Getting the Strain Under Control: Trans-Varestraint Tests for Hot Cracking Susceptibility
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INTRODUCTION
VARIOUS methods for assessing hot cracking susceptibility of materials have been explored since Prokhorov[1,2] and Matsuda[3–7] defined the term brittle temperature range (BTR) and introduced the working principle of Varestraint and Transverse Varestraint (Trans-Varestraint) tests. Other methods for assessing hot cracking susceptibility include the Cast-pin tear test,[8,9] ductility-dip cracking,[10] and Gleeble tests.[11,12] All of these methods have improved the assessment and quantification of hot cracking but still lack the repeatability and reliability required to give a definitive assessment of hot cracking susceptibility.[13] Furthermore, as the hot cracking phenomenon is more extensively researched, new models for crack generation and
DIMITRIOS STATHARAS, ROB THORNTON and HONGBIAO DONG are with the Department of Engineering, EPSRC Centre for Doctoral Training in Innovative Metal Processing (IMPaCT), University of Leicester, University Road, Leicester, LE1 7RH, UK. Contact e-mail: [email protected] HELEN ATKINSON is with the School of Aerospace, Transport and Manufacturing, Cranfield University, Cranfield, MK43 0AL, UK. JOHN MARSDEN is with Tata Steel, Research and Development, Swinden Technology Centre, Moorgate, Rotherham, S60 3AR, UK. SHUWEN WEN is with the Dongguan Centre of Excellence for Advanced Materials, Dongguan, Guangdong, China. Manuscript submitted August 3, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
development are emerging. Recent developments that have been presented in 2017 and 2018 by Aucott et al. include the three-stage mechanistic model for solidification cracking during welding of steel[14] and the initiation and growth kinetics of solidification cracks during welding.[15] Solidification in general is affected by the temperature gradients that are forming during the process and the direction of heat flow.[16] During welding the heat flow is not the same as it would be during the free solidification of materials because of the movement of the heat source and the existence of solid material at the edge of the weld pool. This acts as a nucleation area for the solidification of the material and allows for the material to solidify in a specific direction forming columnar grains that are oriented towards the heat source.[17] Adding to that the grains that grow during this process are competing for their growth in a similar way that grains compete during the directional solidification.[18,19] Because of the heat exchange and the difference in temperature during the solidification, material properties like density and heat capacity are changing. These changes in combination with the changes on the composition of the molten liquid in the solidification front has shown to create strains and stresses in the solidifying materials.[19,20] It is during these processes, both during welding and casting, that defects like hot cracking manifest. The combination of the improved understanding of the hot cracking phenomenon and the need for further development of methods for assessing hot cr
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