Elements Of X Ray Diffraction

Small Angle Scattering of X-Rays

Plastic deformation of metals

Additive manufacturing (AM) is an advanced technology used for the manufacture of products that have intricate shapes and complex inner geometries. Various metal powders can be used for AM; however, the resulting microstructures will differ profoundly from those obtained via the casting, heat treatment, or thermomechanical processing of metals with the same chemical composition. This is because of the rapid heating and cooling rates used during three-dimensional (3D) printing. Further complications arise from the repeated heating and cooling of some regions, which is owed to the step-by-step formation of the solidified layers. A powder consisting of 1.2709 (X3NiCoMoTi 18-9-5) low-carbon maraging steel was used in an AM experiment. Given the high residual stresses that exist within printed metals, a post-processing heat treatment is desirable to limit the risk of cracking. In this study, solution annealing and hardening treatments were applied to the printed samples to induce changes in their microstructures and mechanical properties. The mechanical properties and microstructures of the builds were characterised and compared to those of a bar of conventional steel with the same chemical composition. During tensile loading, the fracture that was initiated at the sites of metallurgical defects was observed in situ.

Microstructural characterisation and in-situ straining of additive-manufactured X3NiCoMoTi 18-9-5 maraging steel

Hydrogen diffusion and trapping in X70 pipeline steel

Maraging steels gain many of their beneficial properties from heat treatments which induce the precipitation of intermetallic compounds. We consider here a two-stage heat-treatment, first involving austenitisation, followed by quenching to produce martensite and then an ageing treatment at a lower temperature to precipitation harden the martensite of a maraging steel. It is shown that with a suitable choice of the initial austenitisation temperature, the steel can be heat treated to produce enhanced toughness, strength and creep resistance. A combination of small angle neutron scattering, scanning electron microscopy, electron back-scattered diffraction, and atom probe tomography were used to relate the microstructural changes to mechanical properties. It is shown that such a combination of characterisation methods is necessary to quantify this complex alloy, and relate these microstructural changes to mechanical properties. It is concluded that a higher austenitisation temperature leads to a greater volume fraction of smaller Laves phase precipitates formed during ageing, which increase the strength and creep resistance but reduces toughness.

Deri Rhys Galvin

Papers

The Effect of a Two-Stage Heat-Treatment on the Microstructural and Mechanical Properties of a Maraging Steel