# Tempcore Process Simulator to Analyze Microstructural Evolution of Quenched and Tempered Rebar
## 2 Development of Tempcore Process Simulator  
As TPS has been designed to simulate shop floor operation, a simulator capable of producing high-fidelity data that shows strong similarity with shop floor operational data has been developed in this study.  
Figure 3 shows an industrial Tempcore production line. The length of the Tempcore production line is about 40 m, and more than 20 coolers are installed. Water spraying is performed under condition of a water pressure of 10-12 bar and a water flow rate of 1500 m\({}^{3}\)/h so as to cool the steel bars to martensite-forming temperature.  
Figure 2: Comparison of hardness profiles of rebars after Tempcore treatment and 5 s water quenching.  
TPS mainly consists of a vacuum induction furnace, pilot rolling mill, box furnace, and cooling unit, as shown in Figure 4. The 125 kW/3 kHz vacuum induction furnace has a capacity of 50 kg/charge, maximum heating temperature of 1700 \({}^{\circ}\)C, and vacuum level of 8\(\times 10^{-3}\) Torr. The two-high rolling mill equipped with two 630 kW motors and 720 mm roll diameter has a maximum load capacity of 600 tons and maximum rolling speed of 150 mpm. The dimensions of the heating chamber are \(600(\mathrm{W})\times 600(\mathrm{H})\times 800(\mathrm{D})\). As a heating source, KANTHAL(r)Hallstahammar, Sweden) A-1 has been used. The maximum heating temperature is 1100 \({}^{\circ}\)C, and Ar has been used as an environmental gas.  
The layouts of the Tempcore process for the production line and process simulator are compared in Figure 5. The specifications of the subsystems of TPS have been determined to generate data that show strong similarity with shop floor operational data.  
Figure 4: Sequential layout of Tempcore process simulator (TPS): (**a**) induction furnace; (**b**) pilot rolling mill; (**c**) box furnace; (**d**) cooling unit.  
Figure 3: Industrial Tempcore production line.  
To fabricate test specimens, a 50 kg ingot having 120 mm \(\times\) 120 mm cross-section has been heated to 1150 \({}^{\circ}\)C in a vacuum induction furnace and plate rolled to 28 mm thickness. Then, square bars are cut from the as-rolled plate, and specimens having a 25 mm diameter and 360 mm length were machined from square bars by lathe. Figure 6 shows the sequence of fabrication of the test specimen.  
Figure 7 shows the main features of the system. Figure 7a shows the schematic drawing of TPS. Figure 7b shows that the dual cylinder consists of a high-speed air cylinder and a low speed air cylinder. The cooling time can be adjusted by a speed control valve. Figure 7c shows the specimen transfer  
Figure 5: Similarity of cooling system for the Tempcore process: (**a**) production line; (**b**) TPS.  
Figure 6: Sequence of fabrication of test specimen: (**a**) ingot; (**b**) plate rolled; (**c**) cylindrical specimen.  
frame used to ensure circumferentially uniform temperature. Figure 7d shows the specimen clamping device. A screw-type specimen clamping device has been designed that can reduce temperature drop by fast clamping. The main specifications of TPS are shown in Table 1.  
Figure 7: **(a)** Schematic of TPS system; **(b)** dual cylinder; **(c)** specimen transfer frame; **(d)** screw type specimen clamping device.  
For the metallographic examination, the specimen was cut from the predetermined position in tested rebar. Microstructure was observed by an optical microscope after mechanical polishing with alumina powder of 0.5 micron in size and etching with 3% vital for 5 s. Vickers micro-hardness test has also been performed from the center to outer surface of the rebar with 10 kg load.