High-Temperature Mechanical Behavior and Fracture Analysis of a Low-Carbon Steel Related to Cracking
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CRACKING at the surface of continuously cast steel slabs has been one of the main problems in casting for many years. Many of the cracks that occur during solidification are hot tears. In recent years, the use of computational models has led to a significant improvement in insight in caster performance and product quality. However, these models require accurate thermomechanical properties as input data, which are often unreliable or even nonexistent for many alloys of commercial interest.[1,2] Moreover, the thermomechanical properties of steels are still poorly known at high temperatures, close to the solidus. BEGON˜A SANTILLANA, Principal Researcher, is with Tata Steel Europe Research Development & Technology, P.O. Box 10000, 1970CA IJmuiden, The Netherlands. Contact e-mail: begona.santillana@ tatasteel.com ROB BOOM, Emeritus Professor and Senior Advisor M2i, is with the Department of Materials Science and Engineering, Delft University of Technology and Materials innovation institute M2i, Mekelweg 2, 2628CD, Delft, The Netherlands. DMITRY ESKIN, Professor, is with the Brunel Centre for Advanced Solidification Technology, Brunel University, Uxbridge UB8 3PH, U.K. HIDEO MIZUKAMI, Senior Research Engineer, and MASAHITO HANAO, Researcher, are with the Corporate Research & Development Laboratories, Sumitomo Metal Industries, LTD, 16-1 Sunayama, Kamisu, Ibaraki-Pref. 314-0255, Japan. MASAYUKI KAWAMOTO, General Manager, is with the Sumitomo Metal Industries, LTD, Triton Square Office Tower Y 8-11, Harumi 1-Chome, Chuo-Ku, Tokyo 104-6111, Japan. Manuscript submitted January 25, 2012. Article published online August 11, 2012 5048—VOLUME 43A, DECEMBER 2012
A major reason for this lack of reliable data is that high-temperature mechanical properties are difficult to measure. Several methods developed to assess the material strength during solidification and close to the solidus, particularly for aluminum alloys,[3] could be adapted for steel. On the other hand, the problem of hot tearing during continuous casting of steels has been extensively studied in the literature from the viewpoint of the casting process. Numerous studies refer to the influencing process parameters, such as chemical composition, cooling rate, or strain rate. The treatment of hot tearing in steels has some peculiarities as compared to aluminum alloys. This is mostly related to the specific solidification structure that is formed during steel solidification. The solidification process in steel is conventionally divided into three different stages[3,4] schematically shown in Figure 1: Stage 1: Formation of dendrites during solidification and mass feeding. As the steel starts to solidify, it does so in a dendritic structure. While cooling, secondary dendrite arms form at a short distance behind the primary dendrite tips. These dendrites have no mechanical bond with each other, as they are separated by liquid steel. Consequently, the shell at this location has little or no strength as both liquid and solid are free to move. At this stage, the name ‘‘mushy zone’’ is mi
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