Precipitation Characteristics and Mechanism of Vanadium Carbides in a V-Microalloyed Medium-Carbon Steel

doi:10.1007/s40195-018-0775-8

Abstract

Abstract:

The precipitation characteristics and mechanism of vanadium carbides during isothermal transformation at 650 °C in a V-microalloyed medium-carbon steel were investigated through scanning electron microscopy and transmission electron microscopy as well as dilatometry test. Five morphologies of vanadium carbides were found to precipitate at different nucleation sites during the transformation. Two kinds of interphase precipitation form simultaneously in both pro-eutectoid and pearlitic ferrites. The linear arrays of fine interphase precipitates are parallel to the γ/α interface, and the fine needles of interphase precipitates are perpendicular to the γ/α interface. The vanadium carbides of long or short fibers, coarse particles and fine particles form in both pro-eutectoid and pearlitic ferrites, displaying different precipitation distributions and orientation relationships with ferrite. The precipitation mechanisms of vanadium carbide precipitates with different modes were proposed, and the precipitation sequence of various vanadium carbide precipitates was finally ascertained.

Key words: Microalloyed steels, Carbide precipitation, Isothermal transformation, Precipitation sequence, Orientation relationship

Xiao-Lin Pan, Minoru Umemoto. Precipitation Characteristics and Mechanism of Vanadium Carbides in a V-Microalloyed Medium-Carbon Steel[J]. Acta Metallurgica Sinica (English Letters), 2018, 31(11): 1197-1206.

Figures/Tables 13

Fig. 1 Microstructures of the as-received steel: a SEM micrograph of pro-eutectoid ferrite and pearlite; b dark-field TEM micrograph of VC precipitates in pro-eutectoid ferrite

Fig. 2 Dilatometry results of the steel during the isothermal transformation

Fig. 3 SEM micrographs after isothermal transformation at 650 °C for 1 h: a low magnification; b typical pearlite morphology; c, d short and long precipitates of VC in pro-eutectoid ferrite

Fig. 4 TEM micrographs of coarse VC precipitation in austenite along the ferrite grain boundaries (holding for 1 h): a bright-field image; b dark-field image

Fig. 5 TEM micrographs of planar interphase precipitation in pro-eutectoid ferrite (holding for 1 h): a bright-field image; b dark-field image; c SAED pattern; d corresponding analysis

Fig. 6 TEM micrographs of fine needles of interphase precipitates in pro-eutectoid ferrite (holding for 1 h): a dark-field image; b, c bright-field and dark-field images of higher magnification of rectangular area in a; d SAED pattern; e corresponding analysis

Fig. 7 TEM micrographs of co-precipitation of banded interphase precipitates and needlelike interphase precipitates in pro-eutectoid ferrite (holding for 1 h): a bright-field image; b dark-field image

Fig. 8 TEM micrographs of fibrous VC precipitation in pro-eutectoid ferrite (holding for 1 h): a, c bright-field image; b, d dark-field image

Fig. 9 TEM micrographs of matrix precipitation in pro-eutectoid ferrite (holding for 1 h): a bright-field image; b, c dark-field image showing different orientations

Fig. 10 TEM micrographs of VC precipitates in pearlite (holding for 1 h): a, c, e, g bright-field image; b, d, f, h dark-field image

Fig. 11 Schematic diagrams of VC precipitation: a planar interphase precipitation; b needlelike interphase precipitation; c matrix precipitation; d fibrous precipitation

Fig. 12 TEM micrographs of VC precipitates nucleated on dislocations near the ferrite grain boundary after isothermal transformation at 650 °C for 100 s: a bright-field image; b dark-field image

Table 1 Precipitation sequence of various morphologies of VC precipitates

Sequence	Morphology	Nucleation site
1	Coarse particles	γ/grain boundary
2	Fine particles on planar sheets	γ/α interface
3	Fine needles on planar sheets	γ/α interface
4	Long or short fibers	Dislocations in α
5	Fine particles	α matrix

[1]	Yongkui Li, Jianxin Lou, Hongtao Ju, Li Lin. Impact Toughness of Heat-Affected Zones of 11Cr Heat-Resistant Steels [J]. Acta Metallurgica Sinica (English Letters), 2020, 33(6): 821-827.
[2]	Zhiying Zheng, Linjiang Chai, Kang Xiang, Weijiu Huang, Yongfeng Wang, Liangliang Liu, Lin Tian. Typical Microstructural Characteristics of Ti-5Al-5Mo-5V-3Cr-1Fe Metastable β Ti Alloy Forged in α+β Region [J]. Acta Metallurgica Sinica (English Letters), 2020, 33(12): 1601-1608.
[3]	Qiang Yang, Shu-Hui Lv, Fan-Zhi Meng, Kai Guan, Bai-Shun Li, Xu-Hu Zhang, Jing-Qi Zhang, Xiao-Juan Liu, Jian Meng. Detailed Structures and Formation Mechanisms of Well-Known Al₁₀RE₂Mn₇ Phase in Die-Cast Mg-4Al-4RE-0.3Mn Alloy [J]. Acta Metallurgica Sinica (English Letters), 2019, 32(2): 178-186.
[4]	Yong-Jin Wang, Ren-Bo Song, Ren-Feng Song. Phase Transformation and Carbide Precipitation of Functional Gradient Semi-solid 9Cr18 Steel [J]. Acta Metallurgica Sinica (English Letters), 2018, 31(8): 823-830.
[5]	Li-Na Wang, Ping Yang, Ting Jin, Wei-Min Mao. Different Mechanisms of ε-M and α′-M Variant Selection and the Influencing Factors of ε-M Reversion During Dynamic Tension in TRIP Steel [J]. Acta Metallurgica Sinica (English Letters), 2018, 31(5): 449-455.
[6]	Wen-Sheng Xu, Xiao-Peng Yang, Wen-Zheng Zhang. Interpretation of the Habit Plane of δ Precipitates in Superalloy Inconel 718 [J]. Acta Metallurgica Sinica (English Letters), 2018, 31(2): 113-126.
[7]	Ba Li, Qing-You Liu, Shu-Jun Jia, Yi Ren, Bing Wang. Effect of Pre-deformation on Grain Ultrafining by Intercritical Deformation in Low-Carbon Microalloyed Steels [J]. Acta Metallurgica Sinica (English Letters), 2018, 31(10): 1038-1048.
[8]	Wei-Min Gui, Hong-Yu Zhang, Hai-Bo Long, Tao Jin, Xiao-Feng Sun, Qi Zheng. Formation Mechanism of Lamellar M ₂₃C₆ Carbide in a Cobalt-Base Superalloy During Thermal Exposure at 1000 °C [J]. Acta Metallurgica Sinica (English Letters), 2018, 31(1): 27-32.
[9]	Hai-Yan Yang, Jing Li, Ping Yang. The Change of Orientation Relationships Between Austenite and α′-Martensite During Deformation in High Manganese TRIP Steel [J]. Acta Metallurgica Sinica (English Letters), 2015, 28(3): 289-294.
[10]	Xinli Wang, Wenbin Dai, Rui Wang, Xinzhong Tian, Xiang Zhao, Jianming Li. A Method to Distinguish Twinning Variants and Second Twins by EBSD Measurements [J]. Acta Metallurgica Sinica (English Letters), 2014, 27(2): 267-271.
[11]	Z.Q. Sheng and H. Xiao(National Key Laboratory for Nuclear Fuel and Material, Nuclear Power Institute of China, Chengdu 610041,China)Manuscript received in revised form 16 October 1998). MATRIX INVESTIGATION ON ISAICHEV ORIENTATION RELATIONSHIP [J]. Acta Metallurgica Sinica (English Letters), 1999, 12(2): 185-190.
[12]	LI Douxing PING Dehai NING Xiaoguang YE Hengqiang Laboratory of Atomic Imaging of Solids,Institute of Metal Research,Academia Sinica,Shenyang.China Professor,Institute of Metal Research,Academia Sinica,Shenyang 110015,China. FINE STRUCTURES OF BOTH INTERFACES AND INTERFACIAL REACTION PRODUCTS [J]. Acta Metallurgica Sinica (English Letters), 1993, 6(1): 1-20.
[13]	YANG Liu FANG Hongsheng CHEN Nanping Tsinghua University,Beijing,China [Originally published in ACTA METALL SIN (CHINESE EDN) 25 (4) 1989 pp A264--A269 Correspondent:FANG Hongsheng Department of Materials Science and Engineering,Tsinghua University,Beijing,China. DRIVING FORCE OF BAINITE TRANSFORMATION FOR Fe-C-Mn ALLOYS [J]. Acta Metallurgica Sinica (English Letters), 1990, 3(1): 29-34.
[14]	XU Wenchong MA Xiang SUN Fuyu ZONG Guisheng Central Iron and Steel Research Institute,Ministry of Metallurgical Industry,Beijing,China XU Wenchong,Senior Engineer,Department No.13,Central Iron and Steel Research Institute,Ministry of Metallurgical Industry,Beijing,China. STRAIN-INDUCED ISOTHERMAL PRECIPITATION OF Nb,V AND Ti CARBONITRIDES IN MICROALLOYED STEELS DURING CONTROLLED ROLLING [J]. Acta Metallurgica Sinica (English Letters), 1989, 2(3): 174-180.
[15]	KANG Mokuang SUN Jialin Northwestern Polytechnical University,Xi'an,China Dept.of Materials Science and Engineering Northwestern Polytechnical University,Xi'an,710036,China. IN SITU OBSERVATION OF LOWER BAINITIC CARBIDES PRECIPITATION [J]. Acta Metallurgica Sinica (English Letters), 1989, 2(3): 222-224.