Effect of Composition on the Corrosion Behavior of Stainless Steels Brazed with Silver-Base Filler Metals
An electrochemical galvanic action between coexisting phases is responsible for the corrosion of filler metal and interface
BY T. TAKEMOTO AND I. OKAMOTO
ABSTRACT. The effect of composition of been known to fail by interfacial corro improve the corrosion resistance of stain silver-base filler metals and austenitic sion. Sistare et al. tested the corrosion less steel brazed with silver-base filler stainless steels on the corrosion of stain resistance of Type 430 stainless steel metals. However, even the fundamental less steel joints brazed with silver-base joints (brazed with silver-base filler met aspects concerning the effect of compo filler metals was investigated in aqueous als) in running tap water and paid atten sition of Ag-Cu-Zn ternary filler metals sodium chloride solution. The depth of tion to the corrosion at the braze inter and stainless steel composition and also corrosion in the filler metal increased with face (Ref. 1). They considered the interfa the improvement mechanism by nickel the increase of zinc content in filler metal cial corrosion was similar to the crevice addition on the corrosion resistance of and (Ni + Cr) content of base metal. The corrosion which was accelerated by the stainless steels brazed with silver-base interfacial corrosion was promoted by formation of an oxygen concentration filler metals has not yet been clarified the increase of silver content in the filler cell. They used 40 kinds of silver-base sufficiently. metal. filler metals and recommended several The joint is usually made by the aid of The phenomena are explained by the relatively corrosion resistant filler metals flux to remove the passive oxide films galvanic cells such as the stainless steel containing nickel. and thereby permit intimate contact bulk surface/a-Cu phase in filler metals, Kawakatsu (Ref. 2) evaluated the cor between filler and base metal. Hence, the and the arAg phase/active stainless steel rosion resistance of Type 430 and 304 stainless steel is brazed to filler metal after at the braze interface. The brazing flux stainless steel joints brazed with silver- removal of the protective passive film leaves the active layer at the braze inter base filler metals. He did this by measur without repassivation; this leaves the thin face by the removal of protective passive ing the decrement of tensile strength active layer in stainless steel base metal at films; this is believed to be one of the after immersion in various acids and alka the interface. In addition to this, at the causes of interfacial corrosion. line aqueous solutions. This work pointed braze interface, various phases with dif A nickel-depleted ferrite phase is out that a nickel-rich layer was formed ferent electrochemical properties such as observed at the interface brazed with along the interface in nickel bearing BAg arAg, a-Cu, and austenite (passive sur nickel-free filler metals; however, the for filler metal joints; it stated that the layer face and active interface) coexist; this mation of a nickel-depleted zone is pre was responsible for the improvement of suggests galvanic corrosion cells may vented by the use of filler metals with 2% corrosion resistance. Other work also function among them. Ni. Addition of nickel to filler metals is referred to the advantageous effect of This paper describes the effect of Ag- found to prevent the formation of the nickel additions to filler metals on joint life Cu-Zn ternary silver filler metal composi less corrosion resistant nickel-depleted (Ref. 3) and dezincification in sea water tion and stainless steel composition on zone. (Ref. 4). The use of zinc-free, nickel- the corrosion behavior of brazed joints. It bearing filler metal is also found to be does so by considering the metallurgical beneficial (Refs. 5,6,7). introduction factors and electrochemical galvanic The selection of appropriate combina effects. The improved mechanism result Stainless steel joints brazed with silver- tions of silver-base filler metal and stain ing from nickel addition to silver filler base filler metals have been widely less steel appears to be important to metals was also investigated. employed for piping, industrial heat exchangers and other conventional joints. The joints are expected to be corrosion resistant in the atmosphere Table 1—Chemical Composition of Filler Metals, Wt-% containing moisture, aggressive gases and chloride ions. However, these joints have Brazing temperature Paper presented at the 15th International Filler metals Ag Cu Ni Zn °C CF) A WS-WRC Brazing and Soldering Conference held in Dallas, Texas, during April 10-12, BAg-6 50.50 34.90 Balance 800 (1472) 1984. BAg-5 45.11 30.53 Balance 800 (1472) CF-12
300-s | OCTOBER 1984 Table 2—Chemical Composition of Stainless Steel Base Metals, Wt-°o
Element'3' Type stainless steel base metal Ni Cr Mn Mo Fe 304 8.71 18.04 0.06 0.61 1.04 0.029 Balance 304L 10.29 18.17 0.014 0.65 1.60 0.030 Balance 321 9.10 17.15 0.06 0.66 0.96 0.031 0.31 Balance 316 11.80 17.07 0.05 0.80 1.02 0.025 2.65 Balance 309 14.29 22.59 0.06 0.70 1.56 0.040 Balance 310S 19.80 24.64 0.06 0.73 1.68 0.024 Balance
(a) S-0.001 to 0.009.
Experimental Procedures 0.4 mol/liter NaCI + 0.005 mol/liter shown in Fig. 2. The BAg-6 consisted of CuCb • 2H20 aqueous solution; the tem a-Cu primary phase and eutectic struc The chemical compositions of filler perature was maintained at 25°C (77°F) ture (arAg + a-Cu). BAg-5 and BAg-4 metals and stainless steels are presented by a controlled water bath. After immer consisted mainly of a-Cu primary phase in Tables 1 and 2, respectively. The sion for certain days in test solution, and eutectic structure; however, in many machined dimensions (in mm) of the specimen cross sections were examined instances very small amounts of /? phase stainless steel base metals were: thick by an optical microscope and a profile is observed by x-ray diffraction analysis. ness—8, width—12, and length-60 projector with digital read-out facility. The microstructure of CF-12 is markedly (0.315 X 0.47 X 2.36 in.) with a center Metallurgical studies using an x-ray dif- different from others due to the exis groove of 2.5 mm (0.1 in.) radius. fractometer and scanning electron micro tence of (3 phase. Continuous crystalliza The filler metals and commercial braz scope with an energy dispersive x-ray tion of a-Cu primary phase at the braze ing flux were put in the groove. They analyzer, and electrochemical studies interface is dominant in BAg-4 brazed were heated to the brazing temperature were also carried out. specimens. in an air atmosphere furnace and held for The morphology of corrosion can be 1 min and then air cooled. Prior to the Experimental Results grouped in three types —Fig. 3. All speci brazing, the materials were rinsed in an mens underwent corrosion in the filler Microstructure and Corrosion Morphology acetone-ultrasonic bath. After brazing, metal and interface. The former was the the specimens were rinsed in warm The microstructure of filler metals is selective dissolution of a-Cu phase in filler water to remove the flux residues. The brazed specimens were then cut to 15 mm (0.59 in.) lengths and polished with no. 600 emery paper and subjected to immersion type corrosion test —Fig. 1. The specimens were designed to elimi nate voids at the brazed interfaces. Also, the area where filler metal thinly spread was eliminated by polishing. The speci x mens made it possible to measure the » S i.* ^p. ; Jfe;P A, 'mi.. interfacial corrosion length and corrosion &i* :*//i' fI Vl. ** ** depth of filler metal, respectively, and 304 304 were useful to discussion of the corrosion mechanism. y- a <% i BAe-4 'AA^ Corrosion tests were carried out using *5C *.) 12 j • ,T»
2.5R (01R)
30^
Fig. 2 — Microstructure of brazed specimens, Type 304 stainless steel base meta! X500
\ Cut after corrosion test
^" For corrosion test
mm { in) ® ® © Fig. 1—Shape and size of stainless steel (A), Fig. 3-Schematic illustration of corrosion, interfacial corrosion at stainless steel side (A), both and corrosion test specimen (B) stainless steel and filler metal (B), and dominant corrosion of filler metal (C)
WELDING RESEARCH SUPPLEMENT 1301-s 1700 3300 >4Q00 Base >4000 3 1000 g 6 b metal: SUS30A 6
CJ) c
c o \n o L- k_ 500 o o
o rd a*L—. Cb CF-12 C 10 20 30 Ti me , day
Fig. 4 — Corrosion depth of filler metals brazed with Type 304 Fig 5 —Effect of filler metal on interfacial corrosion length stainless steel
metals, similar to the dezincification of rich filler metal had superior corrosion on the corrosion depths of BAg-4 and 5 is a-brass (Refs. 8,9), and proceeded almost resistance compared to zinc-rich. Owing represented in Fig. 6. BAg-4 is more homogeneously from its surface. to the less corrosion resistant /3 phase corrosion resistant than BAg-5 on all base The corrosion path in the latter was (Refs. 8, 10, 11, 12), CF-12 showed deep metals. The depth of BAg-5 becomes somewhat complicated, depending on corrosion depth. The substitution of 2% great when combined with Type 310S the filler metal composition. In BAg-6 and Zn in CF-12 for 2% Ni in BAg-4 improved stainless steel containing much (Ni 4- Cr). BAg-5 brazed specimens, the path was the corrosion resistance remarkably. BAg-4 shows a similar tendency, but the stainless steel side (Fig. 3A), in BAg-4 the ln contrast to the corrosion depth dependency on base metal is slight. The paths were both a-Cu phase crystallized experienced with filler metals, the interfa fact that the corrosion depth of filler along interface and stainless steel (Fig. cial corrosion length on the stainless steel metal depends on the base metal compo 3B), and in CF-12 the corrosion of filler side increased with increasing filler metal sition suggests the existence of a galvanic metal from its surface was dominant — silver content —Fig. 5. Here interfacial cell between the stainless steel surface Fig. 3C. As a basic principle, the interfacial corrosion proceeded mainly along base (which is stable in test solution except at corrosion length means the length of h metal. The broken line for CF-12 brazed the braze interface) and filler metal — and l2, but in CF-12, l3 was also mea specimens shows the interfacial corrosion especially the preferentially attacked a- Cu phase. sured. length on the filler metal side (l3 in Fig. 2). Due to the specimen shape and high Interfacial corrosion length decreased corrosion rate for CF-12 filler metal, cor in high (Ni + Cr) content base metals such Effect of Filler Metal Composition rosion from the filler metal surface as Types 310S, and 309 stainless steel — The results of corrosion tests on Type resulted in a long interfacial corrosion Fig. 7. The decrease is larger for BAg-5 304 stainless steel base metal brazed by length. From a practical viewpoint, corro filler metal than for BAg-4. Since the different filler metals are shown in Fig. 4. sion at the braze interface may have stainless steel base metal suffered corro Almost parabolic corrosion depth- significance and control joint life because sion at the braze interface, the interfacial immersion time relations are shown. Cor it proceeds faster than the corrosion of corrosion resistance should depend on rosion resistance decreased in this order: filler metal. Within the range of the inves that of the base metal. BAg-6, BAg-4, BAg-5, and CF-12. tigation reported here, BAg-4 filler metal The results shown in Fig. 7 coincided The copper content in the filler metals will be desirable for practical use. well with the above idea, because the may be regarded as having been con high Ni + Cr content base metal showed stant. It is when zinc content was good interfacial corrosion resistance. The Effect of Stainless Steel Composition increased that filler metal became less interfacial corrosion length brazed with corrosion resistant. In other words, silver- The effect of base metal composition BAg-4 has a slight dependence on base
Test period : 01Odays , []28days Filler metal : BAg-4 Filler metal : BAg- 5 E E 200 - 1 r =1. • 1000
I c
0>
100 500
Base metal 30A30AL321 316 309 310S 304 304L321 316 309 310S Base metal 304 304L 321 316 309 310S 304 304L321 316 309 310S Fig. 6 — Effect of base metal on corrosion depth of filler metal Fig. 7 —Effect of base metal on interfacial corrosion length
302-s | OCTOBER 1984 700 as already indicated in Fig. 8. Thus, the SUS SUS SUS Condition Anodic , 10 mV/min braze interface on the stainless steel side 600 304 309 310S is less corrosion resistant than the bulk Emery polished O A a stainless steel surface. Therefore, the gal Flux-treated • A • vanic effect among the following four ui 500 phases are expected: stainless steel sur
Table 3—Estimated Composition of a-Cu and «i-Ag Phase in Each Filler Metal, Wt- %
arAg phase a-Cu phase Lattice Lattice Filler metal constant, A Ag Zn Cu constant, A Cu Zn Ag BAg-6 4.0445 89 8 3 3.7220 66 31 3 BAg-5 4.0143 77 20 3 3.7225 57 40 3 CF-12 4.0065 74 23 3 3.7000 57 40 3
WELDING RESEARCH SUPPLEMENT 1303-s Fig. 9. Saturated calomel electrode cathodes and that the flux-treated stain SUS310S (S.C.E.) was used as a reference elec less steels are anodes. SUS309 trode. The potentials of stainless steel The increase in zinc content decreased LU 200 SUS304 base metal and arAg phase are shown the galvanic current between the arAg (J to be higher than potentials for filler phase and flux-treated stainless steel. to metals and a-Cu phase. The corrosion Therefore, the low zinc content arAg Ui 100- potential of the brazed specimen was phase in BAg-6 (Table 3) seems to be > about -80 100mV (S.C.E.) irrespec responsible for the increased interfacial > tive of base metal and filler metal compo corrosion; however, the contact current E -— tfi-Ag sitions. dependence of zinc is somewhat slight in 0 y> Flux-treated Potential measurements revealed that the range of 8 ~ 23% Zn. ln addition, due .12 stainless steal stainless steel and arAg phase have the to the high silver content of BAg-6, the c ability to act as effective cathodes. The surface area of the arAg phase is larger Of -100-—Brazed specimen potentials of previously flux-treated stain than that of BAg-5 and CF-12. An o ir BAg-6 less steels were higher than brazed spec increase of cathode area provides large imens, indicating that the phases are rela anodic current density. Thus, the reason Q. BAg-5, BAg-4 a tively stable in the test solution. But as for the marked increase in the interfacial 200-|\ -Cu already mentioned, the flux treated sur corrosion length in stainless steel brazed CF-12 face was repassivated. Considering the with high silver content BAg-6 filler metal repassivation of the flux treated speci may be attributed to the increase of Fig. 9 — Corrosion potentials of various men, the potential at the braze interfaces contact current due to the decrease of phases should be much lower and more active zinc in arAg phase and the increase of than observed ones. cathode area (amount of arAg phase) by the increase of silver content. the 40% Zn in a-Cu phase of BAg-5 and CF-12 is almost the solubility limit (Refs. Current between <*rAg Phase and Stainless 14, 15). Therefore, it was to be expected Steel Current between Stainless Steels and a-Cu that zinc additions to CF-12 would allow Phase the existence of much /3 phase. Zinc in Galvanic currents between arAg arAg phase increased in the following phases (Ag-Zn-3Cu alloys) of various zinc The galvanic current between the order: BAg-6, BAg-5, CF-12. This coincid contents and stainless steels were mea stainless steel (emery polished) and a-Cu ed with the order of zinc content in filler sured by obtaining the polarization phase (Cu-31Zn-3Ag alloy) was measured metals. curves between them. The contact cur to clarify the effect of stainless steel rent between the arAg phase cathode composition on the corrosion of filler and flux-treated stainless steel anode metal. Furthermore, the galvanic current Potential Measurements depends on the zinc content in arAg between the emery polished and flux- The corrosion potentials of the alloys phase —Fig. 10. The positive current in treated stainless steels was also mea and brazed specimens were measured — Fig. 10 means that arAg phases are sured. The results are shown in Table 4.
500 Cathode : Ag-Zn-3Cu alloys CNI 2 Anode : Flux-treated stainless steels O -— G 1
200 .• Uncoated(Ci) Test period : 28days. E 0 Coated (C2) Ha SUS 309
SUS310S Q. di 10 20 T3 100 i ft at Zinc content , wt % C Fig. 10 — Contact current between arAg phases with different zinc o '(/> content and flux-treated stainless steels o ol_ u 0 Base metal 304 309 310S 304 309 310S Fig. 11 (right) — Effect of stainless steel surface on corrosion depth of (SUS) filter metals Filler metal BAg-4 BAg-5
304-s | OCTOBER 1984 Table 4—Galvanic Current Measured By Polarization Curves, Surface Area Ratio Of Cathode to Anode Is Unity
Current density Type stainless steel cathode'3' Anode /nA/cm2 (fiA/'in.2) a 304 ,, a, Cu-31Zn-3Ag< > 110 (710) 309 |Emery 1 Cu-31Zn-3Ag 130 (840) 310S \P°ilsned/ Cu-31Zn-3Ag(a> 150 (970) (b) 304 /Emer v Type 304 100 (650) Type 309"" 85 (550) Polished 310S \ / Type 310S(bl 85 (550)
{a) Emery polished, (b) Flux treated.
Here it may be seen that the stainless after the flow of filler metal yields saturat (Ref. 16). The nickel content in the a-Cu steel surface acts as an effective cathode ed a-Cu and arAg phase. This means phase of BAg-4 is estimated to be 4.7% to the a-Cu phase, indicating that the that a-Cu phase with high silver and when neglecting the mutual solubility stainless steel surface accelerates the cor arAg phase with high copper are co between arAg and a-Cu phase and zinc rosion of filler metal. existent. This may relieve the galvanic fluctuation. Nickel in a-Cu phase appears The cathodic effect of the stainless current between arAg phase and stain to be effective for the suppression of steel surface is also clear from the results less steel at the interface, and between dezincification type corrosion. A similar of experiments indicating that the corro stainless steel surface and a-Cu phase. effect was confirmed in Ag-Cu-Cd-Zn-Ni sion depth of filler metal was unaffected The results of corrosion tests on BAg-3 type filler metal (Ref. 4). when the stainless steel surface was cov quenched specimens brazed with BAg-4 Nickel in filler metal affects interfacial ered by silicon resin —Fig. 11. The corro and 5 filler metals are shown in Figs. 13 corrosion. Figure 16 shows the line analy sion depths of filler metal with coated and 14. The corrosion of both the filler sis of nickel, chromium and iron at a base metal were almost the same, irre metal and the interface are improved by brazed interface. The nickel-depleted spective of the base metal composition. quenching. However, the application of zone was formed by the use of nickel- The corrosion resistance of BAg-4 is quenching for commercial use seems to less filler metals, irrespective of stainless always superior to that of BAg-5. The be somewhat impractical because steel composition; however, the addition C1/C2 ratio of the corrosion depth of quenching may yield torsion and because of 2%Ni (BAg-4) prevented the formation filler metal with uncoated base metal (C-i) of the difficulty of quenching tempera of a nickel-depleted zone over a depth of to coated base metal (C2) increased with ture control. On the other hand, it is several microns. the increase in Ni + Cr content of base noteworthy that quenching is effective in The line profiles of chromium and iron metal; this indicated that the corrosion improving the corrosion resistance of are homogeneous and decreased drasti depth increased through contact with stainless steels brazed with silver-base cally only at the interface. However, the high Ni + Cr content stainless steel, coin filler metals. nickel-depleted zone changed into ferrite ciding well with the galvanic current mea phase —Table 5. The composition of the surement. nickel-depleted zone in Type 304 stain Effect of Nickel Addition The above results confirm that the less steel is similar to that of Type 430 presence of stainless steel — especially Nickel has been known as a dezincifi- stainless steel. The corrosion potential of high Ni + Cr content stainless steels — cation suppressing element for brass (Ref. flux treated Type 430 stainless steel was accelerates the corrosion of filler metal. 10). Fortunately, nickel added to a ternary less than —660 mV (S.C.E.) and showed Galvanic current between emery pol alloy is preferentially distributed in the large anodic current under small anodic ished and flux-treated stainless steels is a-Cu phase (Fig. 15), because both silver polarization by a potentiostat. This not changed with Ni -I- Cr content. This and zinc have little solubility of nickel served to confirm that the phase is less means that the high Ni + Cr content stainless steel is less susceptible to the flux treatment due to its high corrosion resis tance, even though its surface has a great affinity for cathodic effects. _0J Ik S.S., Figure 12 shows the cathodic effects of o - Ag phase a stainless steel surface and arAg phase. Increasing the Ni + Cr content in the stainless steel or the silver content in the filler metal shifts the cathodic polarization curve from A to B as indicated by an arrow. The shift increases the anodic current from i to i and gives large c A B
The results of experimentation suggest WELDING RESEARCH SUPPLEMENT 1305-s 200 1000 Base metal :SUS304 Base metal: SUS304 E Test period: 01Odays Test period: 01Odays, • 28days E D 28days 3. cn c f 100 A 2 500 - c o o & o ri oin a— HI i_ u o (TJ u a+- f 1_ rf c . 1 0 s 1 Air Quench Air Quench Air Quench Air Quench cool cool cool cool i i I BAg-5 BAg-4 BAg-5 BAg-4 Fig. 14 — Improvement of interfacial corrosion length by quenching Fig. 13 —Improvement of corrosion depth of filler metals by quench ing corrosion-resistant than nickel containing corrosion. It may be attributable to the BAg-4 ones. use of brazing flux which leaves the Instead of nickel, filler metal constitu active thin layer free of protective pas ents (Ag,Zn,Cu) are observed in the sive films. In addition, once interfacial zone. The formation rate of the nickel- corrosion starts due to the galvanic depleted zone is controlled by the diffu effect, corrosion may proceed by the aid sion of nickel in austenitic stainless steel of the oxygen concentration cell (Ref. 17). Nickel depletion may be attrib between the penetrating corrosion tip uted to the fact that the molten filler and the surface bulk area. metal has extensive solubility only for nickel. Thus, the addition of nickel in filler Conclusion metal prevented the dissolving of nickel in filler metal and also prevented the Investigation on the effect that brazing formation of a nickel-depleted zone. The with silver-base filler metal and stainless effect of nickel in filler metal on the steel compositions have on the corrosion Fig. 15 —Line analysis of BAg-4 by electron improvement of the interfacial corrosion behavior of brazed joints in chloride probe micro-analyzer is attributed to the prevention of forma solution led to the following: tion of a less corrosion resistant nickel- 1. In ternary Ag-Cu-Zn silver-base filler depleted zone at braze interface. metals with almost equal copper, an Even in nickel bearing filler metals, increase of silver (i.e., decrease of zinc) however, stainless steel suffers interfacial improves the corrosion resistance of the Table 5—X-Ray Diffraction Analysis of Stainless Steel Base Metals and Nickel-Depleted Zones, (CoKa, Fe filler, 40kV, 20mA) Calculations Austenite Observations Ferrite Fe- Fe- ned, after brazing heat cycle Nickel-depleted zone Emery polls 16.1G- 23.390- Fe- ASTM data for Type 304 Type 309 Type 310S Type 304 Type 309 Type 310S 12.0Ni 21.39Ni 18.1Cr pure a-Fe d I d I d I d I d I d I d d d d (hkl) 2.070 VS 2.073 S 2.073 S 2.070 vs 2.073 W 2.073 W 2.069 2.071 2.029 S 2.031 S 2.033 S 2.031 2.0268 110 1.794 M 1.798 M 1.798 M 1.794 M 1.798 vw 1.798 vw 1.792 1.794 1.438 W 1.438 vw 1.438 vw 1.436 1.4332 200 1.269 M 1.270 W 1.271 W 1.269 W (a) d-spacing. A; I-intensity, VS>S>M>W>vw 306-s I OCTOBER 1984 Fig. 16-Line analysis of nickel, chromium and iron at brazed interface showing nickel-depleted zone in stainless steels brazed with nickel-less filler metals. X960 (reduced 26% on reproduction) filler metal, itself; however, it increases sion resistance of a brazed joint. 7. Steffens, H. D., Richer, B., und Lange, H. the interfacial corrosion on the stainless 1975. Einfluss korrosiver Medien auf die steel side. Lebensdauer hartgeloter Verbindungen (Teil I). 2. The substitution of Type 304 base A ckno wledgment Werkstoffe und Korrosion 26(11):836-843. 8. Langenegger, E. E., and Robinson, F. P. A. metal for high Ni + Cr content stainless The authors would like to thank Mr. steels (such as Type 31 OS) increases the 1969. A study of the mechanism of dezincifica- Chikara Fujiwara for the experimental tion of brasses. Corrosion 25(2):59-66. corrosion of filler metal but decreases the work. 9. Natarajan, R., Angelo, P. C, George, N. interfacial corrosion. T., and Tamhankar, R. V. 1975. Dezincification 3. Corrosion depth dependency on of cartridge brass. Corrosion 31(8): 302-303. References the base metal and interfacial corrosion 10. Roges, T. H., 1968. Marine Corrosion: length dependency on the filler metal 1. Sistare, C.H., Halbig, IT, and Crenell, L.H. 118 London: George Newhes Ltd. composition are explainable in terms of 1954. Silver brazing alloys for corrosion-resis 11. Butts, A. 1954. Copper-the science the galvanic effect between the a-Cu tant joints in stainless steels. Welding Journal and technology of the Metal, its alloys and phase and stainless steel surface, and 33 (2):137-143. compounds, p. 383. New York: Reinhold Pub between the flux-affected stainless steel 2. Kawakatsu, I. 1973. Corrosion of BAg lishing Corp. (nickel-depleted zone) at the braze inter brazed joints in stainless steel. Welding Journal 12. Poling, G. W., and Notoya, T. 1979. Corrosion pretreatments for copper-zinc face and arAg phase, respectively. 52 (6):233-s to 239-s. 3. Stock, D. C, and Smellie, W. ). 1960. alloys. Corrosion 35 (1): 33-38. 4. A nickel-depleted zone is formed in Soldering stainless steels. Welding and Metal 13. Pearson, W. B. 1967. A handbook of stainless steel at the braze interface when Fabrication 23(4):160-161. lattice spacings and structures of materials and nickel-free filler metal is used. The zone 4. Mahler, W., und Zimmerman, K. F. 1977. alloys: Oxford: Pergamon Press. showed ferrite structure. The zone and Beitrag zur Frage der Meerwasserbestandig- 14. Weigert, K. M. 1954. Constitution and the removal of passive films by brazing keit von Hartlotverbindungen-Entzinkungskor- properties of Ag-Cu-Zn binary alloys. Journal flux are believed to be responsible for the rosion. /Vfefa//31(9):971-974. of Metals 6 (2):233-237. enhanced interfacial corrosion. 5. Jarman, R. A., Myles, ). W7, and Booker, 15. Gebhardt, E., Petzow, G., and Krauss, W. 1962. Uber den Aufbau des Systems Kup- 5. The addition of nickel in filler metal C. ). L. 1973. Interfacial corrosion of brazed stainless steel joints in domestic tap water. fer-Silver-Zink. Z. Metallkde. 53(6):372-379. relieves the interfacial corrosion by pre British Corrosion Journal 8(1):33-37. 16. Hausen, M. 1958. Constitution of binary venting the formation of a less corrosion 6. Herbsleb, C. und Schwenk, W. 1975. alloys, New York: McGraw-Hill Book Compa resistant nickel-depleted zone in the Korrosionsverhalten von Edelstahlrohren und ny. stainless steel at the brazed interface. Rohrverbindungen bei der Warmwasserver- 17. Takemoto, T. and Okamoto, L. 1984. 6. Quenching the specimen is effec teilung in der Hausinstallation. Werkstoffe und Quarterly journal of Japan Welding Society. tive tor the improvement of the corro Korrosion 26(2):93-103. 2(2):300-308. WELDING RESEARCH SUPPLEMENT 1307-s