scholarly journals Analysis of thermal embrittlement of a low alloy steel weldment using fracture toughness and microstructural investigations

2022 ◽  
pp. 108248
Author(s):  
Magnus Boåsen ◽  
Kristina Lindgren ◽  
Martin Öberg ◽  
Mattias Thuvander ◽  
Jonas Faleskog ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Alloy Steel ◽  
Low Alloy Steel ◽  
Steel Weldment ◽  
Thermal Embrittlement

Thermal Aging Assessment and Microstructural Investigations of Alloy 52 Dissimilar Metal Welds for Nuclear Components

2019 ◽  
Author(s):  
Miguel Yescas ◽  
Pierre Joly ◽  
François Roch
Keyword(s):  
Fracture Toughness ◽  
Alloy Steel ◽  
Thermal Aging ◽  
Base Alloy ◽  
Narrow Gap ◽  
Low Alloy Steel ◽  
Nickel Base Alloy ◽  
Pressurized Water ◽  
Dissimilar Metal ◽  
Nickel Base

Abstract Dissimilar Metal Welds (DMW) are commonly found between the ferritic low alloy steel heavy section components and the austenitic stainless steel piping sections in nuclear power plants. In the EPR™ design which is the latest FRAMATOME Pressurized water reactor (PWR) these DMW involve a narrow gap technology with no buttering, and only one bead per layer of a nickel base alloy weld filler metal (Alloy 52). In order to assess the thermal aging performance of this relatively new narrow gap DMW design, a significant internal R&D program was launched some years ago. Several representative mock-ups were thoroughly characterized in the initial condition as well as in the thermal aged condition, up to 50,000 hours aging at 350°C. The characterisations were focused on the fusion line between the ferritic low alloy steel (LAS) and the nickel base alloy since a particular microstructure is present in this area, especially in the carbon depleted area of the Heat Affected Zone (HAZ) which is often regarded as the weak zone of the weld joint. Metallography, hardness, nanohardness, chemical analyses, and Atom Probe Tomography, as well as fracture toughness tests were carried out on different specimens in different thermal aging conditions. The results show that the fracture toughness behaviour in the ductile-brittle domain of the low alloy steel carbon depleted HAZ at the interface with the alloy 52 weld metal of the DMWs is excellent, even for a thermal ageing equivalent to 60 years at service temperature. This was found in spite of the carbon depleted zone of the HAZ, the variations of hardness, chemical composition, particularly the carbon gradients, and the thermal aging effect induced by phosphorous segregation at grain boundaries.

Fracture Toughness in the Ductile-Brittle Transition and Thermal Ageing Behavior of Decarburized Heat Affected Zone of Alloy 52 Dissimilar Metal Welds of Nuclear Components

2014 ◽  
Author(s):  
Pierre Joly ◽  
Miguel Yescas ◽  
Elisabeth Keim
Keyword(s):  
Fracture Toughness ◽  
Stainless Steel ◽  
Alloy Steel ◽  
Heat Affected Zone ◽  
Power Plants ◽  
Base Alloy ◽  
Thermal Ageing ◽  
Low Alloy Steel ◽  
Dissimilar Metal ◽  
Brittle Transition

Dissimilar metal welds (DMW) are used in nuclear power plants between the nozzles of main components in low alloy steel and stainless steel pipes, or safe-ends connected to the main coolant line pipes. AREVA proposes for EPR™ an improved design of DMW involving narrow gap welding without buttering between the low alloy steel nozzles and the stainless steel safe-ends, and the use of a corrosion resistant weld filler metal (Alloy 52). AREVA performed a thorough characterization of this type of welds, which shows a particular microstructure close to the fusion line between the low alloy steel and the nickel base alloy, where the heat affected zone of the low alloy steel is decarburized. This paper presents results of fracture toughness tests performed with the crack tip located in this area, in the ductile to brittle transition in the as post-welded heat treated condition and after thermal ageing. The results show an excellent fracture toughness behavior of this particular area, compared to that of low alloy steel parent metal.

Mechanical Properties of a Medium Carbon Low Alloy Steel Processed by Two Step Austempering Process

2010 ◽  
Vol 638-642 ◽  
pp. 3453-3458 ◽  
Author(s):  
Susil K. Putatunda ◽  
Abhijit Deokar ◽  
Gowtham Bingi
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Yield Strength ◽  
Alloy Steel ◽  
High Yield ◽  
Bainitic Steel ◽  
Low Alloy Steel ◽  
High Yield Strength ◽  
Medium Carbon

A new bainitic steel with a combination of exceptionally high yield strength and fracture toughness has been developed. This steel has been synthesized by austempering a medium carbon low alloy steel by a novel two-step austempering process. The influence of this two-step austempering on the microstructure and the mechanical properties of this new steel have been examined.

Application of Master Curve Method to Fracture Toughness Estimation of the Transport and Storage Cask Material

2008 ◽  
Author(s):  
Kiminobu Hojo ◽  
Kentaro Yoshimoto ◽  
Ryuichi Yamamoto ◽  
Toshihiro Matsuoka ◽  
Uwe Mayer
Keyword(s):  
Fracture Toughness ◽  
Transition Temperature ◽  
Alloy Steel ◽  
Master Curve ◽  
Structural Integrity ◽  
Scale Model ◽  
Low Alloy Steel ◽  
Brittle To Ductile Transition ◽  
Data Scatter ◽  
And Storage

The transportation and storage casks have to be designed by considering transport and handling accidents. IAEA safety standard [1] requires drop test using a scale model and demonstration of structural integrity of the cask container vessel from the view point of leakage and instable fracture. For the fracture evaluation, it has to be verified that brittle fracture does not occur at the lowest temperature −40degC. MHI has developed the MSF-57BG cask whose body is made of forged low alloy steel LF3-m. It is well known that low alloy steel has the brittle-to-ductile transition temperature range of fracture toughness and large scatter of toughness value in this region. For the cask’s integrity evaluation, it is needed to obtain the fracture toughness dependent on temperature of this material by considering data scatter. The Master curve procedure [2] was proposed for estimation of fracture toughness of the pressure vessel on the basis of statistical procedure by using relatively small number of specimens. This paper examined the determination method of fracture toughness considering dynamic loading effect and data scatter in the brittle-to-ductile transition temperature by using the Master curve procedure.

Alternative Approach for Qualification of Temperbead Welding in the Nuclear Industry

2012 ◽  
Author(s):  
Steven L. McCracken ◽  
Richard E. Smith
Keyword(s):  
Heat Treatment ◽  
Fracture Toughness ◽  
Alloy Steel ◽  
Nuclear Power ◽  
Post Weld Heat Treatment ◽  
Nuclear Power Industry ◽  
Low Alloy Steels ◽  
Low Alloy Steel ◽  
Alloy Steels ◽  
Weld Heat

Temperbead welding is common practice in the nuclear power industry for in-situ repair of quenched and tempered low alloy steels where post weld heat treatment is impractical. The temperbead process controls the heat input such that the weld heat-affected-zone (HAZ) in the low alloy steel is tempered by the welding heat of subsequent layers. This tempering eliminates the need for post weld heat treatment (PWHT). Unfortunately, repair organizations in the nuclear power industry are experiencing difficulty when attempting to qualify temperbead welding procedures on new quenched and tempered low alloy steel base materials manufactured to modern melting and deoxidation practices. The current ASME Code methodology and protocol for verification of adequate fracture toughness in materials was developed in the early 1970s. This paper reviews typical temperbead qualification results for vintage heats of quenched and tempered low alloy steels and compares them to similar test results obtained with modern materials of the same specification exhibiting superior fracture toughness.

Modeling and computation by artificial neural network of fracture toughness of low alloy steel to study the effect of alloy composition

2018 ◽  
Vol 09 (06) ◽  
pp. 1850051
Author(s):  
Subir Paul ◽  
Shibasish Bhattacharjee
Keyword(s):  
Neural Network ◽  
Fracture Toughness ◽  
Artificial Neural Network ◽  
Alloy Steel ◽  
Alloy Composition ◽  
Low Alloy Steel ◽  
Ann Model ◽  
Material Chemistry ◽  
Artificial Neural ◽  
Artificial Neural Network Ann

The unpredictable structure failures of carbon steel and low alloy steel leading to accidents may be caused by the propagation of a flaw or crack already present in the structure. Fracture toughness which describes the ability of a material containing a crack to resist fracture is one of the most important material properties for design applications of metallic structures. Since this material property is influenced by several parameters, namely material chemistry, heat treatment, morphology of structure, it requires millions of experiments to be conducted to understand and predict it. So, mathematical modeling is one of the solutions to find the effect of these parameters and design future alloys. Stress–intensity factor [Formula: see text] is a quantitative parameter of fracture toughness determining a maximum value of stress which may be applied to a specimen containing a crack (notch) of a certain length. An artificial neural network (ANN) model was developed using over 100 sets of data to study the effect of alloying elements on fracture toughness, [Formula: see text] for the low alloy steel. 20% of data was used for training, 60% to develop predictive model and rest of the 20% for validation. The model can predict the fracture toughness of unknown new data close to 80% accuracy which is good enough for statistical modeling. The details of program code with ANN modeling steps have been explained. Prediction of fracture toughness by the model with variation of alloy composition as well as yield stress gives interesting and important information which may help in designing alloy which will resist crack propagation in a structure and hence enhance the life of structure to fail.

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