Structure and Elevated Temperature Properties of Type 308 Stainless Steel Weld Metal with Varying Ferrite Contents

Transcription

1 Sucture and Elevated Temperature Prperties f Type 308 Stainless Steel Weld Metal with Varying Ferrite Cntents The ferrite phase mrphlgy change frm islated patches t a cntinuus phase paralleling subsuctural bundaries with increasing ferrite cntent affects creep ductility BY R. G. BERGGREN, N. C. COLE, G. M. GOODWIN, J. O. STIEGLER, G. M. SLAUGHTER, R. J. GRAY AND R. T. KING ABSTRACT. The as-depsited micrsucture, creep and tensile prperties at 649 C (200 F), and fracture behavir f shielded metal-arc Type 308 stainless steel welds having nminal ferrite cntents frm 0 t 5% were investigated. The ferrite phase mrphlgy varied frm islated patches in nminally 0% ferrite welds t a nearly cntinuus phase in nminally 5% ferrite welds in metallgraphic studies. Lw ductility creep failures ccurred when extensive interphase cracking ccurred at austenite-sigma phase bundaries (i.e., fr welds with high initial ferrite cntent tested under lw sess). The fractin f creep test time befre third-stage creep was usually less than 0.3 fr specimens that exhibited high ductility. Inductin It is well-knwn that the micrsucture f nminally austenitic stainless steel welds can cntain varying amunts f ferrite and that the mrphlgy f the ferrite can vary, depending n the chemical cmpsitin f the weld and the welding cnditins. ""' Since the presence f a limited amunt f ferrite is cnsidered desirable t prduce resistance t ht cracking, '-' nrmal practice invlves cnl f chemical cmpsitin f depsited weld meta! and ther prcess variables s that a cnlled amunt f ferrite is present in the depsits. The ASME Biler and Pressure Vessel Cde requires 3 t 9% ferrite in austenitic stainless steel welds fr many nuclear cntainment systems, except Type weld metal depsits." Hwever, there is als evidence that in high-temperature service, ferrite in austenitic steel welds ansfrms t sigma phase, 7 " which smetimes plays a rle in lw-ductility creep failure." The ansfrmatin reactin kinetics depends n temperature and metallurgical sucture, but the reactin tends t ccur at least ver a range f temperatures frm abut 538 t 87 C F).'- This temperature range is imprtant t many users f welded austenitic steel. Hence, ferrite, a metallurgical phase that is desirable fr making sund welds, may be undesirable fr sme elevated-temperature service applicatins where creep defrmatin f the weld material ccurs. Attempts t directly characterize the effect f ferrite cntent and subsequently frmed sigma phase n prperties are cnfunded by the need t vary either the chemical cmpsitin f the weld metal r the welding R. C. BERCCREN, C. M. GOODWIN, /. O. STIEGLER, G. M. SLAUGHTER, R. I. GRAY AND R. T. KING are with the Metals and Ceramics Divisin, Oak Ridge Natinal Labray, Oak Ridge, Tennessee; N. C COLE is with Cmbustin Engineering, Chattanga, Tennessee. prcess variables t cause variatins in ferrite cntent. It is knwn that mechanical prperties can be related t chemical cmpsitin in fully austenitic welds." Hwever, there is an urgent practical need t determine whether the creep prperties f welds are related t the amunt r mrphlgy f ferrite present. If such a critical prperty f weld metal as creep ductility culd be even empirically related t ferrite cntent fr limited ranges f chemical cmpsitin and prcess variables, then the perfrmance f welds might be imprved by cnlling ferrite cntent t prduce acceptable weldability and prperties fr specific applicatins. T investigate that pssibility, Type 308 stainless steel cvered elecdes were purchased frm a cmmercial vendr. The elecdes were intended t yield ferrite cntents in the final depsit f abut 0, 2, 5, 7,0, and 5%. This paper details the preparatin and testing f the weld metal, and examines the crrelatin between ferrite cntent and elevated temperature mechanical prperties in these Type 308 stainless steel welds. Experimental Materials and Prcedures Six batches f 4 mm (%a in.) diameter cvered Type 308 stainless steel elecdes were purchased frm a cmmercial vendr. They were depsited manually by the shielded metal- WELDING RESEARCH SUPPLEMENT I 67-s

2 Table -Chemical Cmpsitin f Cvered Elecdes, Type 308 Stainless Steel s, Type 304 Stainless Steel Base Metal, and Measured Ferrite Cntent f Weld Metal Element Analysis f: 0% 2 Weld Cntent, wt-% metal f each nminal ferrite cntent 5% 7% 0% 5% Base Metal Cr Ni C s Mn Cu P Si M C H O N Measured ferrite number (FN) Cvered elecde Cvered elecde Cvered elecde Cvered elecde Cvered elecde Cvered elecde arc (SMA) prcess in V-grve weld jints in 3 passes under identical cnditins with mechanical resaint t keep the plates frm flexing abut the weld. The jint had a 75 deg included angle and 0.37 t 0.85 mm (0.05 t in.) rt face, with n gap. The welds were made with apprximately 50 A dcrp at 35 V. The rt pass in each case was made frm anther batch f Type 308 stainless steel filler metal that was depsited by the gas-tungsten-arc prcess. Interpass temperatures were belw 93 C (200 F). The chemical cmpsitin f the 2.5 mm thick (0.5 in.) Type 304 stainless steel base metal (Heat ) is given in Table tgether with the cmpsitins f the weld metal samples frm each weld at a lcatin several passes away frm the rt pass. The analyses fr several elements in the cvered elecdes are als given. Ferrite numbers were determined fr the weld depsits by the Magnegage technique, and they are als included in Table. They agree sufficiently well with the intended ferrite cntents that the intended values will be retained fr simplicity in discussing this wrk. The cmpleted welds were sectined and used t prepare fur buttnhead, all-weld metal specimens (gage length parallel t the welding directin) frm each f the six different depsits. These specimens had 28.6 mm (.25 in.) lng by 3.2 mm (0.25 in.) diameter gage sectins, and their center lines were lcated 5 mm (0.20 in.) belw the weld surface. All specimens were checked fr sundness by radigraphy and fr the absence f base metal in the gage sectin by eddy-current techniques. One specimen f each depsit was tensile tested at 649 C (200 F) at nminally 0.005/min sain rate n an Insn machine in air. The ther three specimens were creep tested in air at 649 ± 3 C (200 ± 5 F) at sesses ranging frm 0 t 72 MPa (6,000-25,000 psi). The sesses were selected t prduce rupture in times frm abut 0 t 000 h. Creep tests were manually stepladed n dead-lad frames. The peridic sain measurements were based n displacements f the lad ain 5 0 NOMINAL FERRITE CONTENT (%) Fig. Tensile prperties f Type 308 stainless steel weld metals with different ferrite cntents at 649 C (200 E) members, and are nt cnsidered t have better accuracy than ±0.5% sain. Minimum creep rates and times t characteristic features f the creep curves are based n these measurements, while the ttal sain is btained frm after-test micrmeter measurements. A sectin f each f the six welds was munted, plished, and etched. These sectins were used t examine the micrsucture and macrsucture f the welds, and the plished surfaces were used fr the Magnegage ferrite determinatins. Halves f the tested creep specimens were examined by ptical metallgraphic techniques, while the fracture surfaces were investigated by scanning elecn micrscpy t reveal the predminant mde f fracture. Results Mechanical Prperties The results f the tensile tests are summarized in Fig., in which the ultimate tensile sength, 0.2% ffset yield sess, reductin f area, ttal elngatin, and unifrm sains are pltted against nminal ferrite cntent. Sme variatins f tensile prperties with ferrite cntent were nted:. The ultimate tensile and yield sesses f nminally 0% ferrite material are higher than any thers. 2. A minimum in ttal and unifrm elngatin may ccur near the 5% ferrite level. Except fr the variatins nted, they d nt differ significantly. Hwever, these bserved variatins have nearly 68-s I IUNF 978

3 t - WELDING RESEARCH SUPPLEME NT I 69-s B 5 E 5 :5 s 6 s E 5 6 s O OJ m I s - O m 0 < < Q - f"';"i." & l\-\ ^.j j --J4---t--f -j 't- : Mi:-: ^ -.fi:.: -- * ^g..*.- v. " ]0- : " *r ' Ft. r.4^. J:.«: : ' 4> fc : r I i %...:. L.~#^r- ->.,...,.,,.,..., ;:.-!...:: :$: '" \ u-~:avm * * (%) vaav JO Nunad (%) N0llW9N0n3 "IV0 U (»dw) SS38S (DdW) SS3HS ::H:: -H &* B 5 B 9 6 s 6 s 6 s O OJ «r- in < * 0.C _J LaJ LaJ h- t!2 K 5?s D O LU CL t «::::ij::;:: i *? <... r~ *s UJ ryi O UJ " } 4 i i!$ ] t, i ii :. : ft i A.\.'.. t J / / a cn LU LL - \ \ r (O OJ CM I t- r- 0 *<} " (!Sd 0000 SSB-dlS EC. t > - UJ * 3 " - cn cc -J - lo t- LU -» 5UJ- 9 ^w- f OJ CO ld ^ (!Sd 0000 SS3US i!-- 0 a a a a; 5 0 I

4 < < LL O O Q LU to 5 NOMINAL FERRITE CONTENT (%) NOMINAL FERRITE CONTENT (%) Fig. 3 Variatin f ductility f Type 308 stainless steel weld metal at 649 C (200 E) with ferrite cntent: A (left)-ftacture sain and sain t third-stage creep; B (right) reductin f area the same magnitude as the experimental scatter fund in replicated tests n ther austenitic weld metal " and hence cannt be cnsidered cnclusive by themselves. The basic creep-rupture prperties f the weld metals with different ferrite cntents are displayed in Fig. 2. Althugh brad scatter bands are drawn thrugh the sess-rupture time, reductin f area, minimum creep rate, and ttal elngatin data, certain ends are evident in these plts:. The rupture times fr the nminally 0% ferrite weld metal are cnsiderably greater and the minimum creep rates are cnsiderably less than fr the higher ferrite welds. 2. The high-ferrite weld metals tend t exhibit the smallest reductins f area and ttal elngatins fr lngtime tests. Reductin f area and ttal elngatin that ccur during creep are bth useful measures f the ductility f weld metal. Bth these measures f ductility tend t decrease with increasing rupture time (decreasing sess) r increasing ferrite cntent. The sains that ccur at the nset f tertiary creep (by the 0.2% sain ffset methd)* d nt have a definable dependence n sess Fig. 3. Sains at the nset f tertiary creep f % r less ccurred fr the material cntaining 2 and 5% ferrite, and these sains never exceeded 6%. It is nt clear frm these limited data whether there is any statistically significant end in the behavir f this ductility measure with ferrite cntent. Metallgraphy The plished and etched micrsuctures f the six welds in the aswelded cnditin are shwn in Fig. 4. These micrsuctures are representative f a regin apprximately 5 mm (0.2 in.) belw the weld surface, near the center f the mechanical prperties specimens; hwever, there was sme variatin in the micrsucture with lcatin in the weld. Quite clearly, the mrphlgy f the ferrite becmes mre nearly cntin- *Determined frm a sain-time plt as the pint f intersectin f a line, displaced by + 0.2% sain frm a line passed thrugh the regin f minimum creep rate, with the sain-time curve. uus with increasing ferrite cntent. The nminally 0% ferrite weld metal has 0.6 FN (see Table ), and the ferrite is present as widely separated patches in the subsucture. The nminally 5% ferrite weld metal with an.6 FN has an almst cntinuus ferrite phase alng subsuctural bundaries. The apparent subgrain dimensins d nt vary appreciably with ferrite level by visual inspectin. The micrsucture f the as-depsited weld metal near the lcatin f test specimen center lines was investigated by 500-keV ansmissin elecn micrscpy. N attempts were made t investigate ther regins. At this lcatin, the micrsuctures f all welds were primarily austenite with a high dislcatin density and sme disibutin f ferrite with a lwer dislcatin density. (Cmpare Fig. 5A and B with C, where dislcatins in the ferrite phase are imaged.) The nminally 0% ferrite as-depsited weld had islated ferrite patches, cnsistent with the ptical micrsucture; the austenite-ferrite bundaries were heavily decrated with carbide precipitates. Dislcatins in the austenite phase frmed a cell sucture 70-s DUNE 978

5 ' '., ' -< ' ' J,' ' ; :' ':; /-,»«' _ A V -la --. '. '. ** > _ L.' ' - * X. "W 8 ;>%':$ A 2H A Wl, '*;': > *.', " - /',-. * i c. J r - < a. ' "\ -> -*f f -* -- > a /^ fc " ' "*. ; r '» N v '.*-* < ' II j - *. *- *» s * «";.7.^7 ' N, -^ * ". X \> > 7 $ A * -\ 7? P if A -mt J > - '. / * -'./ f A <'. /, ' 'A A Ar^ * - ra--.., 'f- -'\cv- y*^ ^J''.\ *>'v : V ^.S- <? r5 -._ >...,-/;.y.. '/' ''7 * '_.. 'AW'W'm. # * VJ * - -^-k _t ; >. : a > ^ ^. 4 >C"- ' ^. i / *"-.' ^,*-c7-. *~*-\T^ Fig. 4 Micrsuctures f as-depsited Type 308 stainless steel welds with different nminal ferrite cntents; ferrite is dark phase. Ferrite cntent (FN) l the welds is nminal (measured): A-0% (0.6); 8-2% (2.8); C-5% (5.2); D-7% (6.2); E-0% (9.4); F-5% (.6). X500 (reduced 56% n reprductin) with sme dislcatins within cells (see Fig. 5A), and the dislcatin density was generally higher than fr ther welds. Ferrite in nminally 2, 5, 7, 0, and 5% ferrite as-depsited welds tended t be elngated and thin in crss sectin; again, this is cnsistent with ptical metallgraphy. Carbide precipitates n austenitic-ferrite bundaries were relatively rare and tended t be sheetlike when they ccurred. Negligible carbides were bserved in the 0 and 5% ferrite welds. The tendency fr dislcatin cell frmatin in austenite was generally less than in the nminally 0% ferrite welds (see Fig. 5C), and the cells that frmed were relatively carse. Fracture surfaces f the nminally 0 and 5% ferrite weld metal are shwn in Figs. 6 and 7, respectively. Fr each weld depsit, lng- and shrt-time rupture surfaces are shwn. Regardless f rupture time, the 0% ferrite weld metal fracture surface is cmpsed f ductile dimples, and the fracture surfaces are predminantly shear with nly a few areas that might be interpreted as subsuctural r interphase fracture. Cnversely, the nminally 5% ferrite weld metal fractures are markedly affected by subsuctural separatins, the mre s with increasing rupture time, and nly in islated regins des ductile shear fracture ccur (presumably during the rapid saining that ccurs after the specimens had nearly separated). Optical metallgraphy has been used t verify that the ferrite ansfrms t sigma phase Fig. 8. The sigma that frms des s in clusters f ferrite grains as was previusly reprted frm ther welds'' that were thermally aged in the absence f sess. Large regins in which nearly n ansfrmatin t sigma ccurs cexist with clusters f ferrite grains underging relatively rapid ansfrmatin. Within individual ferrite grains at shrt times, the sigma phase apparently nucleates and grws frm several sites Fig. 8. Fr specimens in test at 649 C (200 F) fr times appraching 000 h, in the clusters f ferrite grains where the ansfrmatin has ccurred, all r nearly all the riginal ferrite has ansfrmed. The fracture paths tend t cincide with regins having high sigma phase cntent. Details f these bservatins n sigma phase frmatin under sess are being published separately. Lw magnificatin ptical metallgraphic examinatin f sectins Fig. 5 Transmissin elecn micrgraphy at 500 KeV f Type 308 shielded metal-arc weld depsits; ^ -ferrite, A -Austenite, A M a,ci carbide precipitate: 5A nminally 0% ferrite weld shwing dislcatin cell sucture in austenite and dense carbn decratin f austeniteferrite bundaries; 56 nminally 5% ferrite weld, imaging dislcatins in ferrite; 5C nminally 5% ferrite weld, shwing dislcatin sucture in austenite thrugh the fracture regins reveals the patterns f internal cracking at fracture. Nminally 0% ferrite material (Fig. 9) develps islated cracks that becme equiaxed during defrmatin, but the cracks d nt link up t frm cntinuus netwrks at small sains. Nearly the same ccurrence is bserved in the 5% ferrite weld tested t fracture at 72 MPa (25,000 psi) in shrt enugh time t avid massive sigma phase frmatin-see Fig. 0 (tp). The 5% ferrite weld tested t fracture at 0 MPa (6,000 psi) cntains many lng cracks, frmed at relatively lw sain Fig. 0 (bttm). Discussin This discussin is limited t the WELDING RESEARCH SUPPLEMENT 7-s

6 Fig. b-fracture surfaces f nminally 0% ferrite weld metal tested at 649 C (200 F): A and B-l72 MPa (25,000 psi); C and D-0 MPa (6,000 psi) Fig. 7 Fracture surfaces f nminally 5% ferrite weld metal tested at 649 C (200 F): A and MPa (25,000 psi); C and D-0 MPa (6,000 psi) experimental results presented in this paper. N claim is made that the results are applicable t all Type 308 stainless steel welds. A much brader study invlving statistical analyses f data frm many mre weld depsits is recgnized t be desirable frm the standpint f the develpment f engineering cde rules that might bear n the desirable range f ferrite cntent and mrphlgies in austenitic stainless steel weld metal fr elevated temperature service. Several variables, including chemical cmpsitin and ferrite mrphlgy and cntent, are cnfunded in this experimental series f welds. Hwever, the cmbinatin f micrsuctural bservatins, fractgraphy, and test data allws cnclusins t be reached regarding sme facs imprtant t defrmatin and failure f these welds. The sength f the nminally 0% ferrite weld metal was greater than that f any ther welds, by the measures f yield sength and ultimate sength (Fig. ), and minimum creep rate and rupture time (Fig. 2). The nminally 0% ferrite weld als had a relatively high density f dislcatins with a cellular disibutin in the aswelded cnditin (Fig. 6) and the highest measured carbn cntent (Table ).., These bservatins are* cnsistent: either the micrsucture r relatively high carbn cntent might cnibute t the bserved relatively high sength in the 0% ferrite weld. Hwever, the interrelatin between the variables f carbn cntent and as-welded dislcatin sucture is nt clear. The ductility f the nminally 0% ferrite weld metal is relatively high in bth shrt (Fig. ) and lng term (Fig. 2) tests. The shrt-term tensile ductility f all these welds is relatively high, as measured by reductin f area, ttal elngatin, and unifrm sain Fig.. Hwever, the creep ductility decreases with increasing sigma cntent and cntinuity and with decreasing applied sess. The creep rupture ttal elngatins r the creep reductins f area may be used almst interchangeably as measures f ductility fr this purpse Fig. 3. N significance can presently be attached t the bserved variatins in sain at the nset f tertiary creep (Fig. 3A), which range between and 6%. These bservatins, taken with the bservatins f initial ferrite mrphlgy (Fig. 4), scanning elecn fractgraphs (Figs. 6 and 7), and ptical metallgraphic bservatins n plished and etched crss sectins f failed specimens (Figs. 8,9, and 0), are cnsistent with the explanatin that fllws. 72-s I IUNE 978

7 CM ci a -M. A" ^y**-^-" ^ k x v. % A&s^v tiy - v 7 Fig. 8 Crack prpagatin during creep test at 649 C (200 F). O xide; a sigma; I, ~ incmpletely ansfrmed sigma; f ferrite; mc micr crack; cr* sigma apparent n bth sides f crack. Sigma phase frmatin frm ferrite in Type 308 stainless steel weld metal. Fracture prpagatin ccurs in a regin having high density l sigma phase. Nte cracks frming at austenite-sigma phase particles away frm main fracture regin (X500). Nte ferrite particle partially ansfrmed t sigma phase at (,0) V h \ Fig. 9 Internal cracking in crack-tested Type 308 stainless steel weld metal with 0% nminal ferrite cntent: tp 72 MPa (25,000 psi); bttm 0 MPa (6,000 psi) sesses. Tensile axis is hrizntal; fracture surface is t the right. X50 (reduced 53% n reprductin) In all the welds, the ferrite that is present ansfrms t sigma phase during creep testing at 649 C (200 F). In all the welds, interphase cracking ccurs at the austenite-sigma phase bundaries during testing. The frmatin f a crack sets up a lcal sess field that may affect the rate f ansfrmatin f neighbring ferrite grains r accelerate the rate f fracturing f adjacent austenite-sigma phase bundaries, but these hyptheses can nt be prven frm the bservatins reprted here. In the relatively lw-ferritic welds, the internal cracks tend t be islated, Fig. 0 Internal cracking creep-tested Type 308 stainless steel weld metal with 5% nminal ferrite cntent: tp 72 MPa (25,000 psi); bttm-0 MPa (6,000 psi) sesses. Tensile axis is hrizntal; fracture surface is t the right. X50 (reduced 53% n reprductin) and final fracture requires ductile tearing f a nearly cntinuus austenite phase; tertiary creep behavir is prbably sngly influenced by the extensive necking (reductin f area) that ccurs. In the relatively high-ferrite welds in shrt-time tests, the ansfrmatin t sigma phase is nly partially WELDING RESEARCH SUPPLEMENT I 73-s

8 Q. Q CC I r- CL LU LL Ld CC CL Z> rr u_ r- 5 0 NOMINAL FERRITE CONTENT (%) Fig. Fractin f ttal test time prir t third-stage creep by 0.2% sain ffset methd fr Type 308 SMA welds with different ferrite cntents cmplete, and internal cracks at austenite-sigma phase bundaries tend t be islated. As a result, fracture requires ductile tearing thrugh the austenite phase and remaining ferrite phase. In lnger time tests in relatively high-ferrite-cntent welds, the sigma phase is mre nearly cntinuus, and extensive intercnnected cracks are linked t frm the final fracture surface with very little reductin f area r necking. This is reflected in the bservatin that the fractin f rupture time befre tertiary creep is highest fr high-ferrite-cntent welds having lng rupture times Fig.. By this mechanism, the ferrite cntent and mrphlgy f these experimental welds are felt t have prfund influence n the creep ductility f the weld metal. Fr creep tests n weld metal specimens invlving high ductility, the fractin f the ttal test time befre tertiary creep was usually less than 0.3. Only fr cnditins that prduce relatively nnductile failures des the fractin f the test time befre tertiary creep apprach r exceed 0.5. This is an imprtant cnsideratin in determining apprpriate design limits fr welded cnsuctin. Summary A series f stainless steel shielded metal-arc welds having nminal ferrite cntents ranging frm 0 t 5% was investigated. The as-depsited micrsuctures, tensile and creep prperties at 649 C (200 F), and fracture behavir f the weld metal were investigated. The results indicated that fr these -5 materials and tests:. The nminally 0% ferrite weld had the highest tensile and creep sength f the welds investigated. It als had the highest carbn cntent and greatest dislcatin density in the as-welded cnditin. 2. The ferrite phase mrphlgy changes frm islated patches t a cntinuus phase paralleling subsuctural bundaries with increasing ferrite cntent. Ferrite ansfrmed t sigma phase during creep testing at 649 C (200 F). 3. In creep tests at 649 C (200 F), lw ductility ccurred fr high-ferrite welds in relatively lng-time (appraching 000 h) tests. 4. Metallgraphic and fractgraphic bservatins are cnsistent with fracture initiating at austenite-sigma phase bundaries. When the ferrite cntent, mrphlgy, and time at test temperature prduce a nearly cntinuus sigma phase, extensive intercnnected interphase cracking ccurs and leads t lw-ductility failure. 5. The fractin f ttal test time befre tertiary creep is usually less than 0.3 fr tests that resulted in relatively ductile failure. This wrk indicates a sng need fr a brader study invlving statistical analyses fr a number f stainless steel filler metals r elecdes and ther welding prcesses and cnditins. It als shws advantages f mechanistic interpretatin f data as well as statistical evaluatin. Acknwledgments The authrs wish t thank V. T. Huchin fr preparing the test welds and E. Biling and. K. Alley fr the testing wrk. We are indebted t D. R. Cune fr the scanning elecn micrscpy, t J. T. Hustn fr preparing the ansmissin micrscpy specimens, and t W. H. Farmer fr the ptical metallgraphy. We thank P. Paiarca and W. R. Martin fr their suggestins and supprt in this wrk. We als thank A. ). Mrhead and R. G. Dnnelly fr reviewing, S. Petersn fr editing, and Regina Cllins fr preparing the manuscript. The research described in this paper was spnsred by the Energy Research and Develpment Adminisatin under cnact with Unin Carbide Crpratin. References. Hull, F. C, "Effect f Delta Ferrite n the Ht Cracking f Stainless Steel," Welding lurnal, 46 (9), Sept. 967, Research Suppl., pp. 399-s t 409-s. 2. Reid, H. F., and Delng, W. T., "Making Sense Out f Ferrite Requirements in Welding Stainless Steels," Met. Prg., 03 (6), pp ('973). 3. Schaeffler, A. L., "Cnstitutin Diagram fr Stainless Steel Weld Metal," Met. Prg., 56, p. 680 (949). 4. Slaughter, C. M., Welding and Brazing Reac Cmpnents, Rw and Littlefield, Inc., New Yrk, pp (964). 5. Gdwin, C. M., Cle, N. C, and Slaughter, C. M., "A Study f Ferrite Mrphlgy in Austenitic Stainless Steel Weldments," Welding lurnal, 5 (9), Sept. 972, Research Suppl., pp. 425-s t 429-s. 6. ASME Biler and Pressure Vessel Cde, Sect. Ill, 974, American Sciety f Mechanical Engineers, New Yrk (974). 7. Henry, O. H., Crdvi, M. A., and Fischer, G.., "Sigma Phase in Austenitic Stainless Steel Weldments," Welding Jurnal, 34 (2), Feb. 955, Research Suppl., pp. 75-s t 8-s. 8. Ple, L. R., "Sigma An Unwanted Cnstituent in Stainless Weld Metal," Met. Prg., 65 (6), pp (954). 9. Stiegler,. O., King, R. T., and Gdwin, G. M., "Effect f Residual Elements n Fracture Characteristics and Creep Ductility f Type 308 Stainless Steel Weld Metal," /. ng. Mat. TechnL, 97H (3), pp (975). 0. King, R. T., Stiegler,. O., and Gdwin, G. M., Creep Prperties f a Type 308 Stainless Steel Pressure Vessel Weld with Cnlled Residual Elements, ORNL-TM- 43 (May 973). I I. Binkley, N. C, Gdwin, G. M., and Harman, D. G., "Effect f Elecde Catings n Elevated-Temperature Prperties f Austenitic Stainless Steel Weld Metal," Welding Jurnal, 52 (7), July 973, Research Suppl., pp. 306-s t 3-s. 2. Cle, N. C, Gdwin, G. M., and Slaughter, G. M "Effect f Heat Treatments n the Micrsucture f Stainless Steel Weld Metal," pp in Micrsuctural Science, Vl. 3, ed. by P. M. French, R.. Gray, and. L. McCall, American Publishing Cmpany, New Yrk, Hull, F. C, "Effects f Cmpsitin n Embrittlement f Austenitic Stainless Steels," Welding lurnal, 52 (3), March 973, Research Suppl., pp. 04-s t 3-s. 4. Gray, R. J., private cmmunicatin. 74-sl JUNE 978