Toughness Of Steel Research Articles

Research on the Low-Temperature Impact Toughness of a New 100-mm Ultra-Thick Offshore Steel Fabricated Using the Narrow-Gap Laser Wire Filling Welding Process.

Ultra-thick offshore steel, known for its high strength, high toughness, and corrosion resistance, is commonly used in marine platforms and ship components. However, when offshore steel is in service for an extended period under conditions of high pressure, extreme cold, and high-frequency impact loads, the weld joints are prone to fatigue failure or even fractures. Addressing these issues, this study designed a narrow-gap laser wire filling welding process and successfully welded a 100-mm new type of ultra-thick offshore steel. Using finite element simulation, EBSD testing, SEM analysis, and impact experiments, this study investigates the weld's microstructure, impact toughness, and fracture mechanisms. The research found that at -80 °C, the welded joint exhibited good impact toughness (>80 J), with the impact absorption energy on the surface of the weld being 217.7 J, similar to that of the base material (225.3 J), and the fracture mechanism was primarily a ductile fracture. The impact absorption energy in the core of the weld was 103.7 J, with the fracture mechanism mainly being a brittle fracture. The EBSD results indicated that due to the influence of the welding thermal cycle and the cooling effect of the narrow-gap process, the grains gradually coarsened from the surface of the welded plate to the core of the weld, which was the main reason for the decreased impact toughness at the joint core. This study demonstrates the feasibility of using narrow-gap laser wire filling welding for 100-mm new type ultra-thick offshore steel and provides a new approach for the joining of ultra-thick steel plates.

Optimizing crack initiation energy in austenitic steel via controlled martensitic transformation

Although the seemingly negative effect of deformation-induced martensite (DIM) volume fraction on the impact toughness of austenitic steels has been well documented, it relies mostly on analyzing crack propagation without explicitly considering the crack initiation process which, however, plays a crucial role in these ductile alloys. The dependence of crack initiation energy (Ei) on martensitic transformation mechanisms is still ambiguous, inhibiting the precise design of damage-tolerant and ductile alloys. Here, we explore the temperature-dependent crack initiation energy of a SUS321 stainless steel at various temperatures (25, –50, and –196 °C). Contrary to the crack propagation energy (Ep), the Ei has a weak correlation with the volume fraction of α′-martensite but a strong correlation with the martensitic transformation rate. Also contrary to the traditional viewpoint of Ep considering ε-martensite as a detrimental phase, a high volume fraction of ε-martensite turns out to be beneficial to the increase of Ei, thereby enhancing impact toughness. As such, an optimal value (15 mJ/m2) for the stacking fault energy (SFE), which dictates the γ→ε→α′ transformation sequence, is given as a new design guideline for enhancing the Ei and consequently the impact toughness of ductile steels. The generality of this guideline is further validated in multiple austenitic steels with different compositions and grain sizes.

Statistical characterization of specimen size and temperature dependence of cleavage fracture toughness of ferritic steels

AbstractBased on the numerical results on the non‐linear correlation between volume of plastic zone and global loading level represented by stress intensity factor, the dependence of cleavage fracture toughness of ferritic steels on specimen size and temperature is evaluated based on an empirical statistical model. The statistical correlation is supported by two sets of toughness data measured from different sized compact tension specimens at different temperatures. To further improve the accuracy of the statistical model, future work is identified to quantify the variation of volume of plastic deformation zone with loading level and measure the average volume for each microcrack at different temperature.

The effect of hydrogen and notch orientation in SENT specimens on the fracture toughness of an API 5L X70 pipeline steel

Transporting hydrogen gas through pipelines is an important topic within the context of energy transition. An essential challenge hereto is the phenomenon of hydrogen embrittlement of pipeline steels which includes a reduction in fracture toughness. As the theories accounting for hydrogen embrittlement are still debated, improving fundamental insights into the underlying mechanisms is crucial. Fracture toughness tests on single edge notched tension (SENT) specimens have been performed to examine the influence of hydrogen on the fracture behavior of a pipeline steel. An API 5L X70 steel was selected for this purpose, characterized by a distinctive banded microstructure commonly seen in pipeline steels. The test specimens were extracted from the steel pipe, and a notch in two different orientations was machined. By using a combination of fractography and X-ray micro-CT (Computed Tomography), the fracture mechanisms are revealed. The tearing resistance characteristics of the steel, with and without the presence of hydrogen, are demonstrated through tearing resistance curves. The experiments show that the banded microstructure plays a key role in the results through the development of splits at the microstructural bands. While these splits are also present in uncharged toughness test specimens, they are increasingly present in hydrogen charged specimens suggesting a hydrogen related weakening of the banded microstructure. In addition, it is demonstrated that hydrogen induces an increasingly zigzagged crack path. This is attributed to a potential combination of accelerated void nucleation at the microstructural bands, and accelerated shear-driven fracture.

Study on the effect of microstructure change of 20CrNiV5 high strength and toughness steel on hardenability

High-pressure and high-load drilling environment in the deep soil requires high strength and toughness of the oil well pipe, so the oil well pipe steel must be heat-treated, and the hardenability of the steel is particularly important in manufacturing. In this paper, Gleeble-3500 thermal simulator is used to measure the CCT curves of 20CrNiV5 steel, and the influence of microstructure on hardenability is studied. Deformation inhibits the martensitic transformation of the steel and leads to the decrease of its hardenability; the inhomogeneity of the steel pipe after hot forming also has an important impact on the hardenability, and the multiphase microstructure of bainite and ferrite after hot rolling leads to austenitic heating. Austenite grains are small and uneven, which reduces the hardenability of the steel. The microstructure of the inner and outer layers of the hot-formed steel pipe is smaller than that of the middle layer. After heat treatment, its smaller austenite results in weak hardenability.

Preface

The 2023 4th International Conference on Advanced Materials and Intelligent Manufacturing (ICAMIM 2023) was held in Guangzhou, China during December 1st to 3rd, 2023. The series of ICAMIM conference was created with the aim to be an interdisciplinary incubator for the worldwide exchange of information and innovative ideas about the latest research results in the fields of advanced materials and intelligent manufacturing.At ICAMIM 2023, we wished to bring together a broad community of researchers from different branches of the rapidly developing complex science to discuss the fundamental theoretical challenges as well as experimental and applied aspects of many practical problems. The agenda was conducted mainly based on three parts, covering keynote speeches, oral & poster presentations, and academic tour.There were six keynote speeches and many regular oral talks in the morning and afternoon sessions. The topics of keynote speeches cover: a) Scientific Carbon Reduction, Green Development, Manufacturing Industry to Achieve the Goal of “Double Carbon” Efforts; b) ChatGPT with Intelligent Manufacturing System; c) Challenges Facing the Industrialization of Sodium-Ion Batteries; d) Microstructure Control and Application Properties of Ultra-High Strength and Toughness Steels; e) Double Growing Carbon Background Material Base Environmental Functional Materials Development Prospects; f) Current Status and Development of the New Materials Industry in Guangdong. These speeches allowed all the participants to interact with the speakers and people around and get some new insights from each other. An academic discussion part was also held, the topic of which was related to the recent and anticipated future progress in advanced materials and intelligent manufacturing, discussing a variety of questions and opinions important for the understanding of the technology and management methods of the industry itself.The papers submitted to this Conference were carefully reviewed by expert referees, covering topics on: Composites, New feature Materials, Integrated Manufacturing Systems, Advanced Manufacturing Technology, Intelligent Mechatronics, etc. We are very grateful to the reviewers for their efficient and thoughtful actions. Various excellent papers were included here based on the referee reports.We are thankful to the members of Technical Program Committee for their time and efforts in preparing the program of ICAMIM 2023. We also appreciate the behind-the-scenes work of the members of Organizing Committee in preparing the conference site, arrangements for excursions and accommodation, handling the financial support for participants, and so on. Finally, we acknowledge the publishing support from Journal of physics: Conference SeriesThe Committee of ICAMIM 2023List of Committee Member is available in this pdf.

Obtaining the percentages of ductility and brittleness of AISI/SAE 1020 and 304 steels, using digital image processing.

This research is the integration of a set of elements in a system of capturing, processing, and digital image analysis. It allows a better visual and numeric interpretation to determine the toughness, ductility percentage, and fragility of steel AISI/SAE 1020 and 30, getting better qualitative and quantitative observation of the results from the impact test (Charpy test). Patterns in the standard form, ASTM E23, were digitalized to evaluate the percentage of ductility/fragility of specimen testing. After, we calculated the area and the equivalent diameter of the material. using digital image processing and numerical comparison between the patterns specified in the standard form ASTM E23 and the testing in the impact test, and it allows to find the kind of pattern it is closest and determine which degree of ductility. Finally, the results were compared by three experts. The algorithm accuracy was 80%.

Effects of Lath Boundary Segregation and Reversed Austenite on Toughness of a High-Strength Low-Carbon Steel

Effects of Lath Boundary Segregation and Reversed Austenite on Toughness of a High-Strength Low-Carbon Steel

Pure niobium manufactured by Laser-Based Powder Bed Fusion: influence of process parameters and supports on as-built surface quality

Niobium (Nb) is a transition metal commonly used as an alloying element for increasing strength, toughness, corrosion resistance, and other properties of steel and superalloys. Pure Nb, however, is a very interesting metal for its excellent superconductivity. This makes it suitable for producing superconducting magnets and devices for particle acceleration systems and particle physics research (e.g., superconducting resonant cavities). In this work, the production of Nb by the Laser-Based Powder Bed Fusion (PBF-LB/M, also known as Laser Powder Bed Fusion or LPBF) process was examined. Manufacturing parameters were investigated to achieve additively manufactured parts with a relative density higher than 99.5% and showing a down-skin surface roughness in the range of 20–70 μm, depending on the inclination angle. Studies related to the limiting angle of self-supported Nb parts were also conducted, and innovative non-contact supporting structures were successfully developed. These allowed to creation of parts with very small overhang angles, without compromising the downward-facing surfaces; indeed at the same time, the as-built surface finish was improved.

Excellent low-temperature toughness of 1 GPa grade microlaminated 5Mn steel containing retained austenite

The development of high-strength steels with excellent low-temperature toughness continues to present significant challenges. Delamination toughening and retained austenite (RA) toughening are effective methods for improving the low-temperature toughness of steels. In the present study, medium manganese steel with a microlaminated microstructure containing blocky RA is prepared by intercritical rolling (IR). A comparative steel with a microstructure containing annealed martensite and film-like and blocky RA is generated by hot rolling and intercritical annealing (HRIA). The different microstructure morphologies lead to different fracture characteristics. The IR steel plate exhibited a delaminated fracture that changes the crack propagation path, inducing large-scale and severe plastic deformation in the area below the delaminated crack in the entire temperature range (RT ∼ −196 °C). The Charpy impact V-notch absorbed energy (CVN) is as high as 450 ± 7 J at −60 °C. Moreover, the fracture behavior of the HRIA steel was similar to that of steels with equiaxed microstructures; ductile fracture takes place (above −40 °C) first, followed by brittle fracture, and the CVN is only 150 ± 83 J at −60 °C. The RA contents of the IR and HRIA steels at RT are 25.8% and 22.3%, respectively. Upon impact at −60 °C, the RA content becomes 0 and 4% in the IR and HRIA steels, respectively. Finally, a toughening mechanism is established for IR steel from the perspectives of crack propagation and microstructure evolution.

Effect of Manganese on the Strength-Toughness Relationship of Low-Carbon Copper and Nickel-Containing Hull Steel.

The influence of varying the manganese (Mn) contents of high-strength copper-containing hull steel on its microstructural evolution and mechanical properties was investigated. With increasing Mn content from 2 to 5%, the tensile strength of the steel increased by ~100 MPa, while the elongation of steel remained at ~23.5%, indicating good plasticity. However, the 2Mn sample had 128 J higher low-temperature (-84 °C) impact work than the 5Mn sample. The microstructures of different Mn steels were composed of fresh martensite (FM), ferrite/tempered martensite (F/TM), and reversed austenite (RA). The increase in Mn content markedly increased the presence of RA and intensified the work hardening caused by the transformation-induced plasticity (TRIP) effect during the tensile process. However, as the phase transformation in different Mn steels occurred in the early stage of strain and did not extend throughout the entire plastic deformation process, increasing plasticity via phase transformation was difficult. In addition, although the volume fraction of RA increased significantly in 4Mn and 5Mn steels, the stability of RA significantly decreased. The presence of numerous metastable blocks and coarse lath-like RA contributed little to low-temperature impact work and was even detrimental to toughness. The substantial fresh martensite resulting from phase transformation facilitated microcrack generation, owing to rapid volume expansion and mutual impacts, thus reducing the work required for crack formation. Additionally, the abundance of deformation twins significantly reduced the work needed for crack propagation. These combined actions significantly reduced the low-temperature toughness of 4Mn and 5Mn steels.

Transitioning solidification mode via electroplated Ni coatings in martensitic stainless steel resistance spot welds: new insights into fabricating tough microstructure

The present study addresses the enhancement of fracture toughness of martensitic stainless steel (MSS) spot welds by utilizing through electroplating of Ni on MSS sheets. The equilibrium and non-equilibrium solidification modelling showed that by Ni coating with 50 μm thick on 1.5 mm thick MSSs, the solidification mode changes from δ-ferrite to γ-austenite, leading to a weld nugget (WN) dominated by austenite grains. Moreover, electron backscatter diffraction (EBSD) and electron probe microanalysis (EPMA) showed that the other phases (martensite, δ-ferrite) appeared in band areas of WN owing to incomplete mixing of MSS and the Ni-coating. The tough microstructure in the Ni-coated MSS spot welds provided superior mechanical properties compared to non-coated welds, both in cross-tension (CT) and tensile-shear (TS) tests. Notably, the TS and CT strengths of the Ni-coated MSS spot welds showed a remarkable increase of 57% and 127%, respectively, in comparison to the conventional bare MSS spot welds. Furthermore, in terms of failure energy, the Ni-coated MSS spot welds demonstrated a substantial enhancement of 296% in TS and 520% in CT, when compared to their non-coated counterparts. This research study showcased the effectiveness of Ni electroplating as an industrial method for improving the spot weldability of MSSs.

Embrittlement Mechanisms of HR3C Pipe Steel at Room Temperature in Ultra-Supercritical Unit

HR3C steel is an austenitic high-temperature-resistant steel. Because of its good strength and high-temperature performance, it has been widely used in ultra-supercritical power plant boilers. With the increasingly frequent start-up and shutdown of thermal power units, leakages of HR3C steel pipes have occasionally occurred due to the embrittlement of HR3C pipe steel after a long service duration. In this study, the embrittlement mechanisms of HR3C pipe steel are investigated systematically. The mechanical properties of the pipe steel after running for 70,000 h in an ultra-supercritical unit were determined. As a comparison, the pipe steel supplied in the same batch was aged at 700 degrees Celsius for 500 h. The mechanical properties and the micro-precipitation of the aged counterparts were also determined for comparison. The results show that the embrittlement of HR3C pipe steel in service for 70,000 h is obvious. The average impact absorption is only 5.5 J, which is a decrease of 96.7%. It is found that embrittlement of HR3C steel also occurs after 500 h of aging at 700 °C, and the average value of impact absorption energy decreases by 70.4%. The comparison experiment between the in-service pipe steel and the aged pipe steel shows that in the rapid decline stage of the impact toughness of HR3C steel, the M23C6 carbide in the microstructure has a continuous chain distribution in the grain boundary. There were no other precipitated phases observed. The rapid precipitation and aggregation of M23C6 carbides leads to the initial embrittlement of HR3C steel at room temperature. The CRFe-type σ phase was found in the transmission electron microscope (TEM) image of the steel pipe after 70 thousand hours of use. The precipitation of the σ phase further induces the embrittlement of HR3C pipe steel after a long service duration.

Effect of Bain Unit Size on Low-temperature Fracture Toughness in Medium-carbon Martensitic and Bainitic Steels

Effect of Bain Unit Size on Low-temperature Fracture Toughness in Medium-carbon Martensitic and Bainitic Steels

Physics informed ensemble learning used for interval prediction of fracture toughness of pipeline steels in hydrogen environments

Hydrogen embrittlement leads to a loss of plasticity and a decrease in fracture toughness in pipeline steels. Fracture toughness is a critical factor in the design and safety assessment of hydrogen-carrying pipelines. However, conducting large-scale fracture toughness testing on hydrogen-charged materials is time-consuming and expensive. Analytical approaches based on micromechanics often involve numerous undetermined (or assumed) parameters. Therefore, this study presents an approach that combines physical information and ensemble learning for predicting the fracture toughness range under hydrogen environments. Initially, detailed experimental data are gathered from a series of fracture tests conducted on pipeline steels under hydrogen environments, as published in the literature. Subsequently, Given the limited availability of experimental data, a feature space was constructed, taking into account the physical information as well as the distributions of yield strength and tensile strength. Furthermore, a predictive model based on Population-Based Training (PBT) optimization and Category Boosting (CatBoost) methodology was developed. Comparative experimentation substantiated its superior predictive accuracy in comparison to Random Forest, Adaptive Boosting (AdaBoost), Gradient Boosting Decision Tree (GBDT), Light Gradient Boosting Machine (LightGBM), and Extreme Gradient Boosting (XGBoost). The MAE, MSE, R2, VAF, a20_index and MAPE, was 0.02139, 0.00096, 0.98741, 98.98%, 0.83 and 0.1552. Building upon these foundations, this study proposes an interval prediction method by combining Monte Carlo simulation with point prediction results to obtain fracture toughness interval prediction results with different confidence intervals (80%, 85%, 90% and 95%).

Crystal plasticity finite element model of the brittle–ductile transition temperature and fracture toughness of irradiated A508-3 steel

Crystal plasticity finite element model of the brittle–ductile transition temperature and fracture toughness of irradiated A508-3 steel

Advancement of strength and toughness in ultra-low carbon martensitic stainless steel by reversed austenite

It has been proven that martensite matrix accompanied by fine reversed austenite is beneficial to improve the strength and toughness in martensitic steels to a certain extent. In order to achieve this unique microstructure, the existing methods, like quenching at high temperatures, multiple heat treatment processes, increasing Ni content, raise the economic cost and operation difficulty. In this work, fine reversed austenite was formed in Fe13Cr4NiMo steel with relatively low nickel content (4 wt%) by one-time relatively low temperature quenching (860 °C) and tempering process. Then the formation mechanism and effect on mechanical properties of reversed austenite were discussed. The 0.55 vol% reversed austenite with the size of 260 nm can be formed in Fe13Cr4NiMo steel under quenching at 860 °C for 40 min and tempering at 650 °C for 2 h. The reversed austenite maintained a deviation of ∼2° from K-S relationship with the martensite matrix. In addition, the formation of reversed austenite was caused by short circuit diffusion of element-free redistribution, which caused the reversed austenite to be more inclined to nucleate at subgrain boundaries and grow up restrictedly. Furthermore, the Fe13Cr4NiMo steel that contained reversed austenite hindering dislocation movement and coordinating deformation possessed excellent plasticity of 18.4 % and Charpy impact energy of 289 J while maintaining high strength of 872 MPa at room temperature.

Effect of V and Nb on the microstructure and properties of high strength and toughness steel for petroleum casing

The utilization of high-strength and tough petroleum casing steel has become the focus of various research groups worldwide, particularly in the past decade. However, defining its forming behavior presents several challenges, stemming from the complexity of enhancing strength and toughness on the steel's characteristics. To address this issue, this study employed a low-carbon microalloyed steel and introduced V and Nb elements sequentially, resulting in three groups of steels under investigation. Subsequently, mechanical properties and microstructure characteristics were examined. Interestingly, the addition of V and Nb elements resulted in both tensile and yield strengths above 1200 MPa and 1173 MPa, respectively, satisfying the criteria for the V170 oil casing. Furthermore, after adding V, V(C,N) precipitates uniformly in the steel. Still, the Nb element is not completely precipitated as there is a significant amount of Nb in solid solution. The effective grain size of the investigated steel increases from 0.92 μm to 0.98 μm after adding V and Nb elements, accompanied by a reduction in the fraction of HAGB from 47.4 % to 42.4 %. Therefore, V element plays a vital and positive role in improving the mechanical properties of the experimental steel, while Nb element has only a minor effect.

The Effect of Multi-Step Tempering and Partition Heat Treatment on 25Cr2Ni3MoV Steel's Cryogenic Strength Properties.

In this study, the refinement of two microstructures was controlled in medium carbon 25Cr2Ni3MoV steel via multi-step tempering and partition (MTP) to achieve high cryogenic strength-ductility combinations. Microstructure evolution, the distribution of stress concentration, and microcrack formation and propagation during cryogenic Charpy impact testing were investigated. Compared with their performance in the quenching and tempering states (QT), the MTP steels showed a significant improvement in yield strength (1300 MPa), total elongation (25%), and impact toughness (>25 J) at liquid nitrogen temperature (LNT). The strengthening contributions mainly originated from the high dislocation density and refinement cementite (size: 70 nm) in the martensite lath (width: 1.5 μm) introduced by refined reversed austenite and its latter decomposition. The instrumented Charpy impact results indicated that cracks nucleated in the primary austenite grain (PAG) boundary for two steels due to the strain concentration band preferring to appear near PAGs, while cracks in the QT and MTP samples propagated along the PAGs and high-angle grain boundary (HAGB), respectively. The crystallized plasticity finite element simulation revealed that the PAG boundary with cementite precipitates of large size (>200 nm) was less able to dissipate crack propagation energy than the HAGBs by continuously forming a high strain concentration area, thus leading to the low-impact toughness of the QT steel.

Effect of long-term aging on the microstructure evolution and fracture mechanism of 9% Cr steels

The fracture toughness of pressure pipe steels is vital for their design and safe operation. Understanding the deterioration of the fracture toughness and the corresponding fracture mechanisms is instructive and meaningful for material selection and development. The elastic–plastic fracture toughness of 9% Cr steels aged at 873 K and 923 K from the initial state to 20000 h was investigated at ambient temperature and 873 K. The deterioration of the fracture toughness and the corresponding fracture mechanisms are discussed in detail. For 9% Cr steels, voids mainly initiated from primary inclusions such as silicides, sulfides, alumina and manganides in as-received state, while voids initiated from both primary inclusions and secondary particles such as the Laves phase after long-term aging. These voids grew and coalesced with neighboring voids and crack tips subsequently until ultimately fracture. After aging at 873 K, the fracture toughness values tested at 873 K decreased from the initial state to 3000 h and then increased to 10000 h. The peculiar deterioration of the fracture properties after 3000 h of aging at 873 K can be attributed to the high number density of Laves phase particles in the steels. It was found that the densely distributed hard Laves phase particles induced strain concentration at the interface between the Laves phase and the matrix under plane-strain tension condition and promoted nucleation of voids. It was suggested that the spatial distribution of the Laves phase played a significant role on the void formation. 9% Cr steels with a denser distribution of Laves phases brings about voids with shorter interspaces, which are more susceptible to coalesce into crack tip, resulting in lower fracture resistance. After aging at 923 K from 10000 h to 20000 h, the number density, size and volume fraction of precipitates, block size, misorientation angle and dislocation density remained almost constant. The slight increase in the fracture toughness from 10000 h to 20000 h can be mainly ascribed to the coarsening of the martensite lath in this stage.