Materials

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11 pages, 5594 KiB

Open AccessArticle

Microstructures and Fatigue Properties of High-Strength Low-Alloy Steel Prepared through Submerged-Arc Additive Manufacturing

by Mei-Juan Hu, Ling-Kang Ji, Qiang Chi and Qiu-Rong Ma

Materials 2022, 15(23), 8610; https://doi.org/10.3390/ma15238610 - 02 Dec 2022

Cited by 2 | Viewed by 1111

Abstract

Submerged arc additive manufacturing (SAAM) is a viable technique for manufacturing large and complex specialized parts used in structural applications. At present, manufacturing high-strength low-alloy steel T-branch pipe through SAAM has not been reported. This paper uses this technology to manufacture low-alloy structural [...] Read more.

Submerged arc additive manufacturing (SAAM) is a viable technique for manufacturing large and complex specialized parts used in structural applications. At present, manufacturing high-strength low-alloy steel T-branch pipe through SAAM has not been reported. This paper uses this technology to manufacture low-alloy structural steel parts. The microstructures of the samples were characterized, which revealed that they were mainly composed of polygonal ferrites. The tensile properties in the horizontal and vertical directions of deposits were studied. Results show that the horizontal tensile strength of deposits was quite close to the vertical one, while the elongation rate in the vertical direction was obviously lower than that in the horizontal direction. Fatigue results indicate that the strain fatigue limit of high-strength low-alloy steel samples in vertical direction was 0.24%. The fatigue fractures of fatigue samples of deposits showed multi-source crack initiation characteristics and the crack propagation regions exhibited typical fatigue striations, so the final instantaneous fracture region showed a ductile fracture. Fatigue performance is very important for the safe service of structural parts, but there is a lack of relevant research on this additive manufacturing part. The results of this paper may support the popularization of the SAAM for high-strength low-alloy steel T-branch pipe. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Pipeline Steel)

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15 pages, 5392 KiB

Open AccessArticle

The Flow Stress–Strain and Dynamic Recrystallization Kinetics Behavior of High-Grade Pipeline Steels

by Lei Wang, Lingkang Ji, Kun Yang, Xiongxiong Gao, Hongyuan Chen and Qiang Chi

Materials 2022, 15(20), 7356; https://doi.org/10.3390/ma15207356 - 20 Oct 2022

Cited by 1 | Viewed by 1166

Abstract

The hot deformation behavior of high-grade pipeline steels was studied in the strain rate range of 0.001~0.1 s⁻¹ and the temperature range of 1050~1200 °C by using hot compression tests on a Gleeble 3500 thermomechanical simulator. The flow stress increases with the [...] Read more.

The hot deformation behavior of high-grade pipeline steels was studied in the strain rate range of 0.001~0.1 s⁻¹ and the temperature range of 1050~1200 °C by using hot compression tests on a Gleeble 3500 thermomechanical simulator. The flow stress increases with the increase in strain rate and the decrease in deformation temperature, and the deformation activation energy is about 358 kJ/mol. The flows stress–strain behavior of the work-hardening and dynamic recovery (DRV) was calculated using the Estrin–Mecking equation, and the kinetics model of the dynamic recrystallization (DRX) was established based on the Avrami equation through characteristic strains. Furthermore, the flow stress–strain behavior of high-grade pipeline steels was predicted by the established model based on the coupling effects of DRV and DRX. The corresponding predicted results are in good agreement with the experimental results according to standard statistical parameters analysis. Finally, the economic strain (ε₃) is proposed by the third derivative of the given kinetic model. Based on these calculation results, when the economic strain (ε₃) is reached, uniform and refined DRX grains can be obtained, the energy consumption reduced, and the production costs controlled, which is of great significance to actual factory production. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Pipeline Steel)

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17 pages, 6362 KiB

Open AccessArticle

Tensile Strain Capacity Prediction Model of an X80 Pipeline with Improper Transitioning and Undermatched Girth Weld

by Hongyuan Chen, Lianshuang Dai, Heng Xuan, Xiongxiong Gao, Kun Yang, Lei Wang, Qiang Chi and Chunyong Huo

Materials 2022, 15(20), 7134; https://doi.org/10.3390/ma15207134 - 13 Oct 2022

Viewed by 1554

Abstract

As an important component of strain-based design, the tensile strain capacity (TSC) concept has been extensively used for pipelines that experience expectable plastic strain for both installation and service. However, some stress-based designed pipelines have experienced unforeseen plastic strain in the past decade [...] Read more.

As an important component of strain-based design, the tensile strain capacity (TSC) concept has been extensively used for pipelines that experience expectable plastic strain for both installation and service. However, some stress-based designed pipelines have experienced unforeseen plastic strain in the past decade that resulted in failure. It seems that the tensile strain capacity has gradually become an important requirement for geohazard risk management and pipeline maintenance of stress-based design pipelines. The tensile strain capacity of an X80 pipeline is investigated. The assessment in this work was based on the fracture initiation–control-based limit state. This limit state corresponds to the onset of stable tearing and generally provides a reasonably conservative estimate. Besides that, factors such as wall thickness, material’s strain hardening capacity, toughness, weld strength mismatch, HAZ (heat-affected zone) softening, pipe wall thickness, high–low misalignment, and internal pressure were also investigated to construct a prediction model of the X80 vintage pipeline. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Pipeline Steel)

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19 pages, 6051 KiB

Open AccessArticle

Statistical Assessment of Fracture Toughness Results from the HAZ of X80 Pipeline FCAW Girth Weld

by Hongyuan Chen, Qingshan Feng, Ying Bi, Xiongxiong Gao, Lianshuang Dai and Qiang Chi

Materials 2022, 15(17), 6157; https://doi.org/10.3390/ma15176157 - 05 Sep 2022

Cited by 1 | Viewed by 1508

Abstract

Due to the wide application of flux-cored arc welds (FCAW) susceptible to significant scatter in weld and Heat Affected Zone (HAZ) fracture toughness, there is an interest in methods for evaluating the reliability of welds containing defects. The mechanical properties of the FCAW [...] Read more.

Due to the wide application of flux-cored arc welds (FCAW) susceptible to significant scatter in weld and Heat Affected Zone (HAZ) fracture toughness, there is an interest in methods for evaluating the reliability of welds containing defects. The mechanical properties of the FCAW girth weld of an X80 pipeline are tested and then analyzed. By obtaining fracture toughness results from a statistically significant number of SENB specimens, with notches positioned in different HAZ locations, the effect of variation within the results can be evaluated. The results of the fracture toughness tests were analyzed using statistical methods, to compare both the difference in behavior between HAZ microstructures and the variation when a similar microstructure has been sampled. The range of different characteristic toughness values was analyzed using a postulated ECA case to illustrate the sensitivity of the results to how toughness is defined. The analyses supported recommendations to be made on the optimum approach to characterizing HAZ fracture toughness for reliable pipeline assessments in multi-pass girth welds with complex HAZ microstructure distributions. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Pipeline Steel)

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15 pages, 5804 KiB

Open AccessArticle

Study of Strain Capacity for High-Strain Marine Pipe

by Kun Yang, Ting Sha, Xiongxiong Gao, Hongyuan Chen, Qiang Chi and Lingkang Ji

Materials 2022, 15(16), 5793; https://doi.org/10.3390/ma15165793 - 22 Aug 2022

Cited by 1 | Viewed by 1195

Abstract

In this paper, a strain capacity assessment on high-strain marine pipe was carried out by comparing the crack growth driving force and the crack growth resistance. The crack growth driving force was given by FEA, the stress-stain relationship was given by a DIC [...] Read more.

In this paper, a strain capacity assessment on high-strain marine pipe was carried out by comparing the crack growth driving force and the crack growth resistance. The crack growth driving force was given by FEA, the stress-stain relationship was given by a DIC tensile test, and the crack growth resistance was given by a single-edge notched tensile (SENT) test using a single-specimen flexibility method. The proposed approach was compared with the failure assessment curve and validated against full-scale tests with a girth weld notch. The results of the full-scale tests showed that the assessment method using FEA was more accurate and the result of the failure assessment curve assessment was more conservative. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Pipeline Steel)

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14 pages, 129675 KiB

Open AccessArticle

Effect of V Content and Heat Input on HAZ Softening of Deep-Sea Pipeline Steel

by Ba Li, Qingyou Liu, Shujun Jia, Yi Ren and Ping Yang

Materials 2022, 15(3), 794; https://doi.org/10.3390/ma15030794 - 21 Jan 2022

Cited by 17 | Viewed by 1314

Abstract

In this paper, the welding thermal cycle process of deep-sea pipeline steel was investigated by welding thermal simulation. The microstructure evolution, crystallology and second-phase precipitation behavior of the soft zone of the heat-affected zone (HAZ) were characterized and analyzed by combining scanning electron [...] Read more.

In this paper, the welding thermal cycle process of deep-sea pipeline steel was investigated by welding thermal simulation. The microstructure evolution, crystallology and second-phase precipitation behavior of the soft zone of the heat-affected zone (HAZ) were characterized and analyzed by combining scanning electron microscopy, electron back-scattered diffraction, transmission electron microscopy and hardness testing. The results show that HAZ softening appeared in the fine-grained zone with a peak temperature of 900–1000 °C for deep-sea pipeline steel, the base metal microstructure of which was the polygonal ferrite and acicular ferrite. Using V microalloying and low welding heat input could effectively decrease the softening of the HAZ fine-grained region, which was achieved by reducing the effective grain size, increasing the proportion of the dislocation substructures, and precipitating the nanoscale second-phase particles. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Pipeline Steel)

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14 pages, 6415 KiB

Open AccessArticle

Tensile Deformation and Fracture Behavior of API-5L X70 Line Pipe Steel

by Mikhail L. Lobanov, Vladislav A. Khotinov, Vladimir N. Urtsev, Sergey V. Danilov, Nikolay V. Urtsev, Sergey I. Platov and Stepan I. Stepanov

Materials 2022, 15(2), 501; https://doi.org/10.3390/ma15020501 - 10 Jan 2022

Cited by 9 | Viewed by 1542

Abstract

Thermo-mechanical controlled processing (TMCP) is employed to obtain the required level of mechanical properties of contemporary HSLA steel plates utilized for gas and oil pipeline production. The strength and crack resistance of pipeline steels are mainly determined by its microstructure and crystallographic texture. [...] Read more.

Thermo-mechanical controlled processing (TMCP) is employed to obtain the required level of mechanical properties of contemporary HSLA steel plates utilized for gas and oil pipeline production. The strength and crack resistance of pipeline steels are mainly determined by its microstructure and crystallographic texture. In this study, the influence of the structural and textural states of industrially produced API-5L X70-X80 pipeline steels on tensile mechanical properties was analyzed. TMCP routes with different hot rolling temperatures and cooling rates were employed. The texture of steel was assessed using the Taylor factor, which was calculated based on electron backscatter diffraction (EBSD). The decrease in rolling temperature resulted in the sharper texture characterized by {001} planes banding (cleavage planes in the bcc lattice) parallel to rolling direction. The tensile deformation behavior at the stage of necking was determined by the crystallographic and morphological texture of the material and demonstrated significant anisotropy. Rupture of all investigated samples was accompanied by the development of splitting on the fracture surface. The splitting was localized in the rolling plane similar to the splitting in standard Charpy tests of pipeline steels. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Pipeline Steel)

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16 pages, 5070 KiB

Open AccessArticle

Enhancing Strain Capacity by the Introduction of Pearlite in Bainite and Polygonal Ferrite Dual-Phase Pipeline Steel

by Xingyang Tu, Yi Ren, Xianbo Shi, Changsheng Li, Wei Yan, Yiyin Shan and Ke Yang

Materials 2021, 14(18), 5358; https://doi.org/10.3390/ma14185358 - 17 Sep 2021

Cited by 2 | Viewed by 2026

Abstract

In this study the strain capacity and work-hardening behavior of bainite (B), bainite + polygonal ferrite (B + PF), and bainite + polygonal ferrite + pearlite (B + PF + P) microstructures are compared. The work hardening exponent (n), instantaneous work hardening value [...] Read more.

In this study the strain capacity and work-hardening behavior of bainite (B), bainite + polygonal ferrite (B + PF), and bainite + polygonal ferrite + pearlite (B + PF + P) microstructures are compared. The work hardening exponent (n), instantaneous work hardening value (n_i), and differential Crussard-Jaoul (D_C-J) analysis were used to analyze the deformation behavior. The best comprehensive mechanical properties were obtained by the introduction of the pearlite phase in B + PF dualphase with the tensile strength of 586 MPa and total elongation of 31.0%. The additional pearlite phase adjusted the strain distribution, which increased the initial work hardening exponent and then maintained the entire plastic deformation at a high level, thus delayed necking. The introduction of pearlite reduced the risk of micro-void initiation combined with the high frequency of high angle grain boundaries (HAGBs) in triple-phase steel, which led to a low crack propagation rate. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Pipeline Steel)

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12 pages, 3336 KiB

Open AccessArticle

Effect of Bainite to Ferrite Yield Strength Ratio on the Deformability of Mesostructures for Ferrite/Bainite Dual-Phase Steels

by Gui-Ying Qiao, Zhong-Tao Zhao, Xian-Bo Shi, Yi-Yin Shan, Yu Gu and Fu-Ren Xiao

Materials 2021, 14(18), 5352; https://doi.org/10.3390/ma14185352 - 16 Sep 2021

Cited by 5 | Viewed by 1692

Abstract

The strength and plasticity balance of F/B dual-phase X80 pipeline steels strongly depends on deformation compatibility between the soft phase of ferrite and the hard phase of bainite; thus, the tensile strength of ferrite and bainite, as non-negligible factors affecting the deformation compatibility, [...] Read more.

The strength and plasticity balance of F/B dual-phase X80 pipeline steels strongly depends on deformation compatibility between the soft phase of ferrite and the hard phase of bainite; thus, the tensile strength of ferrite and bainite, as non-negligible factors affecting the deformation compatibility, should be considered first. In this purely theoretical paper, an abstract representative volume elements (RVE) model was developed, based on the mesostructure of an F/B dual-phase X80 pipeline steel. The effect of the yield strength difference between bainite and ferrite on tensile properties and the strain hardening behaviors of the mesostructure was studied. The results show that deformation first occurs in ferrite, and strain and stress localize in ferrite prior to bainite. In the modified Crussard-Jaoul (C-J) analysis, as the yield strength ratio of bainite to ferrite (

σ_{y, B} / σ_{y, F}

) increases, the transition strain associated with the deformation transformation from ferrite soft phase deformation to uniform deformation of ferrite and bainite increases. Meanwhile, as the uncoordinated deformation of ferrite and bainite is enhanced, the strain localization factor (SLF) increases, especially the local strain concentration. Consequently, the yield, tensile strength, and yield ratio (yield strength/tensile strength) increase with the increase in

σ_{y, B} / σ_{y, F}

. Inversely, the strain hardening exponent and uniform elongation decrease. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Pipeline Steel)

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16 pages, 7996 KiB

Open AccessArticle

Effects of the Primary NbC Elimination on the SSCC Resistance of a HSLA Steel for Oil Country Tubular Goods

by Tianyi Zeng, Shuzhan Zhang, Xianbo Shi, Wei Wang, Wei Yan, Yan Tian, Mingchun Zhao and Ke Yang

Materials 2021, 14(18), 5301; https://doi.org/10.3390/ma14185301 - 14 Sep 2021

Cited by 8 | Viewed by 1738

Abstract

Sulfide stress corrosion cracking (SSCC) has been of particular concern in high strength low alloyed (HSLA) steels used in the oil industry, and the non-metallic inclusions are usually considered as a detrimental factor to the SSCC resistance. In the present work, continuous casting [...] Read more.

Sulfide stress corrosion cracking (SSCC) has been of particular concern in high strength low alloyed (HSLA) steels used in the oil industry, and the non-metallic inclusions are usually considered as a detrimental factor to the SSCC resistance. In the present work, continuous casting (CC) and electroslag remelting (ESR) were adopted to fabricate a 125 ksi grade steel in order to evaluate the effect of microstructure with and without primary NbC carbides (inclusions) on the SSCC resistance in the steel. It was found that ESR could remove the primary NbC carbides, and hence, slightly increase the strength without deteriorating the SSCC resistance. The elimination of primary NbC carbides caused two opposite effects on the SSCC resistance in the studied steel. On the one hand, the elimination of primary NbC carbides increased the dislocation density and the proportion of high angle boundaries (HABs), which was not good to the SSCC resistance. On the other hand, the elimination of primary NbC carbides also induced more uniform nanosized secondary NbC carbides formed during tempering, providing many irreversible hydrogen traps. These two opposite effects on SSCC resistance due to the elimination of primary NbC carbides were assumed to be offset, and thus, the SSCC resistance was not greatly improved using ESR. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Pipeline Steel)

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