Effect of prior martensite on bainite transformation in nanobainite steel

https://www.repository.cam.ac.uk/bitstream/1810/278764/1/MaragingSteels-V04-Researchgate.pdf

Predicting microstructure and strength of maraging steels: Elemental optimisation

Neutron diffraction in situ monitoring of the dislocation density during martensitic transformation in a stainless steel

Influence of microstructure and manganese sulfides on corrosion resistance of selective laser melted 17-4 PH stainless steel in acidic chloride medium

Four groups of low transformation temperature (LTT) deposited metals with different Ni contents were prepared, and their microstructures were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and electron backscattered diffraction techniques. The relationship between the microstructures of the mixed martensite–retained austenite (RA) phases and their impact toughness were investigated; it was found that the impact toughness of the LTT deposited metals increased with increasing volume fraction of RA. In particular, its magnitude was higher for the specimens containing the lath martensite, interlath RA, and intercellular RA phases than for those composed of the lath martensite and interlath RA. The toughness of the lath martensite–RA mixed microstructure was primarily determined by the presence of the soft RA phase (containing film interlath RA and stringer intercellular RA), while lath martensite phase characterized by a high density of tangled dislocations and relatively small amount of twinned substructures resulted in the embrittlement of the LTT deposited metals. The dislocation absorption by the retained austenite and transformation-induced plasticity (TRIP) effects of RA were found to be main reasons for the improvement in materials toughness during crack initiation stage. The subsequent crack propagation proceeds via the TRIP and the transformation-induced crack termination mechanisms; it is also significantly affected by the increased fraction of martensite/RA boundaries. The optimization of the RA fraction in the martensite–RA dual structure is a potentially effective method for the toughness enhancement of the LTT deposited metals containing martensite–RA dual phases.

Toughening mechanisms of low transformation temperature deposited metals with martensite–austenite dual phases

The volume fraction of austenite and dislocation density in electron beam weld joints of a martensitic-austenitic age-hardenable CrNiMoTiAl stainless steel were investigated using neutron diffraction. Experiments were performed on a high-resolution diffractometer which resolved microstrains of the order of 10 −4 . The effect of post-weld heat treatment on austenite content and dislocation density was investigated. As in other maraging steels, the maximum volume fraction of austenite was obtained after quenching and intercritical annealing. Dislocation densities computed on the base of mean-square microstrain values were about 10 11 cm −2 . These densities were systematically higher in martensite than in austenite, with very small differences between the weld metal and base metal.

Austenite content and dislocation density in electron-beam welds of a stainless maraging steel

Three unique high resolution experimental arrangements for nondestructive strain measurements which are based on neutron Bragg diffraction optics with cylindrically bent perfect crystals are reviewed. Using focusing in momentum and real space these techniques yield Δd/d (d-lattice spacing) resolution of 10 -4 -10 -3 and considerably higher luminosity in comparison with the current dedicated instruments. They permit measurements not only macrostrain components resulting in angular shifts of diffraction peaks but also of microstrains by means of profilebroadening analysis

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Advanced neutron diffraction techniques for strain measurements in polycrystalline materials

The dependence of residual stresses in martensitic-austenitic age-hardenable steels on a different technological treatment (welding by electron beam, postweld heat treatment) were investigated using neutron diffraction. Experiments were performed in NPI Rez on a high-resolution diffractometer equipped with cylindrically bent perfect crystals. The resolution of the instrument ({Delta}d/d {approx} 10{sup {minus}4}; d-lattice spacing) enabled the authors to investigate plastic strains in weld joints.

K. Macek

Papers

Austenite content and dislocation density in electron-beam welds of a stainless maraging steel

Advanced neutron diffraction techniques for strain measurements in polycrystalline materials

Micro Stresses in Welded High-Strength Stainless Steels