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The microstructural evolution, precipitation, and mechanical properties of 27Cr-4Mo-2Ni steels were investigated by using SEM/EBSD and TEM/STEM technique, and the RT impact test. Experimental results demonstrate that the elongated grains are gradually transformed to recrystallization grains after high temperature annealing. Both sigma and Laves phase were found nucleated at grain boundaries and/or sub-grain boundaries during annealing below 1100 °C except for Nb(C, N) and TiN particles. Recrystallization of 〈111〉 orientated deformation regions were impede due to the pinning effect of Laves phase particles at sub-grain boundaries accompanied by the missing of γ-fiber texture. The recrystallization grains are still kept elongated along the rolling direction for the hindrance of fine Nb(C, N) formed at initial hot rolled grain boundaries. Formation of Laves and sigma phase particles shows great influence on the mechanical properties, such as the decrease of the tensile elongation and the impact toughness, and the emergence of brittle fracture during the tensile or impact test. Solution treatment should be strictly controlled above 1050 °C with water quenching to avoid the embrittlement of the test steels. • Laves and sigma phase nucleated at grain/sub-grain boundaries during solution annealing. • Prior-formation of Laves phase particles impeded the recovery and recrystallization of the deformed microstructure. • Precipitation of sigma and Laves phase particles at boundaries led to the embrittlement. [ABSTRACT FROM AUTHOR]

Hot-rolled 430 ferritic stainless steel samples were annealed at 840–1150 °C together with water or air cooling to study their microstructural evolutions, mechanical properties and corrosion resistances via a scanning electron microscopy (SEM), electron back scattering diffraction (EBSD), tensile tests and immersion tests. The experimental results demonstrate that after annealing below 880 °C, the microstructure consists of ferrite grains and (Fe, Cr) 23 C 6 particles at the grain boundaries, whereas abundant martensitic phase is observed at the grain boundaries after annealing above 950 °C. The ferrite grains coarsen as the annealing temperature increases. Martensitic transformation after high-temperature annealing results in a sharp increase in both the tensile strength and Vickers hardness and a substantial decrease in the elongation. Both the formation of (Fe, Cr) 23 C 6 particles and martensitic transformation at the grain boundaries are detrimental to the corrosion resistance in Cl-rich environments due to the Cr depletion in the ferrite among the (Fe, Cr) 23 C 6 particles. The annealed samples with water quenching show higher hardness and better corrosion resistance than that with air cooling. Annealing at intermediate temperatures (900–950 °C) and then cooling in air is an appropriate method for fabricating 430 ferritic stainless steel with good mechanical properties and high corrosion resistance. [ABSTRACT FROM AUTHOR]