Abstract
	Microstructure is one of the most important features to mechanical properties. It can strongly influence on strength, creep, and fatigue behaviours. Grain size is basic consideration which uniform coarse grain size is favouring creep strength, crack growth resistance, and ductility for next step forming. Optimisation and control of uniform grain size and morphology can be achieved by recrystallization process from annealing treatment after hot working. It was found that annealed microstructure resulting from only one or two steps of hot working in NiMoCr alloy was not uniform through out specimens as desired. Therefore breaking down the casting ingot structure by hot working process could provide only non-uniform recrystallized grain structure. In order to obtain more uniform grain structures an additional cold working was utilized. The following annealing process was supposed to achieve uniform recrystallized grain structure. It was found that annealed microstructures after cold working were much more uniform and homogeneous than those without any cold working. Furthermore, the uniformity of microstructure increased with higher amount of introduced deformation.
	In this study, creep behaviour of modified microstructure in NiMoCr alloy, which has very similar chemical composition like in Hastelloy N, after different hot and cold working conditions and various annealing times was investigated. Creep tests were performed with stress level at 160 MPa and temperature at 710°C using uniaxial creep specimens. The results of creep tests showed that creep characteristics such as rupture strain, strain rate, and lifetime of the tested alloy were greatly dependent on the initial hot working conditions (temperature and amount of deformation in the process) and various annealing times.