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| Ferrite Evolution During Isothermal Process in a High Deformability Pipeline Steel |
| TAN Feng-liang1,2,LIU Qing-you2,LEI Ting3,JIA Shu-jun2,DUAN Lin-na2,4 |
1. Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, Yunnan, China
2. Institute for Structure Materials, CISRI, Beijing 100081, China
3. Kunming Metallurgy College, Kunming 650033, Yunnan, China
4. School of Material Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China |
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Abstract In order to ensure the safety of long-distance oil and natural gas transmission pipeline installed in seismic and/or permafrost region, high strength pipeline steel with excellent deformability has been developed. The ferrite and bainite dual phase pipeline steel is a very important kind of high deformability pipeline steel. Polygonal ferrite is a key microstructure in ferrite and bainite dual phase deformability pipeline steel. Ferrite evolution during isothermal process at 700 �� after 50% deformation at 800 �� was conducted by using a Gleeble-3800 thermal simulator, and microstructure was characterized by using an optical microscope, a scanning electron microscope and a transmission electron microscope. There are two types of ferrite, ferrite with high density dislocation and ferrite with a little dislocation. There is about 7% (volume percent) deformation induced ferrite (DIF) for compression of 50% at 800 �� and strain rate of 1 s-1. During the isothermal process at 700 ��, with the holding time increasing, ferrite volume percent, ferrite grain number and average ferrite grain size increase. As the holding time is prolonged, dislocation recovery occurs in DIF. There are secondary phases in ferrite when the holding time is too long, and secondary phases and dislocation formation in dislocation pinning.
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Received: 07 March 2012
Published: 16 July 2013
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2013, Vol. 20 
