Search Results for tensile test

Material properties and damage mechanisms exhibit significant variation across weldments. Micro tensile (MT) testing of specimens machined from specific narrow weldment zones is one method to characterize local property variation. Although limited, the literature data on micro-tensile specimen testing reports on low-temperature behavior. However, cross-weld local material data at high service temperatures have not been reported yet. In the present study, MT tests are conducted across similar P22 and P91 steel welds at 550°C and 600°C, respectively. To study deformation mechanisms and the role of surface condition on properties, specimens with different surface conditions (machined, polished, and electropolished) are tested. Two different loading rates of 0.2 mm/min and 0.5 mm/min are used to study the effect of loading rate on deformation and mechanical properties. Variations in weldment material properties are presented as a function of specimen surface conditions and loading speeds. Deformation behavior is studied on the side surfaces of tested micro-tensile specimens using SEM. Deformation is correlated to the microstructural constituent observed on side surfaces.

The efforts of the European Union and Germany in particular to realize the transformation towards a climate-neutral economy over the coming decades have the establishing of a hydrogen economy as a fundamental milestone. This includes production, import, storage, transportation and utilization of great amounts of gaseous hydrogen in existing and new infrastructure. Metallic materials, mainly steels, are the most widely used structural materials in the various components of this supply chain. Therefore, the accelerated use of hydrogen requires the qualification of materials (i.e., ensuring they are hydrogen-ready) to guarantee the sustainable and safe implementation of hydrogen technologies. However, there is currently no easily applicable and standardized method to efficiently determine the impact of gaseous hydrogen on metallic materials. The few existing standards describe procedures that are complex, expensive, and only available to a limited extent globally. This article outlines the key milestones towards standardizing an efficient testing method as part of the TransHyDE flagship project. This new approach enables testing of metallic materials in gaseous hydrogen using tubular specimens. It uses only a fraction of the hydrogen required by the traditional autoclave method, significantly reducing costs associated with technical safety measures. Among the topics to be discussed are the factors influencing the test procedure, including geometrical considerations, surface quality, gas purity and strain rate.

Dissimilar metal welds (DMWs) between ferritic and austenitic materials at elevated temperatures have long posed challenges for boiler manufacturers and operators due to their potential for premature failure. As the industry moves towards higher pressures and temperatures to enhance boiler efficiencies, there is a need for superior weld metals and joint designs that optimize the economy of modern boilers and reduce reliance on austenitic materials for steam headers and piping. EPRI has developed a new filler metal, EPRI P87, to enhance the performance of DMWs. Previous work has detailed the development of EPRI P87 for shielded metal arc welding electrodes, gas-tungsten arc welding fine-wire, and its application in an ultra-supercritical steam boiler by B&W. This study examines the weldability of EPRI P87 consumables through various test methods, including Varestraint testing (both trans and spot), long-term creep testing (approximately 10,000-hour running tests), procedure qualification records for tube-to-tube weldments between traditional/advanced austenitic steels and creep-strength enhanced ferritic steels, and elevated temperature tensile testing. Macroscopic examinations from procedure qualification records using light microscopy confirmed the weldability and absence of cracking across all material combinations. The findings demonstrate that EPRI P87 is a weldable alloy with several advantages for DMW applications and highlight that specific weld joint configurations may necessitate the use of high-temperature tensile data for procedure qualifications.

Welding processes and fabrication techniques have been studied in the development of Advanced USC boilers. Advanced 9Cr steels, Fe-Ni alloy (HR6W) and Nickel base alloys (HR35, Alloy 617, Alloy 263, Alloy 740 and Alloy 740H) have been selected as candidate materials for the boiler. The weld joints of these alloys were prepared from plates, small diameter tubes and large pipes, and welding procedure tests were performed. In this study, TIG and SMAW were applied. Both welding process produced good weld joints, and they showed good results in bending tests, tensile tests and the Charpy impact test. To select the annealing conditions for stress relief, stress relaxation tests and hardness tests were conducted on the weld joints after various heat treatments. The microstructure was also evaluated by SEM and TEM. Creep rupture tests are being performed for the weld joints with and without heat treatment. The maximum creep rupture tests are expected to take over 100,000 hours. In the study of fabrication techniques, hot bending tests by high frequency induction heating for large pipes and cold/hot bending tests for small diameter tubes were established. After the bending tests, mechanical property tests such as tensile tests, impact tests and creep rupture tests were conducted. The effect of pre-strain on creep strength was studied to take the creep test results after bending into consideration. The creep rupture test will be continued for specimens from weld joints and bending pipes to show their long term reliability.

To develop 10-ton class forgings with adequate long-term strength and without segregation defects for A-USC steam turbine rotors, researchers modified the chemical composition of Alloy 706 to improve its microstructure stability and segregation properties. The modified Alloy, named FENIX-700, is a γ' phase strengthened alloy without a γ" phase, and its microstructure stability is superior to Alloy 706 at 700°C, as demonstrated by short-term aging tests and phase stability calculations using the CALPHAD method. A trial disk 1-ton class forging of FENIX-700 was manufactured from a double-melted ingot, with tensile and creep strength of the forging equivalent to that of 10-kg class forgings, indicating a successful trial. Long-duration creep tests were performed using 10-kg class forgings, revealing an approximate 105-hour creep strength at 700°C higher than 100 MPa. Manufacturability tests showed that FENIX-700 performs better than Alloy 706, as evidenced by segregation tests using a horizontal directional solidification furnace and hot workability tests. Microstructure observation and tensile tests on 10,000-hour aged specimens (at temperatures of 650, 700, and 750°C) revealed degradation of tensile strength and yield stress due to coarsening of the γ' phase, but also showed enhanced ductility through aging. The microstructure stability of FENIX-700 at 700°C was confirmed as excellent through microstructure observation of the 10,000-hour aged sample and supporting thermodynamic considerations.

Gas turbine efficiency is typically limited by the maximum allowable temperature for components at the inlet side and in the hot gas flow. Refractory alloys and SiC/SiC ceramic-matrix composites (CMCs) are promising candidates for advancing operating temperatures beyond those of Ni-based alloys (>1200 °C). Refractory alloys are more suitable than SiC/SiC CMCs for dynamic components, due to the latter's low toughness and ductility. However, it is well known that refractory alloys suffer from poor oxidation behavior under service lifetimes and conditions, leading to embrittlement concerns. The ARPA-E ULTIMATE program has set out to combine new alloys with advanced coatings to mitigate oxidation/embrittlement effects, while increasing the mechanical performance benefits of refractory materials. Low oxygen (inert gas) or vacuum systems are needed to assess high temperature mechanical performance of developed alloys. To investigate the environmental sensitivity of candidate alloys and develop high temperature testing capabilities, four argon tensile frames were upgraded as well as a single vacuum system at Oak Ridge National Laboratory. Digital image correlation was incorporated into the vacuum frame allowing for surface strain determination and refined insight into thermomechanical response. Creep testing was performed at 1300 °C on two alloys, C-103 and MHC in vacuum and high purity argon environments. The Mo-based alloy showed less sensitivity to oxygen, indicating that testing in well-controlled argon environments may be suitable. The C-103 alloy demonstrated a stronger sensitivity to oxygen in the well-controlled argon environment, illustrating the need for the developed vacuum testing capabilities. “Small” 25 mm and “large” 76 mm MHC specimens showed comparable results in terms of strain rate during creep testing and ultimate tensile strength during tensile testing, suggesting the viability of smaller geometries that use less material of advanced developmental alloys.

This study investigates the impact of adding small amounts of rare earth (RE) elements on the properties and microstructures of SA335P91 steel welds. The RE elements were incorporated into the weld metal using a coating process. The researchers then proposed an optimal RE formula aimed at achieving improved properties and microstructures. To evaluate the effectiveness of this approach, various tests were conducted on both welds with and without RE additions. These tests included tensile testing (both at room and high temperatures), impact testing, metallographic analysis to examine the microstructure, determination of phase transformation points, scanning electron microscopy, and X-ray diffraction. The results revealed that the addition of RE elements has the potential to enhance the properties and modify the microstructure of SA335P91 welds.

In order to establish a induction bending technique for Ni-based alloy HR6W large pipe, induction bending test was conducted on HR6W, which is a piping candidate material of 700°C class Advanced Ultra-Super Critical. In this study, a tensile bending test in which tensile strain was applied and a compression bending test in which compression strain was applied to the extrados side of the pipe bending part. As the results of these two types of induction bending tests, it was confirmed that a predetermined design shape could be satisfied in both bending tests. In addition, the wall thickness of the pipe was equal to or greater than that of the straight pipe section in compression bending. Therefore, if compression bending is used, it is considered unnecessary to consider the thinning amount of the bent portion in the design. Next, penetrant test(PT) on the outer surface of the bending pipes were also confirmed to be acceptable. Subsequently, metallographic samples were taken from the outer surface of the extrados side, neutral side and intrados side of the pipe bending portion. Metallographic observation confirmed that the microstructures were normal at all the three selected positions. After induction bending, the pipe was subjected to solution treatment. Thereafter, tensile tests and creep rupture tests were carried out on samples that were cut from the extrados side, neutral side and intrados side of the pipe bending portion. Tensile strength satisfied the minimum tensile strength indicated in the regulatory study for advanced thermal power plants report of Japan. Each creep rupture strength was the almost same regardless of the solution treatment conditions. From the above, it was possible to establish a induction bending technique for HR 6W large piping.

By utilizing computational thermodynamics in a Design of Experiments approach, it was possible to design and manufacture nickel-base superalloys that are strengthened by the eta phase (Ni3Ti), and that contain no gamma prime (Ni3Al,Ti). The compositions are similar to NIMONIC 263, and should be cost-effective, and have more stable microstructures. By varying the aging temperature, the precipitates took on either cellular or Widmanstätten morphologies. The Widmanstätten-based microstructure is thermally stable at high temperatures, and was found to have superior ductility, so development efforts were focused on that microstructure. High temperature tensile test and creep test results indicated that the performance of the new alloys was competitive with NIMONIC 263. SEM and TEM microscopy were utilized to determine the deformation mechanisms during creep.

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).

Creep-resistant austenitic stainless steels are known to be the potential candidate materials for use as super- and re-heater tubes in ultra-super critical (USC) power plants. Among them, ASTM A213/A213M S30432, a novel 18-8 stainless steel (18Cr- 9Ni-3Cu-Nb-N), has attracted considerable attention from electric industry due to its combined lower cost and more excellent performance in contrast to traditional TP347H steel. More than 10 years of service in Japan laid a solid foundation for the steel being selectable USC boiler materials. Steels of S30432 have been recently developed in China during the past few years. This paper presents the evaluation results of S30432 tubes manufactured by four steel plants in China as well as Sumitomo super304H tubes for comparison. A detailed microstructural analysis of the tubes has been performed by using optical and electron microscope, and mechanical properties of the tubes have been evaluated using hardness testing as well as tensile testing up to 700°C. It was found that the impurity elements, nonmetallic inclusions and grain size of the S30432 tubes were well controlled. TEM observation revealed the microstructural changes for a selected batch of S30432 specimens in condition of hot rolled material, as-extruded tube, solution treated tube and 650°C/1000h aged tube. Most attention was paid to the morphology and distribution of precipitates in the microstructure which should be responsible for the enhanced performance of the steel. Although the hardness of all the evaluated tubes was measured to be similar, they showed more or less differences in tensile properties between each other. Creep rupture testing is still in progress, and the steel might exhibit excellent long-term creep rupture strength at 650°C as was predicted from the currently available testing results.

This study examines the deformation behavior of P92 steel (ferritic, 9% Cr) at high temperatures (600°C to 900°C) using isothermal hot tensile tests. Particular focus is placed on the stress-strain behavior around its alpha-gamma transition temperature (825°C). Additionally, fire accident simulation heating tests were conducted to assess the integrity of P92 beyond 650°C (relevant for short-term creep) and compare it to stainless steel 1.4404 (potential building material). Finally, microstructural analysis was performed on tested samples, revealing that the martensitic structure with characteristic laths was retained at temperatures up to 750°C.

The powder metallurgy (P/M) process has been applied to a high strength turbine disk alloy. It is known that P/M alloys show characteristic microstructures such as prior powder boundaries (PPB) compared to microstructures of conventional cast and wrought (CW) alloys. High temperature tensile tests were conducted on CW and P/M processed alloy720Li in order to reveal the effect of temperature and strain rate on deformation behavior and to demonstrate the effect of microstructure derived from P/M process on deformability. The fracture mode of the P/M material changed from grain interior fracture to fracture around large PPB with an increment of strain rate. In addition, samples ruptured at higher temperature showed grain boundary fracture regardless of strain rate. On the other hand, the CW material showed good deformability with chisel point fracture in the entire temperature and strain rate condition range. In the P/M material, melting of grain boundaries occurred at super solvus temperature conditions. Large PPB acts as nucleation site of voids at higher strain rate conditions. Precipitation strengthening by γ’ phase degrades deformability at sub solvus temperature conditions. However, deformability near the solvus temperature and low strain rate condition in as HIPed P/M material increased with fine grain size distribution in spite of the presence of large grains resulting from PPB.

The effects of pre-strain on creep properties of Alloy 740 have been investigated. Tensile strain was 7.5% and introduced by room temperature tensile test. Creep tests were conducted under 750 degree C, 275-350MPa. Creep rupture life of pre-strained sample decreased by half compared with as-heat treated sample. Creep behaviors of both samples were almost similar in primary creep stage, but onset of creep rate acceleration of pre-strained sample was faster than those of as-heat treated sample. As a result, minimum creep rate of pre-strained sample were two times larger than that of as-heat treated sample. From the observation of ruptured specimen, pre-strained sample had much more sub cracks than as-heat treated sample. On the other hand, microstructure of both samples was also different. There were MC precipitates on grain boundary in both ruptured specimens, but both size and number of MC precipitates were larger in pre-strained sample although creep life of pre-strained sample was shorter than that of as-heat treated sample. In this paper, the difference of creep behavior will be discussed in terms of both the microstructural change and mechanical damage.

High temperature strength of a nickel-based superalloy, Alloy 740H, was investigated to evaluate its applicability to advanced ultrasupercritical (A-USC) power plants. A series of tensile, creep and fatigue tests were performed at 700°C, and the high temperature mechanical properties of Alloy 740H was compared with those of other candidate materials such as Alloy 617 and Alloy 263. Although the effect of the strain rate on the 0.2% proof stress was negligible, the ultimate tensile strength and the rupture elongation significantly decreased with decreasing strain rate, and the transgranular fracture at higher strain rate changed to intergranular fracture at lower strain rate. The time to creep rupture of Alloy 740H was longer than those of Alloy 617 and Alloy 263. The fatigue limit of Alloy 740H was about half of the ultimate tensile strength. Further, Alloy 740H showed greater fatigue strength than Alloy 617 and Alloy 263, especially at low strain range.

T24 tube material (7CrMoVTiB10-10), with its combination of high creep strength and potential to be welded without using preheat, is regarded as a candidate waterwall material for Ultra Supercritical (USC) boilers. However, its reputed sensitivity to hydrogen and potential for secondary hardening may have adverse impacts on construction of waterwall panels. Doosan Babcock Ltd have investigated the response of welds made in T24 tubing to secondary hardening via changing hardness in a series of ageing heat treatment trials. Also, the response of the material to hydrogen infusion has been investigated

The long-term creep strength of creep strength-enhanced ferritic steels has been overestimated due to changes in the stress dependence of creep rupture life at lower stress levels. To address this, creep rupture strength has been reassessed using a region-splitting analysis method, leading to reductions in the allowable tensile stress of these steels as per Japan’s METI Thermal Power Standard Code in December 2005 and July 2007. This method evaluates creep rupture strength separately in high and low stress regimes, divided at 50% of the 0.2% offset yield stress, which corresponds approximately to the 0% offset yield stress in ASME Grade 122-type steels. In the high-stress regime, the minimum creep rate follows the stress dependence of flow stress in tensile tests, with the stress exponent (n) decreasing from 20 at 550°C to 10 at 700°C. In contrast, the low-stress regime exhibits an n value of 4 to 6 for tempered martensitic single-phase steels, while dual-phase steels containing delta ferrite show an even lower n value of 2 to 4. The significant stress dependence of creep rupture life and minimum creep rate in the high-stress regime is attributed to plastic deformation at stresses exceeding the proportional limit. Meanwhile, creep deformation in the low-stress regime is governed by diffusion-controlled mechanisms and dislocation climb as the rate-controlling process.

Carbon Capture and Storage (CCS) has become promising technology to reduce CO 2 emissions. However, as a consequence of CCS installation, the electrical efficiency of coal fired power plant will drop down. This phenomenon requires increase in base efficiency of contemporary power plants. Efficiency of recent generation of power plants is limited mainly by maximum live steam temperature of 620°C. This limitation is driven by maximal allowed working temperatures of modern 9–12% Cr martensitic steels. Live steam temperatures of 750°C are needed to compensate the efficiency loss caused by CCS and achieve a net efficiency of 45%. Increase in the steam temperature up to 750°C requires application of new advanced materials. Precipitation hardened nickel-based superalloys with high creep-rupture strength at elevated temperatures are promising candidates for new generation of steam turbines operating at temperatures up to 750°C. Capability to manufacture full-scale forged rotors and cast turbine casings from nickel-based alloys with sufficient creep-rupture strength at 750°C/105 hours is investigated. Welding of nickel-based alloys in homogeneous or heterogeneous combination with 10% Cr martensitic steel applicable for IP turbine rotors is shown in this paper. Structure and mechanical properties of prepared homogeneous and heterogeneous weld joints are presented.

Metallographic tests, micro-hardness tests, mechanics performance tests and Energy Dispersion Spectrum (EDS) were conducted for a 2.25Cr-1Mo main steam pipe weldment served for more than 32 years. Microstructural evolution of the 2.25Cr-1Mo base metal and weld metal was investigated. Degradation in micro-hardness and tensile properties were also studied. In addition, the tensile properties of subzones in the ex-service weldment were characterized by using miniature specimens. The results show that obvious microstructural changes including carbide coarsening, increasing inter lamella spacing and grain boundary precipitates occurred after long-term service. Degradation in micro-hardness is not obvious. However, the effects of long term service on tensile deformation behavior, ultimate tensile strength and yield stress are remarkable. Based on the yield stress of micro-specimens, the order of different subzones is: WM>HAZ>BM, which is consistent with the order of different subzones based on micro-hardness. However, the ultimate tensile strength and fracture strain of HAZ are lower than BM.

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.