Flash processing of an AISI8620 steel sheet, which involves rapid heating and cooling with an overall process duration of <10 s, produced a steel microstructure with a high tensile strength and good ductility similar to that of advanced high strength steels. Flash processed steel [ultimate tensile strength (UTS): 1694 MPa, elongation: 7·1], showed at least 7 higher UTS and 30 greater elongation than published results on martensitic advanced high strength steel (UTS: 1585 MPa, elongation: 5·1). The underlying microstructure was characterised with optical, scanning electron, transmission electron microscopy as well as hardness mapping. A complex distribution of bainitic and martensite microstructures with carbides was observed. A mechanism for the above microstructure evolution is proposed.

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High temperature brazing of nickel-based superalloys often produces joints containing hard, brittle micro-constituents that can be detrimental to mechanical properties and challenging to characterise consistently. In this study, techniques including low angle micro-sectioning, image analysis with ImageJ and electron probe micro-analysis were used to determine the composition, hardness and dispersion parameters of phases in single crystal superalloy CMSX-4, vacuum furnace brazed with BNi-2 and BNi-9 filler metals (FMs). Both FMs produced similar joints with hard centreline eutectic phases, a soft isothermally solidified zone and boron diffusion-affected zone in the CMSX-4. The volume fraction, particle size distribution and interparticle spacing data generated will provide a framework for future metallurgical characterisations and assist in the development of microstructure-mechanical property relationships.

The weld solidification cracking susceptibility of several solid-solution strengthened Ni-base filler metals was evaluated using the transverse Varestraint test. The alloys tested included Inconel 617, Inconel 625, Hastelloy X, Hastelloy W, and Haynes 230W.* Susceptibility was quantified by determining the solidification cracking temperature range (SCTR) which is a direct measurement of the range over which cracking occurs. This temperature range was then compared to the equilibrium solidification temperature range derived from Calphad-based ThermoCalc™ calculations, Scheil-Gulliver solidification simulations, and in-situ measurements using the single sensor differential thermal analysis (SS-DTA) technique.Good correlation among the simulated and measured solidification temperature ranges, and SCTR values were found for the 617 and 230W filler metals. These two filler metals exhibited the best resistance to weld solidification cracking. Correlation among measured and simulated temperature ranges, and SCTR was poor for Hastelloy alloys X and W. Alloy 625 was found to be the most susceptible to solidification cracking, but this result is in conflict with fabrication experience. This appears to be the result of the inability of the Varestraint test to account for crack "healing" during the final stages of solidification.

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