This study is focused on the effect of boron addition, in the range of 0.0007wt% to 0.03wt%, on the microstructure and stress-rupture properties of a directionally solidified superalloy. With increasing boron content in the as-cast alloys, there is an increase in the fraction of the γ′/γ eutectic and block borides precipitate around the γ′/γ eutectic. At a high boron content of 0.03wt%, there is precipitation of lamellar borides. Upon heat treatment, fine block borides tend to precipitate at grain boundaries with increasing boron content. Overall, the rupture life of the directionally solidified superalloy is significantly improved with the addition of nominal content of boron. However, the rupture life decreases when the boron content exceeds 0.03wt%.

Ca deoxidation has been acknowledged recently as an effective oxide metallurgy technology that improves the toughness of the heat affected zone (HAZ) in high-strength low-alloy (HSLA) steel plates after large heat input welding. This paper describes the effect of Ca concentrations on the formation behavior of the non-metallic inclusions in the HAZs of a series of thick HSLA steel plates after large heat input welding at 400 kJ cm⁻¹. The quantitative statistics on the inclusions show that the Ca addition significantly decreases the quantity of the pure MnS sulfide, but increases that of the complex oxysulfide. The pure MnS sulfide precipitates below the solidus temperature, while the complex oxysulfide forms in the molten liquid, leading to the core (oxide) and shell (sulfide) structure. The Ca addition proportionally improves the HAZ toughness of these thick HSLA steel plates, primarily owing to the positive effect of the complex oxysulfides on the refinement of the HAZ microstructure.

The hot deformation behavior of an advanced nickel-based Haynes282 superalloy was systematically investigated employing isothermal compression tests in the sub-solvus and super-solvus temperature with various strain rates. The influence of deformation temperature and strain rate on the microstructure was studied by transmission electron microscope. The results reveal that the interaction between work hardening and dynamic softening did not reach equilibrium under lower deformation temperature and higher strain rate. The active energy of alloy is around 537.12 kJ/mol and its hot deformation constitutive relationship equation was expressed. According to the processing map and microstructure observations, two unsafe flow instability domains should be avoided. The optimum hot processing condition for homogeneous and fine dynamic recrystallization grains are obtained. TEM micrograph observations indicated that deformation temperature and strain rate affected recrystallization by affecting the evolution of dislocation substructures within the alloy. The nucleation and growth of DRX grains can be promoted by the relatively high deformation temperature and low strain rate. The main mechanism of dynamic recrystallization nucleation preferred to discontinuous dynamic recrystallization and the typical feature of discontinuous dynamic recrystallization showed grain boundary migration nucleation. The findings improve the understanding of hot deformation behavior and dislocation substructures evolution of the superalloy, which benefits the accurate control of microstructures of nickel-based superalloys, and tailors the properties of final components used in the land-based gas turbine.