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Zhengdong Liu - One of the best experts on this subject based on the ideXlab platform.

  • correlation of creep fracture lifetime with microstructure evolution and cavity behaviors in g115 martensitic heat Resistant Steel
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2020
    Co-Authors: Zhengdong Liu, Hansheng Bao, Chi Zhang, Zhongding Fan, Zhengzong Chen, Hao Chen, Zhigang Yang
    Abstract:

    Abstract In order to deepen the understanding towards the creep rupture lifetime of G115 martensitic heat-Resistant Steel, a series of creep tests using 130–200MPa loading stresses at 923K were carried out to investigate the as-crept microstructural characteristics and cavity behaviors. The significant microstructure deformation and a dramatic increase in the areal density of high-angle grain boundaries occur when the stress loading is over 160MPa. Apart from the strain concentration at elongated grain boundaries and refined grains, the elevated stress also leads to the appearance of a strong α-fiber texture with {001} //RD. The nucleation and growth of cavities can be effectively accelerated by the stress elevation, and ductile fracture is determined as the dominate mechanism within the test stresses. However, a transition towards brittle intergranular fracture is observed due to the rapid coarsening of Laves phase. Furthermore, a good prediction for creep lifetimes of G115 Steel has been obtained based on the constrained diffusional cavity growth model.

  • toughness evolution of 9cr 3w 3co martensitic heat Resistant Steel during long time aging
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016
    Co-Authors: Peng Yan, Zhengdong Liu
    Abstract:

    Abstract Toughness of G115 martensitic heat Resistant Steel after heat treatment and aging for different time at 650 °C was tested at room temperature. The corresponding microstructure was also experimentally obtained by field emission scanning electron microscope (FESEM), field emission transmission electron microscope (FETEM), X-Ray diffraction (XRD), electron back-scattered diffraction (EBSD) characterization and phase analysis. The results show that the absorbed energy of G115 Steel can reach 115 J after heat treatment. After the first 300 h aging, the absorbed energy decreases drastically to just 36 J and then keeps almost stable with further increasing aging time to 8000 h. The hardness of base metal and the amount of large angle (LA) boundaries (>15°) are not the main factors dominating the toughness of G115 Steel during aging process. The main reason for the change of toughness can be attributed to the precipitation of Laves phase. Since Laves phase particles are large, angular and hard, it is difficult for them to harmonize with the matrix during deformation, resulting that the crack initiation and propagation become easy and then the toughness of the Steel sharply decreases. The reason why the toughness keeps nearly stable from 300 h to 8000 h can be attributed to that the negative effect of the precipitation of Laves phase and the decrease of LA boundaries is counteracted by the positive effect of the softening of metal matrix.

  • effect of tempering temperature on the toughness of 9cr 3w 3co martensitic heat Resistant Steel
    Materials & Design, 2014
    Co-Authors: Peng Yan, Zhengdong Liu, Hansheng Bao, Yuqing Weng, Wei Liu
    Abstract:

    Abstract Effect of tempering temperature on the toughness of 9Cr–3W–3Co martensitic heat Resistant Steel was studied on the basis of the microstructures after normalized at 1100 °C for 1 h and then tempered at 740–780 °C for 3 h. With increasing tempering temperature from 740 °C to 780 °C, the absorbed energy of the 9Cr–3W–3Co Steel increased greatly from 26 J to 115 J. The change of the toughness with increasing tempering temperature was attributed to the softening of the base metal and the increase of the crack propagation path. The softening of the base metal was caused by the decrease of the dislocation density and the supersaturation of the interstitial atoms. The reason for the increase of the crack propagation path was that the length of the large angle boundaries increased and then the propagation direction of the cleavage crack was deflected more frequently.

  • effect of preferential heat treatment on microstructure of new martensitic heat Resistant Steel g115
    Energy Materials 2014, 2014
    Co-Authors: Peng Yan, Zhengdong Liu, Yuqing Weng
    Abstract:

    Intermediate heat treatment and thermo-mechanical treatment are the two possible ways of preferential heat treatment. Microstructure of G115 martensitic heat Resistant Steel after traditional heat treatment and preferential heat treatment was tested by field emission scanning electron microscope (FESEM) and electron back-scattered diffraction (EBSD). The results show that intermediate heat treatment can hardly change the size of precipitates while the precipitates can be obviously refined after thermo-mechanical treatment. Additionally, there is no obvious difference in precipitate size after deforming at different thermo-mechanical treatment temperatures. The reason why intermediate heat treatment failed in G115 Steel can be attributed to that the content of Nb is low and most of V is in solution. The reason for the success of thermo-mechanical treatment is that after thermo-mechanical treatment but without tempering, the amount of large angle boundaries has a three-fold increase compared with that after traditional heat treatment. Since M23C6 particles are mainly precipitated along large angle boundaries, the increase of large angle boundaries can induce the increase of the precipitation site of M23C6 particles, resulting in the refinement of M23C6 particles. After deforming at different temperatures, the amount of large angle boundaries is close, so the size of M23C6 is nearly the same.

  • the precipitation strengthening behavior of cu rich phase in nb contained advanced fe cr ni type austenitic heat Resistant Steel for usc power plant application
    Progress in Natural Science: Materials International, 2012
    Co-Authors: Chengyu Chi, Zhengdong Liu, Jianxin Dong, Wenqing Liu, Shichang Cheng, Xishan Xie
    Abstract:

    Abstract Copper has been used as a strengthening element in newly developed Fe–Cr–Ni type austenitic heat Resistant Steel for inducing Cu-rich phase precipitation to meet high temperature strength requirement for 600 °C Ultra Super-Critical (USC) coal fired power plants for many years. However, the precipitation behavior and strengthening mechanism of Cu-rich phase in these advanced austenitic heat Resistant Steels is still unclear. In order to understand the precipitation strengthening behavior of Cu-rich phase and to promote high strength austenitic heat Resistant Steel development, 18 Cr9 NiCuNb Steel which is a Cu-added Nb contained advanced Fe–Cr–Ni type austenitic heat Resistant Steel has been selected for this study to be aged at 650 °C till to 10,000 h. Micro-hardness and room temperature tensile test were conducted after long-time aging. SEM, TEM, HRTEM and three dimensional atom probe (3DAP) technology accompanying with thermodynamic calculation have been used to investigate the Cu-rich phase precipitation behavior during 650 °C aging. The experimental results showed that Cu atoms can quickly concentrate in clusters at very early precipitation stage to form the fine nano-size Cu-rich “segregation areas” within less than 1 h at 650 °C. With increasing aging time at 650 °C Cu atoms continuously concentrate to Cu-rich segregation areas (clusters) and simultaneously other kinds of atoms such as Fe, Cr and Ni diffuse away from Cu-rich segregation areas to austenitic matrix, and finally to complete the transformation from Cu-rich segregation areas to Cu-rich phase. However, there is only Cu atoms concentration but not crystallographic transformation from early stage of Cu-rich clusters forming to the final Cu-rich phase formation. Even the Cu atom becomes the main composed element after 500 h aging at 650 °C the Cu-rich phase still keeps coherent relationship with austenitic matrix. According the experimental results in this study, Cu-rich phase precipitation sequence which starts from the Cu atom segregation followed by the Cu diffusing from matrix to segregation areas and Fe, Cr and Ni atoms diffuse out from Cu-rich areas to matrix without crystallographic transformation is proposed. The Cu-rich phase is the most dispersed phase and contributes the most important strengthening effect among all precipitated phases (M23C6, MX and Cu-rich phase). It has been found that Cu-rich phase is very stable and still keeps in nano-size even for 10,000 h aging at 650 °C. The unique precipitation strengthening of Cu-rich phase in combination with nano-size Nb-rich MX phase and grain-boundary M23C6 carbide contributes excellent strengthening effect to 18 Cr9 NiCuNb austenitic heat Resistant Steel.

Yuqing Weng - One of the best experts on this subject based on the ideXlab platform.

  • effect of tempering temperature on the toughness of 9cr 3w 3co martensitic heat Resistant Steel
    Materials & Design, 2014
    Co-Authors: Peng Yan, Zhengdong Liu, Hansheng Bao, Yuqing Weng, Wei Liu
    Abstract:

    Abstract Effect of tempering temperature on the toughness of 9Cr–3W–3Co martensitic heat Resistant Steel was studied on the basis of the microstructures after normalized at 1100 °C for 1 h and then tempered at 740–780 °C for 3 h. With increasing tempering temperature from 740 °C to 780 °C, the absorbed energy of the 9Cr–3W–3Co Steel increased greatly from 26 J to 115 J. The change of the toughness with increasing tempering temperature was attributed to the softening of the base metal and the increase of the crack propagation path. The softening of the base metal was caused by the decrease of the dislocation density and the supersaturation of the interstitial atoms. The reason for the increase of the crack propagation path was that the length of the large angle boundaries increased and then the propagation direction of the cleavage crack was deflected more frequently.

  • effect of preferential heat treatment on microstructure of new martensitic heat Resistant Steel g115
    Energy Materials 2014, 2014
    Co-Authors: Peng Yan, Zhengdong Liu, Yuqing Weng
    Abstract:

    Intermediate heat treatment and thermo-mechanical treatment are the two possible ways of preferential heat treatment. Microstructure of G115 martensitic heat Resistant Steel after traditional heat treatment and preferential heat treatment was tested by field emission scanning electron microscope (FESEM) and electron back-scattered diffraction (EBSD). The results show that intermediate heat treatment can hardly change the size of precipitates while the precipitates can be obviously refined after thermo-mechanical treatment. Additionally, there is no obvious difference in precipitate size after deforming at different thermo-mechanical treatment temperatures. The reason why intermediate heat treatment failed in G115 Steel can be attributed to that the content of Nb is low and most of V is in solution. The reason for the success of thermo-mechanical treatment is that after thermo-mechanical treatment but without tempering, the amount of large angle boundaries has a three-fold increase compared with that after traditional heat treatment. Since M23C6 particles are mainly precipitated along large angle boundaries, the increase of large angle boundaries can induce the increase of the precipitation site of M23C6 particles, resulting in the refinement of M23C6 particles. After deforming at different temperatures, the amount of large angle boundaries is close, so the size of M23C6 is nearly the same.

  • effect of microstructural evolution on high temperature strength of 9cr 3w 3co martensitic heat Resistant Steel under different aging conditions
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013
    Co-Authors: Yuqing Weng
    Abstract:

    Abstract Evolution of microstructures and high-temperature strength at 650 °C of 9Cr–3W–3Co martensitic heat Resistant Steel after aging at 650 °C and 700 °C for different time durations have been experimentally investigated using field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), field emission transmission electron microscopy (FETEM) and post-aged tensile tests. The results show that after aging at 650 °C, the high-temperature strength and the microstructures of 9Cr–3W–3Co Steel keep almost stable with increasing aging time from 300 h to 3000 h. In comparison, after aging at 700 °C, there are obvious changes in the high-temperature strength and the microstructures. The strengthening mechanisms of the 9Cr–3W–3Co Steel were also discussed and the athermal yield stresses were calculated. The change of the high-temperature strength is mainly affected by the evolution of dislocations and laths. The precipitates mainly act as obstacles against motion of dislocations and lath boundaries.

Peng Yan - One of the best experts on this subject based on the ideXlab platform.

  • toughness evolution of 9cr 3w 3co martensitic heat Resistant Steel during long time aging
    Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2016
    Co-Authors: Peng Yan, Zhengdong Liu
    Abstract:

    Abstract Toughness of G115 martensitic heat Resistant Steel after heat treatment and aging for different time at 650 °C was tested at room temperature. The corresponding microstructure was also experimentally obtained by field emission scanning electron microscope (FESEM), field emission transmission electron microscope (FETEM), X-Ray diffraction (XRD), electron back-scattered diffraction (EBSD) characterization and phase analysis. The results show that the absorbed energy of G115 Steel can reach 115 J after heat treatment. After the first 300 h aging, the absorbed energy decreases drastically to just 36 J and then keeps almost stable with further increasing aging time to 8000 h. The hardness of base metal and the amount of large angle (LA) boundaries (>15°) are not the main factors dominating the toughness of G115 Steel during aging process. The main reason for the change of toughness can be attributed to the precipitation of Laves phase. Since Laves phase particles are large, angular and hard, it is difficult for them to harmonize with the matrix during deformation, resulting that the crack initiation and propagation become easy and then the toughness of the Steel sharply decreases. The reason why the toughness keeps nearly stable from 300 h to 8000 h can be attributed to that the negative effect of the precipitation of Laves phase and the decrease of LA boundaries is counteracted by the positive effect of the softening of metal matrix.

  • effect of tempering temperature on the toughness of 9cr 3w 3co martensitic heat Resistant Steel
    Materials & Design, 2014
    Co-Authors: Peng Yan, Zhengdong Liu, Hansheng Bao, Yuqing Weng, Wei Liu
    Abstract:

    Abstract Effect of tempering temperature on the toughness of 9Cr–3W–3Co martensitic heat Resistant Steel was studied on the basis of the microstructures after normalized at 1100 °C for 1 h and then tempered at 740–780 °C for 3 h. With increasing tempering temperature from 740 °C to 780 °C, the absorbed energy of the 9Cr–3W–3Co Steel increased greatly from 26 J to 115 J. The change of the toughness with increasing tempering temperature was attributed to the softening of the base metal and the increase of the crack propagation path. The softening of the base metal was caused by the decrease of the dislocation density and the supersaturation of the interstitial atoms. The reason for the increase of the crack propagation path was that the length of the large angle boundaries increased and then the propagation direction of the cleavage crack was deflected more frequently.

  • effect of preferential heat treatment on microstructure of new martensitic heat Resistant Steel g115
    Energy Materials 2014, 2014
    Co-Authors: Peng Yan, Zhengdong Liu, Yuqing Weng
    Abstract:

    Intermediate heat treatment and thermo-mechanical treatment are the two possible ways of preferential heat treatment. Microstructure of G115 martensitic heat Resistant Steel after traditional heat treatment and preferential heat treatment was tested by field emission scanning electron microscope (FESEM) and electron back-scattered diffraction (EBSD). The results show that intermediate heat treatment can hardly change the size of precipitates while the precipitates can be obviously refined after thermo-mechanical treatment. Additionally, there is no obvious difference in precipitate size after deforming at different thermo-mechanical treatment temperatures. The reason why intermediate heat treatment failed in G115 Steel can be attributed to that the content of Nb is low and most of V is in solution. The reason for the success of thermo-mechanical treatment is that after thermo-mechanical treatment but without tempering, the amount of large angle boundaries has a three-fold increase compared with that after traditional heat treatment. Since M23C6 particles are mainly precipitated along large angle boundaries, the increase of large angle boundaries can induce the increase of the precipitation site of M23C6 particles, resulting in the refinement of M23C6 particles. After deforming at different temperatures, the amount of large angle boundaries is close, so the size of M23C6 is nearly the same.

Wei Sun - One of the best experts on this subject based on the ideXlab platform.

  • Galvanic corrosion of duplex corrosion-Resistant Steel rebars under carbonated concrete conditions
    RSC Advances, 2018
    Co-Authors: Jinyang Jiang, Danqian Wang, Hong Yan Chu, Dong Guo, Yao Liu, Wei Sun
    Abstract:

    Galvanic corrosion between two different kinds of Steel rebars is usually the case in practical engineering. Open circuit potential (OCP), linear polarization resistance (LPR), Tafel polarization, scanning vibrating electrode technique (SVET), scanning electron microscopy (SEM) and reflection digital holographic microscopy (DHM) were used to study the galvanic corrosion of a novel corrosion-Resistant Steel bar (CR) and low-carbon Steel bar (LC) in simulated concrete pore solutions with different pH values and a chloride ion concentration of 5 mol L−1. The pH of the simulated concrete pore solution had a significant impact on the corrosion behaviour of CR and LC when they were in contact and were attacked by chloride ions. As the pH increased, the potential between CR and LC decreased and the driving force for the galvanic corrosion decreased. When the pH was 9.0, galvanic corrosion occurred on CR and LC at a high rate. CR developed local pitting corrosion, while LC mainly developed uniform corrosion, each with an apparent accumulation of corrosion products on the sample's surfaces. When the pH was 11.3, galvanic corrosion occurred when CR and LC were in contact. CR showed a relatively smooth surface, with only a small amount of pitting corrosion. In contrast, LC developed both pitting corrosion and uniform corrosion, and both apparent pitting corrosion and an accumulation of corrosion products on the sample surface were observed. When the pH was 13.6, there was no galvanic corrosion when CR and LC were in contact; the corrosion of CR and LC was mainly pitting corrosion. Therefore, for regions with chloride ion corrosion and severe carbonization, the galvanic corrosion between CR and LC cannot be ignored.

  • the passive film growth mechanism of new corrosion Resistant Steel rebar in simulated concrete pore solution nanometer structure and electrochemical study
    Materials, 2017
    Co-Authors: Jinyang Jiang, Danqian Wang, Hong Yan Chu, Yao Liu, Yun Gao, Jinjie Shi, Wei Sun
    Abstract:

    An elaborative study was carried out on the growth mechanism and properties of the passive film for a new kind of alloyed corrosion-Resistant Steel (CR Steel). The passive film naturally formed in simulated concrete pore solutions (pH = 13.3). The corrosion resistance was evaluated by various methods including open circuit potential (OCP), linear polarization resistance (LPR) measurements, and electrochemical impedance spectroscopy (EIS). Meanwhile, the 2205 duplex stainless Steel (SS Steel) was evaluated for comparison. Moreover, the passive film with CR Steel was studied by means of X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Atomic Force Microscope (AFM), and the Mott‑Schottky approach. The results showed that the excellent passivity of CR Steel could be detected in a high alkaline environment. The grain boundaries between the fine passive film particles lead to increasing Cr oxide content in the later passivation stage. The filling of cation vacancies in the later passivation stage as well as the orderly crystalized inner layer contributed to the excellent corrosion resistance of CR Steel. A passive film growth model for CR Steel was proposed.

Jinyang Jiang - One of the best experts on this subject based on the ideXlab platform.

  • Galvanic corrosion of duplex corrosion-Resistant Steel rebars under carbonated concrete conditions
    RSC Advances, 2018
    Co-Authors: Jinyang Jiang, Danqian Wang, Hong Yan Chu, Dong Guo, Yao Liu, Wei Sun
    Abstract:

    Galvanic corrosion between two different kinds of Steel rebars is usually the case in practical engineering. Open circuit potential (OCP), linear polarization resistance (LPR), Tafel polarization, scanning vibrating electrode technique (SVET), scanning electron microscopy (SEM) and reflection digital holographic microscopy (DHM) were used to study the galvanic corrosion of a novel corrosion-Resistant Steel bar (CR) and low-carbon Steel bar (LC) in simulated concrete pore solutions with different pH values and a chloride ion concentration of 5 mol L−1. The pH of the simulated concrete pore solution had a significant impact on the corrosion behaviour of CR and LC when they were in contact and were attacked by chloride ions. As the pH increased, the potential between CR and LC decreased and the driving force for the galvanic corrosion decreased. When the pH was 9.0, galvanic corrosion occurred on CR and LC at a high rate. CR developed local pitting corrosion, while LC mainly developed uniform corrosion, each with an apparent accumulation of corrosion products on the sample's surfaces. When the pH was 11.3, galvanic corrosion occurred when CR and LC were in contact. CR showed a relatively smooth surface, with only a small amount of pitting corrosion. In contrast, LC developed both pitting corrosion and uniform corrosion, and both apparent pitting corrosion and an accumulation of corrosion products on the sample surface were observed. When the pH was 13.6, there was no galvanic corrosion when CR and LC were in contact; the corrosion of CR and LC was mainly pitting corrosion. Therefore, for regions with chloride ion corrosion and severe carbonization, the galvanic corrosion between CR and LC cannot be ignored.

  • the passive film growth mechanism of new corrosion Resistant Steel rebar in simulated concrete pore solution nanometer structure and electrochemical study
    Materials, 2017
    Co-Authors: Jinyang Jiang, Danqian Wang, Hong Yan Chu, Yao Liu, Yun Gao, Jinjie Shi, Wei Sun
    Abstract:

    An elaborative study was carried out on the growth mechanism and properties of the passive film for a new kind of alloyed corrosion-Resistant Steel (CR Steel). The passive film naturally formed in simulated concrete pore solutions (pH = 13.3). The corrosion resistance was evaluated by various methods including open circuit potential (OCP), linear polarization resistance (LPR) measurements, and electrochemical impedance spectroscopy (EIS). Meanwhile, the 2205 duplex stainless Steel (SS Steel) was evaluated for comparison. Moreover, the passive film with CR Steel was studied by means of X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Atomic Force Microscope (AFM), and the Mott‑Schottky approach. The results showed that the excellent passivity of CR Steel could be detected in a high alkaline environment. The grain boundaries between the fine passive film particles lead to increasing Cr oxide content in the later passivation stage. The filling of cation vacancies in the later passivation stage as well as the orderly crystalized inner layer contributed to the excellent corrosion resistance of CR Steel. A passive film growth model for CR Steel was proposed.

  • passive behaviour of alloy corrosion Resistant Steel cr10mo1 in simulating concrete pore solutions with different ph
    Applied Surface Science, 2016
    Co-Authors: Zhiyong Ai, Jinyang Jiang, Dan Song, Jianchun Zhang, Danqian Wang
    Abstract:

    Abstract The passive behaviour of new alloy corrosion-Resistant Steel Cr10Mo1 and plain carbon Steel (as a comparison) in simulating concrete pore solutions of different pH (ranging from 13.5 to 9.0) under open circuit potential conditions, was evaluated by various electrochemical techniques: potentiodynamic polarization, capacitance measurements and electrochemical impedance spectroscopy. The chemical composition and structure of passive films were investigated by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). The electrochemical responses of passive films show that Cr10Mo1 Steel has an increasing passivity with pH decreasing while carbon Steel dose conversely, revealing carbonation does no negative effect on passivation of the corrosion-Resistant Steel. SIMS reveals that the passive film on the corrosion-Resistant Steel presents a bilayer structure: an outer layer mainly consisting of Fe oxides and hydroxides, and an inner layer enriched in Cr species, while only a Fe-concentrated layer for carbon Steel. According to the XPS analysis results, as the pH decreases, more stable and protective Cr oxides are enriched in the film on Cr10Mo1 Steel while Fe oxides gradually decompose. Higher content of Cr oxides in the film layer provides Cr10Mo1 corrosion-Resistant Steel more excellent passivity at lower pH.