Tensile Properties of A514 Steel Butt Joints Containing Cluster Porosity

8/16/2019 Tensile Properties of A514 Steel Butt Joints Containing Cluster Porosity

1/5

Tensile Properties of A 5 1 4 Steel ButtJoints Containing Cluster Porosity

Tensile tests sugges t w eld inspection specifications fortensile applications could be relaxed for working stressdesign, n ot for limit stress design

B Y E. M . H O N I G , J R . A N D K . W. C A R L S O N

ABSTRACT. The e ffec t s o f c lu s te rpo ros i ty on the t ens i l e p roper t i es o fA514 s tee l bu t t we ldmen ts wereassessed . C lus te r po ros i ty was measu red bo th in t e rms o f the ac tua l to ta larea of pores and of the area of thec lu s te r ( inc lud ing meta l l igamen ts , o rwebs , tha t connec t po res ) . Resu l t sshowed tha t the t ens i l e s t reng th o f thewelded meta l i s no t s ign i f i can t ly reduced i f the area of pores and thec lu s te r a rea a re be low cr i t i ca l s i zes ;

however, duc t i l i ty is rap id ly redu cedun t i l these s i zes a re reached .

Cons idera t ion o f the imp l ica t ions o ft ens i l e t es t da ta on bo th work ings t res s des ign and l imi t s t res s des ignind ica te tha t re laxa t ion o f weld ingcod es may be con s ide red fo r ce r t a intens i l e load ing app l ica t ions i f thecodes a re based on work ing s t res sdes ign . Th i s wou ld be benef ic ia l inte rms o f reduced p ro jec t cos t s fo rweld rework . Re laxa t ion o f codes

E. M. HONIG, JR. is Metallurgist, U.S.

Army Construction Engineering ResearchLaboratory, P.O. Box 4005, Champaign, IL61820 and K. W. CARLSON is GraduateResearch Assistant, Dept. of Theoreticaland Applied Mechanics, University of Illi-nois, Urbana, IL 61801.

Paper to be presented at 57th AWS Annual Meeting, St. Louis, MO, May 10-14,1976.

based on l imi t s t res s des ign shou ldno t be cons idered fo r the cond i t ionso f po ros i ty covered in th i s s tudy.

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

Problem

There i s a need fo r a cce p tan cegu ide spec i f i ca t ions fo r welds basedon ac tua l mechan ica l behav io r o f as t ruc tu ra l we ld in any g iven app l ica

t i o n . To th is end i t is necessary to rel a te w e l d d i s c o n t i n u i t y c h a r a c t e r i st i cs — such as s i ze , type , shape , locat i on , o r i en ta t ion , and spac ing — tomechan ica l p roper t i es o f the weld .Such a re la t ion i s neede d to rep la cet h e e m p i r i c a l a p p r o a c h c u r r e n t l yused in mos t cases o f spec i f i ca t ion fo rs t r u c t u r a l w e l d s — a n a p p r o a c h t h a to f ten resu l t s in ove rdes igned o r un -d e r d e s i g n e d w e l d s .

Objective

Va r i o u s t y p e s o f w e l d d i s c o n t i n u

i t i es , such as c racks , po ros i ty and inc lu s ions , have been shown d i rec t lyr e s p o n s i b l e f o r p r e ma t u r e b r i t t l e f r a ct u r e o f s t r u c t u r a l c o mp o n e n t s . T h epurpose o f th i s s tudy was to eva lua tethe effect of clus ter porosi ty on thetens i l e p roper t i es o f A514 s tee l w e l dmen ts . Nondes t ruc t ive t es t s and s t a t i c

t ens i l e t es t s were u sed to es tab l i sht h e d e p e n d e n c e o f t e n s i l e p r o p e r t i e son c lu s te r po ros i ty s i ze .

Th is inves t iga t ion p rov ides a part ial bas is for the evaluat ion of inspect ion c r i t e r i a re la t ing a l lowab le d i scont inu i ty paramete rs to g iven l eve l s o fp e r f o r ma n c e . T h e s e c r i t e r i a w o u l dfulfi l l part of the needs s tated above.

P r o c e d u r e

T h e p r o c e d u r e c o n s i s t e d o f f a b r ic a t i n g t h e s p e c i m e n s , d e t e r m i n i n gthe i r t ens i l e p roper t i es , examin ingthe i r f rac tu re su r faces , and e v a lua t ing the rad iog raphs o f the welds .

MaterialsThe base meta l u sed was an ASTM

A514 g rad e F s t ruc tu ra l s t ee l . Thee l e c t r o d e w a s E 11 0 S . * T h e c h e mi c a lcompos i t ions o f the base and f i l l e rmeta ls are g iven in Ta ble 1 , and theirmec han ic a l p rop er t i es in Tab le 2.

Fabrication

T h e t e n s i l e s p e c i me n s w e r e f a b r ica ted f rom 6 x 10 f t (1.83 X 3.05 m)

'Minimum tensile and yield strengths 110and 98 ksi respectively, according to A W SStructural Welding Code, Table 4.1.1. Air-co s AX110 was used, although otherproprietary bare wire electrodes are available.

Table 1 — Chemica l Com position of A514 Base Metal (% In. Thick) and E110S Electrode (1/16 In. Diam)

Material

A514


2/5

A514 s teel p late s tock. The p lateswe re f lam e cut in to 10 X 36 in . (25 .4 X91 .4 cm) b lanks , and each o f thesewas sawed in ha l f . The sawed edgesw e r e ma c h i n e d t o f o r m a d o u b l e - V 60d e g g r o o v e . B e f o r e w e l d i n g , t h ebeve led edges o f the b lanks werec leaned wi th ace tone to in su re o i l andd i r t - f re e weld in g su r fac es . A 100 F(38 C) p rehea t was u sed to removea n y mo i s t u r e o n t h e ma c h i n e d s u rfaces .

A l l w e l d i n g w a s p e r f o r me d u s i n gt h e g a s me t a l - a r c w e l d i n g ( G M AW )process wi th an a rgon -2 percen t oxyg e n s h i e l d i n g g a s mi x t u r e ; t h e w e l ding param ete r s a re l i s t ed in Tab le 3 .T h e p r o c e d u r e c o n s i s t e d o f t h e d epos i t ion o f two weld passes , wh ichcomple te ly f i l l ed one-ha l f o f the weldg roove . The roo t pass was then backg r o u n d u s i n g d i s c a n d c a r b i d e g r i n ders , a f t e r wh ich two add i t iona l passeswere p laced to comple te the welddepos i t .

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

d i s c o n t i n u i t i e s w e r e p r o d u c e d

Table 2 — Tensile Properties ofBase Metal and Weld

Basemetal a)

Weldmetal"

Tensile str. , ksiYield str. , ksiElong . in 2 in., %R e d . in area, %

120.8113.1

36.066.4

140.0126.350+ (c »

—(a) Properties of base metal provided by manufacturer(b) Average of three specimens taken from weld metal(Ref. 1)(c) Elongation in 3/4 in.

s imi la r ly to the sound welds excep ttha t the f low o f the sh ie ld ing gas wasi n t e r r u p t e d d u r i n g t h e p l a c e me n t o fthe th i rd pa ss (Ref . 2 ) . Th i s c rea ted anuns ta b le a rc , wh ic h in tu r n p rod uce dthe c lu s te red po ros i ty. In te r rup t ion o ft h e ga s f l o w w a s a c c o m p l i s h e d u s i n ga s o l e n o i d - a c t i v a t e d v a l v e s i t u a t e dbe tween the weld ing gun and thesh ie ld ing gas t ank ; the sh ie ld ing gaswas reduced o r tu rned o ff fo r vary ingleng ths o f t ime , depend ing upon thes ize o f c lu s te r des i red .

Af te r we ld ing , the weld re in fo rcemen t was rem ove d by d i sc g r in d ingand an in i t i a l rad iog raph was t aken tod e t e r m i n e t h e a p p r o x i m a t e n a t u r eand s ize o f the po ros i ty c lu s te r p rod u c e d . U s i n g a t e mp l a t e a n d s h a p e -cu t t ing un i t , the welded b lanks werethen f l ame cu t to the t es t spec imenconf ig u ra t io n sh own in F ig . 1 . Thef lame cu t edges were f i l ed and sanded in the d i rec t ion o f the long i tud ina la x i s o f t h e s p e c i me n . T h e s p e c i me nfaces were then mi l l ed f l a t and sand

ed to the same smoo thness as thee d g e s .

E a c h w e l d me n t w a s f i r s t e x a mi n e db y n o r ma l i n c i d e n c e r a d i o g r a p h y t ode te rmine the ex ten t and loca t ion o fw e l d d e f e c t s . S t e r e o r a d i o g r a p h s ,t aken u s ing the p roce du r e o f Car l so nand La wren ce (Ref. 3 ), then p rov idedg r e a t e r u n d e r s t a n d i n g o f t h echarac te r o f each defec t .

Mechanical Testing

T h e s p e c i me n s w e r e mo u n t e d i n a6 x 105 l b capac i ty MTS tens i l e loadf rame and loaded d i rec t ly to f rac tu re

Ta b l e 3 —

Vol tage ,V

22-24

We l d i n g P a r a m e t e r s

C u r r e n t ,A

3 4 0 - 3 6 0

Trave ls p e e d ,in./min

11

In te rpass andp r e h e a t t e m p ,

F

200

Heatinput ,k J / i n .

44

S h i e l d i n gg a s c o m p ,

%

98Ar-2 0 ,

:i.25"

3 6

6 5

I 0.700

Fig. 1 — Tensile specimen configuration

104-s I A P R I L 1 9 7 6

a t the cons tan t c ro ss hea d ra te o f 0 .03in . /min . Al l t e s t s were conduc ted a tr o o m t e mp e r a t u r e . T h e d e f o r ma t i o nocc u rr in g in a 1 in . (2 .54 cm ) g agel e n g t h s t r a d d l i n g t h e w e l d w a s me as u r e d w i t h a l i n e a r v a r i a b l e diff e r e n t i a l t r a n s f o r me r ( LV D T ) e x t e nsometer a t t ached to the cen te r l ine o feach spec ime n . The load and LVDTe x t e n s i o n s i g n a l s w e r e r e c o r d e dth roughou t the t es t wi th x -y p lo t t e rs ,and the load and LVDT s igna l s wereconver ted f rom ana log dc to d ig i t a ls i g n a l s a n d r e c o r d e d o n ma g n e t i ctape . The l a t t e r s t ep was per fo rmed tore ta in a sepa ra te perm an en t rec o rd o fthe da ta , e spec ia l ly i f au tog raph icp lo t t ing e r ro rs shou ld l a te r be d i sc o v e r e d .

T h e p e r c e n t s t r a i n w a s d e t e r mi n e das the rat io ( t im es 100) of the m easu red ex tens ion to the gage l eng th .The s t ra in and s t res s a t max imumload were t e rmed the un i fo rm s t ra in ,e u , and the u l t imate ( t ens i l e ) s t res s ,o-u, re spec t ive ly. The y ie ld s t res s , o -y,

was de te rmined a t 0 .2% p las t i c s t ra inoffset .

Fracture Surface Examination

After tes t ing , the ends of thespec ime n ha lves were sawed o ff top e r m i t e a s y m e a s u r e m e n t o f t h epo ros i ty c lu s te rs and s to rage o f thef r a c t u r e s u r f a c e s . E a c h f r a c t u r e s u rface was examined to de te rmine i t sna tu re and the ac tua l d imens ions o fthe c lu s te r po ros i ty. A pho tog raph ,roughly 2X, was made of each pair off r a c t u r e s u r f a c e s , a s s h o w n(som ewha t red uce d ) in F ig . 2 . Twomea su res o f the po ro us a rea , the a reaof the pores and the area of the regionenc los ing the po res on the f rac tu res u r f a c e , w e r e de te rminedby us ing ap o l a r p l a n i m e t e r d i r e c t l y o n t h ep h o t o g r a p h .

Radiographic Evaluation

The weld qua l i ty o f each spec imenw a s e v a l u a t e d b y u s i n g t h er a d i o g r a p h of t h e s p e c i m e n a n dmi l i t a ry spec i f i ca t ion MIL-R-11468(ORD), Radiographic Inspection.

Results an d DiscussionThe two mea su res o f the po rous

area men t ioned above a re the key independen t var iab les in the ana lys i s o fth i s p rob lem. I t i s u se fu l to cons iderthe p ro jec t ion o f the f rac tu re s u r fac eon the p lane t ransverse to the t ens i l eaxis, as in Fig. 2. The porous regionintercepted by the fracture surface isdefined here as the leas t area, in th isp lane o f p ro jec t ion , tha t con ta in s a l lthe p ro jec t ions o f the po res v i s ib le onthe f rac tu re s u r fac e . In th i s reg ion theg rea tes t d imens ion para l l e l to the


3/5

weld axis is defined as the clusterlength (fracture surface). The clus te rwid th i s the g rea tes t d im ens ion , in th i sr e g i o n , t r a n s v e r s e t o t h e c l u s t e rl eng th . Bo th the c lu s te r wid th andleng th a re t ransverse to the t ens i l eaxis.

Th e porous region intercepted by aradiograph is def ine d here as theleas t area that contains al l the v is ib lerad iog raph ic images o f the po res . Inth i s reg ion , the g rea tes t d im ens ionparal lel to the weld axis is defined asthe cluster length (radiogra phic). Thisc lu s te r l eng th is the in fo rm at ion an inspe ctor in the f ield wou ld have ava i lab le fo r mos t nondes t ruc t ive weld examina t ions . Th i s d imens ion i s pa ra l l e lbut not necessari ly equ al to the clu ste r l eng th ( f rac tu re su r face) . Th i s inequal i ty fo l lows from the fact that ac lu s te r o f po ros i t i es i s th ree -d imens i o n a l , o f unequa l ex ten t among thed ime ns ions . Hence the p ro jec t ion o fthe c lu s te r on the rad iog raph ic p laneis not necessari ly the same as thep ro jec t ion on any o ther p lane . Moreover, th rough e r ro rs o f rad iog raph ict e c h n i q u e , t h e r a d i o g r a p h i c i ma g e s(o r p ro jec t ions ) o f som e po res ma yno t be d i scerned .

Results

Some o f the da ta , no t dep ic ted , a regiven in Table 4. Figure 3 shows therap id decre ase o f un i fo rm s t ra in , eu ,wi th pore area. Only about 0 .03 in .2

pore a rea can be to le ra ted before e uis red uce d to less than 5%. How ever,

up to 0.20 in .2

pore area can beto le ra ted fo r wh ich e u e x c e e d s 3 % .Sim ilar resu l ts app ear in Fig . 4 fo r e^as a func t ion of the area of the po rou sr e g i o n . Th i s reg ion , the f rac tu re s u rface p ro jec t ion def ined above , includes not only the pore area, but alsothe a rea o f the connec t ing l igamen tsbetween the pores . If i t i s assumedtha t these l igamen ts rup tu re very ea rly in the loading of the specimen, thenthe area of the cracked region at largeloads wou ld be th i s a rea enc los ing thepores . A region about 0 .09 in .2 causesEu to d rop b e l o w 5% , y e t up to 0.62

in .2

po rous reg ion can be to le ra ted fo rwhich e u exce eds 5%.

Figure 5 shows a nearly l ineardependence o f the u l t imate t ens i l es t r e n g t h , n u on the area of the pores .However, the sca t t e r in the dependence o f the y ie ld s t res s , rjy, i s b road ,and no a t t emp t has been made topass a l ine o r cu rve o f co r re la t ionthrough those data. I t is again cleartha t a po re a rea l a rger than a bou t0.03 in.2 cause s a s ign i f i can t redu ct ion in t ens i l e p rop er t i es , wh i le suchan area up to about 0.20 in .2 doe s n otr e d u c e


4/5

6 ,

1

3

\ O

o

0.09

1 1

X

OD

0V0

o

sASASASA SA SA S


5/5

p r o b a b l y w o u l d a c c o mp l i s h n o t h i n gbu t inc reased p ro jec t cos t s . Lesss t r i n g e n t r a d i o g r a p h i c s t a n d a r d smigh t thus be benef ic ia l .

However, as Figs . 3 and 4 show, ama r k e d r e d u c t i o n i n d u c t i l i ty o f w e l dm e n t s o c c u r s w h e n e v e n s m a l lamoun ts o f po ros i ty a re in t roduced .Th is imp l ies tha t re laxa t ion o f weld ingcodes based on l imi t des ign concep t s

wou ld be undes i rab le , s ince the duct i l i ty required in that des ign is los t inp o r o u s w e l d me n t s . O n e e x a mp l e o fsuch a l imi t des ign app l ica t ion i sfound in Sect ion III of the ASME Boilerand Pressure Vessel Code (Ref. 8). Inth i s cod e , the a lgeb ra ic d i ffe ren cebe tween the l a rges t and smal les tp r inc ipa l s t res ses i s de f ined as thes t r e s s i n t e n s i t y, S . F o r a g i v e nmater ia l , the l a rges t S permi t t ed i sd e n o t e d S m , and is usual ly o-um /3. Inthe code requ i remen ts fo r C las s 1c o m p o n e n t s o p e r a t i n g u n d e r n o r ma la n d u p s e t c o n d i t i o n s , s o me c o m

bined load ing cases a l low a peakstress in tensi ty of 3 S n , which is essent ial ly the y ield s t rength value. I t isev iden t tha t no reduc t ion in duc t i l i tyo r t ens i l e s t reng th cou ld be to le ra tedin such a c r i t i ca l des ign . A cce p tan ceo f on ly the mos t duc t i l e welds wou ldbe es sen t i a l to the p roper imp lementa t ion o f a l imi t des ign . Thus , a reduct ion in the qua l i ty of rad io g ra ph ics tandards wou ld no t be benef ic ia l in al imi t des ign .

S u m m a r y

Conclusions1. There i s a com bina t ion o f po re

s ize ( in terms of to tal area of pores)and d i s t r ibu t ion o f po ros i ty ( in t e rmsof a rea encompassed by po res , i . e . ,the area of the porous region) that iscri t ical in the sense that the tensi les t reng th i s no t deg raded un t i l tha tpo re s i ze o r po ros i ty d i s t r ibu t ion i ssu rpassed . In th i s s tudy the c r i t i ca lpore area is about 0 .03 in . 2 and thecri t ical area of the porous region isabout 0 .09 in .2

2. There i s a s imi la r co mb ina t ion o f

po re s i ze and d i s t r ib u t ion o f po ro s i tythat is cri t ical in that the duct i l i ty (asme a s u r e d b y e u ) i s sha rp ly de g ra dedun t i l tha t po re s i ze o r po ros i ty d i st r ibu t io n is su r pas sed ; beyo nd thecri t ical poin t the rate of degradat ion isreduced . In th i s s tudy the c r i t i ca l po re

area is about 0 .03 in . 2 and the cri t ica la rea o f the po rous reg ion i s abou t0 .09 in .2 .

3 . T h e r e i s a n e f f e c t i v e r a d i o -g rap h ic l eng th o f c lu s te r po ros i tyassoc ia ted wi th the c r i t i ca l combinat ion s in Conc lus ion s 1 and 2 . In th iss tudy, the t ens i l e s t reng th was unaffec ted fo r rad iog raph ic l eng ths l es st h a n 0.6 i n . , w h i l e t h e d u c t i l i t y

d ropped sharp ly un t i l tha t l eng th wasr e a c h e d .4. In v iew of the relat ion of tensi le

s t reng th to c r i t i ca l c lu s te r po ros i tysize , re l axa t ion o f weld in spec t ionspec i f i ca t ions may be poss ib le fo rcer ta in app l i ca t ions i f the spec i f i c at ion i s based on work ing s t res s s t ructu ra l des ign c r i t e r i a . However, c o ns ider ing the marked reduc t ion in duct i l i ty wi th inc reas ing po ros i ty, re laxat ion o f weld spec i f i ca t ions based onl imi t des ign c r i t e r i a shou ld no t bec o n s i d e r e d .

Future Work

T h e AW S , A I S C , a n d A A S H TOcodes con ta in spec i f i ca t ions fo r theshear o f weldmen ts tha t a re d i s t inc tf rom those fo r the t ens ion o f w e l dm e n t s . D a t a o n t h e s h e a r o fweldmen ts con ta in ing c lu s te r po ros i tyshou ld be acq u i red to de te rmin e theex ten t o f deg rada t ion o f the y ie ld andu l t imate shear s t res ses an d un i fo rmshear s t ra in . Th i s wi l l t e s t the quest ion o f whe ther work ing s t res s des ignmay be unnecessar i ly conserva t ive inshear as wel l as in tension of w e l dme n t s .

Acknowledgments

This investigation was performed for theOffice of the Chief of Engineers. U. S. Army, as covered in Ref. 10. The ableassistance of Mr. F. Kisters of theMetallurgy Branch, CERL, is gratefullyacknowledged.

The views of the authors do not purportto reflect the position of the Departme nt ofthe Army or of the Department of Defense.

References

1. Law rence, F. v. , Jr., and Cox, E. P.,"The Influence of Incomplete Joint Penetration on the Tensile Behavior of A514Steel Welds", Welding Journal, to be published.

2. Carlson, K. W., Lawrence, F. V.. Jr..and Radziminski, J. B., "The Introductionof Discontinuities in High Strength Steel

LENGTH OF POROUS REGION INTERCEPTED BYRADIOGRAPH (IN.)

Fig. 8 — Ultimate tensile strength vs.length of porous region intercepted byradiograph

Weldments," U. S. Army CERL PreliminaryReport M-27, December 1972. AD 755 524.

3. Carlson, K. W., and Lawrence, F. V.,Jr., "The Examination of Discontinuities inWelds by Stereoradiography." U. S. ArmyCERL Technical Report M-24. September1972. AD 749 945.

4. The American Welding Society, AWSStructural Welding Code, AWS D1.1-72,1972, pp 80 and 86.

5. The A merica n Institute of SteelConstruction. Specification for the Design,Fabrication, and Erection of StructuralSteel Buildings, 1969, pp 5-16.

6. The Am erican Institute of SteelConstruction, Commentary on the Specification for the Design, Fabrication, andErection ot Structural Steel for Buildings,1969, pp 5-122.

7. The American Association of StateHighway and Transportation Officials,Standard Specifications for HighwayBridges. 11th ed.. 1973. p 112.

8. United States Steel Co., Steel DesignManual, 1968, p 32.

9. The American Society of Mechanical Engineers, "Nuclear Power Components ," ASME Boiler and Pressure

Vessel Code, Section III. Subsections NAand NB, 1974.10. Hon ig. E. M., Jr.. "Effects of Cluster

Porosity on the Tensile Properties of Butt-Weldments in T-1 Steel," U. S. Army CERLTechnical Report M-109, November 1974.ADA 004 001.

T h e A m e r i c a n We l d i n g S o c i e t y p u b l is h e s o v e r a h u n d r e d d i ff e r e n t C o d e s , S t a n d a r d s ,R e c o m m e n d e d P r a c t ic e s , G u i d e s , H a n d b o o k s a n d o t h e r b o o k s r e l a t e d t o w e l d i n g . If y o u

w o u l d li ke a co p y o f o u r P u b l i c a t i o n s L i s t , s i m p l y c i r c l e N o . 1 5 0 o n o u r R e a d e r I n f o - C a r da n d m a i l i 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 107-s

Documents

Tensile Properties of A514 Steel Butt Joints Containing Cluster Porosity