Abstract: Induction pressure welding is often used to manufacture the butt joints of steam pipe of power plant. However, the so called white speck, as sometimes appeared on the fractography of the checked sample weld, may lead to fracture or burst of steam pipes during high temperature operation.The investigation indicated that the white speck implied the weak linkage between the ends welded. In order to reduce the white speck region, It is necessary to increase upsetting. At the same time,the abutting ends should be first machined or ground to a smooth clean surface. On the basis of experiments, two kinds of butt joint forming physical models and three types of dimple models of fractography have been proposed. These models reveal the essence of welding process and the forming mechanism of white speck.