Microstructural Evolution and Tensile Properties of Nb-V-Ti-N Microalloyed Steel with Varying Nitrogen Contents
With the rapid development of long-distance transmission pipelines for oil and natural gas, pipeline steel is continuously evolving towards higher pressure, larger diameter, and thicker wall thickness. Many extensive studies and research have been conducted on X70 pipeline steel produced through tra...
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2025-02-01
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| author | Jiangcheng Liu Kai Guo Haote Ma Jiangli He Junchao Wang Chuanyou Zhang Tiansheng Wang Qingfeng Wang |
| author_facet | Jiangcheng Liu Kai Guo Haote Ma Jiangli He Junchao Wang Chuanyou Zhang Tiansheng Wang Qingfeng Wang |
| author_sort | Jiangcheng Liu |
| collection | DOAJ |
| description | With the rapid development of long-distance transmission pipelines for oil and natural gas, pipeline steel is continuously evolving towards higher pressure, larger diameter, and thicker wall thickness. Many extensive studies and research have been conducted on X70 pipeline steel produced through traditional processing routes. This study focuses on Nb-V-Ti-N microalloyed steel with different nitrogen contents, systematically investigating the variations in microstructure and tensile properties after quenching and tempering processes. The results indicate that after quenching treatment, when the nitrogen content of the tested steel is 0.0020 wt%, its primary microstructure consists of granular bainitic ferrite (GBF), acicular ferrite (AF), and residual M/A (martensite/austenite) components. As the nitrogen content increases, the contents of acicular ferrite and M/A constituents gradually rise, while granular bainitic ferrite correspondingly decreases. After tempering treatment, the microstructure of the tested steel transforms into granular bainitic ferrite, acicular ferrite, and carbonitrides. Notably, with the elevation of nitrogen content, the number of high-angle grain boundaries in the microstructure significantly increases. Meanwhile, the mean equivalent diameter (MED) defined by the misorientation angle (MTA) ranging from 2 to 15° and the dislocation density (ρ) exhibit an overall decreasing trend. Both of these factors contribute significantly to yield strength, resulting in a gradual increase in yield strength (YS) as the nitrogen content rises. Additionally, the study finds that as the nitrogen content increases, the size of precipitated particles continuously enlarges, and their proportion in the microstructure gradually increases. This discovery provides important theoretical basis and practical guidance for further optimizing the microstructure and mechanical properties of X70 pipeline steel. |
| format | Article |
| id | doaj-art-e7104db591fa4ca89c8853972c8cfb97 |
| institution | Kabale University |
| issn | 2075-4701 |
| language | English |
| publishDate | 2025-02-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Metals |
| spelling | doaj-art-e7104db591fa4ca89c8853972c8cfb972025-08-20T03:43:37ZengMDPI AGMetals2075-47012025-02-0115326610.3390/met15030266Microstructural Evolution and Tensile Properties of Nb-V-Ti-N Microalloyed Steel with Varying Nitrogen ContentsJiangcheng Liu0Kai Guo1Haote Ma2Jiangli He3Junchao Wang4Chuanyou Zhang5Tiansheng Wang6Qingfeng Wang7Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, ChinaSchool of Materials Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, ChinaLaboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, ChinaLaboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, ChinaSchool of Materials Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, ChinaTechnical Center, Tianjin Pipe (Group) Corporation Limited, Tianjin 300301, ChinaLaboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, ChinaLaboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, ChinaWith the rapid development of long-distance transmission pipelines for oil and natural gas, pipeline steel is continuously evolving towards higher pressure, larger diameter, and thicker wall thickness. Many extensive studies and research have been conducted on X70 pipeline steel produced through traditional processing routes. This study focuses on Nb-V-Ti-N microalloyed steel with different nitrogen contents, systematically investigating the variations in microstructure and tensile properties after quenching and tempering processes. The results indicate that after quenching treatment, when the nitrogen content of the tested steel is 0.0020 wt%, its primary microstructure consists of granular bainitic ferrite (GBF), acicular ferrite (AF), and residual M/A (martensite/austenite) components. As the nitrogen content increases, the contents of acicular ferrite and M/A constituents gradually rise, while granular bainitic ferrite correspondingly decreases. After tempering treatment, the microstructure of the tested steel transforms into granular bainitic ferrite, acicular ferrite, and carbonitrides. Notably, with the elevation of nitrogen content, the number of high-angle grain boundaries in the microstructure significantly increases. Meanwhile, the mean equivalent diameter (MED) defined by the misorientation angle (MTA) ranging from 2 to 15° and the dislocation density (ρ) exhibit an overall decreasing trend. Both of these factors contribute significantly to yield strength, resulting in a gradual increase in yield strength (YS) as the nitrogen content rises. Additionally, the study finds that as the nitrogen content increases, the size of precipitated particles continuously enlarges, and their proportion in the microstructure gradually increases. This discovery provides important theoretical basis and practical guidance for further optimizing the microstructure and mechanical properties of X70 pipeline steel.https://www.mdpi.com/2075-4701/15/3/266Nb-V micro-alloy steelmartensitic steelquenching and temperingprecipitatedislocationsyield strength |
| spellingShingle | Jiangcheng Liu Kai Guo Haote Ma Jiangli He Junchao Wang Chuanyou Zhang Tiansheng Wang Qingfeng Wang Microstructural Evolution and Tensile Properties of Nb-V-Ti-N Microalloyed Steel with Varying Nitrogen Contents Metals Nb-V micro-alloy steel martensitic steel quenching and tempering precipitate dislocations yield strength |
| title | Microstructural Evolution and Tensile Properties of Nb-V-Ti-N Microalloyed Steel with Varying Nitrogen Contents |
| title_full | Microstructural Evolution and Tensile Properties of Nb-V-Ti-N Microalloyed Steel with Varying Nitrogen Contents |
| title_fullStr | Microstructural Evolution and Tensile Properties of Nb-V-Ti-N Microalloyed Steel with Varying Nitrogen Contents |
| title_full_unstemmed | Microstructural Evolution and Tensile Properties of Nb-V-Ti-N Microalloyed Steel with Varying Nitrogen Contents |
| title_short | Microstructural Evolution and Tensile Properties of Nb-V-Ti-N Microalloyed Steel with Varying Nitrogen Contents |
| title_sort | microstructural evolution and tensile properties of nb v ti n microalloyed steel with varying nitrogen contents |
| topic | Nb-V micro-alloy steel martensitic steel quenching and tempering precipitate dislocations yield strength |
| url | https://www.mdpi.com/2075-4701/15/3/266 |
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