Stress Relief Heat Treatment Research Articles

Revealing the embrittlement phenomena after post-weld heat treatment of high-strength weld metal using high-resolution microscopy

High strength combined with sufficient toughness is a fundamental prerequisite for steel in the field of lightweight construction. Joining high-strength steels by means of welding requires the use of highly advanced filler metals and a stress-relief post-weld heat treatment (PWHT) for optimum performance of the joint. However, such a heat treatment can lead to embrittlement in the weld metal. In this context, the present work deals with the influence of different PWHT holding temperatures on the microstructure and mechanical properties of a high-strength multipass all-weld metal to reveal the embrittlement phenomena. The all-weld metal was fabricated via gas metal arc welding using a metal cored wire with a minimum yield strength of 690 MPa. Charpy V-notch impact testing and tensile testing were carried out to characterize the strength and toughness of the all-weld metal in the as-welded condition and after a 2 h stress-relief PWHT at 520 °C, 580 °C, and 620 °C. The microstructure was characterized utilizing high-resolution techniques such as atom probe tomography and high-energy X-ray diffraction. The strength and toughness of the all-weld metal both decrease after PWHT with different holding temperatures. The cause for the observed embrittlement was found to be the formation of Mn-rich cementite precipitates. These carbides increase in size and phase fraction with increasing holding temperature and lead to a brittle transcrystalline cleavage fracture. Consequently, it was concluded that a gas metal arc welded joint with the investigated filler metal should not be exposed to stress-relief PWHT at temperatures higher than 580 °C.

A Bibliometric Analysis of the Global Trend of Residual Stress Induced by WAAM Process and Stress Relief Heat Treatment

Gathering data from previous research and incorporating it into a scientometrics investigation can provide valuable insights into a particular area of study. Wire Arc Additive Manufacturing (WAAM) is currently popular for producing customized metal products quickly. Despite this, there have been lack of studies on implementing stress relief heat treatment after the manufacturing process to reduce residual stress in the resulting parts potentially. This paper represents the first bibliometric analysis study focusing on the application of stress-relief heat treatment as a post-processing method for wire arc additive manufacturing (WAAM). Given the exploratory nature of this research, it is expected that future investigations will continue to delve into these areas, ultimately contributing to a better understanding of the effects of stress-relief heat treatment on the additively manufactured materials.

Stress Corrosion Cracking of Manganese Bronze in Water

AbstractContinuous and centrifugal cast manganese bronze parts (C86300) experienced intergranular cracking in as few as 24 h after being stored outside. C-ring tests according to ASTM G38 were conducted to assess the material’s susceptibility to stress corrosion cracking (SCC) susceptibility and found that water was the most likely agent. The failure mechanism has been identified as intergranular SCC due to a combination of residual stress from a rough machining operation and water from rain or dew. To prevent cracking, a stress relief heat treatment immediately after the rough machining operation is recommended.

Indentation parameters and corrosion resistance of explosive welded S30400/Q345R clad plates with heat treatment cycles

This study aims to clarify the indentation parameters and corrosion resistance of explosive welded S30400/Q345R clad plates with heat treatment cycles. A series of tests on the mechanical properties of the clad plate in the unseparated state of clad material (CM) and base material (BM) and its free surface corrosion resistance, as well as their evolution with stress relief heat treatment are studied and discussed. The results show that the severely carburised layer (SCL) that occurs on the stainless steel side of the heat treatment was the peak hardness of the entire clad plate, which was significantly reduced after four heat treatments. The worst mechanical performance was observed in three heat treatments. The reduction in free surface corrosion resistance of CM is linearly correlated with the number of heat treatments, but this does not hold true for BM. This study provides valuable references for the assessment of performance loss under heat treatment of clad plates.

Effects of stress-relief and natural aging on the geometric tolerances and functional requirements of ferritic nitrocarburized gray cast iron brake rotors

Gray cast iron (GCI) brake rotors are prone to corrosion, particularly in electric vehicles (EVs), owing to their regenerative braking systems. Ferritic nitrocarburizing (FNC) heat treatment has been used to improve the corrosion resistance and cleanability of GCI rotors. However, pre-existing residual stresses in the rotors can lead to distortion after FNC processing, thereby affecting the functional and tolerance requirements. This study investigated the effects of stress-relief (SR) heat treatment and natural aging (NA) on the natural frequency, damping properties, surface roughness, and geometric tolerances of GCI brake rotors before and after FNC treatment. The GCI brake rotors were subjected to SR and NA processes, followed by FNC treatment. The natural frequency, damping Q-factor, surface roughness, and geometric tolerances were measured and analyzed using two-way ANOVA at a 95% confidence level (α = 0.05). The results showed that SR heat treatment significantly reduced the effect of residual stresses and improved geometric tolerances compared to NA. The FNC treatment increased the surface roughness and slightly improved the damping properties but had an insignificant effect on the natural frequency. The combination of SR and FNC treatments provided the best overall performance in terms of quality, geometric tolerance, and surface finish. This study highlights the importance of SR heat treatment for optimizing the manufacturing process of FNC-treated GCI brake rotors for EVs.

Effect of stress-relief heat treatment on the stress-rupture properties of a nickel-based superalloy manufactured by laser powder bed fusion

Residual stress is a ubiquitous phenomenon in laser powder bed fusion (LPBF) metal parts due to high temperature gradients and uneven heating during building processes. Subsequent stress-relief (SR) heat treatment is usually conducted to reduce the geometrical distortion and microscopic cracks induced by residual stress after the LPBF process. Using electron microscopy, X-ray diffraction, and stress-rupture tests, the experimental results revealed that the stress-rupture life of a nickel-based superalloy, IN625 alloy, subjected to SR treatment at 870°C and 980°C is inferior to that of the as-built (AB) alloy. The fundamental cause for this phenomenon is that more δ phase precipitates in the grains of the AB alloy during the stress-rupture test at 750°C/230 MPa, resulting in an increased dispersion hardening effect and a decreased ductility. Furthermore, the Laves and δ phases along grain boundaries in the SR treated alloys are more likely to coarsen, which is the second reason for the decreased stress-rupture life of the SR treated alloys.

Evolution of Microstructure During Stress Relieving Heat Treatment of 1S Aluminium

Aluminium and its alloys are extensively used in nuclear research reactors due to its low neutron absorption coefficient, good heat transfer properties, excellent corrosion and oxidation resistance in air and water environment combined with desirable mechanical properties along with considerable radiation stability. The thin walled tubes are normally manufactured through port hole die extrusion route and used in 'O' tempered condition. The thin tubes in 'O' tempered condition are undergone canning operation which may alter the microstructural features to some extent which may affect mechanical properties. The paper describes the extent to which microstructural and subsequently mechanical properties are altered due to the simulated canning process and further requirements of stress relieving heat treatment to restore the microstructural features and mechanical properties. The following studies are carried out with 1S aluminum tube in 'O' tempered state, simulated canning condition and stress relieved at different temperature, - hardness measurement, X ray line profile analysis for dislocation density measurement, tensile properties measurement using ring tensile testing, electron back scattered diffraction (EBSD) analysis for recrystallization fraction determination and changes in texture components. It is found that the canning operation changes dislocation density, micro-strain, coherent domain size which are well reflected in hardness and ring tensile testing. Subsequent stress relieving at 350°C for 2 hrs. leads to improvement of mechanical properties appreciably.

Fatigue Strength Assessment of Friction Welds under Consideration of Residual Stress.

A reliable local-fatigue assessment approach for rotary friction-welded components does not yet exist. The scope of this paper is to present test results for the fatigue behaviour of rotary friction-welded solid shafts made of structural steel S355J2G3 (1.0570) and an approach to fatigue assessment considering residual stress. In contrast to fusion-welded joints, components made by rotary friction welding usually contain compressive residual stress near the weld, which can significantly affect the fatigue strength. For this purpose, specimens were welded and characterised, including metallographic micrographs, hardness measurements, and residual stress measurements. The fatigue tests were performed with a constant amplitude loading in tension/compression or torsion with R = -1. All specimens were investigated without machining of the weld flash, either in the as-welded state or after a post-weld stress-relief heat treatment. In addition, the friction welding process and the residual stress formation were analysed using numerical simulation. The characterisation results are integrated into a fatigue assessment approach. Overall, the specimens perform comparatively well in the fatigue tests and the experimentally observed fatigue behaviour is well described using the proposed local approaches.

Electrodeposited Ni–Co–B coatings: Preparation and evaluation of its wear resistance

Ni–Co–B coating was electrodeposited in sulfate bath with dimethylamine borane (DMAB) as reducing agent. The experiment explored the effect of DMAB concentration (CDMAB, 1–10 g/L), current density (Jk, 2–8 A/dm2), bath temperature (Tbath, 30–60 °C) on the coating morphology and hardness, and determined the best parameters: CDMAB = 8 g/L, Tbath = 60 °C, Jk = 4 A/dm2. The average hardness of the crack-free coating is 818 HV, and the B content is about 2 wt%. In order to develop a stress-relieving heat treatment scheme, the effects of heat treatment temperatures (100–500 °C) and holding times (1.5 h and 3 h) on the hardness of Ni–Co–B coating were studied. The highest hardness (1130 HV) is obtained at 350 °C for 1.5 h. The heat-treated Ni–Co–B coating was characterized by XRD, SEM and EPMA, and the second phase Ni3B was detected. In addition, the wear resistance and wear mechanism of the coating at room temperature and high temperature (300 °C) were studied. The results show that the wear volume of Ni–Co–B coating is reduced by more than 55% compared with Ni–Co coating. In general, Ni–Co–B coating can be used as an alternative to Ni–Co wear-resistant coating.

Evolution of interphase stress over a crack propagation plane as a function of stress relief heat treatments in a PBF‐LB/M AlSi10Mg alloy

AbstractIn this study, we compare the residual stress state in a laser powder bed fusion (PBF‐LB/M) AlSi10Mg alloy in the as‐built (AB) condition with that after two different heat treatments (265 °C for 1 h, HT1; and 300 °C for 2 h, HT2). The bulk residual stress (RS) is determined using synchrotron X‐ray diffraction (SXRD), and near‐surface profiles are determined using laboratory energy‐dispersive X‐ray diffraction (EDXRD). The EDXRD results do not reveal any notable difference between the conditions at a depth of 350 μm, suggesting that the machining process yields a comparable residual stress state in the near‐surface regions. On the other hand, the SXRD results show that HT1 is more effective in relieving the bulk RS. It is observed that HT1 reduces the RS state in both the aluminium matrix and the silicon network. In addtion, HT2 does not have a significant impact on relaxing the RS as‐built state of the matrix, although it does induce a reduction in the RS magnitudes of the Si phase. It is concluded that the heat treatment stress relieving is effective as long as the Si‐network is not disaggregated.

Modelling and characterization of novel honeycomb structures with mass gradient produced by additive manufacturing

The dissemination of additive manufacturing methods has facilitated the design and production of complex structures which have a high strength-to-weight ratio. Cellular materials such as honeycombs have low-weight and high capacity to absorb energy which makes them desirable for the aerospace and automotive industries. The present work covers the study and comparison of metal-based regular honeycombs and functionally graded honeycombs. The latter encompass radial and linear/longitudinal gradients. Three repeating unit cells were studied: regular hexagons, Plateau and lotus. The structures were produced in aluminium using the laser powder bed fusion technique. Selected samples were submitted to a stress-relieving heat treatment. Numerical and experimental methods were used to assess the in-plane compressive properties. Finite element analysis was used to obtain the simulated force–displacement curves of each structure, allowing for the calculation of specific stiffness, absorbed energy and yield strength. The experimental method consisted of the compression of three specimens of three types of regular structures with and without stress-relieving heat treatment. The heat treatment reduced the yield strength and stiffness whilst increasing the ductility of the samples. The mechanical behaviour of the structures was found to depend upon a combined effect of the type of gradient, relative density, and unit cell structure. The results showed that an increase in the relative density would enhance the specific mechanical properties. The lotus configuration displayed the highest specific mechanical properties, as its geometry reduces the stress concentrations. The numerical results showed a reasonable match with the experimental results.

Assessment of Residual Stresses in Laser Powder Bed Fusion Manufactured IN 625.

Residual stresses pose significant challenges in the powder bed fusion of metals using a laser (PBF-LB/M), impacting both the dimensional accuracy and mechanical properties. This study quantitatively analyzes deformation and residual stresses in additively manufactured Inconel 625. Investigating both as-built and stress-relieved states with varied scanning strategies (90°, 67°, strip, and 90° chessboard) in PBF-LB/M/IN625, distortion is evaluated using the bridge curvature method. Quantitative measurements are obtained through 3D laser surface scanning on pairs of bridge specimens-one measured before and after detachment from the build plate, and the other undergoing stress-relieving heat treatment at 870 °C for 1 h. The findings reveal that, among as-built specimens, the 90° and 90° strip strategies induce the least distortion, followed by the 67° and chessboard 90° strategies. Furthermore, stress-relief treatment significantly reduces residual stress levels. After post-treatment, the deformation in X-axis samples with 90° and 90° strip strategies decreases by 39% and 42%. In contrast, the samples with the 67° and 90° checkerboard strategies exhibit more pronounced reductions of 44% and 63%, respectively. These quantitative results contribute useful insights for optimizing PBF-LB/M/IN625 processes in additive manufacturing.

L-PBF of the Metastable β Titanium Alloy Ti-5553: Microstructure and Mechanical Properties

Ti-5Al-5V-5Mo-3Cr or Ti-5553 is a metastable β Titanium alloy with excellent mechanical properties. Compared to the most common titanium alloy, the α and β Ti6Al4V, even at high cooling rates as present in the laser powder bed fusion process, it establishes an β dominant microstructure which is further highly tunable by heat treatment at lower temperatures than Ti6Al4V.In the scope of this contribution, the processability of T‑5553 is investigated, and the effects of stress relief heat treatment are evaluated. Its influence of achieved microstructures on hardness and impact strength is shown.

Influence of stress-relieving heat treatments on the efficacy of Co-Cr-Mo-W alloy copings fabricated using selective laser melting.

Purpose This study aimed to evaluate the influence of stress-relieving heat treatments on the metal-ceramic bond strength and fitness accuracy of selective laser melting (SLM)-fabricated Co-Cr alloy copings.Methods SLM-manufactured Co-Cr samples were stress-relieved at 750 (Ht-750) and 1150 °C (Ht-1150). The microstructure, surface roughness, metal-ceramic bond strength, marginal and internal fit, Vickers hardness, and residual stress were then compared with those of the non-heat-treated group (As-built). The results were analyzed using one-way ANOVA and post-hoc tests (Tukey's or Student's t test) (P = 0.05).Results The microstructure of the Ht-1150 samples had a brittle oxide layer and lower surface roughness, resulting in significantly lower bond strength values than those of the other groups. The As-built group exhibited significantly lower marginal gap values than the Ht-750 and Ht-1150 groups. Therefore, the post-heat treatments degraded the marginal fitness. The surface residual stress in all sample groups were compressive because of the sandblasting effect. The compressive stresses were larger in Ht-1150 than in As-built and Ht-750 owing to their low hardness values.Conclusions Stress-relief annealing porcelain-fused-to-metal single crowns does not improve bond strength and degrades fitness accuracy because additional post-heat treatments induce thermal distortion. These findings are expected to facilitate the direct application of As-built SLM single crowns in dentistry to minimize post-manufacturing costs and time.

Simulation of a liquid propellant rocket engine manufacturing assembly line utilizing the PFS/PN methodology

The system addressed in this paper pertains to an assembly line for liquid propellant rocket engines equipped with turbopump. The challenge involves automating the process of metal 3D printing for the turbopump and combustion chamber, followed by heat treatment for stress relief, X-ray computed tomography inspection, and the subsequent movement of components throughout the factory. To achieve this, the PFS/PN methodology was employed to facilitate a detailed analysis of the system, ensuring control over its inputs and outputs. The system was simulated using the ProModel Discrete Event Simulator, and the results were scrutinized, indicating the robustness of the simulation. Following the Ladder methodology, programming for Programmable Logic Controllers was also developed.

Microstructure and Mechanical Properties of Copper/Graphene Composites Fabricated via Accumulative Roll Bonding and Heat Treatment without a Controlled Atmosphere

Copper and its alloys are structural materials used in industries and engineering applications due to their excellent thermal and electrical conductivity and chemical stability. Integrating graphene, known for its exceptional electrical conductivity, into the copper matrix is a promising strategy to enhance mechanical properties without sacrificing electrical conductivity. The Accumulative Roll Bonding (ARB) process can effectively and homogeneously introduce graphene into the metal matrix and is adaptable to an industrial scale. This study investigates the impact of varying graphene concentrations and two heat treatment protocols (without a controlled atmosphere) on the mechanical and electrical properties of ARBed copper/graphene composites. Optical microscopy revealed minimal voids and graphene clumps, and the energy dispersive spectroscopy analysis revealed the absence of copper oxide in some samples. The conductivity test showed little influence of the graphene content and stress relief heat treatment temperature on electrical conductivity (~86% of the International Annealed Copper Standard) within a limited number of ARB cycles. The tensile tests did not reveal a significant influence of the graphene content and stress relief heat treatment temperature on the ultimate tensile strength (220–420 MPa) and elongation (~2%).

INFLUENCE OF HEAT TREATMENT AND DIFFERENT CUTTING CONDITIONS ON THE MACHINABILITY IN ADDITIVE-SUBTRACTIVE PROCESSING

For many applications, the surface quality, geometric accuracy and stress state of parts produced using laser-based powder bed fusion (PBF-LB) are insufficient. A stress relief and machining as post-processing operations allow to overcome these issues. PBF-LB materials have a unique microstructure. Their machinability therefore differs from that of cast or wrought materials. The microstructure can be altered by a stress relief heat treatment, which can change the machinability further. In this paper, the machinability of AlSi10Mg parts in the as-built condition and stress relieved condition is examined when wet and dry peripheral milling with cutting speeds up to 1,000 m/min. The PBF-LB parts were manufactured in different build-up directions. The stress relief decreased the material microhardness by approximately 16 %. This lower microhardness did not significantly affect the process forces but influenced the surface characteristics. The best surface quality was achieved when milling with the highest considered cutting speed of 1,000 m/min and when using metalworking fluids. Particularly the number of surface defects such as the smearing of material could thus be reduced. For the as-built conditions, good surface qualities can be achieved in dry cutting with high cutting speeds.

Investigating mechanical and surface porosity values of high-performing 3D-printed titanium alloys along with stress-relieving heat treatments

Investigating mechanical and surface porosity values of high-performing 3D-printed titanium alloys along with stress-relieving heat treatments

Effect of shot peening on fatigue behavior and microstructure of additively manufactured Co‐Cr‐Mo alloy

AbstractThis investigation delved into the impact of shot peening on the fatigue properties of Co‐Cr‐Mo samples manufactured through laser powder bed fusion. Two primary groups were established, one subjected to stress relief heat treatment. Each group underwent further division, with one subgroup undergoing shot peening. Comprehensive microstructural, fractographic analyses and fatigue tests were conducted. Statistical analysis of fatigue results demonstrated a noteworthy difference (p < 0.05) between machined and shot‐peened samples across stress levels of 700–70, 600–60, and 500–50 MPa. A statistical significance was observed between machined and heat‐treated, then machined samples within 700–70 and 600–60 MPa stress levels. Fatigue analysis of heat‐treated, then machined samples revealed a shorter life comparing with machined samples at low cycle fatigue (<105), but superior performance at high cycle fatigue (>105). Fracture surface examinations indicated a planar structure with a distinctive quasi‐cleavage texture, affirming that shot peening enhances fatigue behavior by refining mechanical properties.

Effect on microstructural and mechanical properties of selective laser melted pure Ti parts using stress relief heat-treatment process

This study investigated the correlation between the microstructure and the mechanical properties of pure Ti specimens manufactured via selective laser melting (SLM) using the stress relief heat-treatment process. Similar heat treatments were performed at a rate of 10 °C/min with a dwell time of 2 h to reach post-treatment temperatures ranging from of 490–890 °C in intervals of 100 °C. Phase change analysis using X-ray diffraction was conducted to verify the effects of the post-treatment process, while electron backscatter diffraction analysis was conducted to study the effects of microstructural changes induced by the post-treatment process on the mechanical properties of pure Ti specimens. In addition, a comprehensive analysis was performed to analyze residual stress following the stress relief heat treatment. The findings of this study establish a clear relationship between the mechanical properties and microstructural changes in SLM-manufactured pure Ti after heat treatment across a broad temperature range. Furthermore, the study confirms that heat treatment effectively relieves the residual stress in SLM Ti specimens.