Low-cycle fatigue of welded joints of 08Kh18N10T steel

We present systematized experimental data on low-cycle fatigue strength at 20 and 350°C for 08Kh18N10T steel and its welds, made by manual electric arc welding with EA-400/10U electrodes and argon-arc welding with a nonconsumable electrode and using Sv-04Kh19N11M3 filler wire. The data obtained are compared with the “Standards for Strength Analysis” PNAé G-7-002-86. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 1, pp. 104–109, January–February, 2007.     

Influence of weld parameters on the mechanical properties of spot-welded Fe-Mn-Al-Cr alloy

The static weld strength, hardness and microstructure evolution of a Fe-Mn-Al-Cr alloy during spot welding were investigated. A nugget can be formed for weld times as low as 5 cycles at 60 Hz (83 ms). The nugget growth rate is different between the front and the rear of the acceptable weld region. In the acceptable weld region, the tensile-shear strength ranges from 3038 to 3626 N, and the cross-tension strength varies from 2356 to 3136 N. The static weld strength strongly depends on the nugget size, and the dependence of the static weld strength on the electrode force is affected by the weld time and weld current. Evolution of spot-welded nuggets indicates that the hardness in the nuggets is, on average, about 100 H _V higher than that in the base unwelded metal, which is attributed to a cooling effect after welding.     

Pollution of the Heat Carrier and Its Influence on the Service Life of Power-Generating Units of Nuclear Power Plants

We present the data of autoclave testing of 10GN2MFA and 08Kh18N10T steels for cyclic crack-growth resistance in reactor borated water at a temperature of 300°C. We tested standard 25-mm-thick specimens for two values of the load ratio equal to 0.2 and 0.7. The loading frequency of specimens in the autoclave did not exceed 0.0167 Hz. We propose a model and a procedure of numerical evaluation of the increments of crack length according to the mechanisms of corrosion-fatigue and static corrosion cracking under the conditions of their combined action based on the analysis of principal characteristics of structural materials. Unlike the method based on the use of the Paris equation proposed by foreign standards, the method developed in the present work is more general and informative. Moreover, it includes the method used in standard specifications as a special case and enables one to explain the premature fracture of collectors of steam generators at the South-Ukrainian Nuclear Power Plant and other elements of power-generating units of the nuclear power plants. It is shown that, in the absence of corrosion-fatigue cracking, power-generating units of nuclear power plants can operate without emergency shutdowns for the entire service life. In the case where the heat carrier is polluted to a level sufficient for the initiation of the mechanism of static corrosion cracking, the service life of units to the time where the crack attains its critical size sharply decreases. We propose to improve the systems of water supply and perform continuous monitoring of the controlled parameters of the heat carrier and, in particular, of the contents of admixtures promoting the static corrosion cracking of steels.     

Corrosion of composite welded joints

The process of corrosion of composite welded joints of 20 steel and 08Kh18N9T stainless steel produced by manual argon-arc welding is investigated by electrochemical methods. It is shown that a contact galvanic couple is formed in the zone of the welded joint and, as a result, the surface of 20 steel in the vicinity of the weld turns into the anode and intensely corrodes. For this reason, composite welded joints should not be used in heart-power engineering. Odessa State Academy of Food Technologies, Odessa. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 6. pp. 33–36, November–December, 1996.     

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.     

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.     

Experimental study of variation of 08Kh18N12T steel properties in the npp main circulating pipeline during its operation

We present results of experimental studies of crack growth resistance characteristics and hardness of 08Kh18N12Tsteel specimens in the initial condition and after 100 thousand hours of operation in NPP main circulating pipeline.     

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.     

Evaluation of the resistance of corrosion-proof steels to corrosion cracking in hydrogen sulfide solutions

We study the tendency of corrosion-proof steels of the martensitic, martensite-ferritic, austenitic, austenite-martensitic, and ferrite-austenitic classes to corrosion cracking in hydrogen-sulfide-containing media. We have established that austenitic chromium-nickel-molybdenum (08Kh17N15M13T and 10Kh17N13M2T) and ferrite-austenitic (12Kh21N5T and 02Kh22N6AM3 steels are the most resistant to fracture: the threshold stresses in NACE solution (5% NaCl solution + 0.5% CH₃ COOH saturated with H₂S, 20±2°C, pH ∼ 3) are not less than 90% of the yield point. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 6, pp. 103–107, November–December, 2005.     

Strength and ductility of welded joints working in contact with liquid lithium

Results of short- and long-time tensile tests on welded steel 1Kh18N10T and 2Kh13 specimens in liquid lithium are reported, and the effect of molten lithium on welded joints in relation to the gaseous impurity content in the weld is analyzed.     

Evaluation of the electrode potential near the weld in NaCl solutions

We estimate the influence of residual stresses induced by a weld on the electrode potential in elements of welded structures. For half planes welded by a base weld, the distribution of stresses is specified by the corresponding relation of the Nikolaev-Trochun approach. It is shown that, in the accepted scheme, the 12Kh1MF and Kh18N10T steels play the roles of anode and cathode, respectively. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 5, pp. 35–40, September–October, 2006.     

Serviceability of nickel alloys and some types of steel in hydrogen-sulfide-containing media

We analyze the sensitivity of 36NKhTYu, 36NKhTYuM5, 40NKKhTYuMD, and 75NKhTYuB nickel alloys and 17G1S and 08Kh17N15M3T steels to the action of hydrogen sulfide according to the criteria of threshold stressesK _Iscc by the method of tension with low strain rates. We study the electrochemical characteristics of the indicated materials and show that 75NKhTYuB and 36NKhTYu alloys are unsuitable for application in the oil and gas industry. The parameters of 40NKKhTYuMD alloy and 17G1S steel must be improved. The best operating characteristics are exhibited by 36NKhTYuM5 alloy and 08Kh17N15M3T steel (produced by the “Dneprospetsstal” plant). These metals can guarantee the required level of serviceability of equipment used in the oil and gas industry and operating in contact with hydrogen-sulfide-containing media. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 3, pp. 102–108, May–June, 1997.     

Effect of the Specimen Geometry on Strength and Plasticity Characteristics of Steels on Subzero Cooling

We present the results of investigations into the deformability and strength of conical and tubular specimens of 03Kh20N16ÀG6 and 12Kh18N10Ò steels in uniaxial tension over a temperature range of 293–4.2 K. It is demonstrated that the deformability of the above steels is related to the geometry of the test object, whereas the character of this relation is determined by the test temperature and class of steel. At a temperature of 4.2 K, a qualitative change in the deformation mechanisms occurs, as a result of which the influence of the design factors changes significantly. A drop in the plasticity for both types of the specimens and a considerable hardening of the 03Kh20N16ÀG6 steel thin-walled tubular specimens are noted.     

Electrochemical behavior of 15Kh2NMFA steel in borate-buffered reactor water at temperatures of 22–300°C under equilibrium pressures

We study the corrosion-electrochemical behavior of 15Kh2NMFA steel in borate-buffered reactor water within the temperature range 22–300°C and establish the relationship between the temperature dependences of the corrosion-fatigue crack growth rates and the electrochemical behavior of steel. The influence of the galvanic couple formed by the refreshed and passivated surfaces on the acceleration of growth of corrosion-fatigue cracks is revealed. It is shown that this type of steel is susceptible to passivation in the entire temperature range.     

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.     

Effect of Hydrogen on the Mechanical Properties of Welded Joints of 03Kh12N10MT Steel and KhN55MBYu Alloy

We have studied the hydrogen degradation of welded joints of 03Kh12N10MT steel and KhN55MBYu alloy, used in the aerospace industry. We have established that the highest level of strength, plasticity, and low-cycle durability in gaseous hydrogen under a pressure of 35 MPa is provided by argon-arc welding for joining homogeneous materials and by electron-beam welding for dissimilar materials.__________Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 6, pp. 55–61, November–December, 2004.     

Fatigue fracture resistance of metals at different temperatures

At temperatures within the range 0.06–0.6T _m (°K), we study the process of fatigue fracture of M1 copper, L63 brass, V95pchT2 aluminum alloy, and 40Kh, 20Kh13, 14Kh17N2, 08kp, 08ps, and 07GSYuFT steels subjected to preliminary deformation (5–30%) at room temperature. It is shown that the effect of preliminary deformation of metals and alloys on their fatigue fracture resistance becomes more intense as testing temperature increases and significantly depends on the amplitude of loading. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv; Nizhni Novgorod State Technical University, Nizhni Novgorod, Russia. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 1, pp. 75–82, January–February, 1997.     

Empfehlungen zur Werkstoffauswahl und zu den Schweißdaten für NH3-Lagerbehälter und NH3-Kesselwagen

Recommendations for Selection of Material and welding Electrodes for NH₃-storage Vessel and NH₃-Transport Container In liquid ammonia mostly only weld seams show cracks. Extensive SEM-investigations have shown that these are hydrogen induced cracks. During weld tests with the base materials St E 335 and St E 460 in different charges high yield strengths were determined in the weld material. Very often the yield strength values increase after stress relieving. This is caused by precipitation, which leads to a bracing of the lattice, thus raising the yield point. To ensure one of the base material adapted yield strength in the weld it is only possible in very rare cases with suitable weld additives. In the St E 460 with nitrogen and vanadium the yield strength value in the weld is even by use of the wire S 1 and neutral powder over 600 N/mm². It was found out that hydrogen induced cracks in the weld above 550 N/mm² yield strength occur very likely below 550 N/mm² occur very little. In the base material St E 355 the yield strength was limited for this reason in the weld with 500 N/mm² in the base material St E 460 limited with 550 N/mm². Proof has to be furnished for all welding procedures, sheet charges and weld additives applicable by means of welding probes.     

Structural strength of steels of the austenitic and transition classes at low temperatures

The article investigates the structural strength of the metastable austenitic steel 03Kh16N9M2 and of the steel of the transition class (martensite + residual austenite) 05Kh14N5DM in the temperature range from 293 to 77°K for the purpose of determining their suitability for large components in cryogenics. It is shown that for their characteristics of impact toughness and low-cycle fatigue steel 05Kh 14N5DM containing up to 15% residual austenite cannot be recommended as material of cryogenic structures operating at 77°K.Translated from Probiemy Procnnosti, No. 5, pp. 43–50, May, 1993.     

Effect of modification of the surface on the hydrogen permeability of reactor steels and their welded joints

We study the characteristics of hydrogen permeability of 10Kh9VFA and 12Kh18N10T reactor steels in the intact state and in the presence of welds and analyze the influence of oxidation and irradiation with protons on these characteristics. It is shown that the proton irradiation increases the thermal stability and the degree of protection against the penetration of hydrogen into the oxidized specimens. To determine the contribution of the welds to the solubility of hydrogen, we apply, for the first time, a combined approach, namely, the diffusion coefficient of hydrogen in the weld is found according to the changes in the electric resistance in the process of hydrogenation and the hydrogen permeability of the welded joint is determined from the ratio of the areas of the base metal and the weld. It is shown that the oxide films with structures of chromium spinel formed on the surface of steels decrease their hydrogen permeability by 1.5–2 orders of magnitude.