Embrittlement of reduced-activation ferritic/martensitic steels irradiated in HFIR at 300°C and 400°C

Validity of nickel isotope tailoring (NIT) method to be able to generate a large amount of transmutation helium in 9%Cr-2%W reduced activation ferritic (RAF) steel for fusion reactor structural material was investigated and discussed through mechanical properties and microstructural evolution after fission neutron irradiation. Miniature tensile and Charpy impact specimens of RAF steels and 1% nickel added RAF steel were irradiated in the ATR-A1 to evaluate irradiation hardening and shift in ductile-brittle transition temperature (ÁDBTT). The amount of transmutation helium in all the RAF steels with and without nickel addition was calculated as only about 0.6 appm. After irradiation at 621 K, the ÁDBTT for the 1% nickel added steel was similar for the JLF-1. After irradiation at 543 K, however, the ÁDBTT for the 1% nickel added steel was significantly larger than that for the JLF-1. Microstructure observations revealed that irradiation-induced dislocation loops in the 1% nickel added steel were finer and denser than in the RAF steel without nickel addition, suggesting that the nickel addition to the RAF steels directly affected nucleation and growth processes of dislocation loops and enhanced irradiation hardening and embrittlement. Therefore, there is a limit in the NIT method as a simulation method for understanding effects of helium on irradiation embrittlement of RAF steels.

Section: Effect Of Nickel Addition On Mechanical Properties After Irrmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of Nickel Addition on Microstructural Evolution and Mechanical Properties of Reduced Activation Martensitic Steels Irradiated in the ATR-A1

Kasada

Kimura

2005

“…Therefore, the effects of neutron irradiation on tensile deformation, ductile to brittle transition temperature (DBTT), and microstructures of F82H and the other ferritic/martensitic steels have been extensively investigated. [1][2][3][4][5][6][7][8][9][10][11][12][13] On the course of these research activities, hardening and upward shift of DBTT induced by neutron bombardment have been commonly regarded as crucial problems. Radiation hardening occurs mainly at irradiation temperatures lower than about 400 C, and it increased with decreasing irradiation temperature down to about 250 C. The DBTT tends to increase with decreasing irradiation temperature as well, and the shift increases largely at 250 C. The issue of helium accumulation effects on these properties has been an ongoing concern.…”

Section: Introductionmentioning

confidence: 99%

Effects of Helium Production and Heat Treatment on Neutron Irradiation Hardening of F82H Steels Irradiated with Neutrons

Wakai¹,

Taguchi²,

Yamamoto³

et al. 2005

The influcence of addition of 10 B and 11 B on radiation hardening as a function of irradiation temperature was examined in reducedactivation martensitic F82H+B steels (8Cr-2W-0.2V-0.04Ta-0.1C-0.006B). Specimens used were 10 B doped, 10 B+ 11 B doped and 11 B doped F82H steels. Helium concentration produced in the specimens through 10 B(n, ) 7 Li reaction was measured from about 15 to about 330 appm. Radiation hardening of the specimens irradiated at 300 C to 2.3 dpa and 150 C to 1.9 dpa was observed. Increment of radiation hardening possibly due to helium in the specimen irradiated at 300 C tended to increase slightly with increasing helium production in tensile test at 20 C, but it was not observed for 150 C irradiation. Therefore, it can be mentioned that the enhancement of radiation hardening in the 10 B( 11 B) doped steels depends on irradiation temperature. The dependence of radiation hardening on tempering time was also examined for F82H-std irradiated at 150 C to 1.9 dpa. Increment of yield strength of F82H-std tended to increase with increasing tempering time. The relation between the shift of DBTT and the increment of yield strength due to irradiation suggest that the extension of tempering time or the increase of tempering temperature would be beneficial for mechanical properties of F82H-std.

“…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. [4][5][6][7] Boron doping has been adopted for steels to modify the toughness by boron segregation and/or precipitation at prior austenitic grain boundaries. 8) The boron doping technique is also a promising method for the simulation of the helium production effects in fusion reactors, utilizing a 10 B(n; ) 7 Li reaction under mixed spectrum irradiation of thermal and fast neutrons in fission reactors.…”

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

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