FURNACE BRAZING IN DRY HYDROGEN FURNACE CONTINUOUS CONVEYOR (A) FIXTURES NONE FURNACE TEMPERATURE, °C (°F) 980 ± 5 (1800 ± 10) BRAZING TEMPERATURE, °C (°F) 925 ± 5 (1700 ± 10) HYDROGEN DEW POINTS, °C (°F) -75 (-100) (B) ; -60 (-70) (C) HYDROGEN FLOW RATE, M 3 /H (FT 3 /H) 11 (400) FILLER METAL (D) BAG- 13 JOINT POSITION DURING BRAZING HORIZONTAL CONVEYOR TRAVEL SPEED, M/H (FT/H) 9 (30) TIME AT BRAZING TEMPERATURE, MIN (E) 5 PRODUCTION RATE, ASSEMBLIES/H 120 (A) ELECTRICITY HEATED (60 KW), CONSTRUCTED WITH HEATING CHAMBER HIGHER THAN ENTRANCE AND DISCHARGE ENDS. (B) INCOMING. (C) EXHAUST. (D) IN FORM OF 1 MM (0.040 IN.) DIAMETER WIRE-RING PREFORMS. FIG. 3 RETAINER ASSEMBLY FURNACE BRAZED WITH BAG-13 FILLER METAL The components were vapor degreased, assembled (keeping their outside diameters concentric), and spot welded (to make them self-jigging) at four locations 90° apart (Fig. 3). A ring of brazing filler metal wire in a 1 mm (0.040 in.) diameter was preplaced at the joint, and assemblies were loaded two-across on the mesh belt of a conveyor-type furnace. The heating chamber of the furnace was elevated from the entrance and discharge level to conserve the lighter-than-air hydrogen and to prevent oxygen in the atmosphere from mixing with the hydrogen, which could either raise the dew point or cause an explosion. Quality standards for brazed assemblies, which were checked by 100% visual inspection, required that the joint exhibit full braze penetration (360° fillets on both sides of the joint) and be pressure-tight. Example 4: Use of a Gold Brazing Filler Metal for Brazing in an Aerospace Heat Exchanger. In the fabrication of a high-reliability heat exchanger for manned space flights, 2552 fins of 0.10 mm (0.004 in.) thick type 347 stainless steel were brazed to 0.64 mm (0.025 in.) thick type 347 stainless steel side panels, as shown in Fig. 4. The 5104 fin-to-panel joints had to be strong and corrosion resistant. FURNACE BRAZING IN DRY HYDROGEN FURNACE BELL (A) FIXTURES (SEE ILLUSTRATION) BRAZING TEMPERATURE, °C (°F) 1015 (1860) HYDROGEN DEW POINT (MAX), °C (°F) -60 (-80) (B) PURGING (C) 5 FILLER METAL (D) BAU-4 NUMBER OF ASSEMBLIES PER LOAD 1 PROCESSING TIME PER ASSEMBLY CLEAN COMPONENTS, MIN 45 PREPLACE FILLER METAL, H 1.25 ASSEMBLE COMPONENTS IN FIXTURE, H 4 TIME AT BRAZING TEMPERATURE, MIN 7-10 TOTAL TIME IN FURNACE (E) , H 4 INSPECT, H 1 PRESSURE TEST, H 40 (A) ELECTRICALLY HEATED, WITH 36 IN. DIAM RETORT WITH WATER- COOLED RUBBER SEALS. (B) HYDROGEN WAS PURCHASED AS CYLINDER HYDROGEN, THEN PASSED THR OUGH AN ELECTROLYTIC DRIER. (C) NUMBER OF VOLUME CHANGES IN RETORT. (D) 200-MESH POWDER SUSPENDED IN AN ORGANIC BINDER. (E) INCLUDING COOLING TO 150 °C (300 °F) IN RETORT, WHICH WAS PURGE D WITH ARGON BEFORE BEING OPENED FIG. 4 HEAT-EXCHANGER ASSEMBLY IN BRAZING FIXTURE AND DETAIL OF JOINTS B RAZED WITH GOLD BRAZING FILLER METAL Silver and copper brazing filler metals could not be used, because of their incompatibility with sulfur-bearing rocket fuel. The BNi series of nickel brazing filler metals had the necessary compatibility, but made nonductile joints that were unreliable under tension peel stress. Therefore, gold brazing filler metals were used. The necessary brazing characteristics for the fin-to-panel joints were present in BAu-4 (nominal composition, 82Au-18Ni). The strength and ductility of the resulting brazed joints justified the high cost of this particular brazing filler metal. The fins and side panels were cleaned by vapor degreasing. The side panels were then pickled, rinsed in clean water, and dried. The brazing filler metal was deposited on the panels in the form of a powder suspended in an organic binder. Multiple lap joints were made between the flat-crown-hairpin ends of the fins and the flat side panels. The assembly was placed in a fixture (Fig. 4), and then the entire assembly and fixture were placed in the retort of a bell-type furnace and sealed. The sealed retort was purged with a volume of hydrogen that was equivalent to five times that of the retort. The retort was then heated to a brazing temperature of 1020 °C (1860 °F) and held for 7 to 10 min. The joint gaps at brazing temperature ranged from 0.000 to 0.254 mm (0.010 in.). After brazing, the retort was purged with argon while being cooled to 150 °C (300 °F) and was not opened until after purging and cooling. The joints brazed by this procedure were the final brazed joints in the assembly. In a prior brazing operation, tubes had been joined to the fins (Fig. 4) by brazing at 1080 °C (1970 °F) using a higher-melting-point gold brazing filler metal of 70Au-22Ni-8Pd. The completed assemblies were visually inspected and pressure tested at pressures that far exceeded those of the intended service environment: 1.86 MPa (270 psi) on the outside of the tubes and 11.8 MPa (1710 psi) on the inside. Acceptance pressure test values were 3.7 MPa (540 psi) on the outside and 15.7 MPa (2275 psi) on the inside of the tubes. Selected brazed assemblies were tested to bursting. These assemblies were required to withstand at least three times the service pressures before bursting. The assemblies that were brazed with gold brazing filler metals passed all tests and had three times the bursting strength of the assemblies brazed with undiffused nickel brazing filler metal. Example 5: Combination Brazing and Solution Heat Treatment of an Assembly of Three Types of Stainless Steel. Three different stainless steels were selected to make the cover for a hermetically sealed switch. The switching action had to be transmitted through the cover without breaking the seal. This was accomplished by providing a diaphragm through which a shoulder pin was inserted, as shown in Fig. 5. The switch was actuated by depressing the pin, which in turn deflected the diaphragm. The pin (type 303), the diaphragm (PH 15-7 Mo), and the cover (type 305) were assembled as shown in Fig. 3, and then brazed using a silver-base filler metal in a furnace with dry hydrogen. FURNACE BRAZING IN DRY HYDROGEN FURNACE (A) BATCH-TYPE TUBE FIXTURE MATERIAL (B) STAINLESS STEEL BRAZING TEMPERATURE, °C (°F) 955 ± 8 (1750 - 15) FILLER METAL (C) BAG-19 TIME AT BRAZING TEMPERATURE, MIN 10 TIME IN FIRST COOLING ZONE (D) , MIN 5 TIME IN FINAL COOLING ZONE (D) , MIN 5 (A) THREE-ZONE FURNACE WITH A HIGH-HEAT ZONE 125 MM (5 IN.) IN DIAME TER BY 460 MM (18 IN.) LONG. (B) FIXTURE LOCATED AND HELD COMPONENTS OF ASSEMBLY TOGETHER AND WAS PLACED ON A STAINLESS STEEL SLED FOR TRANSPORT THROUGH THE FURNACE. (C) PREFORMED WIRE RINGS. (D) AT 540 °C (1000 °F). (E) WATER-COOLED ZONE, IN WHICH ASSEMBLY WAS COOLED TO ROOM TEMPERATURE. TO COMPLETE HEAT TREATMENT OF THE PH 15-7 MO DIAPHRAGM, ASSE MBLY WAS FIG. 5 THREE-STEEL SWITCH-COVER ASSEMBLY THAT UTILIZED BRAZING TEMPERATURE AS PA RT OF SOLUTION HEAT TREATMENT Silver brazing filler metal BAg-19 was chosen because it flowed at a temperature that coincided with the solution heat- treating temperature for the PH 15-7 Mo diaphragm (950 °C, or 1750 °F). A holding fixture was needed to keep the PH 15-7 Mo diaphragm in position during the brazing cycle. To avoid carburizing the diaphragm, the material selected for the fixture was stainless steel, rather than graphite. The furnace was a batch-type tube furnace with a 120 mm (5 in.) diameter high-heat zone that was 460 mm (18 in.) long. The moisture content of the hydrogen atmosphere was carefully controlled, because the lithium-containing filler metal flowed too freely when the atmosphere was too dry, and it did not seal the joints. After being cleaned, the components were assembled with two preform rings of BAg-19 wire. Tweezers were used to avoid contaminating the cleaned surfaces. Each assembly was held in a stainless steel fixture, which in turn was placed on a stainless steel furnace sled. The sled was pushed into the high-heat zone of the furnace and held at 950 °C (1750 °F) for 10 min, before being pulled into an intermediate cooling zone at 1830 °C (1000 °F) and held for 5 min. Finally, it was pulled to the water-cooled zone, where it cooled to room temperature. The brazing of the two joints and the solution treating of the PH 15-7 Mo diaphragm were accomplished simultaneously at the brazing temperature of 950 °C (1750 °F). To complete the heat-treating process, the assembly was cooled to -70 °C (-100 °F), held for 8 h, and then aged at 510 °C (950 °F) for 1 h. A 25 mm (1 in.) square piece of PH 15-7 Mo was processed with each batch of cover assemblies and used as a hardness test specimen to verify that the diaphragms had been correctly heat treated. Brazed assemblies were inspected by the brazing operator. The joints were required to be fully sealed and to not have any voids. The pins were required to be perpendicular within 4°. Perpendicularity was measured on a comparator. Randomly selected samples were given a push- out test, in which joints had to withstand a push of 60 N (14 lbf). All assemblies were given 100% visual inspection at high magnification. Example 6: Simultaneous Brazing of a Heat-Exchanger Assembly. An air-to-air heat-exchanger assembly, shown in Fig. 6, consisted of 185 thin-walled (0.20 mm or 0.008 in.) tubes and two 1.6 mm ( 1 16 in.) thick headers. All components were made of type 347 stainless steel. The tubes were assembled with the headers by flaring the tube ends to lock them in place and provide metal-to-metal contact for the brazing filler metal. All 370 joints were brazed during a single pass through a continuous conveyor-type electric furnace. FURNACE BRAZING IN DRY HYDROGEN FURNACE (A) CONTINUOUS CONVEYOR FIXTURE MATERIAL (B) TYPE 347 STAINLESS STEEL FURNACE TEMPERATURE, °C (°F) 1120 ± 5 (2050 ± 10) BRAZING TEMPERATURE, °C (°F) 1065 ± 5 (1950 ± 10) HYDROGEN DEW POINTS, °C (°F) -75 (-100) (C) ; -60 (-70) (D) HYDROGEN FLOW RATE, M 3 /H (FT 3 /H) 17 (600) FILLER METAL (E) BNI-3 POWDER CONVEYOR TRAVEL SPEED, M 3 /H (FT 3 /H) 9 (30) TIME AT BRAZING TEMPERATURE, MIN 5 COOLING IN HYDROGEN ATMOSPHERE ASSEMBLY PRODUCTION RATE/H 15 (A) ELECTRICALLY HEATED (60 KW), CONSTRUCTED WITH HEATING CHAMBE R HIGHER THAN ENTRANCE AND DISCHARGE ENDS. (B) HOLDING FIXTURE FABRICATED FROM 3.2 MM ( 1 8 IN.) THICK SHEET. (C) INCOMING. (D) EXHAUST. (E) MIXED TO A SLURRY WITH ACRYLIC RESIN AND XYLENE THINNER; POWDER-TO- VEHICLE RATIO, 70/30 FIG. 6 HEAT-EXCHANGER ASSEMBLY WITH TUBE-TO-HEADER JOINTS BRAZED IN ONE PASS THROUGH A FURNACE Although a nickel brazing filler metal was preferred for this high-temperature application, because of the resistance to heat and corrosion that it provides, the selection of a specific nickel brazing filler metal presented a problem. Higher- melting-point, boron-containing nickel brazing filler metals, such as BNi-1 and BNi-3, will react with the base metal, partially dissolve, and therefore are likely to erode thin materials. Fortunately, the extent of erosion can be modified by controlling the brazing temperature and time, as well as the amount of filler metal. Although there are nickel brazing filler metals that contain silicon in place of boron, they generally require much higher brazing temperatures, which can result in grain coarsening in the base metal. Therefore, after numerous tests, BNi-3 filler metal was selected on the basis of its brazing temperature and excellent fluidity. The problem of applying the correct amount of filler metal to avoid erosion was solved by preparing a slurry from an accurately controlled mixture of filler- metal powder, acrylic-resin binder, and xylene thinner. Before the filler metal was applied, the heat-exchanger assembly was cleaned ultrasonically in acetone and carefully weighed to determine the proportionate weight of filler metal that would be required. Half of the total amount of filler metal was then applied to one end of the assembly by spraying. The assembly was reweighed, and the remaining filler metal was applied to the opposite end. At all stages of processing, the assembly was handled by operators wearing clean, lint-free cotton gloves. The assembly was placed on a holding fixture made of stainless steel sheet, on which a stop-off compound had been applied to prevent the assembly from brazing to the fixture if the brazing filler metal flowed excessively. Assemblies were placed 300 mm (12 in.) apart on the conveyor, as they traveled through the furnace at 9 m/h (30 ft/h) under the protection of dry hydrogen. After brazing, each side was subjected to 100% visual inspection to detect the presence of fillets, and the assemblies were pressure tested in accordance with customer requirements. Because of the thin-walled (0.20 mm, or 0.008 in.) tubing, this assembly was brazed more consistently and at a lower cost than could have been achieved by other joining processes. Example 7: Combined Brazing and Hardening of a Shaft Assembly. The shaft assembly shown in Fig. 7 consists of three bars or screw machine products (a shaft, a drive pin, and a guide pin) and two stampings (upper and lower mounting plates), all made from type 410 stainless steel and furnace brazed together using four joints. By brazing with copper filler metal at 1120 °C (2050 °F), it was possible to austenitize and harden the assembly to the required minimum hardness value of 40 HRC during the brazing and cooling operations, thereby avoiding separate hardening operations after brazing. FURNACE BRAZING IN DRY HYDROGEN FURNACE (A) CONTINUOUS CONVEYOR FIXTURES (B) NONE FURNACE TEMPERATURE, °C (°F) 1175 ± 5 (2150 ± 10) BRAZING TEMPERATURE, °C (°F) 1120 ± 5 (2050 ± 10) HYDROGEN DEW POINTS, °C (°F) -75 (-100) (C) ; -60 (-75) (D) HYDROGEN FLOW RATE, M 3 /H (FT 3 /H) 11 (400) FILLER METAL (E) BCU-1 WIRE, BCU-2 PASTE CONVEYOR TRAVEL SPEED, M/H (FT/H) 6 (20) TIME AT BRAZING TEMPERATURE (F) , MIN 8 COOLING IN HYDROGEN ATMOSPHERE ASSEMBLY PRODUCTION RATE/H 800 (A) ELECTRICALLY HEATED (60 KW), CONSTRUCTED WITH HEATING CHAMBER HIGHER THAN ENTRANCE AND DISCHARGE ENDS. (B) COMPONENTS WERE STAKED, FOR SELF-FIXTURING. ASSEMBLIES, SUPPORTED BY CERAMIC SPACERS TO KEEP SHAFT END UP, WERE BRAZED ON TRAYS. (C) INCOMING. (D) EXHAUST. ONE END OF DRIVE PIN, BOTH ENDS OF GUIDE PIN. (F) ASSEMBLIES WERE IN HIGH HEAT ZONE FOR ABOUT 10 MIN. FIG. 7 FOUR-JOINT SHAFT ASSEMBLY THAT WAS SIMULTANEOUSLY FURNACE BRAZED AND HEA TED FOR HARDENING Because the joints were all relatively short, an interference fit of 0.000 to 0.025 mm (0.001 in.) was satisfactory. Typically, a clearance fit between mating parts is required with longer joints in stainless steel. The automatic staking of components was used to make the assembly self-fixturing. As shown in Fig. 7, a full ring of 0.50 mm (0.020 in.) diameter BCu-1 copper wire was preplaced around the 13 mm ( 1 2 in.) diameter shaft to braze the shaft to the upper and lower mounting plates. A small amount of BCu-2 copper paste was applied at one end of the drive pin to braze it to the two mounting plates. Because of the separation between the two plates on the guide-pin side, a small amount of BCu-2 copper paste was manually applied on each end of the guide pin. The assemblies were placed in brazing trays, with the shaft in a vertical position, and were supported in this position by ceramic spacers. The brazing trays were then placed on the mesh belt of a continuous-type conveyor furnace containing a dry hydrogen atmosphere. They were transported up an incline to the horizontal preheat and high-heat chambers at a speed of 6 m/h (20 ft/h). Because the assemblies were small, they became heated to the brazing temperature in about 2 min. After 8 min at the brazing temperature, the assemblies were conveyed into water-jacketed cooling chambers, where they cooled rapidly in the hydrogen atmosphere to room temperature. Brazed assemblies that were bright and oxidation-free emerged from the exit end of the furnace. The brazed assemblies were 100% visually inspected for complete joint coverage. Hardness tests on a sampling basis were used to determine whether the assemblies had responded properly to hardening. Tempering to the desired final hardness followed the simultaneous brazing and hardening operation. Example 8: Medical Device Brazed, Rather than Welded, in Hydrogen. Because of the need for strong, corrosion-resistant, and leak-proof joints in a stainless steel blood-cell washer (Fig. 8), the process that was selected was hydrogen furnace brazing with BNi-7 brazing filler metal. The devices are used to expedite and standardize cell-washing procedures in blood banks and hematology laboratories. Therefore, neither voids nor cracks could be tolerated, because the possibility of breeding bacteria in the devices had to be avoided. FIG. 8 MANIFOLD AND CANNULAS TUBE ASSEMBLY OF A BLOOD-CELL WASHER THAT WAS HYDROGEN FURNACE BRAZED WITH BNI-7 BRAZING FILLER METAL AT 1040 °C (1900 °F). COURTESY OF WAL L COLMONOY CORPORATION Brazing, rather than welding, was chosen to join the manifold and the delicate tube parts of the washer, a rake-like component with twelve prong-like cannulas tubes that extend approximately 150 mm (6 in.) from a cylindrical manifold. The manifold assembly was brazed using BNi-7 nickel brazing filler metal in a hydrogen atmosphere at 1040 °C (1900 °F). After assembling the tubes to the manifold, the brazing filler metal was applied to the joints and the assembly was placed in the furnace. Components were wired to stainless steel fixtures to maintain uniform tube spacing. The brazing permitted the filler metal to flow completely around the thin-walled tubes, which was not possible with welding, leaving smooth fillets without voids that could trap harmful bacterial particles. Additional advantages of brazing were that it: minimized the amount of assembly distortion, eliminated flux hazards, simplified inspection procedures, and prevented the oxidation. Brazing of Stainless Steels Revised by Matthew J. Lucas, Jr., General Electric Aircraft Engines Furnace Brazing in Dissociated Ammonia When ammonia is free of moisture and is 100% dissociated, it becomes a suitable atmosphere for the brazing of stainless steel using selected brazing filler metals without requiring a flux. Although dissociated ammonia is strongly reducing, it is less so than pure, dry hydrogen. Consequently, it will promote wetting action by reducing chromium oxide on the surface of stainless steel, but it may not be sufficiently reducing to promote the flow of some brazing filler metals, such as copper oxide powders. Because of its high (75%) hydrogen content, dissociated ammonia forms explosive mixtures with air and must be handled with the same precautions as those required for the handling of hydrogen. A dissociated-ammonia atmosphere is prepared by heating anhydrous liquid ammonia in the presence of an iron or nickel catalyst. The decomposition of ammonia to form hydrogen and nitrogen begins at 315 °C (600 °F), and the rate of decomposition increases with temperature. Unless the atmosphere used in brazing stainless steel is completely decomposed, that is, 100% dissociated, even minute amounts of raw ammonia (NH 3 ) in the atmosphere will cause the nitriding of stainless steel, especially steels containing little or no nickel. In addition, because of the solubility of ammonia in water, the atmosphere that comes from the dissociator must be extremely dry (preferably having a dew point of -60 °C, or -80 °F, or lower). To ensure a very low dew point, the atmosphere that comes from the dissociator is commonly processed by being passed through a molecular-sieve dryer. To avoid the oxidation of base metal and brazing filler metal, the atmosphere must be kept pure and dry while it is inside the furnace. In the following examples of production practices, dissociated ammonia was used successfully in the furnace brazing of austenitic and precipitation-hardening (PH) stainless steels. Example 9: Brazing in Dissociated Ammonia Without Flux. The pressure gage subassembly shown in Fig. 9 comprises five diaphragms of 17-7 PH stainless steel, a deep-drawn cup and a top fitting of type 304 stainless steel, and a connector of copper alloy 145 (tellurium-bearing copper). Originally, these subassemblies were furnace brazed with a silver brazing filler metal that required a flux. Because applying flux and assembling the fluxed components with gloved hands was time consuming, the decision was made to change to fluxless brazing in an atmosphere of dissociated ammonia. Although this necessitated using a more-expensive brazing filler metal (BAg-19), the higher cost was offset by the greater productivity of each operator. In addition, subassemblies brazed with BAg-19 in dissociated ammonia exhibited fewer leaks and had improved corrosion resistance and a better appearance than those brazed with the original filler metal and a flux. FURNACE BRAZING IN DISSOCIATED AMMONIA FURNACE (A) CHAIN-BELT CONVEYOR FURNACE TEMPERATURE (B) , °C (°F) 980 (1800) DISSOCIATED-AMMONIA DEW POINT (C) , °C (°F) -60 (-80) FILLER METAL (D) BAG-19 FLUX (E) NONE FURNACE BELT SPEED, MM/MIN (IN./MIN) 255 (10) HEATING TIME, MIN 5 COOLING-CHAMBER TEMPERATURE (F) , °C (°F) 15 (60) PRECIPITATION-HARDENING TEMPERATURE (G) , °C (°F) 510 (950) (A) ELECTRICALLY HEATED, WITH ELEVATED HIGH-BEAT ZONE. (B) FOR BRAZING THE SUBASSEMBLY AND SIMULTANEOUSLY SOLUTION HEAT TRE ATING THE 17-7 PH DIAPHRAGMS. (C) ACHIEVED BY RUNNING THE DISSOCIATED AMMONIA THROUGH A MOLECULAR- SIEVE DRYER AFTER CRACKING. (D) CROSS-SECTIONAL DIMENSIONS (AND PRODUCT FORMS) OF PREPLACED RING S WERE: FOR JOINT BETWEEN DIAPHRAGM AND TOP FITTING (DETAIL A), 1.3 MM (0.050 IN.) WIDE BY O.10 TO 0.13 MM (0.004 TO 0.005 IN.) THICK STAMPING; FOR OUTSIDE JOINTS BETWE EN DIAPHRAGM SEGMENTS (DETAIL D) AND JOINT BETWEEN DIAPHRAGM AN D CUP (DETAIL B), THICK (RIBBON); FOR INSIDE JOINTS BETWEEN DIAPH RAGM SEGMENTS (DETAIL C), 0.76 MM (0.030 IN.) WIDE BY 0.13 MM (0.005 IN.) THICK (RIBBON); AND FOR JOINT BETWEEN CUP AND CONNECTOR (DETAIL E), 1.52 BY 0.254 MM (0.060 BY 0.010 IN. ) (WIRE). (E) USE OF BAG-19 ELIMINATED THE NEED FOR FLUX, WHICH HAD BEEN REQU IRED WITH THE SILVER FILLER METAL ORIGINALLY USED. (F) TO COOL RAPIDLY FROM 980 °C (1800 °F) AND ENSURE SOLUTION TR EATMENT OF THE 17-7 PH DIAPHRAGMS. (G) IN DRY DISSOCIATED AMMONIA, AFTER SUBASSEMBLY HAD BEEN COOLED TO -40 °C (- FIG. 9 PRESSURE-GAGE SUBASSEMBLY THAT COMBINED FURNACE BRAZING WITH SOLUTION HEAT TREATMENT [...]... 13. 015. 0 0.01 0.10 NI OTHER ELEMENTS TOTAL 37. 0-3 8.0 BAL 79. 5-8 0.5 BAL 34. 5-3 5.5 BAL 81. 5-8 2.5 29. 5-3 0.5 33. 5-3 4.5 COMPOSITION, WT% 2. 5-3 .5 BAL 35. 5-3 6.5 0 .15 0 .15 0 .15 0 .15 0 .15 Cr PRECIOUS METALS BAU-1 BAU-2 BAU-3 BAU-4 BAU-5 AWS CLASSIFICATION LIQUIDUS Fe NICKEL-BASE ALLOY FILLER METALS(A) BNI-1 13. 0- 2.7 5- 4. 015. 0 3.50 5.0 BNI-1A 13. 0- 2.7 5- 4. 015. 0 3.50 5.0 BNI-2 6.02.7 5- 4.08.0... BNI-3 2.7 5- 4.03.50 5.0 BNI-4 1.53.02.2 4.0 BNI-5 18. 5- 0.03 9.7519.5 10.50 BNI-6 BNI-7 SOLIDUS Fe Ni Si COBALT-BASE ALLOY FILLER METALS W B C 21. 5- 4. 0- 0.05 BAL 0.50 24.5 5.0 SOLIDUS LIQUIDUS BRAZING RANGE °F °C °F °C °F °C 990 890 975 950 1135 P S 1 815 1635 1785 1740 2075 Al 1 015 890 1030 950 1165 Ti 1860 1635 1885 1740 2130 Zr 101 5-1 095 89 0-1 010 103 0-1 090 95 0-1 005 116 5-1 230 Co 186 0-2 000 163 5-1 850... Darrell Manente, Vac-Aero International Inc Introduction PROCEDURES for brazing heat-resistant alloys, low-alloy steels, and tool steels share much in common This article focuses primarily on brazing of heat-resistant alloys; some information about particulars involved in the brazing of lowalloy steels and tool steels is also provided Brazing of Heat-Resistant Alloys, Low-Alloy Steels, and Tool Steels... 2050 1150 2100 1150 1230 21002250 Many nickel-palladium-base brazing filler metals exhibiting good wetting and flow are not classified by AWS but are also available These filler metals have been developed to replace gold-containing (BAu) brazing filler metals, which are more expensive Another group of brazing filler metals not classified by AWS are used for repair and overhaul of nickel- and cobalt-base... corrosion and discoloration in the joint area The nickel brazing filler metal selected for this application was BNi-9 (81.5Ni-15Cr-3.5B), because of its excellent capillary flow characteristics, low base-metal erosion, and self-fluxing properties In addition, the alloy would be unaffected by subsequent processing operations, which include passivation and electropolishing The stainless parts were degreased and. .. electron- and laser-beam brazing are performed in a manner similar to electron- and laser-beam welding, except that the beam is defocused to provide a larger beam and to reduce the power density to prevent the base metal from melting Generally, the speed at which the beam is swept is increased so that a larger area of the part is heated and more uniform heating of the part occurs In electron-beam brazing, the... of 540 to 815 °C (1000 to 150 0 °F), brazing at or above these temperatures may alter the alloy properties This frequently occurs when using silver-copper filler metals, which occasionally are used on heat-resistant alloys Liquid metal embrittlement is another difficulty encountered in brazing of precipitation-hardening alloys Many nickel-, iron-, and cobalt-base alloys crack when stressed parts are... settings and other brazing conditions specified in Fig 17 Sensitizing the austenitic stainless steel was not a problem in this application, because the service environment was not significantly corrosive The relatively short-time brazing cycle minimized grain growth and the dilution of the thin-walled tubing with copper brazing filler metal Brazing of Heat-Resistant Alloys, Low-Alloy Steels, and Tool... coated with type FB3-A brazing flux, and the assemblies were brazed in a continuous-belt conveyor furnace Brazing filler metal BAg-3 was chosen, in preference to BAg-1 or BAg-1a, in order to avoid the risk of interface corrosion Brazing of Stainless Steels Revised by Matthew J Lucas, Jr., General Electric Aircraft Engines Furnace Brazing in a Vacuum Atmosphere The majority of vacuum brazing is performed... cast and wrought alloys and powder metallurgy (P/M) products Powder metallurgy products may be produced in conventional alloy compositions and as oxide-dispersion-strengthened (ODS) alloys Almost any metal, as well as nonmetallics, can be brazed to these heat-resistant alloys, if it can withstand the heat of brazing For additional information on these alloys, see Volume 1 of the ASM Handbook Brazing . coated with type FB3-A brazing flux, and the assemblies were brazed in a continuous-belt conveyor furnace. Brazing filler metal BAg-3 was chosen, in preference to BAg-1 or BAg-1a, in order to avoid. INDUCTION-BRAZED ASSEMBLY Because the assembly was not intended for high-temperature service, the selection of the low-melting-point silver brazing filler metal (BAg-1) and a relatively low brazing. 10) BRAZING TEMPERATURE, °C (°F) 1065 ± 5 (1950 ± 10) HYDROGEN DEW POINTS, °C (°F) -7 5 (-1 00) (C) ; -6 0 (-7 0) (D) HYDROGEN FLOW RATE, M 3 /H (FT 3 /H) 17 (600) FILLER METAL (E) BNI-3