The Effect of P and S t Hot Crack Austenitic SS

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, ~ . : . ~ . , @ > - . . , a e - " " ~ ' ~ . ~ , ~ ; " , - " : ' " ' : ~ : , i ' , ' ' ~ , ' ~ - , '

• . ~ : . + •

"

" ' ~ . ' , ~ i ~ ' : . ' ~ ' - ' 8 " ~ ' " : ? , ~ ~ ;

F i g, 1 - - T h e W R C - 9 2 D i a g r a m w i t h t e s t m a t e r i a l s p l o t t e d a s p o i n t s .

c o n t a i n i n g u p t o 0 . 0 2 % P . A s a n e x t re m e

case , i n we l d m e t a l con t a i n i ng 0 . 1% P ,

f i lm - l i k e p h o s p h i d e s ( o r p h o s p h i d e - c o n -

t a i n i ng eu t ec t i cs ) were obse rved . D i rec t

o b s e r v a t i o n o f m e l t i n g b e h a v i o r o f t h e

su l f i des us i ng ho t -s t age m i c roscopy de -

t e r m i n e d t h e i r m e l t i n g t e m p e r a t u r e s

w e r e i n t h e r a n g e b e t w e e n 1 2 6 0 ° a n d

1 3 1 0 ° C ( 2 3 1 0 ° a n d 2 3 9 0 ° F ) , w h i c h is

h i ghe r t han t he b r i t t l e t em pera t u re range

f o r ho t c rack i ng .

A n o b s e r v a t io n o f th e m o r e d e t r im e n -

t a l e f f ec t o f P t han S on ho t c rac k i ng i n

austen i t i c s ta in less s tee ls was made by

Brooks (Re f . 7 ) . E l ect ron p rob i ng sh owe d

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

s p o n s i b l e f o r c r a c k i n g a r e h i g h l y e n -

r i ched i n M n and P , w i t h S t i ed up i n d is -

c r e t e , a n d s e e m i n g l y b e n i g n , M n S

part i c les.

Fe r ri te l eve l s i n we l ds have bee n un i -

(Re f s . 10 -12 ) t o

0 . 0 3 % ( R e f . 1 3 )

f o r a u s t e n i t i c

s t a i n l ess s t ee l s

t h a t s o l i d i fi e d i n

t h e p r i m a r y

a u s t e n i t e m o d e .

T h e y n o t i c e d , a s

d i d e a r l i e r r e -

searchers, that for

a l l oys t ha t so l i d i -

f i e d i n t h e p r i -

m a r y f e r r i t e

m ode , t he t o l e ra -

b l e P + S c o n t e n t

w a s h i g h . T o r e -

d u c e c r a c k i n g

t endency , a c r i t i -

c a l c o m b i n a t i o n

o f P + S c o n t e n t

a n d C req / N i eq

t . . B , ; , " , , - ' . ' + - ~ ; . - " " . , ,- . , ,~ " . "

I ' " . ' J ; , , ~ - . " , ~ , " ' . : , , , " ." :. +. . . . ' : " ' - . ' : . " . . .

K ' , . " ', ~ * ' ,, " '- . ' , + : , ~ ' - . ' " . . . . C ' . .,

~ , ' ~ ' . . - . - / " n , . . - ' % . ~ . ~ ,... " , . . ' i . "

' , , . - . ~ - ~ . , , . , . 4 . . , , % : ~ : ' ~ . , ' : ,, . . + ~ --

" ~ - " " ~ " P - - ' ~ ' - " % - ~ - * ' ~ a . h " ~ " " ' . '- " % " " a . " ,- ,L ,# i~ . - . I P . - " ~ J

, + ~ e . , a ~ . , a ~ • , .~ • ~ J . ~ ~ e .. . ~ l ~ l + e . ~ r - J l ;

~ . , , , . ' ~ " : ' ~ s > ~ - . ~ - ' > " . . ,

, . - ' , . , 2 $ . . I ~ / ' ~

, . ' . , ~ ' , +

+ + ~ . _ . . , ; ~ ; ] ; , ~ Z " r ~ ' ~ +' -~ < * Z , ~ * ' , [ . . , • ~ ' . +,, ;~;~'. , "

, , . ~ , ~ , ' . : ~ . . ' - , - ' • : , . > ~ . ~ _ . . ~ . , - : ....

I ~ . . h i < . . ~ , , ~ . . . , .. . ~ d ~ * - , . ~ .

F i g . 2 - - T h e fu s i o n z one m i c r o s t r u c t u r e f o r H e a t 1 3 5 6 . M i x e d a c i d et c h .

A - - 5 0 X ; B - - 4 0 0 X .

ve rsa l l y i den t i f i ed t o be i n t e rac t ive w i t h P

and S l eve ls . An exa m p l e i s a s t udy by

Brooks and Lam ber t (Re f. 8 ) on t he co m -

b i ned e f fec ts o f P+ S l eve l and f e r r i te c on -

t e n t o n t h e w e l d c r a c k i n g o f T y p e 3 0 9 S

sta in less s tee l . The ferr i te leve l that pre-

v e n t e d c r a c k i n g w a s fo u n d t o b e d e p e n -

den t on i m pu r i t y l eve l . L it t le o r no f e r r i te

w a s r e q u i r e d t o p r e v e n t c r a c k i n g fo r l o w

P+ S, wh i l e l a rge P+ S l eve ls co u l d be ac -

c o m m o d a t e d w i t h o u t c r a c k in g p r o v i d e d

f e r ri te c o n t e n t e x c e e d e d F N 1 3 - 1 4 .

O g a w a a n d T s u n e t o m i ( R e f . 9 ) r e -

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

c rack i ng suscep t i b i l i t y o f f u l l y aus t en i t i c

w e l d m e ta l w h e n P a n d S c o n te n t s e x -

ceeded 0 . 015 and 0 . 010% , respec t i ve l y .

Hea t s w i t h ex t ra - l ow P and S (bo t h l ess

t h a n 0 . 0 0 2 % ) e x h i b i t e d s u p e r b h o t

c r a c k i n g r e s i s t a n c e e v e n i n f u l l y

aus t en i t i c m i c ros t ruc t u re . Ku j anpaa , e t

al.,

p r o p o s e d a c o m b i n e d P + S l i m i t f o r

c rack res is t ance i n the range f rom 0 . 01 %

r a t i o w a s s u g -

gested: P+S < 0.01 % and Creq/Nie. > 1 .5 .

. H .

For segregatnon re la ted to s ta in less

s t ee l we l d c rack i ng , P con t en t was be -

l ieved t o be h i gh e r i n de l t a f e r r i te t han i n

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

som e ev i de nce f ound by B rooks (Re f . 14 )

u s in g A u g e r e l e c t ro n m i c r o s c o p y ( A E M ),

a n d w a s a ls o p r e d i c t e d f r o m p h a s e d ia -

grams (Ref . 15) . I t i s reas ona ble to be l ieve

t ha t l ess P shou l d be re j ec t ed du r i ng p r i -

m ary de l t a so l id i f i ca t ion , t he reby caus i ng

a lesser deg ree o f P segregat ion.

The ob j ec t i ves o f t h i s s t udy were t o

i den t i f y and quan t i f y the i nd i v i dua l ro les

o f P and S w i t h i n an ove ra l l P+ S l eve l on

t he suscep t i b i l i t y t o we l d ho t -c rack i ng o f

a w ide ly used austen i t i c s ta in less s tee l .

T e s t M a t e r i a l s

Cus t om hea t s o f Type 308 t o spec i f i -

c a t i o n s f o r c a s t g r a d e C F - 8 a u s t e n i t i c

s ta in l ess s t ee l we re d es i gned t o con t a i n a

c o n s t a n t c o m b i n e d l e v e l o f P +S o f

0 . 0 3 2 % , w i t h a l l o t h e r e le m e n t s h e l d

cons t an t (based on a l l oy spec i f i ca t i ons )

a s f o l lo w s : H e a t 1 : 0 . 0 3 0 % P a n d

0 . 0 0 2 % S ( H i g h P , L o w S ); H e a t 2 :

0 . 0 1 6 % P a n d 0 . 0 1 6 % S ( M e d i a n P , M e -

d i a n S ); H e a t 3 : 0 . 0 0 2 % P a n d 0 . 0 3 0 % S

(Low P, H igh S)

This set o f three a l loys (Heats 13 56,

1 3 5 7 a n d 1 3 5 8 ) a l l h a v e C r e q / N i e q =

1.32.1 S i l i con c on tent in these cast a l loys

r u n h i g h e r t h a n f o r t h e w r o u g h t g r a d e

(ASTM A240) . Two add i t i ona l hea t s w i t h

Creq /N i eq = 1 . 22 and l ow P / l ow S and m e-

d i a n P / m e d i a n S ( 1 5 6 4 a n d 1 5 6 5 , r e -

spec t i ve l y ) we re p roduced t o assu re so -

l i d if i c a t io n o c c u r r e d a s p r i m a r y

aus ten it e , so t ha t the co m p l ex i t y o f i n t e r -

I. Creqand N ieq def ined by the W RC- 1992 D i-

agram ( R e f. 2 0 ) w e r e u s e d f o r c a l c u l a t io n s .



a c t io n s o f f e r r it e w i t h P a n d S c a n b e

avo i ded •

A l l t es t hea ts were m e l t ed f rom h i gh -

pu r i t y sc rap m a t e r i a l con t a i n i ng ve ry l ow

P and S . The t a rge t P and S leve ls we re

ob t a i ned by ad d i ng P and S t o t he m e l ts .

Ingots f rom no min al 50-1b (23-kg) labo-

ra tory VIM test heats were processed to

~ /~-in . (15.8-m m) th ick p la te• H ot ro l l i ng

w a s d o n e fr o m 1 2 3 2 ° C ( 2 2 5 0 ° F ) . T h e

p la tes were po s t - ro ll an nea l ed a t 1065°C

(1950°F ) f o r 40 m i n , f an coo l ed , sand

b l as ted and p i ck l ed .

T a b le 1 s h o w s th e c h e m i c a l c o m p o s i -

t ions for a l l f i ve heats o f test mater ia l .

F i gu re 1 shows t he W RC-1992 D i ag ram

wi th test heats p lo t ted as po in ts•

E x p e r i m e n t a l P r o c e d u r e s

A Subscale Varestraint test apparatus

based on the or ig ina l Varest ra in t by Sav-

age and Lund i n (Re f. 16) was em p l oye d t o

evalua te hot crack ing suscept ib i li ty • Con -

d i t ions for these tests we re as fo l lows: 1)

GT AW bea d-on -p l a t e on Y~ x 1 x 5 - i n .

(3 . 18 x 25 . 4 x 127 -m m ) coupons ; 2 ) cu r -

ren t was D CEN, 100 A ; 3 ) vo l tage was 12

V ; 4 ) t rave l speed was 1 0 i n . /m i n (4 .2

mm/s) , w i th a we ld h eat input o f 7 .2 kJ / in . ;

5 ) 2 % T h O 2 W e l e c tr o d e w i t h p o i n t e d t i p

w i t h 9 0 - d e g a n g l e ; a n d 6 ) a u g m e n t e d

st ra in o f 0 .5 , 1 .75, 2 .5 , 3 .75%.

To ta l c rack l eng t h (TCL) and m ax i m u m

crack l eng t h (M CL) were m easured u nder

5 0 X m a g n i f i c a ti o n u s i n g a n e l e c t r o n i c

m i c rom et e r • C racks in bo t h t he f us i on

zon e and t he hea t-a ff ec ted zone f o r each

coupon were m easured separa t e l y . Two

coupons were t es t ed f o r each cond i t i on ,

and th e average resu l ts are repo rted.

Op t ica l meta llography, scan ning e lec-

t ron m i c roscopy (SEM ) and e l ec t ron m i -

Table

1 - -

Chem ica l Com posi t ions or the F ive Heats o f Test Ma ter ia l

H e a t N o . 1 3 5 6 1 3 5 7 1 3 5 8 1 5 6 4 1 5 6 5

C 0 . 0 5 9 0 . 0 6 0 0 . 0 6 0 0 . 0 6 2 0 . 06 1

M n 1 . 2 5 1 . 2 6 1 . 2 6 1 . 2 9 1 .3 1

P 0 . 0 2 7 0 . 0 1 6 0 . 0 0 4 0 . 0 0 5 0 . 0 1 6

S 0 . 0 0 4 9 0 . 0 1 9 0 . 0 3 2 0 . 0 0 4 8 0 . 0 1 5 9

S i 1 . 7 9 1 . 8 0 1 . 8 0 1 . 9 2 1 . 9 2

C r 1 8 . 8 6 1 8 . 9 8 1 9 . 1 0 1 8 . 0 8 1 8 . 1 0

N i 1 1 . 2 9 1 1 . 4 0 1 1 . 4 2 1 1 . 6 5 1 1 . 6 3

A I 0 . 0 0 4 0 . 0 0 4 0 . 0 0 4 0 . 0 0 5 0 . 0 0 2

M o 0 . 0 1 0 0 . 0 1 0 0 . 0 1 0 0 . 0 1 0 0 . 0 1 0

C u 0 . 0 1 0 0 . 0 1 0 0 . 0 1 0 0 . 0 1 4 0 . 0 1 3

N 0 . 0 4 9 0 . 0 4 8 0 . 0 4 8 0 . 0 5 5 0 . 0 5 4

N i~ q 1 4 . 3 4 1 4 . 4 6 1 4 . 4 8 1 4 . 9 2 1 4 . 8 5

C r~ q 1 8 . 8 7 1 8 . 9 9 1 9 .1 1 1 8 . 0 9 1 8. 1 1

C r e q /N e q 1 . 3 1 6 1 . 3 1 3 1 . 3 1 9 1 . 2 1 3 1 . 2 1 9

H-P , L -S M-P , M- S L -R H-S L -P , L -S M-P , M- S

Cr¢. ,i and Ni¢ . used were def ined by the WRC-1992 Diagram (Ref . 20) .

c rop rob e ana lys is we re conduc t ed on t he

as-rece ived base meta l , GTA weld ed, an d

Subscale-Varest ra in t- tested coup ons• A l l

S E M an a ly s es w e r e c o n d u c t e d u s i n g a

Jeol JSM-840 at an acce lerat ing v o l tage of

15 kV . Sam p l es were e i t he r i n t he as -

t es t ed cond i t i on f o r su r f ace c rack m or -

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

c o n d i t i o n f o r m i c r o s t r u c t u r e e x a m i n a -

t i on . Sam p l e e t ch i ng was done us i ng a

m i x e d - a c i d s r e a g e n t c o n s i s ti n g o f 4 2 %

hydroch l o r i c ac i d , 29% ace t i c ac i d and

2 9 % n i t r i c a c i d . A l t h o u g h , i d e a l l y , a n

A u g e r E l e c t r o n S p e c t r o s c o p e ( A E S )

shou l d be used f o r de t ec t i ng P and S seg -

r e g a t i o n , e l e c t r o n m i c r o p r o b e a n a l y s i s

w i t h a m uch b i gge r ana l ys i s vo l um e ( -1

m i c ron ) was em p l oyed because o f equ i p -

me nt const ra in ts . Q uan t i ta t i ve con cen t ra-

t ions o f phosphorus an d su l fu r , a l ong w i t h

other major e lements in the const i tuents

o f r e s u lt in g m i c r o s t r u c t u r e , w e r e o b -

t a i n e d u s i n g a J e ol 7 3 3 m i c r o p r o b e

Tab le

2 - -

Fer r it e Nu m b er Measu rem en t s

by Fer i tscope and Ma gneGa ge o f Test

Mater ia l

Weld Weld

H e at B a s e M e t a lFN Metal FN

No. Me ta l (MagneGage) (Fer it scope)

1 3 5 6 0 0 . 3 0 . 5

1357 0 0.65 1.1

1358 0 0.5 0.9

1 5 6 4 0 0 0 . 0

1 5 6 5 0 0 0 . 1

equ i pp ed w i t h f i ve wave l eng t h -d ispe rs i ve

s p e c t r o m e t e r s • A l l a n a l y s e s w e r e c o n -

duc t ed a t an acce l e ra t i ng vo l tage o f 15 kV

and a beam cu r ren t o f 20 m A. A l l sam p l es

were po l i shed and ca rbon coa t ed be f o re

analys is• For each sample, m ore than 30

i nc l us i ons , i n add i t i on t o t he aus t en i t e

mat r i x and any ferr i te s t r ingers, were an-

a l yzed f o r chem i ca l com pos i t i ons , w i t h

the representat i ve va lues be ing reported.

~ 3 ~ • ~ ' ~ :~L: .'~,.. ,,: :~ ~ %~:~

• % ~ . • , . , , , , ~

B •

; . . '

. . s . : . .

, '

.~, "~

, , ~ . . . ~ :

T ~

~ -

. . ; 1 ~ , , , .

• . , ~ , . ; ~ . 4 .. , . : . : . l . ~ ; i l z ~ . .

• , . . . . .. . . . . . ~ . . . ~ . . . . ~ - , ' . ~ . .

'. .. , . ~ . Z ~ ' ~ ~ , , , ; ' ; . : . ", .~ ~ . Z ' " ; , x ~ - , ' '

F i g . 3 - - T h e f u s i o n z o n e m i c r o s t r u c t u r e f o r H e a t 1 3 5 7 . M i x e d a c i d e tc h . A - - 5 0 ) ( ; B - - 4 0 0 X .

W E L D I N G R E S E AR C H S U P P L E M E N T I 3 8 9 - s



F ig . 4 - - T h e f u s io n z o n e m i c r o s t r u c t u re f o r H e a t 1 3 5 8 . M i x e d a c i d e t ch . A - - 5 0 X ; B - - 4 0 0 X .

t t + + C ~ + ~ + + ++ + + + ++ + : ~ + + 3 + + ~ + +++ ~ + l + + + ~ + ~ ' ~ e + + ' r + +

F ig . 5 T h e f u s io n z o n e m i c r o s t r u c tu r e f o r H e a t 1 5 6 4 . M i x e d a c i d e t ch . A - - 5 0 X ; B - - 4 O O X .

R e s u l t s

Base Me ta l and Fus ionZo n e M ic ro s t ru c tu re

A l l base m e t a l m i c ros t ruc t u re sha red

the same features,

i . e . ,

an aus t en i t e m a-

t r i x w i t h som e un i f o rm l y d i s t r i bu t ed ca r -

b i de pa r t i c l es . N o base m e t a l f e r r it e was

f ound . The aus t en i t e g ra i n s i ze (ASTM

N o . 5 ) w a s c o n s i s t e n t a n d c o m p a r a b l e

a m o n g t h e h e a t s . T h e f u s i o n z o n e m i -

c ros t ruc t u re f o r Hea t s 1356 , 1357 and

1 3 5 8 c o n s i s t e d o f c e l l u l a r d e n d r i t i c

aus t en i t e to t he cen t e r o f we l ds - - F igs .

2 -4 . The m i c ros t ruc t u re f o r t hese hea t s

appeared t o be f u l l y aus t en i t i c nea r t he

we l d cen t er . Ne ar t he f us i on bou ndar i es ,

however , som e i n t e rdendr i t i c f e r r i t e was

v i s i b l e . The f us i on zone m i c ros t ruc t u re

f o r t he t wo l ower f e r r i t e con t en t hea t s

( 1 5 6 4 a n d 1 5 6 5 ) w a s a ls o c e l l u la r d e n -

d r i t i c au s t en i t e - - F igs . 5 and 6 . The so -

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

p e a r e d t o b e p r i m a r y a u s t e n i t e

e v e r y w h e r e .

M e a s u r e m e n t s o f F N v a l u e s u s i n g

bo t h Fe r i tscope and M ag neG age f o r bo t h

t he f us i on zones and base m e t a l s o f t he

test heats are show n in Table 2 . These FN

m easurem en t s seem t o con f i rm t he m i -

c ros t ruc t u re obse rva t i ons and C req /N i eq

rat io ca lcu la t ions as shown in F ig .1 .

Subscale Vares traint Test Results

A p rev i ous s t udy (Re f. 17 ) showed t ha t

t he c rack i ng res i s t ance o f we l d j o i n t s i n

austen i t i c s ta in less s tee ls might rank d i f -

f e r e n tl y d e p e n d i n g o n w h e t h e r t h e r a n k -

i n g w a s b a s e d o n f u s i o n z o n e o r H A Z

c r a c k i n g s u s c e p t i b i l i t y . I n t h e p r e s e n t

s t udy , a c l ea r d i s t i nc t i on i s m ade when

discuss ing fus ion and heat -a f fected zone

c rack i ng behav i o rs .

Fusion Zone Cracking Susce pt ib i li t y

F i gu re 7 shows pho t om acrog raphs o f

t h e S u b s c a l e V a r e s t r a i n t c o u p o n s a f t e r

t es ti ng w i t h a 2 . 5% augm en t ed s t ra in . Fo r

a cons t an t P+ S l eve l o f 0 . 032% , h i ghe r P

con t en t resu l ted i n a g rea t e r f us i on zon e

crack ing suscept ib i l i t y . Th is can be seen

b y c o m p a r i n g t o t a l c r a c k l e n g t h ( T C L )

a n d m a x i m u m c r a c k le n g t h (M C L ) c u r ve s

(F ig . 8) for heats w i th increas ing amo unts

o f P , such as 1358 , 1357 and 1 356 . W hen

v i ew ed i n te rm s o f S con t en t , t he sam e set

o f cu rves a l so shows t he l ower po t ency

o f S fo r ca us i ng f us i on zone c rack i ng ( i. e. ,

f r o m l o w t o h i g h S , 1 3 5 6 , 1 3 5 7 a n d

1358).

The t wo f u l l y aus t en i t i c hea t s (1564

and 1565) showed a g rea t e r suscep t i b i l -

i ty f o r fus i on z one c ra ck i ng t han t he t h ree

f e r r i t e -con t a i n i ng hea ts . Be t ween t he t wo

f u l l y a u s t e n i t i c h e a t s , H e a t 1 5 6 5 w a s

m ore suscep t i b l e t han Hea t 1564 , s i nce

1565 con t a i ned m ed i an l eve ls o f bo t h P

a n d S , w h i l e 1 5 6 4 c o n t a i n e d v e r y l o w

leve ls o f both e lements.

Com par i son o f cu rves f o r Hea t s 1357

and 1565 con f i rm s t he bene f i c i a l e f f ec t o f

ferr i te on fus ion zon e crack ing res is tance.

I n these t wo hea ts w i t h a l m os t t he sam e

l e v e l o f P a n d S ( - 0 . 0 1 6 % e a c h ) , th e

h i ghe r f e r r i t e con t en t i n Hea t 1357 re -

su l ted in much greater crack res is tance.

3 9 0 - s I D E C E M B E R 1 9 9 9



¸

F i g. 6 - - T h e f u s io n z o n e m i c r o s t ru c t u r e f o r H e a t 1 5 6 5 . M i x e d a c i d et ch . A - - 5 0 X ; B - - 4 0 0 X .

The cu rves f o r Hea t s 1357 an d 1 565 a re

I

I

I

I

i

I

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a l m os t pa ra l l e l, so t he d i s tance b e t ween

them sho uld b e due to the ef fect o f ferr ite .

The de t r i m en t a l e f f ec t o f P as m o re

p r o n o u n c e d t h a n o f S i n fu s i o n z o n e s o -

l i d i f i ca t i on h o t c r a c k i n g o b s e r v e d h e r e is

con f i rm ed by som e ea r l i e r s t ud ies (Re fs .

5, 6).

H A Z C r a c k i n g S u s c e p t i b i l i t y

For HA Z ho t c rack i ng , S seem s t o be

t he m ore de t r i m en t a l t race e l em en t . Fo r

a cons t an t P+ S l eve l o f 0 . 032% , h i ghe r S

c o n t e n t r e s u l t e d i n g r e a t e r H A Z h o t

c r a c k i n g s u s c e p t i b i l it y . T h i s t r e n d a p -

pea red t o be va l i d f o r augm en t ed s t ra i n

l eve ls up t o 2% - - F i g . 9 . Cu rves fo r hea ts

w i t h h i g h e r S c o n t e n t a r e a b o v e c u r v e s

for heats w i th low er S con tent , regard less

of ferr i te content .

Fo r augm en t ed s t ra i n l eve l s g rea t e r

t han 2% , Hea t s 1357 and 1358 showed

an unusua l and unexp ec t ed d rop o f c rack

length wi th increasing strain levels, so no

c o n s i s t e n t c o m p a r i s o n o f c r a c k i n g t e n -

denc i es was o b t a i ned f o r t he h i ghe r s t ra in

leve ls . As can be seen in F ig . 9 , 2% st ra in

does not cons t i tu te saturation. C arefu l ex-

am inat ion of Subscale Varest ra in t samples

tested at s t ra in leve ls h igher than 2% re-

vea l ed tha t a po r t i on o f HA Z c racks were

cove red by t he we l d beads f o r Hea ts 13 57

and 1358 . Apparen t l y , when h i ghe r aug -

m en t ed s tra ins were a pp l i ed (by t he pneu -

mat ica l l y actuated ram in the Varest ra in t

appara t us ) , t he we l d poo l was d i s t u rbed

and m o l t en m e t a l sp i ll ed ou t o f t he poo l

because o f t he sudden and p ronounced

bend i ng de f o rm a t ion o f t he sam p l e . Th is

p h e n o m e n o n w a s o b s e r v e d m o s t i n t h e

tw o heats w i th h ighe r S conten t , cons is-

t e n t w i t h t h e k n o w n e f f e c t o f S o n i n -

creas ing f lu id i t y o f l i qu id s tee ls (Ref. 18) .

Thus, the unusual change of crack ing re-

T a b l e 3 - - M i c r o p r o b e A n a l y s i s R e s u l t s ( w t - % )

M a t e r i a l C r N i

1 3 5 6 f e r r it e 2 3 . 4 2 6 . 0 8

1 3 5 6 a u s t e n i t e 1 9 .1 5 1 0 . 5 9

1356 P-rich 27.01 14.04

i n c l u s i o n

1 3 5 6 S - ri ch 2 1 . 4 2 1 1 . 8 5

i n c l u s i o n

135 7 P - r ic h 26 . 01 13 . 91

i n c l u s i o n

135 7 S - r ic h 19 . 96 11 .83

i n c l u s i o n

1 3 5 8 S - ri ch 2 0 . 2 3 1 0 . 7 8

i n c l u s i o n

156 4 S - r ic h 18 . 05 12 . 35

i n c l u s i o n

1565 aus t en i t e 17 . 51 10 . 81

1565 f e r r i t e 24 . 65 7 . 42

1565 P - r ic h 31 . 8 8 13 .63

i n c l u s i o n

1565 S - r ic h 20 . 7 6 12 .01

i n c l u s i o n

M i n . D e t e c t 0 . 0 5 0 . 0 4 5

L i m i t

M n S i S P F e

0 . 97 1 . 87 0 0 66 . 71

1.21 1.63 0 0 66.11

2.12 3.47 0.034 1 .6 0 49.49

3 . 6 9 2 . 51 1 . 94 0 . 0 5 5 4 . 7 8

1 . 1 9 2 . 9 4 0 . 1 3 0 . 8 9 5 3 . 4 3

1 . 4 9 1 . 9 8 0 . 6 4 0 6 2 . 1 5

5 . 02 2 . 01 2 . 74 0 57 . 41

4 . 5 7 3 . 2 6 1 . 3 7 0 5 5 . 6 5

1 . 2 9 1 . 5 9 0 0 6 7 . 0 6

1 . 19 2 . 91 0 0 62 . 25

1 .1 2 3 . 5 4 0 . 0 7 4 . 0 5 4 4 . 2 3

1 . 91 2 . 13 1 . 25 0 59 . 43

0 . 0 2 0 . 0 1 5 0 . 0 6 0 . 0 3 0 . 0 6

T a b l e 4 - - F r e e E n e r g y o f F o r m a t i o n ( - A G ) D a t a f o r C a r b i d e s , P h o s p h i d e s a n d S u l f i d e s o f F e ,

N i , M n a n d C r

F e N i C r M n

- A G F e3 C N i 3 C C D C ] M n T C 3

C a r b i d e s 4 . 9 - 2 6 8 2 0 4 1 1 3 . 9

(1227°C) (727°C) (1227°C) (1227°C)

- A G F eS N i3 S - - M n S

Su l f ides 99 . 2 252 170 . 4

(727°C) (227°C) (1227°C)

-A G F e3P N i2P C r3P (R e f . 1 M n P 3 (R e f . 2 )

P h o s p h i d e s - 1 4 7 . 4 - 2 0 1 1 2 3 . 4 1 .7 5

(635°C) (630°C) (1427°C) (951 °C)

N o t e s : U n l e s s i n d i c a t e d , m o s t o f t h e d a t a w e r e c o l l e c t e d f r o m

M etal R eference Book,

C . J . S m i t h e l l s , e d . , 5 ~h E d i t i o n , 1 9 7 6 .

R e f 1 . Z a i t s ev , A. I . , S h e l k o v a , N . E . , L i t v in a , A . D . , M o g u t n o v , B . M . , D o b r o k h o t o v a , Z h . V . 1 9 9 8 . T h e r m o d y n a m i c p r o p e r t i e s a n d

p h a s e e q u i l i b r i a i n t h e C r- P s y s te m .

Journal of Phase Equilibria

1 9 ( 3 ) .

R e f . 2 . K u b a s c h e w s k i , O . , a n d C a t t e r a l l , J . A. 1 9 5 6 .

ThermochemicalData o f Al loys,

P e r g a m o n P r es s , p . 1 3 3 .

,

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W E L D I N G R E S E AR C H S U P P L E M E N T [ 3 9 1 - s



F i g. 7 - - P h o t o m a c r o g r a p h s o f t h e a s - te s t e d s u r f a c e o f S u b s c a l e V a r e -

s t r a in t c o u p o n s a ft e r a 2 . 5 a u g m e n t e d s t ra i n w a s a p p l i e d 3 0 X . A - -

H e a t 1 3 5 6 ; B - - H e a t 1 3 5 7; C - - H e a t 1 3 5 8; D - - H e a t 1 5 6 4 ; E - -

H e a t 1 5 6 5 .

s i s t ance rank i ng a t

high strain levels was

most l i ke ly the resu l t

o f t he above a r t i f ac t

a s s o c i a t e d w i t h t h e

Subsca l e V a res t ra i n t

test.

A l t hough con t a i n -

i ng no f e r r i t e , Hea t

1 5 6 4 s h o w e d t h e

l owes t suscep t i b i l i t y

t o H A Z h o t c r a c k i n g

- - c l e a r l y t h e r e s u l t

o f t h e l o w P a n d S

concen t ra t i ons . Th i s

o b s e r v a t i o n a g r e e d

w i t h a p rev i ous s tudy

t ha t sugges t ed t ha t

f o r HAZ c rack i ng (as

o p p o s e d t o f u s i o n

zone c rack i ng ) sus -

cep t i b i l i t y , i m pur i t y

i n t he f o rm o f P+ S

l eve l i s o f p r i m ary

i m p o r t a n c e , w h i l e

ferr i te i s o f secon dary

impo rtance (Ref . 17) .

Discuss ion

T y p i c a l f u s i o n z o n e c r a c k m o r p h o l -

ogy in the as- tested con di t ion is sho wn in

F i g . 10 . Apparen t l y , c rack i ng occu r red

t h rough t he separa t i on o f i n t e rdendr i t i c

in ter faces of the ce l lu la r den dr i t i c so l id i -

f ica t ion substructure. Figure 11 shows an

S E M i m a g e o f a f u s i o n z o n e c r a c k f o r

Hea t 1356 a f t e r po l i sh i ng and e t ch i ng .

Spher i ca l i nc l us i ons and f i l m - l i ke f ea -

t u res can be obse rved on t he c rack su r -

faces. The d is t r ibut ion of these inc lus ion s

i n t he f us i on zone (F i g . 12 ) i s m os t l y

a lon g the in terde nd r i t i c in ter faces. These

i nc l us ions ( -1 m i c ron ) a re be l ieved t o be

one o f t he f i na l cons t i t uen t s o f s o l i d if i ca -

t i on based on t he i r l oca t i on . A t t he edge

o f t h e w e l d f u s i o n z o n e i n H e a t 1 3 5 6

where some ferr i te i s present , a lmost no

such i nc l us i ons can be obse rved - - F i g.

13. Th is e f fect o f ferr i te i s most notab le a t

t he j unc t u re w here f e r r i te -con t a i n i ng m i -

c ros t ruc t u re is changed t o f u l l y aus t en i t ic

m i c ros t ruc t u re nea r t he cen t e r o f t he fu -

s i on zone i n Hea t 1356 - - F i g . 14 .

Q u a n t i t a t i v e m i c r o p r o b e a n a l y s i s

3 9 2 - s I D E C E M B E R 1 9 9 9







F i g. 1 3 - - A t t h e e d g e o f th e w e l d f u s i o n z o n e i n H e a t 1 3 5 6 w h e r e

s o m e f e r r it e i s p r e s e nt , a l m o s t n o i n c l u s i o n s c a n b e o b s e r v e d .

M i x e d a c id s e tc h . 3 0 0 0 X .

F i g. 1 4 - - T h e j u n c t u r e w h e r e f e r r i t e - c o n t a i n in g m i c r o s t r u c t u r e i s

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

z o n e i n H e a t 1 3 5 6 . A - - p o i n t s t o a n in c l u s i o n ; B - - t o f e rr it e .

F ig . 1 5 - - M o r p h o l o g y o f H A Z c r a c k i n g i n a s -t e st e d c o n d i t io n . A - - H e a t 1 3 5 6 ; B - - H e a t 1 3 5 8 .

F i g. 1 6 - - M o r p h o l o g y o f H A Z c r a c k i ng , a f t e r p o l i s h i n g a n d e t c h in g . A - - H e a t 1 3 5 6 ; B - - H e a t 1 3 5 8 .

W E L D I N G R E SE AR C H S U P P L E M E N T [ 3 9 5 - s



b o u n d a r i e s b e c a u s e o f f a s te r m o v i n g S

a t o m s , a n d t h e S s e g r eg a t ed m a y n o t b e

t ie d u p b y t he l i m i t e d s u p p l y o f M n o r C r

t h r o u g h s o l i d - s t a te d i f f u s i o n . T h i s r e a -

s o n i n g h e l p s t o u n d e r s t a n d t h e s t r o n g e r

e f fe c t o f S t h a n P o n H A Z c r a c k i n g .

Conc lus ions

1 ) F o r t e s t e d h e a t s o f 3 0 8 a u s t e n i t i c

s t a in l e ss ste e l w i t h a c o m b i n e d l e v e l o f

P + S o f 0 . 0 3 2 % , P is m o r e p o t e n t i n e x -

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

w h i c h is c o n s i s t e n t w i t h t h e l i te r a t u r e . S

i s m o r e p o t e n t i n e x a c e r b a t i n g H A Z h o t

c r a c k i n g , w h i c h h a s n o t b e e n r e p o r t e d i n

t h e r e v i e w e d l i te r a t u re .

2 ) Z e r o f e r r it e c o n t e n t ( f o r H e a ts 1 5 6 4

a n d 1 5 6 5 ) r e s u l t e d i n g r e a te r fu s i o n z o n e

h o t c r a c k i n g s u s c e p t i b i l i t y , a s i s c o n s i s -

t e n t w i t h t h e l i te r a t u r e . H o w e v e r , t h e

H A Z h o t c r a c k in g s u s c e p t i b il i ty o f H e a t

1 5 6 4 ( 0 . 0 0 5 % P , 0 . 0 0 4 8 % S ), a l t h o u g h

c o n t a i n i n g z e r o f e r r i t e , w a s t h e l e a s t

a m o n g a l l t e s t e d h e a t s . T h i s s h o ws t h a t ,

f o r p r e v e n ti n g H A Z c r a c k in g , i n t r o d u c -

t i o n o f f e r r i te i s n o t a s e f f e c t i v e a s r e d u c -

i n g S a n d P i m p u r i t y l e v e ls .

3 ) S e g r e g a ti o n o f P a n d S w a s f o u n d t o

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

z o n e i n c l u s i o n s . T w o t y p e s o f i n c l u s i o n s

w e r e p r e s e n t i n t h e t es t h e a ts t h a t c o n t a i n

m e d i a n t o h i g h e r P ( i .e . , H e a t s 1 3 5 6 ,

1 3 5 7 a n d 1 5 6 5 ) . S u l f u r - r i c h i n c l u s i o n s

c o n t a i n e d h i g h e r l e v e ls o f M n . P h o s p h o -

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

e l s o f C r a n d S i. H o w e v e r , i n h e a t s c o n -

t a i n i n g l o w P ( i. e ., H e a t s 1 3 5 8 a n d 1 5 6 4 ) ,

o n l y S - r ic h i n c l u s i o n s w e r e d e t e c te d .

N e i t h e r P - r i c h n o r S -r ic h i n c l u s i o n s w e r e

d e t e c t e d i n t h e H A Z c r a c k s u s i n g t h e m i -

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

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

a n d p h o s p h i d e s a n d d i f f u s i o n r a t e s o f P

a n d S i n a u s t e n i t e .

Acknowledgments

T h i s p r o j e c t w a s f u n d e d b y t h e H i g h

A l l o y s C o m m i t t e e o f t h e W R C . T h e fo l -

l o w i n g o r g a n i z a t i o n s a n d i n d i v i d u a l s

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

d u c t o f t h e p r o j e c t a n d a r e g r a t e f u l l y a c -

k n o w l e d g e d : A l l e g h e n y - L u d l u m T e c h n i -

c a l Ce n t e r ( D r . J o h n G r u b b , Pa u l L o v e jo y )

f o r p r o v i d i n g t h e t e st m a t e r i a l a n d i ts p r o -

c e s s i n g ; P r o f e s s o r Ca r l D . L u n d in o f t h e

U n i v e r s i t y o f T e n ne s s e e a t K n o x v i l l e a n d

F r a n k L a k e o f E S A B f o r p r o v i d i n g F N

m e a s u r e m e n ts ; N o r m a n G e n d r o n o f

M e t a l l o g r a p h y L a b a t R P I f o r h i s a s s i s -

t a n c e w i t h m e t a ll o g r a p h y; a n d D r . D a v i d

W a r d o f R P I f o r h i s a s si s ta n c e w i t h m i -

c r o p r o b e w o r k .

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Documents

The Effect of P and S t Hot Crack Austenitic SS