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Metal Science and Heat Treatment l,b/. 41. Nos. 11 12, 1999

U D C 6 6 9 . 1 4 . 0 1 8 . 2 5 8 . 8 : 6 6 9 . 1 3 1 . 6 : 6 2 1 . 7 8 5 . 5 3

B O R O N I Z I N G A N D R E S I S T A N C E O F S T E E LA N D C A S T I R O N T O T H E R M A L E R O S I O NS. V . Zagulyaeva , A . K. Deni syuk, and L . S . Makashova

T r a n s l a t e d f r o m M e t a l l o v e d e n i e i T e r m i c h e s k a y a O b r a b o t k a M e t a l l o v , N o . 1 1, p p . 1 0 - 1 2, N o v e m b e r , 1 9 9 9 .

T h e e f f e c t o f b o r o n i z i n g o n t h e s tr u c t u r e o f s t e e ls 3 K h 2 V 8 F , 4 K h 5 M F S , a n d 4 0 K h a n d g r a y c a s t ir o n S C h I 5a n d t h e i r r e s i s t a n c e t o t h e rma l e ro s i o n i s i n v e s t i g a t e d . A me t h o d fo r te s t i n g t h e re s i s t a n c e o f t h e ma t e r i a l s t ot h e r m a l e r o s i o n u s i n g h i g h - f r e q u e n c y c u r r e n t ( H F C ) i s d e s c r i b e d . I t is s h o w n t h a t b o r o n i z i n g b y t h e s u g g e s t e dr e g i m e i n c r e a s es t h e r e s i s ta n c e o f a ll t h e s t u d i e d m a t e r i a l s t o t h e r m a l e r o s i o n .

I N T R O D U C T I O NP a r t s o f p r e s s m o l d s a n d p l u n g e r p a i r s f o r p r e s s u r e c a s t -

i n g o f a l u m i n u m a l l o y s a r e f a b r i c a t e d f r o m d i e s te e l s3 K h 2 V 8 F a n d 4 K h 5 M F S , s t ru c t u ra l s t e el s , a n d c as t ir o n . T h er e s i s t a n c e o f t h e p a r ts t o t h e r m a l e r o s i o n a n d w e a r i s i n -c r e a s e d b y u s i n g v a r i o u s k i n d s o f c h e m i c a l h e a t t r ea t m e n t[ 1 - 3 ] .M E T H O D S O F S T U D Y

I n t h e p r e s e n t w o r k w e s t u d i e d t h e e f f e c t o f b o r o n i z i n go n t h e s t r u c tu r e a n d r e s i s t a n c e t o th e r m a l e r o s i o n o f s t e e ls

T A B L E 1

3 K h 2 V 8 F , 4 K h 5 M F S a nd 4 0 K h a n d gr a y c as t i ro n S C h I 5 ,o f t e n u s e d f o r p l u n g e r - p a i r r o d s .

T h e s t e el s p e c i m e n s ( 6 0 m m l o n g an d 2 0 m m i n d i a m e -t er ) w e r e f a b r ic a t e d f r o m h o t - d e f o r m e d a n n e a l e d p r e f o n n s ,a n d t h e ir o n s p e c i m e n s w e r e f a b r i c at e d f r o m c a st p r e f o r m s o fr o d s o f p l u n g e r p a i r s .

T h e r e s i s t a n c e t o t h e r m a l e r o s i o n w a s d e t e r m i n e d b y t h ef o l l o w i n g m e t h o d . C y l i n d r i c a l s p e c i m e n s w i t h a p o l is h e ds u r f a c e (R a = 0 ,6 3 j a m ) , a f t e r b o r o n i z i n g , w e r e h e a t e d i n a nL Z - 1 3 H F C i n s t a l l at i o n to 9 2 0 - 9 5 0 ~ w i t h h o l d o f 1 5 s e c .T h e l e n g t h o f t h e p a r t o f t h e s p e c i m e n f r o m t h e e n d u n i -f o r m l y h e a t e d i n t h e in d u c t o r w a s 2 5 - 3 0 m m .

Gradesof steels Heat-treatment regimes withoutand cast iron boronizing

Hardness, HRCc Layer thickness, mmafter boronizing continuous individual N." cycles

borides boridessurface core3 K h 2 V 8 F

4 K h 5 M F S

4 0 K h

S C h I 5

Q u e n c h i n g f r o m 1 1 0 0 ~ i n o i l + t e m -p e r i n g a t 5 5 0 ~ fo r 1 .5 h 5 0 5 1

B o r o n i z i n g + q u e n c h i n g + t e m p e r i n gQ u e n c h i n g f r o m 1 0 2 0 ~ i n o i l +

t e m p e r i n g a t 5 5 0 ~ fo r 1 .5 h 4 9 - 5 0B o r o n i z i n g + q u e n c h i n g + t e m p e r i n gQ u e n c h i n g f r o m 8 5 0 ~ i n o i l + t e m -

p e r i n g a t 5 5 0 ~ fo r 1 .5 h 4 9 5 0B o r o n i z i n g + q u e n c h i n g + t e m p e r i n gN o h e a t t r e a t m e n tB o r o n i z i n g + q u e n c h i n g

- - 3 0( 1 5 5 8 - 1 7 0 0 H I / ') 4 5 - 4 5 . 5 0 . 0 5 0 .1 5 0

7 6 - 7 8- - 3 0

( 1319 HI/" ) 55 - 56 0 ,06 0 .2 4573- - 0 .0 6 0 .1 2 2 5

(7 4 2 7 8 6 HI , ' ) 2 2 2 3 - 4 06 0 6 1

8( 2 5 7 2 7 6 H V ) 1 7 0 H B - 0 . 12 l 0

2 4 2 7* N i s t h e n u m b e r o f c y c l e s t o t h e a p p e a r a n c e o f th e r m a l - e r o s i o n c r a c k s.

4 7 3 0026-0673/99/I 112-0473$22.00 ~ 2000 K luwer Academic/PlenumPublishers

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4 7 4 S .V. Za g u ly a ev a e t a L

Fig. 1. M icrostmcture o f the surface layer of steels 4K h5M FS (a)and 40Kh (h) after boron izing and cooling in the container. 250.

Fig. 2. Microstructure of the surface layer (a) and core (b) of graycast iron SCh 15 after boronizing. 250.

T he e l eva ted t empera t u r e comp ared t o t ha t o f t he pouredl iquid alum inum 1720 - 75 0~ was cho sen in order to createt es t cond i t ions c l ose t o t hose o f ope ra t ion o f p r es s mol ds andreduce t he numbe r o f hea t i ng cyc l es t o t b rmat i on o f t he r-ma l - e ros i on c r acks on t he su r f ace o f t he spec i mens . T hehea t ed spec i mens were coo l ed i n co l d wa t e r . Af t e r eve ry5 cyc l es s ca le r emova l was pe r fo rme d i n a 25% so l u t i on o fsul fur ic acid for 10 rain. Then the spec ime ns we re wash edwi th water , neut ral ized in a solut ion o f a lkal i, and w ashe d inwa t e r aga in . Next t he su r f ace o f t he spec i men was ca r e fu l l yexami ned under a mi c roscop e i n o rde r to de t ec t the rmal - e ro-s i on c racks . T he nu mbe r o f cyc l es t o t he appea rance o f thef i rs t crack was determined.

T he r e s i s tance t o t he rmal e ros i on w as eva l ua t ed on spec -imens subjected to heat t reatment by the fol lowing regimes:(1) a s tandard reg ime for the s tudied s teels and i ron and (2)boron i z i ng , quench i ng , and t emper i ng ( see T ab l e 1 ).

T he spec i mens were boron i zed i n a boron i z i ng powderof g r ade BKB -2 . T hey w ere degreased and p l aced i n a con-tainer wi th the boronizing agent , which was then put in achamb er fu rnace hea t ed to 1030~ Af t e r a 2 .5 -h ho l d thecontainer wi th the specimens was cooled in water . The tul lycoo l ed spec i mens , a f t e r boron i z i ng , were un l oaded f rom t hecontainer and temp ered at 550~ for 1.5 h.

T hen we s t ud i ed t he s t ruc t u r e , measured t he ha rdness o fthe surface and the core , and determined the res is tance tot heml a l e ros i on .R E S U L T S A N D T H E I R D I S C U S S IO N

A s t udy of t he mi c ros t ruc t u r e sho wed t ha t t he boron i zedl aye r i n s t ee l s 3Kh2V8F , 4Kh5M F S , and 40Kh cons i s t s o ftwo par ts (F ig. 1) . At the very surface we observe a whi telayer of bor ides that penet rate into the depth of the metal astongue s , and then there i s a layer of f ine globular b or ideswho se densi ty d ecreases f rom the surface to the core . In s teel40Kh t he so l i d boron i zed l aye r pene t r a t e s i n t o t he dep t h o ft he me t a l by coa r se r " ' tongues" t han i n s t ee ls 3 Kh2 B8F and4Kh 5M F S , and t he amount o f f i ne bor i des i s much l ower.T he s t ruc t u r e o f t he core o f t he spec i men s o f st ee ls 3 Kh2 VFand 4Kh5M F S i s r epresen t ed by f i ne ac i cu l a r manens i t e ;that of s teel 40K h co nsis t s o f t roost i te wi th fer r i te grains o fs i ze No . 4 (GO S T 5965 -70) .

The b or ide lay er in the s t ructure of gray cas t i ronS Ch l 5 has a nonun i fo rm dep t h (F i g . 2a ) . T here a r e no" t ongu es" a s obse rved i n t he s tee ls . T he s t ruc tu r e o f t he ma-t r ix i s represented by pear l ite . The graphi te inclus ions at ad i s t ance over t .5 m m f rom t he sur f ace ar e su r rounded by f e r -ri te (Fig. 2b ).

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B o r o n i z i n g a n d R e s i s t a n c e o f S t e e l a n d C a s t I r o n t o T h e r m a l E r o s i o n 4 7 5

I t c a n b e s e e n f r o m T a b l e 1 t h a t b o r o n i z i n g h a s a p o s i t i v ee f f e c t o n t h e r e s i s t a n c e t o t h e r m a l e r o s i o n a n d t h e h a r d n e s so f t he s t u d i e d m a t e r i a l s . S t e e l 3 K h 2 V 8 F h a s t h e h i g h e s t s ur -l h c e h a r d n e s s a f t e r b o r o n i z i n g , a n d g r a y c a s t i r o n h a s th el o w e s t h a r d n e s s ( s e e T a b l e 1) . T h e c o r e h a r d n e s s i n s t e e l s3 K h 2 V S F a n d 4 K h 5 M F S a f te r bo r o n i z i n g a t 1 0 3 0~q u e n c h i n g ( c o o l i n g i n t h e c o n t a i n e r w i t h t h e b o r o n i z i n ga g e n t a n d t h e s p e c i m e n s in w a t e r ) , a n d t e m p e r i n g ( 5 5 0 ~ i sh i g h ( 4 5 - 4 6 HRCe ) .C O N C L U S I O N

T h e r e s i s t a n c e o f a l l t h e s t u d i e d s t e e l s t o t h e r m a l e r o s i o na f t e r b o r o n i z i n g i n c r e a s e s , w h e r e a s t h a t o f t h e c a s t i r o n r e -

m a i n s v i r t u a l l y th e s a m e . I t s e e m s t h a t th e g r a p h i t e i n c l u -s i o n s i n t h e c a s t i r o n h a v e a m o r e n e g a t i v e e f f e c t o n t h e r e s i s -t a n c e t o t h e n n a l e r o s i o t h a t e x c e e d s t h e p o s i t i v e e f f e c t o f t h eb o r o n i z e d l a y er .

R E F E R E N C E S1. S. N. Pik alov et al . , (Jke o/B(,'cmizing Agent o[Grade BMB.#,"Local Bolwnizing olDies. Methodological Recommendations [inR u s s i an ] , V N I T E M R ( t 9 8 9 ) .2. S. N. Polevo i and V. D. Evdokim ov, Rein[i~rcement Of Me tals [inRuss ian] , M ash inos t roen ie , M oscow ( I 986).3. V. N. Zhuravlev, R. R. Faskhutdinov, and A. N. Chernyi, " ' In-

c reas ing the endurance o f s tee ls fo r p ress m olds , " Metalloved.Term. Ohrah. Met., No. 5. 18 23 (1989).