Special Issue "High-Strength Low-Alloy Steels"

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (31 December 2019).

Special Issue Editors

Prof. Dr. Ricardo Branco
Website
Guest Editor
Department of Industrial and Mechanical Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway
Interests: fatigue of advanced and traditional materials; fracture mechanics; solid mechanics; structural integrity; additive materials
Special Issues and Collections in MDPI journals
Prof. Dr. Filippo Berto
Website
Guest Editor
Department of Industrial and Mechanical Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway
Interests: fatigue of advanced and traditional materials; fracture mechanics; solid mechanics; structural integrity; additive materials
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

High-strength low-alloy steels are designed to provide specific desirable combinations of properties, such as strength, toughness, formability, weldability, and corrosion resistance. These features make them ideal for critical applications that operate under severe service conditions and in aggressive environments, namely automotive and aeronautical components, offshore and bridge structures, construction machinery and pipelines, to mention just a few.  Despite the huge progress achieved over time on the behaviour of high-strength low-alloy steels, the development of more sophisticated products, combined with new manufacturing methodologies and new processing techniques, require additional research to address the new unsolved questions and to strengthen the existing knowledge in the field.

The goal of this Special Issue is to foster the dissemination of the latest research devoted to high-strength low-alloy steels from different perspectives, more specifically: the assessment of structural integrity, experimental analysis and numerical modelling of mechanical behaviour, damage and failure under static and dynamic loading, alloy design and microstructural evaluation, the influence of environmental mediums, and advanced applications. Both experimental and numerical approaches are encouraged. Literature review articles are also welcome.

Prof. Ricardo Branco
Prof. Filippo Berto
Guest Editors

Manuscript Submission Information

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Keywords

  • High-strength steels
  • Manufacturing and processing techniques
  • Alloy design
  • Microstructure and texture
  • Loading history
  • Environmental conditions
  • Advanced applications

Published Papers (22 papers)

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Research

Open AccessArticle
Failure Mechanisms of Mechanically and Thermally Produced Holes in High-Strength Low-Alloy Steel Plates Subjected to Fatigue Loading
Metals 2020, 10(3), 318; https://doi.org/10.3390/met10030318 - 28 Feb 2020
Cited by 1
Abstract
High-strength low-alloy steels (HSLA) are gaining popularity in structural applications in which weight reduction is of interest, such as heavy duty machinery, bridges, and offshore structures. Since the fatigue behavior of welds appears to be almost independent of the base material and displays [...] Read more.
High-strength low-alloy steels (HSLA) are gaining popularity in structural applications in which weight reduction is of interest, such as heavy duty machinery, bridges, and offshore structures. Since the fatigue behavior of welds appears to be almost independent of the base material and displays little improvement when more resistant steel grades are employed, the use of bolted joints is an alternative joining technique which can lead to an increased fatigue performance of HSLA connections. Manufacturing a hole to allocate the fastener elements is an unavoidable step in bolted elements and it might induce defects and tensile residual stresses that could affect its fatigue behavior. This paper studies and compares several mechanical (punching, drilling, and waterjet-cut) and thermal (plasma and laser-cut) hole-making procedures in HSLA structural plates. A series of 63 uniaxial fatigue tests was completed, covering three HSLA grades produced by thermomechanically controlled process (TMCP) with yield strength ranging from 500 to 960 MPa. Samples were tested at single load level, which was considered representative in HSLA typical applications, according to the input received from end users. The manufactured holes were examined by means of optical and electron microscopy, 3D point measurement, micro hardness tests, X-ray diffraction, and electron backscatter diffraction (EBSD). The results give insight on cutting processes in HSLA and indicate how the fatigue failure is dominated by macro defects rather than by the steel grade. It was shown that the higher yield strength of the HSLA grades did not lead to a higher fatigue life. Best fatigue results were achieved with laser-cut specimens while punched samples withstood the lowest amount of cycles. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessFeature PaperArticle
Low Cycle Fatigue Behavior of Elbows with Local Wall Thinning
Metals 2020, 10(2), 260; https://doi.org/10.3390/met10020260 - 17 Feb 2020
Abstract
There have been a number of studies concerning the integrity of high-strength carbon steel pipe elbows weakened by local pipe wall thinning, the latter can be typically caused by flow accelerated erosion/corrosion. In particular, the focus of several recent studies was on low [...] Read more.
There have been a number of studies concerning the integrity of high-strength carbon steel pipe elbows weakened by local pipe wall thinning, the latter can be typically caused by flow accelerated erosion/corrosion. In particular, the focus of several recent studies was on low cycle fatigue behavior of damaged elbows, mainly, in relation to strength and integrity of piping systems of nuclear power plants subjected to extreme loading conditions, such as earthquake or shutdown. The current paper largely adopts the existing methodology, which was previously developed, and extends it to copper-nickel elbows, which are widely utilized in civil infrastructure in seismically active regions. FE (finite element) studies along with a full-scale testing program were conducted and the outcomes are summarized in this article. The overall conclusion is that the tested elbows with various severity of local wall thinning, which were artificially introduced at different locations, demonstrate a strong resistance against low cycle fatigue loading. In addition, elbows with wall thinning defects possess a significant safety margin against seismic loading. These research outcomes will contribute to the development of strength evaluation procedures and will help to develop more effective maintenance procedures for piping equipment utilized in civil infrastructure. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessArticle
Effect of Sign-Alternating Cyclic Polarisation and Hydrogen Uptake on the Localised Corrosion of X70 Pipeline Steel in Near-Neutral Solutions
Metals 2020, 10(2), 245; https://doi.org/10.3390/met10020245 - 12 Feb 2020
Abstract
The effect of sign-alternating cycling polarisation (SACP) on the localised corrosion of X70pipeline steel in solutions of various compositions was studied. Localised corrosion of steel at anodic potentials was accelerated with an increase in the duration of the cathodic half-cycle, in the presence [...] Read more.
The effect of sign-alternating cycling polarisation (SACP) on the localised corrosion of X70pipeline steel in solutions of various compositions was studied. Localised corrosion of steel at anodic potentials was accelerated with an increase in the duration of the cathodic half-cycle, in the presence of a promoter of hydrogen absorption in aqueous electrolyte, and with an increase in the concentrations of chloride and bicarbonate ions. It was pointed out that the corrosion rate is determined by the amount of hydrogen absorbed by the steel. A quantitative indicator to determine the intensity of localised corrosion under SACP was suggested. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessArticle
Effect of the t8/5 Cooling Time on the Properties of S960MC Steel in the HAZ of Welded Joints Evaluated by Thermal Physical Simulation
Metals 2020, 10(2), 229; https://doi.org/10.3390/met10020229 - 07 Feb 2020
Cited by 1
Abstract
The heat input into the material during welding significantly affects the properties of high-strength steels in the near-weld zone. A zone of hardness decrease forms, which is called the soft zone. The width of the soft zone also depends on the cooling time [...] Read more.
The heat input into the material during welding significantly affects the properties of high-strength steels in the near-weld zone. A zone of hardness decrease forms, which is called the soft zone. The width of the soft zone also depends on the cooling time t8/5. An investigation of the influence of welding parameters on the resulting properties of welded joints can be performed by thermal physical simulation. In this study, the effect of the cooling rate on the mechanical properties of the heat-affected zone of the steel S960MC with a thickness of 3 mm was investigated. Thermal physical simulation was performed on a Gleeble 3500. Three levels of cooling time were used, which were determined from the reference temperature cycle obtained by metal active gas welding (MAG). A tensile test, hardness measurement, impact test with fracture surface evaluation, and microstructural evaluation were performed to investigate the modified specimen thickness. The shortest time t8/5 = 7 s did not provide tensile and yield strength at the minimum required value. The absorbed energy after recalculation to the standard sample size of 10 × 10 mm was above the 27 J limit at −40 °C. The hardness profile also depended on the cooling rate and always had a softening zone. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessArticle
Fatigue Examination of HSLA Steel with Yield Strength of 960 MPa and Its Welded Joints under Strain Mode
Metals 2020, 10(2), 228; https://doi.org/10.3390/met10020228 - 07 Feb 2020
Abstract
The full benefits of application the high strength low alloyed steels HSLA can be achieved if the structures will be able to carry the alternate loads and fatigue cracks will not be formed, even in the vicinity of welded joints. For this reason [...] Read more.
The full benefits of application the high strength low alloyed steels HSLA can be achieved if the structures will be able to carry the alternate loads and fatigue cracks will not be formed, even in the vicinity of welded joints. For this reason the purpose of this study is to find and to explain the influence of different factors on fatigue crack initiation and the nature of crack propagation in HSLA steel and its welded joints. The S960QL steel and two types of welded joints were subjected to low cycle fatigue (LCF) tests at a strain mode and the received surfaces of fractures were analyzed using SEM microscope. Additionally, the microhardness measurements and the residual stress analyze in a cross-section of the joint were conducted. The maximum hardness was determined on the fusion line and more favorable hardness distribution was in the square joints than in single-V. Compiled maps of residual stresses have shown that the local orientation and values of the principal stress vector near the fusion line can influence negative the fatigue life. Finally, the square joints tested in the low cycle fatigue regime have shown a slightly higher fatigue life in comparison with single-V. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessFeature PaperArticle
The Effect of Mean Load for S355J0 Steel with Increased Strength
Metals 2020, 10(2), 209; https://doi.org/10.3390/met10020209 - 01 Feb 2020
Cited by 2
Abstract
The paper presents an algorithm for calculating the fatigue life of S355J0 steel specimens subjected to cyclic bending, cyclic torsion, and a combination of bending and torsion using mean stress values. The method of transforming cycle amplitudes with a non-zero mean value into [...] Read more.
The paper presents an algorithm for calculating the fatigue life of S355J0 steel specimens subjected to cyclic bending, cyclic torsion, and a combination of bending and torsion using mean stress values. The method of transforming cycle amplitudes with a non-zero mean value into fatigue equivalent cycles with increased amplitude and zero mean value was used. Commonly known and used transformation dependencies were used and a new model of the impact of the mean stress value on the fatigue life of the material was proposed. The life calculated based on the proposed algorithm was compared with the experimental life. It has been shown that the proposed model finds the widest application in the load cases studied, giving good compliance of the calculation results with the experimental results. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessArticle
A New Electron Backscatter Diffraction-Based Method to Study the Role of Crystallographic Orientation in Ductile Damage Initiation
Metals 2020, 10(1), 113; https://doi.org/10.3390/met10010113 - 12 Jan 2020
Abstract
The third generation of advanced high strength steels shows promising properties for automotive applications. The macroscopic mechanical response of this generation can be further improved by a better understanding of failure mechanisms on the microstructural level and micro-mechanical behavior under various loading conditions. [...] Read more.
The third generation of advanced high strength steels shows promising properties for automotive applications. The macroscopic mechanical response of this generation can be further improved by a better understanding of failure mechanisms on the microstructural level and micro-mechanical behavior under various loading conditions. In the current study, the microstructure of a multiphase low silicon bainitic steel is characterized with a scanning electron microscope (SEM) equipped with an electron backscatter diffraction detector. A uniaxial tensile test is carried out on the bainitic steel with martensite and carbides as second phase constituents. An extensive image processing on SEM micrographs is conducted in order to quantify the void evolution during plastic deformation. Later, a new post-mortem electron backscatter diffraction-based method is introduced to address the correlation between crystallographic orientation and damage initiation. In this multiphase steel, particular crystallographic orientation components were observed to be highly susceptible to micro-void formation. It is shown that stress concentration around voids is rather relaxed by void growth than local plasticity. Therefore, this post-mortem method can be used as a validation tool together with a crystal plasticity-based hardening model in order to predict the susceptible crystallographic orientations to damage nucleation. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessFeature PaperArticle
Impact of Precipitate Morphology on the Dissolution and Grain-Coarsening Behavior of a Ti-Nb Microalloyed Linepipe Steel
Metals 2020, 10(1), 89; https://doi.org/10.3390/met10010089 - 04 Jan 2020
Abstract
The relationship between precipitate morphology and dissolution on grain coarsening behavior was studied in two Ti-Nb microalloyed Linepipe (LP) Steels. The developed understanding highlights the importance of the complex relationship between precipitate constitutive make-up, dissolution mechanism and grain boundary (GB) pinning force. Equilibrium-based [...] Read more.
The relationship between precipitate morphology and dissolution on grain coarsening behavior was studied in two Ti-Nb microalloyed Linepipe (LP) Steels. The developed understanding highlights the importance of the complex relationship between precipitate constitutive make-up, dissolution mechanism and grain boundary (GB) pinning force. Equilibrium-based empirical solubility products were used to calculate precipitate volume fractions and compared to experimental measurements. Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD) and Electron Probe Micro-Analysis (EPMA) were conducted on bulk samples. Transmission Electron Microscopy (TEM)-based techniques were used on C-replica extractions and thin-foils. A retardation in the grain-coarsening temperature compared to the predicted coarsening temperature based on equilibrium calculations was noticed. In addition, a consistent NbC epitaxial formation over pre-existing TiN was observed. The resulting reduction in total precipitate/matrix interface area and the low energy of the TiN/NbC interface are pointed to as responsible mechanisms for the retardation in the kinetics of precipitates’ dissolution. This dissolution retardation mechanism suggests that a lower Nb content might be effective in controlling the grain coarsening behavior of austenite. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessArticle
The Significance of Central Segregation of Continuously Cast Billet on Banded Microstructure and Mechanical Properties of Section Steel
Metals 2020, 10(1), 76; https://doi.org/10.3390/met10010076 - 02 Jan 2020
Cited by 1
Abstract
The solidification structure and segregation of continuously cast billets produced by different continuous casting processes are investigated to elucidate their effect on segregated bands in hot-rolled section steel. It suggested that segregated spots are mainly observed in the equiaxed crystal zone of a [...] Read more.
The solidification structure and segregation of continuously cast billets produced by different continuous casting processes are investigated to elucidate their effect on segregated bands in hot-rolled section steel. It suggested that segregated spots are mainly observed in the equiaxed crystal zone of a billet. The solidification structure is directly related to superheating and the intensities of secondary cooling. To a certain extent, the ratio of the columnar crystal increases with the increase of superheating and secondary cooling. Moreover, the number of spot segregations decreases with the decrease of the equiaxed crystal ratio. After hot rolling, the segregation spots are deformed to form segregated bands in steels. The severe segregation of Mn in segregated bands corresponds with that in the segregation spots. The elongation ratio and low temperature toughness deteriorate significantly by a high fraction of degenerate pearlite caused by central segregation. With a decrease of central segregation, the total elongation is increased by 10% and the ductile–brittle transition temperature (DBTT) is also reduced from −10 to −40 °C. According to the experimental results, columnar crystal in billets is preferred to effectively reduce the degree of central segregation and further improve low temperature toughness and the elongation ratio. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessFeature PaperArticle
New Insights into the Microstructural Changes During the Processing of Dual-Phase Steels from Multiresolution Spherical Indentation Stress–Strain Protocols
Metals 2020, 10(1), 18; https://doi.org/10.3390/met10010018 - 21 Dec 2019
Abstract
In this study, recently established multiresolution spherical indentation stress–strain protocols have been employed to derive new insights into the microstructural changes that occur during the processing of dual-phase (DP) steels. This is accomplished by utilizing indenter tips of different radii such that the [...] Read more.
In this study, recently established multiresolution spherical indentation stress–strain protocols have been employed to derive new insights into the microstructural changes that occur during the processing of dual-phase (DP) steels. This is accomplished by utilizing indenter tips of different radii such that the mechanical responses can be evaluated both at the macroscale (reflecting the bulk properties of the sample) and at the microscale (reflecting the properties of the constituent phases). More specifically, nine different thermo-mechanical processing conditions involving different combinations of intercritical annealing temperatures and bake hardening after different amounts of cold work were studied. In addition to demonstrating the tremendous benefits of the indentation protocols for evaluating the variations within each sample and between the samples at different material length scales in a high throughput manner, the measurements provided several new insights into the microstructural changes occurring in the alloys during their processing. In particular, the indentation measurements indicated that the strength of the martensite phase reduces by about 37% when quenched from 810 °C compared to being quenched from 750 °C, while the strength of the ferrite phase remains about the same. In addition, during the 10% thickness reduction and bake hardening steps, the strength of the martensite phase shows a small decrease due to tempering, while the strength of the ferrite increases by about 50% by static aging. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessArticle
Study of Nanometer-Sized Precipitation and Properties of Fire Resistant Hot-Rolled Steel
Metals 2019, 9(11), 1230; https://doi.org/10.3390/met9111230 - 18 Nov 2019
Abstract
Nanometer-sized precipitated carbides in a low carbon Ti-V-Mo bearing steel were obtained through hot rolling and air cooling and were investigated by transmission electron microscopy (TEM). The nanometer-sized interphase-precipitated carbides have been found to exhibit an average diameter of ~6.1 ± 2.7 nm, [...] Read more.
Nanometer-sized precipitated carbides in a low carbon Ti-V-Mo bearing steel were obtained through hot rolling and air cooling and were investigated by transmission electron microscopy (TEM). The nanometer-sized interphase-precipitated carbides have been found to exhibit an average diameter of ~6.1 ± 2.7 nm, with an average spacing of ~24–34 nm. Yield strength of 578 ± 20 MPa and tensile strength of 813 ± 25 MPa were achieved with high elongation of 25.0 ± 0.5% at room temperature. The nanometer-sized precipitation exhibited high stability after annealing at high temperatures of 600 °C and 650 °C for 3 h. Average diameters of carbides were statistically measured to be ~6.9 ± 2.3 nm and 8.4 ± 2.6 nm after tempering at high temperatures of 600 °C and 650 °C, respectively. The micro-hardness was ~263–268 HV0.1 after high temperature tempering, which was similar to the hot-rolled sample (273 HV0.1), and yield strength of 325 ± 13 MPa and 278 ± 4 MPa was achieved at elevated temperatures of 600 °C and 650 °C, respectively. The significant decrease of yield strength at 650 °C was attributed to the large decrease in shear modulus. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessArticle
Effect of Welding Heat Input on Simulated HAZ Areas in S960QL High Strength Steel
Metals 2019, 9(11), 1226; https://doi.org/10.3390/met9111226 - 16 Nov 2019
Cited by 4
Abstract
When the weldability of high strength steels is analyzed, it is the softening in the heat-affected zone (HAZ) that is mostly investigated, and the reduction of toughness properties is generally less considered. The outstanding toughness properties of quenched and tempered high strength steels [...] Read more.
When the weldability of high strength steels is analyzed, it is the softening in the heat-affected zone (HAZ) that is mostly investigated, and the reduction of toughness properties is generally less considered. The outstanding toughness properties of quenched and tempered high strength steels cannot be adequately preserved during the welding due to the unfavorable microstructural changes in the HAZ. Relevant technological variants (t8/5 = 2.5–100 s) for arc welding technologies were applied during the HAZ simulation of S960QL steel (EN 10025-6) in a Gleeble 3500 physical simulator, and the effect of cooling time on the critical HAZ areas of single and multipass welded joints was analyzed. Thermal cycles were determined according to the Rykalin 3D model. The properties of the selected coarse-grained (CGHAZ), intercritical (ICHAZ) and intercritically reheated coarse-grained (ICCGHAZ) zones were investigated by scanning electron microscope, macro and micro hardness tests and instrumented Charpy V-notch pendulum impact tests. The examined HAZ subzones indicated higher sensitivity to the welding heat input compared to conventional structural steels. Due to the observed brittle behavior of all subzones in the whole t8/5 range, the possible lowest welding heat input should be applied in order to minimize the volume of HAZ that does not put fulfillment of the allowed maximal (450 HV10) hardness at risk and does not lead to the formation of cold cracks. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessArticle
Carbide Precipitation, Dissolution, and Coarsening in G18CrMo2–6 Steel
Metals 2019, 9(9), 916; https://doi.org/10.3390/met9090916 - 22 Aug 2019
Cited by 2
Abstract
The precipitation, dissolution, and coarsening of different carbides at 680 °C in G18CrMo2–6 steel was investigated experimentally combined with Jmatpro simulation. The G18CrMo2–6 steel was normalized at 940 °C, followed by tempering at different times at a constant temperature of 680 °C. During [...] Read more.
The precipitation, dissolution, and coarsening of different carbides at 680 °C in G18CrMo2–6 steel was investigated experimentally combined with Jmatpro simulation. The G18CrMo2–6 steel was normalized at 940 °C, followed by tempering at different times at a constant temperature of 680 °C. During the tempering process, there are mainly two kinds of carbide, namely M3C and M23C6. Through characterization of microstructural evolution, thermodynamic calculation, and kinetic simulation, it was observed that during the tempering process, the stable M23C6 carbide was growing, whereas the metastable M3C carbide was disappearing. At the end, the M3C carbide was dissolved and the M23C6 carbide was in equilibrium with the matrix. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessArticle
Controlling Variability in Mechanical Properties of Plates by Reducing Centerline Segregation to Meet Strain-Based Design of Pipeline Steel
Metals 2019, 9(7), 749; https://doi.org/10.3390/met9070749 - 04 Jul 2019
Cited by 1
Abstract
Low variability in mechanical properties is required for pipeline project designs to meet a strain-based design, which is used in regions of large ground movements. The objective of this study is to elucidate the influence of centerline segregation in continuously cast slab on [...] Read more.
Low variability in mechanical properties is required for pipeline project designs to meet a strain-based design, which is used in regions of large ground movements. The objective of this study is to elucidate the influence of centerline segregation in continuously cast slab on variability in the mechanical property of pipeline steel, and controlling centerline segregation can meet the requirements of a strain-based design. Mannesmann rating method was used to evaluate the degree of segregation of two slabs and its effect on variability in mechanical properties of corresponding plates. Microstructural characterization indicated that bainite/martensite was formed in a segregated area where the content of C and Mn enriched. The mechanical property results indicated that controlling the degree of centerline segregation can reduce tensile strength variability and improve ductile-brittle transition temperature (DBTT). Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessArticle
Determination of Grain Growth Kinetics and Assessment of Welding Effect on Properties of S700MC Steel in the HAZ of Welded Joints
Metals 2019, 9(6), 707; https://doi.org/10.3390/met9060707 - 24 Jun 2019
Cited by 3
Abstract
The welding of fine-grained steels is a very specific technology because of the requirement for the heat input limit value. Applying temperature cycles results in an intense grain growth in a high-temperature heat-affected zone (HAZ). This has a significant effect on the changing [...] Read more.
The welding of fine-grained steels is a very specific technology because of the requirement for the heat input limit value. Applying temperature cycles results in an intense grain growth in a high-temperature heat-affected zone (HAZ). This has a significant effect on the changing of strength properties and impact values. The intensity of grain coarsening in the HAZ can be predicted based on the experimentally determined activation energy and material constant, both of which define grain growth kinetics. These quantities, together with real measured welding cycles, can be subsequently used during experiments to determine mechanical properties in a high-temperature HAZ. This paper shows a methodical procedure leading to the obtainment of the material quantities mentioned above that define the grain growth, both at fast and slow temperature cycles. These data were used to define the exposure temperature and the soaking time in a vacuum furnace to prepare test samples with grain sizes corresponding to the high-temperature HAZ of welded joints for the testing procedures. Simultaneously, by means of the thermo-mechanical simulator Gleeble 3500, testing samples were prepared which, due to a temperature gradient, created conditions comparable to those in the HAZ. The experiments were both carried out with the possibility of free sample dilatation and under a condition of zero dilation, which happens when the thermal expansion of a material is compensated by plastic deformation. It has been found that shape of the temperature cycle, maximal achieved cycle temperature, cooling rate, and, particularly, the time in which the sample is in the austenite region have significant effects on the resulting change of properties. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessArticle
Strength and Fracture Toughness of Hardox-400 Steel
Metals 2019, 9(5), 508; https://doi.org/10.3390/met9050508 - 30 Apr 2019
Cited by 4
Abstract
This paper presents results of strength and fracture toughness properties of low-carbon high-strength Hardox-400 steel. Experimental tests were carried out for specimens of different thickness at wide temperature range from −100 to 20 °C. The dependences of the characteristic of material strength and [...] Read more.
This paper presents results of strength and fracture toughness properties of low-carbon high-strength Hardox-400 steel. Experimental tests were carried out for specimens of different thickness at wide temperature range from −100 to 20 °C. The dependences of the characteristic of material strength and fracture toughness on temperature based on experimental data are shown. Numerical calculation of the stress and strain distributions in area before crack tip using the finite element method (FEM) was done. Based on results of numerical calculation and observation of the fracture surfaces by scanning electron microscope (SEM), the critical local stress level at which brittle fracture takes place was assessed. Consideration of the levels of stress and strain in the analysis of the metal state at the tip of the crack allowed to justify the occurrence of the brittle-to-ductile fracture mechanism. On the basis of the results of stretch zone width measurements and stress components, the values of fracture toughness at the moment of crack initiation were calculated. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessArticle
Influence of Welding on Dynamic Fracture Toughness of Strenx 700MC Steel
Metals 2019, 9(5), 494; https://doi.org/10.3390/met9050494 - 28 Apr 2019
Cited by 1
Abstract
Thermomechanically processed high-strength steels feature specific fracture behavior. One of the decisive criteria for their application is their stability against internal defects during impact loads, especially in connection with the welding. The work is focused on experimental analyses of the influence of welding [...] Read more.
Thermomechanically processed high-strength steels feature specific fracture behavior. One of the decisive criteria for their application is their stability against internal defects during impact loads, especially in connection with the welding. The work is focused on experimental analyses of the influence of welding on static and dynamic fracture toughness of Strenx 700MC steel. The fracture toughness was determined using the circumferentially notched round bar specimens during static loads and two dynamic load levels. To achieve a homogeneous zone for the requirements of fracture toughness tests, simulation of the welding influence was performed. Fractographic and metallographic analyses described a specific fracture behavior controlled by the internal structural heterogeneity. A limiting degradation process due to welding was identified by the microstructural analysis. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessArticle
Mechanical Properties of Direct-Quenched Ultra-High-Strength Steel Alloyed with Molybdenum and Niobium
Metals 2019, 9(3), 350; https://doi.org/10.3390/met9030350 - 19 Mar 2019
Cited by 3
Abstract
The direct quenching process is an energy- and resource-efficient process for making high-strength structural steels with good toughness, weldability, and bendability. This paper presents the results of an investigation into the effect of molybdenum and niobium on the microstructures and mechanical properties of [...] Read more.
The direct quenching process is an energy- and resource-efficient process for making high-strength structural steels with good toughness, weldability, and bendability. This paper presents the results of an investigation into the effect of molybdenum and niobium on the microstructures and mechanical properties of laboratory rolled and direct-quenched 11 mm thick steel plates containing 0.16 wt.% C. Three of the studied compositions were niobium-free, having molybdenum contents of 0 wt.%, 0.25 wt.%, and 0.5 wt.%. In addition, a composition containing 0.25 wt.% molybdenum and 0.04 wt.% niobium was studied. Prior to direct quenching, finish rolling temperatures (FRTs) of about 800 °C and 900 °C were used to obtain different levels of austenite pancaking. The final direct-quenched microstructures were martensitic and yield strengths varied in the range of 766–1119 MPa. Mo and Nb additions led to a refined martensitic microstructure that resulted in a good combination of strength and toughness. Furthermore, Mo and Nb alloying significantly reduced the amount of strain-induced ferrite in the microstructure at lower FRTs (800 °C). The steel with 0.5 wt.% Mo exhibited a high yield strength of 1119 MPa combined with very low 28 J transition temperature of −95 °C in the as-quenched condition. Improved mechanical properties of Mo and Mo–Nb steels can be attributed to the improved boron protection. Also, the crystallographic texture of the investigated steels showed that Nb and Nb–Mo alloying increased the amount of {112}<131> and {554}<225> texture components. The 0Mo steel also contained the texture components of {110}<110> and {011}<100>, which can be considered to be detrimental for impact toughness properties. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessFeature PaperArticle
Influence of Mechanical Anisotropy on Micro-Voids and Ductile Fracture Onset and Evolution in High-Strength Low Alloyed Steels
Metals 2019, 9(2), 224; https://doi.org/10.3390/met9020224 - 13 Feb 2019
Cited by 2
Abstract
In this paper results of a wide and innovative mechanical assessment, that was performed on large diameter spiral line pipes for gas transportation, are reported. The anisotropic material hardening has been characterized by tensile (smooth and notched specimens), torsion, and compression tests. Tests [...] Read more.
In this paper results of a wide and innovative mechanical assessment, that was performed on large diameter spiral line pipes for gas transportation, are reported. The anisotropic material hardening has been characterized by tensile (smooth and notched specimens), torsion, and compression tests. Tests were performed in the pipe of the pipe with specimens machined along several orientations, taking into account the pipe through thickness direction. The influence of different triaxiality stress states on anisotropic behavior of the material have also been analyzed by means of tensile tests on notched specimens. After the experiments, the material was assessed by measuring the void distribution on the material as is, and on many deformed and fractured specimens, including tensile tests at different triaxiality, and torsion tests. The results showed that in such a class of materials, the experimental void fraction is fully negligible and not related to the applied plastic strain, even at the fracture proximity. As a consequence it can be concluded that, the plastic softening hypothesis may be dropped and damage due to void evolution hypothesis is not adequate. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessArticle
Modelling and Microstructural Aspects of Ultra-Thin Sheet Metal Bundle Cutting
Metals 2019, 9(2), 162; https://doi.org/10.3390/met9020162 - 01 Feb 2019
Cited by 3
Abstract
The results of numerical simulations of the cutting process obtained by means of the finite element method were studied in this work. The physical model of a bundle consisting of ultra-thin metal sheets was elaborated and then submitted to numerical calculations using the [...] Read more.
The results of numerical simulations of the cutting process obtained by means of the finite element method were studied in this work. The physical model of a bundle consisting of ultra-thin metal sheets was elaborated and then submitted to numerical calculations using the computer system LS-DYNA. Experimental investigations rely on observation of metallographic specimens of the surfaces being cut under a scanning electron microscope. The experimental data showing the microstructure of an ultra-thin metal bundle were the basis for the verification of the numerical results. It was found that the fracture area consists of two distinct zones. Morphological features of the brittle and ductile zones were identified. There are distinct differences between the front and back sides of the knife. The experimental investigations are in good agreement with the simulation results. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessArticle
Multiaxial Fatigue Life Prediction on S355 Structural and Offshore Steel Using the SKS Critical Plane Model
Metals 2018, 8(12), 1060; https://doi.org/10.3390/met8121060 - 13 Dec 2018
Cited by 9
Abstract
This work analyses the prediction capabilities of a recently developed critical plane model, called the SKS method. The study uses multiaxial fatigue data for S355-J2G3 steel, with in-phase and 90° out-of-phase sinusoidal axial-torsional straining in both the low cycle fatigue and high cycle [...] Read more.
This work analyses the prediction capabilities of a recently developed critical plane model, called the SKS method. The study uses multiaxial fatigue data for S355-J2G3 steel, with in-phase and 90° out-of-phase sinusoidal axial-torsional straining in both the low cycle fatigue and high cycle fatigue ranges. The SKS damage parameter includes the effect of hardening, mean shear stress and the interaction between shear and normal stress on the critical plane. The collapse and the prediction capabilities of the SKS critical plane damage parameter are compared to well-established critical plane models, namely Wang-Brown, Fatemi-Socie, Liu I and Liu II models. The differences between models are discussed in detail from the basis of the methodology and the life results. The collapse capacity of the SKS damage parameter presents the best results. The SKS model produced the second-best results for the different types of multiaxial loads studied. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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Open AccessArticle
Austenite Decomposition and Precipitation Behavior of Plastically Deformed Low-Si Microalloyed Steel
Metals 2018, 8(12), 1028; https://doi.org/10.3390/met8121028 - 06 Dec 2018
Cited by 3
Abstract
The aim of the present study is to assess the effects of hot deformation and cooling paths on the phase transformation kinetics in a precipitation-strengthened automotive 0.2C–1.5Mn–0.5Si steel with Nb and Ti microadditions. The analysis of the precipitation processes was performed while taking [...] Read more.
The aim of the present study is to assess the effects of hot deformation and cooling paths on the phase transformation kinetics in a precipitation-strengthened automotive 0.2C–1.5Mn–0.5Si steel with Nb and Ti microadditions. The analysis of the precipitation processes was performed while taking into account equilibrium calculations and phase transitions resulting from calculated time–temperature–transformation (TTT) and continuous cooling transformation (CCT) diagrams. The austenite decomposition was monitored based on thermodynamic calculations of the volume fraction evolution of individual phases as a function of temperature. The calculations were compared to real CCT and DCCT (deformation continuous cooling transformation) diagrams produced using dilatometric tests. The research included the identification of the microstructure of the nondeformed and thermomechanically processed supercooled austenite products formed at various cooling rates. The complex interactions between the precipitation process, hot deformation, and cooling schedules are linked. Full article
(This article belongs to the Special Issue High-Strength Low-Alloy Steels)
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