Effect of carbon on the structure and properties of cold-rolled transformer steel

Abstract

1. The formation of stable austenite zones becomes possible in cold-rolled transformer steel with 2.80–3.20% Si when the proportion of carbon in it exceeds 0.018–0.020%. This impairs texture formation during secondary recrystallization and lowers the magnetic properties (particularly magnetic induction in high fields). 2. In the process of regular vacuum annealing a decarburization process develops in the steel, which in the case of a high initial carbon content may assume considerable proportions. However, secondary recrystallization and the concomitant processes of texture formation occur during heating at 900–1000° before the beginning of decarburization. 3. Of great importance for the production of finished steel with high magnetic properties is the securing of a sufficient degree of decarburization (in the process of black anneal or special decarburizing treatment in an annealing furnace) prior to vacuum annealing. 4. With increasing carbon content the ductility of an annealed hot-rolled transformer steel strip initially decreases and then begins to increase as a result of grain refinement and the appearance of pearlite.