time-independent mechanical properties of a chromium-manganese austenitic steel weldment

8/9/2019 Time-Independent Mechanical Properties of a Chromium-manganese Austenitic Steel Weldment

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J O U R N A L O F M A T E R I A L S S C I E N C E 2 1 ( 1 98 6 ) 2 3 3 9 - 2 3 4 6

T i m e - i n d e p e n d e n t m e c h a n i c a l p ro p e r tie s o f a

c h r o m i u m - m a n g a n e s e a u s te n it ic s te el

w e l d m e n t

G . P I A T T I , G . M U S S O

M a t e r i a l s Sc ie n ce D i v i s i o n , C o m m iss io n o f th e Eu r o p e a n C o m m u n i t ie s , Jo in t R e se a rch C e n tr e,

I sp ra Es tab l i shment , 1 -21020 Isp ra (Varese) , I ta ly

R oom and e l ev a t ed ( 450 ~ C ) t em p er a t u r e t ens il e da t a and r oom t em per a t u r e no t c h i m pac t da ta

o n w e l d m e t al a n d a w e l d e d jo i n t o f 1 0 w t C r - 1 7 . 5 w t M n a u s t e n it ic s te e l, a c a n d i d a te

mater ia l f o r t hermonuc lear f us ion reac tor f i r s t wa l l and b lanket s t ruc tures , a re repor ted and

d iscussed in t e rms o f t he mic ros t ruc tura l f ea tures observed.

1 . I n t r o d u c t i o n

Chromium-manganes e steels (nickel-, molybdenum-

and niobium-free grades) are of interest for use in

thermonuclear fusion reactor first wall and blanket

structures because of low long-term activation which

is lower than that of type 316 stainless steel [1, 2].

This family of steels has been investigated in dif-

ferent laboratories in order to characterize and

optimize structural and mechanical behaviour in non-

irradiated and irradiated conditions [3-10]. However,

although high manganese steels show improved weld-

ing characteris tics [11, 12], only a few results related to

physical and mechanical properties of weldments are

reported in the literature ~13].

The present paper deals with work carried out on

the time-independent mechanical behaviour o f a weld

joint of 10Cr-17.5Mn (Ni-free grade) austenitic steel

plates realized with a shielded metal arc welding

process using a flux-covered consumable electrode of

composition similar to the base metal. Thus the

properties of the joint can match those of the metal

joined. The time-independent properties were deter-

mined by room and high (450 ~C) temperature tension

tests and room temperature Charpy V-notch impact

tests on small specimens taken from weld metal, heat

affected zones and base metal regions of the arc-

welded joint. Factors influencing the mechanical

weldment behaviour were studied by optical and

scanning electron microscopy.

Time-dependent (creep and creep fatigue) tests

were not considered because in the temperature range

which is of interest in the first wall service condit ions,

and which extends up to approximately 450~ [14],

time-independent tests are sufficient to describe the

AMRC 0033 alloy with respect to design and safety

analysis considerations for potential fusion reactor

applications. In this material, in fact, time-dependent

behaviour becomes significant from 500~ (the tem-

perature at which there is superposition with the time-

independent behaviour) and becomes dominan t above

550 ~c [151.

2 . M a t e r i a l s

The material selected for the present study was

the experimental AMCR 0033-Creusot-Loire steel,

(France) supplied as 30ram thick solution annealed

plate and was used by the authors in the as-received

conditions. Its chemical analysis is given in Table I. I t

should be observed that the material concerned in-

cluded a relatively high amount of carbon (0. l wt %)

and nitrogen (0.2wt%), the composition being

balanced to avoid the ~(h c p) and ~'(b c c) martensite

phases and to stabilize the 7(fc c) austenitic phase. In

fact, because the manganese is not as powerful a 7

stabilizer as nickel, the interstitial element additions

listed in Table I are necessary to lower the M~(e) and

Ms d)

points below the room temperature [16] Ms(e)

and Ms(~') being the upper temperature at which the

e(h c p) and the W(b c c) martensite, respectively, begin

to form spontaneously from austenite on cooling.

However, in the AMCR 0033, during deformation at

room temperature, 7 --* e transformations can occur

with a considerable increase of the strain hardening

rate [5].

3 . E x p e r i m e n t a l t e c h n i q u e s

The welding procedure applied in this study, as

previously mentioned, was a shielded metal-arc elec-

trode having a core composition (Table II) similar to

that of the base metal. The diameter of the core wire

was 4 mm and the flux-cover was o f the ruffle-basic

type. The choice of this electrode was made after a

series of selection trials with different candidate elec-

trodes by testing the sensitivity to hot cracking in the

T A B L E I C h e m i c a l c o m p o s it i o n (w t % ) o f al lo y s tu d i e d ( A M C R 0 0 3 3 - C R E U S O T L o ir e )

C r M n N i S i C N P S M o C u A 1 P b B F e

1 0 .0 9 1 7 .3 7 < 0 .1 0 0 .5 5 0 .0 9 5 0 .1 9 5 0 .0 2 0 0 .0 0 9 < 0 .0 6 5 < 0 .0 6 0 < 0 .0 0 5 1 p .p . m . 2 5 p .p . m , b a l a n c e

0 0 2 2 - 2 4 6 1 / 8 6 $ 0 3 . 0 0 . 1 2 9

1986 Chapman and Hall Ltd. 2339



t

30 ~

( o )

( b )

Figure I Details of the weld process: (a) shape an d d imensions (mm)

of the asymmetric double-V groove profile; (b) sequence of weld

passes.

weld deposit by the FISCO test (Italian standard

regulation UNI 8096). The assembly consisted of two

plates (dimensions 2000 mm • 250 mm x 30 mm)

joined along the longest side. The joint configuration,

an asymmetrical double-V groove, is shown in

Fig. l a. A multipass procedure was adopted because

of the thick section (30mm) and the sequence of

build-up operations is presented in Fig. 1b. An inter-

pass temperature lower than 200~ was maintained

and the plates were mechanically restrained during

welding. The welded joint was checked by non-

destructive testing techniques (fluorescent penetrant

liquid method and radiography) prior to tensile speci-

men machining. A satisfactory weld soundness was

found. No defects such as incomplete fusion, shrink-

age or inclusions were encountered. However, because

of the poor inspectability of the austenitic steels, it is

difficult to detect such defects as microporosities and

they could be present. No post-weld heat treatment

was performed. The details of welding and post-

welding procedure have been given elsewhere [17].

TA BL E II Chemical composition (wt%) of filler metal and

shielded metal-arc weld deposit

Cr Mn Ni Si C N P S Fe

Filler metal 10 17 0.1 0.30 balance

Weld deposit 13.6 3 17.69 0.03 - 0.37 0.05 balance

Several round tensile specimens (diameter 4mm

and gauge length 20mm) were machined from the

welded joint with the tensile axis parallel to the weld

axis. The sampling map is shown in Fig. 2. Some flat

specimens (section 25 x 12 mm) with the tensile axis

transverse to the weld axis were also machined.

Tensile tests were performed at a strain rate of

10 3sec-' at room temperature and at 450~ on the

longitudinal-to-weld specimens but only at room tem-

perature on the transverse specimens. Moreover, stan-

dard 10mm x 10mm cross-section Charpy V-notch

(CVN) samples were machined at different locations:

(a) all weld metal near core; (b) all weld metal near

surface; (c) transverse to weld metal; (d) all parent

metal in a direction parallel to the weld axis, and were

notched (10 mm x 8 mm cross-section) perpendicular

to the weld surface. Impact tests were performed at

room temperature.

Transverse sections cut from the welded joint and

transverse and longitudinal specimens taken from

selected deformed tensile specimens, were prepared by

mechanical polishing and electrochemical etching

for observation with optical and scanning electron

microscopes (Philips SEM 505). Great care must be

taken during the polishing stage because this steel is

susceptible to work hardening [5] and surface defor-

mation, and consequently to the development of

layers of disturbed metal. SEM analysis was also

employed to investigate the fracture surface of some

i

, ~ 3 0 0

- I I I V l

. . . .

/

, A F A G A l l A , A I ~ / ~ A N A O A P A ID /

I

i

F + , +

+

- - - I I ~ , II I I

B G B H B I E lL ~ N B O B P B O

/

Figure 2 Sections of welded joint of 10Cr 17.5Mn austenitic steel plates showing sampling location of longitudinal-to-weld specimens.

Shaded area represents weld metal. Dimensions in millimetres.

2 3 4 0



Figure 3 Optical micrograph of a se c t i o n o f we l de d j o i n t o f

10Cr 17.5M n austenitic steel plates.

b r o k e n t e n s i l e s p e c i m e n s . F i n a l l y , th e e f f e c ts o f m i c r o -

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

t e s ts m a d e o n t h e t r a n s v e rs e s e c t i o n s f i' o m t h e w e l d e d

j o i n t .

4 . R e s u l t s a n d d i s c u s s i o n

4.1. Welding characteristics

T h e w e l d i n g c h a r a c te r i s ti c s w e r e s a t i s f a c t o r y a n d w e r e

c o m p a r a b l e f r o m a g e n e r a l p o i n t o f v ie w to t h o s e o f

o t h e r a u s t e n i t i c s t a i n l e s s s t e e l s . I n f a c t , t h e w e l d s

s h o w e d g o o d w e t t i n g , s i d e w a l l f u s i o n a n d l i q u i d

p e n e t r a ti o n . T h i s m e a n s t h a t t h e w o r k i n g p o o l o f

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

p r o c e ss w a s a b l e t o s o l i d i f y w i t h i n t h e jo i n t b y e p i t ax -

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

f a c e s . T h e s e f e a t u r e s a r e s e e n i n F i g . 3 w h i c h s h o w s

a m i c r o g r a p h o f a s e c t i o n o f t h e w e l d e d j o i n t .

1 0 C r 1 7 . 5 M n a u s t e n i t ic st ee l c a n h e n c e b e c o n s i d e r e d

a s w e l d a b l e .

4 . 2 . M i c r o s t r u c t u r e s

T h e f u l l y , / - a u s te n i t i c s t r u c t u r e o f t h e b a s e m e t a l

( a s - r e c e i v e d ) a c c o r d i n g t o p r e v i o u s s t u d i e s o n t h i s

s t e e l [4 , 5] i s s h o w n i n F i g . 4 a . A t y p i c a l f c c a n n e a l e d

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

t w i n n i n g , i s e v i d e n t . A m e a n g r a i n si ze o f 7 0 + 1 0 # m

w a s m e a s u r e d [ 5]. T h e r e i s a l s o t h e p r e s e n c e o f n o n -

m e t a l l i c i n c l u s i o n s s u c h a s M n S a n d A 1 20 3 b u t t h e r e i s

n o e v id e n c e o f c a r b i d e p r e c i p i t a t i o n [ 4 ]. T h e w e l d

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

m i c r o s t r u c tu r a l o b s e r va t i o n s p e r f o r m e d b y R u e d l a n d

c o - w o r k e r s a n d p u b l i s h e d e l s ew h e r e [ 1 6] a n d a c c o r d -

i n g t o t h e S c h a e f f l e r d i a g r a m [ 1 8 ], w h i c h s h o w s t h e

p h a s e f i el d s i n t e r m s o f t h e n i c k e l a n d c h r o m i u m

e q u i v a l e n t s , s p e c i a ll y m o d i f i e d f o r C r - M n s t e el [1 9 ].

T h e w e l d m a t e r i a l p r e s e n t s a n a s - c a s t t y p e s t r u c t u r e

( F i g . 4 b ) w i t h a d e n d r i t e m o r p h o l o g y . M o r e o v e r , i t

s h o u l d b e m e n t i o n e d t h a t t h e s e g re g a ti o n p h e n o m e n a

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

Figure Microstructure of the welded jo int o f lOCr -17.5M n austenit ic stee l pla tes: (a) base meta l , (b) fusion a nd heat-affected zones .

2 3 4 1



/ ~ ( M P o )

6 0 0 -

5 0 0 -

4 0 0 -

3 0 0

i i L

( o )

_ d l L O 9 9 l

b ~ ~ cl ~ i [ b ~ 6 b 6 i + § ~ ~

R

9 A

- 6 0

- 5 0

- 4 0

- 3 0

(O/o)

R(MPo)

1 0 0 0 -

8 0 0 -

6 0 0 -

4 0 0 -

2 0 0

ii

( b )

9 9 9 9 $ ~ d l ~ g ~ l lh . ._

9 9 e " - ' = ' a m - " 9 9 # ~ )

1 9 - o " e ' o ~ ' ' - - - e 9 9 A

A O l o )

- 7 0

- 6 0

5O

4 0

-r-- - 30

Z

Figure 5 Plot o f tensile characteristics: ultimate tensile strength (R) and total elonga tion (A), determined at (a) room t emperature and (b)

at 450 ~ C, against sampling location. Fo r reason of clarity, samples AF, AG, etc. (see Fig. 2) are not indicated.

process are particularly significant in iron alloys with

a high percentage of manganese and are difficult to

avoid [20, 21]. Carbide precipitation in the fusion

zone, due to the high carbon-content (0.37 wt %), was

detected. The usual heat input limitations were not

sufficient to avoid this phenomenon which is also

present in the heat-affected zone. The latter is not fully

austenitic because of the presence of a certain amount

of strain-induced e martensite due to thermal and

mechanical cycling occurring in the region near the

weld during the welding process. This feature is in

agreement with observations of martensitic trans-

formation during room temperature deformation

of AMCR 0033 [5] as previously mentioned. More-

over, the results show an appreciable austenite grain

coarsening.

4.3. Mechanical properties

The results (Fig. 5) related to tensile tests performed

on longitudinal-to-weld specimens, taken in different

, G ~ l

A 2 68

B 2 68 2 7 1

C 2 7 4

D 2 7 4

E 300 301

F 302

G 2 68

H 2 6 2 2 7 2

I 280

L 2 80

M 3 0 2

N 3 4 8 3 1 9

O 3O8

P 2 62 2 68

Q 2 7 4

Figure 6 Hardness distribution (HV 30) in a section of the welded

joint of 10Cr 17.5Mn austeni tic steel plates.

positions according to the map o f Fig. 2, show tha t the

specimens from the heat-affected zone (L, AL and BN,

for instance) and from the fusion zone (M) differ

significantly in their behaviour from specimens from

unaffected zone regions of the weld (A, AF and BG,

for instance). The tensile s trength of the weld metal is

increased by 10% at room temperature and 30% at

450~ of the tensile strength of the base metal,

whereas the ductility of the weld metal is strongly

reduced to 60% of that of the parent metal at both the

temperatures investigated. The weld metal and the

metal near to the fusion zone were then found to be

stronger than base metal.

Clearly, probably a solid solution hardening effect

occurs because of the high interstitial carbon content

[22] (C = 0.37%, see Table II) in the weld metal, and

also near to the fusion zone due to diffusion processes

operating during welding. Moreover, there may be

also an appreciable contribution to the hardening due

to the probably higher dislocation density on the

fusion zone and especially in the core, as shown for

type 316 stainless steel [23]. It should be mentioned

that the 0.2 yield strength (not plotted in Fig. 5 for

reasons of clarity) of the weld and of the HA Z zone

were also above those of parent metal.

TA BL E III Charpy V-notch impact data

Sample locat ion Resilience*

(Jcm 2)

All weld metal near to core 73

All weld metal near to surface 108

Transverse to weld metal 161

All base metal with specimen axis parallel to

weld axis 254

9 Average values.

2342



Figure 7 Tensile specimen (B, see F ig, 2)

t a k e n f r o m t h e b a s e me t a l d e f o r me d a t r o o m t e mp e r a t u r e :

(a) lo ngitudin al section (optical

micrograph), and (b) fracture surface (SEM image).

T h i s h a r d e n i n g e f f e c t i s s h o w n i n F i g . 6 s h o w i n g

t h e V ic k e rs h a r d n e s s m e a s u r e m e n t ( H V 3 0) i n a tr a n s -

v e r s e s e c t i o n o f th e w e l d e d j o i n t . T h e r e i s a c o n s i d e r -

a b l y d i f f e r e n c e b e t w e e n V i c k e r s h a r d n e s s n u m b e r s

c o r r e s p o n d i n g t o t h e b a s e m e t a l ( a v e r a g e v a l u e 2 6 8 )

a n d t h o s e c o r r e s p o n d i n g t o t h e i n si d e o f t h e w e l d

( a v e ra g e v a lu e 3 1 9) w h e r e t h e a m o u n t o f c a r b o n i s

h i g h e r .

F i g . 5 a l so s h o w s t h a t t h e w e l d m e t a l i s l e ss d u c t i l e

t h a n t h e b a s e m e t a l a t b o t h t h e t e m p e r a t u r e s i n v e s t i -

g a te d . P r e s u m a b l y t h e s e g re g a ti o n p h e n o m e n a m e n -

t i o n e d , w h i c h o c c u r o n t h e f u s i o n w e l d z o n e , i n d u c e

i n h o m o g e n e i t i e s a n d m i g r a t i o n o f i m p u r i t i e s in t h e

g r a i n b o u n d a r i e s a n d i n s id e t h e g r a in s w i t h a n e g a t iv e

b u t n o t s e r i o u s e f fe c t o n t h e r u p t u r e e l o n g a t i o n s o f t h e

w e l d ; t h e m i n i m u m v a l u e s r e p o r t e d a r e s t i l l a t a r e l a -

t i v e ly h i g h l e v e l, gr e a t e r t h a n a d u c t i l i t y o f 3 0 % .

C o n c e r n i n g t h e t r a n s v e r s e - t o - j o i n t s p e c i m e n s

r e s u l t s , a t e n s i l e s t r e n g t h a v e r a g e v a l u e ( 7 3 5 M P a )

l o w e r t h a n t h a t ( 8 6 0 M P a f r o m F i g . 5 a ) o f b a s e m e t a l

a n d a l s o t h a n t h a t ( 9 4 0 M P a f r o m F i g . 5 a ) o f th e

w e l d e d m e t a l w a s o b t a i n e d . T h i s b e h a v i o u r c a n b e

e x p e c t e d w i t h c o m p o s i t e t y p e s p e c i m e n s . A c o m p l e x

g e o m e t r i c a l r e s t r a in t , b e c a u s e o f t h e d i f f e re n t d e f o r -

m a t i o n r e s is t a n c e s o f t h e v a r i o u s z o n e s o f t h e w e l d

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

m a t i o n . I t i s i n t e r e s t i n g t o n o t e t h a t t h e f r a c t u r e

p o s i t i o n w a s i n t h e w e l d m e t a l .

T h e r e s u l t s c o n c e r n i n g t h e C h a r p y V - n o t c h i m p a c t

t e st s (T a b l e I I I ) s h o w t h a t t h e t o u g h n e s s p r o p e r t i e s o f

t h e w e l d m e t a l s a r e d i f f e r e n t f r o m t h o s e o f b a s e m e t a l

a s w a s t h e c a s e f o r t h e t e n s i l e p r o p e r t i e s . M o r e p r e -

c i se l y t h e w e l d p r e s e n t s a n a v e r a ge e n e r g y a b s o r p t i o n

v a l u e (7 3 t o 1 0 8 J c m - 2 ) lo w e r t h a n t h a t o f t h e b a s e

m e t a l ( 2 5 4 J c m - 2 ) . H o w e v e r , a c c o r d i n g t o v a r i o u s

t o u g h n e s s d a t a e v a l u a ti o n s o f F e - C r - M n a l lo y s [2 0],

t h e C h a r p y V - n o t c h i m p a c t d a t a m e a s u r e d n e a r t o t h e

c o r e ( 7 3 J c m 2 ) i s t o b e c o n s i d e r e d s a ti s f a c t o r y a n d

t h e d a t a m e a s u r e m e n t n e a r t o t h e s u r f a c e (1 08 J c m - 2 )

e x c e l le n t . T h e a v e r a g e v a l u e r e l a t i n g t o t r a n s v e r s e - t o -

w e l d m e t a l s p e c i m e n s ( 1 6 1 J c m -2 ) c a n a l s o b e c l a s s i-

f ie d a s e xc e l le n t . T h u s t h e w e l d e d j o i n t h a s a l o w n o t c h

sens i t iv i ty .

4 . 4 . F r a c t u r e

T h e r e s u l t s a r e s u m m a r i z e d i n F i g s 7 t o 1 2, F i g s 7 a n d

8 r e f e r r in g t o t h e b a s e m e t a l b r o k e n s p e c i m e n s ( B , s e e

F i g . 2) , F i gs 9 a n d 1 0 t o t h e h e a t - a f f e c t e d z o n e b r o k e n

s p e c i m e n s ( B M , s e e F i g . 2 ) a n d F i g s 1 1 a n d 1 2 t o

f u s i o n z o n e b r o k e n s p e c i m e n s ( M , s e e F i g . 2 ) . I n t h e

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

m a r t e n s i t e ) o c c u r a t r o o m t e m p e r a t u r e ( F i g . 7 a ) a s

p r e v i o u s l y o b s e r v e d i n t h i s m a t e r i a l [ 5 ]. e - m a r t e n s i t e

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

a s ~ 5 0 % w h e r ea s a l o w c o m p o n e n t ( ~ 1 0 % ) o f

e ' - m a r t e n s i t e w a s a l s o f o u n d [ 1 6]. T h e f r a c t u r e p r o f i l e

Figure

8

Tens i l e specime n (B, see Fig. 2 ) taken from the base me ta l de formed a t 450 ~ C: (a) l ongi tu din a l sect io n (opt i c a l micrograph), a nd

(b)

f r a c t u r e s u r f a c e

(SEM image).

2 3 4 3



Figure 9 Tensile specimen BM , see Fig. 2) t a k e n f r o m t h e h e a t - a f f e c t e d z o n e d e f o r m e d at room temperature: (a) longitudinal ection (optical

micrograph), and (b) fracture surface (SEM image).

( F i g . 7 a ) s h o w s a p r e m a t u r e f a i l u r e w i t h o u t n e c k i n g

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

m i x e d ( b r i t t l e p l u s d u c t i l e ) a p p e a r a n c e ( F i g . 7 b ) . I n

f a c t , c l e a v a g e a n d m i c r o v o i d s o c c u r . H o w e v e r , i t

s h o u l d b e o b s e r v e d t h a t t h e s t r a i n - i n d u c e d ~ - - *

t r a n s f o r m a t i o n , e v e n i f r e s p o n s i b l e f o r t h e p a r t i a l l y

b r i t tl e a p p e a r a n c e o f t h e f r a c t u r e s u r f a c e o f t h e b a s e

m e t a l b r o k e n s p e c i m e n s , d o e s n o t e x c l u d e t h e o c c u r -

r e n c e o f t h e la r ge e l o n g a t i o n a t r u p t u r e v a l u e s ( 6 0 %

f r o m F i g . 5 ) a c c o r d i n g t o a m e c h a n i s m t y p i c a l o f th e

T R I P s t e e l s , a s w a s p r o p o s e d p r e v i o u s l y [ 5 , 2 0 ] . A t

4 5 0 ~ t h e d e f o r m a t i o n o c c u r s b y s li p p r o c e s s es a n d

t h e r e is n o e v i d en c e o f m a r t e n s i t e f o r m a t o n ( F i g. 8 a ) .

T h e f r a c t u r e i s c o m p l e t e l y d u c t i le a n d t h e r e i s a l a rg e

r a n g e o f d i m p l e s i ze s ( F i g. 8 b ).

I n t h e h e a t - a f f e c t e d z o n e b r o k e n s p e c i m e n s , m a r -

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

( F i g. 9 a) w h e r e t h e d e f o r m a t i o n i s m o r e i m p o r t a n t . I n

f a c t , th e h i g h e r l e ve l o f c a r b o n i n t h e h e a t - a f f e c t e d

z o n e , b e c a u s e o f t h e d i f f u s i o n p r o c e s s o p e r a t i n g

d u r i r r g . t h e w e l d i n g p r o c e d u r e , s t a b i l i z e s t h e ; ~ - p h a s e

a n d p r e v e n t s t h e s t r a i n - c o n t r o l l e d 7 ~ e t r a n s f o r -

m a t i o n . T h e f r a c t u r e ( F i g. 9 a ) p r e s e n t s a s h e a r r u p t u r e

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

( d i m p l e d ) t r a n s g r a n u l a r s u r f a c e ( F i g . 9 b ) . A t 4 5 0 ~

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

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

v i e w ( c u p a n d c o n e p r o f i l e , F i g . 1 0 a ) a n d f r o m a

m i c r o s c o p i c p o i n t o f v i e w ( s h e a r d i m p l e s , F i g . 1 0 b) .

T h i s c a n b e s e e n fr o m t h e v o i d n u c l e a t i o n , gr o w t h a n d

c o a l e s c e n c e m i c r o m e c h a n i s m c h a r a c t e r i s t i c o f t h e

d i m p l e f r a c t u r e . In t h e f u s i o n z o n e b r o k e n s p e c i m e n s

t h e f r a c t u r e p r o f i l e s h o w s n o n e c k i n g ( F i g . 1 a ) a n d

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

i z e d c l e a v a g e ( F i g . l l b ) . M i c r o v o i d s b e g i n a t t h e

i n t e r fa c e b e t w e e n t h e m a t r i x a n d t h e p a r t i cl e s ( i n c lu d -

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

a r y m i c r o c r a c k s . T h e s e v e r a l i n c l u s i o n s a n d p r e c i p i -

t a t e s a r e t r a p p e d b e t w e e n t h e d e n d r i t e b r a n c h e s . T h e

f r a c t u r e b e h a v i o u r i s t h e n c l e a rl y l es s d u c t il e t h a n i n

t h e b a s e m e t a l a n d h e a t a f f e c te d z o n e . A t 4 5 0 ~

( F i g . 1 2 a ) t h e b e h a v i o u r i s s i m i l a r t o t h a t a t r o o m

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

s e e n ( F i g. 1 2 b ). I n c o n c l u s i o n c o n c e r n i n g f r a c t u r e ,

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

d e p e n d i n g o n t h e s a m p l i n g l o c a t i o n o f th e t e n s il e

s p e c im e n s , e s p e c ia l ly a t r o o m t e m p e r a t u r e .

4 . 5 . D e s i g n i m p l i c a t i o n s

T h e r o o m a n d h i g h te m p e r a t u r e w e l d m e n t b e h a v i o u r

o f 1 0 C r - 1 7 . 5 M n a u s t e n i t i c s t e e l i s c h a r a c t e r i z e d b y

t h e d i f f e r e n t i n e l a st i c p r o p e r ti e s o f t h e b a s e m e t a l a n d

o f t h e w e l d m e t a l . I t fo l l o w s t h a t t h i s m u s t h a v e s o m e

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

Figure T e n s i l e s p e c i m e n ( B M , s e e F i g . 2 ) t a k e n f r o m t h e h e a t - a f f e c t e d z o n e d e f o r m e d a t 4 5 0 ~ C : (a ) l o n g i t u d i n a l s e c t i o n ( o p t i c a l

micrograph), and (b) fractu re surface (SEM im age).

2344



Figure 11 T e n s i l e s p e c i m e n ( M , s e e F i g. 2 ) t a k e n f r o m t h e f u s i o n z o n e a n d d e f o r m e d a t r o o m t e m p e r a t u r e : ( a ) l o n g i tu d i n a l s e c t io n ( o p t ic a l

m i c r o g r a p h ) , a n d ( b ) f ra c t u r e s u r f a c e ( S E M i m a ge ) .

o f th i s p o t e n t i a l m a t e r i a l c a n d i d a t e f o r f u s i o n r e a c t o r

c o m p o n e n t s . G e n e r a l l y a d e s i g n s t r e ss f a c t o r , f , i s

o b t a i n e d b y d i v i d i n g t h e s t r e n g th o f th e w e a k e s t z o n e

o f t h e w e l d e d j o i n t b y t h e s t r e n g t h o f th e p a r e n t m e t a l.

B e c a u s e o f th e t e n s i l e s t r e n g t h a n d 0 . 2 y i e l d s t r e n g t h

w e l d r e g io n v a l u e s h i g h e r t h a n t h o s e o f p a r e n t m e t a l ,

a d e s i gn s t r e ss f a c t o r 1 c a n b e a s s u m e d . H o w e v e r , t h e

d e s i g n st r es s f a c t o r m e t h o d d o e s n o t c o n s i d e r r e d u c e d

d u c t i l i t y v a l u e s in i n d i v i d u a l p o i n t s o f w e l d s , w h i c h

a r e p o s s i b l e i n t h is c a s e b e c a u s e o f t h e a c c e p t a b l e , b u t

n o t v e r y h ig h , m e a n v a l u e o f t h e w e l d e d z o n e d u c t i l i ty .

H e n c e , i t is p r e f e r a b l e t o c o n s i d e r a s t r a i n b a s e d e s i gn

c o n c e p t w i t h a r e d u c t i o n f a c t o r b a s e d o n s t r a i n v a l u e s.

T h e A S M E C C N 4 7 a s s u m e s th e d es i gn s t r ai n f o r t h e

w e l d e d jo i n t a s h a l f t h e a l l o w a b l e v a l u e f o r b a s e m e t a l .

5 . C o n c l u s i o n s

1 . T h e 1 0 C r - 1 7 . 5 M n a t t st e n i ti c s te e l c a n b e c o n -

s i d e r e d a s w e l d a b l e w i t h a s h i e l d e d m e t a l - a r c p r o c e s s

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

p o s i t i o n s i m i l a r t o t h e b a s e m e t a l .

2 . T h e r o o m a n d 4 5 0 ~ w e l d m e n t b e h a v i o u r o f

1 0 C r - 1 7 . 5 M n a u s t e n i t ic s t e el is in f l u e n c e d b y t h e d if -

f e r e n t in e l a s ti c p r o p e r t i e s o f t h e b a s e m e t a l a n d o f t h e

w e l d m e t a l.

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

z o n e a r e s t r o n g e r t h a n t h e b a s e m e t a l b u t a r e l e s s

d u c t i l e .

4 . A s t r o n g s o l i d s o l u t i o n h a r d e n i n g e f f e c t o c c u r s i n

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

c o n t e n t ( C = 0 . 3 7 w t % ) o f t h e c o n s u m a b l e e le c t r o d e .

5 . R e s u l t s c o n c e r n i n g t h e t r a n s v e r s e - t o - w e l d s p e c i-

m e n s s h o w t h a t t h e t e n s i l e s t r e n g t h a v e r a g e v a l u e

( 7 3 5 M P a ) is i n f e r io r t o t h a t o f b a s e m e t a l ( 8 6 0 M P a ) .

6 . T h e w e l d e d j o i n t s s h o w a l o w n o t c h s e n s i t iv i t y .

A c k n o w l e d g e m e n t s

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

I t a l i a n o d e l l a S a l d a t u r a o f G e n o a ( I t a l y ) w i t h t h e

s u p e r v i s i o n o f C . M a s e t t i . T h a n k s a r e a l s o d u e t o

D r P . S c h i l l e r , D r E . R u e d l a n d D r D . G . R i c k e r b y

f o r h e l p f u l d i sc u s s i o n s a n d c r i t i c al c o m m e n t s , a n d t o

E . H a i n e , G . P . O s s o l a a n d H . P . W e i r f o r e x p e r -

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

p a r t o f t h e T e c h n o l o g y o f t h e r m o n u c l e a r fu s i o n

p r o g r a m m e o f t h e J R C I s p r a E s t ab l i sh m e n t .

R e f e r e n c e s

1 . P . F E N I C I ,

D . B O E R M A N , V . C O E N , E . L A N G ,

C . P O N T I a n d W . S C H O L E ,

Nucl Eng De sign/Fusion 1

(1984) 167 .

R . W . C O N N , E . E . B L O O M , J . W . D A V I S , R . E .

G O L D , R . L I T T L E , K . R . S C H U L T Z , D . L . S M I T H

a n d F . W . W I F F E N ,

Nucl Technol /Fusion 5 (1984) 291 .

G . P I A T T I , S . M A T T E A Z Z I a n d G . P E T R O N E , MOrn

Etud Sci Rev Metall

7 9 ( 1 9 8 2 ) 7 9 4 .

Figure 12 T e n s i l e t e s t ( M , s e e F ig . 2 ) t a k e n f r o m t h e f u s i o n z o n e a n d d e f o r m e d a t 4 5 0 ~ C , ( a ) l o n g i t u d i n a l s e c t i o n ( o p t i c a l m i c r o g r a p h ) , a n d

( b ) f r a c t u r e s u r f a c e ( S E M i m a g e ) .

2345



4 . E . R U E D L a n d T . S A S A K 1 , J. Nucl. Mater. 122 ( 1984)

794.

5 . G . P I A T T I , S . M A T T E A Z Z I a n d G . P E T R O N E ,

Nucl,

Eng. Design~Fusion 2 (1985) 391.

6 . D . G . R I C K E R B Y , T . S A S A K I a n d E . R U E D L , i n

P r o c e e d i n gs o f th e 8 t h E u r o p e a n C o n g r e s s o n E l e c t ro n

M i c r o s c o p y , B u d a p e s t , A u g u s t ( 1 9 8 4 ) , e d i t e d b y A . C s a n a d y ,

P . R 6 h l i c h a n d D . S z a b o , p . 7 7 7 .

7 . M . S N Y K E R S a n d E . R U E D E ,

J. Nucl. Mater.

103, 104

(1981) 1075.

8 . D. J . M A Z E Y , J . A . H U D S O N a n d J . M . T I T C H -

M A R S H , J. Nucl. Mater. 107 (1982) 2 .

9~ H . R . B R A G E R , F . A . G A R N E R , D . S . G E L L E S a n d

M . L . H A M I L T O N , J. Nucl. Mater. 133 , 134 ( 1985) 907 .

I 0. R . L . K L U E H a n d M . L . G R O S S B E C K , J. Nucl. Mater.

122, 123 (1984) 294.

11 . J . H O C H M A N N ,

MatOr. Tech. December)

(1977) 69.

1 2. W . T . D E L O N G a n d H . F . R E I D , Welding J . 1 ( 1957 )

41 - S .

1 3. S . H O R V A T H ,

Zvaranie

18 (1969) 25.

1 4. I N T O R W o r k s h o p , I A E A , V i en n a , R e p o r t E U R F U B R U /

X I I / 1 - S G - E D V I 0 , C E C - B R U S S E L , J a n u a r y ( 1 9 8 4 ) .

1 5. G . B E R N A S C O N I , S . M A T T E A Z Z I , G, P E T R O N E a n d

R . M A T E R A , o r a l p re s e n t a t io n , 9 t h S M I R T , B r u s se l s

( 1985) pa pe r L2 / 8 .

1 6. E . R U E D L , D . G . R I C K E R B Y a n d T . S A S A K I , i n

P r o c e e d i n g s o f t h e 1 3 t h S O F T , V a r e s e , It a l y ( 1 9 8 4)

( P e r ga m on P r e s s , O xf o r d , 1984 ) p . 1029 .

1 7. G . M U S S O , G . P I A T T I A N D C . M A S E T T I , P o s t e r

p r e s e n t a t i o n t o J o u r n 6 e s M 6 t a l l u r g i q u e s d ' A u t o m n e , P a r i s

( O c t obe r , 1983 ) .

1 8. A . L . S C H A E F F L E R , M Met. Progr. 56 (1949) 680.

1 9. M . I . R A Z I K O V , G . N . K O C H E V A a n d L . G . T O L -

S T Y K H ,

Avt. Svarka

21 (1968) 1.

2 0 . J . C H A R L E S , T h e s i s , C a th o l i c U n i v e r s it y o f L o u v a i n ,

Louva i n - l a - N e uve , B e l g i um ( 1982) .

2 l . H . S C H U M A N N a n d K . G O O D K N E C H T , Prakt. Metal-

Iogr. 4 (1967) 173.

2 2. K . J . I R V I N E , T . G L A D M A N a n d F . B. P I C K E R I N G ,

J. Iron Steel Inst. 199 (1961) 153.

2 3. R . G. T H O M A S a n d S . R . K E O W N , i n P r o c e e d i n g s o f

t h e I n t e r n a t io n a l C o n f e r e n c e M e c h a n i c a l B e h a v io u r a n d

N u c l e a r A p p l i c a t i o n s o f S t a i n l e s s S t e e l a t E l e v a t e d T e m p e r a -

t u r e s , V a r e s e , It a l y ( 1981 ) ( The M e t a l S o c i e t y , Lo nd on , 1982)

Book 280, p . 30.

Received 15 July

and accepted 13 September 1985

2 3 4 6

time-independent mechanical properties of a chromium-manganese austenitic steel weldment

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