Search Results for Charpy V-notch impact specimens

The toughness of girth welds in 9Cr-1Mo-V and 9Cr-0.5Mo-V steel seamless pipe (ASME SA-335 Grades P91 and P92, respectively) made using the flux-cored arc welding (FCAW) process was evaluated. Electrodes from two different suppliers were used for production quality welding of each steel. The welds received post-weld heat-treatment (PWHT) in accordance with the requirements of the ASME Code. The objective of the work was to determine if the fracture toughness of the FCAW welds was acceptable for high-temperature steam piping. Toughness was measured using standard sized Charpy V-notch impact specimens. The specimens were oriented transverse to the weld seam with notch located approximately in the center of the weld metal and parallel to the direction of weld seam. Full-range (lower to upper shelf) Charpy impact energy and shear area curves were developed for each weld joint. These were used to estimate the temperatures corresponding to 30 ft-lb average impact energy. The estimated temperatures were well below the service temperature but were above the typical hydrostatic test temperature.

Nimonic 263 alloy was selected for gas turbine combustor transition piece due to its excellent high temperature mechanical performance. In present work, Nimonic 263 alloy plate with thickness of 5mm was welded using 263 filler metal by GTAW, then post weld heat treatment of 800℃/8h/air cool was carried out. The hardness and impact toughness of welded joints were measured, and the microstructure evolution after aging at 750℃ for 3000h was investigated by scanning electron microscopy(SEM). The results show that, during the aging process, the hardness of weld metal increases firstly and then decreases. The impact toughness decreases significantly at first and then increase. Furthermore, some fluctuations can be detected in hardness and impact toughness after long-term thermal exposure. The significant decrease in the impact toughness of the aged welded joints mainly results from the precipitation of η phase around grain boundary and intergranular MC phase. The hardness of weld metal increases due to the precipitation of more carbides and γ′ phase after 1000h aging, then decreases owing to the growth of γ′ phase after 3000h aging.

Recent years high strength 9Cr1MoNbV steel developed in USA has been major material in boiler high temperature components with the increase of steam parameters of coal fired thermal power plants. As the microstructure of this steel is tempered martensite, it is known that the softening occurs in HAZ of the weldment. In the creep rupture test of these welded joints the rupture strength is lower than that of the parent metal, and sometimes this reduction of strength is caused by TypelV cracking. To develop an effective method to improve the rupture strength of welded joint, advanced welding procedure and normalizing-tempering heat treatment after weld was proposed. 9Cr1MoNbV plates with thickness of 40-50mm were welded by 10mm width automatic narrow gap MAG welding procedure using specially modified welding material. After normalizing at 1,050°C and tempering at 780°C, material properties of the welded joints were examined. Microstructure of HAZ was improved as before weld, and rupture strength of the welded joints was equal to that of the parent metal. The long term rupture strength of the welded joints was confirmed in the test exceeded 30,000hours. This welding procedure has been applied to seam weld of hot reheat piping and headers in USC boilers successfully.

To meet worldwide emission targets many Government policies either avoid the use of coal burning plant for future energy production, or restrict emissions per kilogram of coal consumed beyond the capability of most conventional plant. As a result this has accelerated current worldwide developments of steel and nickel alloys for coal-fired plant to operate at temperatures in excess of 625°C. Within the UK a modified 9%Cr steel has been developed which is based on the MarBN steel first proposed by Professor Fujio Abe of NIMS Japan, and has been designated IBN-1. The steel is modified by additions of, typically, 3% cobalt and tungsten with controlled additions of boron and nitrogen. While development of 9%Cr steels has continued since the last EPRI high temperature material conference in 2016 (Portugal), parallel developments in nickel alloy castings for even higher temperature and pressure applications have also continued. This paper summarises the latest developments in both of these material types.

CrMoV cast steels are widely utilized for steam turbine and valve casings, and are subjected to operating and loading conditions which can promote damage mechanisms such as thermal fatigue, creep, erosion, etc. These components are subjected to variable, and sometimes severe conditions because of flexible operation. Therefore, there is a growing need for weld repair techniques including those which do not mandate post weld heat treatment (PWHT), e.g. so-called ‘temper bead’ weld repair. In this study, a simulated weld repair was performed using a temper bead technique. The maximum hardness in the heat affected zone (HAZ) CrMoV steel was ≤400HV. The integrity of the repair methodology was investigated using destructive testing, including hardness mapping, Charpy impact tests, tensile tests, low cycle fatigue and cross-weld creep, and the microstructure was assessed using light optical microscopy and scanning electron microscopy (SEM).

In this study, 25Cr2Ni2Mo1V filler metal was deposited to weld low pressure steam turbine shafts, which are operated in fossil power plants. A comparison experiment was conducted on the weld metals (WMs) before and after varied various aging duration from 200 hours up to 5000 hours at 350 ℃. Microstructure was characterized by means of scanning electron microscopy (SEM) and electron back-scattered diffraction (EBSD) techniques. In addition, mechanical properties of corresponding specimens were evaluated, e.g. Vickers microhardness, Charpy V impact toughness and tensile strength. It is shown that the tensile strength remained stable while impact energy value decreased with increasing aging duration. Based on the experiment above, it was concluded that the variation of mechanical properties can be attributed to the redissolution of carbides and reduction of bainite lath substructure.

Additive manufacturing is a groundbreaking manufacturing method that enables nearly lossless processing of high-value materials and produces complex components with a level of flexibility that traditional methods cannot achieve. Wire arc additive manufacturing (WAAM), utilizing a conventional welding process such as gas metal arc welding, is one of the most efficient additive manufacturing technologies. The WAAM process is fully automated and guided by CAD/CAM systems on robotic or CNC welding platforms. This paper explores the fundamental concepts and metallurgical characteristics of WAAM. It focuses primarily on the mechanical properties of printed sample structures made from P91, X20, and alloys 625 and 718 wire feedstock. The study particularly addresses the anisotropy of mechanical properties through both short-term and long-term testing, comparing these results to materials processed using conventional methods.

A compositional modification has been proposed to validate an alloy design which potentially eliminates the requirement of post-weld heat treatment (PWHT) while preserving the advantage of mechanical properties in a reduced activation bainitic ferritic steel based on Fe-3Cr-3W-0.2V- 0.1Ta-Mn-Si-C, in weight percent, developed at Oak Ridge National Laboratory in 2007. The alloy design includes reducing the hardness in the as-welded condition for improving toughness, while increasing the hardenability for preserving the high-temperature mechanical performance such as creep-rupture resistance in the original steel. To achieve such a design, a composition range with a reduced C content combining with an increased Mn content has been proposed and investigated. Newly proposed “modified” steel successfully achieved an improved impact toughness in the as- welded condition, while the creep-rupture performance across the weldments without PWHT demonstrated ~50% improvement of the creep strength compared to that of the original steel weldment after PWHT. The obtained results strongly support the validity of the proposed alloy design.

9-12%Cr martensitic steels can be applied to the next highest temperature components such as boiler tracts, steam pipelines and turbines of advanced ultra-supercritical power plants with steam temperatures of 650°C. New 10%Cr martensitic steels with high B and low N contents can be a worthy candidate for use in production because it has superior creep resistance. At the same time, resistance to cyclic and dynamic loads is very important. In this work, we studied the low cycle fatigue (LCF) properties at room and elevated (500-650°C) temperatures and Charpy impact toughness at temperatures ranging from -196…100°C of advanced 10% Cr martensitic steel with high B and low N contents. The effect of new alloying scheme and corresponding peculiarities of M 23 C 6 carbides on the low cycle fatigue resistance and impact toughness of the 10%Cr martensitic steel is analyzed. It is revealed that fine and densely distributed carbides has no effect on the fatigue resistance except for the slight improvement of fatigue life at small strain amplitudes and shift the ductile-brittle transition temperature (DBTT) to higher but satisfactory value of +10°C as compared to other high-chromium martensitic steels.

The creep enhanced low alloy steel with 2.25Cr-1.6W-V-Nb (HCM2S; Gr.23, ASME CC2199) has been originally developed by Mitsubishi Heavy Industries, Ltd. and Sumitomo Metal Industries, Ltd. The steel tubes and pipe (T23/P23) are now widely used for fossil fired power plants all over the world. Recently, the chemical composition requirements for ASME Code of the steel have been changed and a new Code Case 2199-4 has been issued with the additional restriction regarding Ti, B, N and Ni, and the Ti/N ratio incorporated. In this study, the effects of additional elements of Ti, N and B on the mechanical properties and microstructure of T23/P23 steels have been evaluated. It is found that N decreases the hardenability of the steel by forming BN type nitride and thus consuming the effective B, which is a key element for hardening of the steel. The addition of Ti, on the other hand, enhances the hardenability of the steel by precipitating TiN and thus increasing the effective B. It is also found that too much addition of Ti degrades the Charpy impact property and creep ductility of the steel to a great extent. This phenomenon might affect the steel's long-term creep rupture properties, although a steel with the original chemical composition has demonstrated high creep strength at temperatures up to 600°C for more than 110,000 h.

The microstructures of an advanced Ta-added 9Cr-3Co-2W-Mo steel with increased boron content that has been homogenized at different temperatures were investigated. The chains of coarse W-rich particles were observed in the steel after homogenization at 1150°C for 24 h. These particles remained in the microstructure after normalization and tempering. Such additional dispersion hardening in the initial state of the studied steel decreased the creep rate in transient region. However, the duration of steady state creep and overall creep time was increased in the samples homogenized at 1200°C. Despite of the presence of coarse W-rich particles, the impact toughness of the low-temperature- homogenized steel in the tempered condition was significantly higher than that of the steel homogenized at 1200°C

This study investigates the mechanisms of temper embrittlement in 410 martensitic stainless steel, a material widely used in steam turbine blades due to its excellent corrosion resistance and high strength achieved through quenching and tempering heat treatments. While the material’s hardness and impact toughness strongly depend on tempering temperatures, significant embrittlement occurs around 540°C, manifesting as decreased Charpy impact energy alongside increased strength and hardness. To understand this phenomenon at the nanometer scale, high-resolution transmission electron microscopy (TEM) analysis was performed, focusing on electron diffraction patterns along the <110>α-Fe and <113>α-Fe zone axes. The analysis revealed distinctive double electron diffraction spots at 1/3(211) and 2/3(211) positions, with lattice spacing of approximately 3.5 Å—triple the typical α-bcc lattice spacing (1.17 Å). These regions were identified as metastable “zones” resembling ω-phase structures, potentially responsible for the embrittlement. While this newly identified phase structure may not fully explain the complex mechanisms of temper embrittlement, it provides valuable insights for developing improved alloying and heat treatment methods to mitigate embrittlement in martensitic steels.

Nickel-based Alloy 617B (DIN 2.4673) and Alloy C-263 (DIN 2.4650) with high creep strength and good fabricability are promising material candidates for the design of next generation coal-fired “Advanced Ultra-Super-Critical A-USC” power plants with advanced steam properties and thus higher requirements on the material properties. Microstructural studies of the precipitation hardened alloy C-263 were performed with Electron Microscopy (TEM) with respect to their strengthening precipitates like carbides and intermetallic gamma prime. Specimens were subjected to different ageing treatments at elevated temperatures for different times. The microstructural results of the investigated nickel alloy C-263 are presented and discussed with respect to their correlation with required properties for A-USC, e.g. the mechanical properties, the creep resistance and the high temperature stability and compared to Alloy 617B. The manufacturing procedure for the prematernal and forgings as well as for thin walled tube components for A-USC power plants is presented.

A new martensitic steel for power generation applications was developed: Tenaris High Oxidation Resistance (Thor) is an evolution of the popular ASTM grade 91, offering improved steam oxidation resistance and better long-term microstructural stability, with equal or better creep strength. Thanks to its design philosophy, based on consolidated metallurgical knowledge of microstructural evolution mechanisms, and an extensive development performed in the last decade, Thor was engineered to overcome limitations in the use of ASTM grade 91, above 600 °C, particularly related to scale growth and liftoff. After laboratory development, Thor was successfully validated at the industrial level. Several heats up to 80 metric tons were cast at the steel shop, hot rolled to tubes of various dimensions, and heat treated. Trial heats underwent extensive characterization, including deep microstructural examination, mechanical testing in the as-received condition and after ageing, long-term creep and steam oxidation testing. This paper presents an overview of metallurgical characterization performed on laboratory and industrial Thor material, including microstructural examination and mechanical testing in time-independent and time-dependent regimes. Data relevant to the behavior and the performance of Thor steel are also included.

A new 9%Cr steel with high boron levels (boron steel) has been developed by optimization studies on steels and alloys that are applicable to advanced ultra-super critical power plants operated at steam conditions of 700°C and 30 MPa and above. The composition and heat treatment condition of boron steel was optimized by the initial hardness, tensile strength, yield strength, and Charpy impact values on the basis of the fundamental investigation with the stability of the long-term creep strength. Creep testing of boron steel was conducted at temperatures between 600 and 700°C. The creep rupture strength at 625°C and 105 h is estimated to be 122 MPa for the present 9% Cr steel with high boron by Larson-Miller parameter method. Furthermore, physical properties as a function of temperature, metallurgical properties, tensile properties, and toughness were examined to evaluate the applicability of the steel for a 625°C USC power plant boiler. It was also confirmed that the steel has good workability for such an application by the flaring and flattening tests with tube specimens having an outer diameter of approximately 55 mm.

Development of steels used in the power generation industry for the production of boilers characterized by supercritical parameters poses new challenges. The introduction of new combinations of alloying agents aimed at obtaining the best possible mechanical properties, including creep resistance, affects the weldability of new steels. Each of the latter has to undergo many tests, particularly as regards bending and welding, in order to enable the development of technologies ensuring failure-free production and assembly of boiler systems. Martensitic steels containing 9% Cr, used in the manufacturing of steam superheaters, are characterized by excellent creep resistance and, at the same time, low oxidation resistance at a temperature in excess of 600°C. In turn, steels with a 12% Cr content, i.e., VM12-SHC or X20CrMoV12-1 are characterized by significantly higher oxidation resistance but accompanied by lower strength at higher temperatures, which translates to their limited application in the production of boilers operating at the most top parameters.X20CrMoV12-1 was withdrawn from most of the power plants, and VM12-SHC was supposed to replace it, but unfortunately, it failed in regards to creep properties. To fulfill the gap a new creep strength-enhanced ferritic steel for service in supercritical and ultra-supercritical boiler applications was developed by Tenaris and it is designated as Thor115 (Tenaris High Oxidation Resistance). This paper covers the experience gained during the first steps of fabrication, which includes cold bending and welding of homogenous joints.

Welding of collector pipes, flat heads, dished ends and connector pipes performed with high temperature and creep-resistant steels most often has been performed using GTAW process combined with MMA processes. Progress in GMAW process and availability of high quality filler materials (solid wires) enables welding of the above connections also using this method. In order to prove its efficiency, this article presents the results of related tests. The range of tests was similar to that applied during the qualification of welding procedure. The investigation also involved microscopic and fractographic examinations and creep tests. The results reveal that welding with GMAW is by no means inferior to a currently applied SMAW method yet the time of the process is shorter by 50%. The article presents the world’s first known positive results in welding of P92 grade steel using GMAW welding method.

A new martensitic steel was developed for power generation applications. Tenaris High Oxidation Resistance (Thor) is an evolution of Grade 91, designed to have improved steam oxidation resistance and better long-term microstructural stability, with equal or better creep strength. Based on consolidated metallurgical knowledge of microstructural evolution mechanisms, and extensive development performed in the last decade, Thor was engineered to overcome temperature limitations of Grade 91, yet it can be processed in the same fashion, permitting the use of existing best practices for Grade 91 boiler fabrication. Welding trials were performed on Thor tubes and pipe using welding procedures that are routinely employed in the construction of Grade 91 steel components. A summary of relevant results is presented, demonstrating the applicability of long-established and tested welding procedures to components manufactured with Thor steel.

Improvement of thermal efficiency of new power plants by increasing temperature and pressure of boilers has led us to the development of high creep strength steels in the last 10 years. HCMA is the new steel with base composition of 1.25Cr-0.4Mo-Nb-V-Nd, which has been developed by examining the effects of alloying elements on microstructures, creep strength, weldability, and ductility. The microstructure of the HCMA is controlled to tempered bainite with low carbon content and the Vickers hardness value in HAZ is less than 350Hv to allow the application without preheating and post weld heat treatment. The HCMA tube materials were prepared in commercial tube mills. It has been demonstrated that the allowable stress of the HCMA steel tube is 1.3 times higher than those of conventional 1%Cr boiler tubing steels in the temperatures range of 430 to 530°C. It is noted that creep ductility has been drastically improved by the suitable amount of Nd (Neodymium)-bearing. The steam oxidation resistance and hot corrosion resistance of the HCMA have been proved to be the same level of the conventional 1%Cr and 2%Cr steels. It is concluded that the HCMA has a practical capability to be used for steam generator tubing from the aspect of good fabricability and very high strength. This paper deals with the concept of material design and results on industrial products.

Dynamic development of steels used in power engineering industry for the production of boilers characterised by supercritical parameters poses new welding challenges. The introduction of new combinations of alloying agents aimed at obtaining the best possible mechanical properties, including creep resistance, affects the weldability of new steels. Each of the latter have to undergo many tests, particularly as regards bending and welding, in order to enable the development of technologies ensuring failure-free production and assembly of boiler systems. Martensitic steels containing 9% Cr, used in the manufacturing of steam superheaters, are characterised by good creep resistance and, at the same time, low oxidation resistance at a temperature in excess of 600°C. In turn, steels with a 12% Cr content are characterised by significantly higher oxidation resistance, but accompanied by lower strength at higher temperatures, which translates to their limited application in the production of boilers operating at the highest parameters. The niche between the aforesaid steels is perfectly filled by austenitic steels, the creep resistance and oxidation resistance of which are unquestionable. This article presents experience gained while welding dissimilar joints of advanced steels TEMPALOY AA-1 and T92, with the use of EPRI P87, Inconel 82 and Inconel 617 filler metals. The tests involving the said steel grades belong to the very few carried out in the world.