This study presents the investigation on how heat treatment parameters, which are temperature, cooling method, and residence time, influence the microstructural and hardness properties of Ti6Al4V components produced on Ti6Al4V substrate using high speed selective laser melting technique. Heat treatment was performed on the produced samples before they were characterized for microstructure and hardness. The microstructure of the as-built sample contained large columnar β-grains that were filled with martensite α’ phase and had a high hardness of 383 ± 13 HV. At 1000 °C and residence time of maximum 4 h, better heat treatment parameters were seen for the selective laser melting (SLM) produced Ti6Al4V sample since an improved lamellar α + β microstructure was obtained at this condition. This microstructure is known to have improved tensile properties.

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Grain growth equation constants n, Q and A for Nb bearing steels with the Nb varying from 0.002 wt% to 0.1 wt%, were experimentally determined under reheating and high temperature hot rolling roughing conditions. The constants from these treatments were then used to develop constitutive equations that incorporate the initial grain size D o and a Nb-effect for grain growth predictions in these steels. Comparative analysis of the results showed that the values of the constants generated under rough rolling deformation conditions were slightly higher than those generated under reheating conditions. The activation energy for grain boundary migration Q was found to be in the range of 256 to 572 kJ/mol, the exponential constant n ranged from 2.6 to 6.5 and the material and processing condition's constant A was found to range from 5.23 × 10 11 to 4.96 × 10 28 in all cases as a function of the Nb content. Analysis of the influence of the initial grain size D o showed that any contribution of D o can be neglected unless it is equal or more than 70 percent of the average size of the measured austenite grain size D. A logical degree of precision in predicting austenite grain growth in microalloyed steels with different Nb contents, has been achieved in the current work.

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The effect of thermal processing (TMP) parameters on grain growth in a low C - Mn steel and a C - Mn steel microalloyed with Nb, Ti and V were compared as part of a wider study on grain growth in microalloyed steels. The grain growth rate was found to be low at low temperatures and short soaking times but increases significantly with both increasing temperature and time. The activation energy Q, the grain growth equation constants n and A were found to be higher in the microalloyed steel than the plain C-Mn steel. A constitutive model for predicting austenite grain growth in the low C-Mn steel and the microalloyed steel has been developed. The predictive potential of the model is in good agreement with the experimental data.