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This paper describes a metallographic preparation of the heat-exchanger austenitic stainless steels, i.e., SUPER 304H, HR3C and Sanicro 25. The as-received materials delivered after the solution annealing are very resistant to the chemical etchants. Therefore, it is more efficient to optimize the parameters of the electrolytic etching in the acidic or basic electrolytes. After the materials’ operation under elevated temperatures (600–750 °C), the microstructure is easier to etch due to the reduction of corrosion resistance. For the following analyses, it is necessary to think of the etching purpose in advance. For the grain size determination, it is sufficient to use electrolytic etching in the oxalic acid solution or chemical swabbing in the combination of 15 ml HCl, 10 ml acetic acid and 5 ml HNO3. For the image analysis of the intermetallics, the previous methods can be too invasive and give skewed results. In many cases, this leads to the overetching and thus removal of the observed particles (intermetallics, carbides, etc.). It is suitable to use selective etching methods or only polishing for a more precise evaluation, e.g., electron microscopy.

Martensitic creep-resistant P92 steel was deformed by different methods of severe plastic deformation such as rotation swaging, high-pressure sliding, and high-pressure torsion at room temperature. These methods imposed significantly different equivalent plastic strains of about 1&ndash, 30. It was found that rotation swaging led to formation of heterogeneous microstructures with elongated grains where low-angle grain boundaries predominated. Other methods led to formation of ultrafine-grained (UFG) microstructures with high frequency of high-angle grain boundaries. Constant load tensile creep tests at 873 K and initial stresses in the range of 50 to 300 MPa revealed that the specimens processed by rotation swaging exhibited one order of magnitude lower minimum creep rate compared to standard P92 steel. By contrast, UFG P92 steel is significantly softer than standard P92 steel, but differences in their strengths decrease with increasing stress. Microstructural results suggest that creep behavior of P92 steel processed by severe plastic deformation is influenced by the frequency of high-angle grain boundaries and dynamic grain coarsening during creep.

The influence of the application of severe plastic deformation on microstructure changes and creep deformation behaviour was investigated in P92 creep-resistant pipe steel. P92 steel in its as-received state, with a microstructure typical of tempered martensite, was subjected to high-pressure torsion at room temperature. An investigation of the microstructure using an electron backscatter diffraction technique revealed that severe plastic deformation led to the subsequent formation of an ultrafine-grained microstructure, containing {110} fibre texture and randomly misoriented boundaries. The microstructure characteristics and hardness measurements exhibited saturated values at an equivalent strain of higher than about 20. The creep behaviour of the ultrafine-grained specimen produced in the saturated region exhibited a minimum creep rate that was about two orders of magnitude faster, and a larger creep ductility, in comparison with the as-received state. Creep exposure at 873 K with a time to fracture of about 3 h led to a slight grain coarsening and to the formation of Laves phase.

We have investigated the effect of prior short-term ageing on the mechanical and creep properties of tungsten and boron modified 9%Cr ferritic steel (ASTM Grade P92 steel), to provide material data base for the estimation of material degradation due to occurrence of accidental overheating in the early stage of service loading. The steel was aged at 650 °C for up to 100, 200, 500, 1000, 2000 and 5000 h prior to mechanical and creep testing. Changes in the microstructure during ageing had a slight effect on the reduction of room temperature tensile properties. A sudden decrease on impact properties occurred after ageing for 2000 h, but the occurred impact energy of about 70 J is in accordance with the specified minimum value of 68 J at room temperature for the virgin condition. The creep behaviour of P92 steel in the as-received condition and after different isothermal ageing exposures prior to creep was investigated at 600 and 650 °C in the power-law creep regime. The initial applied tensile stress ranged from 90 to 200 MPa. The results clearly show a detrimental influence of isothermal ageing on creep properties even after a few hundred hours. Based on microstructure analysis, which was done mostly in a qualitative way, a significant decrease in the creep life after ageing resulted from changes of the dislocation substructure and instability of Laves phase and M23C6 particles.

This work investigates creep and microstructure characteristics in P92 martensitic and 304L austenitic stainless steel after the imposing of large value of plastic strain. The as-received coarse-grained steels were strongly deformed at room temperature (RT) before tensile creep testing. The flat specimens were tested at 873 K and 923 K under different applied stresses. Microstructures were analysed by means of scanning electron microscope with EBSD (electron back-scatter diffraction) camera and transmission electron microscope. It was observed that application of severe plastic deformation (SPD) techniques at RT significantly reduces grain size and changes phase structure of 304L austenitic steel. The microstructure investigations revealed that the growth of new phases is enhanced in plastically deformed P92 martensitic and 304L austenitic stainless steels compared to their undeformed states. Creep results showed that the mean grain size of SPD-processed steels is still near ultrafine-grained region even after long-term creep testing and the coarsening of microstructure is predominantly influenced by creep time and strain.

The microstructure and creep behaviour of the welded joints of P92 steel pipe were investigated in order to determine the influence of orbital heat welding technology on the creep resistance. Creep specimens were machined from the welded joints. Tensile creep tests of welded joints were performed at 873 K using different stresses. The microstructure of tested specimens was investigated by scanning electron microscope Tescan equipped with an electron-back scatter diffraction. The creep results showed that the creep fracture strain of the welded joints decreases with decreasing value of applied stress. Microstructure investigation showed that fracture behaviour of welded joints is influenced by an enhanced cavity formation at grain boundaries in the heat-affected zone causing lower fracture ductility.

The problematic of pitting corrosion on blades of Kaplan turbine is discussed. Corrosion behaviour was observed during the first year of service. Material of the water turbine blades is martensitic stainless steel GX4CrNi13-4. Chemical composition and hardness of blades was measured, EDS analysis of corrosion products and microstructural evaluation on replicas were carried out. The main problem was found in heterogeneities in the cast microstructure and local disproportions in chemical composition. Influence of microbiologically induced corrosion and surface roughness is considered.

This article deals with the results of mechanical testing and structural analysis of sections of narrow gap orbital welded P91 steel on tube OD 355.6 x 40 mm. The evaluation of mechanical properties was based on tensile test at room temperature on mini-tensile specimens and on measurement of modulus of elasticity. Weld was cut longitudinally into 9 narrow slices by using waterjet. From these slices 108 flat mini-tensile specimens (dimensions of gauge is 2 x 2 mm) were prepared. In experimental part microstructure evaluation and documentation of fracture surface of each mini-tensile specimen were carried out. The aim of these experiments was to assess the mechanical properties of the individual sections of the weld (base metal, heat affected zone and weld metal). These data can be used for new approaches of FEM modelling of welds considering heat affected zone like a combination of different materials with different mechanical properties, which connect the thermally unaffected base metal and weld metal.

The creep behaviour of a welded joint of a real thick-walled P92 steel pipe was investigated at 600 and 650 °C and a stress ranging of 60–250 MPa using uniaxial tensile creep tests. Creep smooth cross-weld specimens were machined from different positions of the weld representing the welding sequence. Following analysis of creep data, all creep tests were performed in the region of power-law creep. The rate-controlling creep deformation mechanism is most probably climb of intergranular mobile dislocations for both the weld and base P92 steel. The creep resistance of the weld joint was lower than that of the base metal. No substantial differences were found in the minimum creep, the time to fracture and creep ductility for creep specimens taken from different locations of the weld. The fracture morphology of the crept welded specimens was found to be a mixture of transgranular ductile and intergranular mode. The fracture locations were found to shift from the weld metal in the higher stress region to the heat affected zone in the lower stress region. Many cavities formed at grain boundaries during creep. It was considered that the coarse precipitates of Laves phase acted as the preferential nucleation sites for cavities.

This paper deals with an evaluation of mechanical properties and microstructures of similar and dissimilar narrow gap orbital welds of martensitic steels P91 and P92 after long-term laboratory ageing at elevated temperatures (650, 675 and 700 °C, 5000 to 30 000 h). Conclusions of this assessment are the kinetic dependencies of structural and mechanical properties changes during long-term exposure to high temperatures.

The austenitic stainless steel 304 L was subjected to severe plastic deformation using high-pressure torsion technique at room temperature. The severe plastic deformation led not only to the grain size reduction but also to the transformation of austenite into deformation-induced martensite. At high imposed strains the martensitic boundaries disappeared and misorientation distribution exhibited nearly random misorientation distribution. The thermal exposure and tensile creep tests under constant load performed at 923 K and stresses ranging from 50 to 150 MPa revealed that austenitic microstructure contains σ phase. The ultrafine-grained microstructure coarsens during creep testing but the mean grain size is significantly finer than the predicted stationary subgrain. The results demonstrate that during creep testing new grains at precipitates of σ phase are formed and texture changes. The formation of new grains during creep keeps the microstructure of being ultrafine-grained and thus grain boundary mediated processes are enhanced in this steel.

In this work, the creep behaviour of an actual thick-walled P92 steel pipe bent (90°) using local induction heating was investigated at 600 and 650 °C using uniaxial tension creep tests. Creep specimens were machined from the bend at different positions, namely at the intrados and extrados areas and neutral position and from the straight part of the pipe. Creep tests were followed by metallographic and fractographic analyses of the crept specimens to explain the observed creep behaviour. In order to accelerate the microstructural changes and thus to simulate long-term service conditions, isothermal ageing at 650 °C for 10,000 h was applied to selected creep specimens before creep exposures. The results of the creep tests performed on specimens extracted from the intrados and extrados of the thick-walled bent P92 steel pipe fall into the scatter band of the base P92 steel average line. No substantial differences were found at different positions of the pipe in the minimum creep rate, the time to fracture and creep fracture strain. However, significant detrimental effects on the creep resistance of the pipe were found after long-term static thermal ageing due to the microstructural instability of the material. The large Laves phase particles, which coarsened during ageing and creep testing, served as preferential sites for cavity nucleation leading to an accelerated tertiary stage of creep and/or premature creep fracture. Activation analysis of the creep data leads to the conclusions, that the creep tests were undertaken in the region of the power-law creep regime and the rate controlling creep deformation mechanism is most probably the climb of the intragranular dislocations.

The microstructure of P92 steel pipe processed by hot bending was evaluated in order to characterize the influence of hot bending on microstructure changes in extrados and intrados of bend. The straight pipes, with an outer diameter 350 mm and wall thickness of 39 mm (Productos Tubulares, s.a.u. Spain), were normalized at 1050°C/60min/air and tempered at 740°C/140min/air.The thick-walled P92 pipe was hot bended at 920-960 °C using bending rate 7 mm/min. The bends were normalized at 1050°C/60min/air and tempered at 775°C/140min/air after hot bending. The selected specimens, machined from different locations of pipe, were additionally thermal ageing at 650 °C to simulate microstructure degradation typical for long-term service conditions.Microstructure was investigated by scanning electron microscope Tescan Lyra 3 equipped with NordlysNano EBSD detector operating at an accelerating voltage of 20 kV with specimen tilted at 70° and by transmission el. microscope JEM-2100F.Microstructure investigation revealed that different processing history influenced distribution and size of secondary phases and caused changes in interboundary spacing in straight pipe and bends. It was found that microstructure changes induced during hot bending and subsequent post-bending heat treatment caused deterioration in creep properties of bends in comparison with those of straight pipe.

Thermally loaded assemblies in the energy and chemical industries require materials that provide the necessary functional characteristics, even after very long periods of operation. For the assessment of these materials are used expression grade of degradation in the basic meaning of the original English word grade = quality grade, Where the degradation is cumulative deterioration of quality (properties) and thereby reduce the utility value. Knowledge of these mechanisms acting simultaneously allows determining the boundary conditions and more efficient utilization of used materials. Alternatively, it may give information to a qualified estimate of the causes of failure. Degradation starts its own production of semi-finished products (purity, structural homogeneity) continues through technological factors of production (welding) and the last part of degradation is during service of the parts (corrosion, hydrogen embrittlement, etc.). The aim of this article is at bases information obtained from fifty years of degraded materials to obtain information for more accurate reference catalogue. This catalogue can on bases information obtained from the microstructure and hardness estimate the state of degradation or possible time to rupture for the material.

The paper deals with phase diagram calculations and predictions of selected binary, ternary, and Zr-Nb-O-H quaternary system. These systems are important as alloy base for cladding materials involving fissionable fuel in nuclear industry. The main attention is focused on the phase diagram prediction of Zr-1wt.%Nb-O alloy system at temperature conditions up to 2 000 °C. In addition, the influence of hydrogen content on the Zr-1wt.%Nb-O phase diagram is discussed. According to service conditions in nuclear industry, 1 000, 2 000 and 3 000 ppm of hydrogen contents are considered. The achieved results are presented as iso-concentration section of the phase diagrams. Impact on mechanical properties of the material under view is discussed.

This paper summarizes the achieved results of microstructure analysis and mechanical testing of long-term degradation of Mn-V steel (W. Nr. 1.1133, ČSN 41 3123) frequently used in small and middle boiler pressure systems operating under creep conditions. In these systems, non-exchangeable components often limit a safety of their service operation. Therefore in view of the monitoring, non-destructive methods like replica technique, hardness testing and defectoscopy, and probabilistic approach to residual life assessment seems to be the only way how to quantitatively determine a residual life of the boiler pressure system. Achieved results of as-exposed and as-secondary aged Mn-V steel confirmed that besides NDT controlling of sheet welds due to possible cracks, the replica technique (on available component surface) accompanied by hardness measurement on each segment of weldment should be sufficient for residual life assessment of thick-walled components of boiler pressure system operating under creep conditions. Additionally as a very rough estimate, a value of limit hardness of steel for safety operation is estimated at about 150 HV.

This paper deals with changes in mechanical and structural properties of Steel T23 during long-time annealing at high temperatures. The research is focused on the degradation of the base material (steel T23), where the samples of steel, after the initial heat treatment, were annealed at temperatures of 600, 650 and 700 °C for 10 to 10 000 hours in a furnace with air atmosphere. This contribution summarizes the experimental results of mechanical and structural measurements and gives the relations between them.

Monoclonal mouse anti-Thy-1.2 antibody of IgG3 isotype (MTA) inhibits in a significant and long-term manner the regional graft-versus-host reaction (GVHR) when administered to donors as well as to recipients. The process of sensitization in the reaction of delayed type hypersensitivity to SRBC (DTH) is, on the other hand, suppressed only if MTA is administered immediately prior to sensitization. If the time interval between the injection of MTA and of SRBC is extended, the resulting DTH is stimulated. Similarly, the titers of total Ig against SRBC are decreased only if MTA is administered shortly before immunization. Contrasting effects of MTA on the production of IgM and IgG were observed. While the production of IgG was inhibited even after the time interval between the administration of MTA and immunization had been increased, the production of IgM antibodies was stimulated. In recipients of allogeneic Sarcoma I treated with MTA, the primary growth of the tumor is enhanced and the percentage of permanent progressors is increased. Mechanisms of MTA activity are discussed.

Environmental light entrains the rat pineal N-acetyltransferase rhythm which controls melatonin production. One day after 1 min light pulses applied before midnight, or after delays in the evening switch off of light, or after a delay of the light-dark cycle, the evening N-acetyltransferase rise and the morning decline are phase delayed almost to the same extent. Consequently, the pattern of the rhythm does not change. One day after 1 min light pulses applied past midnight, or after bringing forward the morning light onset, or after an advance of the light dark-cycle, the morning N-acetyltransferase decline is phase advanced, but the evening rise is either not phase shifted or it may be even phase delayed. Consequently, the pattern of the rhythm may be changed considerably or the rhythm may be abolished. The data are consistent with an hypothesis of a two-component pacemaker controlling the N-acetyltransferase rhythm. Under all photoperiods which we encounter in nature, the pattern of the N-acetyltransferase rhythm is determined by the entraining effect of light on the pacemaker, but not by the suppressant effect of light.

Summary By use of staining with toluidine blue, the changes in the nucleoli of lymphocytes in 150 healthy women were studied. The patients were divided into five groups: non-pregnant women; women in the first, second and third trimesters of pregnancy; and women who were five days post parturn. A progressive and statistically significant rise in the number of lymphocytes with micronucleoli was found during pregnancy and there was a fall after delivery. This increase was associated with a decrease in the incidence of ring-shaped nucleoli. There were no significant changes in the absolute number of lymphocytes and in “active” lymphocytes during pregnancy.