Base Filler Metal Research Articles

Henry Granjon Prize Competition 2006 Winner, Category B “Materials behaviour and weldability” The Influence of Molybdenum on the Microstructure of Stainless Steel Welds

The excellent corrosion resistance of superaustenitic stainless steel (SASS) alloys has been shown to be a direct consequence of high concentrations of Mo. The presence of Mo can have a significant effect on the microstructural development of welds in these alloys. In this research, the microstructural development of welds in the Fe-Ni-Cr-Mo system was analyzed over a wide variety of Cr/Ni ratios and Mo contents. The system was first simulated by construction of multi-component phase diagrams using the CALPHAD technique. Data gleaned from vertical sections of these diagrams were inserted in the compositional range of a liquidus projection to produce diagrams that can be used as a guide to understand the influence of composition on microstructural development. A large number of experimental alloys were then prepared via arc-button melting for comparison with the diagrams. Each button was characterized using various microscopy techniques. The expected δ-ferrite and γ-austenite phases were accompanied by martensite at low Cr/Ni ratios and by σ-phase at high Mo contents. The results were used to construct a map of expected phase transformation sequence and resultant microstructures as a function of composition. Electron microprobe measurements of selected alloys were performed to compare the distribution of Mo solute between different solidification modes. Severe Mo microsegregation was observed in alloys that solidified directly as austenite; this was attributed to the low diffusivity of Mo in austenite. The level of Mo microsegregation could be significantly reduced in alloys that solidified as δ-ferrite first and subsequently transformed to austenite by a solid state transformation. Magnetic ferrite measurements were also used to produce quantitative relationships between alloy composition and ferrite content, and the results were then plotted on the WRC-1992 diagram. The results of this work provide a working guideline for future base metal and filler metal development of these alloys.

Dilution and microsegregation in dissimilar metal welds between super austenitic stainless steel and nickel base alloys

Super austenitic stainless steels are often welded using high Mo, Ni base filler metals to maintain the corrosion resistance of the weld. An important aspect of this processing is the weld metal dilution level, which will control the composition and resultant corrosion resistance of the weld. In addition, the distribution of alloying elements within the weld will also significantly affect the corrosion resistance. Dissimilar metal welds between a super austenitic stainless steel (AL-6XN) and two Ni base alloys (IN625 and IN622) were characterised with respect to their dilution levels and microsegregation patterns. Single pass welds were produced over the entire dilution range using the gas tungsten arc welding process. Microstructural characterisation of the welds was conducted using light optical microscopy, scanning electron microscopy, and quantitative image analysis. Bulk and local chemical compositions were obtained through electron probe microanalysis. The quantitative chemical information was used to determine the partition coefficients k of the elements in each dissimilar weld. The dilution level was found to decrease as the ratio of volumetric filler metal feedrate to net arc power increased. Reasons for this behaviour are discussed in terms of the distribution of power required to melt the filler metal and base metal. In addition, the segregation potential of Mo and Nb was observed to increase (i.e. their k values decreased) as the Fe content of the weld increased. This effect is attributed to the decreased solubility of Mo and Nb in austenite with increasing Fe additions. Since the Fe content of the weld is controlled by dilution, which in turn is controlled by the welding parameters, the welding parameters have an indirect influence on the segregation potential of Mo and Nb. The results of the present work provide practical insight for corrosion control of welds in super austenitic stainless steels.

Interfacial distribution of elements and fracture behaviour of metal inert gas brazed joint with copper based filler metals

Metal inert gas brazing for joining galvanised A3 steel sheets or 1Cr18Ni9Ti stainless steel with Cu- 3 wt-%Si- 1 wt-%Mn or Cu- 10 wt-%Mn- 6 wt-%Ni brazing filler metal has been investigated. The experiment results indicate a Si and Mn rich band was produced at the interface of filler metal and base metal. X-ray diffraction analysis shows that Si existed as Fe2Si and Mn existed in the form of solid solution. Tensile testing specimens using Cu–3Si–1Mn and Cu–10Mn–6Nias the filler metal fractured at the base metal with joint strengths of 308·2–308·7 MPa. The joint specimens of stainless steel 1Cr18Ni9Ti fractured at the brazing seam with strengths of 331·5 and 423·6 MPa. Tensile fracture analysis shows that the fracture area originated at the bottom of the lap brazing seam (brittle fracture composed of the components of base metal and filler metal), and ended in the brazing seam (Cu–3Si–1Mn/filler metal) or in the vicinity of the Cu–10Mn–6Ni/filler metal interface (ductile fracture).

Welding of High Nitrogen Superaustenitic and Superduplex Stainless Steels

High nitrogen containing stainless steels have been welded using various nickel and iron base filler metals. The best corrosion resistance in chloride containing environments was obtained with the high chromium and molybdenum containing fillers Thermanit Nimo C or Thermanit Nimo C 24. The iron base filler Thermanit 25/22/5 is a good compromise in respect to strength, ductility and corrosion resistance in chloride containing or oxidizing environments.

Solidification phenomena in nickel base brazes containing boron and silicon

1. 1. The intermetallic compounds formed in brazes of nickel base filler metals containing chromium, boron and silicon are nickel boride, nickel silicide and chromium boride. 2. 2. The intermetallic compounds are found to form as constituents of binary or ternary eutectics with γ-nickel. The binary eutectics are γ-nickel/nickel boride, γ-nickel/nickel silicide and γ-nickel/chromium boride. The ternary eutectics are γ-nickel/nickel boride /chromium boride and γ-nickel/nickel boride/nickel silicide. 3. 3. Upon cooling from the brazing temperature, the first formed solid is primary γ-nickel, which either nucleates within the melt as nodules or nodular dendrites or simply grows onto the partially melted filler metal particles. On further cooling, boron and silicon in the melt tend to exclude one another, solidifying into different types of eutectics the constituents of which depend on the composition of the filler metal. 4. 4. When only silicon is present, the remaining melt simply solidifies into an eutectic of γ-nickel and nickel silicide. 5. 5. For boron-containing filler metals, the first formed eutectic is usually the binary eutectic of γ-nickel and nickel boride; this in turn enriches the melt with chromium. In the absence of silicon, this chromium-enriched melt will eventually solidify into a ternary eutectic of γ-nickel, nickel boride and chromium boride. When silicon is present, the formation of the above ternary eutectic is suppressed and a binary eutectic of γ-nickel and chromium boride is formed instead. When this happens, the remaining melt will be enriched in silicon and the last portion of the melt solidifies into a ternary eutectic of γ-nickel, nickel boride and nickel silicide. 6. 6. For the filler metal containing nickel, boron and silicon but no chromium, after the formation of binary eutectic of γ-nickel and nickel boride, the melt will become gradually enriched with silicon and eventually solidify into the ternary eutectic of γ-nickel, nickel boride and nickel silicide.

Microstructural evolution and control in BNi-4 brazed joints of nickel 270

Nickel base filler metals are extensively used in wide gap brazing in the repair and joining of aero-engine hot-section components made of nickel base superalloys. This paper reports the microstructural evolution in joints of nickel 270 brazed with BNi-4 filler metal. The effects of brazing temperature and cooling rate on the microstructure of the resultant joint microstructures are studied in details. The results are compiled in the form of braze microstructure map. It shows that through careful selection of brazing temperature and cooling rate, it is possible to engineer the microstructures of the joints, hence the possibility of reducing or eliminating the network of intermetallic compounds and enhancing the mechanical properties of brazed joints.

NICROBRAZ 171

Abstract NICROBRAZ 171 is a base filler metal with extra high strength at temperature. It is good for brazing base metals containing cobalt, tungsten, and molybdenum and has a better flow characteristic than Nicrobraz 170 (Alloy Digest Ni-476, January 1995). This datasheet provides information on composition, physical properties, and hardness. It also includes information on corrosion resistance as well as joining. Filing Code: Ni-478. Producer or source: Wall Colmonoy Corporation.

Ｔｉ‐Ｚｒ基ろうを用いた超高純度アルミナとチタンのろう付性

Brazeability of high purity alumina (99.9 wt% Al2O3) to commercially pure titanium (CP Ti) and Ti-6A1-4V alloy with Ti-Zr base filler metals has been investigated by microscopy, EDX microanalysis, X-ray diffraction, and shear test of the joints. Filler metals used were two types of amorphous foils, developed for trial, of 25Ti-25Zr-5OCu (Type 5000) and 37.5Ti-37.5Zr-l5Cu-lONi (Type 1510), whose melting points were about 815°C and were apploximately 100°C lower than those of conventional Ti-base fillers.Shear strength of joints brazed with Type 5000 filler metal had a tendency to decrease with increase in both brazing temperature and time. However, in case of brazing at comparatively low temperature for a short time using Type 5000 filler metal, it was possible to get sufficient joints having shear strength of above 150 MPa. Metallurgical test results showed that in the joint of alumina to CP Ti with Type 5000 filler metal, (Ti, Zr)2Cu was formed at joint region nearby CP Ti base metal at the beginning of brazing, and that the composition of the region varied with increase in brazing time. A thin titanium and/or zirconium oxide layer was also detected at the interface between alumina and the joint region, and the growth of this oxide layer was related to the decrease in joint strength and to the occurrence of cracking at the joint.As for using Type 1510 filler metal, the joints were flaked during cooling after brazing, because of rapid formation of brittle Ti and Zr rich layer at the joint interface, which indicates that the brazeability of Type 1510 filler metal is fairly inferior to that of Type 5000 filler metal.

ニッケル基ろうによるステンレス鋼のろう接継手強さについて

Mechanical properties of the brazed stainless steel joints with nickel base filler metals (BNi) were studied in relation to the microstructures at the brazing interface. The filler metals used for this experiment were BNi-1, BNi-3 and BNi-7.In this study the brazing phenomena on stainless steel joints with BNi filler metals were discussed from the viewpoints of brazability, shear strength of lap brazed joints at room temperature and elevated temperatures, and the effects of diffusion treatment on the brazed joints. The results obtained are summarized as follows:(1) The BNi filler metals showed satisfactory brazability for stainless steel, and especially BNi-7 were excellent.(2) A defect of the brazed joints with BNi filler metals existed in the brittleness at room temperature. But at elevated temperatures the shear strength of the joints were remarkably improved.(3) The brazed joints with BNi-1 and BNi-3 filler metal were improved in shear strength by the diffusion treatment.(4) The long time brazing process was effective for improving the mechanical strength of the joints.