Inconel alloys development -Development of the advanced nuclear materials-

We surveyed the current status and problems in S/G U-tubes in Korea and worldwide. Also we gathered manufacturing specifications of S/G U-tubes and compared/analyzed the differences in them company by company. We produced alloy 600 tubes (in cooperation with Sammi Special Steels) through V.I.M. (Vacuum Induction Melting; 2 ton capacity), 4 steps of hot press forging, hot extrusion (10:1 of reduction ratio), 3 steps of cold pilgerings and so on. We will continue to characterize the tubes and 2nd time preproduce the tubes using the feed-back data. With regard to alloy 690, which is getting popular for S/G U-tubes worldwide, we cast four 60 Kg ingots and two 6 Kg ingots by V.I.M.. We analyzed the chemical composition, macrostructures, hot workability, and so on ; all ingots were good except on 60 Kg ingot. Finally we produced high quality alloy 690 ingot (about 1 Kg) by E.S.R. (Electroslag Remelting) method (in cooperation with Yeoungnam University). We used CaF/CaO/Al2O3/MgO quartenary slag system. We have made directionally grown good ingots by E.S.R. and especially the hot workability at 1100 deg C - the temperature at which V.I.M. ingots showed very poor hot workability - was very much improved (from 30 to 90 % of reduction of area). We continue to analyze the effects of E.S.R. to the structure and properties of alloy 690 (grain size, morphology, and directionality; any changes of inclusions and so on). (Author)