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3 pages, 148 KiB

Open AccessEditorial

Alloy Steels

by Robert Tuttle

Metals 2018, 8(2), 116; https://doi.org/10.3390/met8020116 - 8 Feb 2018

Cited by 3 | Viewed by 3120

Abstract

Since their invention in 1865, alloy steels have found broad application in multiple industries; the automotive, aerospace, heavy equipment, and pipeline industries to name a few[...] Full article

(This article belongs to the Special Issue Alloy Steels)

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31504 KiB

Open AccessArticle

Effect of Weld Current on the Microstructure and Mechanical Properties of a Resistance Spot-Welded TWIP Steel Sheet

by Mumin Tutar, Hakan Aydin and Ali Bayram

Metals 2017, 7(12), 519; https://doi.org/10.3390/met7120519 - 23 Nov 2017

Cited by 22 | Viewed by 5603

Abstract

In this study the effect of the weld current on the microstructure and mechanical properties of a resistance spot-welded twinning-induced plasticity (TWIP) steel sheet was investigated using optical microscopy, scanning electron microscopy–electron back-scattered diffraction (SEM–EBSD), microhardness measurements, a tensile shear test and fractography. [...] Read more.

In this study the effect of the weld current on the microstructure and mechanical properties of a resistance spot-welded twinning-induced plasticity (TWIP) steel sheet was investigated using optical microscopy, scanning electron microscopy–electron back-scattered diffraction (SEM–EBSD), microhardness measurements, a tensile shear test and fractography. Higher weld currents promoted the formation of a macro expulsion cavity in the fusion zone. Additionally, higher weld currents led to a higher indentation depth, a wider heat-affected zone (HAZ), coarser grain structure and thicker annealing twins in the HAZ, and a relatively equiaxed dendritic structure in the centre of the fusion zone. The hardness values in the weld zone were lower than that of the base metal. The lowest hardness values were observed in the HAZ. No strong relationship was observed between the hardness values in the weld zone and the weld current. A higher joint strength, tensile deformation and failure energy absorption capacity were obtained with a weld current of 12 kA, a welding time of 300 ms and an electrode force of 3 kN. A complex fracture surface with both brittle and limited ductile manner was observed in the joints, while the base metal exhibited a ductile fracture. Joints with a higher tensile shear load (TSL) commonly exhibited more brittle fracture characteristics. Full article

(This article belongs to the Special Issue Alloy Steels)

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10106 KiB

Open AccessArticle

Carbides Evolution and Tensile Property of 4Cr5MoSiV1 Die Steel with Rare Earth Addition

by Hanghang Liu, Paixian Fu, Hongwei Liu, Chen Sun, Jinzhu Gao and Dianzhong Li

Metals 2017, 7(10), 436; https://doi.org/10.3390/met7100436 - 18 Oct 2017

Cited by 33 | Viewed by 4911

Abstract

Studies of 4Cr5MoSiV1 die steel suggest that under appropriate conditions, additions of rare earth (RE) can enhance tensile property. This improvement is apparently due to the more uniform distribution of carbides and the enhancement of precipitation strengthening after RE additions. In this present [...] Read more.

Studies of 4Cr5MoSiV1 die steel suggest that under appropriate conditions, additions of rare earth (RE) can enhance tensile property. This improvement is apparently due to the more uniform distribution of carbides and the enhancement of precipitation strengthening after RE additions. In this present work, the effect of the RE addition on the carbides evolution and tensile property of 4Cr5MoSiV1 steel with various RE contents (0, 0.018, 0.048 and 0.15 wt %) were systematically investigated. The two-dimensional detection techniques such as optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were used to investigate the carbides evolution of as-cast, annealed and tempered with RE addition. The results indicated that the carbides in 4Cr5MoSiV1 steels were modified by adding the suitable amount of RE. The eutectic structure and coarse eutectic carbides were all refining and the morphology of the annealed carbides initiated change from strip shape to ellipsoidal shape compared with the unmodified test steel (0RE). In addition, the amount of the tempered M₈C₇ carbides increased initially and then decreased with the alteration of RE addition from 0.018 to 0.15 wt %. Notably, the tensile test indicated that the average value of ultimate tensile strength (UTS) and elongation rate of 0.048RE steel increased slightly to 1474 MPa and 15%, higher than the 1452 MPa and 12% for the unmodified test steel (0RE), respectively. Such an addition of RE (0.048 wt %) would have a significant effect on the carbides evolution of as-cast, annealed and tempered and resulting in the tensile property of 4Cr5MoSiV1 die steel. Full article

(This article belongs to the Special Issue Alloy Steels)

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5868 KiB

Open AccessArticle

Resistance Upset Welding of ODS Steel Fuel Claddings—Evaluation of a Process Parameter Range Based on Metallurgical Observations

by Fabien Corpace, Arnaud Monnier, Jacques Grall, Jean-Pierre Manaud, Michel Lahaye and Angeline Poulon-Quintin

Metals 2017, 7(9), 333; https://doi.org/10.3390/met7090333 - 29 Aug 2017

Cited by 11 | Viewed by 4822

Abstract

Resistance upset welding is successfully applied to Oxide Dispersion Strengthened (ODS) steel fuel cladding. Due to the strong correlation between the mechanical properties and the microstructure of the ODS steel, this study focuses on the consequences of the welding process on the metallurgical [...] Read more.

Resistance upset welding is successfully applied to Oxide Dispersion Strengthened (ODS) steel fuel cladding. Due to the strong correlation between the mechanical properties and the microstructure of the ODS steel, this study focuses on the consequences of the welding process on the metallurgical state of the PM2000 ODS steel. A range of process parameters is identified to achieve operative welding. Characterizations of the microstructure are correlated to measurements recorded during the welding process. The thinness of the clad is responsible for a thermal unbalance, leading to a higher temperature reached. Its deformation is important and may lead to a lack of joining between the faying surfaces located on the outer part of the join which can be avoided by increasing the dissipated energy or by limiting the clad stick-out. The deformation and the temperature reached trigger a recrystallization phenomenon in the welded area, usually combined with a modification of the yttrium dispersion, i.e., oxide dispersion, which can damage the long-life resistance of the fuel cladding. The process parameters are optimized to limit the deformation of the clad, preventing the compactness defect and the modification of the nanoscale oxide dispersion. Full article

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Bainitic Transformation and Properties of Low Carbon Carbide-Free Bainitic Steels with Cr Addition

by Mingxing Zhou, Guang Xu, Junyu Tian, Haijiang Hu and Qing Yuan

Metals 2017, 7(7), 263; https://doi.org/10.3390/met7070263 - 10 Jul 2017

Cited by 37 | Viewed by 7954

Abstract

Two low carbon carbide-free bainitic steels (with and without Cr addition) were designed, and each steel was treated by two kinds of heat treatment procedure (austempering and continuous cooling). The effects of Cr addition on bainitic transformation, microstructure, and properties of low carbon [...] Read more.

Two low carbon carbide-free bainitic steels (with and without Cr addition) were designed, and each steel was treated by two kinds of heat treatment procedure (austempering and continuous cooling). The effects of Cr addition on bainitic transformation, microstructure, and properties of low carbon bainitic steels were investigated by dilatometry, metallography, X-ray diffraction, and a tensile test. The results show that Cr addition hinders the isothermal bainitic transformation, and this effect is more significant at higher transformation temperatures. In addition, Cr addition increases the tensile strength and elongation simultaneously for austempering treatment at a lower temperature. However, when the austempering temperature is higher, the strength increases and the elongation obviously decreases by Cr addition, resulting in the decrease in the product of tensile strength and elongation. Meanwhile, the austempering temperature should be lower in Cr-added steel than that in Cr-free steel in order to obtain better comprehensive properties. Moreover, for the continuous cooling treatment in the present study, the product of tensile strength and elongation significantly decreases with Cr addition due to more amounts of martensite. Full article

(This article belongs to the Special Issue Alloy Steels)

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Influence of Thickness and Chemical Composition of Hot-Rolled Bands on the Final Microstructure and Magnetic Properties of Non-Oriented Electrical Steel Sheets Subjected to Two Different Decarburizing Atmospheres

by Nephtali Calvillo, Ma. De Jesús Soria, Armando Salinas, Emmanuel J. Gutiérrez, Iván A. Reyes and Francisco R. Carrillo

Metals 2017, 7(6), 229; https://doi.org/10.3390/met7060229 - 21 Jun 2017

Cited by 10 | Viewed by 7269

Abstract

During electrical steel processing, there are usually small variations in both chemical composition and thickness in the hot-rolled material that may lead to different magnetic properties for the same steel grade. Therefore, it is of great importance to know the effects of such [...] Read more.

During electrical steel processing, there are usually small variations in both chemical composition and thickness in the hot-rolled material that may lead to different magnetic properties for the same steel grade. Therefore, it is of great importance to know the effects of such variations on the final microstructure and magnetic properties of these steels. In the present investigation, samples of a specific grade of a commercial hot-rolled grain non-oriented (GNO) electrical steel were taken from different steel batches to investigate the effects of thickness and chemical composition (C, Sn, Mn and Ti) in the hot-rolled material on the final microstructure and magnetic properties (core losses and magnetic permeability) resulting from two different decarburizing annealing cycles. Hot-rolled samples were processed by cold rolling, intermediate annealing, temper-rolling and final decarburization annealing using the same processing parameters. The experimental results show that the minimum core losses and maximum magnetic permeability are obtained with the thinnest steel thickness and the largest grain size. Increasing Sb and Mn contents, and reducing the C and Ti concentrations also improve the magnetic behavior of these steels. It was also found the effect of grain size on the magnetic behavior is more significant than the one of crystallographic texture. Full article

(This article belongs to the Special Issue Alloy Steels)

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10378 KiB

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The Effect of Niobium on the Changing Behavior of Non-Metallic Inclusions in Solid Alloys Deoxidized with Mn and Si during Heat Treatment at 1473 K

by Chengsong Liu, Xiaoqin Liu, Shufeng Yang, Jingshe Li, Hongwei Ni and Fei Ye

Metals 2017, 7(6), 223; https://doi.org/10.3390/met7060223 - 16 Jun 2017

Cited by 2 | Viewed by 4225

Abstract

To clarify the effect of niobium (Nb) on the changing behavior of oxide inclusions in alloys containing different concentrations of Mn, Si, and Nb, heat treatment experiments at 1473 K were conducted and changes in the morphology, size, quantity, and composition of these [...] Read more.

To clarify the effect of niobium (Nb) on the changing behavior of oxide inclusions in alloys containing different concentrations of Mn, Si, and Nb, heat treatment experiments at 1473 K were conducted and changes in the morphology, size, quantity, and composition of these inclusions were investigated. The stability of the oxide inclusions in both molten and solid Fe-Mn-Si-Nb alloys was also estimated by thermodynamic calculation using available data. Results showed that the change in the composition of the oxide inclusions owing to heat treatment depended on the concentrations of Nb and Si in the alloy. MnO-SiO₂-type oxide inclusions gradually transformed into MnO-Nb₂O₅-type or MnO-SiO₂- & MnO-Nb₂O₅-type inclusions in low-Si and high-Nb alloys after heating for 60 min. However, the shape of the inclusions did not change clearly. It was indicated that, during the heat treatment at 1473 K, an interface chemical reaction between the Fe-Mn-Si-Nb alloys and the MnO-SiO₂-type oxide inclusions occurred according to the experimental and calculation results. Full article

(This article belongs to the Special Issue Alloy Steels)

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Studying Mechanical Properties and Micro Deformation of Ultrafine-Grained Structures in Austenitic Stainless Steel

by Na Gong, Hui-Bin Wu, Zhi-Chen Yu, Gang Niu and Da Zhang

Metals 2017, 7(6), 188; https://doi.org/10.3390/met7060188 - 24 May 2017

Cited by 10 | Viewed by 5486

Abstract

Eighty percent heavy cold thickness reduction and reversion transformation in the temperature range 700–950 °C for 60 s were performed to obtain the reverted ultrafine-grained (UFG) structure in 304 austenitic stainless steel. Through mechanical property experiments and transmission electron microscopy (TEM) of micro [...] Read more.

Eighty percent heavy cold thickness reduction and reversion transformation in the temperature range 700–950 °C for 60 s were performed to obtain the reverted ultrafine-grained (UFG) structure in 304 austenitic stainless steel. Through mechanical property experiments and transmission electron microscopy (TEM) of micro deformation of the UFG austenite structure, the tensile fractographs showed that for specimens annealed at 700–950 °C, the most frequent dimple sizes were approximately 0.1–0.3 μm and 1–1.5 μm. With the increase in annealing temperature, the dimple size distribution of nano-sized grains turned to micron-size. TEM micro deformation experiments showed that specimens annealed at 700 °C tended to crack quickly. In the grain annealed at 870 °C, partial dislocations were irregularly separated in the crystal or piled up normal to the grain boundaries; stacking faults were blocked by grain boundaries of small grains; twins held back the glide of the dislocations. In the grain annealed at 950 °C, the deformation twins were perpendicular to ε martensite. Fine grain was considered a strengthening phase in the UFG structure and difficult to break. Full article

(This article belongs to the Special Issue Alloy Steels)

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Effect of Current on Structure and Macrosegregation in Dual Alloy Ingot Processed by Electroslag Remelting

by Yu Liu, Zhao Zhang, Guangqiang Li, Qiang Wang, Li Wang and Baokuan Li

Metals 2017, 7(6), 185; https://doi.org/10.3390/met7060185 - 24 May 2017

Cited by 17 | Viewed by 5904

Abstract

Macrosegregation is a very common problem for the quality control of all cast ingots. The effect of current on the structure and macrosegregation in dual alloy ingot processed by electroslag remelting (ESR) was investigated experimentally with various analytical methods. In this study, the [...] Read more.

Macrosegregation is a very common problem for the quality control of all cast ingots. The effect of current on the structure and macrosegregation in dual alloy ingot processed by electroslag remelting (ESR) was investigated experimentally with various analytical methods. In this study, the electrode consisted of NiCrMoV alloy bar (upper part) and CrMoV alloy (lower part) with a diameter of 55 mm, was remelted in a laboratory-scale ESR furnace with the slag containing 30 mass pct alumina and 70 mass pct calcium fluoride under an open air atmosphere. The results show that the macrostructures of three ingots processed by electroslagremelting with different currents are nearly similar. The thin equiaxed grains region and the columnar grains region are formed under the ingot surface, the latter region is the dominant part of the ingot. The typical columnar structure shows no discontinuity among the NiCrMoV alloy zone, the CrMoV alloy zone, and the transition zone in three ingots. With the increase of the current, the grain growth angle increases due to the deeper molten metal pool. The secondary dendrite arm spacing (SDAS) firstly decreases, then increases. The SDAS is dominated by the combined effect of the local solidification rate and the width of mushy region. With the current increasing from 1500 A to 1800 A and 2100 A, the width of the transition zone decreases from 147 mm to 115 mm and 102 mm. The macrosegregation becomes more severe due to the fiercer flows forced by the Lorentz force and the thermal buoyancy force. The cooling rate firstly increases, then decreases, due to the effect of the flows between the mushy region and metal pool and the temperature gradient at the mushy zone of the solidification front. With a current of 1800 A, the SDAS is the smallest and cooling rate is the fastest, indicating that less dendrite segregation and finer precipitates exist in the ingot. Under the comprehensive consideration, the dual alloy ingot processed by the ESR with a current of 1800 A is the best because it has the smallest SDAS, the appropriate grain growth angle, moderate macrosegregation and thickness of the transition zone. Full article

(This article belongs to the Special Issue Alloy Steels)

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Open AccessArticle

Critical Condition of Dynamic Recrystallization in 35CrMo Steel

by Yuanchun Huang, Sanxing Wang, Zhengbing Xiao and Hui Liu

Metals 2017, 7(5), 161; https://doi.org/10.3390/met7050161 - 9 May 2017

Cited by 13 | Viewed by 5385

Abstract

The compression deformation behaviors of 35CrMo steel at different conditions was studied by using Gleeble-3810 thermo-simulation machine under large strain. The results indicate that the flow stress curves of 35CrMo steel is affected by strain rate and deformation temperature, showing the characteristics of [...] Read more.

The compression deformation behaviors of 35CrMo steel at different conditions was studied by using Gleeble-3810 thermo-simulation machine under large strain. The results indicate that the flow stress curves of 35CrMo steel is affected by strain rate and deformation temperature, showing the characteristics of dynamic recovery (DRV) and dynamic recrystallization (DRX), which is the main softening mechanism of 35CrMo steel. The activation energy (Q) and Zener–Hollomon parameter (Z parameter) expression for thermal deformation of this steel was calculated by linear regression. The inflection point on the curve of strain hardening rate and flow stress (θ-σ curve) corresponds to the beginning of DRX, and the critical strain of DRX increases with the decrease of deformation temperature and the increase of strain rate. Based on the inflection point criterion, the constitutive equation of the critical strain of DRX of 35CrMo steel was established: ε_c = 0.000232Z^0.1673, which reflects the variation of the critical strain of DRX with the Z parameter. In addition, through metallographic observation, the rationality of the inflection point criterion in determining the critical strain of DRX of 35CrMo steel was verified, and the DRX state diagram was established. Full article

(This article belongs to the Special Issue Alloy Steels)

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Tribological Properties of Plough Shares Made of Pearlitic and Martensitic Steels

by Tomasz Stawicki, Beata Białobrzeska and Piotr Kostencki

Metals 2017, 7(4), 139; https://doi.org/10.3390/met7040139 - 14 Apr 2017

Cited by 13 | Viewed by 5999

Abstract

Tribological properties of ploughshares made of pearlitic and martensitic steels were compared in field tests. Sectional ploughshares consisting of separate share-points and trapezoidal parts were subjected to examinations. Contours of the examined parts were similar, but the thickness of the parts made of [...] Read more.

Tribological properties of ploughshares made of pearlitic and martensitic steels were compared in field tests. Sectional ploughshares consisting of separate share-points and trapezoidal parts were subjected to examinations. Contours of the examined parts were similar, but the thickness of the parts made of pearlitic steel was 1 to 3 mm greater for the share-points and 0.5 to 2 mm greater for the trapezoidal parts. Within the tests, sandy loams, loams, and loamy sands with circa (ca.) 13% humidity were cultivated. A greater intensity of thickness reduction and mass wear of the parts made of pearlitic steel was found, which indicates a lower resistance of this steel to wear in soil. However, contour changes of the share-points and the trapezoidal parts made of pearlitic and martensitic steels were comparable, which was probably influenced by the greater thickness of the parts made of pearlitic steel. The roughness of the rake faces of the parts made of pearlitic steel was greater than that for the parts made of martensitic steel, which can be attributed to lower hardness of the former. The largest differences occurred between maximum peak heights of the roughness profile values (R_p), which indicates stronger ridging in the case of pearlitic steel. Scanning electron microscope (SEM) observations of the rake faces showed that martensitic steel was subjected to wear mostly by microcutting, but pearlitic steel was principally worn by microcutting and microploughing. During tillage, only one share-point made of pearlitic steel was broken. However, the main disadvantage of these parts was that their bending was related to the lower mechanical strength of pearlitic steel. Full article

(This article belongs to the Special Issue Alloy Steels)

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Characterization of the Microstructure, Mechanical Properties, and Corrosion Resistance of a Friction-Stir-Welded Joint of Hyper Duplex Stainless Steel

by Jianchun Li, Xinglong Liu, Guoping Li, Peide Han and Wei Liang

Metals 2017, 7(4), 138; https://doi.org/10.3390/met7040138 - 13 Apr 2017

Cited by 22 | Viewed by 5881

Abstract

This study investigates the microstructure, mechanical properties, and corrosion resistance of a friction-stir-welded joint of the hyper duplex stainless steel SAF2707. Friction stir welding (FSW) is performed at a tool rotation rate of 400 rpm and a welding speed of 100 mm/min. The [...] Read more.

This study investigates the microstructure, mechanical properties, and corrosion resistance of a friction-stir-welded joint of the hyper duplex stainless steel SAF2707. Friction stir welding (FSW) is performed at a tool rotation rate of 400 rpm and a welding speed of 100 mm/min. The microstructure of the joints is examined using scanning electron microscopy and X-ray diffraction. Tensile test and fractography are subsequently employed to evaluate the mechanical properties of the joints. Results show that the grain size of the stir zone (SZ) is smaller than that of the base metal (BM). Electron back-scattered diffraction analysis reveals that fine-equiaxed grains form in the SZ because of the dynamic recrystallization during the FSW. These grains become increasingly pronounced in the austenite phase. The tensile specimens consistently fail in the BM, implying that the welded joint is an overmatch to the BM. Moreover, the welded joints consist of finer grains and thus display higher tensile strength than their BMs. Potentiodynamic polarization curves and impedance spectroscopy both demonstrate that the corrosion resistance of the SZ is superior to that of the base material. Full article

(This article belongs to the Special Issue Alloy Steels)

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Corrosion Behavior of API X100 Steel Material in a Hydrogen Sulfide Environment

by Paul C. Okonkwo, Rana Abdul Shakoor, Abdelbaki Benamor, Adel Mohamed Amer Mohamed and Mohammed Jaber F A Al-Marri

Metals 2017, 7(4), 109; https://doi.org/10.3390/met7040109 - 25 Mar 2017

Cited by 20 | Viewed by 6740

Abstract

Recently, the API X100 steel has emerged as an important pipeline material for transportation of crude oil and natural gas. At the same time, the presence of significant amounts of hydrogen sulfide (H₂S) in natural gas and crude oil cause pipeline [...] Read more.

Recently, the API X100 steel has emerged as an important pipeline material for transportation of crude oil and natural gas. At the same time, the presence of significant amounts of hydrogen sulfide (H₂S) in natural gas and crude oil cause pipeline materials to corrode, which affects their integrity. In this study, the effect of H₂S concentration on the corrosion behavior of API X100 in 3.5% NaCl solution is presented. The H₂S gas was bubbled into saline solutions for different durations, and the corrosion tests were then performed using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) techniques were used to characterize the corroded surface. The results indicate that the corrosion rate of API X100 steel decreases with increasing H₂S bubbling time due to the increase in H₂S concentration in 3.5% NaCl solutions. It is noticed that an accumulation of a critical amount of hydrogen in the metal can result in hydrogen-induced crack initiation and propagation. It was further observed that, when the stress limit of a crystalline layer is exceeded, micro-cracking of the formed protective sulfide layer (mackinawite) occurs on the API X100 steel surface, which may affect the reliability of the pipeline system. Full article

(This article belongs to the Special Issue Alloy Steels)

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Effect of Heat Treatment on the Microstructure and Mechanical Properties of Nitrogen-Alloyed High-Mn Austenitic Hot Work Die Steel

by Yi Zhang, Jing Li, Cheng-Bin Shi, Yong-Feng Qi and Qin-Tian Zhu

Metals 2017, 7(3), 94; https://doi.org/10.3390/met7030094 - 14 Mar 2017

Cited by 15 | Viewed by 6997

Abstract

In view of the requirements for mechanical properties and service life above 650 °C, a high-Mn austenitic hot work die steel, instead of traditional martensitic hot work die steel such as H13, was developed in the present study. The effect of heat treatment [...] Read more.

In view of the requirements for mechanical properties and service life above 650 °C, a high-Mn austenitic hot work die steel, instead of traditional martensitic hot work die steel such as H13, was developed in the present study. The effect of heat treatment on the microstructure and mechanical properties of the newly developed work die steel was studied. The results show that the microstructure of the high-Mn as-cast electroslag remelting (ESR) ingot is composed of γ-Fe, V(C,N), and Mo₂C. V(C,N) is an irregular multilateral strip or slice shape with severe angles. Most eutectic Mo₂C carbides are lamellar fish-skeleton-like, except for a few that are rod-shaped. With increasing solid solution time and temperature, the increased hardness caused by solid solution strengthening exceeds the effect of decreased hardness caused by grain size growth, but this trend is reversed later. As a result, the hardness of specimens after various solid solution heat treatments increases first and then decreases. The optimal combination of hardness and austenitic grain size can be obtained by soaking for 2 h at 1170 °C. The maximum Rockwell hardness (HRC) is 47.24 HRC, and the corresponding austenite average grain size is 58.4 μm. When the solid solution time is 3 h at 1230 °C, bimodality presented in the histogram of the austenite grain size as a result of further progress in secondary recrystallization. Compared with the single-stage aging, the maximum impact energy of the specimen after two-stage aging heat treatment was reached at 16.2 J and increased by 29.6%, while the hardness decreased by 1–2 HRC. After two-stage aging heat treatment, the hardness of steel reached the requirements of superior grade H13, and the maximum impact energy was 19.6% higher than that of superior grade H13, as specified in NADCA#207-2003. Full article

(This article belongs to the Special Issue Alloy Steels)

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Assessment of the Residual Life of Steam Pipeline Material beyond the Computational Working Time

by Marek Sroka, Adam Zieliński, Maria Dziuba-Kałuża, Marek Kremzer, Magdalena Macek and Artur Jasiński

Metals 2017, 7(3), 82; https://doi.org/10.3390/met7030082 - 6 Mar 2017

Cited by 27 | Viewed by 4979

Abstract

This paper presents the evaluation of durability for the material of repair welded joints made from (13HMF) 14MoV6-3 steel after long-term service, and from material in the as-received condition and after long-term service. Microstructure examinations using a scanning electron microscope, hardness measurements and [...] Read more.

This paper presents the evaluation of durability for the material of repair welded joints made from (13HMF) 14MoV6-3 steel after long-term service, and from material in the as-received condition and after long-term service. Microstructure examinations using a scanning electron microscope, hardness measurements and creep tests of the basic material and welded joints of these steels were carried out. These tests enabled the time of further safe service of the examined repair welded joints to be determined in relation to the residual life of the materials. The evaluation of residual life and disposable life, and thus the estimation and determination of the time of safe service, is of great importance for the operation of components beyond the design service life. The obtained test results are part of the materials’ characteristics developed by the Institute for Ferrous Metallurgy for steels and welded joints made from these steels to work under creep conditions. Full article

(This article belongs to the Special Issue Alloy Steels)

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Precipitation Behavior of Carbides in H13 Hot Work Die Steel and Its Strengthening during Tempering

by Angang Ning, Wenwen Mao, Xichun Chen, Hanjie Guo and Jing Guo

Metals 2017, 7(3), 70; https://doi.org/10.3390/met7030070 - 23 Feb 2017

Cited by 74 | Viewed by 9103

Abstract

The properties of carbides, such as morphology, size, and type, in H13 hot work die steel were studied with optical microscopy, transmission electron microscopy, electron diffraction, and energy dispersive X-ray analysis; their size distribution and quantity after tempering, at different positions within the [...] Read more.

The properties of carbides, such as morphology, size, and type, in H13 hot work die steel were studied with optical microscopy, transmission electron microscopy, electron diffraction, and energy dispersive X-ray analysis; their size distribution and quantity after tempering, at different positions within the ingot, were analyzed using Image-Pro Plus software. Thermodynamic calculations were also performed for these carbides. The microstructures near the ingot surface were homogeneous and had slender martensite laths. Two kinds of carbide precipitates have been detected in H13: (1) MC and M₆C, generally smaller than 200 nm; and (2) M₂₃C₆, usually larger than 200 nm. MC and M₆C play the key role in precipitation hardening. These are the most frequent carbides precipitating at the halfway point from the center of the ingot, and the least frequent at the surface. From the center of the ingot to its surface, the size and volume fraction of the carbides decrease, and the toughness improves, while the contribution of the carbides to the yield strength increases. Full article

(This article belongs to the Special Issue Alloy Steels)

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Effect of Low-Temperature Sensitization on Hydrogen Embrittlement of 301 Stainless Steel

by Chieh Yu, Ren-Kae Shiue, Chun Chen and Leu-Wen Tsay

Metals 2017, 7(2), 58; https://doi.org/10.3390/met7020058 - 15 Feb 2017

Cited by 6 | Viewed by 5364

Abstract

The effect of metastable austenite on the hydrogen embrittlement (HE) of cold-rolled (30% reduction in thickness) 301 stainless steel (SS) was investigated. Cold-rolled (CR) specimens were hydrogen-charged in an autoclave at 300 or 450 °C under a pressure of 10 MPa for 160 [...] Read more.

The effect of metastable austenite on the hydrogen embrittlement (HE) of cold-rolled (30% reduction in thickness) 301 stainless steel (SS) was investigated. Cold-rolled (CR) specimens were hydrogen-charged in an autoclave at 300 or 450 °C under a pressure of 10 MPa for 160 h before tensile tests. Both ordinary and notched tensile tests were performed in air to measure the tensile properties of the non-charged and charged specimens. The results indicated that cold rolling caused the transformation of austenite into α′ and ε-martensite in the 301 SS. Aging at 450 °C enhanced the precipitation of M₂₃C₆ carbides, G, and σ phases in the cold-rolled specimen. In addition, the formation of α′ martensite and M₂₃C₆ carbides along the grain boundaries increased the HE susceptibility and low-temperature sensitization of the 450 °C-aged 301 SS. In contrast, the grain boundary α′-martensite and M₂₃C₆ carbides were not observed in the as-rolled and 300 °C-aged specimens. Full article

(This article belongs to the Special Issue Alloy Steels)

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The Effects of Cr and Al Addition on Transformation and Properties in Low‐Carbon Bainitic Steels

by Junyu Tian, Guang Xu, Mingxing Zhou, Haijiang Hu and Xiangliang Wan

Metals 2017, 7(2), 40; https://doi.org/10.3390/met7020040 - 31 Jan 2017

Cited by 45 | Viewed by 7134

Abstract

Three low‐carbon bainitic steels were designed to investigate the effects of Cr and Al addition on bainitic transformation, microstructures, and properties by metallographic method and dilatometry. The results show that compared with the base steel without Cr and Al addition, only Cr addition [...] Read more.

Three low‐carbon bainitic steels were designed to investigate the effects of Cr and Al addition on bainitic transformation, microstructures, and properties by metallographic method and dilatometry. The results show that compared with the base steel without Cr and Al addition, only Cr addition is effective for improving the strength of low‐carbon bainitic steel by increasing the amount of bainite. However, compared with the base steel, combined addition of Cr and Al has no significant effect on bainitic transformation and properties. In Cr‐bearing steel, Al addition accelerates initial bainitic transformation, but meanwhile reduces the final amount of bainitic transformation due to the formation of a high‐temperature transformation product such as ferrite. Consequently, the composite strengthening effect of Cr and Al addition is not effective compared with individual addition of Cr in low‐carbon bainitic steels. Therefore, in contrast to high‐carbon steels, bainitic transformation in Cr‐bearing low‐carbon bainitic steels can be finished in a short time, and Al should not be added because Al addition would result in lower mechanical properties. Full article

(This article belongs to the Special Issue Alloy Steels)

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5057 KiB

Open AccessArticle

Effects of Austenitizing Conditions on the Microstructure of AISI M42 High-Speed Steel

by Yiwa Luo, Hanjie Guo, Xiaolin Sun, Mingtao Mao and Jing Guo

Metals 2017, 7(1), 27; https://doi.org/10.3390/met7010027 - 18 Jan 2017

Cited by 38 | Viewed by 8654

Abstract

The influences of austenitizing conditions on the microstructure of AISI M42 high-speed steel were investigated through thermodynamic calculation, microstructural analysis, and in-situ observation by a confocal scanning laser microscope (CSLM). Results show that the network morphology of carbides could not dissolve completely and [...] Read more.

The influences of austenitizing conditions on the microstructure of AISI M42 high-speed steel were investigated through thermodynamic calculation, microstructural analysis, and in-situ observation by a confocal scanning laser microscope (CSLM). Results show that the network morphology of carbides could not dissolve completely and distribute equably in the case of the austenitizing temperature is 1373 K. When the austenitizing temperature reaches 1473 K, the excessive increase in temperature leads to increase in carbide dissolution, higher dissolved alloying element contents, and unwanted grain growth. Thus, 1453 K is confirmed as the best austenitizing condition on temperature for the steel. In addition, variations on the microstructure and hardness of the steel are not obvious when holding time ranges from 15 to 30 min with the austenitizing temperature of 1453 K. However, when the holding time reaches 45 min, the average size of carbides tends to increase because of Ostwald ripening. Furthermore, the value of M_s and M_f decrease with the increase of cooling rate. Hence, high cooling rate can depress the martensitic transformation and increase the content of retained austenite. As a result, the hardness of the steel is the best (65.6 HRc) when the austenitizing temperature reaches 1453 K and is held for 30 min. Full article

(This article belongs to the Special Issue Alloy Steels)

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Open AccessArticle

The Influence of Austenite Grain Size on the Mechanical Properties of Low-Alloy Steel with Boron

by Beata Białobrzeska, Łukasz Konat and Robert Jasiński

Metals 2017, 7(1), 26; https://doi.org/10.3390/met7010026 - 17 Jan 2017

Cited by 65 | Viewed by 11217

Abstract

This study forms part of the current research on modern steel groups with higher resistance to abrasive wear. In order to reduce the intensity of wear processes, and also to minimize their impact, the immediate priority seems to be a search for a [...] Read more.

This study forms part of the current research on modern steel groups with higher resistance to abrasive wear. In order to reduce the intensity of wear processes, and also to minimize their impact, the immediate priority seems to be a search for a correlation between the chemical composition and structure of these materials and their properties. In this paper, the correlation between prior austenite grain size, martensite packets and the mechanical properties were researched. The growth of austenite grains is an important factor in the analysis of the microstructure, as the grain size has an effect on the kinetics of phase transformation. The microstructure, however, is closely related to the mechanical properties of the material such as yield strength, tensile strength, elongation and impact strength, as well as morphology of occurred fracture. During the study, the mechanical properties were tested and a tendency to brittle fracture was analysed. The studies show big differences of the analysed parameters depending on the applied heat treatment, which should provide guidance to users to specific applications of this type of steel. Full article

(This article belongs to the Special Issue Alloy Steels)

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Open AccessArticle

The Structural Evolution and Segregation in a Dual Alloy Ingot Processed by Electroslag Remelting

by Yu Liu, Zhao Zhang, Guangqiang Li, Qiang Wang, Li Wang and Baokuan Li

Metals 2016, 6(12), 325; https://doi.org/10.3390/met6120325 - 21 Dec 2016

Cited by 7 | Viewed by 5503

Abstract

The structural evolution and segregation in a dual alloy made by electroslag remelting (ESR) was investigated by various analytical techniques. The results show that the macrostructure of the ingot consists of two crystallization structures: one is a quite narrow, fine, equiaxed grain region [...] Read more.

The structural evolution and segregation in a dual alloy made by electroslag remelting (ESR) was investigated by various analytical techniques. The results show that the macrostructure of the ingot consists of two crystallization structures: one is a quite narrow, fine, equiaxed grain region at the edge and the other is a columnar grain region, which plays a leading role. The typical columnar structure shows no discontinuity between the CrMoV, NiCrMoV, and transition zones. The average secondary arm-spacing is coarsened from 35.3 to 49.2 μm and 61.5 μm from the bottom to the top of the ingot. The distinctive features of the structure are attributed to the different cooling conditions during the ESR process. The Ni, Cr, and C contents markedly increase in the transition zone (TZ) and show a slight increase from the bottom to the top and from the surface to the center of the ESR ingot due to the partition ratios, gravity segregation, the thermal buoyancy flow, the solutal buoyancy flow, and the inward Lorentz force. Less dendrite segregation exists in the CrMoV zone and the transition zone due to a stronger cooling rate (11.1 and 4.5 °C/s) and lower Cr and C contents. The precipitation of carbides was observed in the ingot due to a lower solid solubility of the carbon element in the α phase. Full article

(This article belongs to the Special Issue Alloy Steels)

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Superior Strength of Austenitic Steel Produced by Combined Processing, including Equal-Channel Angular Pressing and Rolling

by Marina V. Karavaeva, Marina M. Abramova, Nariman A. Enikeev, Georgy I. Raab and Ruslan Z. Valiev

Metals 2016, 6(12), 310; https://doi.org/10.3390/met6120310 - 8 Dec 2016

Cited by 27 | Viewed by 5129

Abstract

Enhancement in the strength of austenitic steels with a small content of carbon can be achieved by a limited number of methods, among which is ultrafine-grained (UFG) structure formation. This method is especially efficient with the use of severe plastic deformation (SPD) processing, [...] Read more.

Enhancement in the strength of austenitic steels with a small content of carbon can be achieved by a limited number of methods, among which is ultrafine-grained (UFG) structure formation. This method is especially efficient with the use of severe plastic deformation (SPD) processing, which significantly increases the contribution of grain-boundary strengthening, and also involves a combination of the other strengthening factors (work hardening, twins, etc.). In this paper, we demonstrate that the use of SPD processing combined with conventional methods of deformation treatment of metals, such as rolling, may lead to additional strengthening of UFG steel. In the presented paper we analyze the microstructure and mechanical properties of the Cr–Ni stainless austenitic steel after a combined deformation. We report on substantial increases in the strength properties of this steel, resulting from a consecutive application of SPD processing via equal-channel angular pressing and rolling at a temperature of 400 °C. This combined loading yields a strength more than 1.5 times higher than those produced by either of these two techniques used separately. Full article

(This article belongs to the Special Issue Alloy Steels)

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1913 KiB

Open AccessArticle

Corrosion of Fe-(9~37) wt. %Cr Alloys at 700–800 °C in (N₂, H₂O, H₂S)-Mixed Gas

by Min Jung Kim, Muhammad Ali Abro and Dong Bok Lee

Metals 2016, 6(11), 291; https://doi.org/10.3390/met6110291 - 23 Nov 2016

Cited by 3 | Viewed by 4099

Abstract

Fe-(9, 19, 28, 37) wt. %Cr alloys were corroded at 700 and 800 °C for 70 h under 1 atm of N₂, 1 atm of N₂/3.2%H₂O mixed gas, and 1 atm of N₂/3.1%H₂O/2.42%H [...] Read more.

Fe-(9, 19, 28, 37) wt. %Cr alloys were corroded at 700 and 800 °C for 70 h under 1 atm of N₂, 1 atm of N₂/3.2%H₂O mixed gas, and 1 atm of N₂/3.1%H₂O/2.42%H₂S mixed gas. In this gas composition order, the corrosion rate of Fe-9Cr alloy rapidly increased. Fe-9Cr alloy was always non-protective. In contrast, Fe-(19, 28, 37) wt. %Cr alloys were protective in N₂ and N₂/3.2%H₂O mixed gas because of the formation of the Cr₂O₃ layer. They, however, became nonprotective in N₂/3.1%H₂O/2.42%H₂S mixed gas because sulfidation dominated to form the outer FeS layer and the inner Cr₂S₃ layer containing some FeCr₂S₄. Full article

(This article belongs to the Special Issue Alloy Steels)

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Review

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Effects of Heat Input on Microstructure, Corrosion and Mechanical Characteristics of Welded Austenitic and Duplex Stainless Steels: A Review

by Ghusoon Ridha Mohammed, Mahadzir Ishak, Syarifah N. Aqida and Hassan A. Abdulhadi

Metals 2017, 7(2), 39; https://doi.org/10.3390/met7020039 - 30 Jan 2017

Cited by 110 | Viewed by 14563

Abstract

The effects of input heat of different welding processes on the microstructure, corrosion, and mechanical characteristics of welded duplex stainless steel (DSS) are reviewed. Austenitic stainless steel (ASS) is welded using low-heat inputs. However, owing to differences in the physical metallurgy between ASS [...] Read more.

The effects of input heat of different welding processes on the microstructure, corrosion, and mechanical characteristics of welded duplex stainless steel (DSS) are reviewed. Austenitic stainless steel (ASS) is welded using low-heat inputs. However, owing to differences in the physical metallurgy between ASS and DSS, low-heat inputs should be avoided for DSS. This review highlights the differences in solidification mode and transformation characteristics between ASS and DSS with regard to the heat input in welding processes. Specifically, many studies about the effects of heat energy input in welding process on the pitting corrosion, intergranular stress, stresscorrosion cracking, and mechanical properties of weldments of DSS are reviewed. Full article

(This article belongs to the Special Issue Alloy Steels)

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