Interactions between fusion materials R&amp;D and other technologies

Effects of doping with 60 ppm B and/or 200 ppm N and heat treatments on the microstructures and the ductile-brittle transition temperature (DBTT) have been studied for ferritic/martensitic steel F82H. Prior austenitic grain size of standard F82H decreased from about 120 to 30 mm and also the DBTT decreased by about 50 C when the normalizing temperatures were changed from 1040 to 950 C. In case of F82H doped with B (F82H+B) normalized at 950 C the grain size increased from 30 to 40 mm and the DBTT increased by about 50 C as compared with that of the standard F82H. In case of F82H co-doped with B and N (F82H+B+N) the grain size and DBTT, however, were comparable to each one of the standard F82H. Localization of B and C with the size of a few mm at grain boundaries was observed in the F82H+B by using a time of flightsecondary ion mass spectroscope, but not in the F82H+B+N. The results indicated that the degradation of fracture toughness in F82H+B was caused mainly by the localization of B at the grain boundaries. The DBTT of F82H+B+N steels normalized at the temperatures from 950 to 1040 C was changed from À96 to À73 C, but the prior austenitic grain size remained nearly unchanged. The precipitate size, however, depended on the normalizing temperature. It was shown that the change of DBTT was related to the change in the mean size of the precipitates in the F82H+B+N steels. Keywords: heat treatment, microstructure, ductile-brittle transition temperature, ferritic/martensitic steel, boron and/or nitrogen doping, time of flight-secondary ion mass spectrometry

Section: Methodsmentioning

confidence: 99%

“…[1][2][3] The fast neutrons cause displacement damage and produce transmutation products such as He atoms in materials. It is necessary to understand the effects of simultaneous formation of the displacement damage and large amounts of He on the mechanical properties and the microstructures of the steels.…”

Section: Introductionmentioning

confidence: 99%

Heat Treatment Effects on Microstructures and DBTT of F82H Steel Doped with Boron and Nitrogen

Okubo¹,

Wakai²,

Matsukawa³

et al. 2005

“…[1][2][3] The fast neutrons cause displacement damage and produce transmutation products such as He atoms in materials. It is necessary to understand the effects of a simultaneous formation of displacement damage and large amounts of He on mechanical properties and microstructures.…”

Section: Introductionmentioning

confidence: 99%

Tempering Treatment Effect on Mechanical Properties of F82H Steel Doped with Boron and Nitrogen

Okubo¹,

Wakai²,

Matsukawa³

et al. 2005

Effects of tempering treatment on mechanical properties and microstructures have been studied for martensitic steel F82H doped with 60 ppm B and 200 ppm N (F82H þ B þ N). The tempering treatments were performed at 700-780 C after the normalizing treatment at 1000 C. Yield stress of the F82H þ B þ N steel tempered at 700, 750 and 780 C was 740, 580 and 500 MPa, respectively, and ductile-brittle transition temperature (DBTT) of the specimens was À55, À85 and À85 C, respectively. The areal density of dislocations decreased from 1:1 Â 10 14 to 2:5 Â 10 13 m À2 with increasing tempering temperature from 700 to 780 C. The number density of precipitates decreased with increasing tempering temperature from 700 to 750 C, while the number density was almost equivalent as increasing tempering temperature from 750 to 780 C. The results indicate that the change of DBTT, depending on tempering temperature, is related with the change of yield strength, size and number density of carbides. Hardening behavior of the F82H þ B þ N steel irradiated by 10.5 MeV Fe 3þ to 10 dpa at 360 C has been also studied by using a micro-indentator. The micro-hardness of the F82H þ B þ N steel tempered at 780 C was changed from 3.6 to 4.8 GPa by the irradiation. Because hardening behavior of the F82H þ B þ N steel was found to be similar with that of F82H non-doped, doping effects of B on irradiation hardening were suppressed by co-doping of B and N.

“…1,2) In fusion reactor environment, nuclear collision and reaction by high-energy neutrons and particles from fusion plasma strongly affect on material properties through the production of displacement damage and transmutation effects. 3,4) Degradation of material performance such as mechanical properties, thermal properties and so on is important issue and extensive efforts have been conducted. 5) Interfacial properties between the fiber and matrix of neutron-irradiated SiC/SiC composite influence mechanical performance.…”

Section: Introductionmentioning

confidence: 99%

Effect of Fiber Properties on Neutron Irradiated SiC/SiC Composites

Hinoki

Katoh

2002

The use of SiC/SiC composites for nuclear application has recently been considered because of intrinsic low activation and superior high temperature mechanical properties of SiC. The property of SiC fiber is a key issue in order to improve mechanical properties of SiC/SiC composites following irradiation. SiC/SiC composites with unidirectional fibers were fabricated by chemical vapor infiltration method. Low oxygen and highly crystalline fibers or just low oxygen fibers were used in the composites. The specimens were irradiated at Japan Material Testing Reactor and High Flux Isotope Reactor. The effects of neutron irradiation on mechanical properties were examined by three points flexural test. Microstructure and fracture behavior were observed by scanning electron microscopy before and after neutron irradiation. The SiC/SiC composites with a low oxygen content, near-stoichiometric atomic composition and highly crystalline SiC fibers showed the excellent stability to neutron irradiation. The mechanical property of this material did not degrade, even after neutron irradiation up to 10 dpa, while the other materials with non-highly crystalline SiC fibers degraded significantly.