Stelite Welding Stanless Steel WJ_1980_07_s213

8/17/2019 Stelite Welding Stanless Steel WJ_1980_07_s213

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I n f l uence o f P rehea t Tempera tu re on

Stell i te Deposits

Preheating to 900°Q followed by air cooling to 450°C after depo sition

to avoid further sensitization of the base metal and then

furnace cooling to room temperature produces sound deposits

without any undesirable features

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BY M. D . MA THE W S. L M A NN A N A ND S. K. GUPTA

ABS TRACT. The in f lue nce o f preheat

temperatures in the range 150-900°C

(302-1.652°F) on S tel l i te dep osit s on

Types 304 and 316 stainless steel has

been s tud ied . S te l l ite g rade 6 (AWS

RCoCr-A) bare rod was used and the

oxyace ty lene we ld ing p rocess was em

p loyed to prepare the over lays . The

meta l lu rg ica l eva lua t ion o f the va r ious

depos i ts inc luded me ta l log raph ic in

ves t iga t ions , m ic roha rdness measu re

men ts and e lec t ron m ic rop robe

stud ies on the S te l l i te dep os i t , the

in te r face be tw een S te l li te and base

and the base mater ia l . Microcracks

wer e observed in the S te l l i te as we l l as

a long the in ter face in depos i ts pre

pa red by em p loy ing p rehea t tempera

tures of 150 and 300°C (302 and

572°F).

Preheat ing to 600°C (1112°F) tends to

sensit ize the base material. I t has been

es tab l ished tha t a p rehea t temp era tu re

of 900°C (1652°F) and a i r coo l ing to

450°C (842°F) a f ter depos i t ion ,

f o l

l owed by fu rnace coo l ing to room

tempera tu re p roduces sound depos i ts

w i thou t any undes i rab le fea tu res .

M ic roha rdness measu remen ts we re

taken a long the m ic rop robe t rave rses

to examine the var ia t ion in hardness

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

across the in ter face. Microhardness

across the in ter face has been found to

co r re la te w i th the coba l t con ten t .

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

Austen i t ic s ta in less s tee ls have been

chosen fo r va r ious s t ruc tu ra l compo-

M. D. MATHEW and S. L. MANNAN are

with the Metallurgy Programme and

S.

K.

GUPTA is with the FBTR Construction

Group, Reactor Research

Center,

Kalpak-

kam Tamil Nadu, India.

nen ts o f sod ium -coo led fas t b reede r

reactors because o f the i r exce l len t cor

ros ion res is tance in l iqu id sod ium and

g o o d e l e v a t e d t e m p e r a t u r e m e c h a n

ica l p ropert ies . The h igh operat ing

temperatures necess i ta te hard fac ing o f

ce r ta in componen ts to avo id ga l l i ng

and a lso to reduce the wear o f the

c o m p o n e n t . I n a d d i t i o n , t h e d e p o s i t

shou ld have good the rma l shock

resistance as w e l l . S te l l i te grade 6 (cor

respond ing to AWS RCoCr-A) has ,

the re fo re , been spec i f ied fo r ha rd fac

ing va r ious com pon en ts l i ke the

c o n

t ro l rod d r i ve mechan ism (CRDM),

co re cove r p la te d r i ve mechan ism, g r id

p la te and var ious subassembl ies in the

reactor core of the fast breeder test

reactor (FBTR) now under construc

t ion at the Reactor Research Centre,

Ka lpakkam.

This paper presents the results of a

de ta i led s tudy o f the in f luence o f p re

hea t tempera tu re on the qua l i t y o f

AW S RCoC r-A depos i ts on Types 316

and 304 sta in less s tee l CR DM co mp o

n e n t . O w i n g t o t h e l o w d u c t i l i t y o f

coba l t -base a l loys , inadequ a te p rehea t

P RE P A RA T I O N

OF CYLINDERS

S TELLIT ING BY

O X Y - A CE T Y LE NE

P RO CE S S

PRE HEAT

150°C

PRE HEAT

300°C

PRE HEAT

600°C

PRE HEAT

900

°C

M AC H INING

METALLURGICAL

E V A L U A T IO N

M I CRO P RO B E

S T U D I E S

H A R D N E S S

M E A S U R E M E N T S

METALLOGRAPHY

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Fig.

1—Block

diagram oi experimental program

W E L D I N G R E S E A RC H S U P P L E M E N T I 213 s


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Fig. 2—Part

of control rod drive mechanism

used for surfacing with AWS

RCoCr-A

type

bare rod

:

C B

8S3 iS i$P% S i l l

:

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•

Fig.

3—Micrographs

showing typical S tellite (i.e., AWS RCoCr-A) deposits prepared by

emp loying prehe at temp eratures of: A-150 °C (302°F);

B-300 C

(572 F);

C-600°

(1112 F);

D-90VC (1652°F)

Table 1 Hardness of AWS RCoCr-A Type

Deposits

HISS

•-

Deposit

A

B

C

D

Rockwell C

45 50

47 49

46 47

47 52

can lead to the c rack ing o f the depos

it s by h igh shr inkage s tresses deve l

oped du r ing we ld ing . P rehea t ing re

duces shr inkage s tresses and e l imi

na tes c rack ing and d is to r t ion , p ro

v ided the p rehea t ing is un i fo rm . In

add i t ion , p rehea t ing to h igh tempera

tures leads to greater d i lu t ion o f the

depos i t w i th the base me ta l impa r t ing

some g rad ien t in i ts mechan ica l p rop

ert ies and consequent res is tance to

shock, though a t the cos t o f wear

resistance. The results of the present

inves t igat io n in d ica te that i t is essen

t ia l to preheat the base meta l to h igher

tempera tu res ~ 900°C (1652°F) f o l

l owed by s low coo l ing in o rde r to

p roduce sound depos i ts w i th the

des i red p rope r t ies .

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

Figure 1 show s the b lock d ia gram of

the expe r imen ta l p rog ram.

Preparation of the Deposits

The

c o m p o n e n t o f C R D M

was

ma chin ed f r om a 55 m m (2.17 in .)

d iam eter rou nd as sho wn in F ig. 2 , and

dye -pene t ran t inspec ted . I t was then

tho rough ly c leaned to remove o i l ,

g rease, e tc . , be fore weld ing. For the

150°C

(302° F) preh eat de po sit T ype

V _ -

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- ''.•*'• 3' V / *%tV-'*

• . . , . ••••;:••$

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Fig. 4—Micrographs showing microcracks in deposits prepared by employing preheat

tempe ratures: A-150 °C (302°F) and B-30 0°C (572°F); interface regions w ith pre heat

temperatures:

C-60VC

(1112°F) an d D-900°C (1652°F)

316 stainless steel was used as base for

p repa r ing the ove r lay , wh i le fo r o the r

depos i ts T ype 304 was used. We do

no t expec t any d i f fe renc e be tw een the

behav ior o f over lays us ing Types 316

and 304 stainless steel as the base

meta l .

The oxyace ty lene we ld ing p rocess

w a s e m p l o y e d f o r p r e p a r i n g th e A W S

RCoCr-A depos i ts . Th is process pro

duces h igh qua l i ty depos i ts re la t ive ly

und i lu te d by the base me ta l , co m

pa red to o the r me thods o f p repa r ing

depos i ts , and a lso is more su i tab le for

com p lex shapes and d ime ns ions . The

nature o f the f lame is an im po rtan t

pa rame te r in de t e rm in ing the s t ruc tu re

and propert ies o f the depos i t . In the

present s tudy, a 3X f lame was used;

th is led to some carbon p ick-up in the

depos i ts .

Fou r depos i ts we re p repa red w i th

preheat tem pera tures o f 150, 300, 600

and 900°C (302, 572,1112 and 1652°F);

these are refer red t o as dep osit s A, B, C

and D, respect ive ly , in fu r ther d iscus

s ions. The depos i t A was a i r coo led to

room tempera tu re wh i le depos i t D

was a i r coo led to about 450°C (842°F)

a f te r depos i t ion to avo id sens i t i za t ion

and then s low ly coo led to room

t e m

pe ra tu re in a fu rnace p rev ious ly

hea ted to 45 0°C (842°F). Sa mples B

and C were fu rnace coo led to room

214-sl

JULY 1980


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Table 2 Chemical Composi t ion o f AWS RCoCr

E l em en t

Coba l t

C h r o m i u m

Tungs ten

Carbon

S i l ic on

I ron

Bare Rod

63.90

26.59

6.02

1.22

1.01

0.80

Depos i t

A

63.25

28.98

4.13

1.62

0.87

—

-A Type Depostis and Bare Rod

Depos i t

B

63.80

26.96

5.02

1.57

1.04

1.03

Depos i t

C

62.67

27.56

5.52

1.64

1.09

0.80

W C - %

Depos i t

D

62.53

26.00

6.13

1.64

0.65

2.36

temp era tu re a f te r dep os i t io n . The s low

cool ing was resorted to to reduce

stresses due to weld ing.

The as-depos i ted th ickness o f the

over lays was in the range 4-5 mm

(0.16-0.20 in.) and bare rods o f d iame

ter 4.1 mm (0.161 in.) were used for

p repa r ing the ove r lays . Mach in ing o f

the over lays was carr ied out to leave a

th ickness o f the depos i t o f 2 .5 mm

(0.098 in . ) . Dye -p ene t ran t inspe c t ion ,

u l t rason ic inspect ion and hardness

measurements were carr ied out on a l l

the depos i ts be fo re and a f te r mach in

ing. Tab le 1 shows the hardness o f the

depos i ts a f te r mach in ing . Ove r lays

w e r e c o l l e c t e d d u r i n g m a c h i n i n g a n d

analyzed for var ious e lements .

Metallurgical Tests

The me ta l lu rg ica l eva lua t ion o f the

A W S R C o C r - A d e p o s i t s i n c l u d e d m e t

a l log raph ic s tudy o f the depos i ts ,

microprobe scans across the over lays

and m ic roha rdness measu rem en ts

a long the m ic rop robe t rave rses .

Metallography. M e t a l l o g r a p h i c i n

ves t igat ions were carr ied out on t rans

ve rse sec t ions removed f rom va r ious

locat io ns o f the S te l l i ted rounds . A

mix ture o f 25 ml g lycer ine, 25 ml HCI

and 10 ml H N O , was used as the

e tchan t fo r m ic ros t ruc tu ra l examina

t i o n . The ent i re surface o f the sample

was exa min ed to assess the q ua l i ty o f

the depos i t . M ic rog raphs were taken

of important features o f the depos i t

and a lso o f typ ic a l a reas o f S te l l i te fo r

each depos i t .

Electron Microprobe and Micro

hardness Examination.

S ma l l samp les

su i tab le fo r m ic rop robe ana lys is we re

sec t ioned f rom the me ta l log raph ic

samples . These were aga in po l ished

and g iven a l i gh t e tch w i th a m ix tu re o f

20 ml HC I, 20 ml

H 0 10

m l H N O , a n d

0.5g FeCI , b e f o re m i c r o p r o b e a n a ly

sis.

S amp les we re ana lyzed fo r coba l t ,

c h r o m i u m , i r o n , tungs ten and n icke l

to s tudy the ex ten t o f d i lu t io n us ing a

C A M E C A M S - 4 6 E l ec tr o n M i c r o p r o b e

Ana lyse r . M ic rop rob e runs we r e made

across the samples s tar t ing f rom the

AWS RCoCr-A reg ion and ex tend ing

we l l i n to the base . M ic roha rdness

measu remen ts we re ca r r ied ou t on

these samp les a long the m ic rop robe

scans us ing a d ia mo nd inden te r to

s tudy the co r re la t ion be tween e le

men ta l d is t r ibu t ion and the m ic ro

hardness.

Resul ts and Discuss ion

The dye -pe ne t ran t inspec t ion and

u l t rason ic inspect ion carr ied out a f ter

depo s i t ion and a f te r ma ch in in g d id

not reveal any cracks. Figure 3 shows

typ ica l m ic ros t ru c tu re o f S te l l ite fo r

the d i f fe ren t depos i ts . The d end r i tes

appear to coarsen wi th h igher preheat

tempera tu res . The p resence o f m ic ro -

c racks in depos i ts p repa red w i th p re

heat temperatures o f 150 and 300°C

(302 an d 572°F) i s shown , respec t i ve ly ,

in Figs. 4A and 4B.

S ome po ros i ty was also de tec te d in

the depo sit wi th 150°C (302°F) pre heat

tempera tu re . No c racks we re obse rved

w i th p rehea t tempera tu res o f 600 and

900°C (1112 and 1652°F). The typical

m ic ros t ruc tu re o f in te r face reg ion o f

depos i ts w i th these p rehea t tempera

tures are sh ow n in F igs . 4C and 4 D.

Howeve r , p rehea t ing to 600°C

(1112°F) tends to sens i t ize the base

mater ia l—Fig. 4C Therefore , a preheat

to 900°C (1652°F) which is above the

sens i t iza t ion range shou ld be pre

fe r red .

In add i t ion to p roduc ing a

sound depos i t , th is p rehea t tempera

ture is a lso expec ted to re duce the

^ ^ • T

J

> ^ » » a ^ r ^

e

»

50 I00 150 200 250 300 350 iOO i5 0 500

( MI CRO NS )

D I S T A N C E F RO M S T E L L I T E TO B A S E M A T E R I A L

(I M I C R O N S )

A S E M A T E R I A L

^ ' n f r n

1

50 100 150 200 250 300 350 iOO i5 0 ( MsCRONS )

D I S T A N C E F R O M S T E L L I T E TO B A S E M A T E R I A L

Too

( MICRONS)

D I S T A N C E F R OM S T E L U T E T O B A S E M A T E R I A L

Fig. 5-Craphs showing distribution of elements and microhardne ss across sample at: A-150°C (302°F); B-300°C (572°F); C-6 00°C (1112°F);

D~~900°C (16S2°F). Legend: solid black circles-cobalt; open face circles with plus sign-chromium ; open face triangles-iron; open face circles

with dot in center-nickel; X's-tungsten; solid black squares-m icrohardness (Vickers hardness number, load = 50 gm)

W E L D I N G R E S E A R CH S U P P LE M E N T I

215 s


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res idua l s tresses. S ens i t iza t ion in the

base mater ia l dur ing coo l ing is

avo ided by fas t coo l ing to about 450°C

(842°F).

Tab le 2 shows the resu lts o f ch em i

ca l ana lys is o f the over lays . The chem

ical analysis of the bare rod used in

prep ar ing these depos i ts is a lso sho wn

in Table 2. It can be seen that no

s ign i f icant d i lu t ion o f the over lays has

taken p lace. Th is is expe cted w he n the

oxyace ty lene p rocess is em p loy ed fo r

d e p o s i t i o n .

The ca rbon con ten t in the

depos i ts is mu ch h ighe r com pared to

that in the bare rod analysis. This has

resu l ted f rom the nature o f the f lame

emp loyed . As the ca rbu r iz ing f lame

(3X) was used in prepar ing these de

pos i ts , excess carbon would have

en te red the depos i ts .

The resu l ts o f the e lec t ron m ic ro

probe and microhardness t raverses are

show n in F ig . 5 . The m ic rop r obe

results are plotted as ratios of X-ray

in tens i t ies f rom the AWS RCoCr-A

depos i t / base to tha t o f pu re e lemen t

for each e lement ana lyzed vs . d is tance

a long t rave rses f rom AWS RCoCr-A to

base me ta l . These in tens i ty p lo ts sho w

d is t r ibu t ion o f each e lemen t in va r ious

reg ions o f the sample . As no correc

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

sys tem, these in tens i ty ra t ios sh ou ld

not be cons idered as represent ing

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

An examina t ion o f the m ic rop robe

resu l ts revea ls that a h igher preheat

tempera tu re resu l ts in smoo the r va r ia

t ion o f compos i t ion ac ross the in te r

face. Th is w ou ld lead to an impro ve

ment in the thermal shock res is tance.

As seen f rom Table 1 , hardness o f the

depos i t is not a f fec ted by th is smal l

am oun t o f d i l u t i on . F igs. 5A and 5 D

also show that there ex is ts a corre la

t ion o f m ic roha rdness w i th the coba l t

content . These resu l ts are s imi la r to

the f ind ings o f Dou ty and S chwar tz -

bart .

1

C o n c l u s i o n

The resu l ts o f th is invest igat ion

revea l that a h igh preheat tem per atu re

is essent ia l to avo id m icro cra ck in g o f

the depos i ts . M ic roc racks we re ob

served in depos i ts prepared by em

p loy ing a preheat o f 150 and 300°C

(302 and 572°F). Preheating to 900°C

(1652°F), fo l lo w ed by ai r co o l i ng to

450°C (842°F) a f ter depo s i t i on to a vo id

any fur ther sens i t iza t ion o f the base

and then fu rnace coo l ing to room

t e m

pe ra tu re p roduced sound depos i ts

w i thou t any undes i rab le fea tu res .

M ic rop robe ana lys is ac ross the de

pos i ts ind ica ted tha t the re i s a sm oo th

e r va r ia t io n in com pos i t ion ac ross the

in te r face in depos i ts w i th h igh p rehea t

tempera tu re . M ic roha rdness measu re

men ts a long the m ic rop robe t rave rses

revea led a co r re la t ion o f m ic roh a rd

ness w i th co ba l t con t en t o f the dep os

its.

Acknowledgments

The authors are indebted to Dr. P.

Rodr iguez for usefu l d iscuss ions.

Tha nks are also due t o S hri K. G.

S amue l fo r he lp in me ta l log raphy , S h r i

S . A rava mu dhan fo r he lp in p repa r ing

the depos i ts and Sh r i S . Venkadesan

fo r m ic rop robe ana lys is .

References

1. Dou ty, R. A., and S chwartzbart, H.,

S urfacing of 304 S tainless S teel for Liquid

S odium S ervice,

Welding lournal,

51(8),

Aug.

1972, Research S uppl., pp. 406-s to

416-s.

WRC Bulletin

257

February 1980

Analysis of the Ultrasonic Examinations of PVRC Weld

Specimens 155

202 and 203 by

Standard

and

Two-Point

Coincidence Methods

by R. A. Buchanan prepared for publication by 0. F.

Hedden

This report descr ibes two me thod s o f ana lys is o f u l t rason ic ex am inat io n data obt a ine d in a 13 team

round - rob in examina t ion o f th ree in ten t iona l l y f lawed we ldmen ts . The ob jec t i ve o f the examina t ions i s to

determine the accuracy o f independent ly detec t ing, locat ing and s iz ing the weld f laws, us ing a f ixed

procedure.

Com pu te r p rog rams to fac i l i ta te comp ar ison o f f law loca t ions w i th the u l t rason ic da ta , fo r each o f the

spec imens and bo th o f the me thods , a re appended to the repo r t .

Pub l i ca tion o f th is repo r t was sponso red by the S ubcom mi t tee on N ondes t ruc t i ve E xamina t ion o f M a te r ia ls

for Pressure Co mp on en ts o f the Pressure Vesse l Research Co m m it t ee o f the We ld in g Research Cou nc i l .

The price of WRC Bulletin 257 is

11.00

per copy, p lus $3.00 for pos tage and hand l ing. Orders shou ld be

sent wi th pa yme nt to the Weld ing Research Cou nc i l , 345 E ast 47t h S t . , Room 8 01 , New York , NY 1001 7.

216-sl JULY 1980

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Stelite Welding Stanless Steel WJ_1980_07_s213