9Cr-1Mo Ferritic Steel Research Articles

電子論によるCr-Moフェライト鋼の相安定性予測

電子論によるCr-Moフェライト鋼の相安定性予測

Corrosion of Standard and Modified 9Cr-1Mo Ferritic Steels in High Temperature Water Containing Acid Sulphate-Chloride

The corrosion behaviour of standard and modified 9Cr–1 Mo ferritic steel tube containing artificial defects (holes formed by spark erosion and drilling) has been investigated under realistic steam generator conditions (334°C, heat flux 860 kW m−2) with acid sulphate-chloride fault water chemistry. Corrosion of the tube was found to be independent of steel type, the presence of heat flux, or acid sulphate-chloride water chemistry. Wide variations were seen in the rate of magnetite deposition in heat flux and non-heat flux regions of the tube. These are attributed to the presence of a thin oxide film on the outer surface of the tube which retards the escape of corrosion hydrogen and reduces the rate of magnetite deposition. Two types of corrosion were observed in defects: accelerated general corrosion to depths of 54μm– ascribed to acid sulphate attack, and intergranular attack (IGA) to depths of ∼80 μm–independent of steel type or the presence of a sensitised structure. Under these test conditions, there appears to be a threshold stress of ∼150 MNm−2 above which stress assisted IGA can occur in sensitised 9Cr–1 Mo steels.

Observation of oscillating reaction rates during the isothermal oxidation of ferritic steels

Oscillating reaction rates have been observed in the steam oxidation of 21/4Cr-1MoNb and 9Cr-1Mo ferritic steels at 500–550°C. Changes in reaction rate are associated with the formation of a laminated, inner-oxide layer, made up of bands of fine and coarse-grain spinel oxide. The lowest reaction rates occur during growth of the fine-grain oxide. Coarse-grain oxide generally contains the same levels of Cr, Mo, and Si as the steel (after allowing for loss of Fe to the outer layer), while the fine-grain material contains three times these levels. Ni builds up in the metal and is present in the oxide as metallic particles (mostly associated with fine-grain oxide). A mechanism is proposed in which the highest reaction rates are controlled by diffusion of Fe ions through the oxide layer (as in normal parabolic oxidation) and the lowest rates by diffusion of Fe through the Ni-rich layer in the metal.

X-ray photoelectron spectroscopic studies of the effect of laser irradiation on the oxidation behaviour of modified 9Cr-1Mo ferritic steel

Modified 9Cr-1Mo ferritic steel has a wide range of special applications, due to its high strength and oxidation resistance behavior. Recently laser irradiation has been found to improve significantly its air oxidation resistance at temperatures above 700 o C. Detailed surface characterization by X-ray photoelectron (XPS) and Auger electron (AES) spectroscopy of the oxidation films has now been undertaken with a view to acquiring an understanding of this phenomenon

Helium effects on the microstructural evolution of reactor irradiated ferritic and austenitic steels

Abstract Microstructural evolution in neutron irradiated austenitic stainless steels and Cr-Mo ferritic steels is reviewed. Important highlights are: (1) there is a strong correlation between precipitation and void evolution in austenitic steels; (2) helium affects precipitate evolution in austenitic steels, but observations indicate no effect on precipitation in ferritic steels; (3) helium has a pronounced effect on the cavity evolution of the two steel types. Helium effects are explained in terms of the interrelationship between microstructural evolution and point-defect annihilation processes. In stainless steel, three relative regimes of microstructural behavior for different helium generation rate-displacement rate ratios are recognized: (1) “low” He/dpa ratio, where helium effects on the radiation-induced microstructural evolution are negligible or develop slowly, (2) “medium” He/dpa ratio, where helium effects strongly enhance the microstructural changes, and (3) “high” He/dpa ratio, where helium e...

The high temperature aqueous corrosion of ferritic steels: Effect of heat flux on corrosion and magnetite deposition

A length of 9Cr-1Mo ferritic steel tube has been exposed to a wide range of heat fluxes (0–1389 kW m −2) under realistic steam generator conditions (355°C, 17.6 MPa, subcooled boiling to 15% steam quality) for 3906 h. Deposition of magnetite on to the tube surface was found at first to increase rapidly with heat flux. At higher heat fluxes the rate of increase slowed down and a maximum was attained at ∼ 1200 kW m −2. The results can be understood in terms of concentration and dryout processes beneath growing steam bubbles. The rate of corrosion was found to be inversely proportional to the deposited oxide thickness and thus consistent with a reaction controlled by diffusion of water molecules through the deposited oxide layer. Particles of metallic iron, observed in the middle oxide layer at high heat fluxes, are thought to be a consequence of the limited diffusion routes for H 2O through the outer layer and the formation of hydrogen within the oxide.

Potentiodynamic studies of modified 9Cr-1Mo ferritic steel in sulphuric acid and seawater

The potentiodynamic behaviour of annealed and cold worked 9Cr-1Mo, modified with V0.198 wt% and Nb 0.072 wt%, ferritic steel has been studied in H 2SO 4 in the concentration range 0.1–5 N at a scan rate of 45 mV min −1 at 25°C. E corr becomes more noble while the other electrochemical parameters, i.c. i corr, i crit, i p and E cp for both states of the modified steel decrease with the increase in acid concentration. This trend was more marked in the annealed than in the cold worked alloy. This alloy shows a higher corrosion resistance in IN H 2SO 4 than pure 9Cr-1Mo steel. Slight passivation at higher potential in both cold worked and annealed modified 9Cr-1Mo was observed in seawater whereas no passivation was indicated in the case of annealed pure 9Cr-1Mo steel under the same experimental condition. The different corrosion behaviour has been explained as a result of microstructural differences.

An assessment of carburization-decarburizatton behaviour of Fe-9Cr-Mo steels in a sodium environment

A critical assessment is made of the carburization-decarburization kinetics of Fe-9Cr-Mo steels exposed to a sodium environment, using the available information on carbide phase morphology, chromium activity in a ferrite matrix, chromium carbide activity in mixed carbides, carbon solubility in Cr-Mo ferritic steels, and activity-concentration relationships based on α-phase/M 6C or M 23C 6carbide equilibrium. Experimental data are presented on the decarburization of Fe-5Cr-Mo and Fe-9Cr-Mo steels at 973 K in a sodium environment to ascertain the long-term behaviour of these steels. The analysis shows that the decarburization of ferritic steels is largely dependent on the chemical reaction at the carbide/α interface and that at carbon activities <0.04, the rate is predominantly determined by the dissolution of (Fe, Mo) 6C carbides.

The Stress Corrosion Cracking of 2¼ Cr–Mo Ferritic Steel in Caustic Environments

Stress corrosion studies in caustic environments have been carried out on the ferritic 2 1/4 Cr–Mo steel, with particular reference to its use in the evaporators of the U.K. prototype fast reactor....

Carbon and nitrogen transfer in Fe-9 Cr-Mo ferritic steels exposed to a sodium environment

Kinetics of carburization/decarburization of five commercial and two high-purity Fe-9 Cr-1 to 2.5 Mo feiritic steels have been studied in a sodium environment at temperatures between 773 and 973 K. Carbon concentration-distance profiles were obtained as a function of sodium-exposure time, temperature, and carbon in sodium and the carburization/ decarburization rate constants were evaluated. The results show that the Fe-9 Cr-Mo steels are more resistant to carbon transfer than the low-alloy Fe- 2 1 4 Cr-1 Mo steel. The conditions of temperature and carbon concentration in sodium for carburization or decarburization of Fe—9 Cr—Mo steels are quite similar to those for stainless steels. However, the extent of carbon transfer in Fe-9 Cr—Mo steels is lower than that of the stainless steels. The composition and carbide structure of the steel had a significant effect on the carburization/decarburization behavior. Fe-9 Cr-Mo steels that decarburize to very low carbon concentrations either contain M 2X phase or have M 6C as the only stable carbide.