AN INVESTIGATION ON THE EMBRITTLEMENT OF COLD ROLLED 3.25% SILICON STEEL WELD JOINTS

One of the main problems encountered during the production of cold-rolled 3.25% silicon steel was the embrittlement of MIG and TIG weld joints.Three new points of view different from the prevalent ones concerning the welding technology of silicon steels were raised in this paper.Most authors of the articles published before overlooked the differences in weldability among different types of silicon steel,and paid less attention to the process of austenite to ferrite transformation at about 950℃ in transformer steel.This investigation revealed that heat treatment after MIG welding not only softened the welds and relieved the residual stress but also much more importantly,dissolved rapidly the cementite precipitated at the grain boundary.Thus the temperature of postweld heat treatment should be higher than 800℃.It was inadequate to improve the ductility of TIG welds by seam rolling process.However,an obvious increase in ductility of welds could be obtained by controlling the orientation of the columnar grains in the weld metal.The new measures described were designed to improve the reliability of both MIG and TIG joints significantly and to eliminate fracture accidents of MIG weld joints.