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MICROSTRUCTURE AND MECHANICAL

OF PRESSED TsM2A ALLOY

Y u . V . M a n e g i n

PROPERTIES

UDC 620.17:620.18:669.28

The TsM2A molybdenum alloy has been used in a number of branche s of industry in recen t yea rs [1].

The alloy ing ele ment s (ChMTU 1313-65) are : 0.07-0.3~0 Ti, 0.07-0.15 Zr; the i mpur itie s (no more than):

0.003 02, 0.005 N2, 0.001 H2, 0.004 C.

Round bar s were prepared from ingots of the TsM2A allo y by hot pressing. We investigated the

struc ture and properties of pressed bars produced by different deformation conditions.

The alloy was smelted in a vacuum arc furnace. The ingots w ere stripped before pressing in a

horizontal 1500-ton hydraulic pre ss. Be fore deformation the bars w ere heated in an electric resistance

furnace (molybdenum heating elements) in a pro tective atmosphere (hydrogen).

Cast bars with a diameter of 78 mm wer e pressed at a rate of 150-200 mm /sec into rods w ith di-

ameters of 45, 40, 35, 25, and 20 mm , which corre sponded to 68, 75, 81, 86, 90, and 94 str ain . The

heating tempera ture was varied from 1000 to 1600~ (intervals of 150~

Samples for examination of the structure in the form of discs w ere cut from the middle of the bars

in the longitudinal and tran svers e directions with res pec t to the pressing direction.

The macrostructure of the cast m etal was characterized by very coarse grain s, reaching a cross

section of 2 mm and more (Fig . 1). During pressing the grains becam e oriented in the pressing di rec -

tion, w ere greatly extended, and developed a fibrous structure.

As a consequence of the nonun iform deformation which is inherent in pressing, the grain size varied

through the cros s section of the rod s. The outer lay er of the metal was subjected to the greatest deforma-

tion. Thi s was the general rule for all the p ressing conditions and pressing temperatures tested. With

increasing degrees of deformation the difference in the grain size between the ou ter lay er and the core

decreased.

The nonuniformity of the deformation through the c ro ss section can be made substantially worse,

depending on the ang le of taper at the entry to the die. It is evident in Fig. 2 tha t with increasing angles of

taper the irregularity of the deformation through the cro ss section of the

rod increas es. The middle layers of the meta l had the sa me deformed

structure in all the varied treatments. The outer layers w ere subjected

to considerably grea ter deforma tion and had finer grains as the angle of

taper was increased. Th is can be explained by the fact that as the angle

increases the additional shearing is increased, which varies linearly with

the cros s section of the rod from zero in the center to the max imum value

at the outer edge.

The influence of the temperature and degr ee of deformation on the

refinemen t of the structure of the cast metal during p ressing is shown in

Fig. 3. Analys is of the structure, phot ogra phed at the point corr espo ndin g

to half the radius of the rods, show s that with 68 strain (~ = 3.2) and pr es-

sing temperatu res of I000-I15 0~ the cast structure still remain unworked .

An increase of the temperat ure to 1300-160 0~ induces more intensive

Fig. i. Microstr ucture of

the ingot of the TsM2 A al- refining of the structure. With 75 strain (p = 4) and press ing temp er-

atures of 1300-160 0~ the cast structure is completely broken down, the

loy in the longitudinal se c- grain s are greatl y elongated in the press ing direction, and the cr oss se c-

tion.

t ion of the grains is red uced to 0.05-0.15 mm.

TsNIIChERMET. Trans late d from Metallovedenie i Term iche skay a Obrabotka Metallov, No. 12,

pp. 44-48, December, 1966.

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F i g . 2. V a r i a t i o n o f t h e m i e r o s t r u c t u r e o f p r e s s e d r o d s w i th

t h e a n g l e o f t a p e r a t t h e e n t r y t o t h e d i e . P r e s s i n g t e m p e r -

a t u r e , 1 30 0~ 86 d e f o r m a t i o n . ( x l 0 0 ) . a ) C e n t e r a r e a ; b )

o u t e r a r e a .

F i g . 3. V a r i a t io n o f t he m i c r o s t r u c t u r e o f p r e s s e d r o d s w i th t he t e m p e r -

a t u r e a n d d e g r e e o f d e f o r m a t i o n . ( x 1 00 ).

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H ~ I

/ - /

/

1 / ~ 600 Cl /

l z T _ . . b / - _ ~ . ~ ~ . . ~ .

7~ 8o 9o

lo

S t r a i n

Fig. 4. Variation of the har d-

ness of pre sse d rods of the

TsM2A alloy with the strain.

5, ~, %; Oh, kg/mm 2

6 S2OOY

~ 1 , '0 i

1 3

~b

2 4 6 B O O I ~

e s t i n g t e m p e r a t u r e

F i g 5 M e c h a n i c a l p r o p e rt i e s

of the TsM2A alloy press ed at

different temperatures with 94%

strain .

6,~, %; o b, kg/mmz

70

50 '

20

0

7O 80 90 %

Strain

Fig. 6. Mechanical proper ties

of the TsM2A alloy pre ss ed at

1300~ with varying degr ees of

stra in. 1) Testing tempe rature,

20~ 2) 1200~

At lower tem pera ture s (1000-1150~ the large

grains st i l l remain, with intense development of shear

l ines.

With further incr eas e of the degree of defo r-

mation the cast st ructu re was completely broken up

at all tem pe rat ure s. With 90% str ain (~ = 10.2) the

cro ss section of the grains was 0.015-0.052 mm at

tem per atu res of 1300-1600~ and 0.08-0.09 mm at

1000-1150~

The intensive refining of the east s truct ure at

higher temperatur es i s the resul t of the consi der -

ably higher degree of shear during pressing.

Recry stall izati on of the TsM2A alloy begins to

develop during press ing at 1600~ Reery stall izatio n

cente rs o ccur on the g rain boundaries and shear l ines

when the defo rmat ion reach es 75%. With an inc reas e

of the degree of deformati on to 81% the rec rys ta ll i za -

tion centers occur uniformly throughout the cro ss

section of the rods , and intense grain growth begins

when the strain is higher than 86%. The re cr ys ta l-

l ization process is not completely f inished at the de-

grees of deformation investigated. With 94% stra in

approxim ately half the metal is rec ryst all ize d. The

cente rs of the rods are the most completely recry sta ll i zed because they rema in at a temp erat ure above the

rec ryst all i zati on tem per atu re (1360~ for a longer t ime. With heating to 1450~ recr ysta ll iz atio n nuclei

occur in the cente rs of the rods during press ing only when the stra in reac hes 90%; with 94% strain they

occu r throughout the cro ss section, but principally in the center .

At 1300~ or lower no rec ryst all i zat ion was observed at any of the de grees of deformati on inve s-

tigated.

The mechanical properti es of the metal after pres sing were determi ned in tensile strength tests in

the UVTI machine [2] at different temper atu res and also by measure ment s of the hardness of the discs.

The tensile str ength sampl es (diameter of 4 mm) were cut from the section of the metal at a point half

way from the cente r to the outer edge of the rods.

To prevent oxidation at high temp erat ures the samples were heated in an atmospher e of inert gas.

The rate of deform ation in the tests was 1-3 sec - t .

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F i g . 7 . D i a g r a m o f t h e s t r u c -

t u r a l c h a n g e s i n t h e T s M 2 A

a l l o y d u r i n g p r e s s i n g . I ) R e -

g i o n o f i n t e n s i v e w o r k h a r d -

e n i n g ; I I ) r e g i o n o f b a l a n c e b e -

t w e e n p r o c e s s o f s t r e n g t h e n i n g

a n d w e a k e n i n g ; I I I ) r e g i o n o f

p a r t i a l r e c r y s t a l l i z a t i o n .

T h e h a r d n e s s o f d e f o r m e d a n d a n n e a l e d s a m p l e s w a s m e a s u r e d

o n t h e R o c k w e l l a p p a r a t u s ( a t l e a s t 2 0 m e a s u r e m e n t s ) i n t w o m u t u a l l y

p e r p e n d i c u l a r d i r e c t i o n s a c r o s s t h e d i s c s ( F i g . 4 ) . T h e h a r d n e s s i n -

c r e a s e d 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 d a t a l l d e g r e e s o f d e f o r -

m a t i o n . T h e h a r d n e s s i n c r e a s e d a s t h e d e g r e e o f d e f o r m a t i o n i n c r e a s e d

o n l y a t t e m p e r a t u r e s o f I 0 0 0 - I 1 5 0 ~ A t t e m p e r a t u r e s o f 1 3 0 0 - 1 6 0 0 ~

t h e h a r d n e s s w a s m a x i m u m a t t h e l o w e s t d e g r e e o f d e f o r m a t i o n .

T h i s p a t t e r n i n t h e v a r i a t i o n o f t h e h a r d n e s s i s i n v o l v e d w i t h t h e

s i m u l t a n e o u s l y o c c u r r i n g p r o c e s s e s o f d e f o r m a t i o n a n d w e a k e n i n g o f

t h e m e t a l b e f o r e r e c r y s t a l l i z a t i o n . I t s h o u l d b e n o t e d t h a t t h e t e m p e r -

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

a t u r e b u t a l s o o n t h e h e a t r e s u l t i n g f r o m t h e w o r k o f d e f o r m a t i o n . T h e

c o n s i d e r a b l e h e a t g i v e n o f f i n t h e p r o c e s s o f d e f o r m a t i o n o f t h e T s M 2 A

a l l o y w a s c o n f i r m e d b y t h e c h a n g e i n t h e t e m p e r a t u r e o f t h e m e t a l

b e f o r e a n d a f t e r p r e s s i n g . F o r e x a m p l e , w i t h h e a t i n g o f t h e s a m p l e s

t o 1 2 0 0 ~ a n d 9 0 s t r a i n t h e t e m p e r a t u r e o f t h e r o d s o n e x i t f r o m t h e

d i e w a s 1 5 0 0 ~ i . e . , a b o v e r e c r y s t a l l i z a t i o n t e m p e r a t u r e .

H o w e v e r , b e c a u s e o f t h e s h o r t n e s s o f t h e p r e s s i n g t i m e ( 0 . 5 s e c )

a n d r a p i d c o o l i n g o f t h e r o d s , w e a k e n i n g d o e s n o t h a v e t i m e f o r c o m -

p l e t e d e v e l o p m e n t , w h i c h i s c o n f i r m e d b y t h e 1 5 - 2 0 r e d u c t i o n o f t h e

h a r d n e s s o f p r e s s e d s a m p l e s p r e v i o u s l y a n n e a l e d 1 h a t 1 2 0 0 ~

T h e v a r i a t i o n o f t h e s t r e n g t h a n d p l a s t i c c h a r a c t e r i s t i c s o f t h e

p r e s s e d T s M 2 A a l l o y w i t h t h e t e m p e r a t u r e i s s h o w n i n F i g . 5 . I n t h e

r a n g e o f p r e s s i n g t e m p e r a t u r e s i n v e s t i g a t e d t h e s t r e n g t h o f t h e m e t a l i s i n c r e a s e d 1 . 5 - 2 . 5 t i m e s a f t e r d e -

f o r m a t i o n . T h e l o w e s t d u c t i l i t y i s f o u n d i n t h e m e t a l p r e s s e d a t 1 4 5 0 - 1 6 0 0 ~ w h i c h i s e x p l a i n e d b y t h e

p a r t i a l r e c r y s t a l l i z a t i o n o c c u r r i n g u n d e r t h e s e c o n d i t i o n s o f d e f o r m a t i o n ( s e e F i g . 3 ) .

T h e s a m p l e s p r e s s e d a t I 1 5 0 - 1 3 0 0 ~ h a d a s a t i s f a c t o r i l y h i g h d u c t i l i t y ( 6 = 1 5 ) i n s p i t e o f t h e c o n -

s i d e r a b l y h i g h e r s t r e n g t h ( Z b = i 0 0 k g / m m 2 ) . W i t h a n i n c r e a s e o f t h e t e m p e r a t u r e b y 3 0 0 ~ t h e s t r e n g t h

o f t h e m e t a l i s r e d u c e d s h a r p l y ( t o 5 7 - 7 5 k g / m m 2 ) a n d t h e d u c t i l i t y i s i n c r e a s e d ( 5 = 1 9 - 3 2 ) .

W i t h f u r t h e r i n c r e a s e i n t h e t e m p e r a t u r e t h e s t r e n g t h c o n t i n u e s t o d e c r e a s e a n d t h e r e i s s o m e d e -

c r e a s e o f t h e s p e c i f i c e l o n g a t i o n . T h e r e d u c t i o n i n s e c t i o n i n c r e a s e s u p t o 6 0 0 ~ a n d t h e n v a r i e s l i t t l e

u p t o 1 2 0 0 ~

T h e e f f e c t o f t h e d e g r e e o f d e f o r m a t i o n o n t h e c h a n g e o f t h e p r o p e r t i e s o f t h e p r e s s e d T s M 2 A a l l o y

( F i g . 6 ) i s i d e n t i c a l t o t h e c h a n g e o f t h e h a r d n e s s f o r t h e d e f o r m a t i o n c o n d i t i o n s g i v e n ( s e e F i g . 4 ) . T h e

v a r i a t i o n o f t h e s t r e n g t h w i t h t h e d e g r e e o f d e f o r m a t i o n i s s i m i l a r a t 1 4 5 0 a n d 1 6 0 0 ~ I t i s c h a r a c t e r -

i s t i c t h a t w i t h i n c r e a s i n g d e g r e e s o f d e f o r m a t i o n o f c a s t s a m p l e s o f t h e T s M 2 A a l l o y t h e d u c t i l i t y o f t h e

m e t a l i n c r e a s e s .

T h e c h a r a c t e r o f t h e e f f e c t o f t h e p r e s s i n g c o n d i t i o n s o n t h e s t r u c t u r e a n d m 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 s M 2 A a l l o y a l l o w s o n e t o d r a w t h e c u r v e s a n ' a n d b b ' o n t h e g r a p h o f t h e h a r d n e s s ( F i g . 4 ) a n d t h e r e -

b y t o d i s t i n g u i s h t h r e e s p e c i f i c r e g i o n s . T h e s e c t i o n t o t h e l e f t o f a a ' i s a r e g i o n o f i n t e n s e c o l d h a r d e n -

i n g o f t h e m e t a l w i t h p a r t i a l r e l i e f o f t h e s t r e s s e s . T h e s e c t i o n t o t h e r i g h t o f b b ' i s a r e g i o n o f p a r t i a l

r e c r y s t a l l i z a t i o n o f t h e d e f o r m e d m e t a l . B e t w e e n a a ' a n d b b ' i s a n i n t e r m e d i a t e r e g i o n i n w h i c h t h e m a g -

n i t u d e o f c o l d h a r d e n i n g d o e s n o t v a r y w i t h t h e d e g r e e o f d e f o r m a t i o n b e c a u s e o f t h e b a l a n c e b e t w e e n t h e

p r o c e s s e s o f s t r e n g t h e n i n g a n d w e a k e n i n g . F r o m t h e p o i n t s o f t h e i n t e r s e c t i o n o f a a ' a n d b b ' w i t h t h e

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

( F i g 7 ) . F r o m t h i s d i a g r a m o n e c a n e a s i l y d e t e r m i n e t h e p r e s s i n g c o n d i t i o n s i n r e l a t i o n t o t h e p r o p e r t i e s

r e q u i r e d f o r p a r t s p r e s s e d f r o m t h e T s l V I 2 A a l l o y .

1

2 .

L I T E R A T U R E C I T E D

N . N . M o r g u n o v a , C o l l . : T s N I I C h M , S p e c i a l S t e e l s a n d A l l o y s [ i n R u s s i a n ] , M o s c o w , i V I e t a l l u r g i z -

d a t ( 1 9 6 3 ) , N o . 3 5 .

B . A . K l y p i n , Z a v o d s k a y a l a b o r a t o r i y a , N o . 5 ( 1 9 6 4 ) .

1 9