AbstractThis paper presents a study of the microstructural changes that occur during warm rolling of a sintered tungsten ingot on a Kocks mill. The material was subjected to between one and four rolling passes. The results show that during warm rolling the grain structure undergoes several dynamic processes. High angle boundaries are formed and then migrate. As the grains grow, they are subdivided by low angle boundaries that are formed by dislocations generated during rolling. These low angle boundaries eventually transform into high angle grain boundaries and in turn begin to migrate. At the same time, potassium containing bubbles that are present in the investigated lamp quality tungsten become narrower and longer. The narrowing that occurs is greater than would be predicted from a constant volume criterion because the density of the material increases during rolling. When the rolled rod is annealed, abnormal grain growth occurs. The grain size depends highly on the amount of work to which the material has been subjected and the variations in grain size across the rod diameter can be explained in terms of the amount of deformation that the material has undergone. Also, during the anneal the potassium containing ellipsoids spheroidise. In most examples spheres form by contraction of the ellipsoid to form a single sphere. However, in the rod subjected to four rolling passes some ellipsoids have a sufficiently high aspect ratio for break-up into two spheres to occur. This behaviour is well explained by the Rayleigh model for break-up of a cylindrical fluid.MST/1430