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Abstract

Internal cracking surrounding primary carbides in high carbon steel as-cast blooms induced by soft reduction is investigated to elucidate their influence of internal cracking on carbide precipitation and the resulting segregated band in hot-rolled wire rods. The primary carbides precipitation in high carbon steel has been investigated using both experimental observations and finite element simulations for as-cast blooms induced by soft reduction. It is found that the carbides precipitation in the vicinity of existing internal cracks is often located midway between the surface and centreline of the bloom, further increases the occurrence of the segregated bands in the hot-rolled wire rods. In addition, the growth of primary carbides surrounding the internal cracking are based on the chemical driving force and high density precipitate zones have been clarified in continuous casting bloom induced by soft reduction. It clearly shows that the spatial distribution of internal cracking surrounding primary carbides that play a key role in the formation of the segregated bands in the final steel products.
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Authors and Affiliations

Nanfu Zong
1 2
ORCID: ORCID
Tao Jing
2
ORCID: ORCID
Yang Liu
3
ORCID: ORCID

  1. R&D Institute of Bengang Steel Plates Co., Ltd., Benxi 117000, China
  2. Key Laboratory for Advanced Materials Processing Technology, Ministry of Education, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China
  3. Jiangsu Changqiang Iron and Steel Corp., Ltd., Jiangsu 214500, China
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Abstract

To comprehensively investigate the diversity of a chamfer technology and a convex roll technology under the same soft reduction process (i.e., section size, reduction amount, casting speed and solid fraction), a three-dimensional mechanical model was developed to investigate the effect of the chamfer profile and roll surface profile on the deformation behavior, cracking risk, stress concentration and reduction force of as-cast bloom during the soft reduction process. It was found that a chamfer bloom and a convex roll can both avoid the thicker corner of the as-cast bloom solidified shell, and significantly reduce reduction force of the withdrawal and straightening units. The convex profile of roll limits lateral spread along bloom width direction, therefore it forms a greater deformation to the mushy zone of as-cast bloom along the casting direction, the tensile strain in the brittleness temperature range (BTR) can obviously increase to form internal cracks. The chamfer bloom is much more effective in compensating the solidification shrinkage of mushy zone. In addition, chamfer bloom has a significant decrease of tensile strain in the brittleness temperature range (BTR) areas, which is expected to greatly reduce the risk of internal cracks.
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Bibliography

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[2] Q . Dong, J. Zhang, B. Wang, X. Zhao, J. Mater. Process. Technol. 81, 238 (2016).
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[4] S. Luo, M. Zhu, C. Ji, Ironmak. Steelmak. 41, 233 (2014).
[5] N. Zong, H. Zhang, Y. Liu, Z. Lu, Ironmak. Steelmak. 46, 872 (2019).
[6] S. Ogibayashi, M. Uchimura, K. Isobe, H. Maede, Y. Nishihara, S. Sato, Proc. of 6th Int. Iron and Steel Cong, ISIJ, Tokyo, 271 (1990).
[7] H.M. Chang, S.O. Kyung, D.L. Joo, J.L. Sung, L. Youngseog, ISIJ Int. 52, 1266 (2012).
[8] J. Zhao, L. Liu, W. Wang, H. Lu, Ironmak. Steelmak. 46, 227 (2017).
[9] N. Zong, H. Zhang, Y. Liu, Z. Lu, Metall. Res. Technol. 116, 310 (2019).
[10] N. Zong, H. Zhang, L. Wang, Z. Lu, Metall. Res. Technol. 116, 608 (2019).
[11] C. Li, B. Thomas, Metall. Mater. Trans. B. 35B, 1151 (2004). [12] B. Li, H. Ding, Z. Tang, Int. J. Miner. Metall. Mater. 19, 21 (2012).
[13] K.O. Lee, S.K. Hong, Y.K. Kang, Int. J. Automot. Technol. 10, 697 (2009).
[14] K. Demons, G.C. Lorraine, S.A. Taylor, Mater. Eng. Perform. 16, 592 (2007).
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Authors and Affiliations

Nanfu Zong
1
ORCID: ORCID
Tao Jing
1
ORCID: ORCID
Yang Liu
2
ORCID: ORCID

  1. Tsinghua University, School of Materials Science and Engineering, Key Laboratory for Advanced Materials Processing Technology, Ministry of Education, Beijing 100084, China
  2. Jiangsu Changqiang Iron and Steel Corp., Ltd., Jiangsu 214500, China
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Abstract

Tilted columnar dendritic morphologies are usually existed in wire and laser additive manufactured parts of GH3039 alloy. Overgrowth behaviors induced by the tilted dendritic arrays with a large tilted angle, and the effect of the angle between the growth direction and the direction vertical locally to the solid substrate on primary spacing, solute concentration and morphological evolution have been investigated at both the converging and the diverging grain boundaries through the phase-field simulation. The formation of cracking depends on solidification behaviors including columnar dendrites growth and micro-segregation in the interdendritic region. Furthermore, the effect of the tilted columnar dendrites on the susceptibility of crack is investigated during wire and laser additive manufacturing.
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Authors and Affiliations

Nanfu Zong
1
ORCID: ORCID
Weizhao Sun
1
ORCID: ORCID
Xinghong Liang
1
ORCID: ORCID
Tao Jing
1
ORCID: ORCID

  1. Tsinghua University, Key Laboratory for Advanced Materials Processing Technology, Ministry of Education, School of Materials Science and Engineering, Beijing 100084, China
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Abstract

The formation of internal cracks in as-cast billet is mainly attributed to the stress and strain states near the solidifying front. This study investigates the effect of chamfer configuration of as-cast billet on the maximal principal stress and the tensile stress during soft reduction process. The LIT and ZDT of GCr15 bearing steel are calculated by the solidification phase transformation model. What’s more, the 3D finite element models is established to investigate stress and strain states in the brittle temperature range. The relationships between chamfer angle and maximal principal stress, internal crack, as well as equivalent plastic strain are analyzed. Numerical results reveal that a chamfer configuration of as-cast billet is much more effective than a rectangular one on decreasing the risk of internal cracks.
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Authors and Affiliations

Nanfu Zong
1 2
ORCID: ORCID
Sida Ma
2
Weizhao Sun
2
ORCID: ORCID
Yang Liu
3
ORCID: ORCID
Tao Jing
2
ORCID: ORCID

  1. R&D Institute of Bengang Steel Plates Co., Ltd., Benxi 117000, China
  2. Tsinghua University, Key Laboratory for Advanced Materials Processing Technology, Ministry of Education, School of Materials Science and Engineering, Beijing 100084, China
  3. Jiangsu Changqiang Iron and Steel Corp., Ltd., Jiangsu 214500, China
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Abstract

Wire and laser additive manufacturing (WLAM) can produce outstanding mechanical properties of GH3039 nickel-based superalloys. A quantitative rapid phase field model with solute trapping kinetics has been developed during the rapid solidification process, where a range of process conditions are considered in terms of thermal gradients and pulling speeds. Intergranular hot cracking is found to occur at boundaries of tilted columnar dendrite in the GH3039 nickel-based superalloys. The simulations demonstrate that the phase field model considering the interface deflection can represent the dendrite growth during additive manufacturing more realistically. With the aid of numerical simulations, it is determined that dendrite growth morphologies transform from symmetrical columnar dendrite to tilted columnar dendrite as the interface crystallographic deflection is increased, while increasing the deflection angle can lead to uneven composition of material matrix, especially at the columnar dendrite interface. Solute concentrations at the columnar dendrite interface tend to promote hot cracking in additively manufactured Ni-based superalloy.
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Authors and Affiliations

Nanfu Zong
1
ORCID: ORCID
Zheng Wang
1
ORCID: ORCID
Yang Liu
2
ORCID: ORCID
Xinghong Liang
1
ORCID: ORCID
Tao Jing
1
ORCID: ORCID

  1. Tsinghua University, Ministry of Education, School of Materials Science and Engineering, Key Laboratory for Advanced Materials Processing Technology, Beijing 100084, China
  2. Jiangsu Changqiang Iron and Steel Corp., Ltd., Jiangsu 214500, China

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