Effect of acicular ferrite on banded structures in low-carbon microalloyed steel

Abstract

The effect of acicular ferrite (AF) on banded structures in low-carbon microalloyed steel with Mn segregation during both isothermal transformation and continuous cooling processes was studied by dilatometry and microscopic observation. With respect to the isothermal transformation process, the specimen isothermed at 550°C consisted of AF in Mn-poor bands and martensite in Mn-rich bands, whereas the specimen isothermed at 450°C exhibited two different morphologies of AF that appeared as bands. At a continuous cooling rate in the range of 4 to 50°C/s, a mixture of AF and martensite formed in both segregated bands, and the volume fraction of martensite in Mn-rich bands was always higher than that in Mn-poor bands. An increased cooling rate resulted in a decrease in the difference of martensite volume fraction between Mn-rich and Mn-poor bands and thereby leaded to less distinct microstructural banding. The results show that Mn segregation and cooling rate strongly affect the formation of AF-containing banded structures. The formation mechanism of microstructural banding was also discussed.

Keywords

low-carbon microalloyed steel / acicular ferrite / microstructure / manganese / segregation

References

[1] Chen BH, Yu H. Hot ductility behavior of V-N and V-Nb microalloyed steels. Int. J. Miner. Metall. Mater., 2012, 19(6): 525.

[2] Popa F, Chicinaş I, Frunză D, Nicodim I, Banabic D. Influence of high deformation on the microstructure of low-carbon steel. Int. J. Miner. Metall. Mater., 2014, 21(3): 273.

[3] Kim YM, Lee H, Kim NJ. Transformation behavior and microstructural characteristics of acicular ferrite in linepipe steels. Mater. Sci. Eng. A, 2008, 478(1–2): 361.

[4] Madariaga I, Gutierrez I, de Andrés CG, Capdevila C. Acicular ferrite formation in a medium carbon steel with a two stage continuous cooling. Scripta Mater., 1999, 41(3): 229.

[5] Zhao AM, Wang Y, Chen YL, Tang D, Gao XT, Zuo BQ. Precipitation behaviors of X80 acicular ferrite pipeline steel. Int. J. Miner. Metall. Mater., 2011, 18(3): 309.

[6] Yakubtsov IA, Boyd JD. Effect of alloying on microstructure and mechanical properties of bainitic high strength plate steels. Mater. Sci. Technol., 2008, 24(2): 221.

[7] Zhou MW, Yu H. Effects of precipitates and inclusions on the fracture toughness of hot rolling X70 pipeline steel plates. Int. J. Miner. Metall. Mater., 2012, 19(9): 805.

[8] Joo MS, Suh DW, Bhadeshia HKDH. Mechanical anisotropy in steels for pipelines. ISIJ Int., 2013, 53(8): 1305.

[9] Eckert JA, Howell PR, Thompson SW. Banding and the nature of large, irregular pearlite nodules in a hot-rolled low-alloy plate steel: a second report. J. Mater. Sci., 1993, 28(16): 4412.

[10] Verhoeven JD. A review of microsegregation induced banding phenomena in steels. J. Mater. Eng. Perform., 2000, 9(3): 286.

[11] Grange RA. Effect of microstructural banding in steel. Metall. Trans., 1971, 2(2): 417.

[12] Caballero F G, García-Junceda A, Capdevila C, García de Andrés C. Evolution of microstructural banding during the manufacturing process of dual phase steels. Mater. Trans., 2006, 47(9): 2269.

[13] Krauss G. Solidification, segregation, and banding in carbon and alloy steels. Metall. Mater. Trans. B, 2003, 34(6): 781.

[14] D’Errico F. Failures induced by abnormal banding in steels. J. Failure Anal. Preven., 2010, 10(5): 351.

[15] Majka TF, Matlock DK, Krauss G. Development of microstructural banding in low-alloy steel with simulated Mn segregation. Metall. Mater. Trans. A, 2002, 33(6): 1627.

[16] McGarrity KS, Sietsma J, Jongbloed G. Characterisation and quantification of microstructural banding in dual-phase steels: Part 2. Case study extending to 3D. Mater. Sci. Technol., 2012, 28(8): 903.

[17] From A, Sandström R. Assessment of banding in steels by using advanced image analysis. Mater. Charact., 1998, 41(1): 11.

[18] Xu W, Rivera-Díaz-del-Castillo PEJ, van der Zwaag S. Ferrite/pearlite band prevention in dual phase and TRIP steels: model development. ISIJ Int., 2005, 45(3): 380.

[19] Krebs B, Germain L, Hazotte A, Gouné M. Banded structure in Dual Phase steels in relation with the austenite-to-ferrite transformation mechanisms. J. Mater. Sci., 2011, 46, 7026.

[20] Caballero FG, Garcia-Mateo C, Santofimia MJ, Miller MK, García de Andrés C. New experimental evidence on the incomplete transformation phenomenon in steel. Acta Mater., 2009, 57(1): 8.

[21] Wang J, Van Der Wolk PJ, Van Der Zwaag S. On the influence of alloying elements on the bainite reaction in low alloy steels during continuous cooling. J. Mater. Sci., 2000, 35(17): 4393.

[22] Bhadeshia HKDH. A rationalisation of shear transformations in steels. Acta Metall., 1981, 29(6): 1117.

[23] Wu K, Li Z, Guo A, He X L, Zhang L, Fang A, Cheng L. Microstructure evolution in a low carbon Nb-Ti microalloyed steel. ISIJ Int., 2006, 46(1): 161.

[24] Calcagnotto M, Ponge D, Raabe D. On the effect of manganese on grain size stability and hardenability in ultrafine-grained ferrite/martensite dual-phase steels. Metall. Mater. Trans. A, 2012, 43(1): 37.

[25] Chang M, Yu H. Kinetics of bainite-to-austenite transformation during continuous reheating in low carbon microalloyed steel. Int. J. Miner. Metall. Mater., 2013, 20(5): 427.