INVESTIGATION OF STRUCTURE, MECHANICAL AND THERMOPHYSICAL PROPERTIES OF ELECTRON BEAM MODIFIED WELDS ON COPPER PARTS OF LANCES

摘要

The study of real operating conditions of the lance for oxygen blasting shows that in its head part, located near reaction zones of the converter, high thermal stresses arise caused by nonuniform heating of different parts of the unit. The nozzles of the head are intensively cooled by water and oxygen, and the tip of the lance, on the contrary, is heated by thermal radiation of a liquid metal pool. Namely, thermal stresses along with mechanical loads (reaction of return effect from oxygen jets flowing from the nozzles) cause a premature destruction of the welds joining the lance nozzles with its tip. The need in developing electron beam welding of components of copper lances is predetermined by disadvantages of using traditional method of their welding - argon-arc method, which does not provide satisfactory properties of welded joints and their stability during operation of a product. The use of electron beam welding in the manufacture of lance heads for oxygen blasting allows increasing their service characteristics by alloying welding pool with the elements, having a deoxidizing effect on a liquid copper. At the same time, in order to increase the service life of lance heads, it is necessary to reduce the level of thermal stresses in them. The latter becomes possible if in terms of thermal conductivity the weld metal is as close as possible to the base metal. The paper presents the results of mechanical tests of electron beam welded joints produced on M1 copper using different alloying inserts. On the basis of studies of microstructure and character of fractures of the modified electron beam welds, the influence of alloying inserts on their operational properties was established. Together with the specialists from the ISM of the NASU, a procedure for conducting investigations on thermal conductivity of welded joints was developed and measurements of thermal conductivity coefficients for the joints produced on M1 copper by AAW and EBW methods using alloying inserts was performed. Computer simulation of the temperature field arising in the areas of welded joints in the conditions of operation of copper lances was also performed.