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20 pages, 7913 KiB

Open AccessArticle

Quenched and Tempered Steels Welded Structures: Modified Gas Metal Arc Welding-Pulse vs. Shielded Metal Arc Welding

by Houman Alipooramirabad, Neville Cornish, Rahim Kurji, Anthony Roccisano and Reza Ghomashchi

Metals 2023, 13(5), 887; https://doi.org/10.3390/met13050887 - 3 May 2023

Cited by 1 | Viewed by 2381

Abstract

Quench and tempered (Q&T) steels are widely used for a diverse range of applications, particularly in the mining and defence industry, where wear and unconventional loading are common. Furthermore, they are particularly prone to hydrogen assisted cold cracking (HACC), imposing a more careful [...] Read more.

Quench and tempered (Q&T) steels are widely used for a diverse range of applications, particularly in the mining and defence industry, where wear and unconventional loading are common. Furthermore, they are particularly prone to hydrogen assisted cold cracking (HACC), imposing a more careful selection of consumables and requiring a comparably higher welder skill level to fabricate defect-free structures. Therefore, the cost of fabrication of welded structures is higher when the more preferred welding technique of shielded metal arc welding, SMAW, is employed. The introduction of the modified pulsed arc mode of depositions, a variation to pulsed arc deposition, has improved the productivity rates and can be utilised by welders with a greater skill variations. In this study, full-strength butt welds of Q&T steel (AS/NZS 3597 Grade 700), with the thickness of 20 mm, are fabricated under a high level of restraint using both conventional SMAW and modified pulse gas metal welding (GMAW-P). The study investigated the economic feasibility of the two deposition modes and the propensity to cracking for the welded joints under high restraint conditions. Utilising the modified GMAW-P resulted in 63% and 88% reduction in the ‘Arc-On’ time and the total normalised fabrication time, respectively. However, strict controls must be implemented, due to the increased propensity to lack of fusion-type defects, to optimise the welding procedure and mediate for such defects if GMAW-P is to provide a techno-economically beneficial alternative to conventional SMAW when welding Q&T steels. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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19 pages, 10494 KiB

Open AccessArticle

Production of a Non-Stoichiometric Nb-Ti HSLA Steel by Thermomechanical Processing on a Steckel Mill

by Cleiton Arlindo Martins, Geraldo Lúcio de Faria, Unai Mayo, Nerea Isasti, Pello Uranga, Jose Maria Rodríguez-Ibabe, Altair Lúcio de Souza, Jorge Adam Cleto Cohn, Marcelo Arantes Rebellato and Antônio Augusto Gorni

Metals 2023, 13(2), 405; https://doi.org/10.3390/met13020405 - 16 Feb 2023

Cited by 7 | Viewed by 2135

Abstract

Obtaining high levels of mechanical properties in steels is directly linked to the use of special mechanical forming processes and the addition of alloying elements during their manufacture. This work presents a study of a hot-rolled steel strip produced to achieve a yield [...] Read more.

Obtaining high levels of mechanical properties in steels is directly linked to the use of special mechanical forming processes and the addition of alloying elements during their manufacture. This work presents a study of a hot-rolled steel strip produced to achieve a yield strength above 600 MPa, using a niobium microalloyed HSLA steel with non-stoichiometric titanium (titanium/nitrogen ratio above 3.42), and rolled on a Steckel mill. A major challenge imposed by rolling on a Steckel mill is that the process is reversible, resulting in long interpass times, which facilitates recrystallization and grain growth kinetics. Rolling parameters whose aim was to obtain the maximum degree of microstructural refinement were determined by considering microstructural evolution simulations performed in MicroSim-SM^® software and studying the alloy through physical simulations to obtain critical temperatures and determine the CCT diagram. Four ranges of coiling temperatures (525–550 °C/550–600 °C/600–650 ° C/650–700 °C) were applied to evaluate their impact on microstructure, precipitation hardening, and mechanical properties, with the results showing a very refined microstructure, with the highest yield strength observed at coiling temperatures of 600–650 °C. This scenario is explained by the maximum precipitation of titanium carbide observed at this temperature, leading to a greater contribution of precipitation hardening provided by the presence of a large volume of small-sized precipitates. This paper shows that the combination of optimized industrial parameters based on metallurgical mechanisms and advanced modeling techniques opens up new possibilities for a robust production of high-strength steels using a Steckel mill. The microstructural base for a stable production of high-strength hot-rolled products relies on a consistent grain size refinement provided mainly by the effect of Nb together with appropriate rolling parameters, and the fine precipitation of TiC during cooling provides the additional increase to reach the requested yield strength values. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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8 pages, 2238 KiB

Open AccessArticle

First-Principles Study of B Segregation at Austenite Grain Boundary and Its Effect on the Hardenability of Low-Alloy Steels

by Jingliang Wang, Xiang Yang, Rongtao Qian, Xuequan Rong, Zhenjia Xie and Chengjia Shang

Metals 2022, 12(12), 2006; https://doi.org/10.3390/met12122006 - 23 Nov 2022

Cited by 4 | Viewed by 1639

Abstract

Addition of B is beneficial for the hardenability of low-alloy steels and the effect is further improved when combined with the addition of Mo. While experiments demonstrated that Mo reduces the M₂₃(C,B)₆ precipitation and indicated an interaction between the alloying [...] Read more.

Addition of B is beneficial for the hardenability of low-alloy steels and the effect is further improved when combined with the addition of Mo. While experiments demonstrated that Mo reduces the M₂₃(C,B)₆ precipitation and indicated an interaction between the alloying elements at the grain boundary, the underlying mechanism remains unclear. In the present study, the segregation behavior of B and its interaction with C and Mo at an austenite grain boundary were investigated using first-principles calculations. It was demonstrated that B has a strong tendency to segregate to the grain boundary and leads to a remarkable reduction in grain boundary energy, which is considered to be responsible for the improvement in hardenability. A strong attractive interaction between B and Mo was revealed, consistent with the experimentally observed co-segregation. The partitioning energies of Mo and B from grain boundary into borocarbide were calculated, and it was found that Mo can suppress the precipitation by increasing the partitioning energy of B and destabilizing the M₂₃(C,B)₆ phase. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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23 pages, 16781 KiB

Open AccessArticle

Strength-Toughness Balance and Hydrogen Embrittlement Susceptibility of a Precipitation-Strengthened Steel Adopted Tempering Process

by Ning Zhao, Yanlin He, Li Lin, Rendong Liu, Qiangqiang Zhao and Weisen Zheng

Metals 2022, 12(9), 1534; https://doi.org/10.3390/met12091534 - 16 Sep 2022

Cited by 2 | Viewed by 2092

Abstract

Two steels with different nickel (Ni) content were investigated to reveal the role of Ni on strength-toughness balance and hydrogen embrittlement susceptibility. Although they were similar in microstructure, i.e., nano-particles were precipitated on martensitic laths, different mechanical behaviors were exhibited. After tempering, the [...] Read more.

Two steels with different nickel (Ni) content were investigated to reveal the role of Ni on strength-toughness balance and hydrogen embrittlement susceptibility. Although they were similar in microstructure, i.e., nano-particles were precipitated on martensitic laths, different mechanical behaviors were exhibited. After tempering, the yield strength of 3.5 Ni steel reached a peak at 500 °C, while that of 2.5 Ni steel kept a downward trend, indicating that precipitation strengthening was significant in 3.5 Ni steel. Combined with thermodynamic and kinetic analyses, it was shown that when the Ni content increased, the rich-copper (Cu) precipitation transformation driving force would be enhanced and the reverse of austenite transformation accelerated to improve its stability. Moreover, the increase of Ni content also induced the increase in high-angle grain boundaries (HAGBs), which could inhibit crack propagation. Under the comprehensive effects of strengthening and ductility mechanism, 3.5 Ni steel exhibited excellent cryogenic toughness. Although it was not possible to obtain the ideal balancing of strength-toughness for the steel with lower Ni content, its hydrogen embrittlement susceptibility is satisfying. The results showed that the increase of grain boundary density caused by the grain refinement of 2.5 Ni steel is the key factor for its lower hydrogen embrittlement sensitivity index. Moreover, with the reduction of Ni content, the decrease of HAGBs and the increase in Σ11 boundary were conducive to reducing hydrogen-assisted cracking, while the residual Fe₃C in 3.5 Ni steel would deteriorate the hydrogen embrittlement resistance. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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14 pages, 8530 KiB

Open AccessArticle

Influence of ICCGHAZ on the Low-Temperature Toughness in HAZ of Heavy-Wall X80 Pipeline Steel

by Chao Fu, Xueda Li, Haichuan Li, Tao Han, Bin Han and Yong Wang

Metals 2022, 12(6), 907; https://doi.org/10.3390/met12060907 - 26 May 2022

Cited by 7 | Viewed by 2017

Abstract

Low-temperature embrittlement in the heat-affected zone (HAZ) of heavy-wall X80 weld joints is a primary challenge for arctic oil & gas exploitation. In this paper, the influence of intercritically reheated coarse-grained HAZ (ICCGHAZ) on the low-temperature toughness of the weld joint in a [...] Read more.

Low-temperature embrittlement in the heat-affected zone (HAZ) of heavy-wall X80 weld joints is a primary challenge for arctic oil & gas exploitation. In this paper, the influence of intercritically reheated coarse-grained HAZ (ICCGHAZ) on the low-temperature toughness of the weld joint in a 22 mm thick X80 spiral submerged arc welded pipe was studied through instrumented Charpy V-notch impact test at −80~20 °C and corresponding fracture surface characterization. The results indicated that the influence of ICCGHAZ on the overall toughness of the weld joint is related to temperature. At temperatures below −45 °C, individual and tiny martensite-austenite (MA) constituent debonding can trigger cleavage fracture–which was proved to be nucleation-controlled–and the probability of embrittlement of the ICCGHAZ increases. At temperatures higher than −45 °C, only relatively large or closely distributed MA constituent in ICCGHAZ satisfies the conditions to trigger propagation-controlled cleavage fractures, and the influence of ICCGHAZ on the overall toughness is not remarkable. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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11 pages, 2825 KiB

Open AccessArticle

Study of Surface Temperature Distribution for High-Temperature U75V Rail Steel Plates in Rolling Process by Colorimetry Thermometry

by Dongdong Zhou, Feng Gao, Junjian Wang and Ke Xu

Metals 2022, 12(5), 860; https://doi.org/10.3390/met12050860 - 17 May 2022

Cited by 4 | Viewed by 2426

Abstract

Surface temperature is a critical operating parameter that influences the phase transition time and rolling quality of U75V rail steel plates in the rolling process. There is still no extensive online detection system for the surface temperature of rail steel plates due to [...] Read more.

Surface temperature is a critical operating parameter that influences the phase transition time and rolling quality of U75V rail steel plates in the rolling process. There is still no extensive online detection system for the surface temperature of rail steel plates due to the hazardous environment, incorrect surface emissivity, and complex backgrounds. In this paper, online surface temperature detection equipment based on multi-spectral photography was built for high-temperature rail steel plates in the rolling processes. Then, the emissivity model for a high-temperature environment, colorimetric thermometry, and noise filtering methods were investigated to improve the accuracy of the temperature detection results of rail steel plates. Finally, the surface temperature of the U75V rail steel plate during three rolling passes could be calculated online point by point, and the greatest error was approximately 0.82% due to the blackbody calibration experiments. The results not only have a positive effect on understanding the temperature declination process of low-alloy rail steel plates during the rolling process, but could also benefit the control of the cooling rate and optimize the rolling model during rolling passes. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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14 pages, 6048 KiB

Open AccessArticle

Effect of Prior Cold Reduction of C–Si–Mn Hot-Rolled Sheet on Microstructures and Mechanical Properties after Quenching and Partitioning Treatment

by Yuanyao Cheng, Gang Zhao, Deming Xu and Siqian Bao

Metals 2022, 12(5), 799; https://doi.org/10.3390/met12050799 - 5 May 2022

Viewed by 1459

Abstract

This paper studies the microstructures and mechanical properties of quenching and partitioning (Q&P) samples prepared with 35% and 75% cold reduction sheets at an annealing temperature of 810 °C (intercritical temperature). The results indicate that prior cold reduction could significantly influence the ferrite [...] Read more.

This paper studies the microstructures and mechanical properties of quenching and partitioning (Q&P) samples prepared with 35% and 75% cold reduction sheets at an annealing temperature of 810 °C (intercritical temperature). The results indicate that prior cold reduction could significantly influence the ferrite recovery and recrystallization during intercritical annealing, which changes the size and distribution of the ferrite and retained austenite in the Q&P samples. Compared with the 75%—Q&P sample, the 35%—Q&P sample had smaller recrystallized ferrite and retained austenite grains, a higher volume fraction of retained austenite, and a more uneven size distribution of retained austenite. The 35%—Q&P sample presented better total elongation and a higher product of strength and elongation (PSE) than the 75%—Q&P sample. The higher total elongation was related to the higher content and uneven size distribution of retained austenite for they strengthened the TRIP effect and improved the uniform elongation of the sample. The results proved that Q&P steel prepared with a cold-rolled sheet with lower reduction exhibits a better combination of strength and plasticity due to the fact that lower reduction can delay the growth rate of austenite and recrystallized ferrite grains during the intercritical annealing stage. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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14 pages, 5416 KiB

Open AccessArticle

Fracture Analysis of Ultrahigh-Strength Steel Based on Split Hopkinson Pressure Bar Test

by Shihong Xiao, Xiaosheng Luan, Zhiqiang Liang, Xibin Wang, Tianfeng Zhou and Yue Ding

Metals 2022, 12(4), 628; https://doi.org/10.3390/met12040628 - 6 Apr 2022

Cited by 5 | Viewed by 2421

Abstract

Impact loading is an important cause of fracture failure of ultrahigh-strength steel parts during service. Revealing the fracture mechanism of ultrahigh-strength steel under impact loading has important reference significance for the material preparation, part design, and manufacturing of such steel. Based on the [...] Read more.

Impact loading is an important cause of fracture failure of ultrahigh-strength steel parts during service. Revealing the fracture mechanism of ultrahigh-strength steel under impact loading has important reference significance for the material preparation, part design, and manufacturing of such steel. Based on the split Hopkinson pressure bar (SHPB) test, the mechanical response characteristics of 45CrNiMoVA steel under impact loading were analyzed, and the true stress–true strain curves under a high strain rate (10³ s⁻¹) were obtained. It was found that under the simultaneous action of forward and tangential loading forces, a severe plastic deformation layer with a thickness of 20–30 μm was generated in the near impact-loading end face, which is the main cause for crack initiation and propagation. Under the condition of a high strain rate, the plastic flow stress of 45CrNiMoVA steel was characterized by the equilibrium of strain hardening and strain softening, and its impact fracture toughness decreased by 43.6%, resulting in increased quasi-cleavage fracture. Hence, severe surface plastic deformation during 45CrNiMoVA steel machining should be avoided, as it may lead to early failure. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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14 pages, 6770 KiB

Open AccessArticle

Investigation of Through-Thickness Residual Stress, Microstructure and Texture in Radial Forged High-Strength Alloy Steel Tubes

by Weisheng Xu and Jin Zhang

Metals 2022, 12(4), 622; https://doi.org/10.3390/met12040622 - 4 Apr 2022

Cited by 5 | Viewed by 2154

Abstract

Gradient variations of through-thickness residual stress, microstructure and texture greatly affect the performance of cold radial forged tubes. In this work, the through-thickness distribution of residual stress was measured based on the Debye ring. The microstructure was characterized with the electron backscattering diffraction [...] Read more.

Gradient variations of through-thickness residual stress, microstructure and texture greatly affect the performance of cold radial forged tubes. In this work, the through-thickness distribution of residual stress was measured based on the Debye ring. The microstructure was characterized with the electron backscattering diffraction technique. The texture was measured by the X-ray diffractometer. The influence of microstructure and texture on the strength and anisotropy of forged tubes with different thickness reductions was analyzed. The results show that the residual stress varies gradually from compressive to tensile from the outer to inner surface. The microhardness of the outer surface is lower than the inner. The dislocation density and low-angle grain boundary fraction are the smallest in the one-third thickness. The dislocation density and low-angle grain boundary fraction increase gradually from the one-third thickness to the inner surface. The main texture components of the forged tube include {111}<110>, {001}<110> and {114}<110>. Texture {111}<110> deflects gradually toward {114}<110>, {112}<110> and {110}<110> from the external tube to the internal tube. The gradient variation of strength mainly resulted from the difference of the dislocation density. The difference of strength along the radial direction is reduced with a larger thickness reduction. This work has important significance for improving the performance of high-strength alloy steel tubes processed by cold radial forging. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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7 pages, 10538 KiB

Open AccessArticle

Formation of Widmanstätten Ferrite and Grain Boundary Ferrite in a Hypereutectoid Pearlitic Steel

by Sixin Zhao, Na Min and Wei Li

Metals 2022, 12(3), 493; https://doi.org/10.3390/met12030493 - 14 Mar 2022

Cited by 5 | Viewed by 2818

Abstract

Accompanied by the formation of pearlite, Widmanstätten ferrite (WF), grain boundary ferrite and cementite are often found to nucleate at the prior austenite grain boundary during isothermal heat treatment. A hypereutectoid pearlitic steel transformed isothermally at temperatures ranging from 607 to 707 °C [...] Read more.

Accompanied by the formation of pearlite, Widmanstätten ferrite (WF), grain boundary ferrite and cementite are often found to nucleate at the prior austenite grain boundary during isothermal heat treatment. A hypereutectoid pearlitic steel transformed isothermally at temperatures ranging from 607 to 707 °C was investigated to clarify the evolution of different phases. At 607 °C, WF grains, which had a Kurdjumov–Sachs orientation relationship with the remaining austenite, were found to be aligned with the grain boundary. At 707 °C, lath WF grains, which were arranged parallel to each other, were at a certain angle to the grain boundary. The formation of pearlite showed two-stage kinetics in the dilatometer curve, and the grain boundary’s abnormal structure was suppressed. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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14 pages, 6008 KiB

Open AccessArticle

Experimental and Simulation Study on the Effect of Reduction Pretreatment on the Void Healing of Heavy Plate

by Zhen Ning, Xue Li, Hongqiang Liu, Qingwu Cai and Wei Yu

Metals 2022, 12(3), 400; https://doi.org/10.3390/met12030400 - 25 Feb 2022

Cited by 6 | Viewed by 1616

Abstract

In addition to eliminating voids in a billet, the reduction pretreatment (RP) process can refine the austenite structure after reheating and can deform the residual voids, which affect the void healing behavior during insulation before rolling, and then can affect the final quality [...] Read more.

In addition to eliminating voids in a billet, the reduction pretreatment (RP) process can refine the austenite structure after reheating and can deform the residual voids, which affect the void healing behavior during insulation before rolling, and then can affect the final quality of the steel plate. In this study, the effect of the RP process on the evolution of voids in billets and steel plates was investigated by experimental and numerical simulation. RP and non-RP billets were reheated and rolled into 60 mm-thick steel plates, respectively, and the evolutionary behavior of voids within the plates was analyzed using ultrasonic flaw detection methods. Finite element method (FEM) and phase-field method (PFM) were used to investigate the mechanism behind improving the quality of steel plates under the RP process. The simulation results show that, in addition to directly closing the voids through plastic deformation, the RP process can promote the diffusive healing behavior during insulation before rolling by refining the reheated austenite organization and by increasing the curvature of the void surface. Due to the reduction in voids inside the steel plate, the impact energy of the RP steel plate is higher. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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8 pages, 6230 KiB

Open AccessArticle

The Effects of Prior Austenite Grain Refinement on Strength and Toughness of High-Strength Low-Alloy Steel

by Xiucheng Li, Guangyi Lu, Qichen Wang, Jingxiao Zhao, Zhenjia Xie, Raja Devesh Kumar Misra and Chengjia Shang

Metals 2022, 12(1), 28; https://doi.org/10.3390/met12010028 - 24 Dec 2021

Cited by 21 | Viewed by 3572

Abstract

The effects of prior austenite grain (PAG) refinement on the mechanical properties of bainitic/martensitic steels not only come from itself, but also have more complex effects by affecting the substructure formed by coherent transformation. In this study, the samples of a low-alloy steel [...] Read more.

The effects of prior austenite grain (PAG) refinement on the mechanical properties of bainitic/martensitic steels not only come from itself, but also have more complex effects by affecting the substructure formed by coherent transformation. In this study, the samples of a low-alloy steel were water quenched from different austenitizing temperatures and the bainitic/martensitic microstructures with different PAG sizes were obtained. Electron back-scattered diffraction was used to characterize the microstructure and different types of boundaries were identified and quantitatively analyzed. The tensile tests and series temperature Charpy impact tests of different heat treatment were also carried out and comprehensively analyzed with microstructure characterization works. The results show that the uniform refinement of prior austenite grain can increases the density of packet boundary and block boundary, which leads to microstructure refinement with higher density of high-angle grain boundaries with misorientation >45°. The contribution of this microstructure refinement to toughness is significant, but its contributions to strength and elongation are relatively limited. Compared to uniform refined PAG, if the PAGs are mixed crystal, the density of block boundary will be reduced, which leads to a lower density of the high-angle boundary with misorientation >45° and the positive effects of microstructure refinement on toughness improvement are weakened. The observation of fracture surface of impact specimens indicates that refining the PAG can delay the tendency of brittle fracture with the decrease in test temperature, and even in the case of brittle fracture, the cleavage facet of the fracture surface is relatively smaller. This result also verifies that PAG refinement can effectively improve toughness by inhibiting cleavage fracture. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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16 pages, 5552 KiB

Open AccessArticle

Enhancement of Uniform Elongation by Temperature Change during Tensile Deformation in a 0.2C TRIP Steel

by Noriyuki Tsuchida and Stefanus Harjo

Metals 2021, 11(12), 2053; https://doi.org/10.3390/met11122053 - 18 Dec 2021

Cited by 2 | Viewed by 2815

Abstract

It is important to control the deformation-induced martensitic transformation (DIMT) up to the latter part of the deformation to improve the uniform elongation (U.El) through the TRIP effect. In the present study, tensile tests with decreasing deformation temperatures were conducted to achieve continuous [...] Read more.

It is important to control the deformation-induced martensitic transformation (DIMT) up to the latter part of the deformation to improve the uniform elongation (U.El) through the TRIP effect. In the present study, tensile tests with decreasing deformation temperatures were conducted to achieve continuous DIMT up to the latter part of the deformation. As a result, the U.El was improved by approximately 1.5 times compared with that in the tensile test conducted at 296 K. The enhancement of the U.El in the temperature change test was discussed with the use of neutron diffraction experiments. In the continuous DIMT behavior, a maximum transformation rate of about 0.4 was obtained at a true strain (ε) of 0.2, which was larger than that in the tensile test at 296 K. The tensile deformation behavior of ferrite (α), austenite (γ), and deformation-induced martensite (α′) phases were investigated from the viewpoint of the fraction weighted phase stress. The tensile test with a decreasing deformation temperature caused the increase of the fraction weighted phase stress of α and that of α′, which was affected by the DIMT behavior, resulting in the increase in the work hardening, and also controlled the ductility of α and α′, resulting in the enhancement of the U.El. Especially, the α phase contributed to maintaining high strength instead of α′ at a larger ε. Therefore, not only the DIMT behavior but also the deformation behavior of γ, α, and α′ are important in order to improve U.El due to the TRIP effect. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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13 pages, 8702 KiB

Open AccessArticle

Effect of Ce Content on Microstructure-Toughness Relationship in the Simulated Coarse-Grained Heat-Affected Zone of High-Strength Low-Alloy Steels

by Yuxin Cao, Xiangliang Wan, Feng Zhou, Yong Wang, Xinbin Liu, Kaiming Wu and Guangqiang Li

Metals 2021, 11(12), 2003; https://doi.org/10.3390/met11122003 - 11 Dec 2021

Cited by 4 | Viewed by 2150

Abstract

The study aimed to identify a moderate degree of Ce addition to improve the toughness in the simulated coarse-grained heat-affected zone (CGHAZ) of high-strength low-alloy steels, based on the effect of the Ce content on particle characteristics, microstructure and impact toughness. Three steels [...] Read more.

The study aimed to identify a moderate degree of Ce addition to improve the toughness in the simulated coarse-grained heat-affected zone (CGHAZ) of high-strength low-alloy steels, based on the effect of the Ce content on particle characteristics, microstructure and impact toughness. Three steels with 0.012 wt.%, 0.050 wt.% and 0.086 wt.% Ce content were subjected to 100 kJ/cm heat input in their thermal welding cycles. The particles and microstructures in the simulated CGHAZ of each steel were characterized and the impact-absorbance energy levels were measured at −20 °C. The results indicated that Ce₂O₂S inclusion compounds were gradually modified to CexSy-CeP and CeP with the increasing of the Ce content. A higher fraction of acicular ferrite was formed in the 0.012 wt.%-Ce-treated steel due to the lower mismatch between Ce₂O₂S and α-Fe. Furthermore, a lower fraction of M-A constituent was obtained in the 0.012 wt.%-Ce-treated steel. As a result, superior toughness and a typical amount of ductile fracture were detected in the simulated CGHAZ of the 0.012 wt.%-Ce-treated steel. Compared with the 0.012 wt.%-Ce-treated steel, a smaller prior austenite grain was observed in the 0.086 wt.%-Ce-treated steel because of the segregation of CeP at the grain boundary. However, the larger size and density of CeP led to poor toughness in the CGHAZ of the 0.086 wt.%-Ce-treated steel. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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16 pages, 6671 KiB

Open AccessArticle

The Influence of Temperature on the Microstructure and Properties of Nb-V-Ti-Mo Complex Microalloyed High-Strength Fire-Resistant Steel

by Xin Wang, Zhaodong Li, Shitong Zhou, Runnong Chen, Guangjie Da, Qilong Yong, Zhongmin Yang, Junchang Shen, Chengjia Shang and Qingyou Liu

Metals 2021, 11(11), 1670; https://doi.org/10.3390/met11111670 - 20 Oct 2021

Cited by 7 | Viewed by 2559

Abstract

Nb-V-Ti-Mo complex microalloyed high-strength fire-resistant steel was obtained through two-stage hot rolling and laminar cooling. The results showed that the microstructure of the steel included bainite ferrite and martensite-austenite constituent (i.e., MA) islands. The experimental steel displayed high strength at room temperature, with [...] Read more.

Nb-V-Ti-Mo complex microalloyed high-strength fire-resistant steel was obtained through two-stage hot rolling and laminar cooling. The results showed that the microstructure of the steel included bainite ferrite and martensite-austenite constituent (i.e., MA) islands. The experimental steel displayed high strength at room temperature, with a yield strength (YS) of 617 MPa and tensile strength of 813 MPa (elongation = 18.5%). As the temperature increased to 700 °C, the high-temperature yield strength gradually decreased. Electron backscatter diffraction (EBSD) was used to analyze the experimental steels at different temperatures. The grain sizes did not grow significantly. A small number of nanoprecipitates with an average diameter of 29.2 nm were distributed in the matrix of the as-rolled specimen. Upon increasing the temperature, the number of fine nanoprecipitates gradually increased, resulting in a gradual decrease in their average diameter, reaching a minimum of 19.4 nm at 600 °C. The Orowan equation explained well the precipitation strengthening effect of the nanoprecipitates that formed at a high temperature. At both room temperature and 300 °C, the Ashby work hardening theoretical curves were consistent with the experimental true stress-strain curves. Dynamic recovery and recrystallization occurred at 600 °C, which caused the experimental true stress-strain curve to deviate from the calculated curve. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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16 pages, 6939 KiB

Open AccessFeature PaperArticle

Deformation Behavior and Constitutive Equation of 42CrMo Steel at High Temperature

by Hongqiang Liu, Zhicheng Cheng, Wei Yu, Gaotian Wang, Jie Zhou and Qingwu Cai

Metals 2021, 11(10), 1614; https://doi.org/10.3390/met11101614 - 11 Oct 2021

Cited by 13 | Viewed by 2306

Abstract

High-temperature reduction pretreatment (HTRP) is a process that can significantly improve the core quality of a billet. The existing flow stress data cannot meet the needs of simulation due to lack of high temperature data. To obtain the hot forming process parameters for [...] Read more.

High-temperature reduction pretreatment (HTRP) is a process that can significantly improve the core quality of a billet. The existing flow stress data cannot meet the needs of simulation due to lack of high temperature data. To obtain the hot forming process parameters for the high-temperature reduction pretreatment process of 42CrMo steel, a hot compression experiment of 42CrMo steel was conducted on Gleeble-3500 thermal-mechanical at 1200–1350 °C with the rates of deformation 0.001–10 s⁻¹ and the deformation of 60%, and its deformation behavior at elevated temperature was studied. In this study, the effects of flow stress temperature and strain rate on austenite grain were investigated. Moreover, two typical constitutive models were employed to describe the flow stress, namely the Arrhenius constitutive model of strain compensation and back propagation artificial neural network (BP ANN) model. The performance evaluation shows that BP ANN model has high accuracy and stability to predict the curve. The thermal processing maps under strains of 0.1, 0.2, 0.3, and 0.4 were established. Based on the analysis of the thermal processing map, the optimal high reduction process parameter range of 42CrMo is obtained: the temperature range is 1250–1350 °C, and the strain rate range is 0.01–1 s⁻¹. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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14 pages, 15283 KiB

Open AccessArticle

Determination of Critical Transformation Temperatures for the Optimisation of Spring Steel Heat Treatment Processes

by Velaphi Jeffrey Matjeke, Josias Willem van der Merwe and Nontuthuzelo Lindokuhle Vithi

Metals 2021, 11(7), 1014; https://doi.org/10.3390/met11071014 - 24 Jun 2021

Cited by 5 | Viewed by 3135

Abstract

Bogie spring performance can be improved by using the exact heat treatment process parameters. The purpose of the study is to determine the critical transformation temperatures and investigate the effect of the cooling rates on microstructural and mechanical properties. The precise determination of [...] Read more.

Bogie spring performance can be improved by using the exact heat treatment process parameters. The purpose of the study is to determine the critical transformation temperatures and investigate the effect of the cooling rates on microstructural and mechanical properties. The precise determination of the required cooling rates for the particular grade of steel is important in order to optimise the heat treatment process of heavy-duty compression helical spring manufacturing. A traditional heat treatment system for the manufacture of hot coiled springs requires heating the steel to homogenize austenite; then, it is decomposed to martensite by rapid cooling. By analyzing the transition properties by heating and differing cooling rates, this analysis examines the thermal behaviour of high strength spring steel. Using the dilatometer and differential scanning calorimeter, scanning electron microscope, optical microscope, and hardness checking, critical transition temperatures and cooling rates of three springs steels were measured. Although the thermal transformation of materials has been researched for decades using dilatometers, not all materials have been characterized. The research offers insights into the critical transformation temperatures for the defined grades of spring steel and the role of cooling rates in the material’s properties. Mechanical properties are influenced by the transition data obtained from the dilatometric analysis. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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14 pages, 15520 KiB

Open AccessArticle

A Comparative Study of Acicular Ferrite Transformation Behavior between Surface and Interior in a Low C–Mn Steel by HT-LSCM

by Xiaojin Liu, Guo Yuan, Raja. Devesh Kumar Misra and Guodong Wang

Metals 2021, 11(5), 699; https://doi.org/10.3390/met11050699 - 24 Apr 2021

Cited by 3 | Viewed by 2074

Abstract

In this study, the acicular ferrite transformation behavior of a Ti–Ca deoxidized low carbon steel was studied using a high-temperature laser scanning confocal microscopy (HT-LSCM). The in situ observation of the transformation behavior on the sample surface with different cooling rates was achieved [...] Read more.

In this study, the acicular ferrite transformation behavior of a Ti–Ca deoxidized low carbon steel was studied using a high-temperature laser scanning confocal microscopy (HT-LSCM). The in situ observation of the transformation behavior on the sample surface with different cooling rates was achieved by HT-LSCM. The microstructure between the surface and interior of the HT-LSCM sample was compared. The results showed that Ti–Ca oxide particles were effective sites for acicular ferrite (AF) nucleation. The start transformation temperature at grain boundaries and intragranular particles decreased with an increase in cooling rate, but the AF nucleation rate increased and the surface microstructure was more interlocked. The sample surface microstructure obtained at 3 °C/s was dominated by ferrite side plates, while the ferrite nucleating sites transferred from grain boundaries to intragranular particles when the cooling rate was 15 °C/s. Moreover, it was interesting that the microstructure and microhardness of the sample surface and interior were different. The AF dominating microstructure, obtained in the sample interior, was much finer than the sample surface, and the microhardness of the sample surface was much lower than the sample interior. The combined factors led to a coarse size of AF on the sample surface. AF formed at a higher temperature resulted in the coarse size. The available particles for AF nucleation on the sample surface were quite limited, such that hard impingement between AF plates was much weaker than that in the sample interior. In addition, the transformation stress in austenite on the sample surface could be largely released, which contributed to a coarser AF plate size. The coarse grain size, low dislocation concentration and low carbon content led to lower hardness on the sample surface. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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Review

Jump to: Research

28 pages, 13958 KiB

Open AccessFeature PaperReview

In Situ Observation of Solidification and Crystallization of Low-Alloy Steels: A Review

by Yong Wang, Qiang Wang and Wangzhong Mu

Metals 2023, 13(3), 517; https://doi.org/10.3390/met13030517 - 3 Mar 2023

Cited by 4 | Viewed by 2556

Abstract

Crystallization during the solidification process of steels is of vital importance for controlling the quality of final products. This paper summarizes the in situ characterization research activities of crystallization behaviors of low-alloy steels during the solidification process. The results obtained using high-temperature confocal [...] Read more.

Crystallization during the solidification process of steels is of vital importance for controlling the quality of final products. This paper summarizes the in situ characterization research activities of crystallization behaviors of low-alloy steels during the solidification process. The results obtained using high-temperature confocal laser scanning microscope (HT-CLSM) are critically reviewed, and other relevant methodologies, i.e., either classical method using differential scanning calorimetry (DSC) or large-scale facility (LSF), are also briefly mentioned. The evolution of the crystallization front from a planar to a cellular and further to a dendritic one, and subsequential microstructure evolutions, i.e., delta-ferrite (δ) formation from the liquid, austenite (γ) transformation and decomposition, are mainly discussed. The current review aims to highlight the state-of-the-art research outputs obtained by the novel in situ characterization techniques, and the obtained knowledge aims to shed light on the further development of the quality low-alloy steel products by controlling the processing and structure correlation. Full article

(This article belongs to the Special Issue Advances in High-Strength Low-Alloy Steels)

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