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Research Papers

Hot Tearing in Steels During Solidification: Experimental Characterization and Thermomechanical Modeling

[+] Author and Article Information
Cerri Olivier, Bellet Michel

 Ecole des Mines de Paris/CEMEF, UMR CNRS 7635, B.P. 207, 06904 Sophia Antipolis Cedex, France

Chastel Yvan

 Ecole des Mines de Paris/CEMEF, UMR CNRS 7635, B.P. 207, 06904 Sophia Antipolis Cedex, France; Ecole Nationale des Arts et Métiers, LIM, UMR 8006, 151 Boulevard de l’Hôpital, 75013 Paris, France

J. Eng. Mater. Technol 130(2), 021018 (Mar 19, 2008) (7 pages) doi:10.1115/1.2870233 History: Received July 10, 2007; Revised January 07, 2008; Published March 19, 2008

Hot tearing is a major defect in castings or semifinished cast products. It corresponds to the opening of cracks in the mushy zone and, more precisely, in the areas with high fraction of solid (typically 0.9 and beyond) when the material is subjected to deformations leading to local tensile stress. Various kinds of criteria have been developed to highlight a risk of formation of hot tears. The aim of this study is to evaluate their capability to predict the occurrence of hot tears correctly. In order to do so, two kinds of tests have been analyzed with the use of a thermomechanical finite element model.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Definition of a (u,v,w) base embedded in the dendritic microstructure in order to deduce ε̂̇ from the strain rate tensor ε̇

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Figure 2

Layout of the experimental setup

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Figure 3

(a) Schematic view of the location of the four thermocouples inserted in the cast ingot. (b) Experimental setup with cradles that provide an additional loading.

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Figure 4

Sketch illustrating the potential location of the cracks (longitudinal symmetry plane)

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Figure 5

Different configurations of solidification tested (location of the cracks illustrated with white lines)

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Figure 6

Macroexamination around the tear in the transverse symmetry plane. The lower surface of the part is on the left of the picture.

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Figure 7

Characteristic hot cracking fractograph: (a) subsurface zone (Zone I) and (b) inside the cast ingot (Zone II)

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Figure 8

HCS from the expression of (a) Clyne and Davies, (b) Prokhorov, (c) Won and Oh, and (d) RDG criteria. For each criterion, the left picture corresponds to the steel insert while the right picture corresponds to the refractory insert.

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Figure 9

Thermal evolution in the cast part. Comparison between experimental results (continuous lines) and thermomechanical simulation (dot lines).

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Figure 10

Expression of HCS given by (a) Clyne and Davies, (b) Prokhorov, (c) Won and Oh, and (d) RDG criteria in the configuration given by Fig. 5 for a 100Cr6 steel grade

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Figure 11

Bending test of partially solidified steel ingots. ((a) and (b)) Schematics of the test. (c) Evolution of critical strain with respect to strain rate.

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Figure 12

Critical curves in the (Δε̂,ε̂̇) plane. (a) Loading path for a 1mm∕s tool speed (thermomechanical simulation). (b) Critical curves for different steel grades (comparison with the expression of Won and Oh criterion in the case of the grade 6).

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