weldability-ferritic stainless steels

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WELDING RESEARCH

S UP P L E M E NT T O T HE W E L DI NG J OURNA L , A UGUS T , 1 9 8 1

S p o n s o r e d b y th e A m e r i c a n W e l d i n g S o c i e t y a n d t h e W e l d i n g R e s e a r c h C o u n c i l I I B I ,

Weldabil i ty of Ferr i t ic Stainless Steels

Investigation shows that it is possible to provide (1) adequate resistance

to hot cracking during welding and (2) usable mech anical properties

and resistance to intergranular cracking in the as-welded condition

by mean s of stabilization

BY D. H. KAH AN D D. W. D ICK INS ON

ABSTRACT. The annealed fer r i t ic s ta in

less steels containing 16 to 18% Cr

o f f e r accep tab le ox ida t ion and cor ro

s ion res is tance in many environments

ranging f rom rura l a tmospheres to

aggress ive, hot ac id so lut ions at lower

mate r ia l cos t t han t he common aus te

n i t ic s ta in less s teels . They are, howev

e r , sub jec t t o embr i t t lement , suscep t i

b le t o ho t c rack ing dur ing we ld ing ,

and their mechanical proper t ies

( t oughness and duc t i l i t y ) and cor ro

sion resistance are adversely af fected

b y we ld i n g .

The ferr it ic stainless steels are gener

a l l y cons idered t o have poor we ldab i l

i t y when compared to t he aus ten i t i c

s ta in less s teels . Co nse que nt ly , fe w sys

temat ic s tud ies have been conduc ted

on the i r we ldab i l i t y o ther t han t o

de te rm ine t he e f f ec t o f we ld ing on

the i r mechan ica l p roper t ies and cor ro

sion resistance. In the f irst phase of

th is program the ef fects of e lements

such as C, N, Cr, Si, M n , M o , N i, P, S, Ti ,

N b , and Ta on the hot crack ing suscep

t ib i l i t y of Type 430 and Type 444L were

s tud ied .

A laboratory subscale Vare

s t ra in t we ldab i l i t y t es te r mod i f ied t o

a l low tes t ing w i t h a t r ave l ing w e ld ing

arc was used. The au gm ente d st ra ins

ach ieved on de fo rmat ion o f t he

w e l d

ment were con t ro l led a t va lues f rom

0.8 to 3.2%. The values of total crack

length (TCL) , number of cracks, and

max imum and m in imum c rack leng ths

were measured. The resul ts of th is

subscale Varest ra int test ing ind icate

tha t t he e lements exh ib i t ing t he

greatest in f luence on the hot crack ing

suscep t ib i l i t y were t he non-metallics

S, C, N, and P. Ot he r e lem ents pro m ot

ing hot crack ing inc lude Ti , Nb, and

Mn.

Based upon these results, a second

series of Type 430 and Type 444L

a l loys , wh ich sho u ld exh ib i t improv ed

res is tance to hot crack ing, we re pre

pared. This ser ies conta ined low levels

of S, C, N, and P and w ere s tabi l ized

with vary ing levels of T i , Nb, and Ta

added e i t he r s ing ly o r in comb ina t ion

to form al loys wi th a wi de range of

tota l s tab i l ize r / (C + N) rat ios. H ot

c rack ing suscep t ib i l i t y , we ldment

toughness , c ross -we ld t ens i le p roper

t ies,

and res is tance to in tergranular

co r ros ion were de te rm ined fo r each o f

these alloys.

The resul ts of the hot crack ing inves

t igat ion conf i rm the ear l ier resul ts that

low su l f u r and phosphorus con ta in ing

unstabi l ized Types 430 and 444L exhib

i t acceptable res is tance to hot crack ing

for (C + N) contents less than 0.03%.

Acceptable levels of Tota l Stabi l izer /

(C + N) rat io were de term ine d for

both the Type 430 and Type 444L base

compos i t ions s tab i l i zed w i t h T i , Nb ,

Ta, T i + Nb , and Ti + Ta. Stab i l izat ion

of

th e

Type 444L

w i th the Ta +

Nbwas

found unacceptable at a l l levels .

Gas tungsten arc weld ing tests on

0.225 in. (5.7 mm) t hic k m ater ia l of

Typ e 430 and T ype 444L does no t resu I t

in any s igni f icant reduct ion of cross

we ld y ie ld o r t ens i le s t reng ths com

pared to that of the base meta l . The

add i t ion o f ca rb ide s tab i l i z ing e le

ments e i ther had no ef fect on the

tensi le proper t ies or caused s l ight

increases in the s t rength. Cross-weld

Paper based on presentation made at the

61st AWS Annual Meeting held in Los

Angeles, California, during April

13-18,

1980.

D. H. KAH is Senior Research Metallurgist

and D . W. D ICKINSON is Supervi

sor—Welding Research and Development,

Research

Center,

Republic Steel Corpora

tion, Independence, Ohio.

tens i le fa i lures of both a l loys occur red

pre fe ren t ia l l y in t he we ld meta l . The

Type 444L a l loys exhib i ted less tough

ness than the Type 430 alloys and

stabi l izat ion of Type 444L wi th Ti

reduced toughness more t han d id t he

o ther s tab i l i z ing add i t ions .

Research ind icates that adequate

resistance of Types 430 and 444L to

both hot crack ing and in tergranular

co r ros ion is ob ta in ed wh en the

(C + N) con ten t is co nt ro l led at a

value less tha n 0.04%, in co nj un ct i on

wi th a T i add i t ion ac cord ing t o t he

re lat ion Ti

>

12.5 (C + N) w it h a max

imum Ti content of 0 .65%. The same

two a l loys can a lso be ef fect ive ly s tabi

l ized w i th Ta i f the (C + N) cont en t is

less than 0.025% and the Ta/(C + N)

rat io is greater than 25 wi t h a ma xi

mum Ta content of 0 .9%. Type 444L

a l loys s tab i l i zed w i t h a com b in a t io n o f

Ti + Nb or T i + Ta a lso exh ib i te d ade

quate res is tance to fus ion zone hot

c rack ing and in te rg ranu la r co r ros ion .

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

The annealed ferr it ic stainless steels

conta in ing 16 to 18% Cr of fer accept

ab le ox ida t ion and cor ros ion res is

t ance in many env i ronments rang ing

f rom rura l a tmospheres to aggress ive

hot ac id so lut ions. Their pr imary

advantages inc lude lower mater ia l cost

t han t he more common ly used aus ten

it ic stainless steels and a greater

resistance to stress corrosion cracking.

A l t hough these p roper t ies make the

al loys commerc ia l ly at t ract ive, they

st i l l exhib i t severa l s ign i f icant draw

backs that l im it the ir use. These

inc lude reduced fo rmab i l i t y , suscep t i

b i l i t y t o em br i t t lem ent , suscep t ib i l i t y

t o ho t c rack ing dur ing we ld ing , and

the adverse ef fect of weld ing on their

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

135-s



mechanical proper t ies ( toughness and

duct i l i t y ) and res is tance to in tergranu

lar cor ros ion. However , the advent of

t he a rgon-oxygen decarbur iza t ion p ro

cess (AOD) for ref ining stainless steels

has resul ted in the abi l i t y to produce

al loys w i th lo w inters t i t ia l conte nts

and conse quen t ly s ign i f ican t im prov e

ments in the above proper t ies.

The subject of so l id i f icat ion hot

cracking in austenit ic stainless steels

dur in g we l d in g has been the sub jec t o f

numerous invest igat ions over the years

(Ref. 1, 2). Ho we ve r, because of the ir

genera l l y in fe r io r we ldab i l i t y , t he sus

cept ib i l i t y of fer r i t ic s ta in less s teels to

sol id i f icat ion hot crack ing has not

been examined in de ta i l . A num ber o f

theor ies have been proposed to

expla in the ex is tence of the hot crack

ing phenomenon. I n t he genera l case ,

hot crack ing or microf issur ing can

occur in tergranular ly in e i ther the

fus ion zone o r t he hea t -a f f ec ted zone

o f a we ld m e n t . In either case, the

propensi ty for hot crack ing has been

related to the presence of a tensile

st ress across a l iquated boundary. The

most p laus ib le theory for hot crack ing,

that of the general ized gra in boundary

l iqua t ion mechan ism, p roposes t ha t

microsegregat ion of a l loy ing and re

s idua l e lements t o t he g ra in bound

ar ies or in terde ndr i t ic region s occurs

dur ing so l id i f i ca t ion . Th is segrega t ion

produc es a solute r ich region that

exh ib i t s a lower m e l t ing po in t t han

that of the matr ix. These regions,

wh ich exh ib i t a l iqu id f i lm wh i le t he

matr ix is

so l id ,

serve as nucleat ion

points for microf issures tha t form as a

result of the stresses produced by

shr inkage, phase t ransformat ions, or

external tens i le rest ra int .

Ferrit ic stainless steels are also sus

cep t ib le t o embr i t t lement ( loss o f

toughness a nd /o r duct i l i t y ) as a resul t

of we ld in g (Ref. 3, 4). If the mate r ials

are not fu l ly fer r i t ic at h igh tempera

tu res, a smal l vo lu me f ra ct ion of aus

ten i t e may be f o rmed; t h is w i l l t r ans

form to m ar tens i te dur ing co ol in g as a

resul t o f the weld ing thermal cyc le.

The format ion of very large fer r i te

g ra ins and /o r t he f o rmat ion o f g ra in

boundary mar tens i te in the fus ion

zone o r hea t -a f f ec ted zone (HAZ)

leads to decreased duct i l i t y and tough

ness of as-w elde d mater ia ls because of

the hard and br i t t le nature of the

mar tens i te . For mater ia ls that do not

form any mar tens i te dur ing the w e l d

i ng ope ra t ion , g ra in g ro wth in t he

fus ion and heat -af fected zones wi l l be

even more exaggerated and toughness

wil l again be decreased. I t has been

suggested that addit ives such as B, A l ,

V, or Zr might fo rm pre c ip i ta tes th at

w ou ld inh ib i t g ra in g ro wth in t he HAZ

and that T iN par t ic les might help to

cont ro l the gra in s ize of the fus ion

zone (Ref. 5).

The ferr it ic stainless steels are also

suscep t ib le t o a h igh - tempera tu re

embr i t t lement where t he s tee l may

lose duct i l i t y or toughness on water

quench ing o r a i r coo l ing f rom temper

atures in excess of 2000°F (1093°C)

(Ref . 6 , 7) . The embr i t t lement is

acco mp an ied by a severe g ra in g row th

associated wi th the d issolut ion of car

b ides,

e tc . , wh ich w ere ac t ing to in h ib

i t the mot ion of the gra in boundar ies.

Embr i t t lement resu l t s f r om one o f two

mechanisms—either a c luster ing or

segregat ing of carbon atoms in the

fer r i te mat r ix that are prevented f rom

pre c ip i ta t in g as carb ides by the rapid

c o o l i n g ,

or by the mar tens i te mecha

nism where regions re lat ive ly h igh in

carbon t ransform f i rs t to austeni te at

h igh t empera tu res and then t rans fo rm

to b r i t t le mar tens i t e on rap id coo l ing .

Th is t ype o f embr i t t lement can be

e l im in a ted by a pos tw e ld annea l ing

t rea tment .

The ferr it ic stainless steels also

suf

fer f rom notch sensi t iv i ty . The notch

toughness of these steels is af fected by

tem pera ture in a man ner s imi lar to

that of carbon and alloy steels, i .e. ,

t hey exh ib i t a duc t i le - t o - b r i t t le t r ans i

t ion temperature. For typ ica l fer r i t ic

s ta in less s teels th is t rans i t ion tempera

ture l ies at or above room temperature

and is a f un c t io n o f chem ica l co mp os i

t i o n , gra in s ize, heat t reatment , sect ion

size ,

and no tch con f igu ra t ion . I n these

a l loys an improvement in t he t rans i

t ion tem pera ture is most readi ly

achie ved by wa y of a decrease in the

inters t i t ia l co nte nt (C + N) an d, sec

ondly, by a decrease in grain size as

f iner gra ined mater ia ls exhib i t inher

ent ly bet ter toughness than coarse

gra ined mate r ia ls o f t he same compo

s i t ion (Ref. 8-10) . As a con sequ ence of

the sensit iv ity of these alloys to

no tches and impac t load ing , ce r ta in

precaut ions may be taken dur ing

w e l d i n g .

A preheat t reatment is of ten

used to help in reducing shr inkage

st resses and may a id in the prevent ion

o f any spon taneous c rack ing dur ing

t h e we ld i n g o p e r a t i o n .

Suscep t ib i l i t y t o in te rg ranu la r co r ro

s ion in the as-welded condi t ion a lso

plagues some of the ferr it ic stainless

steels. Several invest igators believe

that the format ion of austeni te at h igh

tempera tu res and the subsequen t p re

c ip i ta t ion of readi ly d issolved i ron car

b ides at gra in boundar ies leads to the

co r r o s i o n . Others have p roposed tha t

impover ishment o f t he g ra in boundary

aus ten i t e in ch r om ium c on ten t is

responsib le.

T h e m o s t c o m m o n l y a c c e p t e d t h e o

ry for in tergranular cor ros ion of the

ferr it ic stainless steels is that when

they are heated to h igh temperatures,

as in we ld in g , and subseque n t ly

c o o l e d ,

t he C and N in s o l id - so lu t ion

prec ip i ta tes a long gra in boundar ies at

in te rmed ia te t empera tu res , leav ing be

h i n d a c h r o m iu m - d e p le t e d z o n e t h a t

is suscept ible to corrosion (Ref. 11).

The normal h igh in ters t i t ia l levels

observed in commerc ia l s teels and

their rapid d i f fus ion rate in fer r i te

make i t impossib le to prevent prec ip i

t a t ion even by wa te r quench ing ,

except in very thin sect ions. I t has

been shown by Demo tha t p rec ip i t a

t ion o f

Cr

23

C

6

a n d

Cr

2

N

occurs f rom

about 925 to 1750°F (496 to 954°C) and

that sensi t izat ion or loss in cor ros ion

res is tance occurs by hold ing wi th in or

s low coo l ing t h rough the t empera tu re

range of 925 to

1300°F

(496 to

704°C)

(Ref. 7). At tem pe ratu res abo ve 1300°F

(704°C)

t he ch rom ium d i f f us ion ra te is

suf f ic ient ly rapid to h e a l or redis t r i

bu te ch rom ium to t he dep le ted a reas

as p rec ip i t a t ion occurs . There fo re , sen

s i t izat ion is not a pro ble m for a l loys

heat t reated in the temperature range

of 1300 to 1700°F (704 to 927°C).

Because of the sensi t izat ion k inet ics,

i t can be seen that a postweld anneal

ing t reatm ent w i l l be ef fect ive in

improv ing the cor ros ion res is tance of

we lded mate r ia ls. An impro vem ent in

res is tance to in tergranular cor ros ion

can a lso be achieved by s tabi l izat ion

wi th s t rong carb ide and /o r n i t r ide

fo rm ing e leme nts (T i , Nb , e t c . ) , wh ich

pre fe ren t ia l l y comb ine w i t h C and N

to p reven t p rec ip i t a t ion o f ch rom ium

carbides or n i t r ides, or by a reduct ion

in the tota l in ters t i t ia l (C + N) c o n

cent rat ion to ext remely low levels

( < 0.015%). The on ly prac t ical ap

proach for producing a l loys f ree of

sens i t i za t ion a f te r we ld ing us ing e i t he r

c o n v e n t i o n a l o r A O D s t e e lm a k in g

techniques is to add stabi l iz ing e le

ments.

O b j e c t i v e

The p r imary ob je c t ive o f t h is inves t i

gat ion was to determine the ef fect of

a l loy compos i t ion on t he ho t c rack ing

sus cep t ib i l i t y o f the 16 to 18% Cr fer r i t

ic s ta in less s teels . A second object ive

was to determine the ef fect of carb ide

s tab i l i za t ion and we ld ing on t he

toughness, duct i l i t y , and res is tance to

intergranular cor ros ion of a l loys exhib

i t ing good res is tance to hot crack ing.

M a t e r i a l s

Commercial Materials

In the in i t ia l par t o f the hot crack ing

inves t iga t ion , a se ries o f com merc ia l l y

available stainless steel mater ials was

inves t igated. These mater ia ls inc lud ed

a Type 304 austeni t ic s ta in less s teel , a

Typ e 430 ferr it ic stainless ste el, and an

e lec t ron beam me l ted

E-Brite

(26-1)

fer r i t ic s ta in less s teel . The co mp os i

t ions of these three alloys are pre

sente d in Table 1. These alloys served

136-s I A U G U S T 1 9 81



Tab le 1—Compositions o f C o m m e r c i a l

Stain less Steel Invest igated, Wt-%

c

M n

Si

P

S

Cr

Ni

M o

Cu

Al

N

O

Type

430

0.062

0.35

0.30

0.031

0.016

16.6

0.44

0.12

0.14

0.026

0.036

—

E-Brite

26-1

< 0.002

< 0.01

0.26

0.02

0.02

26.4

0.13

1.0

< 0.01

< 0 . 0 1

0.011

< 0.002

Type

304

0.060

1.76

0.50

0.029

0.012

18.3

9.1

0.35

0.28

0.029

0.038

—

a s a b a se l i n e f o r a n a l ys i s o f t h e l a b o

r a t o r y - p r e p a r e d m a t e r i a l s .

Labora to ry Materials—Phase I

T h e b a s i c e x p e r i m e n t a l a p p r o a c h i n

P h a s e I w a s t o e m p l o y a c l a s s i c a l a l l o y

d e s i g n , i. e. , t o m a k e m u l t i - l e v e l , s i n g l e

e l e m e n t v a r i a t io n s t o s t a n d a r d c o m p o

s i t i o n s o f T yp e s 4 3 0 a n d 4 4 4 L . T h e

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

g a t e d i s p r e s e n t e d i n T a b l e 2 . T h e C u

a n d N i c o n t e n t s w e r e h e l d c o n s t a n t

f o r t h e s e m a t e r i a l s .

A l l o f t h e a l l o y s w e r e m e l t e d b y

v a c u u m i n d u c t i o n as 5 0 l b (2 2 . 7 k g )

h e a t s ;

t h e s e w e r e s u b s e q u e n t l y s p l i t

i n t o t h r e e 1 6 l b ( 7 . 2 5 kg ) i n g o t s

u t i

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

d e s i r e d e l e m e n t a l v a r i a t i o n s . T h e 3 i n .

<) X 2.5 in . (j) x 8 in . (76 m m tj) X 64

m m ( j) X 2 0 3 m m ) i n g o t s w e r e p r e ss

fo rg ed to s labs 1 .25 X 3 i n . x L

(32 X 76 m m x L) us ing t h e t e m

p e r a t u r e r a n g e o f 2 0 5 0 ^ 1 4 0 0 ° F

( 1 1 2 0 ^

7 6 0 °C ) , a i r c o o l e d , a n d c o n d i

t i o n e d b y g r i n d i n g . S l ab s h a v i n g t h e

d i m e n s i o n s o f 1 .1 2 5 x 3 x 6 i n .

( 2 9 X 7 6 x 1 5 2 m m ) w e r e s o a ke d a t

2300°F ( 1 2 6 0 °C ) , r e d u ce d t o 0 . 2 2 5 x 3

i n .

x L (5.7 x 76 m m x L) in th re e

p a s se s at t e m p e r a t u r e s o f 2 1 5 0 , 1 9 6 0 ,

a n d

1770°F

( 1 1 7 5 , 1 0 7 0 , a n d 1 9 6 5 °C ) ,

a n d f l a t t e n e d .

Tab le

2-Ranges

o f E lementa l Var ia t i ons

Examined fo r t he Study o f We ld Hot

Cracking in Ferr i t ic Stain less Steels—Phase

I, W t - %

C

Cr

Si

Al

M n

M o

N b

Ti

P

S

Ta

Type

430

al loys

0.004-0.099

15.4-20.0

0.25-1.45

0.02-0.70

0.10-0.70

0.10-2.2

0-1.6

0-0.74

0.008-0.052

0.006-0.061

—

Type

444

L

al loys

0.01 -0.05

0.28-0.88

1.6-2.5

0.23-1.03

0.09-0.44

0.005-0.066

0.45-0.92

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

b o x a n n e a l i n a ir w i t h a 4y2 h o u r ( h )

s o a k a t t h e p e a k t e m p e r a t u r e o f 1500°F

( 8 1 5 ° C ) . T h e p l a t e s w e r e s e c t i o n e d t o

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

w e r e g r o u n d t o 0 . 2 0 0 x 1 x 6 i n .

( 5 X 2 5 X 1 5 2 m m ) f o r t h e h o t c r a c k

ing t es t s .

Labora to ry Mater ia l s -Phase I I

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

i t b e c a m e o b v i o u s t h a t a s e c o n d s e r ie s

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

c o n t a i n e d l o w l e v e l s o f S, C , N , a n d P

a n d w e r e s t a b i l i z e d w i t h v a r y i n g l e v e l s

o f T i , N b , a n d T a a d d e d e i t h e r s i n g l y o r

i n c o m b i n a t i o n . T h e ra n g e o f e l e m e n

t a l v a r i a t i o n s i n v e s t i g a t e d a re p r e

se n t e d i n T a b l e 3 .

Tab le

3—Ranges

o f E lementa l Var ia t i ons

Examined fo r t he Study o f We ld Hot

Cracking in Ferr i t ic Stain less

Steels—Phase

II ,

W t - %

c

N

Ti

Ta

Type 430

al loys

0.001 -0.032

0.014-0.021

0-0.67

0-1.41

T yp e 444L

al loys

0.007-0.035

0.010-0.019

0-0.67

0-1.06

Ti + Nb: Ti

N b

Ti + Ta: Ti

Ta

Ta + Nb: Ta

N b

—

-

-

0.01-0.22

0.15-0.45

0.12-0.35

0.34-0.68

0.33-0.66

0.16-0.57

A l l o f t h e a l l o ys i n Ph a se I I w e r e

v a c u u m i n d u c t i o n m e l t e d as 5 0 l b ( 22 .7

kg ) h e a t s a n d ca s t as a s i n g l e i n g o t 4 %

i n .

<) X 4 i n .

<>

X 1 0 i n . ( 1 2 1 m m

(j) x 102 mm cj) X 254 m m ). Th ey w e re

f o r g e d ,

c o n d i t i o n e d , a n d h o t r o l l e d t o

pla te s 0.5 X 5 in. X L (13 X 127

m m X L ) a t t h e s a m e t e m p e r a t u r e s a s

in Phase I. T h e p l a t e s w e r e t h e n c o l d

ro l l e d t o e i t h er 0 .225 x 5 x L

(5.7 X 127 X L) or 0.050 X 5 in . X L

( 1 .3 X 1 2 7 m m X L ) a n d a n n e a l e d a t

t e m p e r a t u r e s r a n g i n g f r o m 1 5 0 0 t o

2000°F (815 to 1090°C) f o r e i t h e r 1 5 o r

6 0 m i n u t e s ( m i n ) i n s a l t , a i r c o o l e d t o

1 4 0 0 °F ( 7 6 0 °C ) , a n d w a t e r q u e n c h e d

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

H o t C r a c k i n g

Procedures

The Varestra in t and subsca le Vares

t ra in t tests have been the most w ide ly

used tests fo r de termin ing the hot

cracking suscept ib i l i ty in the fusion

and hea t -a f fec ted zones o f we lded

mater ia ls. The major d i f fe rences be

tween these tests are :

1.

The subscale test uses a sta tion ary

arc spot we ld on th in mater ia ls wh i le

the Va restra in t test uses a t rave l ing arc

weld on heavy mater ia ls.

2.

The m eth od o f st ra in ing the

mater ia ls.

In th is invest iga t ion the subsca le

Varestra in t un i t was redesigned to use

a t rave l ing arc we ld and w i l l be

re ferred to as a mod i f ie d subsca le Va

restra in t test . The opera t iona l se

quence fo r th is test consists o f p roduc

ing a t rave l ing bead on p la te w e ld on

the sample mater ia l using the GTAW

process. The we ld i ng proce dures used

are lis ted in Tab le 4. At an app ropr ia te

t ime in the cycle the specimen is

de fo rmed by an a i r -ac tua ted d ie b lock

to prod uce a g iven st ra in . Th is de fo r

ma t ion p roduces an augmen ted s t ra in

a t the top surface o f the specimen tha t

can be ca lcu la ted as sh ow n in equa

t ion (1) :

t / 2

r i .

e

=

X

(D

w h e r e e = augm en ted s t ra in ( in . / i n . )

o r ( m m / m m ) , t = sp e c i m e n t h ickn e ss

( in . ) o r (m m ), and R = rad ius o f curva

tu re o f d ie b lock ( in . ) o r (mm).

The augmen ted s t ra ins u t i l i zed we re

0.8, 1.6, and 3.2%. The amount of

c rack ing obse rved in the we ldmen t a t

the to p surfa ce is take n as a mea sure o f

the ho t c rack ing suscep t ib i l i t y o f the

ma te r ia l .

A f t e r w e l d i n g a n d d e f o r m a

t ion the we lds we re p ick led fo r one

min u te us ing a so lu t io n o f 10%

H N 0

3

-

2% HF at 140°F (60°C), r insed in water,

and d r ied . The c lean we ldm en t was

then exam ined a t a mag n i f i ca t ion o f

X40 to de te rm ine the ex ten t o f ho t

c rack ing in bo th the fus ion and hea t -

a f fected zone s. The to ta l crack lengt h ,

ma x im um crack leng th , ave rage c rack

length , and number o f cracks were

de te rm ined fo r each samp le u t i l i z ing a

b i n o cu l a r m i c r o sco p e a n d a m i c r o m e

ter re t ic le .

Results

Commercial Materials

In o rder to estab l ish a ho t crac king

base l ine , a ho t cracking study was

conducted on the th ree commerc ia l

materia ls. The results of th is testing are

presented graph ica l ly in F ig . 1 .

From the data i t can be seen that the

overa l l resistance to ho t cracking o f

the h igh pur i ty, fe rr i t ic E-Brite 26-1 is

super io r to tha t o f Type 304. Commer

cia l Type 430, however, exh ib i ted as

much c rack ing a t an augmen ted s t ra in

of 0.8% as Type 304 did at an aug

m en ted s train of 3.2%. The average

total crack length (TCL) at 0.8%

aug

men ted s t ra in o f the commerc ia l Type

430 was 0.061 in. (1.5 mm ) co mp are d

to an average TCL fo r n ine labora tory

Type 430 al loys of 0.038 in. (0.97 mm)

wi th a standard dev ia t io n o f 0 .028 in .

(0.71 mm).

The genera l cr i te r ion se lected fo r

acceptab le resistance to ho t cracking ,

W E L D I N G R E S EA R C H SU P P LE M E N T 1137-s



Tab le

4—Welding

Procedures

Subscale Varestraint Test

T o r c h :

Type

Gas cup

Elec t rode : Type

D i a m e t e r

Extens ion f rom

co l lec t

T ip ang le

T i p - t o - w o r k

d is tance

Sh ie ld i ng :

Travel speed:

Vo l t age :

Cur ren t :

A i r accumula to r p ressure :

Bo l t t o rque :

Mechanical properties

Process:

Jo in t des ign :

F i l ler metal :

Sh ie ld i ng :

W eld ing co nd i t i ons f o r passes 1

Cur ren t

Vo l t age

Travel speed

Heat i npu t

Intergranular corrosion

Process:

Joint design:

Sh ie ld i ng :

W eld ing co nd i t i o ns f o r pass 1 :

Cur ren t

Vo l t age

Travel speed

Heat i npu t

and 2:

Wa ter -c oo le d gas t ungs ten a rc

N o.

10

2%

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

0.125 in.

1.40 in.

-

90 deg

0.055 in.

-

Argon gas @ 40 chf

10.5 ipm

14 V

300 A

40 psi

200 in.-lb

Gas tungsten a rc we ld ing (DCSP)

Square bu t t

N o n e

Arg on gas 25 cfh

300 A

12 V

8 ipm

27.0

k j / i n .

Gas tungs ten a rc we ld in g

Bead on plate

Argon gas (cover and back ing)

115 A

11 V

15 ipm

5.1 k j / i n .

w h i c h w a s u s e d t h r o u g h o u t t h e

r e m a i n d e r o f t h is i n v e s t i g a t i o n , w a s a

t o t a l c r a ck l e n g t h o f 0 . 0 2 0 i n . ( 0 . 5 1

m m ) a t 0 . 8% a u g m e n t e d s t r a i n . T h i s

r e p r e s e n t s a n i m p r o v e m e n t o f a t l e a s t

5 0 % i n h o t c r a c k i n g r e s i s t a n c e o v e r

t h a t o f c o m m e r c i a l T y p e 4 3 0. T h e c h o

s e n a u g m e n t e d s t r a i n o f 0 . 8 % i s g r e a t e r

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

e n c o u n t e r e d i n a w e l d i n g o p e r a t i o n .

P r i o r t o e x a m i n i n g t h e e f f e c t o f s p e

c i f i c e l e m e n t s o n h o t c r a c k i n g , i .e ., t h e

l a b o r a t o r y s t u d y , s o m e g e n e r a l o b s e r

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

w i l l b e n o t e d . F i g u r e 2 i l l u s t r a t e s a

t y p i c a l h o t c r a c k in c o m m e r c i a l T y p e

4 3 0 w h e n s u b j e c t e d t o t h e m o d i f i e d

s u b s c a l e V a r e s t r a i n t t e s t . T h i s s c a n n i n g

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

b l u n t e d d e n d r i t e s i n t h e c r a c k , w h i c h

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

l a c k o f l i q u i d f e e d m e t a l . T h i s

i n d i

c a t e s t h a t t h e d e n d r i t e i n t e r f a c e s w e r e

s t il l l i q u i d a t t h e t i m e o f d e f o r m a t i o n ,

w h i c h is c o n s i s t e n t w i t h t h e g e n e r a l

i z e d l i q u a t i o n t h e o r y f o r h o t c r a c k

i n g .

V i s u al e x a m i n a t i o n o f w e l d e d s p e c i

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

c r a c k l e n g t h s w e r e a s s o c i a t e d w i t h

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

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

P o o l s h a p e is a f u n c t i o n o f a l l o y c o m

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

i n p a r t i c u l a r t h e h e a t i n p u t . T e a r d r o p -

s h a p e d p o o l s a r e g e n e r a l l y m o r e s u s

c e p t i b l e t o h o t c r a c k i n g .

Labora to ry Material—Phase I

P l o t s o f t o t a l c r a ck l e n g t h vs . p e r

c e n t a l l o y i n g a d d i t i o n w e r e

c o n

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

a d d i

t i o n s a s i l l u s t r a t e d i n F i g . 3 f o r t h e S

c o n t e n t i n T y p e 4 3 0 a l l o y .

I n g e n e r a l , d u e t o t h e a m o u n t o f

s c a t t er o b s e r v e d , t h e h o t c r a c k i n g

t e n

d e n c i e s w e r e r e p r e s e n t e d b y s t r a i g h t

l i n e s . W h i l e t h e t o t a l r e a s o n f o r t h e

s c a t t e r h as n o t b e e n e x p l a i n e d , a t l e a s t

a p o r t i o n o f i t is d u e t o t h e s u b j e c t i v e

n a t u r e o f t h e c r a c k m e a s u r e m e n t a n d

t h e le v e l o f c r a c k i n g e n c o u n t e r e d . A t

l o w l e v e l s o f c r a c k i n g o f a b o u t 0 . 0 1 0

i n .

(0 .25 m m ) , a A TC L o f 0 .010 in . (0 .25

m m ) r e p r e s e n t s a 1 0 0 % v a r i a t i o n w h i l e

t h e s a m e A T C L a t a c r a c k i n g l e v e l o f

0 . 1 0 0 i n . ( 2 .5 m m ) r e p r e s e n t s o n l y a

1 0 %

v a r i a t i o n .

W h e n t h e d a t a a r e t r e a t e d a s s t r a i g h t

l i n e s , t h e s l o p e o f t h e l i n e r e p r e s e n t s

t h e r a t e o f c h a n g e o f t h e h o t c r a c k i n g

t e n d e n c y d u e t o t h e a l l o y a d d i t i o n .

F i g u r e 4 a n d T a b l e 5 s u m m a r i z e t h e

e f f e c t o f

0 . 1 %

c h a n g e s i n a l l o y e l e m e n t

a d d i t i o n o n t h e T C L o b s e r v e d a t 0 . 8%

a u g m e n t e d s t r a i n .

It

is r e a d i l y o b

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

1 8 %

C r a l l o y s t h a t S , C , P, a n d M n a r e

t h e p r i m a r y c o n t r i b u t o r s t o h o t c r a c k

i n g w h e r e S is a b o u t t h r e e t i m e s a s

d e t r i m e n t a l a s C a n d a b o u t 4 8 t i m e s as

d e t r i m e n t a l a s M n . W h i l e t h e e f f e c t o f

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

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

i n d i c a t e d t h a t it s e f f e c t w o u l d b e

s i m

i l a r t o t h a t o f C . T h e e l e m e n t s C r , A l ,

a n d S i e x h i b i t e d l i t t l e , i f a n y , e f f e c t o n

t h 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 o f t h e

1 6 t o 1 8 % C r f e r r i t i c s t a i n l e ss s t e e l s .

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

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

i ts c o n t e n t i n c r e a s e s f r o m 0 t o 2 .5 % .

T h e e f f e c t o f T i a n d N b o n h o t

c r a c k i n g is n o t as c l e a r b e c a u s e o f t h e

p r e c i p i t a t i o n o f c a r b o - n i t r i d e s , w h i c h

p r e v e n t s t h e s t u d y i n g o f T i a n d N b

d i r e c t l y . It w a s f o u n d t h a t a p l o t o f T C L

vs . N b / ( C + N ) c o u l d b e f i t b y a

s t r a i g h t l i n e a t t h e 0 . 0 3 % C l e ve l w h i l e

f o r t h e 0 . 0 6 % C l e ve l t h e r e i s a n a p p a r

e n t m a x i m u m . T h e s l o p e s o f t h e s e

l i n e s a r e q u i t e s m a l l a n d t e n d t o i n d i

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

m e n t a l e l e m e n t . A d d i t i o n a l l y , m e t a l l o

g r a p h i c e x a m i n a t i o n o f a n u m b e r o f

w e l d c r o s s s e c t i o n s f r o m t h e P h a s e I

m a t e r i a l s r e v e a l e d t h e f o l l o w i n g :

1.

T h e s o l i d i f i e d w e l d m e t a l w a s

ep i tax ia l ly r e l a t e d t o t h e p a r t i a l l y

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

a f f e c t e d z o n e .

2. M o s t o f t h e w e l d m e n t s s o l i d i f ie d

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

d r i t i c s t r u c t u r e . T h e s e s t r u c t u r e s a r e

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

is a f i n e e q u i a x e d d e n d r i t i c s t r u c t u r e .

3 . A l l o f t h e a l l o y s e x h i b i t e d s u b

s t a n t i a l g r a i n g r o w t h i n t h e h e a t -

a f f e c t e d z o n e .

4 .

U n s t a b i l i z e d o r u n d e r - s t a b i l i z e d

a l lo y s e x h i b i t e d u n t e m p e r e d m a r t e n

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

f u s i o n a n d h e a t - a f f e c t e d z o n e s . T h e

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

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

s i te w a s p r e s e n t a t v e r y l o w i n t e r s t i t i a l

c o n t e n t s .

L a b o r a t o r y Material—Phase II

B a s e d u p o n t h e r e s u l t s o f t h e h o t

c r a c k i n g i n v e s t i g a t i o n i n P ha s e

I,

a

s e c o n d s e ri e s o f T y p e 4 3 0 a n d T y p e

4 4 4 L a l l o y s t h a t s h o u l d e x h i b i t i m

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

p r e p a r e d .

T h i s s e r ie s c o n t a i n e d l o w

l e ve l s o f S , C , N , a n d P , w h e r e t h e

( C + N ) l e v e ls w e r e c o n t r o l l e d a n d

t h e s e m a t e r i a l s w e r e s t a b i l i z e d w i t h

v a r y i n g l e v e l s o f T i , N b , a n d T a .

T h e r e s u l t s o f t h e h o t c r a c k i n g

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

s u m m a r i z e d i n F ig s . 5 t h r o u g h 8 . I n

t h e s e f ig u r e s , t h e a l l o y v a r i a t i o n s w e r e

g r o u p e d i n t o t h o s e h a v i n g ( C + N )

l e v e l s o f a p p r o x i m a t e l y 0 . 0 3 % , a p p r o x i

m a t e l y 0 . 0 6 % , a n d i n o n e ca se as h i g h

a s a p p r o x i m a t e l y 0 . 0 9 % . T h e T C L a t

0 .8 % a u g m e n t e d s t r a in as a f u n c t i o n o f

t h e s t a b i l i z e r / ( C + N ) r a t i o w a s t h e n

p l o t t e d f o r e a c h a l l o y a n d g r o u p . T h e

138-s I

AUGU ST 1981



10.0

E

E

I- 7.5

O

z

UJ

* 5 . 0

o

<

tr

o

-J 2 . 5

<

15

3.2 % STRAIN

COMMERCIAL MATERIAL

1.6

STRAIN

-

0 . 8 % ST R A I N

E-BRITE

(26-1)

TYPE

4 3 0

TYPE

3 0 4

E-BRITE

(26-1)

- . 3 5 :?

x

- . 3 0 H

. 25

TYPE

4 3 0

TYPE

3 0 4

E-BRITE

(26-1)

TYPE

4 3 0

TYPE

3 0 4

UJ

. 2 0 -^

O

.15 Q£

O

Kio _i

- . 0 5 O

Fig. l—The hot cracking susceptibility of comm ercial stainless steels; EB 26-1,

Type 304, and Type 430.

-A -

- y^i

Fig.

2—A

scanning electron microscope

view ot a typical hot crack in Type 430.

7.0

E

x

O

5.0

U

<

O

3 0

•

•

.26

- . 2 2

.18

.14

.10

.06

O

UJ

<

rr.

o

0 .02 .04 .0 6 .08

SULFUR IN T Y P E 4 3 0 , %

Fig. 3—The variation of total crack length for Type 430 at 0.

augmen ted strain as a function of S content.

8

E

E

UJ*

H

3

- I

O

CO

o

<

10.0

7.5

5.0

r

P H A S E I

TY P E 4 3 0

PI

J_L

S C P Mn Cr Al SI Mo N

T i

Nb

TYPE 444L

_L_t

. 45

-.40

S Mo Si N

T i

Nb

- . 3 5

.30

- . 2 5

.20

.15

.10

- . 0 5

0

UJ

I -

_ l

o

co

O

_ l

CJ

I -

<

g. 4—Summary

of the change in total crack length for Types 430 and

a function of a 0.1 increase in solute content.

444L

Tab le

5—Effect

o f A l l oy ing Add i t i ons on Hot Crack ing o f Fer r i t i c Sta in less Stee l We lds

Element

C

Cr

Si

M n

Al

M o

P

S

Type 430

0.120

0.00046

0.00035

0.0079

0.00043

-0 .0021

0.0128

0.38

A TCL per 0 .1% so lu te

Type

4 4 4 L

l a l

N D

N D

-0 .0052

N D

N D

-0 .00025

N D

0.42

ND-Not determined.

cu r v e s p r e s e n t e d i n F i g s . 5 - 8 a r e a

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

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

R e m e m b e r i n g t h a t t h e c r i t e r i o n

a d a p t e d a s a b a s e l i n e f o r a c c e p t a b l e

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

m e r c i a l m a t e r i a l w a s 0 . 0 2 0 i n . ( 0 . 5 1

m m ) o f t o t a l c r a c k l e n g t h a t 0 . 8 %

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

t r i a l s c a n n o w b e a n a l y z e d .

T h e e f f e c t o f N b s t a b i l i z a t i o n o n 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 is s h o w n in F i g .

5 . I t ca n be seen tha t t he le ve l o f

c r a c k i n g i n c r e a s e s w i t h t h e ( C 4 - N )

c o n t e n t i n b o t h t h e T y p e 4 30 a n d T y p e

444L a l lo y s . T h e t o t a l c r a c k l e n g t h a l s o

i n c r e a se s w i t h i n c r e a s e i n N b , i. e .,

i n c r e a s e i n t h e N b / ( C + N ) r a t i o . F u r

t h e r m o r e , t h e t o t a l l e v e l o f c r a c k i n g is

l e ss i n t h e T yp e 4 4 4 L a l l o ys t h a n i n t h e

T y p e 4 3 0 a l l o y s . I n t h e T y p e 4 3 0 a l l o y s ,

t h e c r i t e r i o n o f 0 . 0 2 0 i n . ( 0 . 5 1 m m ) T C L

i s m e t o n l y f o r t h e l o w e s t ( C + N )

l e v el s w i t h N b / ( C + N ) r a ti o s b e l o w

a b o u t 2 . I n t h e T y p e 4 4 4 L a l l o ys t h e

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

( C + N ) l e ve l u p t o a N b / ( C + N )

ra t i o i n excess o f 16 .

T h e e f f e c t o f T a s t a b i l i z a t i o n o n t h 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 i s s h o w n i n

Fig . 6 . T h e t o t a l c r a ck i n g is l e ss t h a n

t h a t o b s e r v e d i n t h e N b s t a b i l i z e d

m a t e r i a l .

F o r t h e l o w ( C + N ) l e ve l i n

t h e T y p e 4 3 0 a l l o y , T a c o n t e n t s c o r r e

s p o n d i n g t o a T a / ( C + N ) r a t i o u p t o

a b o u t 3 6 ( 1 . 0 8 % T a ) p r o v i d e a c c e p t -

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



3 . 0

2.0

1.0

0

(C + N) « 0.06

1 \ l

— (C+N)W 0.03

1 \J

TYPE 444L.

C

o

.10 <

tr

.0 8 o

.0 6 _i

<

J .04 H

O

02 I -

2 4

Fig

of

4 8 12 16 2 0

N b / ( C + N )

. 5—The effect of Nb content on the hot cracking susceptibility

Types

430 and

444L

at 0.8 augmented strain.

8 16 2 4

T a / ( C + N )

Fig. 6—The effect of

Ta

content on the hot cracking susceptibility of

Types 430 and

444L


3.0

12 16 2 0

T i / ( C + N )

Fig.

7—The

effect of Ti content on the hot cracking susceptibility of

Types 430 and

444L

at

0.8

augmented strain.

E

E

5 3

z

UJ

* 2

o

<

ce

o

<

o

^^^^

( C +N ) .03

(Nb + Ti )

TYPE 444L

M T I

+

To)

-

-

4 8 12 16 2 0

T i + T a / C + N OR Nb + T i / C + N

.14 ~

I

I

12 I-

O

z

.io UJ

.06 *

o

<

.0 6 (E

O

.0 4 -J

i

.02 O

24

Fig. 8—The

effect of dual stabilization on the hot cracking suscep-

tibilty ot Type

4441


ab le resistance to ho t cracking . In the

Type 444L a l loys, acceptab le resistance

to ho t crack ing is ob ta in ed a t lo w

(C + N) levels for a l l Ta levels investi

ga ted .

Ac cep tab le resistance to ho t

crac king is ob ta i ne d a t h ighe r (C + N),

i .e., 0.06%, up to a Ta /( C + N) ratio of

about 24 (1.44% Ta).

The e f fect o f T i stab i l iza t ion on the

ho t c rack ing susce p t ib i l i t y is show n in

Fig. 7. For the lo w (C + N) Ty pe 430

a l loy acceptab le resistance to ho t

c rack ing is ob ta in ed up to a T i /

(C + N) ra t io o f abo ut 12 . fo r the low

(C + N) Typ e

444L

a l loy ac cepta b le

resistance to ho t cracking is ob ta ined

up to a T i / (C 4- N) ratio of about 24.

Dua l s tab i l i za t ion o f Type 444L w i th

T i + Nb a nd T i + Ta was a lso exam

i n e d . The results are presented in Fig.

8 . Ac cep tab le resistance to ho t crack

ing is observ ed wi th b o th o f these dua l

stab i l izers up to a sta b i l iz er / (C + N)

ra t io o f about 20 .

In summary, i t appears tha t accept

ab le resistance to ho t cracking can be

obt a in ed a t low (C + N) leve ls w i t h T i ,

Ta,

o r dua l s tab i l i za t ion , bu t no t w i th

Nb a lone.

M e c h a n i c a l P r o p e r t i e s

Procedures

Each p la te f rom the Phase I I mater i

a ls was sec t ioned long i tu d ina l l y a long

the p la te cen te r l i ne , su r face g round in

the v ic in i t y o f the we ld jo in t , c leaned ,

and we lde d w i th a two -pass gas tun g

sten arc process as ind ica te d in Fig. 9.

The we ld ing p rocedu res a re de ta i led

in Table 4.

The p la tes were rad iographed a f te r

we ld ing to ensu re tha t they we re

de fec t - f ree . The we lds we re sec t ioned

as sh ow n in Fig. 9 to p rov ide f lat

tens i le , ha l f -s i ze Cha rpy V -no tc h im

pac t , and m e ta l log raph ic samp les. The

no tch on the we ld me ta l Cha rpy sam

p les was loca ted a t the we ld center-

l i ne ,

wh i le the no tch on the hea t -

a f fected zone samples was loca ted a t

the 50% we ld me ta l , 50% hea t -a f fec ted

zo n e l o ca t i o n .

The impact and tensi le samples

were tes ted acco rd ing to s tanda rd

ASTM pract ices.

Results of Tensile Tests

The resu l ts o f the tensi le test ing

ind ic a te tha t , in gene ra l , the ten si le

and yie ld st rengths o f the base meta l

vary on ly s l igh t ly as the T i o r Ta stab i l

iza t ion increases in Type 430, a l though

some random va r ia t ions we re no ted

w i th Ta add i t i ons . The tens i le

strengths were o f the order o f 65 to 70

ksi (448 to 483 MPa) and the yie ld

strengths 40 to 45 ksi (276 to 310 MPa).

The c ross-we ld samp les exh ib i ted ap

p rox ima te ly the same tens i le s t reng th ,

bu t the y ie ld st rength averaged about

5 ksi (34 MPa) higher. Fai lure in the

cross-we ld samples was a lways in the

we ld me ta l w i th T i s tab i l i za t ion and in

e i ther the base meta l o r heat-a f fected

zone w i th Ta s tab i l i za t ion .

The e longa t ions exh ib i ted by the

cross-we ld samp les we re reduced to

abou t 20 to 30% in 2 in . (50.8 mm ) f ro m

140 -s I A U G U S T 1 9 81



METALLOGRAPHY

SAMPLE

CHARF

(2-1/2 )

-

6 3 . 5

mm

(2-1/2 )

5.72 mm (.225 )

Fig. 9—Schematic illustration of sample location and sectioning for mecha nical

property determination.

va l u e s o f a b o u t 3 2 t o 4 0 % i n t h e b a s e

m e t a l s a m p l e s . It i s u n c l e a r a s t o

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

a r e s u l t o f w e l d i n g , s t a b i l i z a t i o n , o r

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

I n b a s e m e t a l s a m p l e s o f T y p e 444L

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

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

s t a b i l i ze d w i t h T i , T i + N b , o r T i + T a .

T h e t e n s i l e s t r e n g t h r a n g e s f r o m 7 0 t o

7 7 ks i ( 4 8 3 t o 5 3 1 M Pa ) a n d t h e y i e l d

s t r e n g t h f r o m a b o u t 4 6 t o 5 3 ks i ( 3 1 7 t o

3 6 5 M P a ) . T h e t e n s i l e s t r e n g t h i n

c r e a se d f r o m a b o u t 7 0 t o 8 8 ks i ( 4 8 3 t o

6 0 7 M P a ) f o r a l l o y s s t a b i l i z e d w i t h T a

o r T a + N b , w h i l e t h e y i e l d s t r e n g t h

i n c r e a s e d f r o m a b o u t 4 6 t o 6 3 ks i ( 3 1 7

t o 4 2 7 M P a ) f o r a l l o y s s t a b i l i z e d w i t h

Ta.

In a m a n n e r s i m i l a r t o t h e T y p e 4 3 0

a l l o y s , t h e c r o s s - w e l d s a m p l e s o f T y p e

4 4 4 L g e n e r a l l y h a d a s l i g h t l y h i g h e r

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

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

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

t h e e x c e p t i o n o f a l l o y s s t a b i l i z e d w i t h

T i + T a , a l l o f t h e c r o s s - w e l d s a m p l e s

f a i l e d in t h e w e l d m e t a l , i n d i c a t i n g

t h a t s t a b i l i z e d T y p e 4 4 4 L m a y b e p r o n e

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

o f c r o s s - w e l d s a m p l e s w e r e al s o l o w e r

t h a n t h o s e o f t h e b a s e m e t a l .

Resul ts of Impact Test ing

I n o r d e r t o c h a r a c t e r i z e t h e i m p a c t

p r o p e r t i e s o f t h e s e a l l o y s , t h e i m p a c t

e n e r g y a t 1 4 0 °F (60°C) a n d t h e 1 5 f t - l b

( 20 .3 J) t r a n s i t i o n t e m p e r a t u r e w e r e

o b t a i n e d u s i n g h a l f - s i z e C h a r p y V -

n o t c h s a m p l e s . R e s u l ts f o r t h e T y p e

4 3 0 a l l o y s e x h i b i t m u c h s c a t t e r a n d n o

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

s t a b i l i z a t i o n w i t h e i t h e r T i o r T a . T h e

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

t e n t l y e x h i b i t a l o w e r i m p a c t e n e r g y a t

140°F (60°Q) a n d a h i g h e r 1 5 f t - l b

( 20 .3 J) t r a n s i t i o n t e m p e r a t u r e t h a n

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

z o n e s a m p l e s .

T h e i m p a c t e n e r g i e s a t 1 4 0 °F (66°C)

f o r s t a b i l i z e d T y p e 4 4 4 L a l l o y s w e r e a l l

b e l o w t h o s e e x h i b i t e d b y t h e T y p e 4 3 0

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

w e r e e x h i b i t e d b y a l l o y s s t a b i l i z e d

w i t h e i t h e r T a o r T a + N b . L i k e w i s e ,

t h e c o r r e s p o n d i n g 15 f t - l b ( 2 0. 3 J)

t r a n

s i t i o n t e m p e r a t u r e s w e r e e q u a l t o o r

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

T y p e 4 3 0 a l l o y s .

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

4 4 4 L a l l o y s a r e n o t a s t o u g h a s t h e

T y p e 4 3 0 a l l o y s a n d t h a t s t a b i l i z a t i o n

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

N b o r T a is d e t r i m e n t a l t o t o u g h n e s s

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

e l e m e n t s . T h i s e ff e c t o f T i o n t o u g h

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

o b s e r v a t i o n s b y B o n d a n d o t h e r s ( R e f .

1 0 ) .

H o w e v e r , i n t h i s i n v e s t i g a t i o n n o

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

t o u g h n e s s d e c r e a s e s a s t h e T i c o n t e n t

i n c r e a se s .

I n t e r g r a n u l a r C o r r o s i o n

Procedures

T h e a ll o y s w e r e e x a m i n e d t o d e t e r

m i n e if t h e y w e r e s u s c e p t i b l e t o i n t e r

g r a n u l a r a t t a c k ( I G A ) o r s e n s i t i z a t i o n

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

w e l d e d a s i n T a b l e 4 w e r e s u b j e c t e d t o

P r a c t i c e Z ( c o p p e r - c o p p e r s u l f a t e - 1 6 %

s u l f u r i c a c i d o r M o d i f i e d S t ra u s s t e s t )

o f t h e p r o p o s e d A S T M s t a n d a r d f o r

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

l a r a t t a ck i n f e r r i t i c s t a i n l e ss s t e e l s . T h e

St rauss t es t is t h e leas t seve re o f t h e

r e c o m m e n d e d t es ts f r o m t h e s t a n d

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

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

T h e S tr a us s t e s t is r e c o m m e n d e d

s p e c i f i c a l l y f o r us e w i t h t h e f e r r i t i c

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

1 6 t o 2 0 % ; i t d e t e c t s s u s c e p t i b i l i t y t o

I G A a s s o c i a t e d w i t h o n l y t h e p r e c i p i

t a t i o n o f c h r o m i u m c a r b i d e s a n d / o r

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

m i u m - d e p l e t e d z o n e s in b o t h s t a b i

l i z e d a n d n o n - s t a b i l i z e d m a t e r i a l s . T h e

p r i m a r y e v a l u a t i o n c r i t e r i o n is a 1 8 0

d e g , 2 -T b e n d tes t ; t o pas s o r t o f a i l i s

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

f i s s u re s o c c u r i n t h e b e n t r e g i o n .

T h e a x is o f t h e b e n d w a s l o c a t e d a t

t h e in t e r f a c e o f t h e h e a t - a f f e c t e d z o n e

a n d b a s e m a t e r i a l . V i s u a l e x a m i n a t i o n

o f t h e w e l d m e n t f o r g r a i n d r o p p i n g

a n d c o r r o s i o n r a t e d a t a w a s a l s o

u t i

l i z e d .

2.0

.02

0 6

.080 4

C + N , %

Fig. 10—The effect of Ta on the intergranular corrosion resistance of

Types 430 and

4441.

s«

a.

IT

LU

N

_J

m

\

co

1.6

1.2

.8

Ta»27.5(C +

X)

Af Nb + Ta-20( C+N)

X^-'**̂ — —

^

Ti 12.5

Ti + Nb 0

I

9(C4

1

(C + N)

» T l+ l

N)

a =

0 .01 .02 .03 .04 .05 .06 .07 .08

C + N , %

Fig. 11—The effect of stabilization on the intergranular corrosion

resistance of Types 430 and

4441.

W E L D I N G R E S E A R C H S U P P L E M E N T I 1 4 1 - s



Results of Corrosion Testing

The resu l ts o f the in te rgranu lar cor

rosion tests were p lo t ted fo r each

g roup o f ma te r ia l s (examp le shown in

Fig. 10 for the Types 430 and 444L

a l loys stab i l ized wi th Ta). I t can be

no ted tha t a re la t io nsh ip exists be

twe en the in te rs t i t i a l con ten t (C + N )

and the stab i l izer content o f the a l loy.

The measured corrosion ra te o f the

Ta -con ta in ing a l loys was gene ra l l y

h igher, and they appeared to be more

suscep t ib le to g ra in d ropp ing in the

Modi f ied Strauss test .

It

is appa rent tha t a cr i t ic a l stab i

l i ze r / in t e rs t i t i a l ra t io ex is ts fo r w h ic h

acceptab le resistance to in te rgranu lar

corr osio n is ob ta in ed . For the Ta stab i

l ized a l loys, Ta contents

>

27.5

(C + N) con fer ac cepta b le resistance

to in te rgranu lar a t tack. Th is va lue rep

resen ts app rox ima te ly tw ice the Ta

requ i red

stoichiometrically

to t ie up

the C and N as TaC and TaN.

F igure 11 summarizes the resu l ts o f

a l l the in te rgranu lar corrosion tests

co n d u c t e d o n w e l d e d sp e c i m e n s o f

Types 430 and 444L. The c r i t ica l va lues

o f s tab i l i z ing e lemen ts requ i red to

obta in resistance to in te rgranu lar a t

tack fo r these a l loys in the as-we lded

cond i t ion a re as fo l lows:

1. Ta

27.5 C + N)

2. Nb + Ta

>

20.0 (C + N)

3. Ti > 12.5 (C + N)

4. Ti + Nb

>

9.0 (C + N)

The best cho ice o f e lements fo r use

in stab i l iz ing these a l loys is e i ther T i o r

a com b in a t io n o f Ti + Nb .

It shou ld be no ted tha t the T i

c o n

ten t requ i red fo r stab i l iza t ion is

approximate ly 3 .4 t imes the average

factor o f 3 .7 requ i red to t ie up a l l o f

the C and N as TiC and TiN. It is

general ly necessary to use and excess

of T i to ensure stab i l iza t ion and

resistance to

IGA

because the T i may

a l so co m b i n e w i t h t h e

O

a nd S in th e

steel.

C o n c l u s i o n s

1.

Th is inves t iga t io n has resu l ted in

the des ign o f a mo d i f ie d subsca le t rav

e l ing Varestra in t test tha t can be

u t i

l i zed in the s tudy o f the ho t c rack ing

resistance o f meta l l ic mater ia ls. The

ho t c rack ing da ta ob ta ined tend to

agree w i t h the resu lts expe cted f ro m

the gene ra l i zed l i qua t ion theo ry fo r

ho t c rack ing .

2. The ho t c rack ing suscep t ib i l i t y o f

16 to 18% Cr ferri t ic stain less steels is at

leas t pa r t ia l l y dependen t on the chem

ica l cons t i tu t ion . Ho t c rack ing i s p ro

mo te d by the fo l low ing e lemen ts in

the app rox ima te o rde r l i s ted :

S > C > N > N b > T i > P > M n

The C co nte nt is especia l ly cr i t ica l

because o f i ts de t r imen ta l i n f luence

on not on l y ho t crac king , bu t a lso on

m i c r o s t r u c t u r e , d u c t i l i t y , t o u g h n e ss ,

and corrosion resistance o f bo th the

fus ion zone and hea t -a f fec ted zone .

N i t rogen appa ren t l y behaves s im i la r l y ,

and bo th e lemen ts shou ld be l im i ted

to a level less than 0.025%.

Unstabilized

Types 430 and 444L

exh ib i t acceptab le resistance to ho t

crac king fo r (C + N) c onte nts less

than 0 .03% i f the S is ma in ta ine d a t a

low leve l . Acc ep tab le res is tance to ho t

cracking can be ach ieved in Types 430

and 444L stab i l ized w i th T i , Ta ,

Ti + Nb , or Ti + Ta i f th e (C + N )

co nte nt is co ntr o l l ed a t leve ls less than

0.04%.

3. In genera l , we l d i ng caused no

de t r imen ta l e f fec ts on the tens i le

prope rt ies o f Types 430 and 444L. Y ie ld

strengths were increased about 5 ksi

(34 MPa) and e long a t ions w e re de

creased, bu t i t was not c lear whether

th is was a resu l t o f we ld ing o r an iso

t ropy o f the mater ia ls. Some increase

in tensi le st rength was noted in Type

444L stab i l iz ed w i th Ta or Ta + Nb .

Cross-we ld tensi le fa i lu res in Types

430 and

444L

a re genera l ly in the we ld

me ta l ,

part icu la r ly when T i is used fo r

stab i l iza t ion . Type 444L appears to be

prone to we ld meta l fa i lu res. The

impact resu l ts exh ib i ted mu ch sca t te r

but do ind ica te tha t the Type

444L

a l loys are less tough than the Type 430

a l loys; they a lso ind ica te tha t T i stab i l

i za t ion is mo r e de t r im en ta l to tou gh

ness than o the r s tab i l i z ing e lemen ts .

4. Types 430 and 444L w i t h (C + N)

contents less than 0.04% are not sus

cep t ib le to IG A a f t e r w e l d i n g w h e n

stab i l i zed w i th T i acco rd ing to the

f o r m u l a T i

>

12.5 (C + N) or w it h Ta

acc ord in g to the f o rm ula Ta > 27.5

(C + N). Dua l stab i l iza t ion can a lso be

u t i l i zed w i th Type 444L to p reven t

susce p t ib i l i t y to IGA . A l loys success

ful ly pass the Strauss test i f the

(T i + Nb) or (T i + Ta )/ ( C + N) ra

t io > 9 or i f the (N b + Ta) / (C + N)

ratio is B > 20.

In con c lus ion th is inves t iga t ion has

shown tha t fe rr i t ic sta in less stee ls

c o n

ta in ing 16 to 18% Cr can be designe d to

provide adequate resistance to ho t

c r a ck i n g d u r i n g w e l d i n g a n d , by t h e

use o f stab i l iza t ion , re ta in usab le

mechan ica l p ropert ies and resistance

to in te rgranu lar a t tack in the as-

w e l d e d c o n d i t i o n .

Acknowledgments

The au tho rs acknow ledge the sup

po r t and con t r ibu t ions o f the i r c o l

leagues at the Republic Steel Research

Cen ter, in pa rt icu lar, G . D. Ries, J. M .

Haser, and J. B. Lee. They also

ack now ledge L. M . Huse , K. W eed en ,

and M. Dav is who pe r fo rmed the

e xp e r i m e n t a l w o r k .

References

1.

Puzak, P. P. and Rischall, H. 1957.

Further studies on stainless steel hot crack

ing.

Welding lournal

36 (2): 57-s to 61-s.

2.

Hull ,

F. C. 1967. Effect of delta ferrite

on the hot cracking of stainless steel.

Weld

ing lournal

46 (9): 399-s to 409-s.

3. Thielsch, H., 1951. Physical and

we ld

ing metallurgy of chro miu m stainless steels.

Welding lournal

30 (5): 209-s to 250-s.

4. Demo, J. J. 1977.

Structure, constitu

tion, and general characteristics of wrough t

ferritic stainless steels.

ASTM STP 619.

5. The So uthern Cross Steel Com pany

(PTY) Ltd., 1976. Cost saving with stainless

steel. 68.

6. Thielsch, H. 1950. We ld em brittlem ent

in chromium stainless steels.

Welding jour

na l

29 (3): 126-s to 132-s.

7. De mo , J. J. 1977. Mec hanism of high

temperature embrittlement and loss of cor

rosion resistance in AISI Type 446 stainless

steel. Corrosion 27

(12): 531 to 544.

8. Plum tree, A. and C ullb erg , R. 1974. The

influence of interstitial content on the duc

tile-brittle transition temperature of Fe-25

Cr ferritic stainless steels,

journal of Testing

and Evaluation

2 (9): 331 to 336.

9. Wright, R. N. 1971. Mechanical behav

ior and weldability of a high chromium

ferrit ic stainless steel as

a

function of purity.

Welding lournal

50 (10): 434-s to 440-s.

10. Semchyshen, M.; Bond, A. P.; and

Dundas, H. J. 1971. Effects of com position

on ductility and toughness of ferritic stain

less steels.

Toward Improved Ductility and

Toughness

Climax: 239 to 253.

11.

Demo, J. J., and Bond, A. P. 1975.

Intergranular corrosion and embrittlement

of ferritic stainless steels.

Corrosion

31 (1):

21-22.

Authors

See page 154-s in this

issue of the W elding journal

weldability-ferritic stainless steels

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