9%-nickel steel is a low alloy steel, which contains lower quantity of carbon and 9% of nickel. This steel after proper heat-treatment shows excellent tensile strength and toughness at extremely low temperatures as low as -200°C. This steel can be used for the construction of rather larger low temperature structures such as the storage vessels containing liquefied natural gases, etc. Comparing to the stainless- and 36%-nickel steel (Invar), etc., 9%-nickel steel seems to be the most reasonable material if considered the strength available for designing. The total cost of 9%-nickel steel welded structures, however, is rather expensive. The most predom-inant reason of expensive cost attributed to the high prices of the welding materials used. The nickel-base alloys such as Inconel, now, are mainly used for the welding of 9%-nickel steel. Weldability of 9%-nickel steel is superior, so that, heat-affected zone cracking, usually, do not occur when without preheating. Melting point of the nickel-base alloy is lower about 100°C than 9%-nickel steel. So, the welding penetration is rather shallow. The affinity between weld-metal and base metal is not so good that, in some cases, the lack of penetration occurs easily. Further, the hot cracking sensitivity of high nickel alloy is rather remarkable, so the creater cracking occurs almost always when omitted crater treatment. Generally speaking, the usability of high nickel alloy welding electrode is not so good. Now, several welding materials used for manual arc-, submerged arc- and gas shielded arc welding processes were developed.
This paper describes characteristics and behaviours of a model superconducting magnet used for a magnetically suspended highspeed train. If the characteristics length of the order of 1m is chosen for a model superconducting magnet as compared with the real vehicle dimension, the dimension 7-10cm would be possible as a dimension between the center of the winding and the surface of the cryostat bottom which faced to the ground coil array; containing the radiation shielding layer as the inner structure of the cryostat. The coil dimension of 1.2m long and 0.3m wide measured to the winding were chosen as a result of the coil configuration studies of the levitation characteritics. The maximum field were 27KG at the designed operating current of 500A. The electromagnetic force on the superconducing coil has three components; the lift force, the transverse and the driving forces. The lift force acting on the entire part of the windings was held with the coil former. And the force on the former was held and transmitted cocen-trically with the four columns to the part of room temperature. For the horizontal components of the force; the transverse force or driving force, the coil was fixed with the thin rods of stainless steel, to the side wall of the outer vessel. The electromagnetic forces acting of the superconducting magnet were determined using a “static levitation experiment” facility in which the superconducting magnet was set above the model ground coils involving a stabilizer coil. In the static test, the rigidity of the cryostats against the lift and transverse force acting on the superconducting coils inside the cryostats was also tested. Finally, the dynamic tests using a disc of 3.1m in diameter as a coil track or a sheet track were performed. The evaporation rate of liquid helium was 5-10l/h throughout those experiments.
The specific heat measurement at low temperatures has been described. In this apparatus we have used a mechanical heat switch with which the thermal contact is done by bringing up a specimen and pressing against the liquid helium temperature part. The specific heat has been measured about some specimens using this apparatus.