Tensile Creep Rupture Research Articles

Analysis of the mechanical characteristics of mild steel using different heat treatment

The specimen used in this study to test various mechanical properties is mild steel. Analyzed are the effects of heat treatment (annealing, hardening, and tempering) on a particular specimen's mechanical characteristics. The most significant heat treatment procedures frequently employed to alter the mechanical properties of engineering materials are annealing, hardening, and tempering. Heat treatment is used to examine the mechanical characteristics of iron, which are typically ductility, hardness, yield strength, tensile strength, and impact resistance. Heat treatment increases mechanical qualities like tensile strength, yield strength, ductility, corrosion resistance, and creep rupture in addition to developing hardness and softness. These procedures also increase the effectiveness of the machining and increase their adaptability. Utilizing universal tensile testing equipment for the tensile test, a compression test, and a Rockwell hardness tester for the hardness test, the mechanical behavior of the samples is examined. Heat treating makes it simple to alter the mechanical properties to meet a specific design objective. To examine the impact of various tempering temperatures on the mechanical properties of mild steel, selected samples are heated to various temperatures above the austenitic area, quenched, and then tempered. Tensile strength variations are used to describe the changes in mechanical behavior compared to unquenched samples. Mild steel is used to create tensile test specimens, which are then heated through a variety of processes, including annealing, hardening, and tempering. The results demonstrated that different heat treatments for a specific application can alter and enhance the mechanical properties of mild steel.

Synergic effects of Si and V micro-additions on microstructural and mechanical properties of a dilute Al–Sc–Zr alloy containing L12 Al3(Sc, Zr, V) nanoprecipitates

This study investigates the impact of incorporating 0, 0.05, 0.10 at% V into a bare Al-0.06Sc-0.06Zr-0.18Si at% alloy on the precipitation behavior of Al3(Sc, Zr, V) (L12-structure) nanoprecipitates and the consequent creep resistance of the alloy. Various techniques were used to obtain results, including Vickers microhardness, Electrical conductivity, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and tensile creep rupture testing. The findings show that the amount of V added affected the nanoprecipitate structures, precipitation kinetics, coarsening resistance, and creep resistance of the alloys. After isochronal aging to 425 °C (25 °C/1 h step), alloy V0.10 had a peak microhardness value of 603 ± 14 MPa. TEM revealed a microstructure with precipitate diameters ranging from 3 to 20 nm. The nanoprecipitates had a core-shell structure with a Sc-enriched core, a Zr-enriched shell, and, in some cases, a V outer shell. The phenomenon of vanadium partitioning at the precipitate shells occurred due to the incremental influence of silicon, which enhanced the diffusion rate of Zr and V. While the alloy V0.10 had a lower steady-state strain rate than the Al-0.06Sc-0.06Zr at% alloy at stresses below 16 MPa, it showed better creep resistance at stresses above 16 MPa. The threshold stress of the alloy V0.10 (10 MPa) was almost equal to that of the previously studied Al-0.06Sc-0.06Zr at% alloy (12 MPa). These results can be explained by the fact that a variation in the lattice parameter of Al3(Sc, Zr, V) (L12) affects the ability of matrix dislocations to traverse the nanoprecipitates, even in the absence of measurable lanthanides.

Simple Estimation of Creep Properties of Negative Electrode for Lithium-Ion Battery

The macroscopic creep properties of negative electrodes in lithium-ion batteries and their estimation methods have been investigated based on the microscopic structure of the electrode. Tensile and creep tests were conducted on a negative electrode consisting of carbon powder and polyvinylidene fluoride (PVDF) binder. The stress-strain curve, the time history of the tensile strain, and the creep rupture time were measured in these tests and estimated using the simple model proposed in this study. The proposed model approximates the alignment of carbon particles as body-centered cubic (bcc) or face-centered cubic (fcc). The external load on the model was supported by a PVDF binder located between carbon particles. The test results showed that PVDF binder mechanical properties affect the macroscopic mechanical properties of the negative electrode, including the creep properties. The stress-strain curve and time history of the tensile strain were located between the upper and lower limits of the proposed model. The tensile strength and creep rupture time agree with the lower limit of the proposed model.

Effect of serrated grain boundary on tensile and creep properties of a precipitation strengthened high entropy alloy

ABSTRACT In this study, tensile and creep deformation of a high-entropy alloy processed by selective laser melting (SLM) has been investigated; hot ductility drop was identified at first, and the loss of ductility at elevated temperature was associated with intergranular fracture. By modifying the grain boundary morphology from straight to serration, the hot ductility drop issue has been resolved successfully. The serrated grain boundary could be achieved by reducing the cooling rate of solution heat treatment, which allowed the coarsening of L12 structured γ′ precipitates to interfere with mobile grain boundaries, resulting in undulation of the grain boundary morphology. Tensile and creep tests at 650°C were conducted, and serrated grain boundary could render a significant increase in tensile fracture strain and creep rupture life by a factor of 3.5 and 400, respectively. Detailed microstructure analysis has indicated that serrated grain boundary could distribute strains more evenly than that of straight morphology. The underlying mechanism of deformation with grain boundary serration was further demonstrated by molecular dynamic simulation, which has indicated that serrated grain boundaries could reduce local strain concentration and provide resistance against intergranular cracking. This is the first study to tackle the hot ductility drop issue in a high-entropy alloy fabricated by SLM; it can provide a guideline to develop future high-entropy alloys and design post heat treatment for elevated temperature applications.

Microstructures and high-temperature failure analyses of 25Cr-35Ni-Nb + MA/32Cr-20Ni-Nb dissimilar welded joint with different filler wires

To address the issue of lacking scientific guidance for welding 25Cr-35Ni-Nb + MA/32Cr-20Ni-Nb joint in petrochemical plant applications, the joint microstructures were studied by adopting four types of filler wires. The high-temperature tensile tests and creep rupture tests were performed to investigate joint failure mechanisms. Cellular/columnar dendritic grains were formed at the fusion line region with similar orientations to adjacent un-melted grains. The fine-sized dendritic grains generated at the central weld seam presented a larger misorientation owing to a lowered cooling rate. The lesser alloying element in filler wire led to a larger area with cellular/columnar dendritic grains. The carbide precipitates mostly located at grain boundaries either in the form of particles or necklace structures depending upon the filler wire compositions. The heterogeneous microstructure was thought to be the main reason for the failure at weld seam and fusion line region with large hardness fluctuations when joints welded by the filler wire with a more diverse alloying element. The filler wire with the least introduction of alloying elements, i.e., ERNiCrCoMo-1, gave rise to a more uniform microstructure and hence higher joint property without failing at the weld seam, which was therefore considered as the most suitable filler wire candidate.

Determination of Activation Energy and Prediction of Long-Term Strength of Creep Rupture for Alloy Inconel 740/740H: A Method Based on a New Tensile Creep Rupture Model

Determination of Activation Energy and Prediction of Long-Term Strength of Creep Rupture for Alloy Inconel 740/740H: A Method Based on a New Tensile Creep Rupture Model

Effect of heat treatment on properties and microstructure of steels

Abstract In this study EN 31, EN 24 and EN 8 (alloy steel) are selected as specimens for testing various mechanical properties and microstructure change. The effects of heat treatment on the mechanical properties and microstructure characteristics change of selected specimen are analyzed. Annealing, normalizing and hardening are the most important heat treatment processes often used to change mechanical properties of engineering materials. The purpose of heat treating is to analyze the mechanical properties of the steel, usually ductility, hardness, Yield strength, tensile strength and impact resistance. The heat treatment develops hardness, softness, and improves the mechanical properties such as tensile strength, yield strength, ductility, corrosion resistance and creep rupture. These processes also help to improve machining effect, and make them versatile. The mechanical properties can easily be modified by heat treating to suit a particular design purpose. In the present study, selected samples are heat-treated at certain temperature above the austenitic region and quenched in order to investigate the effect on the mechanical properties and microstructure of the steel. The changes in mechanical behavior and microstructure as compared with unquenched samples are explained in terms of changes in tensile strength. Results showed that the mechanical properties of mild steel can be changed and improved by various heat treatments for a particular application. It was also found that the annealed samples with mainly ferrite structure gave the lowest tensile strength and hardness value and highest ductility and toughness value while hardened sample which comprise martensite gave the highest tensile strength and hardness value and lowest ductility and toughness value.

Evaluating and Modeling of Tensile Creep Rupture Behavior for Neat and Reinforced Polyamide 6.6

Generally, thermoplastic polymers due to their viscoelastic behavior tend to appear creep deformation at low temperature compared to metals; this continuous creep deformation caused irregular shapes with time and resultant unstable dimensional parts. Therefore, the investigation of creep behavior in thermoplastic polymers must be considered as an essential requirement in the design process. This work exanimated the creep rupture behavior for Polyamide 6.6 and their composites which content of 1%MWCNTS or 30 short carbon fibers under variant applied stresses and temperatures, as well as, to create analytical model to the obtained results Findley power law model was employed for this purpose with a comprehensive verification to their compatibility to the experimental results. The results appeared that the addition of reinforced materials and decreasing applied stresses and temperatures will cause an enhancement in creep resistance by increasing rupture time and decreasing the minimum creep rate values. On the other hand, using of Findley power law model gives a good agreement to the obtained experimental results.

Long-term creep rupture strength prediction for a new grade of 9Cr martensitic creep resistant steel (G115)—An application of a new tensile creep rupture model

A method is presented to firstly rationalise the short-term creep rupture strength data and then to predict the 100,000 h creep rupture strengths of a new 9Cr grade of martensitic creep resistant steels (G115) at different temperatures. The method is made possible by a new tensile creep rupture model, which is formulated by combining a new tensile creep model that integrates tensile strength at creep temperature with the Monkman–Grant relationship. On the basis of this new tensile creep rupture model, the activation energy of creep rupture determined for the steel G115, which is 293 ± 25 kJ/mol, does not depend on stress or stress range, and the creep rupture stress exponent depends only on stress range but not on temperature. The model parameters determined from short-term creep rupture strength data can then be used to predict the long-term creep rupture strengths at different temperatures for this new steel grade. The reliability of the predictions is analysed and the microstructural evolutions occurring during creep that may cause premature creep rupture and hence lead to possible over-predictions are also delineated. Based on the prediction results obtained, the highest applicable temperature of this new steel grade for power plant applications is determined to be slightly higher than 625 °C.

Mechanical properties of Grade 91 steel at high temperatures

The tensile and short-term creep rupture properties of Grade 91 steel at high temperatures were investigated. The tensile tests were conducted at room temperature, 565°C and 650°C. The short-term creep tests were conducted at 565°C and 650°C with stress ranging from 125 to 250MPa. The creep rupture life of Grade 91 steel was found to increase with the decreasing of applied stress. The creep rupture morphology was investigated based on the scanning electron microscope analysis.

Small punch and uniaxial creep fracture behaviours of modified SUS304H steel at various temperatures

Commercial austenitic stainless steel SUS304H with small amount of vanadium addition was used in this study. Small punch (SP) creep and uniaxial tensile creep tests were conducted at 650, 700, and 750 °C to measure creep lives and the minimum displacement rates or the minimum creep strain rates. The measured parameters were compared between the two test methods, seeking empirical relationships among the parameters using Larson-Miller Parameter and Monkman-Grant relation. Magnitude of the applied stress (MPa) in the uniaxial tensile creep test was approximately equal to the applied load value (N) in the SP creep test at all test temperatures. It was shown that during the creep deformation of the SP creep specimen, crack initiation and accompanying crack growth occur simultaneously. Competing failure mechanisms of creep deformation and crack growth may affect the SP creep life and consequently determine the proportionality function, α, in the relation between the SP load and the tensile creep rupture stress in creep tests.

Tensile creep behavior of three-dimensional four-step braided SiC/SiC composite at elevated temperature

This article presents experimental results for tensile creep deformation and rupture behavior of three-dimensional four-step braided SiC/SiC composites at 1100°C and 1300°C in air. The creep behavior at 1300°C exhibited a long transient creep regime and the creep rate decreased continuously with time. The creep behavior at 1100°C exhibited an apparent steady-rate regime and the creep deformation was smaller than that at 1300°C. However, the creep rupture time at both temperatures showed little difference. The mechanisms controlling creep deformation and rupture behavior were analyzed.

Effect of texture on anisotropy at 600 °C in a near-α titanium alloy Ti60 plate

To study the anisotropy of mechanical properties at 600°C in a near-α titanium alloy Ti60, a highly T-type textured plate was prepared, and tensile tests, creep tests and creep rupture tests were carried out at 600°C. Notable anisotropies were observed in all three kinds of mechanical tests. The deformation in TD was much harder than in RD，no matter high or low was the loading stress. The anisotropy of tensile properties was concluded to be related to the different Schmid Factors distribution caused by T-type texture, leading to prismatic <a> slips easily being activated in RD and both prismatic <a> and basal <a> slips hard to be activated in TD. The restriction of creep deformation in TD samples was believed resulting from the effect of T-type texture on self- and solute diffusion. For the anisotropy of creep rupture properties, it was deduced to be a result of the combined anisotropy of diffusion and dislocation slipping.

Analysis of Mechanical Behavior and Microstructural Characteristics Change of ASTM A-36 Steel Applying Various Heat Treatment

In this study ASTM A-36 (mild steel) is selected as specimen for testing various mechanical properties and microstructure change. The effects of heat treatment on the mechanical properties and microstructure characteristics change of selected specimen are analyzed. Annealing, hardening and tempering are the most important heat treatment processes often used to change mechanical properties of engineering materials. The purpose of heat treating is to analyze the mechanical properties of the steel, usually ductility, hardness, Yield strength, tensile strength and impact resistance. The heat treatment develops hardness, softness, and improves the mechanical properties such as tensile strength, yield strength, ductility, corrosion resistance and creep rupture. These processes also help to improve machining effect, and make them versatile. The mechanical properties can easily be modified by heat treating to suit a particular design purpose. In the present study, selected samples are heat-treated at certain temperature above the austenitic region and quenched in order to investigate the effect on the mechanical properties microstructure of the mild steel. The changes in mechanical behavior and microstructure as compared with unquenched samples are explained in terms of changes in tensile strength. Results showed that the mechanical properties of mild steel can be changed and improved by various heat treatments for a particular application.

High temperature tensile test and creep rupture strength prediction of T92/Super304H dissimilar steel weld joints

After short term tensile test at 823–923 K, microstructure, fractography and fracture mechanism of the T92/Super304H dissimilar steel weld joints were studied. In the high temperature tensile process, the fracture location of all joints is in the T92 base metal; however, the fracture mechanism of these joints changes from a normal mode to a shear mode with the increase of the temperature. Moreover, an equation of the creep rupture strength related to the short term tensile strength of the joints was firstly derived in terms of the Goldenberg model. And then the creep rupture strength of the joints was obtained, = 42·7 MPa.

Influence of thermal exposure on the microstructural evolution and mechanical properties of a wrought Ni-base superalloy

Phase transformation and microstructural evolution of a wrought Ni-base superalloy Alloy 263 during long-term exposure to high temperatures have been studied. The influence of thermal degradation on tensile and creep properties of the alloy has been also investigated. Exposure of the alloy to 700°C resulted in precipitation of small blocky type M23C6 carbides in the matrix. Acicular type M23C6 carbides also precipitated at the incoherent twin boundary and grew on the microtwins in front of the incoherent twin boundary. A plate-like η phase precipitated in the alloy with γ′ particle depletion zone around η plate after long-term exposure to 750°C and above. Tensile strength of the alloy increased after exposure to 700°C due to precipitation of M23C6 carbides. Tensile strength and creep rupture life decreased after exposure to 750°C and above due to coarsening of γ′ particle and formation of η phase. Cracks nucleated at the interface between M23C6 carbide and matrix on the grain boundary and grew along the grain boundary irrespective of precipitation of η phase. Formation of η phase might change the deformation behavior, but it does not have influence on the fracture mode of the alloy.

Microstructures and High-Temperature Mechanical Properties of a Martensitic Heat-Resistant Stainless Steel 403Nb Processed by Thermo-Mechanical Treatment

Thermo-mechanical treatments (TMT) at different rolling deformation temperatures were utilized to process a martensitic heat-resistant stainless steel 403Nb containing 12 wt pct Cr and small additions of Nb and V. Microstructures and mechanical properties at room and elevated temperatures were characterized by scanning electron microscopy, transmission electron microscopy, and hardness, tensile, and creep tests. The results showed that high-temperature mechanical behavior after TMT can be greatly improved and microstructures with refined martensitic lath and finely dispersed nanosized MX carbides could be produced. The particle sizes of M23C6 and MX carbides in 403Nb steel after conventional normalizing and tempering (NT) treatments are about 50 to 160 and 10 to 20 nm, respectively, while those after TMT at 1123 K (850 °C) and subsequent tempering at 923 K (650 °C) for 2 hours reach about 25 to 85 and 5 to 10 nm, respectively. Under the condition of 260 MPa and 873 K (600 °C), the tensile creep rupture life of 403Nb steel after TMT at 1123 K (850 °C) is 455 hours, more than 3 times that after conventional NT processes. The mechanisms for improving mechanical properties at elevated temperature were analyzed in association with the existence of finely dispersed nanosized MX particles within martensitic lath. It is the nanosized MX particles having the higher stability at elevated temperature that assist both dislocation hardening and sub-grain hardening for longer duration by pinning the movement of dislocations and sub-grain boundary migration.

High-temperature short-term tensile test and creep rupture strength prediction of the T92/TP347H dissimilar steel weld joints

After short-term tensile test at 848–923K, microstructures, fractographies and fractural mechanisms of the T92/TP347H dissimilar steel weld joints were studied. An equation of the creep rupture strength related to the short-term tensile strength of the joints was firstly derived based on the Goldenberg model [1]. In the high-temperature tensile process, the fracture location of the joints is all in the T92 side fine grained heat affected zone (FGHAZ); however, the fracture mechanism of the joints is changed from a mixed mode (normal plus shear) to a shear mode as the testing temperature risen, which was explained in terms of the stress tri-axiality theory. Moreover, an equation of the creep rupture strength of the weld joints was derived, and then the creep rupture strength of the joints was doped out, σ105873=49.0MPa. It indicates that the joints have a high reliability when used in the USC power units.

Inconel 718 の微視組織と機械的特性に及ぼす TIG 溶接の影響

The effect of welding on microstructure and mechanical properties of Inconel 718 was investigated. In this study, the specimens welded by TIG (Tungsten Inert Gas) welding were subjected to two kinds of post-weld heat treatment (PWHT): 954℃ solution treatment+aging and 1045℃ solution treatment+aging. In both the solution treatments, two kinds of intermetallic compounds were observed in the interdendritic region of the weld metal, where δ-phase (Ni3Nb) and Laves-phase ((Ni,Cr,Fe)2(Nb,Ti,Al)) were precipitated. The relationship between mechanical properties and microstructures was examined. The tensile strength, elongation and creep rupture time of the weld specimen treated at 954℃ were decreased by TIG welding due to the coalescence of voids formed around Laves particles in the weld metal. Compared with the base metal, the hardness was decreased in the weld metal while it increased in HAZ (Heat Affected Zone). The solution treatment at 1045℃ resulted in dissolution of much more detrimental phases than the solution treatment at 954℃. As a result, the ductility and creep strength of weld specimen treated at 1045℃ were better than those of specimen treated at 954℃.

Dependence of Creep Deformation Behavior in the Root of Notch on Creep Rupture Life

The object of the investigation was to examine the dependence of creep strain in root of notch on the creep rupture life for the round bar with the circumferential V-notch during the short-time creep at high temperature. In the long-time creep under the low stress, it is possible to estimate the stress and strain distributions of notch root only from the creep deformation. However, it is necessary to sufficiently consider the plastic deformation under the creep of the load of the relatively high stress, since elastic, plastic and creep deformation are dependent on each other. In this study, the tensile creep rupture tests of the circumferential 60° V-notched bar for a type SUS 304 stainless steel were carried out at 873K in the air, and in order to discussed the deformation at the notch root under short-time creep in the laboratory, elasticity, plasticity and creep analysis were carried out using a finite element method (FEM). The elongation of the notch groove was measured under creep test and compared with the results of FEM analysis using the plastic and creep constitutive equations which were determined from the tension test and the tensile creep testing of smooth specimen. A considerably good agreement is obtained between the numerically computed and the experimentally observed plastic and creep deformation behaviors of the notched bars under constant loading, and the conclusion was got like that the mean creep strain rate between the edges of the V-shaped notch governs creep deformation and rupture under highly constrained deformation in tri-axial states of stress.