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Advanced Technology in Microalloyed Steels
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Advanced Technology in Microalloyed Steels

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

Deadline for manuscript submissions: closed (15 January 2023) | Viewed by 30359

Special Issue Editors

Prof. Dr. Minghui Cai

E-Mail Website
Guest Editor
School of Materials Science and Engineering, Northeastern University, Shenyang 110819, China
Interests: advanced high-strength steels; lightweight alloys (aluminum; titanium); lamellar metallic materials; grain refinement; phase transformation and its reverse transformation; asymmetric rolling; superplastic forming; hot/warm forming; deformation behavior; strengthening and toughening mechanisms; microstructural characterization
Special Issues, Collections and Topics in MDPI journals
Dr. Shuai Tang

E-Mail Website
Guest Editor
The State Key Laboratory of Rolling and Automation, Northeastern University, Shengyang 110819, China
Interests: microalloyed steel; precipitation; density functional theory; hydrogen embrittlement
Dr. Shengjie Yao

E-Mail Website
Guest Editor
School of Materials Science and Engineering, Harbin Institute of Technology at Weihai, Weihai 264-209, China
Interests: hot stamping; ultra-fine-grained steel; heating technology; microstructural evolution

Special Issue Information

Dear Colleagues,

The addition of small amounts of Nb, Ti, or V singly or in combination has been the key to producing high-strength steels at a low cost. Microalloyed steels are now commonplace in a huge variety of applications. The subject of microalloyed steels interacts significantly with many aspects of metallurgy such as strengthening mechanisms, toughness, ductility, hot working, cold working and recrystallization, non-metallic inclusions, precipitation and phase transformation, grain refinement, weldability, etc. With a view to new microalloying technologies in high-strength steels, we offer this Special Issue entitled " Frontiers in Microalloyed Steels". The purpose of this Special Issue is to organize information about the interactions between processing and microstructural development and the effect of microalloying additions to provide a basis for the control of the microstructure, and hence the properties, in microalloyed steels subjected to industrial heat treatments and hot working practices. 

Dr. Minghui Cai
Dr. Shuai Tang
Dr. Shengjie Yao
Guest Editors

Manuscript Submission Information

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Keywords

  • high-strength steel
  • microalloying
  • controlled processing
  • precipitation
  • phase transformation
  • recrystallization

Published Papers (18 papers)

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Research

9 pages, 4064 KiB  
Article
Microstructure and Properties of Press-Bonded Dissimilar Stainless Steel and Mild Carbon Steel Ingots
by Xuqiang Huang and Zhaoyang Lu
Metals 2022, 12(12), 2142; https://doi.org/10.3390/met12122142 - 14 Dec 2022
Viewed by 1360
Abstract
Dissimilar steel welds between stainless and mild steels are necessary for the efficient utilization of stainless steels in construction. In the present work, a dissimilar large-sized steel ingot was fabricated by press bonding a Q235 steel to a SUS 304 steel at 1100–500 [...] Read more.
Dissimilar steel welds between stainless and mild steels are necessary for the efficient utilization of stainless steels in construction. In the present work, a dissimilar large-sized steel ingot was fabricated by press bonding a Q235 steel to a SUS 304 steel at 1100–500 °C. The microstructure of bonded interfaces has been characterized by scanning electron microscopy, electron probe microanalysis, and transmission electron microscopy, together with tensile tests to evaluate the bonding strength. It has been demonstrated that a strong-bonded, high-quality, dissimilar steel ingot could be fabricated by press bonding. The (Fe, Cr)3C carbide is present in the narrow zone of diffusion-bonded stainless steel and mild steel. Interestingly, the maximum hardness is not too high to make the transition zone brittle but enough to constrain the narrow soft ferrite during tensile and fatigue tests, causing the final fracture to occur in the mild steel region rather than the bonding interface. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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15 pages, 9698 KiB  
Article
Effects of Simulated PWHT on the Microstructure and Mechanical Properties of 2.25Cr1Mo0.25V Steel for a Hydrogenation Reactor
by Yanmei Li, Yonghao Cui, Jimou Zhang, Minghui Song and Chen Xu
Metals 2022, 12(11), 1978; https://doi.org/10.3390/met12111978 - 19 Nov 2022
Cited by 1 | Viewed by 2325
Abstract
The effect of post-welding heat treatment (PWHT) on the microstructure and mechanical properties of large-thickness 2.25Cr1Mo0.25V steel was investigated through simulated post-welding heat treatment (SPWHT). The results showed that an increase in the SPWHT time decreased the toughness, hardness, and strength of the [...] Read more.
The effect of post-welding heat treatment (PWHT) on the microstructure and mechanical properties of large-thickness 2.25Cr1Mo0.25V steel was investigated through simulated post-welding heat treatment (SPWHT). The results showed that an increase in the SPWHT time decreased the toughness, hardness, and strength of the steel. After Min.SPWHT, the high-temperature tensile strength decreased more significantly, and the damage of Min.SPWHT to the high-temperature tensile strength reached approximately 80% of the Max.SPWHT. The microstructure of the tested steel before and after SPWHT consisted of granular bainite and lath bainite. After SPWHT, intergranular carbides were precipitated as coarsened carbides, carbide clusters, and chains of carbides; alloy element segregation occurred, and the segregation of Mo was the most serious, followed by Cr, and V. The precipitation behavior of the carbides and the increase in the effective grain size caused by the widening of the bainite–ferrite lath worked together and resulted in the decline of the impact toughness; the reduction in the solid solution and precipitation strengthening effects were the main factors in the strength reduction of the tested steel. In the high-temperature tensile tests, defects first appeared around the coarse carbides and carbide clusters. Controlling the size of the intergranular large-size carbides and the degree of cluster precipitation in the NT state structure may be a means of obtaining higher strength of the base metal subjected to PWHT. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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11 pages, 1835 KiB  
Article
Microstructure, Mechanical Properties, and Fish-Scaling Resistance of a Ti-Nb Microalloyed Hot-Rolled Enamel Steel
by Yi Zhang, Bo Yu, Jian Zhang, Yu Du, Xiaonan Wang, Hongyan Wu, Xiuhua Gao and Linxiu Du
Metals 2022, 12(11), 1970; https://doi.org/10.3390/met12111970 - 18 Nov 2022
Cited by 1 | Viewed by 1291
Abstract
Currently, the fish-scaling resistance of most hot-rolled enamel steels is improved by adding Ti to form fine TiC carbides as hydrogen traps. Given that the hydrogen capture capacity of NbC is higher than that of TiC, the manufacture of hot-rolled enamel steels via [...] Read more.
Currently, the fish-scaling resistance of most hot-rolled enamel steels is improved by adding Ti to form fine TiC carbides as hydrogen traps. Given that the hydrogen capture capacity of NbC is higher than that of TiC, the manufacture of hot-rolled enamel steels via Ti-Nb microalloying has a promising future. In the present study, a Ti-Nb microalloyed hot-rolled enamel steel was developed, and its microstructure, mechanical properties, and fish-scaling resistance were studied by optical microscopy, transmission electron microscopy, tensile test, and hydrogen permeation test. The results show that the microstructure of hot-rolled experimental steel is composed of ferrite and fine carbides, with a large number of fine precipitates uniformly distributed in the ferrite grains. After the first and second enamel firings, the average sizes of ferrite grain and precipitates gradually increase, the yield strength decreases from 711 ± 9 MPa to 471 ± 17 MPa and 409 ± 8 MPa, the tensile strength decreases from 761 ± 7 MPa to 524 ± 15 MPa and 490 ± 12 MPa, and the elongation increases from 21.0 ± 2.8% to 27.8 ± 1.8% and 33.9 ± 1.1%. The hydrogen permeation value (TH value) decreases from 35.9 min/mm2 to 6.8 min/mm2 and 3.9 min/mm2 after the first and second enamel firings. That is, the fish-scaling resistance of hot-rolled experimental steel is significantly reduced after enamel firing, which is caused by the coarsening of precipitates, resulting in a significant reduction in the density of irreversible hydrogen traps (from 1.21 × 1025 cm−3 to 6.50 × 1023 cm−3 and 4.27 × 1023 cm−3). A large amount of semi-coherent precipitates is the key to obtaining the good fish-scaling resistance of hot-rolled enamel steel. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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10 pages, 11386 KiB  
Article
Static Recrystallization Behavior of Low-Carbon Nb-V-Microalloyed Forging Steel
by Yang Zhao, Jiahao Zheng, Liqing Chen and Xianghua Liu
Metals 2022, 12(10), 1745; https://doi.org/10.3390/met12101745 - 17 Oct 2022
Cited by 5 | Viewed by 1254
Abstract
Static recrystallization is a method of tailoring the microstructure and mechanical properties of steels, which is important for microalloyed forging steels as the hot deformation process significantly affects their mechanical properties. In this paper, the static recrystallization behavior of a low-carbon Nb-V-microalloyed forging [...] Read more.
Static recrystallization is a method of tailoring the microstructure and mechanical properties of steels, which is important for microalloyed forging steels as the hot deformation process significantly affects their mechanical properties. In this paper, the static recrystallization behavior of a low-carbon Nb-V-microalloyed forging steel was investigated by double-pass hot compression tests at deformation temperature of 800–1100 °C and interruption time of 1–1000 s. The static recrystallization fractions were determined using the 2% offset method. The static recrystallization activation energy and the static recrystallization critical temperature (SRCT) of the experimental steel were determined. When the deformation temperature was higher than the SRCT, the recrystallization fraction curve conformed to the Avrami equation. When the deformation temperature was below the SRCT, the recrystallization curve appeared to plateau, which was caused by strain-induced precipitation. Before and after the plateau, the static recrystallization kinetics still obeyed the Avrami equation. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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12 pages, 4135 KiB  
Article
Role of Microalloying Elements on Recrystallization Kinetics of Cold-Rolled High Strength Low Alloy Steels
by Shuai Tang, Xiaofang Li, Jianping Li, Zhenyu Liu and Guodong Wang
Metals 2022, 12(10), 1741; https://doi.org/10.3390/met12101741 - 17 Oct 2022
Cited by 3 | Viewed by 1441
Abstract
The recrystallization kinetics of two cold-rolled high strength low alloy steels with the addition of Ti and Ti-V, respectively, during annealing were investigated by means of modeling and experimental validation. The recrystallization kinetics of the Ti-V steel were hindered compared to the Ti [...] Read more.
The recrystallization kinetics of two cold-rolled high strength low alloy steels with the addition of Ti and Ti-V, respectively, during annealing were investigated by means of modeling and experimental validation. The recrystallization kinetics of the Ti-V steel were hindered compared to the Ti steel. Based on solid solution theory, mass conservation law and classical nucleation, growth and coarsening theory, the precipitation behavior of Ti and Ti-V steels was predicted. The radius of TiC is larger, and its number density is lower than (Tix, V1−x)C. On this basis, by considering the comprehensive effect of recrystallization on stored energy, the effect of the microalloyed precipitates and microalloying solute on the driving force and grain boundary mobility, the model of the recrystallization kinetics was proposed, which could well reproduce the effect of microalloying elements on recrystallization. Moreover, it was indicated that solute drag is more effective in retarding recrystallization than the pinning effect of precipitates. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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14 pages, 7065 KiB  
Article
Microstructure and Mechanical Properties of Laser-Welded Joint of Tantalum and Stainless Steel
by Shanshan Feng, Yongqiang Zhou, Zhengqiang Zhu, Yanfei Chen and Yunming Zhu
Metals 2022, 12(10), 1638; https://doi.org/10.3390/met12101638 - 29 Sep 2022
Cited by 1 | Viewed by 1230
Abstract
Bimetallic components welded by Ta and stainless steel have great promise for engineering applications, but there is relatively little relevant research. In this study, 0.6 mm-thick Ta and 304L stainless steel plates were laser welded, and the forming characteristics, microstructure, and mechanical properties [...] Read more.
Bimetallic components welded by Ta and stainless steel have great promise for engineering applications, but there is relatively little relevant research. In this study, 0.6 mm-thick Ta and 304L stainless steel plates were laser welded, and the forming characteristics, microstructure, and mechanical properties of the welded joints were analyzed. First-principles calculations were also performed to explore the structural stabilization mechanisms of the two intermetallic compounds, TaFe2 and TaCr2, in terms of mechanical properties as well as electronic structure. The results showed that the weld surface was smooth and free from any defects. Fe-based solid solutions formed grains, while TaFe2, TaCr2, and some Fe-based solid solutions formed intergranular and eutectic structures. In addition, due to the presence of the brittle phases of TaFe2 and TaFe, the microhardness of the weld area can reach 650HV, with an average hardness of 530HV, which is much higher than that of the base material. The tensile shear of the joint at room temperature was 154.77 N/mm, and the fracture occurred in the weld zone on the steel side, showing brittle fracture. TaFe2 is a brittle intermetallic compound, while TaCr2 is ductile. Both TaFe2 and TaCr2 systems have dual properties of metallic and covalent bonding within them, and metallic bonding dominates. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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14 pages, 7858 KiB  
Article
Evaluation of Mechanical Properties and Microstructure of X70 Pipeline Steel with Strain-Based Design
by Denghui Liu, Yifan Dong, Rutao Li, Jinxing Jiang, Xiaoyuan Li, Zhenlong Wang and Xiurong Zuo
Metals 2022, 12(10), 1616; https://doi.org/10.3390/met12101616 - 27 Sep 2022
Cited by 5 | Viewed by 2079
Abstract
The microstructure and mechanical properties of X70 pipeline steel with a ferrite/martensite dual-phase microstructure produced by thermo-mechanical controlled processing were investigated by tensile tests, Charpy V-notched (CVN) impact tests, drop-weight tear tests, guided-bend tests, scanning electron microscopy and transmission electron microscopy combined with [...] Read more.
The microstructure and mechanical properties of X70 pipeline steel with a ferrite/martensite dual-phase microstructure produced by thermo-mechanical controlled processing were investigated by tensile tests, Charpy V-notched (CVN) impact tests, drop-weight tear tests, guided-bend tests, scanning electron microscopy and transmission electron microscopy combined with thermodynamic simulation analysis. All the mechanical properties met the strength, ductility, toughness and deformability properties requirements of X70 grade pipeline steel with strain-based design. The shear fracture area and absorbed energy of CVN at −10 °C were >97% and >205 J in base metal (BM), weld metal (WM) and heat affected zone (HAZ) with low transition temperature, indicating adequate resistance to propagating fracture. The microstructure of WM was mainly intragranular acicular ferrite that can guarantee high strength, toughness and over matching requirements of the welded joint. Because of being exposed to successive heat inputs, the ferrite plus martensite/bainite microstructure of BM was heated between Ac1 and Ts forming the HAZ. However, a high CVN impact toughness of 345 J at −10 °C in HAZ was obtained, which indicated that the excellent mechanical properties of BM would not be seriously deteriorated during the welding thermal cycles with the reasonable addition of Ti and Nb. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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15 pages, 7394 KiB  
Article
Resistance Spot-Welding of Dissimilar Metals, Medium Manganese TRIP Steel and DP590
by Fufa Wei, Yunming Zhu, Yifeng Tian, Hongning Liu, Yongqiang Zhou and Zhengqiang Zhu
Metals 2022, 12(10), 1596; https://doi.org/10.3390/met12101596 - 25 Sep 2022
Cited by 2 | Viewed by 1333
Abstract
Resistance spot-welding of dissimilar metals, medium manganese TRIP steel 7Mn and DP590, is carried out. The effects of single-pulse welding parameters and a double-pulse-tempering current on the quality characteristic parameters and mechanical properties of 7Mn/DP590 spot-welded joints are studied. The welding process parameters [...] Read more.
Resistance spot-welding of dissimilar metals, medium manganese TRIP steel 7Mn and DP590, is carried out. The effects of single-pulse welding parameters and a double-pulse-tempering current on the quality characteristic parameters and mechanical properties of 7Mn/DP590 spot-welded joints are studied. The welding process parameters are optimized using the control variable method. The results show that the optimal process parameters under a single pulse are as follows: electrode pressure: 4.5 kN, welding current: 9 kA and welding time: 300 ms. The failure mode of the welding joint is partial pull-out failure (PF-TT). The welding parameters have great influence on the nugget diameter and thickness reduction. Expulsion, crack and shrinkage are displayed in the joint under high electrode pressure. Softening occurs in the heat-affected zone due to a strong halo effect in the single-pulse weld. The tempering zone on the DP590 side is 202.49 HV, which is the lowest hardness point, while the hardness of the nugget zone is 450 HV. The addition of the tempering current homogenizes the microstructure with different failure paths and eliminates the stress. The tensile shear force of the joint increases by 17.13%. The 7Mn Steel/DP590 resistance spot-welding joint is from the fusion line to the center of the nugget, and the microstructure is composed of plane crystal, cellular crystal, dendritic crystal and columnar crystal, in turn. The nugget zone is composed of lath martensite and a small amount of residual austenite. Fine quasi-spherical and lamellar interbedded cementites are formed in the tempering zone of the DP590-side heat-affected zone. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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18 pages, 7943 KiB  
Article
Constitutive Equation and Characterization of the Nickel-Based Alloy 825
by Hui Xu, Yugui Li, Huaying Li, Jinbin Wang, Guangming Liu and Yaohui Song
Metals 2022, 12(9), 1496; https://doi.org/10.3390/met12091496 - 09 Sep 2022
Cited by 3 | Viewed by 1342
Abstract
In this contribution, a series of isothermal compression tests for the 825 nickel-based alloy were performed using a Gleeble-3800 computer-controlled thermomechanical simulator at the compression temperature range of 850 °C to 1150 °C and the strain rate range of 0.14 s−1 to [...] Read more.
In this contribution, a series of isothermal compression tests for the 825 nickel-based alloy were performed using a Gleeble-3800 computer-controlled thermomechanical simulator at the compression temperature range of 850 °C to 1150 °C and the strain rate range of 0.14 s−1 to 2.72 s−1. The hot deformation equation of the alloy is derived from the piecewise model based on the theory of work hardening-dynamic recovery and dynamic recrystallization (DRX), respectively. Comparisons between the predicted and experimental data indicate that the proposed constitutive model had a highly accurate prediction. The deformation rate and temperature effect were associated with microstructural change, and the evolution of the microstructure was analyzed through electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The dislocation densities of the alloy at the deformation of 850 °C and 2.72 s−1 is higher than at the other deformation, the higher dislocation density is the higher stored energy and the higher degree of DRX. As well, two types of DRX nucleation mechanisms have been identified: discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX). Changes in grain boundary have significant effect on the DRX nucleation of the alloy, twin boundaries act as potential barriers limiting dislocation slip and motion and eventually leading to the accumulation of dislocation during plastic deformation. This study identified that the major contribution which results in the growth of new twins in DRX grains is the new boundary of Σ3 twins. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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13 pages, 21780 KiB  
Article
Effect of Bending Process on Microstructure, Mechanical Properties and Crack Formation of 5% Ni Steel
by Fengyong Niu, Jingshu He, Denghui Liu, Xiurong Zuo and Minghui Cai
Metals 2022, 12(7), 1188; https://doi.org/10.3390/met12071188 - 12 Jul 2022
Cited by 3 | Viewed by 2284
Abstract
The 5% Ni steel is often used to make steel storage tanks to store liquefied natural gas (LNG). Herein, the microstructure and mechanical properties of 5% Ni steel samples during bending were studied through combining scanning electron microscopy, energy dispersive spectroscopy, optical microscopy, [...] Read more.
The 5% Ni steel is often used to make steel storage tanks to store liquefied natural gas (LNG). Herein, the microstructure and mechanical properties of 5% Ni steel samples during bending were studied through combining scanning electron microscopy, energy dispersive spectroscopy, optical microscopy, X-ray diffraction, and electron backscattered diffractometer methods with tensile tests. The outer and inner arcs underwent tensile and compressive stress, respectively, resulting in a severely deformed microstructure with a high density of dislocation, improving both the tensile and yield strengths. The ductility of the 5% Ni steel samples decreased significantly after bending due to the work hardening and dislocation accumulation. During bending, the shear bands occurred at the surface or subsurface, which were caused by strain localization. Amounts of “harder” grains with high TF and more orange and red KAM areas with high local strain at the outer and inner arcs produced a greater stress concentration than that of the mid-thickness, which can induce crack initiation and propagation due to the large deformation during bending. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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13 pages, 7079 KiB  
Article
Critical Conditions for Dynamic Recrystallization of S280 Ultra-High-Strength Stainless Steel Based on Work Hardening Rate
by Mutong Liu, Ye Tian, Yu Wang, Kelu Wang, Kaiming Zhang and Shiqiang Lu
Metals 2022, 12(7), 1123; https://doi.org/10.3390/met12071123 - 30 Jun 2022
Cited by 5 | Viewed by 1175
Abstract
Isothermal and constant-strain-rate compression experiments for S280 ultra-high-strength stainless steel were carried out under deformation temperatures of 1000–1150 °C and strain rates of 0.001–10 s−1 with a Thermecmaster-Z thermal simulator. The flow–stress behavior of the alloy was studied and the hot deformation [...] Read more.
Isothermal and constant-strain-rate compression experiments for S280 ultra-high-strength stainless steel were carried out under deformation temperatures of 1000–1150 °C and strain rates of 0.001–10 s−1 with a Thermecmaster-Z thermal simulator. The flow–stress behavior of the alloy was studied and the hot deformation activation energy was calculated. A critical strain model of the dynamic recrystallization (DRX) of the alloy was established using the work hardening rate for the first time. The results show that S280 ultra-high-strength stainless steel was positively sensitive to the strain rate and negatively sensitive to temperature, and its flow–stress curve showed characteristics of flow softening. The hot deformation activation energy corresponding to the peak strain was 519.064 kJ/mol. The DRX critical strain of the steel was determined from the minimum value of the −∂(lnθ)/∂ε − ε curve. The relationship between the DRX critical strain and peak strain could be characterized as εc=0.599εp and the relationship between the DRX critical stress and peak stress could be characterized as σc= 0.959σp The critical strain model of DRX could be expressed as εc=0.010Z0.062. The research results can provide theoretical support for avoiding the generation of actual thermal processing microstructure defects such as coarse grains and for obtaining products with excellent microstructure and properties. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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13 pages, 6317 KiB  
Article
Numerical Simulation of Microstructure Evolution of Large GCr15 Bar during Multi-Pass Rough Rolling
by Huaibin Han, Xianming Zhao, Haochen Ding, Chi Zhang, Xueqing Yu and Wei Wang
Metals 2022, 12(5), 812; https://doi.org/10.3390/met12050812 - 07 May 2022
Cited by 1 | Viewed by 1538
Abstract
Severe temperature gradients and inhomogeneous strain distribution exist in the large cross-section of GCr15 bearing steel during the hot bar rolling process, resulting in a complex microstructure evolution in the bar. To promote the performance of the bar, a thermal-mechanical coupled finite element [...] Read more.
Severe temperature gradients and inhomogeneous strain distribution exist in the large cross-section of GCr15 bearing steel during the hot bar rolling process, resulting in a complex microstructure evolution in the bar. To promote the performance of the bar, a thermal-mechanical coupled finite element (FE) model was developed to capture the variations in temperature and deformation strain. A subroutine, considering the dynamic recrystallization (DRX), meta-dynamic recrystallization (MDRX), static recrystallization (SRX), and grain growth (GG) of austenite grains of GCr15 steel, was developed and coupled to the FE model to predict the microstructure’s evolution during rough rolling. The simulation implies that the inner part of the bloom is deformed at high temperatures due to the heat generated by plastic deformation and slow heat conduction, while the surface temperature decreases along with the passes. The heavy reduction design with 11 passes was found to introduce higher strains at the center regions than those of the same rough rolling reduction divided into 13 passes. The higher strains at the center regions refined the grain size and promoted microstructure homogeneity. The observation of the microstructures after hot bar rolling confirmed the refinement of the heavy reduction design for rough rolling. Furthermore, the heavy rough rolling reduction was found to be beneficial for alleviating the macrosegregation of the casting bloom. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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12 pages, 10454 KiB  
Article
Correlation between Microstructure and Mechanical Properties of Welded Joint of X70 Submarine Pipeline Steel with Heavy Wall Thickness
by Yifan Dong, Denghui Liu, Liang Hong, Jingjing Liu and Xiurong Zuo
Metals 2022, 12(5), 716; https://doi.org/10.3390/met12050716 - 22 Apr 2022
Cited by 5 | Viewed by 1667
Abstract
This paper aims to study the relationship between the microstructure and the mechanical properties of X70 submarine pipeline steel with 40.5 mm thickness. The microstructure was examined by using optical microscopy, scanning electron microscopy and an electron backscattered diffractometer, while the mechanical properties [...] Read more.
This paper aims to study the relationship between the microstructure and the mechanical properties of X70 submarine pipeline steel with 40.5 mm thickness. The microstructure was examined by using optical microscopy, scanning electron microscopy and an electron backscattered diffractometer, while the mechanical properties were examined by using a hardness test, a tensile test, a Charpy impact test and a drop weight tear test (DWTT), respectively. The results show that the base metal (BM) of the pipe has a low yield ratio of 0.83 and an excellent elongation of more than 45%. The DWTT shear area of the steel plate reaches 87%, showing excellent low-temperature toughness. The Charpy impact energy increases when the distance from the fusion line increases, and it reaches a maximum at the BM near the heat-affected zone (HAZ) due to the small martensite-austenite (MA) constituents and fine grains. The concentrated distribution of blocky/slender MA constituents along the prior austenite grain boundaries of the intercritically reheated coarse-grained HAZ and the large MA constituents are the main reasons for the deteriorating impact toughness. Delamination cracks in the DWTT fracture surface only occurred in the midthickness of a sample with a small opening width that spread about 2.1 mm perpendicular to the DWTT fracture surface and were finally arrested at the acicular ferrite clusters containing a high density of high-angle boundaries. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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14 pages, 6231 KiB  
Article
Research on Hot Deformation Behavior of F92 Steel Based on Stress Correction
by Jinghui Li, Renhai Yu, Gaoshan Xu, Changhua Chen, Yao Ha, Leijun Song and Huiping Zhang
Metals 2022, 12(5), 698; https://doi.org/10.3390/met12050698 - 19 Apr 2022
Cited by 3 | Viewed by 1344
Abstract
In order to systematically study the stress correction method and hot deformation behavior of F92 stainless steel, the hot compression test was performed using a Gleeble-3500 (DSI USA, Connecticut, CT, USA) at strain rates of 0.01–10 s−1 and deformation temperatures of 750–1150 [...] Read more.
In order to systematically study the stress correction method and hot deformation behavior of F92 stainless steel, the hot compression test was performed using a Gleeble-3500 (DSI USA, Connecticut, CT, USA) at strain rates of 0.01–10 s−1 and deformation temperatures of 750–1150 °C. First, to obtain the truest stress values from the original data, we adopted two stress correction models that did not affect each other, and the order of the two correction models was also different. Second, the adiabatic-friction-corrected stress was used as the input value of the AR model to predict the high-temperature flow behavior of F92 steel. Third, the optimal hot working parameters of F92 steel were determined via modeling and microstructure characterization. The results were as follows: The final correction values for both models were smaller than those from the original data. The stress deviation corrected by model 1 reached a maximum value of 59 MPa at 750 °C and 10 s−1. After establishing the Arrhenius (AR) model, it was determined that the accuracy of stress correction model 2 was stronger than that of model 1. Additionally, the corrected stress improved the predictive power of the AR model. The hot working range of F92 steel falls within a deformation temperature of 850 °C to 1050 °C and strain rate of 0.1 s−1 to 1 s−1. Finally, the AR model was used to describe the high-temperature flow behavior of F92 steel. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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20 pages, 13907 KiB  
Article
Effects of V–N Microalloying on Microstructure and Property in the Welding Heat Affected Zone of Constructional Steel
by Kaiyu Cui, Haifeng Yang, Shengjie Yao, Zhengrong Li, Guodong Wang, Hongyun Zhao and Xinchen Nan
Metals 2022, 12(3), 480; https://doi.org/10.3390/met12030480 - 11 Mar 2022
Cited by 4 | Viewed by 1686
Abstract
Shielded metal arc welding and welding thermal simulation experiment were carried out for constructional steel containing 0% V and 0.10% V, and the microstructure, precipitation feature, microhardness HV0.2, and −20 °C impact value in the welding heat affected zone (HAZ) were investigated. The [...] Read more.
Shielded metal arc welding and welding thermal simulation experiment were carried out for constructional steel containing 0% V and 0.10% V, and the microstructure, precipitation feature, microhardness HV0.2, and −20 °C impact value in the welding heat affected zone (HAZ) were investigated. The results showed that in the coarse-grained heat affected zone (CGHAZ), V and N were completely dissolved in the matrix of steel containing 0.10% V to promote the growth of prior austenite grains, meanwhile the fraction of high angle grain boundaries (HAGBs) decreased, thereby leading to the mean −20 °C impact value decreases from 87 J to 18 J. In the grain refined heat affected zone (GRHAZ), V(C, N) precipitates experience re-dissolution and re-precipitation at grain boundaries, V–N microalloying changes the microstructure from lath bainite + granular bainite + small amount of polygonal ferrite to polygonal ferrite + pearlite + martensite, thereby leading to the mean microhardness decreases from 335 HV0.2 to 207 HV0.2, and the mean −20 °C impact value decreased from 117 J to 103 J. In the intercritical heat affected zone (ICHAZ), V(C, N) precipitates experience re-dissolution, re-precipitation, and growth, causing the formation of micro-sized V(C, N) precipitates, thereby leading to the mean −20 °C impact value decreases from 93 J to 62 J. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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10 pages, 3664 KiB  
Article
Elevated Temperature Tensile Behavior of a Nb-Mo Microalloyed Medium Mn Alloy under Quasistatic Loads
by Wenlong Wu, Minghui Cai, Zeyu Zhang, Weigong Tian and Haijun Pan
Metals 2022, 12(3), 442; https://doi.org/10.3390/met12030442 - 03 Mar 2022
Cited by 2 | Viewed by 1608
Abstract
The elevated temperature tensile behavior of a Nb-Mo microalloyed medium steel was investigated over the −50 to 150 °C temperature range. The ultimate tensile strength was significantly reduced with increasing deformation temperature, but both YS (yield strength) and EI (total elongation) values changed [...] Read more.
The elevated temperature tensile behavior of a Nb-Mo microalloyed medium steel was investigated over the −50 to 150 °C temperature range. The ultimate tensile strength was significantly reduced with increasing deformation temperature, but both YS (yield strength) and EI (total elongation) values changed slightly. The best product of UTS (ultimate tensile strength) and EI (~59.5 GPa·%) can be achieved at the deformation temperature of 50 °C, implying an excellent combination of strength and ductility. Furthermore, the change in strain hardening rate as a function of deformation temperature was further explained by the following two aspects: the dependence of mechanical stability of retained austenite on deformation temperature as well as the dependence of deformation mechanism on deformation temperature. Theoretical models and experimental observations demonstrate that the dominant deformation mechanism of the present medium Mn steel changed from the single transformation-induced plasticity (TRIP) effect at −50 to 50 °C to the multiple TRIP + TWIP (twinning-induced plasticity) effect at 50–150 °C. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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15 pages, 5757 KiB  
Article
Study of the Fracture Behavior of TiN and TiC Inclusions in NM550 Wear-Resistant Steel during the Tensile Process
by Denghui Liu, Zhongyang Wang, Jingjing Liu, Zhenlong Wang and Xiurong Zuo
Metals 2022, 12(2), 363; https://doi.org/10.3390/met12020363 - 21 Feb 2022
Cited by 2 | Viewed by 1670
Abstract
NM550 wear-resistant steel is widely used in large-scale engineering and mining machinery under extremely harsh working conditions. In NM550 steel, the addition of Ti can cause the formation of micron-scale TiN and TiC inclusions, easily triggering cleavage fractures. The fracture behavior and precipitation [...] Read more.
NM550 wear-resistant steel is widely used in large-scale engineering and mining machinery under extremely harsh working conditions. In NM550 steel, the addition of Ti can cause the formation of micron-scale TiN and TiC inclusions, easily triggering cleavage fractures. The fracture behavior and precipitation rule of micron-scale TiN and TiC inclusions on the tensile process in NM550 steel was investigated by scanning electron microscopy, transmission electron microscopy, and energy spectrum analysis combined with thermodynamic theory. The TiN precipitated in the solid–liquid two-phase region at a precipitation temperature of 1710 K, whereas that of TiC was 1158 K along the austenite grain boundary. The sizes of the TiN precipitated in the liquid phase and the TiC precipitated in austenite were both at the micron scale, which is prone to cleavage fracture during the stretching process. Under tensile stress, microcracks were first initiated at the TiN inclusion, which were further separated forming a hole, whereas the TiC inclusion was divided into two sections with a long and narrow gap formed between the substrates. The sizes of the TiN and TiC were related to the cooling rate, Ti, and N contents. The larger the cooling rate and the lesser the Ti and N content, the smaller the TiN and TiC sizes. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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12 pages, 11288 KiB  
Article
Influence of TiN Inclusions and Segregation on the Delayed Cracking in NM450 Wear-Resistant Steel
by Jingjing Liu, Denghui Liu, Xiurong Zuo, Lihua Liu and Qiangjun Yan
Metals 2022, 12(1), 21; https://doi.org/10.3390/met12010021 - 22 Dec 2021
Cited by 7 | Viewed by 2254
Abstract
High-strength, wear-resistant steel often suffers from delayed cracking after flame cutting. Delayed cracking can lead to extremely harmful sudden brittle fracture; therefore, it is necessary to study the formation of delayed cracking in high-strength steel. This work investigated the influence of TiN inclusions [...] Read more.
High-strength, wear-resistant steel often suffers from delayed cracking after flame cutting. Delayed cracking can lead to extremely harmful sudden brittle fracture; therefore, it is necessary to study the formation of delayed cracking in high-strength steel. This work investigated the influence of TiN inclusions and segregation on the delayed cracking in NM450 wear-resistant steel by optical microscopy, scanning electron microscopy, X-ray diffraction, transmission electron microscopy and electron backscattered diffractometer methods. The results indicated that the delayed cracks originated from the segregation zones (SZs) containing multiple high-hardness segregation bands. The tensile strength of the SZ specimens was higher than that of non-segregation zone (NSZ) specimens, while the total elongation and reduction of area of the SZ specimens were relatively lower compared with the NSZ specimens. Therefore, the delayed cracking on the flame cutting surface of the NM450 steel plate was attributed to the existence of SZs that contain a high density of dislocations and considerable micro-sized TiN inclusions. Full article
(This article belongs to the Special Issue Advanced Technology in Microalloyed Steels)
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