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Effects of continuous cooling rate on morphology of granular bainite in pipeline steels

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Journal of Iron and Steel Research International 2020年第6期27卷 681-690页

作者： Shu-jun Jia Ba Li Qing-you Liu Yi Ren Shuai Zhang Hong Gao Department of Structural Steels Central Iron and Steel Research InstituteBeijing 100081China State Key Laboratory of Metal Material for Marine Equipment and Application of Iron and Steel Research Institutes of Ansteel Group Corporation Anshan 114009LiaoningChina

The morphology and characteristics of granular bainite (GB) in pipeline steels at different continuous cooling rates were investigated by scanning electron microscopy, transmission electron microscopy and electron back-scattered diffraction (EBSD). The results show that the morphology of ferrite matrix in GB turned from the lath sheaf structure into the nearly equiaxed large grain with the cooling rate decreasing from high (60℃/s) to low (5-10℃/s). At the medium cooling rate (20-40℃/s), GB consisted of the irregular ferrite matrix, the granular martensite/austenite (M/A) constituents and abundant substructures inside. The formation of the irregular ferrite and substructure was attributed to the high-temperature recovery which occurred at relatively high-temperature stage before phase transformation. The granular morphology of M/A constitu-ents was formed from the carbon-rich triple junctions which were produced by the multidirectional substructure interfaces converged with each other. Particularly, some martensite in M/A constituents was misoriented from the adjacent ferrite by very small misorientation angle, which could be characterized by the mean band contrast function of EBSD qualitatively or semiquantitatively.

关键词： granular bainite Continuous cooling M/A constituent Cooling rate Irregular substructure

Effect of La_2O_3 on granular bainite microstructure and wear resistance of hardfacing layer metal

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Journal of Rare Earths 2014年第1期32卷 83-89页

作者：王亚军陈继刚杨健郝飞飞淡婷杨育林杨庆祥 State Key Laboratory of Metastable Materials Science & Technology Yanshan University College of Mechanical Engineering Yanshan University Capital Aerospace Machinery Corporation

The purpose of this work was to investigate the effect of La2O3 on the granular bainite microstructure and wear resistance of hardfacing layer metal. The hardfacing layer metals with different contents of La2O3 were prepared. The microstructures of the hardfacing layer metals were observed by field emission scanning electron microscopy （FESEM） and transmission electron micros-copy （TEM）. The hardness and wear resistance of the hardfacing layer metals were measured respectively. The results indicated that with the increasing content of La2O3, the amount of granular bainite increased, while that of martensite decreased and that of retained austenite did not change obviously. When the content of La2O3 was 2.55 wt.%, the volume fraction of the granular bainite in the hardfacing layer metal was 73.2%. Meanwhile, the wear resistance of the hardfacing layer metal was the largest, which was 12100 min/g. The mismatch between the face （100） of LaAlO3 and the face （100） ofδ-Fe was 7.1%. Therefore, LaAlO3 could act as moder-ate effective heterogeneous nuclei ofδ-Fe and the granular bainite could be refined.

关键词： La2O3 granular bainite wear resistance heterogeneous nuclei rare earths

DEFORMATION AND MICROFRACTURE OF granular bainite

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Acta Metallurgica Sinica(English Letters) 1992年第6期5卷 432-435页

作者： CHEN Huangpu Xi’an Jiaotong University,Xi’an,China Lecturer,The Research Institute for Strength of Metals,Xi’an Jiaotong University,Xi’an 710049,China Xi'an Jiaotong Univ Xi'an China

Relationship among deformation history,fracture process and stress distribution of granular bainite has been *** main process of fracture of granular bainite is the forma- *** and coalescence of the *** though the microcracks have formed at the earlier stage of deformation,they are not fateful for fracture because in the successive deformation stage the microcracks change their orientation toward the tensile *** strain hardening rate of granular bainite has a minimal value during the deformation process. Before and after the strain of the minimal value,the material shows different stress distribu- tion and microfracture mechanism.

关键词： granular bainite microfracture strain hardening rate

FATIGUE BEHAVIOUR OF granular bainite STRUCTURE

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Acta Metallurgica Sinica(English Letters) 1989年第1期2卷 42-46页

作者： ZHOU Lubin ZHANG Jie KANG Mokuang Northwest Polytechnic University,Xi’an,China ZHOU Lubin,Associate Professor,Dept.of Mater.Sci.and Eng.,Northwest Polytechnic University,Xi’an,China

The strain fatigue,impact fatigue and rotation beam fatigue behaviour of granular bainitic structure has been *** results show that the strain fatigue properties and the impact fatigue properties of granular bainite are superior to that of tempered martensite under the condition that the ultimate tensile strength is *** *** life increases with in- creasing amount of granular bainite,because the M-A islands might retard the propagation of fatigue *** rotation beam fatigue properties of granular hainite are similar to that of tempered *** relationship *** limit S_f,yield strength σ_y and frac- ture strength S_k may be expressed as S_f=4.651+0.1411(σ_y+S_k)

关键词： granular bainite tempered martensite fatigue

Effect of Cerium on Structure and Properties of granular Bainitic Steel

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Journal of Rare Earths 1995年第3期13卷 196-201页

作者：王福明李景慧韩其勇 Univ of Science and Technology Beijing Beijing China

The alloying effect of cerium in low carbon granular bainitic steel has been studied. Cerium increases the incubation time of granular bainitic transformation, exerts an influence on the morphology of nucleation and g... 详细信息

关键词： CERIUM granular bainite ALLOYING EFFECT

Microstructure and mechanical properties of F_(GBA)/B_G air cooling bainitic steels containing niobium

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International Journal of Minerals,Metallurgy and Materials 2010年第4期17卷 429-434页

作者： Chun Feng Hong-sheng Fang Bing-zhe Bai Yan-kang Zheng Department of Materials Science and Engineering Tsinghua University Beijing 100084 China

The effect of different Nb additions on the mechanical properties and microstrucmre evolution of grain boundary allotriomorphic ferrite （FGBA） / granular bainite （BG） air cooling bainitic steels was investigated. The results indicate that the tensile strength and yield strength increase by 157 and 97 MPa, respectively with the addition of 0.02wt% Nb. The steel acquires superior strength and toughness with the addition of 0.06wt% Nb. The results of scanning electron microscopy and transmission electron microscopy reveal that the addition of Nb not only refines the size of granular bainite but also increases the volume fraction of granular bainite in FGBA/BG steels. The refinement effect of granular bainite is improved with the increase of Nb content.

关键词： granular bainite microstructure evolution mechanical properties Nb

RELATIONSHIP BETWEEN M-A CONSTITUENT AND CLEAVAGE FRACTURE BEHAVIOUR OF granular BAINITIC WELD METAL

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Acta Metallurgica Sinica(English Letters) 1989年第2期2卷 143-146页

作者： XU Xiangxing SU Yi ZHOU Wei Tsinghua University,Beijing,ChinaCAI Qigong Central Iron and Steel Research Institute,Ministry of Metallurgical Industry,Beijing,China XU Xiangxing,Dept.of Mechanical Engineering,Tsinghua University,Beijing,100084,China

The cleavage fracture mechanism of granular bainitie weld metal in 15MnVN steel has been *** observation of a special specimen for revealing simultaneously fracture sur- face and microstructure shows that the cleavage of the weld is initiated by M-A constituent. The 95th percentile equivalent diameter of M-A constituent controls the cleavage fracture stress of the weld metal.

关键词： granular bainite M-A constituent weld cleavage fracture

Effects of rare earth on microstructure and impact toughness of low alloy Cr-Mo-V steels for hydrogenation reactor vessels

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Journal of Materials Science & Technology 2020年第10期42卷 1-14页

作者： Zhonghua Jiang Pei Wang Dianzhong Li Yiyi Li Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences72 Wenhua RoadShenyang 110016China School of Materials Science and Engineering University of Science and Technology of China72 Wenhua Road.Shenyang 110016China

The effects of rare earth(RE) on the microstructure and impact toughness of low alloy Cr-Mo-V bainitic steels have been investigated where the steels have RE content of 0 to 0.048 wt.%. The results indicate that the normalized microstructures of the steels are typical granular bainite(GB) composed primarily of bainitic ferrite and martensite and/or austenite(M-A) constituents. The M-A constituents are transformed into ferrite and carbides and/or agglomerated carbides after tempering at 700℃ for 4 h. The addition of RE decreases the onset temperature of bainitic transformation and results in the formation of finer bainitic ferrite, and reduces the amount of carbon-rich M-A constituents. For the normalized and tempered samples, the ductile-to-brittle transition temperature(DBTT) decreases with increasing RE content to a critical value of 0.012 wt.%. Lower DBTT and higher upper shelf energy are attributed to the decreased effective grain size and lower amount of coarse agglomerated carbides from the decomposition of massive M-A constituents. However, the addition of RE in excess of 0.012 wt.% leads to a substantial increase in the volume fraction of large-sized inclusions, which are extremely detrimental to the impact toughness.

关键词： Low alloy Cr-Mo-V steel Rare earth Microstructure Impact toughness granular bainite Martensite-austenite constituents

Relationship between microstructure and corrosion behavior of high-grade pipeline steel in a low-temperature environment

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Journal of Iron and Steel Research International 2021年第8期28卷 1037-1046页

作者： Jia-qiang Jing Jie Guo Ba Li Shu-jun Jia Yi Ren School of Oil and Gas Engineering Southwest Petroleum UniversityChengdu 610500SichuanChina Department of Structural Steels Central Iron and Steel Research InstituteBeijing 100081China State Key Laboratory of Metal Material for Marine Equipment and Application of Iron and Steel Research Institutes of Ansteel Group Corporation Anshan 114009LiaoningChina

The relationship between micro structure and corrosion behavior of high-grade pipeline steel under low-temperature conditions was comparatively investigated by the potentiodynamic polarization and electrochemical impedance spec-troscopy test combining with optical micrographs,scanning electron microscopy,transmission electron microscopy and electron back-scattered *** results showed that,compared with room and high temperature,low temperature could influence the corrosion behavior of high-grade pipeline steel,which means that the corrosion potential and current density decreased and the corrosion resistance increased ***,double layer structures of the interface became thicker and more *** low-temperature environment,acicular ferrite had the martensite/austenite constituents with less amount and smaller size,a higher density of low angle grain boundaries and smaller effective grain sizes compared with granular bainite,which demonstrated higher corrosion resistance.

关键词： Low temperature High-grade pipeline steel Corrosion behavior Resistance Acicular ferrite granular bainite Martensite/austenite constituent