Authors: T Anderson
Publish Date: 2013/01/16
Volume: 50, Issue: 9-10, Pages: 23-34
Abstract
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 FeNiCrMo system was analyzed over a wide variety of Cr/Ni ratios and Mo contents The system was first simulated by construction of multicomponent 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 arcbutton melting for comparison with the diagrams Each button was characterized using various microscopy techniques The expected δferrite and γaustenite phases were accompanied by martensite at low Cr/Ni ratios and by σphase 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 δferrite 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 WRC1992 diagram The results of this work provide a working guideline for future base metal and filler metal development of these alloys
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