Residual Stress Relief Research Articles

Potential of Date-Seed/Snail Shells as a Carburizer for Enhanced Mechanical Properties of Mild-Steel

The suitability of date-seed/snail shells as a carburizer for enhanced mechanical properties of mild-steel using the packed carburization technique was investigated in this work. Standard tensile, impact and hardness test samples prepared from mild-steel were subjected to pack-carburization process using mixtures of date-seed and snail shell in the ratio 60:40 respectively at 800, 900, and 1 000 °C for 3 hours. The carburized samples were quenched in water at room temperature and further tempered at 300 °C for 30 minutes for residual stress relief of the quenching effect. The mechanical properties and optical microstructure of carburized specimen were performed. Results indicated an enhanced mechanical property of the carburized mild-steel using date-steel/snail shell as a carburizer compared to un-carburized same steel material. The tensile strength and hardness increased with increasing carburizing temperature, though with an associated decrease in ductility. The peak hardness (32.82 HRB) and tensile strength (521 MPa) with equivalent 31.28 and 51.45 percentage increments respectively were obtained at carburizing temperature of 1 000 °C. Hence, using date-seed/snail shell powder as a carburizer can enhance the mechanical properties of mild-steel.

Setup of a numerical model for Post Welding Heat Treatment simulation of steel joints

A 3D numerical model aimed at predicting the deformations of a S355 steel T-joint in both as-welded and post-welding heat treated conditions was developed. Experimental tests were carried out with the objective to collect data necessary to the heat source calibration and model validation in terms of microstructure and joint distortions. All metallurgical phenomena were taken into account such as specific volume change and transformation plasticity induced by solid-state phase transformations. A viscoplasticity model for stress relief processing implemented in Sysweld finite elements code was used. Numerical results showed a satisfactory agreement with experimental ones. Further investigations will be necessary to consider also the validation of residual stress relief effects.

Uticaj postupka nakon izrade na površinski zaostali napon kod nerđajućeg čelika 316L proizvedenog aditivnim postupkom

In this work, an investigation was made to analyze the surface residual stresses on additive manufactured stainless steel AISI 316L in as-built and post-treated conditions. Direct metal laser sintering was used to fabricate the metal blocks. X-ray residual stress analysis on the as-fabricated surface revealed the presence of an inhomogeneous and irregular distribution of residual stresses in the as-built condition ranging from - 30 MPa to 111 MPa. It was mainly due to the localized laser heat source that caused variations in stresses at a lattice level. Heat treatment was performed for providing relief to the residual stress from the as-built condition showed significant relief of residual stress, which was lesser than 50% compared to as-built condition. Beneficial compressive residual stress induced by shot peening and lapping resulted in high magnitude compressive stresses on the surface. Also, homogeneous distribution of residual stress was found on the peened and lapped surface layer with an average of - 531 MPa and - 554 MPa, respectively.

Effect of fire exposure on residual stresses relief in welded high strength Q690 steel sections

Welding induced residual stresses in steel sections can be reduced by high temperatures in fire conditions and thus affect the load bearing capacity and stiffness of structural steel members. This paper presents effect of high temperature exposure on residual stresses relief in welded high-strength Q690 steel sections by experimental and numerical studies. The distribution and magnitude of the residual stresses in three Q690 steel H-sections and three Q690 steel box-sections after exposure to 600 °C and 800 °C were investigated by cutting method. In the numerical studies, finite element analysis software ANSYS was employed to simulate residual stress generation and relief in the entire welding and high temperature exposure stages, including the heating and cooling phases. The predicted results of the residual stresses after an exposure to high temperature obtained by the finite element analysis agree well with the test results. Parametric studies were conducted to investigate the influence of exposed temperature, high temperature duration, and creep strain in steel on residual stresses after being exposed to high temperature. For welded Q690 steel H- sections and box-sections, equations to evaluate the corresponding residual stress reduction factor at elevated temperatures and after high temperature exposure were proposed based on the results of finite element analysis.

A detailed analysis on the microstructure and compressive properties of selective laser melted Ti6Al4V lattice structures

In this paper, Ti6Al4V octahedron lattice structures with top cap and bottom base were fabricated through selective laser melting (SLM). The structural integrity, microstructural evolution, compressive properties and failure mechanism of as-fabricated (AF) and vacuum annealing treated (VAT) samples were studied through both experiments and numerical modeling. The X-ray computed tomography analysis revealed that vacuum annealing had an insignificant effect on internal pore elimination and porosity reduction. For both the AF and VAT samples, larger pores exhibited more irregular shape than smaller pores. The microstructural analysis suggested that vacuum annealing was able to transform acicular α/α` martensites into uniformly distributed lamellar α + β phases and also to cause the formation of nano-particle precipitation and dislocation. The compressive test indicted that the lattice structure with confined top and bottom had much better compressive properties than those without. Also, vacuum annealing significantly improved the compressive strength by 26% due to the synergistic effect of residual stress relief, nano-particle precipitation and dislocation strengthening. The ductility of the VAT sample was also improved as compared to the AF sample, which was mainly attributed to the formation of α + β phases.

Formation of Discontinuities in Rectangular Plates as a Result of Residual Stress Relief

The paper deals with the problem of relieving residual stresses in an elastic domain of rectangular shape with free sides as a result of the formation of a discontinuity of particular shape. First, we construct the solution to the problem of residual stresses in an infinite strip with free sides and with a central transverse cut on which a discontinuity of displacements is known. Then, the solution for a rectangle is added to this solution, with the help of which the boundary conditions at the ends are satisfied. The formulas for the residual stresses and for the corresponding displacements are represented in the form of series in Papkovich-Fadle eigenfunctions. The expansion coefficients (Lagrange coefficients) have the form of simple Fourier integrals.

In-situ neutron diffraction study on the high temperature thermal phase evolution of wire-arc additively manufactured Ni53Ti47 binary alloy

In the present research, to further reduce the fabrication and forming cost of NiTi alloy, an innovative wire-arc additive manufacturing process (WAAM), which is simultaneously an in-situ alloying process, has been applied to fabricate polycrystalline Ni53Ti47. The as-fabricated alloy is subsequently subjected to a necessary post-production annealing for additively manufactured metals. During the thermal cycle, to characterize the obtained phases in the Ni53Ti47 alloy and provide dynamic lattice evolution information, neutron diffraction is conducted to the heated sample in real time. It is found that the metastable Ni4Ti3 phase is only obtained in the heat-treated alloy while the as-fabricated NiTi alloy produced by WAAM contains only NiTi and Ni3Ti. The generated Ni4Ti3 precipitates have increased the NiTi phase micro strains. The hcp-Ni3Ti lattice evolution is found inducing converse lattice shrinkage and expansion in bcc-NiTi lattice during the dissolution and precipitation of Ni3Ti, respectively. The WAAM induced residual stress in the as-fabricated alloy is tensile and during the residual stress relief, the thermal expansion rate of Ni and Ni3Ti are reduced. In addition, the thermal expansion coefficient of NiTi and Ni3Ti is measured according to the neutron Rietveld refinement as 0.040 × 10−3 °C−1 and 0.036 × 10−3 °C−1, respectively.

Effects of stress-relief heat treatment on the microstructure and fatigue property of a laser additive manufactured 12CrNi2 low alloy steel

In this study, the impact of stress-relief heat treatment on the microstructure and fatigue property of a laser melting deposited (LMD) 12CrNi2 low alloy steel was analyzed. Microstructural evolution of processed LMD 12CrNi2 steel by heat treatment was studied using electron backscatter diffraction (EBSD) and X-ray diffraction (XRD), aiming to establish a rational microstructure-fatigue property relationship. The results showed that the main phase of the samples before and after heat treatment was α-Fe phase, whereas the lattice parameter slightly decreased after annealing, as a result of stress relief and carbide formation in the heat-treated samples. Meanwhile, the increase of the hard and diffusely distributed carbides inside the matrix was the main contributor for the higher material strength. Based on the EBSD analysis, the heat treatment decreased grain boundary misorientation leading to a corresponding reduction in the dislocation density, and increased the content of high-angle grain boundaries (HAGBs) promoting the toughness of the material. Furthermore, Schmid factor results revealed that the heat-treated samples exhibited a relatively high ductility resulting from the activation for more slip systems during the cyclic deformation. The stress-relief heat treatment significantly improved the fatigue performance of samples, which was attributed to the enhanced strength and ductility owing to the related microstructure change and the relief of residual stresses.

Influence of stress relief annealing temperature on the cutting edge microstructure and on the recovery of magnetic properties of grain oriented electrical steel

The effect of stress relief annealing temperature on the recovery of the magnetic properties deteriorated by strain and stresses introduced by shear cutting was analyzed in this study. Shear cut Epstein samples of grain oriented electrical steel were submitted to heat treatment at different annealing temperatures (600–900 °C). The magnetic properties were measured before and after annealing. The microstructures of the sheared edges before and after annealing were characterized using scanning electron microscope (SEM) equipped with electron backscattered diffraction (EBSD) in which it was possible to characterize the recovery and recrystallization processes responsible for the stored energy release in the shear cut region. The magnetic properties were improved with the increase of the annealing temperature due to recovery, recrystallization and the relief of residual stresses.

Better mechanical properties via uniform microstructure architecture in flash-butt welded TA19 joints

Both ductility and strength are simultaneously improved via the tailoring of uniform microstructure in a flash-butt welded TA19 joint that is subjected to an appropriate post-weld heat treatment (PWHT). The PWHT sample exhibits almost the same ductility (i.e., elongation and reduction in area) as the matrix that was treated at the same conditions. Such uniform microstructural characteristics, including relief of tensile residual stress, formation of large α grains at the welding seam, dissolution of a continuous α phase at the grain boundary, recrystallization and moderate growth of primary α (αp) at the thermo-mechanically affected zone, and recovery, recrystallization and significant growth of αp grains in the stress-affected zone, are responsible for at least ~25% of the ductility improvement. Also, the increase in strength stems mainly from age hardening of the matrix that accounts for ~90% of the material volume at the gauge length. This paper provides a guideline for microstructural architecture that has desirable uniformity in other welded Ti alloys to maintain high performance.

Residual stress relief of welded aluminum alloy plate using ultrasonic vibration

Ultrasonic vibratory stress relief (UVSR) is a novel method for residual stress relieving of metal parts. In this paper, the UVSR method was applied to treat a random-sized plate, which is not designed to match with the resonant frequency of the ultrasonic transducer. The UVSR system includes an ultrasonic generator, a 20 kHz ultrasonic transducer and specially designed fixtures to exert ultrasonic vibration to the treated parts. Based on the experimental results, the average stress relief ratio reached 53% and the final residual stress distribution interval was reduced by 57. The vibratory stress introduced by the ultrasonic vibration was obtained accurately by matching the FE model with the measured vibration amplitude distribution. It is found that local yield stress, instead of macroscopic yield stress, should be used as the threshold of residual stress relieving. Moreover, if the local yield stress of a material is constant, the local yield stress of 6082 aluminum alloy is reduced by at least 27% during the UVSR. Finally, it is found that the residual stress relief rate in one direction is proportional to the vibratory stress introduced in that direction.

Stress relief investigation using creep model considering back stress in welded rotor

Welded ferritic steel rotors are a critical dynamic component of fossil-fired power plants. It is essential to investigate residual stress distribution in welded rotors and investigate methods to reduce residual stress for improving structural integrity. In the present study, a creep model that considers back stress is introduced in the residual stress relief simulation of welded ferritic steel rotors in furnace-based uniform post weld heat treatment. Comparisons between the new and Norton–Bailey creep model were conducted numerically, and results indicate that the new creep model can inherit the as-welded residual stress distribution and simulate post weld heat treatment (PWHT) residual stress more accurately, which has been validated with experimental results. Furthermore, it is discovered that the dominant stress relief mechanism of ferritic steel is creep-strain-induced stress relaxation. The creep strain occurred primarily in a short time with a dislocation creep mechanism, and the holding time hardly affected the generation of creep strain. Increasing the PWHT temperature enables more stress relaxation at low temperatures. Additionally, stress relaxation almost no longer occurred when the PWHT temperature exceeded a critical value (approximately 520 °C in this study) that was lower than the recrystallisation temperature. Hence, it is important to control the welded residual stress.

Study on Residual Stress Relief Technology Using Phase Transformation in Metal Additive Manufacturing

For the manufacture of plastic molds and die casting molds, metal optical modeling of the PBF system capable of creating a cooling pipe inside is effective, and effects of shortening of the production cycle and improvement of the accuracy are obtained. However, the metal optical modeling of the PBF system has problems of warpage and cracking, and it is difficult to manufacture a shape object in which stress concentration occurs or a large modeled.

The use of eigenstrain theory and fuzzy techniques for intelligent modeling of residual stress and creep relaxation in welded superalloys

Ni-base superalloys are used in a wide range of applications where components made from these alloys are exposed to extreme conditions of high temperature and high pressure, and dependable performance is critical for mission success, the safety of human lives, and multi-million commercial investment. To ensure robustness and reliability of highly demanding engineering solutions, it is crucial to advance the development of cutting-edge computational design tools based on artificial intelligence and fuzzy techniques, combined with the application of materials characterization and materials design. In the present study, the use of the contour method in combination with eigenstrain theory provided new insights into 3D residual stress states in Ni-base superalloy samples. As-welded and heat-treated specimens were made using bead-on-plate design to investigate the effect of complex fabrication conditions on welds process in large components. The widely used relief of residual stresses during post-weld heat treatment was simulated using eigenstrain-creep model. Furthermore, artificial intelligence (AI) based eigenstrain-contour and eigenstrain-creep models, that use fuzzy techniques, were developed by the present authors for materials used in advanced ultra-supercritical coal-powered plants, showing good match with experiments. The present study reports the combination of eigenstrain theory with artificial intelligence for the modelling of welding residual stresses and simulation of post-weld heat treatment process and highlights the benefits of AI-based eigenstrain-contour and eigenstrain-creep methods on the development of robust and reliable aeroengine components.

Quantification of CTOD fracture toughness in welded joints to evaluate the efficacy of vibration stress relief compared to thermal stress relief

Resonant vibration residual stress relief (R-VSR) is an alternative method to post-weld heat treatments (PWHT) which is said to lead to less distortion and lower costs. The method of superposition of cyclic stresses and residual stresses, which can lead to localized yielding of the material, dislocation movement and subsequent stress relief. This article aims at investigating the efficiency of resonant vibration in the relief of residual stresses in welded joints of HSLA Domex700 steel sheets. Mechanical stress relief was compared to a common PWHT, and stress levels were then quantified through X-ray diffraction. Samples were also characterized by CTOD fracture toughness tests, fractographic analysis and tensile tests. Results indicate that the mechanical method was significantly less effective in relieving stresses in comparison with the PWHT, but led to apparent improvements in fracture toughness and in tensile tests. FWHM values indicated significant distortion for PWHT and less distortion for R-VSR.

Stub column behaviour of heat-treated and galvanized RHS manufactured by different methods

A complementary study showed that hot-dip galvanizing can sometimes significantly change the residual stress properties of cold-formed rectangular hollow sections (RHS). Hot dipping the RHS specimens in a molten zinc bath maintained at 450 °C for 10 min provided a partial residual stress relief comparable to the onerous heat treatment specified in ASTM A1085 and CSA G40.20/G40.21. Hence, further research is needed to: (1) quantify the effects of galvanizing, and (2) determine the optimized heat treatment duration for a partial residual stress relief for improvement of column behaviour. In this study, the effects of galvanizing and heat treatments to different degrees on the stub column behaviour of cold-formed RHS has been investigated comprehensively for the first time, by means of 36 stub column tests. The RHS specimens were manufactured by two dominant cold-forming methods: (1) indirect-forming from circular to rectangular, and (2) direct-forming. The nominal yield stresses of the materials ranged from 350 to 690 MPa. The RHS stub column test matrix has 10 different width-to-thickness ratios and includes both nonslender and slender sections.

Superior mechanical properties of 40Cr steel obtained by quenching and microstress relieving under electropulsing

High strength (the yield strength and ultimate tensile strength are 1920 ± 17 MPa and 2241 ± 39 MPa, respectively) and good ductility (15.2 ± 1.1%) are achieved simultaneously in 40Cr steel via electropulsing quenching (EQ) and tempering (ET). It was found that EQ contributes to ultra-fine martensite with high dislocation density and grain rotations (<110> texture distributed along the current direction and large Schmid factor). Meanwhile, ET is insufficient to modify the orientation, while it makes a rapid relief of micro residual stress without significantly decreasing the dislocation density. Compared to the conventional heat treatment, it provides a promising approach for enhancing the mechanical properties of steels in a short time.

Microstructural Origin of Residual Stress Relief in Aluminum

Annealing-induced microstructural evolution and associated stress relief were investigated experimentally for various crystallographic orientations and annealing temperatures. Combinations of the site and orientation-specific X-ray plus electron diffraction were used. 2-D discrete dislocation dynamics, oriented for double slip with both dislocation glide and climb mechanisms, was employed to simulate the annealing process. Irrespective of crystal orientation, both experiments and simulations showed the highest stress relief at the intermediate annealing temperature. In the experiments, this was related to the fastest elimination of low angle grain boundaries. In the simulations, it was linked to the largest reduction in the density of pinned dislocations. The simulations also suggested that the non-monotonic temperature dependence of the stress relief, and associated substructural changes, emerged from a balance between dislocation glide and climb processes.

The Effect of Localized Vibration during Welding on the Microstructure and Mechanical Behavior of Steel Welds.

The use of vibratory welding is treated with some caution in the industry due to inconsistent beneficiary results. Here, a partial explanation is suggested by the differentiation between global vibrational effects (GVEs) and local vibrational effects (LVEs), and the latter is investigated experimentally. Two structural plates of steel are welded at three frequency/amplitude combinations using manual gas metal arc welding in an experimental setup that ensures only LVEs. After welding, tensile tests, microhardness tests, and metallurgical characterization are performed locally in the different welding zones and the results are compared to the non-vibrated welds. Novel use of digital image correlation (DIC) is implemented in tensile testing of welded samples, thus enabling the separate determination of local mechanical properties of the base metal, heat-affected zone and fusion zone of the same weld. LVE is found not to promote any distinct difference in weld properties, at least within the vibrational regimes studied. Nevertheless, depending on geometry and structural response, it is explained how vibratory welding may promote residual stress relief due to GVEs of the welded structure.

Effect of heat treatment on microstructure and mechanical behaviours of 18Ni-300 maraging steel manufactured by selective laser melting

Selective laser melting (SLM) of 18Ni-300 maraging steel is an important research area in view of its numerous applications in the automotive domain. Heat treatment plays a significant role in the microstructure and mechanical behaviour of maraging steels and is a major area of interest. This paper investigated the effect of heat treatment on microstructure and mechanical behaviour of SLM-built 18Ni-300 maraging steel. The experimental results showed that the densest parts with the smallest number of defects were fabricated at optimum laser energy density of 70 J/mm3 and laser power of 275 W. When the laser power was fixed at 275 W, lower laser energy density resulted in the formation of balling and irregular pores, while higher laser energy density induced spherical pores and microcracks. The as-built samples consisted of cellular and columnar microstructures due to the fast cooling and solidification rates during SLM. However, solution treatment led to changes in the typical microstructure and massive lath martensite phase. The tensile strength and microhardness decreased slightly due to grain growth and residual stress relief upon solution treatment; an opposite effect was observed when the samples were subjected to solution treatment followed by aging at 490 °C for 2 h. With regard to the tensile anisotropy, yield strength and ultimate tensile strength of the horizontally-built samples slightly exceeded those vertically-built. These findings are significant as they allow an informed prediction about the effect of various heat treatments on the microstructure and mechanical behaviour of components manufactured from 18Ni-300 maraging steel using the SLM process.