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This paper presents the results of an experimental study aimed to identify hot working domains in oxide dispersion strengthened (ODS) 18Cr ferritic steel over a wide range of temperatures (1323-1473 K) and strain rates (0.01-10 s−1). The experimental data were obtained by uniaxial compression test using the Gleeble-1500D simulator in this range of temperature and strain rate. An inverse relationship with temperature and positive strain rate sensitivity associated with dynamic recovery and recrystallization, which is influenced by temperature and strain rate, was derived from the flow stress. Based on the processing map generated at 0.5 true strain, using rate dynamic material model (DMM) approach and the calculated instability parameter ξϵ´>0, the optimum processing domain has been determined for this steel. The most favorable processing parameters are found in the temperature ranges of 1350-1450 K with a strain rate of 0.01 s−1 and 1473 K with a strain rate 0.1 s−1 with peak efficiency of 30 and 35%, respectively. The material flow behavior was studied using scanning electron microscopy (SEM)-based EBSD microstructural characterization. The steel subjected to 1323 K at high strain rate 10 s−1 in the low-efficiency workability region showed low aspect ratio as compared to the elongated bamboo-like initial microstructure; however, minimum strain rate (0.01 s−1) showing that localized slip/shearing is the key mechanism and fiber texture studied from the intensity distribution of inverse pole figure showed the presence of significant amount of θ-fibers. In contrast, dynamic recrystallization dominated at higher efficiency region in the safe domain of processing map and γ-fiber texture was evident in the specimen deformed at 1373 and 1473 K with strain rate of 0.01 and 0.1 s−1, respectively, which is responsible for the change in the initial 〈1 1 0〉//ED α-fiber texture. [ABSTRACT FROM AUTHOR]

The effect of ‘conventional normalizing and tempering’ (CNT) and ‘double austenitization based normalizing and tempering’ (DNT) heat treatments on the microstructure, tensile, creep and impact toughness properties of 9Cr-1Mo steel has been studied. The tempered martensite microstructure obtained through DNT treatment exhibited smaller sizes of prior-austenite grains/martensite packets (28 μm/11 μm) compared to the CNT treatment (44 μm/14 μm). The tempered martensite morphology was largely retained after long-term thermal aging at 550 °C/5000 h, while the M 23 C 6 and M 2 (C,N) type of precipitates were found to act as nucleation sites for precipitation of brittle Fe 2 Mo Laves phase. The grain refinement by DNT was found to be beneficial for minimizing the ductile-to-brittle transition characteristics (25 °C lower ductile-to-brittle transition temperature and 70 J higher upper shelf energy) over the CNT. Thermal embrittlement occurred in both heated treated steels, but the transition temperature of aged DNT steel remained below room temperature. Fractured Charpy specimens revealed ductile failure by void coalescence for high temperature tests, and a quasi-cleavage fracture at low temperatures with few isolated occurrence of intergranular crack in thermal embrittled steel. The DNT treated steel resulted in similar or better tensile and creep properties, when compared to the CNT treatment. The homogeneous fine grained tempered martensite microstructure obtained by DNT treatment resulted in improved embrittlement resistance and mechanical properties over the conventional treatment. [ABSTRACT FROM AUTHOR]

A methodology for classifying the hierarchy of martensite boundaries from the EBSD microtexture data of low-carbon steel is presented. Quaternion algebra has been used to calculate the ideal misorientation between product α variants for Kurdjumov–Sachs (KS) and its nearby orientation relationships, and arrive at the misorientation angle-axis set corresponding to packet (12 types), block (3 types) and sub-block boundaries. Analysis of proximity of experimental misorientation between data points from the theoretical misorientation set is found to be useful for identifying the different types of martensite boundaries. The optimal OR in the alloy system and the critical deviation threshold for identification of martensite boundaries could both be ascertained by invoking the ‘Enhancement Factor’ concept. The prior-γ grain boundaries, packet, block and sub-block boundaries could be identified reasonably well, and their average intercept lengths in a typical tempered martensite microstructure of 9Cr–1Mo–0.1C steel was estimated as 31 μm, 14 μm, 9 μm and 4 μm respectively. [ABSTRACT FROM AUTHOR]

Abstract A study of microstructure and volumetric dilution of Cold Metal Transfer (CMT) clad of Nickel based super alloy, Inconel 617M on type 316L stainless steel (SS) substrate was carried out. Overlay coatings were deposited at three different current inputs (80, 90 and 100 A) to synergetic CMT welding set while the wire feed rate and pulse frequency were pre-programmed. The ability of CMT to produce very low dilution and low heat input with the minimal heat affected zone (HAZ), when compared to conventional Tungsten Inert Gas welding (TIG) process was successfully demonstrated. Detailed microstructural evaluation of the cross sections revealed porosity and crack free Inconel 617M overlay with complete fusion, making a metallurgical bonding at the interface. Transverse micro Vickers hardness evaluation from clad to substrate showed the absence of significant HAZ for overlay produced by CMT. Calculation of percentage volumetric dilution, based on elemental Energy Dispersive Spectroscopy (EDS) of Fe-K counts, revealed that the cladding deposited at 100 A current exhibited low dilution value of 6.3% at 100 μm away from the interface while clad produced by TIG show significantly higher dilution value of ~50% at 100 μm from interface. Electron Backscattered Diffraction (EBSD) studies revealed morphology similar to epitaxial growth, with same crystallographic orientation of grains across the interface for CMT overlaid coatings. Highlights • Cold Metal Transfer (CMT) is renowned to be a low heat input welding process. • CMT can produce porosity and defect free overlays of IN 617M over SS 316L. • CMT can produce low dilution (~6%) overlays of IN 617M over SS 316L. • CMT is advantageous over conventional weld overlay process in many aspects. [ABSTRACT FROM AUTHOR]