New factor causing discontinuities in the dilution zone of dissimilar steels

In welds consisting of two different metals the different coefficients of linear expansion of the metals result in stresses and, subsequently, in structural heterogeneity in the welding zone. After a high alloy 07Kh25N13 has been overwelded on carbon steel 20 and the sample heated for 300 hours at 600 deg C, the microstructure of the bimetal and the distribution of carbon in the butt of the sample have been compared to those in the bulk. Stresses in the weld cross-section have been observed to enhance carbon diffusion, which, in its turn, causes development of structural heterogeneity. Therefore, the coefficients of linear expansion of metals to be welded are to be closer to each other in order to dreduce stresses in the weld when it is being run at high temperatures and to stabilize the structure in the welding zone. A review is presented of papers published in 1975-1976 on underground leaching of uranium ores at industrial scale in the U.S.A. (in Texas and Wioming) and in Canada (Ontario province). Active plants for underground leaching are described as well as those to be launched. Organizing of the process is discussed, the technological schematic of semi-industrial plant is given. Advantages of underground leaching are discussed