Evaluation Of Embrittlement Research Articles

Evaluation of Embrittlement of Construction Steels by Microindentation

Evaluation of Embrittlement of Construction Steels by Microindentation

Probabilistic fracture mechanics analyses of a reactor pressure vessel using the irradiation embrittlement evaluation based on the Bayesian nonparametric method

In the structural integrity assessment of an embrittled reactor pressure vessel (RPV) based on probabilistic fracture mechanics (PFM), it is crucial to consider both of the mean value and the uncertainty of the embrittlement prediction. Typically, the embrittlement prediction uncertainty is given by a normal distribution, and its standard deviation is determined from the residuals of the measured and predicted values of all data used to develop the embrittlement prediction method. Therefore, the same uncertainty is assumed regardless of neutron fluence and the available data. To overcome this issue, the Japan Atomic Energy Agency recently developed the embrittlement prediction method based on machine learning and Bayesian statistics, i.e., the Bayesian nonparametric (BNP) method, and introduced it to the PFM analysis code. The BNP method can predict the probability distribution according to data scarcity and provide more reasonable uncertainty because it estimates significant uncertainties where the scatter of actual measured data is large and the number of data is small. In this study, PFM analysis for a Japanese model RPV in a pressurized water reactor is conducted using the PFM analysis of structural components in aging light water reactors, where the embrittlement probability distribution calculated using the BNP method is used. Furthermore, the effects of different embrittlement prediction methods and uncertainties on the failure frequency of RPVs are investigated in the PFM analyses, and the results are presented.

Evaluation of embrittlement of construction steels by microindentation

The mechanical characteristics of a metal are determined by a combination of three groups of factors: the chemical composition, structural features and the deformation ability of the structure, i.e., the ability of elements to relax internal stresses during deformation through dislocation sliding which does not lead to the crack formation and destruction. The possibility of using microindentation to assess the deformation ability of the structure of structural steels with a relatively high ductility is the goal of the study. The theoretical analysis revealed that an increase in the stiffness and a decrease in the plasticity of a metal leads to a change in the deformation model during indentation and, in particular, to the occurrence of deformation effects of various morphologies on the surface near the imprint, which can be indicative of the metal plasticity. Experimental studies performed on pipe steels of various strength and types of the structure confirmed that as the deformation ability of the metal decreases (primarily as a result of deformation hardening), a system of localized shears is formed near the imprint along the lines of action of maximum tangential stresses. A scale for ranking data of localized shears is proposed and the optimal load value and shape of the indenter are determined which provide gaining maximum information by microindentation. A methodology for assessing the embrittlement of plastic construction steels based on the results of microindentation has been developed, which can form a basis for creating an effective technology of nondestructive evaluation of the metal state.

In-situ hydrogen embrittlement evaluation of as-built and heat treated laser powder bed fused Ti-6Al-4V versus conventionally cold rolled Ti-6Al-4V

In-situ hydrogen embrittlement evaluation of as-built and heat treated laser powder bed fused Ti-6Al-4V versus conventionally cold rolled Ti-6Al-4V

Hydrogen Embrittlement Evaluation and Prediction in Press‐Hardened Steels

The application of press‐hardened steels (PHSs) in automotive body‐in‐white components using the hot‐stamping technique is growing thanks to its impressive strength and formability. Unfortunately, hydrogen embrittlement (HE), an issue that generally exists in high‐strength steels, impedes the PHSs rising application trend by causing catastrophic mechanical property degradation. Thus, detailed evaluation and prediction of HE risk throughout PHSs manufacture and service condition are necessary. This study highlights techniques to characterize the hydrogen content and distribution, techniques to evaluate HE susceptibility, and potential models to simulate the in‐service performance of PHS. The survey of existing studies has revealed the gaps between laboratory measurement and industry application, including but not limited to 1) the accelerated experiment‐induced discrepancies against real‐life applications, 2) a selection of the appropriate HE indicators, 3) an accurate risk prediction model, and 4) efficient feedback to the industry based on both experimental and simulated results. Based on the review, future studies are expected to establish a conclusive HE evaluation standard for PHS.

Method for Evaluating Hydrogen Embrittlement of High-Strength Steel Sheets Considering Press Formation and Hydrogen Existence State in Steel

High strength steel sheets are increasingly being used due to the growing need to improve fuel efficiency by reducing vehicle weight. Steel sheets are usually used as automotive parts formed by pressing, etc., and complicated strain is generated in the steel sheet after forming. This strain is thought to affect the occurrence of hydrogen embrittlement. In this study, a new hydrogen embrittlement evaluation method using a forming limit diagram was devised. A forming limit diagram of a steel sheet with a strength level adjusted to 1470 MPa was prepared for uniaxial, plane strain and biaxial modes, and stress and hydrogen were applied to the specimens formed with respective strain modes to evaluate the occurrence of fracture. In order to examine the relationship between the hydrogen content and the cracking, evaluation of the hydrogen content by Thermal Desorption Analysis, visualization of hydrogen by Secondary Ion Mass Spectrometry and microstructure analysis by Electron BackScatter Diffraction were carried out. It was found that cracks are generated in the strain mode in which hydrogen accumulates locally in the steel even when the apparent hydrogen content is small, and it was clarified experimentally that evaluation of local hydrogen concentration is important for the evaluation of hydrogen embrittlement.

Hydrogen Embrittlement Evaluation of Micro Alloyed Steels by Means of J-Integral Curve.

The aim of this work is the evaluation of the hydrogen effect on the J-integral parameter. It is well-known that the micro alloyed steels are affected by Hydrogen Embrittlement phenomena only when they are subjected at the same time to plastic deformation and hydrogen evolution at their surface. Previous works have pointed out the absence of Hydrogen Embrittlement effects on pipeline steels cathodically protected under static load conditions. On the contrary, in slow strain rate tests it is possible to observe the effect of the imposed potential and the strain rate on the hydrogen embrittlement steel behavior only after the necking of the specimens. J vs. Δa curves were measured on different pipeline steels in air and in aerated NaCl 3.5 g/L solution at free corrosion potential or under cathodic polarization at −1.05 and −2 V vs. SCE. The area under the J vs. Δa curves and the maximum crack propagation rate were taken into account. These parameters were compared with the ratio between the reduction of area in environment and in air obtained by slow strain rate test in the same environmental conditions and used to rank the different steels.

Material degradation and embrittlement evaluation of ethylene cracking furnace tubes after long term service

Abstract The material degradation of ethylene cracking furnace tubes after 7 years service was investigated in this study. The results showed that carburization and creep damage were occurred during service. Significant degradation of microstructures and decrease of mechanical properties were revealed for these tubes, based on the experiment including micro-structural observations, SEM observations, and tensile tests at room temperature and service temperature. Then, quantitative relationships between metallurgical characteristics and mechanical properties were established according to statistical measurements of carbide parameters, which provides an useful approach for estimation the mechanical properties of tube. Furthermore, a classification criteria for material deterioration and embrittlement evaluation of furnace tube was proposed based on average carbide width, which can be used for life assessment and failure prediction of ethylene cracking furnace tube.

Evaluation of Embrittlement of Reactor Pressure Vessel Steel by Sub-size Charpy Impact Test

Evaluation of Embrittlement of Reactor Pressure Vessel Steel by Sub-size Charpy Impact Test

A case of hydrogen embrittlement evaluation of steel

A case of hydrogen embrittlement evaluation of steel

Comparison of Constant Load, SSRT and CSRT Methods for Hydrogen Embrittlement Evaluation Using Round Bar Specimens of High Strength Steels

Comparison of Constant Load, SSRT and CSRT Methods for Hydrogen Embrittlement Evaluation Using Round Bar Specimens of High Strength Steels

Hydrogen Embrittlement Evaluation of Subsurface Zone in 590DP Steel by Micro-Vickers Hardness Measurement

This study describes a hydrogen embrittlement evaluation of the subsurface zone in 590DP steel by micro-Vickers hardness measurement. The 590DP steel was designed to use in high-strength thin steel sheets as automotive materials. The test specimens were fabricated to 5 series varying the chemical composition through the process of casting and rolling. Electrochemical hydrogen charging was conducted on each specimen with varying current densities and charging times. The relationship between the embrittlement and hydrogen charging conditions was established by investigating the metallography. The micro-Vickers hardness was measured to evaluate the hydrogen embrittlement of the subsurface zone in addition to the microscopic investigation. The micro-Vickers hardness increased with the charging time at the surface. However, the changing ratio and maximum variation of hardness with depth were nearly the same value for each test specimen under the current density of 150 mA/ and charging time of 50 hours. Consequently, it appears that hydrogen embrittlement in 590DP steel can be evaluated by micro-Vickers hardness measurement.

Evaluation of Embrittlement in Isochronal Aged Fe-Cr Alloys by Magnetic Hysteresis Loop Technique

Fe-Cr alloys with different Cr contents were prepared by an arc melting technique. The alloys were isochronally aged in the range from <TEX>$400^{\circ}C$</TEX> to <TEX>$900^{\circ}C$</TEX> with <TEX>$50^{\circ}C$</TEX> steps with a holding time of 100 hours. The ageing produced embrittlement in the alloys due to either the formation of a Cr-rich <TEX>${\alpha}'$</TEX> phase or a <TEX>$\sigma$</TEX> phase at high temperatures. Magnetic Hysteresis Loop (MHL) and Micro-Vickers hardness were measured at each step to correlate the magnetic and mechanical properties. Coercivity and hardness of the alloys were increased and remanence decreased up to 500-<TEX>$550^{\circ}C$</TEX> due to formation of a Cr-rich <TEX>${\alpha}'$</TEX> phase. Beyond 500-<TEX>$550^{\circ}C$</TEX> range, the coercivity and hardness decreased and remanence increased due to the coarsening or dissolution of the Cr-rich <TEX>${\alpha}'$</TEX> phase. In the Fe-48% Cr alloy, formation of the <TEX>$\sigma$</TEX> phase at <TEX>$700^{\circ}C$</TEX> reduced the maximum induction of the alloy significantly.

Thermal Aging Embrittlement Evaluation of Nuclear Primary Pipe Steel by Ductile to Brittle Transition Test

In order to determine the ductile to brittle transition behavior of nuclear primary pipe material (Z3CN20.09M) during the thermal aging procedure, instrumented impact tests at different temperatures were performed on Z3CN20.09M aged at 400°C for up to 3000 hours. The load-deflection curves from the instrumented impact tests described both the loading and the fracture stages, from which the dynamic strengths and energy were calculated. The results indicated that the thermal aging decreases the impact energy and shifts the ductile-to-brittle transition curves to higher temperatures.

1Pa-21 Non-Destructive Evaluation of Embrittlement in Isochronal Aged Fe-Cr Alloy by EMAR Technique(Poster Session)

1Pa-21 Non-Destructive Evaluation of Embrittlement in Isochronal Aged Fe-Cr Alloy by EMAR Technique(Poster Session)

Hydrogen Embrittlement Evaluation Methods for Ultra-high Strength Steel Sheets for Automobiles

Hydrogen Embrittlement Evaluation Methods for Ultra-high Strength Steel Sheets for Automobiles

Embrittlement evaluation and lifetime assessment of hydrocracking pressure vessel made of 3Cr–1Mo low-alloy steel

The Cr–Mo steels which are widely used for pressure vessels in refineries and petrochemical plants, have a potential for hydrogen and temper embrittlement. During long-time service the embrittlement leads to decrease of the critical flaw size of brittle fracture and/or to the reduction of the remaining life of a pressure vessel. In this investigation the effect of high temperature and high pressure hydrogen on a vessel, made of 3Cr–1Mo low-alloy steel is studied. Inspections show that the only detected crack in the base metal is originally formed by welding defects and calculations show that it will not grow up. Therefore, it is predicted that the operation of the pressure vessel in normal condition and under regular supervision can be continued.

An Energy-Based Crack Extension Formulation for Crack Resistance Characterization of Ductile Materials

Abstract Crack resistance behavior is an important property for reactor pressure vessel embrittlement evaluation as reactors operate in the upper shelf ductile regime. This property consists in evaluating the change of crack length with the applied loading expressed in terms of the J-integral. While J-integral formulation is available for standard geometries and it is relatively easy to determine, crack extension is either measured directly on the fracture surface of a number of specimens or estimated from one single specimen, necessitating sophisticated instrumentation. Based on a number of experimental observations, a simple procedure is presented which is based solely on the load-displacement test record and the initial and final crack length to determine the full crack resistance curve. The reliability of this new procedure for determining the crack resistance, the initiation toughness, and the tearing resistance is illustrated by several examples covering a wide range of materials and cracked specimen configurations.

Beyond RPV Design Life

A set of standard surveillance programs for monitoring the design life of reactor pressure vessels (up to 40 years of operation) has been analyzed. In view of the improved test methods and embrittlement evaluation procedures, the necessity has been shown of introducing modifications in the present surveillance programs aiming at a more precise reactor pressure vessel integrity evaluation facing a possible service life of 60 years. Service life predictions are performed for reactor pressure vessels, based on the available surveillance data, reconstituted Charpy specimens, and Master Curve testing.

Application of the Master Curve Approach for the Irradiation Embrittlement Evaluation of Pressure Vessel Steels

The Master Curve (MC) approach and the associated reference temperature, T0, as defined in the test standard ASTM E1921, is rapidly moving from the research laboratory to application in integrity assessment of components and structures. T0 is the index temperature for the universal MC, which considers the toughness behaviour of a specific material. “The Structural Integrity Assessment Procedures for European Industry” (SINTAP) contain a MC extension for analysing the fracture behaviour of inhomogeneous ferritic steels. This paper presents the application of the MC approach to the T0 determination of different types of Russian WWER‐type reactor pressure vessel (RPV) steels. In addition the SINTAP‐MC approach was applied to determine an alternative reference temperature, TR.The influence of different microstructures and compositions within one type of RPV steel and the effect of irradiation with fast neutrons on T0 are experimentally evaluated. In general the MC based T0 is about 72 K below the Charpy V‐notch transition temperature related to an impact energy of 48 J. The paper demonstrates the application of MC based T0 and TR as an alternative reference temperature for neutron embrittled RPV steels used in the RPV integrity assessment.