# Tempcore Process Simulator to Analyze Microstructural Evolution of Quenched and Tempered Rebar
## 1 Introduction  
Theromechanical processing is a metallurgical process that combines plastic deformation process with thermal processes like heat-treatment, water quenching, heating, and cooling at various rates into a single process. Due to wide range of applications, many studies dealing the effect of thermomechanical processing on metallurgical and mechanical properties have been carried out [1; 2; 3]. The reinforced steel bars can be produced by the thermomechanical processing, microalloying with V or Nb, and work-hardening etc. [4]. Tempcore is one of thermomechanical processes developed by CRM [5; 6] to produce high yield strength weldable rebars from mild steel without the addition of microalloying elements. The strength of rebar originates from the formation of a surface layer of quenched and tempered martensite that surrounds a core made of ferrite and pearlite. Such a composite structure is the result of processing hot rolled rods through water coolers that rapidly cool the surface. The martensitic structure is tempered by the heat from the core of the rod, which transforms into ferrite and pearlitewhile the rod is in the cooling beds [7; 8]. Tempcore rebars are characterized by high mechanical properties and excellent weldability, ductility, and bendability. Tempcore rebar can be problematic due to its heterogeneous structure. It has been reported that the Tempcore rebars presented the more stable behavior up to temperatures of 500 \({}^{\circ}\)C, while the microalloyed steel, although it presented very satisfactory tensile properties, displayed low impact toughness due to coarsening of vanadium carbides [4]. Figure 1 schematically shows the temperature profile and microstructural evolution in Tempcore treated rebars [9]. The Tempcore process significantly increases both tensile strength and ductility. The economic advantages of this process are huge in comparison with processes that require alloying elements or further metal working to improve mechanical properties [4]. There has been an increasing need to relate the microstructures to the resulting properties of quenched and tempered rebar [10; 11; 12]. However, information on such relationships typically requires precise thermal histories. On the viewpoint of product quality and operational performance, the accurate measurement and control of temperature during high temperature processes are very important. A number of attempts have been made to measure the temperature during the thermal process, but accurate thermal histories are hard to obtain due to the complexity of high temperature process and harsh conditions that exist both in the tool and workpiece [13; 14; 15]. Furthermore, the manufacturing process for the rebar does have an effect on the residual yield and tensile strength, but the quantitative evaluation of process-induced stress-strain relationship is not easy [16; 17; 18]. Therefore, many studies have been performed to develop thermal models that can accurately predict the temperature during thermal processing [19; 20; 21; 22; 23]. While a shop floor test can provide very exact and desirable thermal history, it is not easy to achieve due to the busy production schedule. Furthermore, because the average material amount per heat exceeds 100 tons, shop floor testing requires large investment of both time and capital. Therefore, there would be a significant advantage if cost-effective methods capable of producing high-fidelity data could be developed. Regarding thermomechanical processing, one way to reduce the time and cost of developing large variations in thermal histories is through the use of well-established thermomechanical simulators (e.g., the GleebleTM, New York, NY, USA) and an electro-thermal mechanical tester (Instron's ETMTTM, Norwood, OH, USA) [24; 25]. However, there is a risk associated with sub-scale mechanical tests to determine bulk mechanical properties.