s aconseque nce, the general features of K420 inclu de moderatehardness, high thermal shock resistance, relatively high impactstrength, and relatively high transverse rupture strength.

K 6 8 i s a low-cobalt unalloyed grade with intermediate car-bide grain sizes, which acc ounts for i ts high hardness, m oderateimpact strength, and moderate transverse rupture strength. Thisgrade o f carbide also exhibits high edge w ear resistance in ma-

Fig. 3 Dimensions o f the M46 high-speed steel specimen usedfor im pact testing. Fig. 4 Microstructure of K3109, which consists of the coarse-WC grains and the large volume fraction o f the binder phase.

T a b l e I N o m i n a l C o m p o s i t i o n s o f C a r b i d e T o o l M a t e r i a l sComposition,wt%Cobalt Tantalum Titanium Other Carbide size

K3109 ...................................................................... 12.2K313 ........................................................................ 6.0K420 ........................................................................ 8.5K68 .......................................................................... 5.7SP274 ...................................................................... 5.85Note: Provided by Kennametal, Inc.

0.3 0 0 Large0 0 0.4% Cr Fine10.2 5.9 0 Large1.9 0 0 Medium5.2 2.0 0 Medium

Journal of Materials Engineering and Performance Volume 1 5) October 1992 --707


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chin ing s ta in less s tee ls , cas t i rons , nonfer rous meta ls , non-me ta l s , a n d mo s t h ig h - t e mp e r a tu r e a l lo y s .

SP274 is an a l loyed grade w ith low b inder conten t . I t is nor -mall y used as a subs tra te mate r ia l for coa ted ca rb ide too l mate -r ia ls . The mate r ia l is charac te r ized by h igh hardness andmode ra te t r ansverse rupture s t r ength .

3.1 .2 I mpact StrengthThere a re two approaches ( techniques) used in def in ingtoughness of ca rb ide too l mate r ia ls , namely , f r ac ture toughness

and f rac ture energy . Frac ture toughness has been proven to bean e f fec t ive measure of ca rb ide mate r ia l toughness , in whichthe onse t of uns tab le c rack growth domina tes the f rac turee v e n t . No d i r e c t me a s u r e me n t o f f r a c tu re to u g h n e s s wa s m a d e

in th is work . As wil l be d iscu ssed la te r , indenta t ion tes t ing per -f o r me d a t b o th r o o m te mp e r a tu r e a n d l iq u id n i t r o g e n t e mp e r a -ture presented some evidence about the var ia t ion in c rackres is tance with tempera ture .

An a l te rna te technique for measur ing the toughness of ca r -b id e ma te r i a l s i s e v a lu a t in g th e e n e r g y a b s o r b e d d u r in g th ef rac tur ing . This is ac tua l ly the to ta l energy required to in i t ia teand propaga te the f rac ture through the spec ime n. The load/ t im ecurve and the abso rbed energy/ t im e curve ( see Fig . 1 ), r ecordedby an ins trumented impac t tes te r , ind ica te tha t the f rac tures ofcarb id e-coba l t a l loys a re charac te r is t ic of br i t t le f r ac tures . F ig-ures 9 to 12 present the p lo ts of the absorb ed energy and m axi-mum load ver sus tes t ing tempera tures for the ca rb ide too lmate r ia l s tes ted . As expec ted , each ca rb ide too l mate r ia l exhib-i ts sca t te red impac t s t r ength va lue s to d if fe ren t degrees . This is

Fig. 5 (a) Optical micrograph of the microstructure of K313. (b) SEM micrograph of K313 at higher magnificatio n reveals fine carbidegrains.

Fig. 6 Microstructure of K420. Fig. 7 Microstructure of K68.

708- -Vo lum e 1(5) October 1992 Journa l of Mate r ia ls Engineer ing and Per formance


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primarily due to the variations in internal stress concentrators,such as pores and inclusions in the samples. Among all thetested grades, the toughest grade, K3109, with evenly distrib-uted data, exhibits a remarkable increase in impact strength astemperature decreases. Fo r the grades K313 and K 420, i t is dif-ficult to derive a quantitative temperature depe ndence of theirimpact strengths due to the inherent nonductile nature of car-bide tool materials. There is no evidence that indicates thatthese carbide tool materials becom e more britt le and weaker atcryogenic temperatures. K68, with the lowest binder contentamo ng the materials tested, sho ws a decreasing tende ncy in im-pact strength as the temperature decreases.

3.1.3 Tr ansverse Ru ptur e StrengthThe transverse rupture strengths of carbide tool materials

depend on temperature, as shown in Fig. 13 to 17. K313, K68,

Fig. 8 Microstructure o f SP274.

and SP274, which have relatively low transverse rupturestrength at room tem perature, tend to experience an increase intransverse rupture strength as the temperature decreases. Onthe o ther hand, K3109 and K420 possess h igher room-tempera-ture transverse rupture strength and exhibit the opposite ten-dencies. Their strength levels decrease insignificantly at l iquidnitrogen temperature, and they still maintain higher levels thanthose of K313, K68, and SP274.

3.1.4 I ndentat ion Test ing, H ardn ess, an d Crack Resis tanceBy com bining the h igh- tempera ture da ta provided by Ken-

nametal, Inc. and the test results at cryo genic temperature, Ta-ble 2 summarizes the hardness of carbide tool materials atvarious temperatures. The low-temperature hardnesses wereobtained by using the Rockwell Brale indenter. The effect oftemperature on hardness is obvious. At l iquid nitrogen tem-perature, the indentations from the load produce smaller per-manent impress ions than at room temperature. T his displays anincrease in hardness as the temperature decreases.

For hard, brit t le materials, a sharp indentation m ay result incracking. This phenomenon has rece ived considerable a t ten-tion because of i ts potential in evaluating the toughn ess o f WC -Co materials. For the toughest grade, K3109, no cracks wereobserved from the indentat ion made under 60 kg a t both roomtemperature and liquid nitrogen temperature. This is consistentwith its relatively low hardness and high to ughness.

For K313, K420, K68, and SP274, c racks of var ious lengthswere induced by indentations. As an example, Fig. 18 showsthe permanent impressions of K68 a t room tempera ture and a tliquid nitrogen temperature. The parameter, P/l, where P is theindentation load, and I is the average length o f the cracks, w asused to evaluate the cra ck resistance of the britt le materials. [9]Comparison of c rack lengths a t c ryogenic and room tempera-tures indicates crack resistance to cryogenic temperatures.Cracks at l iquid nitrogen temperature are of comparable o reven shorter lengths than those at room temperature for all thecarbide-co balt alloys. This may be indicative of the comparab le

Fig. 9 (a) Impact strength of K3109 versus ternperature. (b) Maximum load on K3109 during impact testing versus temperature.

Journal of Materials Engineering and Performance Volume 1 5) October 1992 --70 9


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1 0A~ 8i-

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- 3 0 0 - 2 0 0 - 1 0 0 0 1 0 0T e s t i n g t e m p e r a t u r e ( F )

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Fig . 10 (a ) Impac t s t reng th o f K313 versus tempera tu re . (b ) Maximum load on K313 dur ing impac t te s t ing ve rsus tempera tu re .

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T e s t i n g T e m p e r a t u r e ( F )

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Fig . 11 (a ) Impac t s t reng th o f K420 versus tempera tu re . (b ) Maximum load on K420 dur ing impac t te s t ing ve rsus tempera tu re .

o r h i g h e r c r a c k r e s i s t a n c e o f t h e t e s t e d c a r b i d e t o o l m a t e r i a l s a tc r y o g e n i c t e m p e r a t ur e .

3 . 1 . 5 D i s c u s s i o nT h e b e h a v i o r s o f c a r b i d e t o o l m a t e r i a l s at c r y o g e n i c t e m -

p e r a t u r e s i n d i c a t e t h e i r a p p l i c a b i l i t y in c r y o g e n i c m a c h i n i n g .T h e c h a r a c t e r i s t i c s o f c a r b i d e - c o b a l t a l l o y s a n d t h e i r c r y o g e n i cp r o p e r t i e s i n d i c a t e t h e i r p o t e n t i a l n o t o n l y i n c r y o g e n i c m a -c h i n i n g , b u t a l s o i n o t h e r a p p l i c a t i o n s in t h e c r y o g e n i c i n d u s t r yw h e r e a n e x t r e m e l y h i g h Y o u n g ' s m o d u l u s , h i g h c o m p r e s s i v es t r e n g t h , tr a n s v e r s e r u p t u r e s t r e n g t h , a n d e x c e p t i o n a l w e a r r e -s i s t a n c e a re r e q u i r e d . C a r b i d e - c o b a l t a l l o y s h a v e a l r e a d y b e e nu s e d s u c c e s s f u l l y a s s e a l m a t e r i a l s . [6 ]

I n c o n s i d e r i n g t h e t e m p e r a t u r e e f f e c t s o n m e c h a n i c a l p r o p -e r t i e s , o n e o f t h e m o s t i m p o r t a n t f a c t o r s i s t h e c r y s t a l l i n e s t r u c -

t u r e o f t h e m a t e r i a l . C a r b i d e - c o b a l t a l l o y s p o s s e s s h e t e r o g e n e -o u s s t r u c t u r e s t h a t h a v e c o m p o s i t e n a t u r e s . B o t h t h e h a r d , b r i t -t l e c a r b i d e s a n d t h e d u c t i l e b i n d e r p h a s e s i n t h e m i c r o s t r u c t u r ea c c o u n t f o r t h e u n i q u e c o m b i n a t i o n s o f t h e p r o p e r t i e s o f c a r -b i f i e - c o b a l t a l l o y s . A m o n g m e c h a n i c a l p r o p e r t i e s , h a r d n e s sm a y b e d u e t o t h e c o m p o s i t e n a t u r e o f t h e m i c r o s t r u c t u r e . An u m b e r o f c o r r e l a t i o n s h a v e b e e n p r o p o s e d t o e x p l a i n t h e e f-f e c t s o f t h e m i c r o s t r u c t u r e o n h a r d n e s s . T h e o n e t h a t s e e m s t oh a v e a f i r m p h y s i c a l b a s i s i s p r o p o s e d b y L e e a n d G u r l a n d , [1~w h i c h s t a te s t h at V i c k e rs h a r d n e s s o f W C - C o a l l o y s a re r e l a t e db y :

H v = H w c f w c + H Co (1 - f w c C ) [1 1w h e r e H w c a n d H c o a r e t h e h a r d n e ss e s o f W C a n d C o , r e s p ec -t i v e l y ; f w c r e p re s e n t s t h e v o l u m e f r a c ti o n o f t h e c a r b i d e g r a i n s;

7 1 0 - - - V o l u m e 1 5 ) O c t o b e r 1 9 92 J o u r n a l o f M a t e r i a l s E n g i n e e r i n g a n d P e r f o r m a n c e


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................................................................................................................................ . . . . . . . . . . . . . . . . . . . . . . . . .I I I- 3 0 0 - 2 0 0 0 0 0

T a s t i n g T e m p e r a t u r e ( F )0 0

F i g . 1 2 ( a ) I m p a c t s t r e n g t h o f K 6 8 v e r s u s t e m p e r a t u r e . ( b ) M a x i m u m l o a d o n K 6 8 d u r i n g i m p a c t te s t i n g v e r s u s t e m p e r a t u r e .

6 . 0 0 0 1 0 55 . 0 0 0 1 0 5

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....................................................................................................................................................

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F i g , 1 3 T r a n s v e r s e r u p t u r e s t r e n g t h o f K 3 1 0 9 v e r s u s t e m p e r a -tu r e .

II CI --

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T e s t i n g t e m p e r a t u r e ( F )

F i g . 1 4 T r a n s v e r s e r u p t u r e s t r e n g t h o f K 3 1 3 v e r s u s t e m p e r a -tu r e .

0 0

Ta b le 2 Vick ers Ha rd n ess o f Tested M a ter ia ls a t Va r io u s Tem p era tu resV i c k e r s h a r d n e s s a t t e s t t e m p e r a t u r e , ~

- 3 2 2 8 0 3 9 0 7 5 0 1 8 3 0High-sp eedsteel, M 46 .............................................. 1054K3 109 ....................................................................... 1489K3 13 ........................................................................ 212 3K 42 0 ........................................................................ 1848K6 8 .......................................................................... 209 2SP 274 ....................................................................... 203 4

914 . . . . . . . . .12134 1051 901 ...1831 1649 1497 4861546 1341 1147 3651703 1413 1454 3971 6 9 5 . . . . . . . . .

a n d C i s th e i r c o n t i g u i ty . T h e m i c r o h a r d n e s s o f e a c h i n d i v i d u a lc o n s t i t u e n t o f W C , T a C , T i C , a n d c o b a l t i n c r e a s e s a s te m p e r a -t u r e d e c r e a s e s . [ 11] T h u s , t h e i n c r e a s e i n h a r d n e s s o f t h e c a r b i d e -a l l o ys a t c r y o g e n i c t e m p e r a t u r e s c a n b e r e g a r d e d a s a c o m m o ne l e m e n t o f b o t h t h e c a r b i d e s a n d t h e c o b a l t b i n d e r p h a s e.

T h e c o m p o s i t e n a t u r e o f t h e m i c r o s t r u c tu r e a l s o a f f e c ts t h ef r a c t u r i n g o f c a r b i d e - c o b a l t a l l o y s . O b s e r v i n g t h e f r a c t u r em e c h a n i s m r e v e a l s t h a t t h e f r a c t u r i n g p r o c e s s i s d u a l i s ti c . I t i sa m a c r o s c o p i c , q u a s i b r it t l e p h e n o m e n o n , a n d e v i d e n c e o f e x -t e n s i v e p l a s t i c d e f o r m a t i o n i n t h e b i n d e r p h a s e i n d i c a t e s a m i -

J o u r n a l o f M a t e r i a l s E n g i n e e r i n g a n d P e r f o r m a n c e V o l u m e 1 ( 5 ) O c t o b e r 1 9 9 2 - - 7 1 1


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6 . 0 0 0 1 0 5

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2 . 0 0 0 1 0 51 . 0 0 0 1 0 5

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!

[I

0 - 3 0 0 - 2 0 0 - 1 0 0 0Testing temperature( F )

0 0

Fig. 15 Transverse rupture strength of K420 versus tempera-ture.

6 . 0 0 0 1 0 5

5 . 0 0 0 1 0 5

~ ' 4 . 0 0 0 1 0 5I,-,-

3 . 0 0 0 1 0 5

2 . 0 0 0 1 0 5

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b.................. ~ . . i

I I- 3 0 0 - 2 0 0 - 1 0 0 0 1 0 0

Te s t ing t e mpe ra t u re ( F )Fig, 16 Transverse rupture strength of K68 versus temperature.

c r o s c o p i c d u c t i l e p r o c e s s . [ ]2 ] T h e e n e r g y c o n s u m e d i n p l a s ti cd e f o r m a t i o n c o n t r i b u t e s a m a j o r i t y o f t h e to t a l a b s o r b e d e n e r g yin impac t t e s t ing .

D e s p i t e t h e c o m p o s i t e n a t u r e o f th e m i c r o s t r u c t u r e , i t h a sb e e n w e l l e s ta b l i s h e d t h a t t h e a m o u n t o f b i n d e r p h a s e g r e a t l ya f f e c t s th e m e c h a n i c a l p r o p e r t i e s a n d o t h e r p r o p e r t i es o f t heca rb ide -co ba l t a l loys.J13] Th e b inder ph ase m ay a l so p lay a p re -d o m i n a n t r o l e i n d e t e r m i n i n g c r y o g e n i c p ro p e r t i e s. U n d e r -s t a n d i n g t h e t e m p e r a t u r e v a r i a t i o n s i n f r a c t u r e - r e l a t e dp r o p e r t i e s , s u c h a s i m p a c t s t r e n g t h a n d t r a n s v e r s e r u p t u r es t r e n g th , a l l o w s o n e t o c o n s i d e r t h e t e m p e r a t u r e e f f e c t s o n t h eb i n d e r p h a s e c o b a l t . T h i s i s p a r ti c u l a r l y i m p o r t a n t f o r c a r b i d e -c o b a l t a l l o y s w i t h l a r g e a m o u n t s o f b i n d e r, i n w h i c h t h e c a r b i d eg r a i n s a r e h i g h l y c o n t i g u o u s . T h e b i n d e r c o b a l t p h a s e c o n s i s t so f (~-coba lt w i th the hcp s t ruc tu re and re ta ined ) , - coba l t w i th thef c c s t r u c t u r e . C l o s e - p a c k e d h e x a g o n a l m e t a l s u s u a l l y b e c o m eb r i tt l e a t l o w t e m p e r a t u r e s , w h e r e a s m e t a l s w i t h t h e f c c s t r u c -t u r e a r e g e n e r a l ly d u c t i l e a t r o o m t e m p e r a t u r e a n d b e l o w . H o w -e v e r , o r - c o b a l t , l i k e t i t a n i u m , m a y b e a n e x c e p t i o n . S o m ec o b a l t - b a s e a l l o y s a r e c o n s i d e r a b l y t o u g h a t c r y o g e n i c te m -p e r a tu r e s .I t 4 ,1 5 ] T h e h i g h t o u g h n e s s o f t h e b i n d e r p h a s e m a y e x -p l a i n w h y c a r b i d e - c o b a l t a l l o y s g e n e r a l l y r e t a i n t h e i r i m p a c t

6 . 0 0 0 1 0 5

5 . 0 0 0 1 0 5

4 . 0 0 0 10 5 ............................................................................................................~ i- 3 . 0 0 0 10 5 ...................~....i....................... ? 5 .......... . ~ ............. ~' ~ .............................. g .................. 5 ....

2 . 0 0 0 1 0 51 . 0 0 0 1 0 5

- 4 0 0 - 3 0 0 - 2 0 0 - 1 0 0 0 O 0Testing temperature( F )

Fig. 17 Transverse rupture strength of SP274 versus tempera-ture.s t r e n g t h a t c r y o g e n i c t e m p e r a t u r e s . T h i s a l s o i m p l i e s t h a t th ec a r b i d e - c o b a l t a l l o y s w i t h l o w e r b i n d e r c o n t e n t m a y l o s e t h e i ri m p a c t s t r e n g t h a t c r y o g e n i c t e m p e r a t u r e s d u e t o t h e s i g n i f i c a n td e c r e a s e i n t h e m e a n f r e e p a t h o f t h e b in d e r p h a s e . D e c r e a s i n gi m p a c t s t r e n g t h s a r e a c t u a l l y o b s e r v e d i n K 6 8 , w h i c h h a s t h el o w e s t c o b a l t c o n t e n t a m o n g t h e t e s te d c a r b i d e - c o b a l t a l l o y s .

S i m i l a rl y , t h e e f f e c ts o f t e m p e r a t u r e o n t h e b i n d e r p h a s e a r ea l s o e x p e c t e d t o i n f l u e n c e t h e s t r e n g t h s o f t h e c a r b i d e - c o b a l ta l l o y s. T h e s t r e n g t h o f c o b a l t in c r e a s e s a s t h e t e m p e r a t u r e d e -c r e a s e s ; t h e r e f o re , t h e s t r e n g t h o f t h e c a r b i d e - c o b a l t a l l o y sw o u l d b e e x p e c t e d t o s h o w t h e s a m e t e n d e n c i e s . T h e t e s t r e -s u l ts o f th e K 3 1 3 , K 6 8 , a n d S P 2 7 4 g r a d e s , w h i c h h a v e l o wb i n d e r c o n t e n t s , a r e c o n s i s te n t w i t h t h i s p r e d ic t i o n . K 3 1 3 a n dK 4 2 0 , w h i c h h a v e h i g h c o b a l t c o n t e n t s , h o w e v e r , e x h i b i t t h eo p p o s i t e e f f e c t . T o i n t e rp r e t t h i s d i s c r e p a n c y , a n o t h e r t e m p e r a -tu re e f fec t , the rmal s t r ess , needs to be t aken in to accoun t .

T h e s t r e n g th o f t h e b r i tt l e m a t e r ia l i s h i g h l y d e p e n d e n t o nthe va r ia t ion o f in te rna l s t r e ss in the mate r ia l . Due to the l a rged i f f e r e n c e b e t w e e n t h e c o e f f i c i e n t s o f t h e r m a l e x p a n s i o n o f t h ec o b a l t a n d t u n g s t e n c a r b i d e s , c o o l i n g f r o m t h e s i n t e r i n g t e m -pera tu re dur ing fabr ica t ion l eads to a subs tan t ia l ly d i f fe ren tt h e r m a l r e s i d u a l s t r e s s . X - r a y a n d n e u r o n d i f f r a c t i o n s t u d -ies [ t 6 , t 7 ] show tha t the b inder phase i s typ ica l ly t ens i l e , and thec a r b i d e s a r e c o m p r e s s e d . T h e r e s u l t s a l s o i n d i c a t e t h a t t h e c a r -b i d e - c o b a l t a l l o y s w i t h h i g h e r b i n d e r c o n t e n t s h a v e h i g h e r r e -s i d u a l s t re s s l e v e ls . A s t h e s a m p l e s a r e c o o l e d f r o m r o o mt e m p e r a t u r e t o c r y o g e n i c t em p e r a t u r e s , n e w t h e r m a l s t r e s s c a nb e i n t r o d u c e d b e s i d e s t h e r e s i d u a l s t r es s . A c c o r d i n g t o T u r n e r ' sfo rmu la t ion , [ 18] the rma l s t r ess can b e expr essed as :

~ w c = K ( c t - ~ w c ) A T [2 ]

w h e r e K i s th e b u l k m o d u l u s o f t h e c a rb i d e , ~ i s th e v o l u m e c o -e f f i c ie n t o f t h e c a r b i d e - c o b a l t a l l o y , a W E is t h e v o l u m e c o e f f i -c i e n t o f t h e c a r b i d e , a n d A T is t h e d i f f e r e n c e b e t w e e n t h e t e s t e da n d r o o m t e m p e r a t u r e s . I f O C o r e p r e s e n t s t h e s t r e s s i n t h eb i n d e r p h a s e , t h e n t h e m e c h a n i c a l e q u i l i b r i u m r e q u i r e s :

f w c ~ w c + f co ~ C o = 0 [ 3]

7 1 2 - - V o l u m e 1 5 ) O c t o b e r 1 9 92 J o u r n a l o f M a t e r ia l s E n g i n e e r i n g a n d P e r f o r m a n c e


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Fig. 18 Permanent impressions of indentation on K68: (a) at roo m temperature and (b) at liquid nitrogen temperature.

Table 3 C he mic a l C ompos i t ion o f M 46 High-Spe e d Ste elElement wt %Carbon ............................................................................. 1.25Tungsten .......................................................................... 2.00Molybdenum ................................................................... 8.25Chromium ....................................................................... 4.00Vanadium ........................................................................ 3.00Cobalt .............................................................................. 8.25

where fw c and fco a re volume frac t ions of the WC and thebinder phase, respectively. It has been shown that carbide-co-balt alloys with higher binder content have larger coefficientsof thermal expansion. It31 This implies that the temperature ef-fect in terms of thermal stress is significant in carbide-cobalt al-loys with higher binder contents.This effect, resulting from thelower temperature and the existing higher residual stress, maycounterbalan ce or exceed the increased strength o f cobalt . Thismay also be the main reason that, as the temperature decreases,K3109 and K420 exhibit decreasing transverse rupturestrength tendencies, whereas K313, K68, and SP274 show theopposite tendency.3. 2 M 46 High-Speed Steel

High-s peed tool steels are highly alloyed steels that are usedfor high cutting rates o f hard metals. In spite of the rapid devel-opmen t of advanced cutting tool materials l ike cemente d car-bides, cermet, sintered diamond, cubic boron nitride (CBN),etc., high-speed steels are sti l l widely used in the m achinin g in-.dustry. High-speed steel can be classified into two main groups :T and M types. In the present study, a widely used grade, M46~was selected as the testing material. Table 3 gives the chemi calcomposi t ion of AISI M46 high-speed stee l. [ l 9]

The microstructure o f M46 high-spe ed steel is shown in Fig.19. The undissolved carbide particles (white color) are dis-persed thro ughout the matrix of tempered m artensite (dark

Fig. 19 Microstructure o f high-speed steel, which consists oftempered martensite as the matrix and dispersed undissolved car-bides.gray) . The coexistence of these two phases accounts for thehigh hardness and high abrasive wear resistance of the mate-rial . Indentation testing indicated that the permanent impres-sion at l iquid nitrogen temperature was obviou sly smaller thanthat at room temperature, which is evident by the increase inhardness of the high-speed steel at low temperature. The low-temperature data are listed in Table 2. Becaus e high-s peed steelsuffers a rapid decrease in hardness at high temperature, wh ichis a severe disadvantage in machining, this tool material pro-vides be t te r performance when used in c ryogenic machining.

Figure 20 shows the impac t s t rength of a C-notched M46specimen at various temperatures. The imp act strength exhibitsa strong dependence on temperature because the matrix phaseis tempered martensite o f distorted bcc structure. Similar vari-

Journal of Materials Engineering and Performance Volume 1 5) October 1992- -713


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13~1 2 -~11=~1o

98

_E 7=

5

I I I i i i

l i I I a l l

00-300-200~100 0 100 200 300 400T e s t in g T e m p e r a t u r e ( F )

Fig . 20 Impac t s t reng th o f M46 h igh-speed s tee l ve rsus tem-pera tu re .

a t i o n s o f i m p a c t s t r e n g t h w i t h t e m p e r a t u r e a r e e x p e c t e d t o o c -c u r w i t h o t h e r k i n d s o f h i g h - s p e e d s t e e l s d u e t o t h e c o m p a r a b l es t r u c t u r e s o f t h e i r m a t r i x p h a s e s . T h i s t e n d e n c y i s l e s s f o r h i g h -s p e e d s t e e l . H o w e v e r , t h e t o u g h n e s s d e c r e a s e s g r a d u a l l y , a n de v e n a t - 3 2 2 ~ M 4 6 h i g h - s p e e d s t e e l i s s t i l l n o t a b l y t o u g h e rt h a n c a r b i d e a n d c e r a m i c t o o l m a t e r i a l s . T h i s i n d i c a t e s t h a t th e ym a y s t i l l b e a p p l i c a b l e i n c r y o g e n i c m a c h i n i n g .

4 . C o n c l u s i o n sC a r b i d e t o o l m a t e r i a l s g e n e r a l l y r e t a i n t h e i r t r a n s v e r s e r u p -

t u r e s t r e n g t h a n d i m p a c t s t r e n g t h , a n d t h e i r h a r d n e s s a l s o i n -c r e a s e s a s t h e t e s t i n g t e m p e r a t u r e d e c r e a s e s t o w a r d l i q u i dn i t r o g e n t e m p e r a t u r e . T h e r e f o r e , c a r b i d e t o o l m a t e r i a l s p o s s e s sg o o d c r y o g e n i c p r o p e r t i e s . T h e q u a n t i t y o f b i n d e r p h a s e d e t e r -m i n e s n o t o n l y t h e r o o m - t e m p e r a t u r e p r o p e r t i e s , b u t a l s o t h ec r y o g e n i c p r o p e r t i e s o f t h e c a r b i d e t o o l m a t e r i a l s . A s t h e t e m -p e r a t u r e d e c r e a s e s , t h e i m p a c t s t r e n g t h a n d t r a n s v e r s e r u p t u r es t r e n g t h e x h i b i t o p p o s i t e t e n d e n c i e s f o r c e r t a i n g r a d e s o f c a r -b i d e - c o b a l t a l lo y s . T h i s s u g g e s t s t h a t a p r o p e r a m o u n t o f b i n d e rp h a s e m a y o f f e r th e a d v a n t a g e o f b o t h r e a s o n a b l e t o u g h n e ssa n d h i g h t r a n s v e r s e r u p t u r e s t r e n g t h a t c r y o g e n i c t e m p e r a t u r e s .W i t h r e g a r d t o h i g h - s p e e d s t e e l , l o w t e m p e r a t u r e i n c r e a s e s i t sh a r d n e s s a n d d e c r e a s e s i t s i m p a c t s t r e n g t h .

A c k n o w l e d g m e n t sT h i s w o r k i s s u p p o r t e d b y T h e E d i s o n M a t e r i a ls T e c h n o l o g y

C e n t e r, G E A i r c r a f t E n g i n e s , G M D e l c o P r o d u c t s a n d D e l c oM o r a i n e N D H D i v i s i o n s , L u c a s L e d e x , C i n c i n n a t i M i l a cr o n ,K e n n a m e t a l , I n c . , a n d t h e B O C G r o u p s . T h e a u t h o r s w i s h t oe x p r e s s t h e i r g r a t i t u d e t o K e n n a m e t a l , I n c . , f o r p r o v i d i n g a l l o ft h e c a r b i d e s p e c i m e n s a n d t h e i n s t r u m e n t s f o r t h e i m p a c t a n dt r a n s v e r s e r u p t u r e s t r e n g t h t e s t i n g . T h e y a l s o a p p r e c i a t e M r .D a v i d S i d d l e a n d h is g r o u p a t K e n n a m e t a l r e s e a r c h l a b o r a t o ryf o r t h e i r s u p p o r t d u r i n g t h e t e s t i n g . D a t a i n T a b l e 1 a n d s o m e o ft h e d a t a i n T a b l e 2 a r e c o u r t e s y o f M r . D a v i d S i d d l e . T h a n k s a r ea l s o d u e t o M r . G a n g C h e n a n d M . M i c h a e l S k a l s k i , tw o r e -s e a r c h a s s i s t a n t s a t W r i g h t S t a t e U n i v e r s i t y , fo r t h e i r a s s i s t a n c ei n t h e e x p e r i m e n t s .R e f e r e n c e s

1. H . Necish i, K. Ao ki, and T. Sata, Ann. CIRP, Vo130, 1981, p 43.2. J . Takagi and M.C. Shaw, Ann, CIRP, Vol 30, 1982, p 53.3 . K. Uehara and S . Kum aga i , Ann. CIRP, Vol 17, 19 68, p 409.4 . K. Uehara and S . Kum aga i , Ann. C1RP,Vol 19, 1970, p 273.5 . "Des ign ing w i th Kennam eta l , " Kennameta l , Inc . , 1980 , p 16-17 .6. G.P. McCleary, Proc. 23rd ASLE Annual Meeting, M a y 6 - 9 ,1968, Cleveland , p 324.7, Annual Book o f ASTM Standards, B406-76 , AST M, 1976 .8. A.T. Santhanam , P. Tierney, and J.L. Hunt, in Metals Handbook,9th ed. , ASM In ternation al, 1991, p 950.9. M .T. Laug ier, Mater. Sci. Eng., Vol A10 5/106, 1988, p 363.

10, H .C. Lee and J. Gu rland, Mater. Sci. Eng., Vo133, 1978, p 125.11. M.S . Kov a l ' chenko , V.V. Dzhem el insk i i , V.N . Skura tovsk i i ,Yu.G. Tkachenko , D.Z. Yurchenko, and V .I . Alak seev, Porosh.Metall., Vo1104, 1971, p 87 (translation).12 . E . Alm ond , in Science of Hard Materials, R.K. Viswanadham,D.J. Row cliffe , and J. Gurland , Ed. , Plenum , 1983, p 517.13 . Principles of Tungsten Carbide Engineering, 2nd ed . , Soc ie ty o fCarbid e and Tool Engine ers, 1989, p 7-15.14 . Source Book on Materials Selection, Vol 1 , Amer ican Soc ie ty fo r

Me tals , 1977, p 27.15. D. Peekuer and M.W. Riley, Materials in Design Engineering,Spec ial Repo rt No. 185, 1986, p 111.16 . A.D. Krawi tz , Mater. Sci. Eng., Vo175, 1985, p 29.17 . A.D. K rawi tz , M.L . C rapenhof t , D.G. Re iche l , and R . Warren ,Mater. Sci. Eng., Vo1105/106, 1988, p 275.18. P.S. Turner, J. Res. Natl. Bur. Stand., Vol 37, 1946, p 239.19 . R.W. Bratt, Cutting Tool Materials, American Society for Metals,1980, p 136.

7 1 4 - - - V o l u m e 1 (5 ) O c t o b e r 1 9 92 J o u r n a l o f M a t e r i a l s E n g i n e e r i n g a n d P e r f o r m a n c e

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