Dissimilar welding of AISI 310 austenitic stainless steel to nickel-based alloy Inconel 657

Joining of Inconel 718 and 316 Stainless Steel using electron beam melting additive manufacturing technology

Characterization of microstructures and mechanical properties of Inconel 617/310 stainless steel dissimilar welds

Parametric study of development of Inconel-steel functionally graded materials by laser direct metal deposition

High temperature oxidation of Fe-Al and Fe-Cr-Al alloys: The role of Cr as a chemically active element

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 w...

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

Microstructural evolution and solidification cracking susceptibility of dissimilar metal welds between AL-6XN super austenitic stainless steel and two nickel-based alloys, IN625 and IN622, were studied using a combination of electron microscopy, differential thermal analysis, and Varestraint testing techniques. Welds were prepared over the entire dilution range (where dilution was determined with respect to AL-6XN as the base metal). The effect of processing parameters and filler metal chemistry on the fusion zone composition, microstructure, and resultant weldability was investigated. Iron additions to the weld (which occur with increasing dilution) increased the segregation potential of Mo and Nb. This behavior was attributed to a reduction in the solubility of Mo and Nb in austenite with increasing iron additions. as inferred from available binary phase diagrams. Welds prepared with IN622 formed a single interdendritic a phase at the end of solidification, and the amount of this secondary phase was not sensitive to changes in dilution. The a phase formed at a relatively high temperature and led to a relatively narrow solidification temperature range for welds prepared with IN622. In contrast, welds prepared with IN625 exhibited NbC and Laves phases in the interdendritic regions, and the total amount of secondary phase decreased with increasing dilution. Solidification of welds prepared with IN625 terminated with formation of the Laves constituent at relatively low temperature and, thus the solidification temperature range of welds involving IN625 was relatively wide. The solidification cracking sensitivity of welds prepared with IN622 was relatively low and independent of weld metal dilution level, while the cracking susceptibility of welds produced with IN62,5 was relatively high and increased with decreasing dilution. The dilution/cracking relation is controlled by the solidification temperature range and amount of secondary phase that forms at the terminal stages of solidification. The good cracking resistance of welds prepared with IN622 is attributed to the small amount of secondary phase and narrow solidification temperature range. The relatively poor cracking resistance of welds prepared with IN625 is attributed to a wide solidification temperature range and increasing amount of secondary phase that forms with decreasing dilution.

Microstructural evolution and weldability of dissimilar welds between a super austenitic stainless steel and nickel-based alloys

The mechanisms for nodular corrosion-product development were investigatedin various high-temperature gaseous environments. Fe–Al alloys, with5–20 wt.% Al, were exposed in both oxidizing and sulfidizing[p(S2)=10−4 atm, p(O2)=10−25 atm] atmospheres at 700°Cfor times up to 100 hr. The corrosion kinetics were monitored by theuse of a thermogravimetric balance and the morphological developmentthrough light-optical and scanning-electron microscopies,energy-dispersive spectroscopy, electron-probe microanalysis,and quantitative-image analysis. Under both conditions, theelimination of nodule formation was observed by increasing thealuminum content of the alloy, above 5 and 7.5 wt.% Al for oxidizingand sulfidizing environments, respectively, which promoted the growthand maintenance of a continuous surface scale of alumina. For thosealloys that were observed to develop nodular corrosion products, theirmorphological appearance was similar in nature regardless of thecorroding species. The nodules typically consisted of an outeriron-rich product, either sulfide or oxide, that was randomly dispersedacross an alumina scale. Samples from the oxidizing atmosphere displayeda single growth-rate time constant from the kinetics data, suggesting thatthe nodule growth mechanism was by the simultaneous or codevelopment oftwo different (Fe and Al) oxides from the onset of exposure. Measurementof nodule planar diameter and depth of penetration into the alloyindicated that growth occurred through diffusional processes. Kineticsdata from the development of sulfide nodules in the reducingenvironment revealed a different type of mechanism. Multiplegrowth-rate time constants were found due to the localized mechanicalfailure of an initially formed surface scale. At early times in thesulfidizing atmosphere, a low corrosion rate was recorded as acontinuous-alumina scale afforded protection from excessive productdevelopment. However, with the mechanical failure of the scale, sulfurwas able to attack the underlying substrate through a short-circuitdiffusion mechanism that resulted in rapid weight gains from nonprotective,iron sulfide growth. The sulfide morphologies observed were very complex ascontinued growth of the nodule did not solely depend upon the diffusingspecies through the previously formed corrosion products, but also,continued mechanical failure of the oxide scale. It is suggested that thedifference in development mechanisms between the two environments may liein the relative growth rates of the nonprotective, Fe-base corrosionproducts formed.

Growth of Nodular Corrosion Products on Fe-Al Alloys in Various High-Temperature Gaseous Environments

The high-temperature corrosion behavior of monolithic Fe-Al alloys, with 0 to 20 wt pct Al, was investigated at 700 °C in a reducing atmosphere (p(S2) = 10−4 atm, p(O2) = 10−25 atm) for up to 100 hours Postexposure characterization of the corrosion reaction products consisted of surface and cross-sectional microscopy, in combination with energy dispersive spectroscopy, electron probe microanalysis, and quantitative image analysis From the kinetic data, three stages of corrosion behavior (ie, inhibition, breakdown, and steady state) were found with the observance and/or duration of each stage directly related to the aluminum content of the alloy The first stage, labeled the inhibition stage, was characterized by low weight gains and the absence of rapid degradation of the alloy Typically observed for compositions with 10 to 20 wt pct Al, protection was afforded due to the development of a thin, continuous alumina scale For alloys with 75 wt pct A1, the ability to maintain the initially formed alumina scale was not observed, resulting in the breakdown stage Localized corrosion product nodules, containing iron sulfide (Fe1-x
 S) and the spinel-type tau phase (FeAl2S4), developed through the alumina scale due to sulfur short-circuit diffusion These growths were accompanied by relatively high corrosion rates Further decreasing the aluminum content to 5 wt pct and below lead to the formation of a continuous sulfide scale whose growth was controlled by iron and sulfur diffusion through the previously formed product The alloy wastage rates in the steady-state stage were relatively high when compared to the previous two regions

S.W. Banovic

Papers

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

Microstructural evolution and weldability of dissimilar welds between a super austenitic stainless steel and nickel-based alloys

Growth of Nodular Corrosion Products on Fe-Al Alloys in Various High-Temperature Gaseous Environments

The effect of aluminum content on the corrosion behavior of Fe-Al alloys in reducing environments at 700 °C

High temperature sulfidation behavior of low Al iron-aluminum compositions