Thermal Embrittlement Research Articles

Snoek relaxation in a copper-precipitated alloy steel

We studied the effect of thermal embrittlement of a steel containing 1.29 at% copper on the Snoek relaxation. The hardness increased with isothermal aging at 723 K and decreased after showing a maximum. Hardness change is governed by bcc–copper clusters precipitated from the ferrite iron crystal. Using a forced-vibration torsion-pendulum method, we studied the internal-friction spectrum and recovery of the maximum relaxation strength after quenching from 723 K. We observed a broad nonsymmetrical spectrum which apparently consists of three Debye peaks. With higher hardness, the recovery rate increased. We interpreted our results in terms of Nowick’s theory of interstitial/substitutional-solute interactions. For recovery, we used the Cottrell–Bilby–Harper t 2/3 model.

Modeling of scatter and size effect in ductile fracture: application to thermal embrittlement of duplex stainless steels

The aim of this work was to investigate the effect of specimen size and geometry on ductile fracture of cast duplex stainless steels after thermal embrittlement. Different specimen geometries, including smooth and notched bars, Charpy and compact tension (CT) specimens, were tested using three different materials. These specimens were used to investigate both crack initiation and propagation. In all cases, a significant scatter was observed. Size effects were also evidenced using homothetic samples having the same geometry. Microstructural investigations have also shown that damage is highly heterogeneous. In order to predict rupture, finite element models were used. The material was described using the Gurson model. In order to model size effects and scatter, it was necessary to account for the distribution of damage nucleation rates which were experimentally measured by quantitative metallography. Comparison of experiments with simulations showed that the model can be applied to describe both crack initiation and propagation. In particular it can predict mean value and scatter observed on strain to failure (tensile bars) and on initiation and propagation energies (Charpy and CT specimens).

About the prediction and assessment of thermal embrittlement of Cr–Ni austenitic–ferritic weld metal and castings at the ageing temperatures 260–425°C

This paper presents impact test results of austenitic–ferritic weld metal of the type 10X18H9F3C2 (12% ferrite) and cast base metal of the type 08X20H10M3C2 (10–32% ferrite) after a prolonged thermal ageing at temperatures 250–450°C. The obtained experimental data give the possibility to predict impact strength degradation of austenitic–ferritic metal after 10 4–10 5 h exposure and to determine thermal embrittlement.

Structural materials for atomic reactors with liquid metal heat-transfer agents in the form of lead or lead—Bismuth alloy

Natural safety nuclear reactors operate at a working temperature of the liquid-metal lead heat-transfer agent equal to 550°C, which intensifies the metal corrosion and is fraught with the danger of thermal embrittlement. It is shown that long-term operation of the equipment requires inhibition of the heat-transfer agent by oxygen and the use of silicon steels. However, alloying with silicon increases the susceptibility of the steel to thermal and radiative embrittlement. This makes it necessary to create new steels with a stable structure. The suggested composition of austenitic steel 04Kh15N11S3MT is designed for shell and internal structures, and steel 10Kh9NSMF is designed for the pipe system of the steam generator.

Hydraulic Bulge Test of Electrodeposited Copper Foil

SUMMARYThe 18 pm to 72 μ thick commercial electrodeposited copper foils GR I and GR 3, the experimentalfoil TCAM and the commercial rolled foil GR 8 are tested in bulge and in tension at temperatures up to 300°C. Utilizing the bulge data, pressure and deflection at rupture, the through-thickness fracture stress (σ,) and fracture strain (€) are calculated and compared to the corresponding average tensile values σav and €av. The effects of foil thickness, orifice size and test temperature on σ1 and €1 are characterized. In many instances approximately one-to-one correspondence exists between σ1, €ε and σav; €avthere are, however, significant exceptions due to texture hardening, thermal embrittlement and grain pancaking. The extent of embrittlement is greatest for the GR 1 foil, increasing with the foil thickness: it is virtually- non-existent for the (rolled) GR 8 foil. Thermal annealing overshadows the embrittlement effects for the GR 3 foil. The TCAM foil embrittles modestly but displays poor resistance to thinning at room temperature; however, the resistance improves markedly with increasing test temperature.

The micro structural study of 15Kh2MFA and 15Kh2NMFA reactor pressure vessel steels using positron-annihilation spectroscopy, mössbauer spectroscopy and transmission electron microscopy

The micro structure of the non-irradiated low-alloyed steels (15Kh2MFA and 15Kh2NMFA) was studied using different spectroscopic methods as the positron annihilation lifetime and Doppler broadening techniques, the Mössbauer spectroscopy, and the Integral low-energy electron Mössbauer spectroscopy as well as the Transmission electron microscopy. Differences in the microstructural parameters of these types of RPV steels are well detectable using all methods. It was confirmed that the heat-affected zone of these steels is the most sensitive place for thermal embrittlement in the reactor. Positron-annihilation lifetime measurements on the successive annealed specimens (XTA, YTA), which simulated the heat-affected zone, showed the rapid increase in the vacancy-type defects formation in the temperature region 525–600°C. Therefore these specimens were studied using Transmission electron microscopy in more detail.

Combined effect of thermal and irradiation embrittlement in the reactor pressure vessel CrNiMoV steel

Combined effects of segregation and irradiation embrittlement in reactor pressure vessel CrNiMoV steel were studied. The study deals with an analysis of conditions affecting the 15Ch2NMFA type CrNiMoV steel susceptibility and the development of microsegregation processes in connection with temper brittleness formed on repeated annealing cycles. Microstructural analysis and results of tensile and impact testing for all the treatment conditions are presented.

Expert system for evaluation of material degradation in a nuclear power plant with the data of material condition monitoring : Araki, K.; Yoshida, K. Proceedings of the 13th International Conference on NDE in the Nuclear and Pressure Vessel Industries, Kyoto (Japan), 22–25 May 1995. pp. 369–380. ASM International (1995) ISBN 0-87170-548-6

In nuclear power plant components, there is the possibility that the material could be degraded due to the operation for many years, that is fatigue damage, irradiated embrittlement and thermal embrittlement. When intending to improve the availability of the plant and to extend the plant life, it is important to identify those material degradations which may cause a component to deteriorate its structure integrity. On this account, many Material Condition Monitoring (MCM) techniques are under development in these days. But no single device is considered to be a perfect candidate to assess the degradation, and one needs to think collectively about the data from two or more examination devices. Thus, the authors are developing a computer system to read data obtained from the devices and to assess the material degradation. This computer system is to assess material degradation with its mode and level using the MCM data and plant information such as operating record. This paper describes an outline of the evaluation system of material degradation, and shows some evaluation results using the neural network inference, which is adopted in the system as a tool to evaluate the degradation quantitatively.

Degradation detection of materials used in nuclear power plant components applying probe-type eddy current sensor—Part 1 detection of thermal embrittlement in duplex stainless steel : Journal of JSNDI, Vol. 45, No. 8 (August 1996) p. 609 Maeda, Noriyoshi; Yamaguchi, Atsunori; Sugibayashi, Takuya; Kono, Katsumi

Degradation detection of materials used in nuclear power plant components applying probe-type eddy current sensor—Part 1 detection of thermal embrittlement in duplex stainless steel : Journal of JSNDI, Vol. 45, No. 8 (August 1996) p. 609 Maeda, Noriyoshi; Yamaguchi, Atsunori; Sugibayashi, Takuya; Kono, Katsumi

Acoustic harmonic generation due to thermal embrittlement of inconel 718

This paper describes an attempt to characterize the deterioration of a structural material's mechanical properties by nonlinear acoustics. In this particular case, the damage was caused by “thermal embrittlement” during which the material, here the nickel-based alloy Inconel 718, loses a significant fraction of its fracture toughness. Harmonic generation was the experimental method used to characterize the microstructural changes in the material as a function of exposure time at elevated temperatures. Tests were performed on two heats of Inconel 718 with slightly different chemistries, with one heat showing particular sensitivity of the fracture toughness to the elevated temperature exposure with corresponding higher changes in the nonlinearity parameter. As a mechanical measure of the fracture toughness deterioration, a small specimen punch test was used in which the ductility of a thin slice of material is determined. A clear difference between the two heats was noted in the metallographic examination, which is reflected in the harmonic generation as well as the punch test data. An explanation for the changes of the harmonic generation during the embrittlement process is speculative at the present time.

Degradation detection of materials used in nuclear power plant components applying probe-type eddy current sensor. Part 1: Detection of thermal embrittlement in duplex stainless steel (In Japanese: English abstract) : Maeda, N.; Yamaguchi, A.; Sugihayashi, T.; Kono, K. Journal of JSNDI, Vol. 45, No. 8, pp. 609–616 (Aug. 1996)

Degradation detection of materials used in nuclear power plant components applying probe-type eddy current sensor. Part 1: Detection of thermal embrittlement in duplex stainless steel (In Japanese: English abstract) : Maeda, N.; Yamaguchi, A.; Sugihayashi, T.; Kono, K. Journal of JSNDI, Vol. 45, No. 8, pp. 609–616 (Aug. 1996)

Application of positron annihilation lineshape analysis to fatigue damage and thermal embrittlement for nuclear plant materials: Uchida, M., Ohta, Y., Nakamura, N. and Yoshida, K. 13th International Conference on NDE in the Nuclear and Pressure Vessel industries, Kyoto, Japan (22–25 May 1995) 349–353

Fatigue crack growth (FCG) threshold has been determined on Ti6A14V, Al 7475-T7351, quenched and tempered steel 24CrMo4 as well as on the Ni-base alloys Inconel 617 and Nicrofer 5219 Nb. The main objective of the studies was to prove the transferability of the experimentally determined FCG threshold to service type fatigue loading. For FCG threshold testing, the following requirements must be fulfilled: 1.(A) a FCG threshold has to be entirely above Kop;2.(B) a FCG threshold has to exist and has to be measured over the fatigue loading range Kmax, i.e. K∗max< Kmax<KIc;3.(C) a FCG threshold has to be the upper bound amplitude of cycles at a given Kmax, the action of which does not produce FCG no matter how these threshold amplitudes are applied:4.(D) a FCG threshold must be a material parameter useful for material characterization and FCG design methodology under all fatigue loading conditions.It was shown that all the experimental procedures, i.e. type I, III and IV tests, furnished ΔK T values for Al 7475-T7351, Ti6A14V and the quenched and tempered steel 42CrMo4. The results suggest that this might be true for all Al alloys, Ti alloys and steels. Therefore, any one test method can be used to determine ΔKT for these materials. The ASTM E 647 recommended procedure for threshold testing furnishes ΔKT values for these materials as well, if the R -ratio is equal to or higher than Rc.For the Ni-base alloys (Inconel 617 and Nicrofer 5219 Nb) only type III and IV tests can be used to determine a FCG threshold ΔKT. This is due to the different behaviour of Ni-base alloys with respect to Kop.

Ultrasonic Noise Relaxation for Evaluating Thermal Aging Embrittlement of Duplex Stainless Steels

A noncontact ultrasonic method is presented to evaluate the thermal aging embrittlement of the cast duplex stainless steels, which uses the shear-wave backscattering noise detected by an electromagnetic acoustic transducer (EMAT). Duplex stainless steel is a highly damping material, and the pulse-echo measurement for the velocity and attenuation is unavailable. High damping comes from the scattering at boundaries between the austenitic and ferritic phases. But, since little energy is absorbed in the material, the elastic waves impinged by an EMAT last in the sample for a long period (in the order of 10 ms) and are received by the same EMAT as a slowly decaying backscattering noise. The relaxation time coefficient is calculated by integrating the digitized noise signal and is correlated with the aging time. It clearly discriminates four duplex stainless steels aged for 0, 300, 1000, and 3000 h at 673K. The noise decays in a shorter time as the aging period increases. The difference of the noise relaxation rate is interpreted by the phase decomposition of ferrite into Cr-rich α′ phase and Fe-rich α phase as supported by transmission electron microscopy (TEM).

Ultrasonic Noise Relaxation for Evaluating Thermal Aging Embrittlement of Duplex Stainless Steels

A noncontact ultrasonic method is presented to evaluate the thermal aging embrittlement of the cast duplex stainless steels, which uses the shear-wave backscattering noise detected by an electromagnetic acoustic transducer (EMAT). Duplex stainless steel is a highly damping material, and the pulse-echo measurement for the velocity and attenuation is unavailable. High damping comes from the scattering at boundaries between the austenitic and ferritic phases. But, since little energy is absorbed in the material, the elastic waves impinged by an EMAT last in the sample for a long period (in the order of 10 ms) and are received by the same EMAT as a slowly decaying backscattering noise. The relaxation time coefficient is calculated by integrating the digitized noise signal and is correlated with the aging time. It clearly discriminates four duplex stainless steels aged for 0, 300, 1000, and 3000 h at 673K. The noise decays in a shorter time as the aging period increases. The difference of the noise relaxation rate is interpreted by the phase decomposition of ferrite into Cr-rich α' phase and Fe-rich α phase as supported by transmission electron microscopy (TEM).

Thermal embrittlement in 18Ni cobalt free and 18Ni–8Co–5Mo maraging steels

The thermal embrittlement behaviour of 18Ni cobalt free (250 grade) maraging steel (T250) compared with that of 18Ni–8Co–5Mo (250 grade) maraging steel (M250) was studied for different heat treatme...

Method for the Nondestructive Evaluation of Thermal Embrittlement of Duplex Stainless Steels.

To verify and maintain the integrity of duplex stainless steels currently in service, we conducted a study aiming to develop a method to nondestructively estimate their Charpy-impact energy at room temperature. Hardness of the ferrite phase was found to be a reliable indicator of the process of embrittlement during long-term heating of duplex stainless steels, but further information on the ferrite phase and the austenite phase is required for the estimation of Charpy-impact energy. An equation involving the hardness values of the ferrite and austenite phases, the ferrite content and the average spacing of ferrite-phase islands was found to be applicable in the nondestructive estimation of Charpy-impact energy at room temperature.

Performance blends based on recycled polymers

AbstractThe recent growth in the post‐consumer recycling of plastics presents an opportunity for developing new, value‐added blend products from the recycled polymers. However, in order to develop blends with useful performance characteristics, suitable techniques of compatibilization and impact modification must be employed. In this study, reactive toughening and compatibilization techniques have been found to be particularly useful in achieving high thermal embrittlement resistance in the blends of recycled poly(ethylene terephthalate) containing functionalized ethylene copolymers and polycarbonate. Reactive compatibilization of recycled polyolefin blends with poly(ethylene terephthalate) and polyamide has also been investigated.

Effects of solution treatment temperatures on microstructure, tensile and fracture properties of Co‐free 18 Ni maraging steel

The study presents the influences of solution treatment temperatures (S.T.T.) on microstructure, tensile and fracture properties of 18 Ni cobalt free maraging steel. The results are thoroughly discussed in light of the prevailing microstructural conditions as revealed by optical and transmission electron microscopy, and detailed scanning electron fractography. It is found that tensile strength in both unaged and aged conditions is independent of solutioning temperature and, consequently, grain size. However, the tensile ductility, CVN and KIC in aged condition get severely affected with the increase in S.T.T. because of a change occurring in the martensitic lath morphology from blocky to stringer type. This transition in the martensitic morphology starts at the prior austenitic grain size of 35‐40 μm and is completed at 120‐130μm. Solutioning at 1323 K followed by air cooling, however, results in thermal embrittlement of the steel due to grain boundary precipitation of TiCN. The prior austenitic grain size in this reaction plays only an indirect role. Based on these results, it has been suggested that the existing controversies on the effect of S.T.T. grain size on tensile ductility and fracture behaviour of maraging steels can be rationalized if the changes in martensitic lath morphology are considered as an important variable.

BWR control rod drive system aging

Abstract This Phase I Nuclear Plant Aging Research (NPAR) study examines the aging phenomena associated with BWR control rod drive mechanisms (CRDMs) and assesses the merits of various methods of “managing” this aging. Information for this study was acquired from (1) the results of a special CRDM aging questionnaire distributed to each U.S. BWR utility, (2) a first-of-its-kind workshop held to discuss CRDM aging and maintenance concerns, (3) an analysis of the Nuclear Plant Reliability Data System (NPRDS) failure cases attributed to the control rod drive (CRD) system, and (4) personal information exchange with nuclear industry CRDM maintenance experts. The report documenting the findings of this research, NUREG-5699, will be published this year. Nearly 23% of the NPRDS CRD system component failure reports were attributed to the CRDM. The CRDM components most often requiring replacement due to aging are the Graphitar seals. The predominant causes of aging for these seals are mechanical wear and thermal embrittlement. More than 59% of the NPRDS CRD system failure reports were attributed to components that comprise the hydraulic control unit (HCU). The predominant HCU components affected by the effects of service wear and aging are valve seals, discs, seats, stems, packing, and diaphragms.

A structural criterion of cracking resistance of steels with weakened grain boundaries

1. A structural criterion of cracking resistance for structural steels has been proposed. The crystalline boundaries of these steels weaken during service in hydrogen charging, precipitation of second phase particles, and segregation of harmful impurities at the crystallite (grain) boundaries. The criterion is based on evaluating the characteristic distance on the basis of the results of fractographic determination of the proportion of transcrystalline cleavage, brittle intercrystalline, and dimpled failure within the limits of the zone of stable crack growth. 2. The results obtained for the low-alloy structural steels with ∼0.2% C and ∼0.4% C, and 10Kh2GNM steel subjected to hydrogen charging and thermal embrittlement, respectively, causing weakening of the crystalline boundaries show that the values of the fraction of intercrystalline failure fm (10–80%) are closely linked over a wide range with the values of KIscc and KIc since KIscc ∼ (1−fm)1/2 and KIc ∼ (1−fm)1/2. 3. For cases of brittle and quasibrittle failure of the bolt steels with ∼0.2% C and ∼0.4% C, tested for SCC in a medium with pH 2.2 we detected a close link of parameter KIscc with the ratio [(1−fm)/(1−fdi)]1/2, where fm and fdi are proportions of intercrystalline dimpled failure, respectively.