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10 pages, 2304 KiB

Open AccessArticle

Influence of Scanning Strategy Parameters on Residual Stress in the SLM Process According to the Bridge Curvature Method for AISI 316L Stainless Steel

by Jiri Hajnys, Marek Pagáč, Jakub Měsíček, Jana Petru and Mariusz Król

Materials 2020, 13(7), 1659; https://doi.org/10.3390/ma13071659 - 03 Apr 2020

Cited by 49 | Viewed by 4450

Abstract

The present paper deals with the investigation and comparison of the influence of scanning strategy on residual stress in the selective laser melting (SLM) process. For the purpose of the experiment, bridge geometry samples were printed by a 3D metal printer, which exhibited [...] Read more.

The present paper deals with the investigation and comparison of the influence of scanning strategy on residual stress in the selective laser melting (SLM) process. For the purpose of the experiment, bridge geometry samples were printed by a 3D metal printer, which exhibited tension after cutting from the substrate, slightly bending the samples toward the laser melting direction. Samples were produced with the variation of process parameters and with a change in scanning strategy which plays a major role in stress generation. It was evaluated using the Bridge Curvature Method (BCM) and optical microscopy. At the end, a recommendation was made. Full article

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

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21 pages, 7114 KiB

Open AccessArticle

Complex Corrosion Properties of AISI 316L Steel Prepared by 3D Printing Technology for Possible Implant Applications

by Josef Hlinka, Martin Kraus, Jiri Hajnys, Marek Pagac, Jana Petrů, Zbigniew Brytan and Tomasz Tański

Materials 2020, 13(7), 1527; https://doi.org/10.3390/ma13071527 - 26 Mar 2020

Cited by 29 | Viewed by 4108

Abstract

This paper deals with the investigation of complex corrosion properties of 3D printed AISI 316L steel and the influence of additional heat treatment on the resulting corrosion and mechanical parameters. There was an isotonic solution used for the simulation of the human body [...] Read more.

This paper deals with the investigation of complex corrosion properties of 3D printed AISI 316L steel and the influence of additional heat treatment on the resulting corrosion and mechanical parameters. There was an isotonic solution used for the simulation of the human body and a diluted sulfuric acid solution for the study of intergranular corrosion damage of the tested samples. There were significant microstructural changes found for each type of heat treatment at 650 and 1050 °C, which resulted in different corrosion properties of the tested samples. There were changes of corrosion potential, corrosion rate and polarization resistance found by the potentiodynamic polarization method. With regard to these results, the most appropriate heat treatment can be applied to applications with intended use in medicine. Full article

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

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13 pages, 5271 KiB

Open AccessArticle

Effect of Grain Size on the Microstructure and Strain Hardening Behavior of Solution Heat-Treated Low-C High-Mn Steel

by Marek Opiela, Gabriela Fojt-Dymara, Adam Grajcar and Wojciech Borek

Materials 2020, 13(7), 1489; https://doi.org/10.3390/ma13071489 - 25 Mar 2020

Cited by 19 | Viewed by 3233

Abstract

The low-carbon high-Mn austenitic steel microalloyed with titanium was investigated in this work. The steel was solution heat-treated at different temperatures in a range from 900 to 1200 °C. The aim was to receive a different grain size before the static tensile test [...] Read more.

The low-carbon high-Mn austenitic steel microalloyed with titanium was investigated in this work. The steel was solution heat-treated at different temperatures in a range from 900 to 1200 °C. The aim was to receive a different grain size before the static tensile test performed at room temperature. The samples of different grain sizes showed the different strain hardening behavior and resulting mechanical properties. The size of grain diameter below 19 μm was stable up to 1000 °C. Above this temperature, the very enhanced grain growth took place with the grain diameter higher than 220 μm at 1200 °C. This huge grain size at the highest temperature resulted in the premature failure of the sample showing the lowest strength properties at the same time. Correlations between the grain size, the major strengthening mechanism, and fracture behavior were addressed. The relationships were assessed based on microstructural investigations and fractography tests performed for the deformed samples. The best combination of strength and ductility was found for the samples treated at 1000–1100 °C. Full article

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

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12 pages, 13297 KiB

Open AccessArticle

Outstanding Tensile Properties and Their Origins in Twinning-Induced Plasticity (TWIP) Steels with Gradient Substructures

by Huihui Zhi, Cheng Zhang, Zihui Guo, Stoichko Antonov and Yanjing Su

Materials 2020, 13(5), 1184; https://doi.org/10.3390/ma13051184 - 06 Mar 2020

Cited by 14 | Viewed by 2512

Abstract

The low yield strength (~300 MPa) of twinning-induced plasticity (TWIP) steels greatly limits their structural applications in the industrial field. Conventional strengthening mechanisms usually cause an enhancement of yield strength but also a severe loss of ductility. In this research, gradient substructures were [...] Read more.

The low yield strength (~300 MPa) of twinning-induced plasticity (TWIP) steels greatly limits their structural applications in the industrial field. Conventional strengthening mechanisms usually cause an enhancement of yield strength but also a severe loss of ductility. In this research, gradient substructures were introduced in the Fe-22Mn-0.6C TWIP steels by different pre-torsional deformation in order to overcome the above limitations. The substructure evolution, mechanical properties, and their origins in gradient-substructured (GS) TWIP steels were measured and compared by electron backscattered diffraction (EBSD), monotonous and loading-unloading-reloading (LUR) tensile tests. It was found that a simple torsional treatment could prepare gradient twins and dislocations in coarse-grained TWIP steel samples depending on torsional strain. The uniaxial tensile tests indicated that a superior combination of high yield strength, high ultimate strength, and considerable ductility was simultaneously obtained in the GS samples. The high yield strength and high ultimate tensile strength were attributed to synergetic strengthening mechanisms, viz., dislocation strengthening, due to the accumulation of high density of dislocations, and very high back stress strengthening due to gradient substructure distribution, which was accommodated through pile-ups of extra geometrically necessary dislocations (GNDs) across the sample-scale. Additionally, high ductility originated from gradient substructure-induced back stress hardening. The present study is also beneficial to the design efforts of high strength and high ductility of other heterogeneous-structured TWIP alloy systems. Full article

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

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15 pages, 21790 KiB

Open AccessArticle

Effects of Silicon Content and Tempering Temperature on the Microstructural Evolution and Mechanical Properties of HT-9 Steels

by Junkai Liu, Wenbo Liu, Zhe Hao, Tiantian Shi, Long Kang, Zhexin Cui and Di Yun

Materials 2020, 13(4), 972; https://doi.org/10.3390/ma13040972 - 21 Feb 2020

Cited by 9 | Viewed by 2597

Abstract

Two kinds of experimental ferritic/martensitic steels (HT-9) with different Si contents were designed for the fourth-generation advanced nuclear reactor cladding material. The effects of Si content and tempering temperature on microstructural evolution and mechanical properties of these HT-9 steel were studied. The microstructure [...] Read more.

Two kinds of experimental ferritic/martensitic steels (HT-9) with different Si contents were designed for the fourth-generation advanced nuclear reactor cladding material. The effects of Si content and tempering temperature on microstructural evolution and mechanical properties of these HT-9 steel were studied. The microstructure of experimental steels after quenching and tempering were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM); the mechanical properties were investigated by means of tensile test, Charpy impact test, and hardness test. The microscopic mechanism of how the microstructural evolution influences mechanical properties was also discussed. Both XRD and TEM results showed that no residual austenite was detected after heat treatment. The results of mechanical tests showed that the yield strength, tensile strength, and plasticity of the experimental steels with 0.42% (% in mass) Si are higher than that with 0.19% Si, whereas hardness and toughness did not change much; when tempered at 760 °C, the strength and hardness of the experimental steels decreased slightly compared with those tempered at 710 °C, whereas plasticity and toughness increased. Further analysis showed that after quenching at 1050 °C for 1 h and tempering at 760 °C for 1.5 h, the comprehensive mechanical properties of the 0.42% Si experimental steel are the best compared with other experimental steels. Full article

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

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15 pages, 6688 KiB

Open AccessArticle

Dilatometric Study of Phase Transformations in 5 Mn Steel Subjected to Different Heat Treatments

by Mateusz Morawiec, Adam Grajcar, Władysław Zalecki, Carlos Garcia-Mateo and Marek Opiela

Materials 2020, 13(4), 958; https://doi.org/10.3390/ma13040958 - 21 Feb 2020

Cited by 12 | Viewed by 2547

Abstract

The work presents results of phase transformation kinetics of hot-rolled 5% Mn steel subjected to different heat treatments. Three different schedules were introduced: isothermal holding in a bainite region, coiling simulation and intercritical annealing. The evolution of microstructure components was investigated using dilatometric [...] Read more.

The work presents results of phase transformation kinetics of hot-rolled 5% Mn steel subjected to different heat treatments. Three different schedules were introduced: isothermal holding in a bainite region, coiling simulation and intercritical annealing. The evolution of microstructure components was investigated using dilatometric and metallographic analyses. According to obtained results, the medium-Mn steel exhibits high resistance for γ/α transformation during the bainite transformation and coiling simulation (upon cooling from the austenite region). During 5 h isothermal holding, no bainite and/or ferrite formation was detected. This results in the formation of martensite upon cooling to room temperature. Differently, when the steel was subjected to the intercritical annealing at 720 and 700 °C (upon heating from room temperature), a final microstructure consisted of ferrite, martensite and retained austenite. At 700 °C, no fresh martensite formation was detected upon cooling to room temperature. This means that the austenite was enriched in carbon during the intercritical annealing step enough to keep its thermal stability. Full article

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

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15 pages, 9472 KiB

Open AccessArticle

The Impact of Isothermal Treatment on the Microstructural Evolution and the Precipitation Behavior in High Strength Linepipe Steel

by Yong Tian, Hongtao Wang, Xiaoning Xu, Zhaodong Wang, R.D.K. Misra and Guodong Wang

Materials 2020, 13(3), 634; https://doi.org/10.3390/ma13030634 - 31 Jan 2020

Cited by 2 | Viewed by 1779

Abstract

Isothermal treatment affects the microstructural evolution and the precipitation behavior of high-strength low alloy (HSLA) steels. In this regard, thermal simulation of different isothermal treatment temperatures was adopted by using a thermomechanical simulator. The results showed that hardness reached the maximum value at [...] Read more.

Isothermal treatment affects the microstructural evolution and the precipitation behavior of high-strength low alloy (HSLA) steels. In this regard, thermal simulation of different isothermal treatment temperatures was adopted by using a thermomechanical simulator. The results showed that hardness reached the maximum value at 600 °C holding temperature, which was related to a finer grain structure and granular bainite. The strengthening effect of precipitates was remarkable due to the combination of small particle size and small interparticle spacing. It is presumed that the precipitation started after 600 s at 600 °C. Precipitation strengthening continued to exist, even though coarsening of ferrite grains led to softening phenomena when the specimen was isothermally held at 750 °C, which led to relatively high hardness. The precipitates were fcc (Ti, Nb) (N, C) particles, and belonged to MX-type precipitates. Average size of precipitates increased from 3.14 to 4.83 nm when the specimens were isothermally held between 600 °C and 800 °C. Interparticle spacing of precipitates also increased with increasing isothermal treatment temperatures. These led to a reduction in precipitation strengthening. At the same time the polygonal ferrite content increased and ferrite grain size got larger, such that the hardness decreased continuously. Full article

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

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18 pages, 15058 KiB

Open AccessArticle

High-Temperature Oxidation Behavior of Fe–1Cr–0.2Si Steel

by Mingxin Hao, Bin Sun and Hao Wang

Materials 2020, 13(3), 509; https://doi.org/10.3390/ma13030509 - 21 Jan 2020

Cited by 22 | Viewed by 3149

Abstract

In the case of Fe–1Cr–0.2Si steel, tube furnace oxidation was carried out for 120 min and 30 min. These studies, along with the high-temperature oxidation behavior of Fe–1Cr–0.2Si steel, were examined from 700 to 1100 °C. It has been observed that with an [...] Read more.

In the case of Fe–1Cr–0.2Si steel, tube furnace oxidation was carried out for 120 min and 30 min. These studies, along with the high-temperature oxidation behavior of Fe–1Cr–0.2Si steel, were examined from 700 to 1100 °C. It has been observed that with an increase in the oxidation time, the oxidation weight gain per unit area of Fe–1Cr–0.2Si steel changed from a linear to a parabolic relationship. The time was shortened when the oxidation phase was linear. When the oxidation temperature exceeded 900 °C, the value of W_Transition decreased, and the oxidation rule changed. It could be considered that overall, the iron oxide structure of Fe–1Cr–0.2Si steel is divided into two layers. The formation of an outer oxide of iron is mainly caused by the outward diffusion of cation, while the inward diffusion of O ion forms the inner oxides of chromium and silicon. As the temperature increases, the thickness of the outer iron oxide gradually increases, and the thickness ratio of the inner mixed layers of chromium- and silicon-rich oxides decreases; however, the degree of enrichment of Cr and Si in the mixed layer increases. After high-temperature oxidation, Cr and Si did not form a composite oxide but were mechanically mixed in the form of FeCr₂O₄ and Fe₂SiO₄, and no significant delamination occurred. Full article

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

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14 pages, 3553 KiB

Open AccessArticle

Preparation and Mechanical Behavior of Ultra-High Strength Low-Carbon Steel

by Zhiqing Lv, Lihua Qian, Shuai Liu, Le Zhan and Siji Qin

Materials 2020, 13(2), 459; https://doi.org/10.3390/ma13020459 - 18 Jan 2020

Cited by 17 | Viewed by 2765

Abstract

The low-carbon steel (~0.12 wt%) with complete martensite structure, obtained by quenching, was cold rolled to get the high-strength steel sheets. Then, the mechanical properties of the sheets were measured at different angles to the rolling direction, and the microstructural evolution of low-carbon [...] Read more.

The low-carbon steel (~0.12 wt%) with complete martensite structure, obtained by quenching, was cold rolled to get the high-strength steel sheets. Then, the mechanical properties of the sheets were measured at different angles to the rolling direction, and the microstructural evolution of low-carbon martensite with cold rolling reduction was observed. The results show that the hardness and the strength gradually increase with increasing rolling reduction, while the elongation and impact toughness obviously decrease. The strength of the sheets with the same rolling reduction are different at the angles of 0°, 45°, and 90° to the rolling direction. The tensile strength (elongation) along the rolling direction is higher than that in the other two directions, but the differences between them are not obvious. When the aging was performed at a low temperature, the strength of the initial martensite and deformed martensite increased with increasing aging time during the early stages of aging, followed by a gradual decrease with further aging. However, the elongation increases with increasing aging time. The change of hardness is consistent with that of strength for the cold-rolled martensite, while the hardness of the initial martensite decreases gradually with increasing aging time. Full article

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

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12 pages, 28329 KiB

Open AccessArticle

The Buckling and Post-Buckling of Steel C-Columns in Elevated Temperature

by Leszek Czechowski, Sławomir Kędziora and Zbigniew Kołakowski

Materials 2020, 13(1), 74; https://doi.org/10.3390/ma13010074 - 22 Dec 2019

Cited by 7 | Viewed by 2163

Abstract

This work deals with the investigation of a steel thin-walled C-column subjected to compression due to temperature increase. These experimental studies of the compressed columns in post-buckling state were conducted to determine their load-carrying capacity. To ensure appropriate supports and keeping of columns, [...] Read more.

This work deals with the investigation of a steel thin-walled C-column subjected to compression due to temperature increase. These experimental studies of the compressed columns in post-buckling state were conducted to determine their load-carrying capacity. To ensure appropriate supports and keeping of columns, plates with grooves were constructed. The tests of the columns’ compression for different preloads were carried out. By comparing the experiment results, numerical calculations based on the finite element method (FEM) and the semi-analytical method (SAM) of solution were performed. The computations were executed with the use of full material characteristics with consideration of large strains and deflections. Furthermore, while observing the deformation of columns, a non-contact Digital Correlation ARAMIS^® system was employed whose calculated results of deformations are very close to the results of the numerical method. The paper revealed that maximum recorded loads under temperature rise are comparable regardless of a value of initial load. A good correlation in results between used methods was achieved. The main goal of the present work was to assess of behavior of thin-walled compressed steel columns in a temperature-controlled environment till their full damage. Full article

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

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18 pages, 10305 KiB

Open AccessArticle

The Influence of Microstructure on the Mechanical Properties and Fracture Behavior of Medium Mn Steels at Different Strain Rates

by Zheng Wang, Juanping Xu, Yu Yan and Jinxu Li

Materials 2019, 12(24), 4228; https://doi.org/10.3390/ma12244228 - 17 Dec 2019

Cited by 7 | Viewed by 2298

Abstract

The primary task of automotive industry materials is to guarantee passengers’ safety during a car crash. To simulate a car crash, the influence of strain rates on mechanical properties and fracture behavior of medium Mn steels with different Si content (0Si without δ-ferrite [...] Read more.

The primary task of automotive industry materials is to guarantee passengers’ safety during a car crash. To simulate a car crash, the influence of strain rates on mechanical properties and fracture behavior of medium Mn steels with different Si content (0Si without δ-ferrite and 0.6Si with about 20% δ-ferrite) was conducted using the uniaxial tensile test. The results show that ultimate tensile strength is higher, whereas total elongation is lower in 0Si than in 0.6Si. As the strain rate increases, ultimate tensile strength and total elongation decrease in both 0Si and 0.6Si; nonetheless, total elongation of 0.6Si decreases faster. Meanwhile, the area reduction of 0.6Si increases as the strain rate increases. The microcrack′s number on a rolling direction (RD)-transverse direction (TD) surface is considerably increased; nonetheless, the microcrack′s size is restrained in 0.6Si compared with 0Si. Microcracks start at γ(α′)/α-ferrite interfaces in both 0Si and 0.6Si, whereas little nucleation sites have also been found at (γ(α′)+α-ferrite)/δ-ferrite boundaries in 0.6Si. Meanwhile, δ-ferrite reveals a higher capacity for microcrack arrest. As the strain rate decreases, increased lower crack growth results in fine and even dimples on fractographs with abundant second cracks on fractographs; meanwhile, the small microcrack′s number increases, while the large microcrack′s number decreases on an RD-TD surface. Full article

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

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14 pages, 6241 KiB

Open AccessArticle

Analysis of Plastic Deformation Instabilities at Elevated Temperatures in Hot-Rolled Medium-Mn Steel

by Aleksandra Kozłowska, Barbara Grzegorczyk, Marcin Staszuk, Paweł M. Nuckowski and Adam Grajcar

Materials 2019, 12(24), 4184; https://doi.org/10.3390/ma12244184 - 12 Dec 2019

Cited by 4 | Viewed by 1997

Abstract

The study addressed the microstructure and mechanical properties of hot-rolled advanced high-strength medium manganese steel. Some of the curves that were obtained in static tensile tests at deformation temperatures of 20–200 °C showed the occurrence of the heterogeneous plastic deformation phenomenon, called the [...] Read more.

The study addressed the microstructure and mechanical properties of hot-rolled advanced high-strength medium manganese steel. Some of the curves that were obtained in static tensile tests at deformation temperatures of 20–200 °C showed the occurrence of the heterogeneous plastic deformation phenomenon, called the Portevin-Le Chatelier (PLC) effect. The deformation temperature significantly influenced a serration character. The correlations between the deformation temperature, serration range, microstructural features, and fracture behavior were investigated. The curves showed no Lüders elongation as a result of the thermomechanical processing applied. The serrated flow phenomenon was observed at 60 and 140 °C. The serration type was different and the most enhanced at 140 °C, where the PLC effect was present in both uniform and post-uniform elongation ranges. The disappearance of serrations at 200 °C was related to the increased diffusion intensity. Full article

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

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15 pages, 5114 KiB

Open AccessArticle

A New Explanation for the Effect of Dynamic Strain Aging on Negative Strain Rate Sensitivity in Fe–30Mn–9Al–1C Steel

by Jia Xing, Lifeng Hou, Huayun Du, Baosheng Liu and Yinghui Wei

Materials 2019, 12(20), 3426; https://doi.org/10.3390/ma12203426 - 20 Oct 2019

Cited by 9 | Viewed by 2414

Abstract

In this study, the evolution of the mechanical properties of Fe–30Mn–9Al–1C steel has been determined in tensile tests at strain rates of 10⁻⁴ to 10² s⁻¹. The results show that the strain rate sensitivity becomes a negative value when [...] Read more.

In this study, the evolution of the mechanical properties of Fe–30Mn–9Al–1C steel has been determined in tensile tests at strain rates of 10⁻⁴ to 10² s⁻¹. The results show that the strain rate sensitivity becomes a negative value when the strain rate exceeds 10⁰ s⁻¹ and this abnormal evolution is attributed to the occurrence of dynamic strain aging. Due to the presence of intergranular κ-carbides, the fracture modes of steel include ductile fracture and intergranular fracture. The values of dislocation arrangement parameter M were obtained using a modified Williamson–Hall plot. It has been found that once the strain rate sensitivity becomes negative, the interaction of dislocations in the steel is weakened and the free movement of dislocation is enhanced. Adiabatic heating promotes the dynamic recovery of steel at a high strain rate. Full article

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

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18 pages, 10514 KiB

Open AccessArticle

Microstructure Evolution and Mechanical Stability of Retained Austenite in Medium-Mn Steel Deformed at Different Temperatures

by Aleksandra Kozłowska, Aleksandra Janik, Krzysztof Radwański and Adam Grajcar

Materials 2019, 12(18), 3042; https://doi.org/10.3390/ma12183042 - 19 Sep 2019

Cited by 17 | Viewed by 3963

Abstract

The temperature-dependent microstructure evolution and corresponding mechanical stability of retained austenite in medium-Mn transformation induced plasticity (TRIP) 0.17C-3.1Mn-1.6Al type steel obtained by thermomechanical processing was investigated using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) techniques. Specimens were deformed [...] Read more.

The temperature-dependent microstructure evolution and corresponding mechanical stability of retained austenite in medium-Mn transformation induced plasticity (TRIP) 0.17C-3.1Mn-1.6Al type steel obtained by thermomechanical processing was investigated using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and X-ray diffraction (XRD) techniques. Specimens were deformed up to rupture in static tensile tests in the temperature range 20–200 °C. It was found that an increase in deformation temperature resulted in the reduced intensity of TRIP effect due to the higher stability of retained austenite. The kinetics of strain-induced martensitic transformation was affected by the carbon content of retained austenite (RA), its morphology, and localization in the microstructure. Full article

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

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15 pages, 12764 KiB

Open AccessArticle

The Microstructure and Mechanical Properties of Multi-Strand, Composite Welding-Wire Welded Joints of High Nitrogen Austenitic Stainless Steel

by Jianguo Li, Huan Li, Yu Liang, Pingli Liu and Lijun Yang

Materials 2019, 12(18), 2944; https://doi.org/10.3390/ma12182944 - 11 Sep 2019

Cited by 43 | Viewed by 3119

Abstract

A multi-strand composite welding wire was applied to join high nitrogen austenitic stainless steel, and microstructures and mechanical properties were investigated. The electrical signals demonstrate that the welding process using a multi-strand composite welding wire is highly stable. The welded joints are composed [...] Read more.

A multi-strand composite welding wire was applied to join high nitrogen austenitic stainless steel, and microstructures and mechanical properties were investigated. The electrical signals demonstrate that the welding process using a multi-strand composite welding wire is highly stable. The welded joints are composed of columnar austenite and dendritic ferrite and welded joints obtained under high heat input and cooling rate have a noticeable coarse-grained heat-affected zone and larger columnar austenite in weld seam. Compared with welded joints obtained under the high heat input and cooling rate, welded joints have the higher fractions of deformed grains, high angle grain boundaries, Schmid factor, and lower dislocation density under the low heat input and cooling rate, which indicate a lower tensile strength and higher yield strength. The rotated Goss (G_RD) ({110}⟨1

\bar{1}

0⟩) orientation of a thin plate and the cube (C) ({001}⟨100⟩) orientation of a thick plate are obvious after welding, but the S ({123}⟨63

\bar{4}

⟩) orientation at 65° sections of Euler’s space is weak. The δ-ferrite was studied based on the primary ferrite solidification mode. It was observed that low heat input and a high cooling rate results in an increase of δ-ferrite, and a high dislocation density was obtained in grain boundaries of δ-ferrite. M₂₃C₆ precipitates due to a low cooling rate and heat input in the weld seam and deteriorates the elongation of welded joints. The engineering Stress–strain curves also show the low elongation and tensile strength of welded joints under low heat input and cooling rate, which is mainly caused by the high fraction of δ-ferrite and the precipitation of M₂₃C₆. Full article

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

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10 pages, 1859 KiB

Open AccessArticle

Improvement of Adhesive Wear Behavior by Variable Heat Treatment of a Tool Steel for Sheet Metal Forming

by Alejandro Gonzalez-Pociño, Florentino Alvarez-Antolin and Juan Asensio-Lozano

Materials 2019, 12(17), 2831; https://doi.org/10.3390/ma12172831 - 03 Sep 2019

Cited by 13 | Viewed by 2128

Abstract

Vanadis 10 steel is a powder metallurgy (PM) processed tool steel. It is a ledeburitic steel with 8% Cr and 10% V. By deliberately varying the process parameters related to the quenching, tempering, and nitriding of these steels, the aim of this study [...] Read more.

Vanadis 10 steel is a powder metallurgy (PM) processed tool steel. It is a ledeburitic steel with 8% Cr and 10% V. By deliberately varying the process parameters related to the quenching, tempering, and nitriding of these steels, the aim of this study is to determine which of these parameters have a significant influence on its adhesive wear resistance. The research methodology employed was a Design of Experiments (DoE) with six factors and two levels for each factor. The tempering temperature, number of temperings, and carrying out of a thermochemical nitriding treatment were found to have a significant effect. To increase adhesive wear resistance, austenitization at 1100 °C with air cooling is recommended, followed by three temperings at 500 °C and a subsequent nitriding treatment. It should be noted that the quench cooling medium does not have a significant influence on wear resistance. Furthermore, (Fe,Cr)₇C₃ (M₇C₃ carbides) are transformed into carbonitrides during nitriding. However, (Fe,V)C (MC carbides) are not affected by this nitriding process. Full article

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

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15 pages, 14861 KiB

Open AccessArticle

Effect of Boron on Hot Ductility and Room-Temperature Tensile Properties of Microalloyed Steels with Titanium and Niobium

by Qi Li and Weijie Liu

Materials 2019, 12(14), 2290; https://doi.org/10.3390/ma12142290 - 17 Jul 2019

Cited by 6 | Viewed by 2543

Abstract

Effect of boron on the hot ductility and room-temperature tensile properties of Ti-Nb-microalloyed steels containing 0.071 wt.% carbon was studied. The thermal stress and thermal strain of continuous casting billets during cooling were simulated via hot tensile tests at the deformation rate of [...] Read more.

Effect of boron on the hot ductility and room-temperature tensile properties of Ti-Nb-microalloyed steels containing 0.071 wt.% carbon was studied. The thermal stress and thermal strain of continuous casting billets during cooling were simulated via hot tensile tests at the deformation rate of (6 mm/11,000)/s, and the hot ductility of different microalloyed steels was evaluated according to the area reduction of hot tensile specimens. It was found that boron addition was beneficial to improve the hot ductility of continuous casting billets during straightening, and the reduction of area exceeded 60%. The addition of boron, as well as the removal of molybdenum and vanadium, can effectively lower the austenite-to-ferrite transformation temperature and restrain the formation of intergranular ferrite, so as to avoid the brittle zone. Moreover, the room-temperature tensile properties of the steels were explored at different cooling rates after the rolling process. The results showed that as the cooling rate increased from 0.0094 to 0.13 °C/s, the amount of carbonitride precipitate gradually decreased, such as titanium carbide, leading to the relatively low tensile strength. On the other hand, the addition of boron, as well as the removal of Mo and V, promoted the formation of bainite and acicular ferrite, playing an important role in structure strengthening, and compensated for the decrease of tensile strength caused by the low precipitation strengthening. Full article

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

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12 pages, 4028 KiB

Open AccessArticle

Analysis of Surface Geometry Changes after Hybrid Milling and Burnishing by Ceramic Ball

by Daniel Grochała, Stefan Berczyński and Zenon Grządziel

Materials 2019, 12(7), 1179; https://doi.org/10.3390/ma12071179 - 11 Apr 2019

Cited by 9 | Viewed by 2641

Abstract

The production of modern machines requires parts with much greater geometric accuracy and surface geometry (SG) precision than several years ago. These requirements are met by so-called hybrid technologies that must simultaneously be inexpensive to implement. The integration of treatment procedures (usually in [...] Read more.

The production of modern machines requires parts with much greater geometric accuracy and surface geometry (SG) precision than several years ago. These requirements are met by so-called hybrid technologies that must simultaneously be inexpensive to implement. The integration of treatment procedures (usually in one operation) is geared towards achieving a synergistic effect. Combining different treatments from various technologies produces synergy, i.e., benefits greater than the optimization of each individual process done separately. This paper presents experimental results and numerical experiment data on surface plastic deformation. The hybrid technology used in the study was a combination of milling and finishing with plastic burnishing using a ceramic ball. These processes were integrated on a multi-axis CNC machining center. The plastic deformations of real surfaces were determined in simulations. The paper also discusses the structure of the model and how to use it to conduct a finite element method (FEM) computer simulation. The aim of the study was to determine how to use the potential developed model of hybrid treatment to predict the surface performance expressed by the amplitude, volume, and functional parameters of the surface geometry, with the EN-ISO 25178-2 profile. Full article

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

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9 pages, 8307 KiB

Open AccessArticle

Effect of Thermo-Mechanical Treatment on the Microstructure Evaluation and Mechanical Properties of Fe-20Mn-12Cr-3Ni-3Si Damping Alloy

by Hyunbo Shim and Changyong Kang

Materials 2019, 12(7), 1119; https://doi.org/10.3390/ma12071119 - 04 Apr 2019

Cited by 2 | Viewed by 2148

Abstract

This study was carried out to investigate the effect of thermo-mechanical treatment on the microstructure of Fe-20Mn-12Cr-3Ni-3Si damping alloy. Dislocation, αʹ, and ε-martensite were formed by thermo-mechanical treatment. The intersections of the surface relief and specific direction due to martensitic transformation were generated [...] Read more.

This study was carried out to investigate the effect of thermo-mechanical treatment on the microstructure of Fe-20Mn-12Cr-3Ni-3Si damping alloy. Dislocation, αʹ, and ε-martensite were formed by thermo-mechanical treatment. The intersections of the surface relief and specific direction due to martensitic transformation were generated by thermo-mechanical treatment. They were then reversed to austenite with an ultra-fine grain size of less than 5 μm by annealing treatment at 700°C for 20min. The volume fractions of dislocation, αʹ, and ε-martensite were increased with the cycle number of thermo-mechanical treatment. In five-cycle number thermo-mechanical treated specimens, more than 45% of the volume fraction of ε-martensite and less than 3% of the volume fraction of α΄-martensite were attained. Therefore, in this article, the effect of thermo-mechanical treatment is briefly introduced, and these phenomena are explained in terms of the grain refinement of austenite, αʹ, and ε-martensite distribution and homogeneous dislocation distribution. Full article

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

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15 pages, 4170 KiB

Open AccessArticle

Structural Properties and Phase Stability of Primary Y Phase (Ti₂SC) in Ti-Stabilized Stainless Steel from Experiments and First Principles

by Deli Zhao, Yu Zhou, Jiangyu Fan, Tianyu Liu, Yihong Nie, Wantang Fu and Zhiqing Lv

Materials 2019, 12(7), 1118; https://doi.org/10.3390/ma12071118 - 04 Apr 2019

Cited by 5 | Viewed by 2762

Abstract

The morphology and microstructural evaluation of Y phases in AISI 321 (a Ti-stabilized stainless steel) were characterized after hot deformation. The electronic structure and phase stability of titanium carbosulfide were further discussed by first-principle calculations. It was found that Y phases, like curved [...] Read more.

The morphology and microstructural evaluation of Y phases in AISI 321 (a Ti-stabilized stainless steel) were characterized after hot deformation. The electronic structure and phase stability of titanium carbosulfide were further discussed by first-principle calculations. It was found that Y phases, like curved strips or bones in AISI 321 stainless steel, mostly show a clustered distribution and are approximately arranged in parallel. The width of the Y phase is much less than the length, and the composition of the Y phase is close to that of Ti₂SC. Y phases have exceptional thermal stability. The morphology of Y phases changed considerably after forging. During the first calculations, the Ti₂SC with hexagonal structure does not spontaneously change into TiS and TiC; however Ti₄S₂C₂ (Z = 2) can spontaneously change into the two phases. The Ti–S bonds are compressed in Ti₄S₂C₂ cells, which leads to poor structural stability for Ti₄S₂C₂. There is a covalent interaction between C/S and Ti, as well as an exchange of electrons between Ti and S/C atoms. Evidently, the mechanical stability of Ti₄S₂C₂ is weak; however, Ti₂SC shows high stability. Ti₂SC, as a hard brittle phase, does not easily undergo plastic deformation. Full article

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

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13 pages, 14344 KiB

Open AccessArticle

Microstructure Evolution and Orientation Relationship of Reverted Austenite in 13Cr Supermartensitic Stainless Steel During the Tempering Process

by Yiwei Zhang, Chi Zhang, Xiaomin Yuan, Diankai Li, Yuande Yin and Shengzhi Li

Materials 2019, 12(4), 589; https://doi.org/10.3390/ma12040589 - 15 Feb 2019

Cited by 20 | Viewed by 4147

Abstract

The transformation mechanism of reverted austenite and the amount of reverted austenite during the tempering process in supermartensitic stainless steel have been investigated by X-ray diffraction (XRD), electron backscattered diffraction (EBSD), and a high-temperature laser scanning confocal microscope (HTLSCM). The results indicate that [...] Read more.

The transformation mechanism of reverted austenite and the amount of reverted austenite during the tempering process in supermartensitic stainless steel have been investigated by X-ray diffraction (XRD), electron backscattered diffraction (EBSD), and a high-temperature laser scanning confocal microscope (HTLSCM). The results indicate that the microstructure mainly consists of tempered martensite and reverted austenite. The reverted austenite nucleates uniformly at the sub-block boundary and prior grain austenite boundary. The amount of reverted austenite strongly relies on the tempering time, showing a positive correlation in the supermartensitic stainless steel. The crystallographic orientation relationship between reverted austenite and martensite meets the Kurdjumov-Sachs(K-S) relationship and the deviation angle is mainly concentrated at about 2 degrees. The mechanism of reverted austenite transformed from martensite is a diffusion mechanism. The growth kinetics of the reverted austenite are dominated by diffusion of the Ni element and there is no shear deformation of the martensite matrix in the in situ observation. It can be deduced that the reverted austenite is formed by nickel diffusion during tempering at 620 °C for different tempering times. Full article

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

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15 pages, 9055 KiB

Open AccessArticle

Influence of Prior Martensite on Bainite Transformation, Microstructures, and Mechanical Properties in Ultra-Fine Bainitic Steel

by Hui Guo, Xianying Feng, Aimin Zhao, Qiang Li and Jun Ma

Materials 2019, 12(3), 527; https://doi.org/10.3390/ma12030527 - 12 Feb 2019

Cited by 26 | Viewed by 4291

Abstract

A multiphase microstructure comprising of different volume fractions of prior martensite and ultra-fine bainite (bainitic ferrite and retained austenite) was obtained by quenching to certain temperatures, followed by isothermal bainitic transformation. The effect of the prior martensite transformation on the bainitic transformation behavior, [...] Read more.

A multiphase microstructure comprising of different volume fractions of prior martensite and ultra-fine bainite (bainitic ferrite and retained austenite) was obtained by quenching to certain temperatures, followed by isothermal bainitic transformation. The effect of the prior martensite transformation on the bainitic transformation behavior, microstructures, and mechanical properties were discussed. The results showed that the prior martensite accelerated the subsequent low-temperature bainite transformation, and the incubation period and completion time of the bainite reaction were significantly shortened. This phenomenon was attributed to the enhanced nucleation ratio caused by the introduced strain in austenite, due to the formation of prior martensite and a carbon partitioning between the prior martensite and retained austenite. Moreover, the prior martensite could influence the crystal growth direction of bainite ferrite, refine bainitic ferrite plates, and reduce the dimension of blocky retained austenite, all of which were responsible for improving the mechanical properties of the ultra-fine bainitic steel. When the content of the prior martensite reached 15%, the investigated steels had the best performance, which were 1800 MPa and 21% for the tensile strength and elongation, respectively. Unfortunately, the increased content of the prior martensite could lead to a worsening of the impact toughness. Full article

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

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20 pages, 13936 KiB

Open AccessArticle

Numerical Simulations of Laser and Hybrid S700MC T-Joint Welding

by Tomasz Kik and Jacek Górka

Materials 2019, 12(3), 516; https://doi.org/10.3390/ma12030516 - 08 Feb 2019

Cited by 47 | Viewed by 4721

Abstract

This article presents examples of numerical simulations done based on the real experiments of S700MC steel T-joint laser and hybrid welding. Presented results of numerical analyses carried out using SYSWELD show the possibilities offered to contemporary engineers by modern software used to make [...] Read more.

This article presents examples of numerical simulations done based on the real experiments of S700MC steel T-joint laser and hybrid welding. Presented results of numerical analyses carried out using SYSWELD show the possibilities offered to contemporary engineers by modern software used to make numerical analyses of production processes. After calibration of a heat source models on the chosen examples of S700MC steel 10-mm-thick T-joint laser and hybrid welding, distributions of temperature fields, thermal cycles, distributions of individual metallurgical phases and hardness, and strains and plastic deformations in simulated processes were calculated for one selected joint from both mentioned methods. The results of the analysis allow determining both the differences in the stress distributions and their minimal and maximal values. This article also presents the benefits resulting from the use of such analyses, due to the significant savings in time and resources to be spent on the development of correct technologies for joining modern construction materials such as thermomechanically treated steels, especially given that some of the results are unavailable or very difficult to collect using conventional measurement methods. Full article

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

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11 pages, 3396 KiB

Open AccessCommunication

Multiscale Analysis of the Microstructure and Stress Evolution in Cold Work Die Steel during Deep Cryogenic Treatment

by Junwan Li, Xin Cai, Yiwen Wang and Xiaochun Wu

Materials 2018, 11(11), 2122; https://doi.org/10.3390/ma11112122 - 29 Oct 2018

Cited by 6 | Viewed by 2428

Abstract

Through a combination of 3D representative volume element (RVE) and the metallo-thermo-mechanical coupling finite element (FE) analysis, a multiscale model was established to explore the localized characteristics of microstructure and stress evolution during deep cryogenic treatment (DCT). The results suggest that after cooling [...] Read more.

Through a combination of 3D representative volume element (RVE) and the metallo-thermo-mechanical coupling finite element (FE) analysis, a multiscale model was established to explore the localized characteristics of microstructure and stress evolution during deep cryogenic treatment (DCT). The results suggest that after cooling to near −160 °C, the largest intensity of martensite is formed, but the retained austenite cannot be eliminated completely until the end of DCT. The driving force for the precipitation of fine and uniform carbides during DCT is provided by the competition between the thermal and phase transformation stresses. Compared with the thermal stress, the phase transformation stress during DCT plays a more significant role. At the interface between retained austenite and martensite, a reduction of around 15.5% retained austenite even induces an obvious increase in the phase transformation stress about 1100 MPa. During DCT, the maximum effective stress in RVE even exceeds 1000 MPa, which may provide a required driving force for the precipitation of fine and homogeneously distributed carbide particles during DCT. Full article

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

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13 pages, 6446 KiB

Open AccessArticle

Synergetic Effects of Ferrite Content and Tempering Temperature on Mechanical Properties of a 960 MPa Grade HSLA Steel

by Shaoyang Wang, Hao Yu, Tao Zhou and Lu Wang

Materials 2018, 11(10), 2049; https://doi.org/10.3390/ma11102049 - 20 Oct 2018

Cited by 4 | Viewed by 4245

Abstract

The synergetic effects of ferrite content and tempering temperature on the mechanical properties of a Q960E steel have been investigated in detail to obtain the optimal combination of strength, ductility, and toughness for ultrahigh strength steels. After quenching from different temperatures between 790 [...] Read more.

The synergetic effects of ferrite content and tempering temperature on the mechanical properties of a Q960E steel have been investigated in detail to obtain the optimal combination of strength, ductility, and toughness for ultrahigh strength steels. After quenching from different temperatures between 790 to 900 °C, the ferrite content in the microstructure containing martensite varies from 56 vol% to 0, and then the specimens were tempered at 180 °C and 450 °C, respectively. High ferrite content reduces both yield and tensile strengths based on the law of mixtures. The tensile strength decreases with the increase of tempering temperature, while the change of yield strength is affected by the ferrite content. When tempering at low temperature, specimens with various ferrite content show different strain hardening behaviors, and the ferrite improves the elongation but deteriorates the toughness with different fracture mechanisms due to the strength difference between ferrite and martensite. Tempering at high temperature increases the ferrite–martensite co-deformation, resulting in the same strain hardening behavior for all specimens and the ferrite is benefit for both elongation and impact properties with similar fracture mechanisms. Moreover, the single martensite with homogeneous microstructure is essential for better toughness. Full article

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

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19 pages, 10210 KiB

Open AccessArticle

Estimation of the Onset of Crack Growth in Ductile Materials

by Andrzej Neimitz, Jaroslaw Galkiewicz, Sebastian Lipiec and Ihor Dzioba

Materials 2018, 11(10), 2026; https://doi.org/10.3390/ma11102026 - 18 Oct 2018

Cited by 19 | Viewed by 3675

Abstract

In this paper, the ductile fracture mechanism is discussed. The results of numerical and experimental analyses were used to estimate the onset of crack front growth. It was assumed that the ductile fracture in front of the crack starts at the location along [...] Read more.

In this paper, the ductile fracture mechanism is discussed. The results of numerical and experimental analyses were used to estimate the onset of crack front growth. It was assumed that the ductile fracture in front of the crack starts at the location along the crack front where the accumulated effective plastic strain reaches a critical value. According to numerous research articles, the critical effective plastic strain depends on the stress triaxiality and the Lode angle. The experimental program was performed using five different specimen geometries, three different materials, and three different temperatures of +20 °C, −20 °C, and −50 °C. Using the experimental data and results of the finite element computations, the critical effective plastic strains were determined for each material and temperature. However, before the critical effective plastic strain was determined, a careful calibration of the stress–strain curves was performed after modification of the Bai–Wierzbicki procedure. It was found that critical effective plastic strain was a function of triaxiality factor and Lode parameter, as expected, and that the fracture locus was useful to estimate the onset of ductile crack growth. Full article

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

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Review

Jump to: Research

14 pages, 2527 KiB

Open AccessReview

Explanation of the PLC Effect in Advanced High-Strength Medium-Mn Steels. A Review

by Aleksandra Kozłowska, Barbara Grzegorczyk, Mateusz Morawiec and Adam Grajcar

Materials 2019, 12(24), 4175; https://doi.org/10.3390/ma12244175 - 12 Dec 2019

Cited by 28 | Viewed by 3786

Abstract

The paper reviews the recent works concerning the Portevin–Le Chatelier (PLC) effect in Advanced High-Strength Steels (AHSSs) with a special attention to high-strength medium-manganese steels. Theories explaining the mechanism of the plastic instability phenomenon in steels with medium- and high-Mn contents were discussed. [...] Read more.

The paper reviews the recent works concerning the Portevin–Le Chatelier (PLC) effect in Advanced High-Strength Steels (AHSSs) with a special attention to high-strength medium-manganese steels. Theories explaining the mechanism of the plastic instability phenomenon in steels with medium- and high-Mn contents were discussed. The relationships between microstructural effects such as TRIP (Transformation-Induced Plasticity), TWIP (Twinning-Induced Plasticity) and the PLC effect were characterized. The effects of processing conditions including a deformation state (hot-rolled and cold-rolled) and strain parameters (deformation temperature, strain rate) were addressed. Factors affecting the value of critical strain for the activation of serrated flow behavior in particular in medium-manganese steels were described. Full article

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

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