Resistivity ferrites

Soft magnetic ferrites are oxides and they are electrical insulators. Because of their exceptionally higher resistivities, ferrites are particularly suitable for high frequency applications, of about 100.000 cycles 110 kHz). 

Hal] Hald, J., Korcakova, L., Precipitate Stabihty in Creep Resistant Ferritic Steels -Experimental Investigation and Modelling , ISIJInt., 43, 420-427 (2003) (Phase Relations, Experimental, Calculation, 22)... 

The rotor was constructed by welding several forgings of heat-resistant ferritic material and was provided with longitudinal grooves for attaching the blading. The turbine was equipped with two blade rows, each consisting of 84 rotor blades and 90 stationary blades, while the... 

Fe—Cr. The Fe—Cr phase diagram. Fig. 3.1-106, is the prototype of the case of an iron-based system with an a-phase stabilizing component. Chromium is the most important alloying element of corrosion resistant, ferritic stainless steels and ferritic heat-resistant steels. If a-Fe—Cr alloys are quenched from above 1105 K and subsequently annealed, they decompose according to a metastable miscibility gap shown in Fig. 3.1-107. This decomposition reaction can cause severe embrittlement which is called 475 C-embrittlement in ferritic chromium steels. Embrittlement can also occur upon formation of the a phase. 

Besides heat-treatment, the nickel content of the alloy also affects SCC behavior. Fig. 1-18 (eopson, 1959). erNi steels containing 10% nickel have the greatest susceptibility to see in boiling Mgei2 solution. With increasing nickel content See susceptibility is reduced and nickel-based alloys are resistant. Ferritic nickel-free stainless chromium steels are also highly resistant. 

Regarding the austenitic steels as materials of core stmctures of post-generation HI nuclear systems, these materials are mainly met in the core of SFR or LFR reactors and as prime candidate materials of the first wall of fusion reactors. In SFR cores, austenitic steels are principally used as reference materials of fuel pins because, for wrappers operating at lower temperature, high swelling-resistant ferritic-martensitic (F-M) materials are now preferred. Nevertheless, it should be noted that austenitic steels have been extensively used in the past as first candidate materials of SFR wrappers too. The other core materials described in this book are the following ... 

Irradiation-resistant ferritic and martensitic steels as core materials for Generation IV nuclear reactors... 

BE-7500 A novel creep resistant tin strengthened 9 12 CR ferritic steel for advanced steam Dower olant. Mr.G. Shrimpton AEA Technology... 

Spinel ferrites, isostmctural with the mineral spinel [1302-67-6] MgAl204, combine interesting soft magnetic properties with a relatively high electrical resistivity. The latter permits low eddy current losses in a-c appHcations, and based on this feature spinel ferrites have largely replaced the iron-based core materials in the r-f range. The main representatives are MnZn-ferrites (frequencies up to about 1 MH2) and NiZn-ferrites (frequencies 1 MHz). 

Ferritic stainless steels depend on chromium for high temperature corrosion resistance. A Cr202 scale may form on an alloy above 600°C when the chromium content is ca 13 wt % (36,37). This scale has excellent protective properties and occurs iu the form of a very thin layer containing up to 2 wt % iron. At chromium contents above 19 wt % the metal loss owiag to oxidation at 950°C is quite small. Such alloys also are quite resistant to attack by water vapor at 600°C (38). Isothermal oxidation resistance for some ferritic stainless steels has been reported after 10,000 h at 815°C (39). Grades 410 and 430, with 11.5—13.5 wt % Cr and 14—18 wt % Cr, respectively, behaved significandy better than type 409 which has a chromium content of 11 wt %. 

Nickel—Iron. A large amount of nickel is used in alloy and stainless steels and in cast irons. Nickel is added to ferritic alloy steels to increase the hardenabihty and to modify ferrite and cementite properties and morphologies, and thus to improve the strength, toughness, and ductihty of the steel. In austenitic stainless steels, the nickel content is 7—35 wt %. Its primary roles are to stabilize the ductile austenite stmcture and to provide, in conjunction with chromium, good corrosion resistance. Nickel is added to cast irons to improve strength and toughness. 

Duplex stainless steels (ca 4% nickel, 23% chrome) have been identified as having potential appHcation to nitric acid service (75). Because they have a lower nickel and higher chromium content than typical austenitic steels, they provide the ductabdity of austenitic SS and the stress—corrosion cracking resistance of ferritic SS. The higher strength and corrosion resistance of duplex steel offer potential cost advantages as a material of constmction for absorption columns (see CORROSION AND CORROSION CONTROL). 

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