Causes and Control Mechanism of Abnormal Structure in the Center of SWRH82B Wire-Rod-Steel

Abstract:

The cause of drawing fracture of SWRH82B wire rods was analyzed by using optical microscopy, scanning electron microscope - energy dispersive spectrometer and electron probe micro-analyzer - wavelength dispersive spectrometer. A multivariate diffusion model was established in Thermo-Cale, and the effects of temperature and time on diffusion behavior of alloys were studied. Results show that cementite network and martensite in the center area of rod is main cause of tensile fracture. There is serious segregation of chromium and manganese in the central area. The CCT curve moves to right, and critical cooling rate of martensite decreases. With high cooling rate, time for eutectoid transition is insufficient, and martensite transformation occurs in segregation band. The segregation of phosphorus further worsen the brittleness of steel. With increase of heating temperature and duration of heating time, segregation in final product is reduced, and content of cementite network and martensite decreases. When the temperature is maintained at 1050 °C for 600 s, there is no segregation of phosphorus and carbon. The diffusion of chromium is even when temperature is maintained at 1150 °C for 5400 s, and an even diffusion of manganese is obtained when temperature is maintained at 1200 °C for 3000 s. In stelmor air cooling process, the key point is keeping cooling rate low to extend holding time, and to optimize microstructure and properties.

• Periodical: Materials Science Forum (Volume 944)
• Pages: 294-302
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.944.294
• Online since: January 2019
• Authors: Lin Lin Liao, He Wei*, Li Zhang Li, Yin Li Chen, Hai Feng Yan, Guang Hua Liu
• Keywords: Abnormal Structure, Composition Segregation, Network Cementite, SWRH82B Rods, Thermo-Cale

References

[1] S. Luo, M. Zhu, C. Ji, Theoretical model for determining optimum soft reduction zone of continuous casting steel, Ironmaking Steelmaking, 41 (2014) 233-240.

DOI: 10.1179/1743281213y.0000000126

[2] D. Jiang, M. Zhu, Flow and solidification in billet continuous casting machine with dual electromagnetic stirrings of mold and the final solidification, Steel Research International, 86 (2015) 993-1003.

DOI: 10.1002/srin.201400281

[3] Y. Tu, Z. Mao, Q. Zhang, X, Zhou, F, Fang, Atomistic interaction between silicon and manganese in pearlitic steel: Combined atom probe tomography and first-principle calculations, Mater. Lett., 134 (2014) 84-86.

DOI: 10.1016/j.matlet.2014.07.057

[4] B. Hutchinson, D. Lindell, M. Barnett, Yielding Behaviour of Martensite in Steel, ISIJ Int., 55 (2015) 1114-1122.

DOI: 10.2355/isijinternational.55.1114

[5] J.Y. Kang, S.C. Kim, J.O. Oh, H.N. Han, K.H. Oh, Martensite in interstitial-free steel obtained by ultra-high pressure, Scr. Mater., 66 (2012) 45-48.

DOI: 10.1016/j.scriptamat.2011.10.002

[6] Y. Chen, Y. Tang, H. Zhang, L. Fu, Effect of Chromium on Oxidation in Wear of Surface Nanocrystalline Martensite Steel, Tribol. Lett., 61 (2016) 1-7.

DOI: 10.1007/s11249-015-0623-1

[7] Y. Ji, P. Lan, H. Geng, Q. He, C. Shang, Behavior of Spot Segregation in Continuously Cast Blooms and the Resulting Segregated Band in Oil Pipe Steels, Steel Res. Int., 89 (2017) 88-96.

DOI: 10.1002/srin.201700331

[8] D. You, C. Bernhard, G. Wieser, S. Michelic, Microsegregation Model with Local Equilibrium Partition Coefficients During Solidification of Steels, Steel Res. Int., 87 (2016) 840-849.

DOI: 10.1002/srin.201500216

[9] K. Niitsu, K. Minakuchi, X. Xu, M. Nagasako, I. Ohnuma, Atomic-resolution evaluation of microsegregation and degree of atomic order at antiphase boundaries in Ni 50 Mn 20 In 30, Heusler alloy, Acta Mater., 122 (2017) 166-177.

DOI: 10.1016/j.actamat.2016.09.035

[10] J. Zhao, L. Liu, W. Wang, W. Zhou, H. Lu, Effects of heavy reduction technology on internal quality of continuous casting bloom, Ironmaking Steelmaking, 2 (2017) 1-8.

DOI: 10.1080/03019233.2017.1366090

[11] X. Zhao, J. Zhang, S. Lei, Y. Wang, The Position Study of Heavy Reduction Process for Improving Centerline Segregation or Porosity with Extra-Thickness Slabs, Steel Res. Int., 85 (2014) 645-658.

DOI: 10.1002/srin.201300192

[12] S. Luo, M. Zhu, C. Ji, Theoretical model for determining optimum soft reduction zone of continuous casting steel, Ironmaking Steelmaking, 41 (2014) 233-240.

DOI: 10.1179/1743281213y.0000000126

[13] R. Bo, L. Ek, Influence of Soft Reduction on the Fluid Flow, Porosity and Center Segregation in CC High Carbon- and Stainless-Steel Blooms, Isij International, 58 (2018) 478-487.

DOI: 10.2355/isijinternational.isijint-2017-534

[14] H. Sun, L. Li, X. Cheng, W. Qiu, Z. Liu, Reduction in macrosegregation on 380 mm×490 mm bloom caster equipped combination M+F-EMS by optimizing casting speed, Ironmaking Steelmaking, 42 (2015) 439-449.

DOI: 10.1179/1743281214y.0000000247

[15] X. Zhong, J. Liu, Z. Zou, Analysis of soft reduction on bloom internal crack by a strain model, Ironmaking Steelmaking, 3 (2017) 1-6.

DOI: 10.1080/03019233.2017.1324600

[16] L.H. Lu, L. Wang, H. Ma, Regularity and Influence Factors of Cementite Network in Center of 82B Wire Rods, Hot Working Technology, 44 (2015) 97-99.

[17] L. Liao, L. Li, H. Yan, G. Liu, S.M. Co, Static CCT curves and microstructure of 82B high carbon steel, Heat Treat. Met., 42 (2017) 30-35.

[18] P. Zhang, Y. Chen, W. Xiao, D. Ping, X. Zhao, Twin structure of the lath martensite in low carbon steel, Progress in Natural Science Materials International, 26 (2016) 169-172.

DOI: 10.1016/j.pnsc.2016.03.004

[19] J. Chen, X. U. Guang, F. Wang, F. Liu, Research on CCT Curves of Fe-C-Mn-Si-Cr-V Superbainite Steel, Hot Working Technology, 35 (2013) 23-25.

[20] S. Lee, H. Na, B. Kim, D. Kim, C. Kang, Effect of Niobium on the Ferrite -Cooling- Continuous Transformation (CCT) Curve of Ultrahigh-Thickness Cr-Mo Steel, Metall. Mater.Trans.A, 44 (2013) 2523-2532.

DOI: 10.1007/s11661-013-1616-z