Study on Diffusion Behavior of 72LX Blooms in the Decarburization Process

Abstract

To elucidate the diffusion behavior of carbon atoms within the austenite region, the decarbonization of 72LX steel bloom was investigated. Experimental studies were performed to obtain the depth profiles of the decarburized layers within the temperature range of 950–1 250 °C. The findings show that, within a temperature range of 950–1 200 °C, both the depth of the decarburization layer of the grain interior (h _in) and the depth of the decarbonization effect zone of the grain boundary (h _b) increase concurrently with increasing holding temperatures and times and an inflection point is observed at 1 200 °C. By measuring the change in the sample diameter before and after the experiment, the change in the radius reduction of h _Fe causes by oxidation is obtained. Minimal changes are observed in h _Fe when the temperature is below 1 050 °C. As the temperature increases to 1 100 °C, a sudden change in h _Fe is observed, which corresponds to a rapid increase in oxidation. At temperatures above 1 100 °C, a more gradual change is observed. From the experimental results, a two-dimensional decarburization mathematical model is established and the carbon diffusion coefficients at different temperatures are obtained by simulation and regression fitting. The simulation values obtain from the carbon diffusion model matched well with the experimental values, thereby confirming the accuracy of the simulation process.

Keywords

72LX steel / diffusion behavior / diffusion coefficient / decarburized layer

References

[1] Xu G, Wang W, Zhang XQ, et al. CCT Curve and Drawing of Metal Materials[M], 2009 Beijing: Chemical Industry Press.

[2] Liu ZC, Ren HP, Song YQ, et al. A Tutorial on the Phase Transition of Metal Solid State[M], 2011 Beijing: Metallurgical Industry Press.

[3] Hu GX, Cai X, Yong YH. Material Science Foundation[M], 2010 Shanghai: Shanghai Jiaotong University Press.

[4] Tu R, Wang Z. Effective Diffusion Energy Barriers with the Boltzmann Distribution Assumption[J]. J. Wuhan Univ. Technol.-Mater. Sci. Ed.., 2019, 34(01): 1-5.

[5] Teng Q, Li X, Wei QS. Diffusion Bonding of Al6061 and Cu by Hot Isostatic Pressing[J]. J. Wuhan Univ. Technol.-Mater. Sci. Ed., 2020, 35(01): 183-191.

[6] Olden V, Alvaro A, Akselsen OM. Hydrogen Diffusion and Hydrogen Influenced Critical Stress Intensity in an API X70 Pipeline Steel Weld-ed Jointe-Experiments and FE Simulations[J]. Int. J. Hydrogen Energ., 2012, 37(15): 11474-11486.

[7] Santofimia MJ, Zhao L, Sietsma J. Model for the Interaction between Interface Migration and Carbon Diffusion during Annealing of Martensite-Austenite Microstructures in Steels[J]. Scripta Mater., 2008, 59(2): 159-162.

[8] Takahama Y, Santofimia MJ, Mecozzi MG, et al. Phase Field Simulation of the Carbon Redistribution during the Quenching and Partitioning Process in a Low-carbon Steel[J]. Acta Mater., 60, 2012 (6): 2916–2926

[9] Lee SJ, Matlock DK, Van Tyne CJ. Carbon Diffusivity in Multi-component Austenite[J]. Scripta Mater., 2011, 64(9): 805-808.

[10] Thibaux P, Metenier A, Xhoffer C. Carbon Diffusion Measurement in Austenite in the Temperature Range 500 °C to 900 °C[J]. Metall. Mater. Trans. A, 2007, 38(6): 1169-1176.

[11] Wang X, Sha G, Shen Q, et al. Age-hardening Effect and Formation of Nanoscale Composite Precipitates in a NiAlMnCu-containing Steel[J]. Metall. Mater. Trans. A, 2015, 627(1): 340-347.

[12] Zhang JQ, Shi Z. Triangulation of Molecular Surfaces based on Extracting Surface Atoms[J]. Comput. & Graph-UK, 2014, 38: 291-299.

[13] Zhu X, Li W, Zhao HS, et al. Hydrogen Trapping Sites and Hydrogen-induced Cracking in High Strength Quenching & Partitioning (Q&P) Treated Steel[J]. Int. J. Hydrogen Energ., 2014, 39(24): 13031-13040.

[14] Wu Y, Duan GS, Lu Y, et al. Effects of Magnetic Field Annealing on Carburizing of Pure Iron[J]. Steel Res. Int., 2011, 82(12): 1404-1407.

[15] GB/T 224-2008, Determination of Decarburization Depth of Steel[S].

[16] Chen WH. Research on Decarburization of Spring Steel[D], 2009 Beijing: Beijing Jiaotong University.