ISSN:0267-0836    

DOI:10.1179/mst.1990.6.3.209

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractCastings to the ASME SA351 CF3 specification used in modern pressurised water reactor nuclear power stations are mainly austenitic, but contain up to 20% ferrite, and as a result are subject to loss of toughness in service at about 300°C. To show adequate end of life toughness, tests are being carried out on material with accelerated aging above 300°C. Data on the kinetics of embrittlement are required, and it must also be shown that the significant metallurgical changes are the same at both temperatures. The kinetics has been investigated using Charpy impact specimens aged at 300, 350, and 400°C and it has been related to the hardening of the ferrite and to the microstructural changes in this phase. The activation energies determined for the embrittlement, for the hardening of the ferrite, and for the underlying spinodal reaction in the ferrite are consistent with that for chemical diffusion in this system.MST/1187

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.3.211

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe long term aging behaviour of a large number of Mo bearing and Mo free heats of cast duplex stainless steels has been studied between 300 and 450°C in terms of hardness and impact Charpy toughness. The results demonstrate the importance of the ferrite, Cr, and Mo contents in controlling aging response. Owing to the complexity of microstructural evolution and related changes in fracture mechanisms, the extrapolation of higher (i.e. 450 and sometimes 400°C) towards lower (i.e. service) temperature is not straightforward. Aging kinetics cannot be accounted for with a single activation energy Arrhenius plot; instead, a range of energies increasing with decreasing temperature must be considered. In the lower temperature range, this energy is of the order of 250 kJ mol−1, in agreement with the metallic element controlled mechanisms of microstructural evolution.MST/1186

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.3.221

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractAn investigation has been undertaken to determine the magnitude of any reduction in properties that may occur in cast duplex stainless steels and weldments during long term exposure to reactor operating conditions. Test panels were fabricated in CF3 stainless steel using a manual metal arc (MMA) process and 19.9.L consumables. The mechanical properties of the parent material and weldments were measured following accelerated aging at 375 and 400°C for up to 20 000 h. Following aging at temperatures up to 400°C, reductions in both the Charpy impact and J integral–crack growth resistance R (J–R) fracture toughness of CF3 cast austenitic steel and 19.9.L austenitic weld metal were observed. For conditions equivalent to the proposed end of life for UK pressurised water reactors, the J–R fracture toughness at 300°C of both cast steel and MMA weld metal was reduced by ~30% for crack extensions of≥1 mm. Hence, it is important that these reductions in weld metal toughness are taken into account during the development of safety cases and structural integrity assessments for any component in the primary loop that contains MMA stainless steel weldments.MST/1198

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.3.230

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractWelded duplex stainless steel castings are used widely in the pressurised water reactor primary coolant circuit at operational temperatures close to 300°C and design lifetimes of several hundred thousand hours. Under these conditions microstructural changes that affect the tensile and fracture properties are known to occur. Results are presented from aging studies over a range of temperatures from 300 to 425°C for durations up to 10000 h. Hardness, impact fracture, and microstructural data are given for weldmetal, heat affected zone (HAZ),and parent casting microstructures. Particular emphasis is placed on HAZ properties and the determination of the fracture mechanism in aged materials. Comparison is made of the activation energy associated with aging induced changes in hardness and impact fracture properties for parent casting and HAZ microstructures. The weldmetal was found to be highly resistant to the effects of aging, thus preventing any determination of activation energy.MST/1183

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.3.237

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractCast duplex stainless steels of CF3, CF8, and CF8M grades, containing a wide range of chemical composition and ferrite content, were aged in the laboratory at 270–450°C to evaluate the kinetics and mechanisms of thermal aging embrittlement. Also, CF8 and CF8A steels were obtained from components of boiling and pressurised water reactors after 12–22 years of service. After mechanical property (namely, Charpy impact, tensile, and J integral–crack growth resistance R curve) and microhardness tests, the aged specimens were examined using transmission electron microscopy and field ion atom probe techniques to identify the aging mechanisms and the critical factors that control the embrittlement kinetics. From the results of microstructural characterisation, the primary and secondary embrittlement mechanisms were identified. A mechanistic correlation was obtained between the microstructural characteristics and the activation energy of aging (namely, the temperature dependence of the aging kinetics) for steels with a range of chemical compositions and subjected to various fabrication and thermal treatment conditions. The unified correlation, based on spinodal decomposition influenced by G phase nucleation and growth in ferrite and M23C6precipitation on ferrite/ austenite boundaries, provides a good explanation of the complex behaviour of the activation energy (ranging from 75 to 230 kJ mol−1) regardless of grade, chemical composition, or fabrication process.MST/1204

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.3.249

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractThe thermodynamic predictions of microstructures in the multicomponent alloys used for duplex stainless steels are discussed in detail in this paper. The production of the duplex ferrite–austenite microstructure by high temperature (1323–1423 K) annealing is considered. Phase diagrams are calculated for Fe–Cr–Ni ternary alloys and the more complex multicomponent systems. It is shown that there is good agreement between the predictions of the thermodynamic models and the measurements carried out on heat treated alloys. The low temperature aging behaviour of Fe–Cr–Ni ternary alloys is discussed and the limitations of activation energy approaches to the modelling of the aging process in these alloys are shown.MST/1201

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.3.263

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractFinite difference methods giving approximate solutions to the Cahn–Hilliard equation for phase separation in binary alloys and the results of numerical experiments in two dimensional space are described. Nucleation and growth and spinodal decomposition are considered.MST/1199

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.3.273

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractAtom probe field ion microscopy, analytical electron microscopy, and optical microscopy have been used to investigate the changes that occur in the microstructure of cast CF8 and CF8M primary coolant pipe steels after long term thermal aging. These cast steels have a duplex microstructure consisting of austenite with approximately 15 vol. -% ferrite. In material aged at 300 or 400°C for up to 70 000 h, the ferrite had spinodally decomposed into a modulated fine scale interconnected network consisting of an iron rich a phase and a chromium enrichedα′phase with a periodicity of between 2 and 9 nm. Roughly spherical G phase precipitates 2 to 10 nm in diameter were also observed at concentrations of more than 1021m−3. The degradation in mechanical properties of these materials is a consequence of the spinodal decomposition and G phase precipitation in the ferrite.MST/1184

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.3.285

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor

摘要:

AbstractFe–Cr alloys and the ferritic phase of duplex stainless steels may undergo embrittlement during aging in the temperature range 300–500°C, owing to a spinodal reaction process. The atom probe at the University of Oxford. has been used to investigate the microstructural changes accompanying the spinodal in a low carbon, low molybdenum steel (ASME SA351 CF3) in the temperature range 300–400°C for aging times of up to 20 000 h. The amplitude and wavelength of the spinodal were determined. In addition, some other steels, which in previous studies by Trautwein and Gysel had exhibited an extremely low value of activation energy for embrittlement, were examined using both the atom probe and the position sensitive atom probe. Some of this material was re-heat treated to attempt to explain its anomalous behaviour. Steel from the primary cooling circuit of the Shippingport reactor was also examined and carbon and phosphorus were found to have segregated to a phase boundary.MST/1202

ISSN:0267-0836    

DOI:10.1179/mst.1990.6.3.293

出版商:Taylor&Francis    

年代:1990

数据来源: Taylor