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Hot Tearing Criteria and Models


It is of practical and great commercial importance to be able to predict hot tearing. Efforts have been made for decades to develop hot tearing criteria and models, and to imple- ment them into casting simulation models and ultimately to be able to predict a priori. Based on the various theories of hot tearing formation mechanisms, hot tearing criteria can be classified into four groupings:5


1) strain-based criteria,


2) stress-based criteria, 3) strain rate-based criteria, and 4) criteria based on non-mechanical principles.


An extensive review of hot tearing criteria5 was carried out


by Eskin et al. in 2004; they made a valiant effort, and in their words: “a quest for a new hot tearing criterion.”65 Most of the criteria can successfully predict hot tearing susceptibility of some binary alloys for their composition sensitivity, i.e., the so-called lambda curve showing the maximum susceptibility for a certain composition range. However, the results are not satisfying when consider- ation is given to other processing parameters. Moreover, and unfortunately, none of the existing models can predict whether hot tearing will occur or not. A generic and robust and reliable hot tearing prediction model is still not avail- able. It is suggested that the mechanisms of nucleation and propagation of a crack should be considered when develop- ing a hot tearing model and criterion.65


On the other hand,


the limitation of the existing models suggests the need for reliable and quantitative input data, which are not easily available and need to be measured experimentally.


A summary of hot tearing criteria is given in the attached ap- pendix. The reader is referred to the detailed reviews5,65-67


references listed in the table for more detailed information. Concluding Comments


Much work on hot tearing has been carried out over the years that have resulted in copious information and postula- tions of various mechanisms. Hot tearing is a complex phe- nomenon that involves heat flow, melt flow, and mass flow, as well as the development of stresses/strains in the coherent network. Its occurrence is well recognized to be the result of combined thermo-mechanical and metallurgical interac- tions. In this work, a chronological review of hot tearing theories, the affecting variables and recently developed hot tearing test methods have been presented. A summary of hot tearing criteria (with equations) is provided as an appendix, which is a useful reference. Though the basic knowledge as- sociated with hot tearing are established and understood, a globally reliable standard hot tearing test method is still not available. Moreover, none of the existing models can predict whether hot tearing will occur or not. A robust and reliable hot tearing prediction model is still not available. Reliable quantitative measurement of hot tearing, as well as reliable modeling and prediction of hot tearing, will be of great value to the casting industry.


International Journal of Metalcasting/Winter 11 and


Acknowledgements


The authors gratefully acknowledge the member companies of the Advanced Casting Research Center (ACRC) for their support of this work, and for their continued support of re- search focused on the science and technology of metal cast- ing at Worcester Polytechnic Institute.


REFERENCES


1. Monroe, C., Beckermann, C., “Development of a Hot Tear Indicator for Steel Castings,” Materials Science and Engineering A, vol. 413-414, pp. 30-36 (2005).


2. Campbell, J., Castings, Oxford: Butterworth- Heinemann (1991).


3. Novikov, I. I., “Goryachelomkost Tsvetnykh Metallov i Splavov (Hot Shortness of Non-Ferrous Metals and Alloys),” p. 299 (1966).


4. Sigworth, G. K., “Hot Tearing of Metals,” AFS Transactions, vol. 104, pp. 1053-1062 (1996).


5. Eskin, D. G., Suyitno, Katgerman, L., “Mechanical Properties in the Semi-Solid Sate and Hot Tearing of Aluminum Alloys,” Progress in Materials Science,” vol. 49, pp. 629-711 (2004).


6. Metz, S. A., Flemings, M. C., “A Fundamental Study of Hot Tearing,” AFS Transactions, vol. 78, pp. 453- 460 (1970).


7. Körber, F., Schitzkowski, G., “Determination of the Contraction of Cast Steel,” Stahl Und Eisen, vol. 15, pp. 128-135 (1928).


8. Briggs, C. W., The Metallurgy of Steel Castings, McGraw-Hill, London, p. 317 (1946).


9. Middleton, J. M., Protheroe, H. T., “The Hot-Tearing of Steel,” Journal of the Iron and Steel Institute, vol. 168, pp. 384-397 (1951).


10. Briggs, C. W., Gezelius, R. A., “Studies on Solidification and Contraction in Steel Castings II-Free and Hindered Contraction of Cast Carbon Steel,” AFA Trans, vol. 42, pp. 449-476 (1934).


11. Briggs, C. W., Gezelius, R. A., “Studies on Solidification and Contraction in Steel Castings IV-the Free and Hindered Contraction of Alloy Cast Steels,” AFA Trans, vol. 44, pp. 1-32 (1936).


12. Verö, J., “The Hot-Shortness of Aluminum Alloys,” The Metals Industry, vol. 48, pp. 431-434, 442 (1936).


13. Pumphrey, W. I., Jennings, P. H., “A Consideration of the Nature of Brittleness at Temperature Above the Solidus in Castings and Welds in Aluminum Alloys,” J. Inst. Metals, vol. 75, pp. 235 (1948).


14. Bishop, H. F., Ackerlind, C. G., Pellini, W. S., “Metallurgy and Mechanics of Hot Tearing,” AFS Transactions, vol. 60, pp. 818-833 (1952).


15. Pellini, W. S., “Strain Theory of Hot Tearing,” Foundry, vol. 80, pp. 125-199 (1952).


16. Bishop, H. F., Ackerlind, C. G., Pellini, W. S., “Investigation of Metallurgical and Mechanical Effects in the Development of Hot Tearing,” AFS


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