Inter-Columnar Macro-Segregation in Continuously Cast Steel; Characterization, Possible Reasons, and Consequences

Rajiah, Seenivasan; Sambandam, Manjini; Shanmugam, Sethu Prasanth; Vikraman, Saju; Taticherla, Rajendra

doi:10.1007/s12666-021-02264-z

Cited by 4 publications

(6 citation statements)

References 19 publications

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“…In contrast, TiN inclusions with a large size caused brittle cleavage (Figure 3i), which was more harmful to plasticity than the small-size TiN and spherical CaO•(Al 2 O 3 ) x inclusions [17,18] 4a), whose hardness value was relatively uniform, with an average value of about 590 HV (Figure 2a). However, the enrichment of elements (C, Cr, Mn and Mo) existed in the segregation band in the SZ by EDS analysis (Figure 4c,d) [2,3], forming a microstructure of martensite in segregation band and bainite plus martensite in surrounding matrix (Figure 4b). As a result, the hardness of the SZ fluctuated greatly.…”

Section: Fractographymentioning

confidence: 99%

“…It was found that coarse TiN inclusions were more prone to form at the thickness center of the steel plate, which almost all existed in segregation bands (Figures 4b and 5c). This was because the continuous casting billet was about 350 mm in thickness; thus, the cooling rate of molten steel in the thickness center of the steel billet was much lower than that in the surface zone, which led to alloy elements including Ti diverging towards the thickness center in the steel [2][3][4].…”

Section: Grain Size Distribution In the Nsz And Szmentioning

confidence: 99%

“…In the continuous casting of thick NM550 steel, alloying elements are enriched in the thickness center of the steel slab owing to the gradual decrease in cooling rates from the surface to the thickness center [2][3][4], which forms the segregation band after rolling. It has been found [5,6] that the delayed crack mostly initiates from the locally harder segregation bands in the center of the steel plate in the flame cutting surface, which fails to withstand the high residual stresses after flame cutting.…”

Section: Introductionmentioning

confidence: 99%

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Influence of TiN Inclusions and Segregation Bands on the Mechanical Properties and Delayed Crack in Thick NM550 Wear-Resistant Steel

Sun,

Du,

Tong

et al. 2023

Materials

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The formation mechanism of the delayed crack after flame cutting and mechanical properties in thick NM550 wear-resistant steel are studied by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and an electron backscattered diffractometer. The delayed crack is formed at the segregation zone (SZ) located in the center of the 65 mm thick steel plate. The strength of the non-segregation zone (NSZ) with a martensite microstructure is slightly higher than that of SZ with a mixture microstructure of martensite plus bainite, and the plasticity of NSZ is significantly better than that of SZ. There exists a more severe segregation in the SZ, and only a slight segregation in the NSZ. The average grain sizes of the segregation bands in the NSZ and SZ are 15.72 µm and 6.76 µm, respectively. The number density of TiN larger than 5 µm in the NSZ and SZ is 0.031 and 1.156 number/mm2, respectively. Therefore, a high hardness segregation band with fine grains and a high dislocation density, along with the large number of coarse TiN inclusions within it, results in delayed cracking. For TiN inclusions close to the crack, microvoids or microcracks around the TiN are formed, and the delayed crack will propagate along the edge of the TiN or through the TiN inclusions.

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Section: Fractographymentioning

confidence: 99%

Section: Grain Size Distribution In the Nsz And Szmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Influence of TiN Inclusions and Segregation Bands on the Mechanical Properties and Delayed Crack in Thick NM550 Wear-Resistant Steel

Sun,

Du,

Tong

et al. 2023

Materials

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“…Due to solute redistribution and forced cooling, the heterogeneous defects, such as macrosegregation and shrinkage cavity, are inevitable in continuous casting and are difficult to eliminate through subsequent processes, which seriously affect the quality of steel products. [1,2] Hence, a variety of technologies have been developed to improve the homogeneity of casting blooms, such as electromagnetic swirling flow, [3,4] electromagnetic stirring, [5][6][7] soft or heavy reduction, [8][9][10][11] and so on. The pulsed electromagnetic field, with advantages such as low energy consumption, convenient application, and significant effects, has become a research hotspot in the field of solidification structure refinement technology.…”

Section: Introductionmentioning

confidence: 99%

Optimization of Process Parameters for 40Cr Steel Continuous Casting Round Bloom with Pulsed Magneto‐Oscillation Treatment

Yang,

Chen,

Zhang

et al. 2024

steel research int.

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To reduce the solidification structure defects and the macrosegregation of the Φ300 mm continuous casting round bloom, the pulsed magneto‐oscillation (PMO) treatment is added at the secondary cooling zone. A numerical model for calculating the pulsed electromagnetic field, flow field, and temperature field in continuous casting is established, and the coupling simulations of multiphysical fields under different casting parameters and PMO parameters are performed. Their influence on solidification process and the appropriate parameters are discussed. The industrial experiments conducted under the recommended parameters yield good results. Industrial experiments show that when the peak current is increased from 1350 to 1550 KIA and the casting speed is increased from 0.75 to 0.90 m min−1, PMO can increase the equiaxed grain zone and reduce the carbon macrosegregation of the bloom. Moreover, at high casting speed, PMO treatment can significantly promote columnar‐to‐equiaxed transition and increase the width of mixed grain zone.

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“…Grundy et al [18] proposed that hard secondary cooling significantly reduces macrosegregation through numerical simulation methods. Rajiah et al [19] proposed that macrosegregation happens as a result of the breakage of columnar dendrites in the low ductility region of steel between zero ductile temperature (ZDT) and zero strength temperature (ZST). Melo et al [20] calculated Secondary Dendrite Arm Spacing and second-phase particles were included, and the measured values are in good agreement with the calculated values.…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulation of Fluid Flow, Solidification, and Solute Distribution in Billets under Combined Mold and Final Electromagnetic Stirring

Feng,

Zhang,

et al. 2024

Materials

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In this study, a three-dimensional segmented coupled model for continuous casting billets under combined mold and final electromagnetic stirring (M-EMS, F-EMS) was developed. The model was verified by comparing carbon segregation in billets with and without EMS through plant experiments. The findings revealed that both M-EMS and F-EMS induce tangential flow in molten steel, impacting solidification and solute distribution processes within the billet. For M-EMS, with operating parameters of 250A-2Hz, the maximum tangential velocity (velocity projected onto the cross-section) was observed at the liquid phase’s edge. For F-EMS, with operating parameters of 250A-6Hz, the maximum tangential velocity occurred at fl=0.7. Furthermore, F-EMS accelerated heat transfer in the liquid phase, reducing the central liquid fraction from 0.93 to 0.85. M-EMS intensified the washing effect of molten steel on the solidification front, resulting in the formation of negative segregation within the mold. F-EMS significantly improved the centerline segregation issue, reducing carbon segregation from 1.15 to 1.02. Experimental and simulation results, with and without EMS, were in good agreement, indicating that M+F-EMS leads to a more uniform solute distribution within the billet, with a pronounced improvement in centerline segregation.

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Inter-Columnar Macro-Segregation in Continuously Cast Steel; Characterization, Possible Reasons, and Consequences

Cited by 4 publications

References 19 publications

Influence of TiN Inclusions and Segregation Bands on the Mechanical Properties and Delayed Crack in Thick NM550 Wear-Resistant Steel

Influence of TiN Inclusions and Segregation Bands on the Mechanical Properties and Delayed Crack in Thick NM550 Wear-Resistant Steel

Optimization of Process Parameters for 40Cr Steel Continuous Casting Round Bloom with Pulsed Magneto‐Oscillation Treatment

Numerical Simulation of Fluid Flow, Solidification, and Solute Distribution in Billets under Combined Mold and Final Electromagnetic Stirring

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