Effect of Process Parameters in the Casting of Large Forging Ingots on the Formation of the Optimum Structure In The Axial Zone

The microstructure and macrostructure of large forging ingots is determined by their geometric parameters and the casting and crystallization conditions. The effect of these factors on the quality of the ingot is manifest in different ways. During the initial stages of crystallization, the rapid transfer of heat between the solidifying metal and the mold leads to the formation of a dense structure with a minimal number of defects. At the end of the ingot's solidification, slowing of the thermal, segregational, and other processes taking place in the axial zone results in the formation of shrinkage-induced cracks. The axial zone of large ingots usually consists of crystals located in the bottom part of the settling cone and arcuate and V-shaped cracks located in succession above those crystals. The degree of opening of the V-shaped cracks varies over the height of the ingot: it increases toward the top part of the axial zone. The formation of the structure of the axial zone of the ingot is influenced by many factors, but the most important are the geometric parameters of the ingot being cast and the casting conditions - the temperature of the metal being cast, the speed of its ascent in the ingot mold, and the ratio of the length of time it takes to cast the top of the ingot to the length of time it takes to fill out the body of the ingot (t sub ht /t sub b ). To determine the effect of these factors on the structure of the axial zone, we studied 12 shortened forging ingots of steel 34KhN3MFA weighing from 8.7 to 43 tons. The steel was made in open-hearth furnaces by the duplex process (the main furnace used had an acid lining).