Fatigue Strength of Austenitic and Martensitic–Ferritic Steels for Nuclear Power Plants

We study the influence of boron-controlled media (12 g/liter H₃BO₃) with pH = 3 and 8 at temperatures of 293 and 353°K on the fatigue and cyclic crack resistance of 08Kh18N10T and 12Kh18N10T austenitic steels and 14Kh17N2 martensitic–ferritic steel. It is shown that 14Kh17N2 steel is characterized by the optimal combination of the long fatigue life with high cyclic crack resistance in inert and corrosive media at temperatures of 293 and 353°K, which gives it serious advantages over 08Kh18N10T and 12Kh18N10T austenitic steels.     

Investigation of structural conditions for improving the characteristics of strength, plasticity, and fracture toughness of maraging steels

The structural parameters governing the embrittlement and plasticizing of stainless (Kh12N10MT, Kh11N10M2T, and Kh13N9D2MT) and high-strength (N18M3T and N18K9M5T) maraging steels are analyzed; they are varied by thermal-kinetic conditions, the sequence and multiplicity of various heat-treatment processes such as austenitization, age hardening, and α↔γ-phase transformation in the subcritical temperature range. We justified both the individual and joint influence of austenite grain size and volume fraction of particles of intermediate phases on the regularities of variation and correlation of characteristics of strength, plasticity, and fracture toughness during thermal hardening. We revealed the role of the austenite which is formed during the α→γ-phase transformation in the increased deformability and fracture toughness of the steels under study, taking into account the character of their alloying. Based on the revealed shift in the temperature range of the α→γ-phase re-transformation toward the temperature range of age hardening, we determined the structural conditions for implementing its plastizicing effect on the high-strength state of the maraging steel. Timoshenko Institute of Mechanics, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 2, pp. 51–61, March–April, 2000.     

Cryogenic-alloy strength and cracking resistance under dynamic loading

Test results are given on 12Kh18N10T and 03Kh20N16AG6 steels and on AMg6 alloy designed to give the dynamic strength and cracking resistance at strain rates of 0.36 m/sec in the temperature range 77–293 K. Cooling raises the strength, plasticity, cracking resistance, and resistance to crack growth in AMg6 alloy. Cooling the two steels increases the strength and cracking resistance, but reduces the plasticity and crack propagation resistance. Compact specimens with small natural thicknesses can be used to determine the correct critical values for the cracking resistance J_Ic for 03Kh20N16AG6 steel and AMg6 alloy. It is possible to determine correctly the critical values for the cracking resistance for 12Kh18N10T steel at 77 K.Translated from Problemy Prochnosti, No. 9, pp. 48–53, September, 1992.     

Specific features of the deformation of steels in hydrogen

We have studied the effect of hydrogen on the mechanical properties of foils made of 08Kh18N12T steel under uniaxial tension. The initial stages of deformation in hydrogen require forces smaller by a factor of 3–5. In the case of biaxial tension of membranes made of this steel, their deformation ability also increases. The effect of hydrogen on the axial residual stresses of the first kind in 08Kh18N12T, 40Kh, and ShKh15 steels manifests itself in the activation of tensile deformation (inducing of compressive stresses). We have recorded a 30% increase in the fatigue limit of an austenitic alloy in hydrogen with a pressure of 30 MPa (the reference medium is air). __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 4, pp. 84–88, July–August, 2008.     

Formation of strain-induced martensite in chromium–nickel steels of the austenitic class

We investigate the formation of the first portions of strain-induced martensite in plastic uniaxial compression of 12Kh18N10T and 12Kh18N9T steels in which δ-ferrite is absent and present, respectively, in the initial state. The true deformation martensitic points ε _s are experimentally determined. It is established that, in 12Kh18N10T steel, there exist one-phase (A) and two-phase (A + M) states for ε < ε _s and ε > ε _s , respectively, whereas, in 12Kh18N9T steel, there exist two-phase (A + F) and three-phase (A + F + M) states for ε < ε _s and ε > ε _s , respectively. The effect of increase in the magnetization of paramagnetic austenite before the formation of strain-induced martensite is detected.     

Autoclave Studies of the Durability of Specimens Simulating Pipe–Collector Joints in Steam Generators of Nuclear Power Plants

We performed studies of welded-pressed (by explosion) joints of pipes made of 08Kh18N10T and 08Kh14MF steels with nozzles made of 10GN2MFA steel in order to simulate the operation of PGV-1000 steam generators. We established that the fatigue limit based on 1·10⁵ cycles is greater for the joints of pipes made of 08Kh14MF steel in tests in air. On the autoclave tests in reactor boron-treated water in the primary contour of a nuclear power plant at a temperature of 350°C, the endurance of the joints of pipes made of 08Kh14MF steel was 39% less that that for the joints made of 08Kh18N10T steel. All specimens failed at the lower ends of joints that were in the water phase of the working medium rather than in the steam one, which corresponds to the service conditions of the output cold collector of a steam generator. We concluded that cracks are initiated due to fretting corrosion and grow by the mechanism of corrosion-cyclic cracking of the steels of pipes.     

Structure and properties of a chromium diffusion coating on the inner surface of 08Kh13G14N4 steel pipes

The processes of diffusion saturation of the surfaces of 08Kh13G14N4 steel pipes with chromium from Li-Cr and Li-Cr₂O₃ melts were studied. It was established that, at high temperatures, the corrosion resistance of 08Kh13G14N4 steel with a chromium coating in liquid lithium depends mainly on the surface chromium concentration.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 5, pp. 41–45, September–October, 1993.     

The use of acoustic methods to investigate the dynamics of recrystallization and phase transitions in Armco iron and structural steel

This paper is devoted to development of acoustic methods for the investigation of the dynamics of structural changes in iron-based alloys, which are associated with phase transitions, processes of recrystallization and relaxation, and physical stimulation of various types. Samples of Armco iron are used to obtain the temperature dependences of the velocity and attenuation of ultrasound in the range from 20 to 1040 °C. The acoustic properties of 08Kh14AN4MDB high-strength corrosion-resistant martensitic steel are measured in the same temperature range. The obtained data on the propagation velocity of sound are used to calculate the values of the elastic modulus of Armco iron and 08Kh14AN4MDB steel in the range from 20 to 950 °C.Translated from Teplofizika Vysokikh Temperatur, Vol. 42, No. 6, 2004, pp. 873–877.Original Russian Text Copyright © 2004 by V. V. Roshchupkin, M. M. Lyakhovitskii, N. A. Minina, M. A. Pokrasin, I. A. Afanasev, N. L. Sobol, and A. I. Chernov.     

Corrosion cracking of chemical and petrochemical equipment

For technological facilities used in chemical and petrochemical industries, we present certain examples of the process of corrosion cracking of copper-lined apparatus and the equipment, manufactured from carbon and stainless steels of the 08Kh18N10T and 10Kh17N13M2T types and bimetals (20 steel+12Kh18N10T steel, 20 steel+10Kh17N13M2T steel). The peculiarities of their behavior under corrosion cracking are studied, and the danger of this phenomenon is discussed. Severodonetsk Research Institute of Chemical Machine-Building (NII Khimmash), Severodonetsk. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 1, pp. 83–94, January–February, 1999.     

Effect of aqueous media on the cyclic cracking resistance of steels at 300°C

We investigate the influence of reactor water (of the boron control system) on the fatigue crack growth rates in 15Kh2NMFA and 08Kh18N10T steels at 300°C. Corrosion-fatigue cracking is found to be typical of 15Kh2NMFA steel. The kinetics of the potentials of newly formed steel surfaces in high-temperature reactor water is studied. A phenomenological model that describes the influence of high-temperature aqueous media on the fatigue crack growth rates in steels is developed on the basis of data of corrosion-mechanical and electrochemical investigations. The results obtained by this model are in good agreement with experimental data.Karpenko Physicomechanical Institute, Ukrainian Academy of Science, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 1, pp. 34–42, January–February, 1994.     

Influence of electrolytic hydrogenation on cyclic crack resistance of chromium-nickel steels

Within the framework of linear fracture mechanics, we estimate the resistance of chromium-nickel 06Kh17N13M3, 07Kh16N6, and 10Kh26N5M steels to hydrogen embrittlement after various thermal treatments. We established that electrolytic hydrogenation leads to a considerable increase in the growth rate of fatigue cracks in steels with maximum in a low-amplitude range (by approximately a factor of 5–25 as compared with tests in air). The optimal mode of thermal treatment of 10Kh26N5M steel corresponds to quenching at 1293 K and annealing at 623 K. This mode ensures high plastic characteristics and maximum resistance to fatigue fracture in air in the course of electrolytic saturation with hydrogen, and long-term holding in a chloride-containing environment. We recommend this steel for the manufacture of critical parts of oil separators of marine ships. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 4, pp. 63–67, July–August, 1999.     

Lattice changes in the martensitic phase due to ageing in 18 wt% nickel maraging steel grade 350

Changes in the lattice parameter of martensite phase in a maraging steel is measured as a function of ageing temperatures. A decrease in the lattice parameter is observed when aged between 400–650°C which is attributed to the depletion of alloying elements in the martensite matrix as a consequence of precipitation and austenite formation. An increase in the lattice from 650 to 710°C was characteristic of enrichment of alloying elements in the martensite matrix due to dissolution of austenite phase. A minimum value of the lattice parameter of martensite is observed at 650 °C which coincides with the maximum vol % of retained austenite. Electrical resistivity, hardness measurements, andin situ high temperature dilatometry was also carried out to delineate various precipitation reactions that occur in this steel.[/p]     

Crack resistance of chromium-nickel steels with impact loading under cryogenic temperature conditions

Results are presented for an experimental study of the effect of cooling to 77 K on resistance to crack development of chromium-nickel steels 12Kh18N10T and 03Kh20N16AG6 with impact loading. The crack resistance characteristics with a rate of crack growth of 1.5 m/sec were determined from the deformation diagram recorded during testing. Features are noted for crack advance with cooling under conditions of a dynamically applied load.Translated from Problemy Prochnosti, No. 7, pp. 26–29, July, 1992.     

Effect of laser microalloying with niobium on the wear resistance of stainless steels

We have studied the effect of laser alloying of 20Kh13 and 12Kh18N10T steels with niobium on their physicochemical properties. Microalloyed surface layers of thickness more than 350 μm, enriched with niobium, carbon, and oxygen in the solid solution and separate oxycarbide inclusions, were formed by means of laser treatment. The microhardness of the external layers of steels becomes 2–3 times higher (up to 7.1–7.7 GPa). Laser alloying reduces the wear of 20Kh13 steel by a factor of 5–6 under a contact pressure of 0.29 MPa and cuts it in half under 0.42 MPa. The wear of 12Kh18N10T steel is reduced by a factor of 2–3. We have also proposed a scheme of the wear of steels, according to which their wear resistance increases owing to the formation of hardened surface layers, where the oxycarbide inclusions exert a reinforcing action on the more plastic solid solution of niobium, carbon, and oxygen in iron.     

Corrosion failure of 1Kh18N9T [1Cr18Ni9Ti] steel in liquid lithium

This article describes corrosion and mechanical tests on 1Kh18N9T[lCrl8Ni9Ti] steel specimens previously held in molten lithium (of various degrees of purity) at 700, 800, and 900° C both under isothermal conditions and in the presence of concentration- and heat-induced mass transfer. The results of gravimetric, spectrographic, and metallographic analyses showed that the corrosive action of lithium on the steel studied takes the form of dissolution of steel constituents and intergranular penetration of the steel by molten lithium. The role of nitrogen and oxygen in the corrosion process was estimated and it was established that even weak currents of liquid lithium intensify its corrosive action on 1Kh18N9T steel.     

Effect of cooling to 4.2 K on the strength and cracking resistance of the parent metal in welded joints in 07Kh13N4AG20 steel

The results are presented of experimental examination of short-term strength and cracking resistance of the parent metal and welded joints in 07Kh13N4AG20 steel in the temperature range 293–4.2 K. The mechanical characteristics of the welded joint in the examined steel are compared with the characteristics of 12Kh18N10T and 03Kh20N16AG6 steels. The results show that the mechanical properties and crack propagation resistance of the weld metal in 07Kh13N4AG20 steel are similar to those of the parent metal.Translated from Problemy Prochnosti, No. 9, pp. 45–48, September, 1990.     

Strength and crack resistance of chromium-nickel-manganese 03Kh19AG3N10 steel in the temperature range 293–4.2 K

We present the results of the experimental investigation of the characteristics of strength and crack resistance of chromium-nickel-manganese 03Kh19AG3N10 steel in the temperature range 293–4.2 K under static (in the initial state and under the action of pulses of electric current) and dynamic loads. We consider some distinctive features of the process of the discontinuous yield of steel at a temperature of 4.2 K and its influence on the kinetics of fracture processes. The comparative analysis of temperature dependences of the characteristics of strength, plasticity, and crack resistance of 03Kh20N16AG6, 03Kh20N16AG6Sh, and 07Kh13N4AG20 steels extensively used in cryogenic engineering and 03Kh19AG3N10 steel demonstrates that 03Kh19AG3N10 steel can be used in the temperature range 293–4.2 K. Translated from Problemy Prochnosti, No. 3, pp. 90–95, May–June, 1997.