Reverse Austenite Transformation and Grain Growth in a Low-Carbon Steel
- PDF / 9,096,998 Bytes
- 13 Pages / 593.972 x 792 pts Page_size
- 6 Downloads / 191 Views
DUCTION
THE demand for extremely thick steel plates has increased significantly in the recent decades. These heavy-gage steel plates are used for the construction of large-scale steel structures such as high-rise buildings, large cargo ships, or ultrahigh-pressure vessels. One of the challenges in the manufacturing of such plates arises from the control of the homogeneity of the microstructure through thickness. It is frequently not possible to apply an adequate amount of deformation during hot rolling limiting the degree of grain refinement in austenite and in the resulting transformation products formed upon cooling.[1,2] In order to obtain the required balance of strength, ductility, and fracture toughness, an additional heat-treatment cycle in the austenite temperature region is introduced to further control the final properties of the plates. The process parameters for this final heat treatment must be carefully controlled such that the core temperature of the plate reaches the austenite region while minimizing the temperature gradient through thickness to avoid extensive grain growth near the plate surface. Although the mechanisms controlling austenite grain growth are relatively clearly established, the processes occurring during the formation of austenite from a
KEIJI UEDA, Senior Research Engineer, is with JFE Steel Corporation, Steel Research Laboratory, 1, Kawasaki-cho, Chuo-ku, Chiba, 2600835, Japan. THOMAS GARCIN, Research Associate, and MATTHIAS MILITZER, Professor, are with the The Centre for Metallurgical Process Engineering, The University of British Columbia, 309-6350 Stores Rd., Vancouver, BC V6T 1Z4, Canada. Contact e-mail: [email protected] Manuscript submitted May 8, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
martensite or bainite microstructure in low-alloyed steels are not yet fully understood. A significant body of research on austenite formation is available in the literature.[3–46] Initial microstructures from which austenite formation has been investigated include ferrite–pearlite,[3–17] ferrite-spheroidized carbide,[3,7,18–21] and ferrite-martensite, and/or bainite[22–25] structures. Systematic experimental studies have been conducted on the interaction between ferrite recrystallization and intercritical austenite formation in low-carbon steels.[27–31] It was found that the heating rate[32–36] as well as the initial microstructure[37,38] has a direct influence on the nucleation and growth of austenite during austenitization treatment. In addition, multiple studies have been conducted to model the austenite formation using local equilibrium concept,[39] cellular automaton,[40] phase field modeling,[41,42] and mean field approaches based on the Johnson–Mehl–Avrami–Kolmogorov equation.[43–45] Clearly, the tempering of the initial microstructure as well as the redistribution of substitutional elements during reheating are important phenomena affecting austenite formation.[46] This is especially relevant for reheat cycles with slow heating rates where the plate is heat treated for extended
Data Loading...
