Plastic deformation is one of the causes of failure of hot forging tools, where the tool deforms to such an extent that parts formed are no longer within dimensional tolerance. Therefore, deformation of H13 tool steel that leads to transformation of the microstructure after forging Inconel 718 at high temperature and load was investigated. For this investigation nonlinear continuum mechanics 3D FE simulation Deform software, Scanning Electron Microscope (SEM), Electron Backscatter Diffraction (EBSD) and Microhardness tests were used. The result of 3D Deform simulation shows high localised stress and high strain of 0.38 on the sharp edge of the tool. This is one of the main reasons behind tool failure as accumulation of strain during deformation at high temperature causes changes in microstructure. SEM results confirm the severe deformation and highlight three different zones of deformation, recrystallization, martensitic and transition between each zone within the microstructure. EBSD results show low angle boundaries of 1~15° which represents mainly the deformation zone and it is associated with different dislocation substructures caused by slip. Furthermore, misorientation angles 28-32° corresponds to special boundaries ∑39a which are believed were created during martensitic lattice transformation when some of the boundaries are not perfectly match the rest. These special boundaries transform to low angle boundaries. The high angle boundaries 58-60° corresponds to twin boundaries and their parent matrix.
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