[en] It has been recognized for several years that carbon and low-alloy steels can exhibit environmentally-assisted subcritical crack growth in high temperature, high purity water when stressed under constant load, monotonically increasing load, or cyclic load. This present review specifically addresses the question of stress corrosion for which it is questionable whether a life prediction code can be currently formulated because of the wide scatter in the data base. The argument is made that knowledge of the mechanism of cracking leads to a deconvolution of the data scatter, and a rationale for life prediction of cracking under light water reactor conditions. The slip dissolution model is used as a working hypothesis for the crack advance mechanism, and this has been quantified via independent formulations of the rate-controlling chemical and mechanical factors in the A533B/A508 steel/288 degrees C water system. This model of cracking is applied to laboratory and service incidences of cracking in this system, with good agreement between observation and prediction. The conditions of corrosion potential, solution flow rate, stress/time, etc. that might give problems in an operating component are defined

[en] The true stress-true strain relation of SA508 steel, the material for reactor pressure vessel, was evaluated with the analytical solutions and experimental equations on the base of the indentation load-depth curve obtained from the modeling of indentation test. The evaluated relation between true stress and true strain is agreed well with that of SA508 steel, which was used to define the plasticity of the material in the modeling. The pile-up deformation on the edge on the indentor began to appear in the stage of fully plastic deformation of material. Because of the pile-up deformation, the contact radius obtained from modeling was larger than those obtained from analytical solutions. The distribution of effective stresses obtained from Tresca criteria along the center axis of indentation was calculated in the modeling. The representative strains, which are defined as the corresponding strains with the maximum effective stresses, have a linear relation with the true strains

[en] Following a series of cooperative studies A-I and A-II (phase III) concerning the inelastic behaviour of high temperature materials under uniform state of stress, finite element analyses were carried out on circumferential notched cylinders subjected to plasticity-creep interaction conditions. Using an electric capacitance type extensometer ''Strain-Pecker'', which is capable of measuring a local strain response with a gauge length of 0.5mm under high temperature conditions, stress-strain responses for both global and local regions near the notch root were evaluated. Ten kinds of inelastic constitutive model were introduced into a finite element code, and the responses for four kinds of loading pattern were examined for two types of notch shape. ((orig.))

[en] High-temperature operating experience is lacking in pressure vessel materials that have strength levels above 586 MPa. Because of their tendency toward strain softening, we have been concerned about their behavior under nonsteady loading. Testing was undertaken to explore the extent of softening produced by monotonic and cyclic strains. The specific materials included bainitic 2 1/4Cr-1Mo steel, a micro-alloyed version of 2 1/4Cr-1Mo steel, a micro-alloyed version of 2 1/4Cr-1Mo steel containing vanadium, titanium, and boron, and a martensitic 9Cr-1Mo-V-Nb steel. Tests included tensile, creep, variable stress creep, relaxation, strain cycling, stress cycling, and non-isothermal creep ratchetting experiments. We found that these steels had very low uniform elongation and exhibited small strains to the onset of tertiary creep compared to annealed 2 1/4Cr-1Mo steel. Repeated relaxation test data also indicated a limited capacity for strain hardening. Reversal strains produced softening. The degree of softening increased with increased initial strength level. We concluded that the high strength bainitic and martensitic steels should perform well when used under conditions where severe cyclic operation does not occur

[en] To develop nonisothermal modeling of inelasticity we postulate a similarity equation, which specifies the positional change of a kinematic hardening variable relative to the bounding surface under temperature variation. It results in a temperature-change induced term in the evolution equation of the kinematic hardening variable. On the assumption that the kinematic hardening variable consists of various components, the proposed model is transformed to an equivalent form based on multisurfaces in which the configuration of nested multisurfaces changes with a similarity under temperature variation. Discussing the condition for the temperature-history independence of the inelastic stress response, which is observed rather often in experiments, we derive analytical expressions for the stress versus strain relations under monotonic and cyclic thermomechanical loadings. Finally we show the validity of the proposed model in comparison with experimental data of 2.25Cr-1Mo steel. (orig.)

[en] The fabrication, inspection, shipment, and mechanical properties of a modified 9 Cr-1 steel test article for exposure in the Sodium Components Test Loop (SCTL) at the Energy Technology Engineering Center (ETEC) are described. The test article delivered consisted of modified 9 Cr-1 Mo steel pipe 232 mm in diameter by 12.7-mm wall by 610 mm long. This pipe was safe ended with type 304L stainless steel spool pieces 152 mm long on each end. The joint between modified 9 Cr-1 Mo and type 304L was made with ERNiCr-3 filler wire. The entire test article was postweld heat treated 1 h at 732⁰C and ultrasonically inspected before use. Radiography was used to inspect the welds between modified 9 Cr-1 Mo and type 304L stainless steel. The test article was delivered to ETEC on schedule on October 4, 1982. After delivery of the test article, we fabricated an additional piece of the same dimensions by the same procedure for archive purposes, mechanical property testing, and comparison with the actual test article after test. A part of this archive piece also provided a nondestructive examination standard for in-service inspection for ETEC. The archive specimen has already been subjected to tensile and creep testing, microstructural evaluation, and thermal aging for 2000 h at 510⁰C. The test article has completed a year of operation in the SCTL. We expect to remove this pipe after three years of operation for testing and examination

[en] This program involved the testing both of SENB- and CT-specimens and model vessels from pressure vessel steel 18CrMoNi5.4 V with the aim of studying specimen size and flaw size effects on the toughness behaviour. A comparison was made between the R-curves J-Δa of usual specimens in fracture-mechanics investigation (CT, SENB, partly 20% side-grooved) and Charpy specimens with static and dynamic loading. The crack blunting line was determined experimentally from SZW-measurements and used as a reference line for determining the crack initiation point. The R6-procedure was used to estimate the influence of flaw size in cylindrical model vessels with axial surface flaws loaded by internal pressure. A failure curve was constructed for option 2 with regard to the material deformation properties by the Ramberg-Osgood law. (orig.)

[en] The cyclic crack growth behaviour was measured by means of d.c. potential drop, a.c. potential drop, ultrasonic and crack-opening displacement (COD) methods. The methods were applied to component tests on straight pipes with an outer diameter of approximately 800 mm and a wall thickness of approximately 50 mm. The pipes were subjected to constant internal pressure (about 15 MPa) and either an alternating (or pulsating) or a quasi-static bending moment using d.c. potential drop, a.c. potential drop, ultrasonic and flaw-opening (COD) methods. The efficiency of the particular methods has been proved by comparison with fractographical analysis of the fracture surfaces. ((orig.))

[en] Results of tensile tests carried out for specimens of steel at the temperatures of 293...973 K and deformation rates of 8.33 (10^-3...10^-7) c^-1 are presented. It is shown that testing conditions affect the strength and ductility characteristics for the 15Kh5M steel. Dependences of the ductility characteristics are of v-like form. Minima of all v-like curves of the uniform component of the relative elongation are at 773 K. A decrease in the deformation rate results in the growth of the relative elongation and its uniform component as well as of a zone of deformation localization in the region of the specimen neck. A considerable local plastic deformation is shown to precede a failure of the 15Kh5M steel pipe under conditions of operation. A low sensitivity of 15Kh5M steel to a stress concentration within the temperature range of 293...843 K is established

[en] Four wide plate specimens manufactured in A533B Class I, 90 mm thick by 500 mm wide containing through-thickness or semi-elliptical surface fatigue cracks were tested at +70⁰C. These specimens were subjected to a series of increasing applied loads, each of 100 h duration, until failure. Testing was performed using a computer interactive 40 MN load controlled tensile testing rig. Values of the fracture toughness parameters J and crack tip opening displacement (CTOD) were derived from the recorded values of applied load, plate extension and crack mouth opening displacement. The influence of loading rate, degree of yield containment and crack orientation on the time dependent behaviour is assessed and compared with data obtained from wide plate and bend tests under monotonic loading and from bend tests conducted with a variable loading rate, with hold periods, under crack mouth opening control. Interpretation of the results provides a clearer understanding of low temperature time dependent ductile crack extension and enables the identification of the conditions under which this phenomenon is apparent, to allow the necessary adjustments to failure assessments. (orig.)