Cryogenic Structural Materials Research Articles

High-strength and high-toughness austenitic stainless steels based on type 316LN at 4.2 K

High-strength and high-toughness prototype steel forgings, N2, N3, and N4, were developed based on type 316LN as a cryogenic structural material. By extrapolating the proportional relationship between carbon plus nitrogen content (C + N) and 0.2 % proof stress (σ0.2) in the range of approximately 0.10–0.25 mass% C + N content, the C + N content was successfully designed to achieve the target σ0.2. To suppress the degradation of the plane-strain fracture toughness (KIC(J)) while increasing the nitrogen solid-solution content, the alloying level was designed by considering the stability of the austenite phase and stacking fault energy. The steel forgings showed a good balance of strength and toughness at 4.2 K, i.e., N2 (σ0.2 = 1142 MPa, KIC(J) = 228 MPa√m), N3 (σ0.2 = 1226 MPa, KIC(J) = 219 MPa√m) and N4 (σ0.2 = 1296 MPa, KIC(J) = 215 MPa√m). The σ0.2 and KIC(J) of ITER-grade 316LN (316LNL, 316LNM, and 316LNH) thick plates with low interstitial (C + N) content of 0.13–0.17 mass% were also evaluated at 4.2 K. Then, the effects of nitrogen content on strength and fracture toughness were successfully clarified in the full range of interstitials concentrations. An alloy design with higher Ni, Mn, and Mo contents in the chemical composition range of 316LN would be desirable for improving the fracture toughness by increasing σ0.2 due to the higher nitrogen content.

Evaluation of Mass Production Results of Cryogenic Structural Stainless Steels for ITER Toroidal Field Coils

The National Institutes for Quantum Science and Technology (QST) has been developing new cryogenic structural materials, such as JJ1 stainless, and nitrogen-enhanced 316L stainless, known as 316LN, since the 1980s for increased tensile strength to comply with the ITER requirements. QST has also developed prediction curves for yield stress and tensile strength at temperatures from room temperature to 4 K based on the actual properties of these materials at room temperature to reduce the number of tensile tests conducted at 4 K, which are costly. After material trials and qualifications, the manufacture of material candidates began in earnest from 2012. In total, over 2400 materials (over 5000 tonne) were manufactured by six fabricators until manufacturing was completed successfully in 2020. The material properties of each material candidate were evaluated by QST and added into a database registry. Sampling tests, e.g., tensile tests were conducted at 4 K and 77 K. The correlations between the mechanical and material properties were evaluated to optimize material specifications of future superconducting magnets. The accuracy of QST's prediction curves was also confirmed. This paper summarizes the evaluation of the material properties and the prediction accuracy of mass-produced materials for the ITER toroidal field coil cases.

Study on development policy for new cryogenic structural material for superconducting magnet of fusion reactor

A fusion DEMO will require large-scale cryogenic structure including TF coil cases. Because of huge electromagnetic forces, extra thick plates and/or wrought products will be supplied. Since the midsection of the huge block is weaker than the block surface region, the design yield stress must be determined taking account of this lower strength part. To search the manufacturing process to improve the midsection strength, the crystal refinement strengthening and the precipitation strengthening are considered together with the carbon and nitrogen solid solution strengthening. XM-19 was focused based on the variation of the yield stress and the fracture toughness, a 100 mm thick block and a 30 mm thick plate were trial produced, and strength and the fracture toughness at the midsection were evaluated. This study will present the experimental data and discuss the development policy for a new cryogenic structural material for a fusion reactor.

Preface

It is our great pleasure to report that the Proceedings of joint meeting of the 10th Asian Conference on Applied Superconductivity and Cryogenics (ACASC), 2nd International Cryogenic Materials Conference in Asia (Asian-ICMC), and the CSSJ meeting held at Okinawa, Japan, between January 6 to 9, 2020 is published in Journal of Physics: Conference Series (JPCS).…Total numbers of participants and presentations of the 10thACASC/2ndAsian-ICMC/CSSJ Joint Conference are 381 from 13 countries and 276 including 4 plenary lectures, 5 invited talks for Asian topics, respectively. This conference consisted of many sessions, such asCryogenic structural materials, Superconducting materials, Wire and Tapes (Nb3Sn, Nb3Al, BSCCO, REBCO, MgB2, Fe-based), Cryogenic Cooling Engineer ing, Magnet Technology, Power Applications (Motors, Generators, Cables, FCL, SMES and others), Liquid Hydrogen, Aircrafts, Motors and Maglevs, Superconducting Bulks, Evaluation and Analysis, Database of Cryogenic Structural Materials, Electronics, Superconducting Joints.…List of Editors and Program Committee, Organizing Committee are availble in this pdf.

Mechanical Properties and Material Code of Cryogenic Structural Materials for Toroidal Field Coils used in Fusion Facilities

Mechanical Properties and Material Code of Cryogenic Structural Materials for Toroidal Field Coils used in Fusion Facilities

Note: Carbon fiber composite arrow shaft as cryogenic structural support material.

The thermal conductivity, electrical resistivity, and bending stiffness of a carbon fiber archery arrow shaft were measured in order to determine if it would be a good material to use as a structural support in a cryogenic environment. It shows promise because of its thin cross section and structural rigidity. The thermal conductivity of the material was measured from 0.1 K to 1 K to be , which is on the order of other thermal insulating materials used at cryogenic temperatures. The electrical resistivity is 0.044 Ω cm at 0.2 K, and the bending stiffness is 243 N m2 at room temperature. The shafts were machined to reduce overall thermal conductance. The reduction in thermal resistivity was calculated, and the change in stiffness was measured after shafts were machined. The shafts were used to form a support structure for an adiabatic demagnetization refrigerator. The heat load was then calculated. The carbon fiber arrow shaft provides an outstanding, thermal insulating support structure.

Temperature dependence on tensile properties of Cu-40mass%Fe dual phase alloy

The binary system of iron and copper shows low mutual solubility and cast Cu-Fe forms an iron (bcc) and copper (fcc) dual phase structure at room temperature. In this study, tensile properties, deformation and fracture behaviour of a rolled Cu-40mass%Fe alloy have been evaluated in order to reveal the temperature dependence on tensile properties in dual phase structures. The material formed a layer structure with ultra-fine grains of 1 μm in diameter. In both iron and copper grains, furthermore, many precipitates of copper or iron were revealed. The strength of this material increased at low temperatures, though the elongation was hardly changed, which suggests that fcc + bcc dual phase structure is effective to improve the tensile property at low temperature. Strain was inhomogeneously distributed at low temperature regardless of Cu and Fe region, and voids and cracks tended to form inside Cu layer. These results imply that the temperature dependence on tensile properties and deformation behaviour of each phase in dual phase structure is different from that of each single phase structure, and dual phase structure materials have a potential for becoming superior cryogenic structural materials.

Properties of radiation stable insulation composites for fusion magnet

High field superconducting magnets made of Nb3Al will be a suitable candidate for future fusion device which can provide magnetic field over 15T without critical current degradation caused by strain. The higher magnetic field and the larger current will produce a huge electromagnetic force. Therefore, it is necessary to develop high strength cryogenic structural materials and electrical insulation materials with excellent performance. On the other hand, superconducting magnets in fusion devices will experience significant nuclear radiation exposure during service. While typical structural materials like stainless steel and titanium have proven their ability to withstand these conditions, electrical insulation materials used in these coils have not fared as well. In fact, recent investigations have shown that electrical insulation breakdown is a limiting factor in the performance of high field magnets. The insulation materials used in the high field fusion magnets should be characterized by excellent mechanical properties, high radiation resistivity and good thermal conductivity. To meet these objectives, we designed various insulation materials based on epoxy resins and cyanate ester resins and investigated their processing characteristic and mechanical properties before and after irradiation at low temperature. In this paper, the recent progress of the radiation stable insulation composites for high field fusion magnet is presented. The materials have been irradiated by 60Co γ-ray irradiation in air at ambient temperature with a dose rate of 300 Gy/min. The total doses of 1 MGy, 5 MGy and 10 MGy were selected to the test specimens.

Cryogenic Fatigue and Stress-strain Behavior of a Fibre Metal Laminate

This paper reports on the cryogenic fatigue life of Al 2024 / Stycast 2850 FT composite sandwiches loaded under cyclic strain, as well as on the strength of their constituent materials at 77K. These Fibre Metal Laminate (FML) specimen serve as a model for an alternative class of cryogenic structural materials that might be used e.g. in downstream LNG applications. FMLs, such as the GLARE ™, are already used in the aeronautic industry, where they provide better damage tolerance, corrosion resistance and lower specific weight. Their cryogenic performance, however, is yet to be understood. Preliminary results show that the metal/filled- epoxy combination presented here withstands repeated cool-down to 77K. Moreover, its cryogenic fatigue life is at least 20 times longer than at room temperature. These observations are consistent with the measured stress-strain behaviour of the metal and the epoxy, as well as with the shear strength of the bond between them. The Youngs modulus, yield strength and tensile strength of the Stycast 2850 FT roughly double when cooled down to 77K. In addition to this, the bond strength with the GLARE-type coated Al increases significantly. These preliminary experiments indicate that cryogenic FML are technically feasible.

Mechanical Characterizations of Structural Materials for Large Superconducting Magnets at Low Temperatures

In the past decades, China was involved in several large superconducting magnet tasks. These magnets require cryogenic structural materials as reinforcement. Within this context, mechanical characterization of these materials at cryogenic temperature obtained with specimens from readily available components is a prerequisite for a safe engineering design. In China, almost all cryogenic mechanical measurements of structural materials dealing with large superconducting magnets have been conducted at the Center of Cryogenic Materials and Applied Superconductivity, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences. This paper shows the recent mechanical measurement results with toroidal-field coils, poloidal-field coils, correction coils, feeders, magnet supports, a full-size conductor, and insulation materials for the International Thermonuclear Experimental Reactor task.

Research Progress on the Transformation, Fracture Mechanism and Properties of Structural Ceramics at Cryogenic Temperatures

Currently,the rapid development of cryogenic techniques makes them required for a wide range of applications such as aeronautics astronautics,superconducting fields,nuclear fusion and so on.Structural ceramics are promising cryogenic structural materials which are prior to some kinds of metals and polymer materials in some specific applications.The research history and progress of several classical types of structural ceramics at cryogenic temperatures are reviewed.The contents of the present paper include the transformation mechanism and properties of zirconia-based ceramics,alumina ceramics and basic mechanical properties and fracture mechanisms of Si3N4and SiC ceramics at cryogenic temperatures.

核融合炉用超伝導コイル構造材料開発の歩み

Cryogenic structuralmaterials are an essential element to fulfill the performanceof superconducting coils for fusion reactors. In this field, there was no specialized steel and mechanical properties data at 4 K until 30 years ago when the Japan Atomic Energy Agency (JAEA) started the development of the Tokomak fusion reactor. JAEA set a target of mechanical characteristics which could satisfy requirements for the coil structure at 4 K and equipped evaluation facilities at 4 K for tensile tests, fatigue tests and so on. At the same time, JAEA initiated collaboration with the steel industries in order to realize new cryogenic structural materials and carried out mechanical evaluation tests at 4 K on numerous samples which were supplied from the industries. There are two areas: a coil case and a conductor jacket for forced flow conductor. The former requires large forging products and thick hot-rolled plates for the coil case. The latter is influenced by heat treatment at approximately 650 °C and more than one-hundred hours to produce Nb3Sn superconducting material at the final stage. This is a unique issue for the jacket. Finally, both the case and the jacket material for construction of the ITER are now being supplied from the Japanese industries through JAEA. In addition, JAEA contributed to the standardization of these testing methods at 4 K in Japanese industrial standards (JIS). Furthermore, JAEA supported the establishment of a design code for the structure of superconducting coil for a fusion facility at the Japan Society of Mechanical Engineers (JSME). This paper describes the more than 30-year history of the development of cryogenic structural material.

1603 核融合設備規格超電導マグネット構造規格(JSME S KA1-2008) : 材料(OS16-1 核融合炉-多種多様な力学的環境における強度・設計問題)

To confirm the design and construction process of large superconducting magnet for fusion application, a rules on superconducting magnet structure has been established as part of a code for fusion facilities in JSME standard. The code consists of Quality assurance, Materials, Design, Fabrication and installation, Non-destructive examination, Pressure and leak testing and glossary. This code is the world first documents covering all manufacturing processes conceming the large scale superconducting magnet for fusion. This report deals with "Materials" section in the code. Although the code specifies the materials that will be applicable to the magnet, cryogenic structural materials will be focused and the contents are expounded. A special point described in the code is skipping of mechanical tests at cryogenic temperature. When the chemical composition is satisfied according to the code and when special and additional heat treatment is not performed, the cryogenic mechanical tests are not required. Chemical composition of a welding wire is also listed.

Evaluation of Thermal Aging Embrittlement of Austenitic Stainless Steels JN1, JJ1 and JK2 by Cryogenic Small Punch Tests

The small punch (SP) tests were conducted at 77 K and 4 K using austenitic stainless steels JN 1, JJ 1 and JK 2, which have been recently developed for use as a cryogenic structural material. The tests were applied to the steels aged at 923-1073 K to investigate changes in their toughness at cryogenic temperature due to thermal aging. The area under the load-deflection curve up to the macro-crack initiation was defined as SP energy to evaluate the fracture toughness of the steels. The experimental results showed that the SP energy of JN 1 decreased monotonously with an increase in aging temperature. On the other hand, the SP energy of JK 2 showed no significant change even after the thermal aging at 923 K and 973 K and decreased after the thermal aging at 1023 K. Metallographic examination revealed that this difference in decrease of SP energy due to thermal aging was caused by the variation in amount and distribution of grain boundary M23C6 carbides. As a consequence, JN 1 was more susceptible to thermal aging embrittlement than the other steels, and high resistance of JK 2 to embrittlement was attributable to the depression of precipitation and coarsening of grain boundary precipitates.

窒素強化オーステナイト系ステンレス鋼の極低温強度の推定(S08-1 極低温材料システム(1),S08 極低温・超電導材料システムの強度・機能特性)

Japan Atomic Energy Research Institute (JAERI) has developed large superconducting magnets and cryogenic structural materials to construct the International Thermonuclear Experimental Reactor (ITER). Material rules in structural design code like ASME Boiler and Pressure Vessel Code is required to construct the ITER or commercial fusion facilities in rational way. From this point of view, it is important to predict the strength at cryogenic temperatures of nitrogen strengthened austenitic stainless steels based on the strength at room temperature. Tensile tests were performed at room temperature, in liquid nitrogen (77K), in liquid helium (4K), and in gaseous helium (about every 50 degrees between 7K and 227K). Empirical prediction quadratic curves in taking account of carbon and nitrogen (C+N) effect on strength were established for JJ1 and 316LN based on the test results. It is expected that cryogenic strength of commercial base materials can be predicted by using these curves.

Cryogenic fracture behaviors and polarization characteristics according to sensitizing heat treatment on structural material of the nuclear fusion reactor

The cryogenic fracture behaviors of austenitic stainless steel HN2 developed for nuclear fusion reactor were evaluated quantitatively by using the small punch(SP) test. The electrochemical polarization test was applied to study thermal aging degradation of HN2 steel. The X-ray diffraction(XRD) analysis was conducted to detect carbides and nitrides precipitated on the grain boundary of the heat treated HN2 steel. The mechanical properties of the HN2 steel significantly decreased with increasing time and temperature of heat treatment or with decreasing testing temperature. The integrated charge(Q) obtained from electrochemical polarization test showed a good correlation with the SP energy(ESP) obtained by means of SP tests. From the results observed in the x-ray diffraction and anodic polarization curve, it was known that the material the grain boundary. Combining SP test and electrochemical polarization test, it could be useful tools to non-destructively evaluate the cryogenic fracture behaviors and the aging degradation for cryogenic structural material.

A study on the fracture toughness evaluating method for cryogenic structural material

This paper was undertaken to develop the fracture toughness testing method using small and single specimen compared to the conventional method in evaluating elastic-plastic fracture toughness of the superconducting magnet structural material at cryogenic temperature. The elastic-plastic fracture toughness test was conducted by using the unloading compliance method recommended by ASTM E813-89 to accomplish the above purpose. And, the 20% side-grooved 0.5TCT and 1TCT specimens were used to evaluate the fracture toughness by using as possible as miniaturized CT specimen. The unloading compliance method was a very useful method in evaluating elastic-plastic fracture toughness at cryogenic temperature. It could be taken valid fracture toughness values by using 20% side-grooved 0.5TCT specimen recommended by ASTM E813-89.

Determination of Cryogenic Fracture Characteristics of Austenitic Stainless Steel JN1 Welded Joint and Heat-Treated Materials by Means of Small Punch Testing Method.

Fracture characteristics of a TIG welded joint and heat treated materials of JNI, which is an austenitic stainless steel recently developed for use as a cryogenic structural material, were evaluated by the small punch (SP) testing method using miniaturized specimens at 77K and 4K. The area under the load displacement curve up to the maximum load was defined as the SP energy to evaluate the fracture characteristics of the materials in SP tests. Fracture surfaces were also observed using a scanning clectron microscope. Solution-treated JN1 steel showed ductile fracture behavior with a high SP energy value even at 4K, and serrations were observed in the load displacement curve at 4K, In the weld metal and fusion line specimens of the TIG welded joint, serrations also occured at 4K, but the fusion line specimens showed lower SP energy values than weld metal and solutiontremed JN1 steel at 77K and 4K. In addition, the fusion line specimens showed pop in behavior at 4K, that is, cracks approximately 0.1-1mm long were induced by pop-in in the vicinity of the fusion line at the early stage of loading. JN1 materials heat treated under the conditions of 650°C 5h and 700°C In showed similar fracture characteristics to those of the fusion line specimens at 77 K and 4 K except for the cracks induced by pop-in. With increasing temperature and time of heat treatment, SP energy decreased significantly, and the fracture surface showed a transition from ductile dimple to brittle intergranular cracking. It is shown that the SP testing method is useful for evaluating the fracture behaviors of microscopic regions such as the fusion lines of welds at cryogenic temperatures.

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

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.

超電導磁石用極低温構造材料の開発

超電導磁石用極低温構造材料の開発