Kiyohiko Nohara

Fine-blanking performance of non-magnetic high manganese cryogenic steel and its application tosuperconducting dipole magnet

Abstract A huge superconducting magnet for the recent particle acceleratorsnecessitates a non-magnetic cryogenic structural material with high strength and toughness. The non-magnetic high manganese steel (KHMN) developed lately is a promising candidate. The fine-blanking performances of 2.5mm thick steel coil were investigated for a magnet collaring in terms of flatness/dimension and press fit/pull-out. The experiment shows that KHMN can availably subjected to fine-blanking and press-fitting. Further KHMN was applied to a 1.5m long superconducting magnet tooling as a form of fine-blanked 1.5mm thick non-magnetic collars. The magnet performances were studied to favorably obtain the data from quench test and magnetic examination.

Cryogenic properties of new austenitic stainless steel for fusion reactor superconducting magnets

Abstract A non-magnetic austenitic stainless steel has been developed, which has an adequate combination of yield strength and fracture toughness at liquid helium temperature, as a candidate structural material for fusion reactor superconducting magnets. The salient feature of the steel is its low-temperature toughness preserved after aging equivalent to the wind-and-react heat treatment of Nb 3 Sn superconducting coil. The steel also keeps its toughness after electron beam welding. Its composition is characterized by addition of vanadium and nitrogen to 25Cr-14Ni-0.5Mo austenitic stainless steel. Microscopic observations have suggested that finely dispersed precipitates, presumably vanadium carbonitrides, are responsible for the excellent cryogenic mechanical properties.

Cryogenic Properties of Austenitic Stainless Steels for Superconducting Magnet

In the field of high-energy physics, large-scale high-energy particle accelerators are either under construction or planning, where the “Wind-and-React” process is possibly applied to employ Nb3Sn superconductor instead of NbTi for the production of over five-tesla-class superconducting magnet. This process necessitates the structural materials with favored properties at cryogenic temperatures before and after Nb3Sn precipitation heat treatment. The present study is carried out to examine the magnetic and mechanical properties of a variety of austenitic stainless steels and high manganese steel which are both considered as candidate structural materials for superconducting magnet attached to high energy particle accelerator and other superconducting applied technologies. In particular attention is paid to the effect of a specified heat treatment for the precipitation of intermetallic compound Nb3Sn to be used as superconductor on the properties such as ductility and toughness as well as serength at lower temperatures.

Cryogenic Toughness and Welding of High Manganese Non-Magnetic Steel: Application to the SSC Dipole Magnet

High manganese austenitic steel was designed to meet the requirements for the SSC superconducting magnet structural material by providing the following characteristics: high yield strength over 90KSI at room temperature, low magnetic permeability below 1.0020 at 4K, thermal expansion coefficient close to that of pure iron, and favored stamping plus spot welding performances. This follows to the present study on (1) toughness and fatigue of this material at 4K, (2) influence of sensitizing treatment and TIG welding on the properties at room temperature and 4K, and (3) application of the steel to superconducting magnet fabrication and its stress measurement and field test. The investigation shows: (1) charpy absorbed energy, vE4k, and fracture toughness, KIC, at 4K are 135J and 198 MPa√m, respectively, exhibiting enough ductility at the ambient temperature of a magnet; (2) adverse effects of either sensitizing or TIG welding on the ductility and toughness of the steel are not shown possibly because of the small addition of vanadium; (3) long trial magnets fabricated using high manganese steel give approximately the same results in the stress measurement and field test as those obtained from the magnets with stainless steel.

Strengthening and Serrated Flow of High-Manganese Nonmagnetic Steel at Cryogenic Temperatures

High-Mn steel is a promising structural material for cryogenic applications in view of its prominent stability in magnetization. Increased yield strength is of great significance along with generation of serrated flow, since such structural materials undergo a vast electromagnetic force, especially in cases of (pulse) SCM for nuclear fusion, SMES, etc.1 With 28Mn-7Cr-lNi selected as the standard high-Mn steel, the effects of composition, thermomechanical treatment, and Nb3Sn superconductor precipitation heat treatment on strength were studied. In connection with serrated flow, the effect of strain rate was checked by detecting the change in the specimen temperature during deformation together with the measurement of specific heat at cryogenic temperatures.

Experiments in Development of Cryogenic Structural Materials for Accelerator (SSC) Superconducting Magnet

As the candidates of structural materials for a collar and a yoke of accelerator superconducting magnets,both non-magnetic high Mn steel (KHMN) and ferro-magnetic ultralow C steel(EFE) have been developed.The current investigation was aimed to study 1) fineblanking and magnet error component with 1.5 and 2.5mm thick KHMN, and 2) compatibility between strength and coercive force with 6 and 1.5mm thick EFE.The positive results were obtained in each subject.

Manufacturing and Magnetic Characteristics of High Purity Ultra Low Carbon Magnet Steel for the SSC

Pure iron sheet or high purity (ultra) low carbon magnet steel sheet is employed as magnetic shield yoke for the SSC magnets of various types. It is required to have adequate magnetic properties as well as suited mechanical properties and usability (fabricability). To meet such requirements the presentation is to be made concerning the status of manufacturing and research work in view of mass production of high purity low carbon magnet steel, the relation between magnetic characteristics and metallurgical factors, and the further development of high purity “ultra” low carbon magnet steel exhibiting lower coercive force plus its laser cut performance for the corrector special magnet.

Production, Metallurgy, and Utilization of High Manganese Nonmagnetic Steel—Its Development for the SSC Magnet

As a candidate of structural material for the SSC magnet cryogenic use, high manganese nonmagnetic steel (KHMN30L) has been developed to give several favorable results in terms of its production, metallurgy and usability. It is proved available to make a mass production of both 1.5mm and 2.5mm thick sheet coil. The suitable balance of nonmagnetism, strength and cryogenic toughness is achieved along with their sufficient stability and unformity. The material usability has been investigated to involve the experiment of semi-perforation / fine blanking of a collar with 2.5mm thick specimen currently manufactured at a factory.

Development of High Manganese Non-Magnetic Steel for SSC Dipole Superconducting Magnet Collar

The SSC dipole magnet collar requires the material that is of high strength and sufficient stability in magnetism along with adequate thermal contraction at liquid helium temperature as well as at room temperature. The newly developed high Mn non-magnetic steel is shown to meet such requirements better than other materials like stainless steel. The new steel is featurized by a marked magnetic stability, temper cold rolling without any rise in magnetic permeability, and a little smaller thermal expansivity. High Mn steel demonstrates a satisfactory stampability and spot weldability similar to those of stainless steel. It is subjected to the fabrication of both short and long model magnets as collar material of a cold mass to exhibit favored results in their fabricability and magnet performance.