Issue 37

U. Muhin et alii, Frattura ed Integrità Strutturale, 37 (2016) 312-317; DOI: 10.3221/IGF-ESIS.37.41 314 Temperature-speed (t-s) mode and the water flow through the between stands cooling section for test modes are presented in Tab. 3. Al Cu Mn N P S Si 0.045 0.037 0.186 0.003 0.008 0.10 0.015 Table 1: Chemical composition of steel 08U (%). In Tabs. 2 and 3: h p , h sp , h 6 -h 12 – metal thickness after: roughing group; descaler; stands of finishing group, acc.; t p and t f – metal temperature before and after finishing group, acc.; V s and a - thred speed and acceleration in finishing group, acc.; Q 1 – Q 6 – finishing stands gaps acc. h p h sp h 6 h 7 h 8 h 9 h 10 h 11 h 12 Thichness,mm 34.7 34.0 20.3 12.5 8.4 5.89 4.45 3.45 3.00 Relative Reduction, % - 9 0.3 8.5 32.8 29.9 24.4 25.5 13.1 Table 2: The deformation mode in finishing group rolling for strip 3x1250 mm, steel 08U. № of regime Rolling parameters Water slow, m 3 /h t р , t f Vs, a τ m , Q 1 , Q 2 , Q 3 , Q 4 , Q 5 , Q 6 , °C °C m/s m/s 2 s m 3 /h m 3 /h m 3 /h m 3 /h m 3 /h m 3 /h 1 1000 840 8.97 0.026 87.4 0 0 0 0 0 0 2 1000 840 11.95 0.026 68.8 200 200 200 200 200 200 3 1000 840 10.25 0.026 78.4 200 200 200 0 0 0 4 1000 840 10.25 0.026 78.4 0 0 0 40 200 200 Table 3: Technological parameters of studied rolling regimes with between stand cooling. Length of hot-rolled strip is 884 m. The research results are presented in Fig. 1. According to the study, the primary recrystallization process time to get fully only in the first three gaps [9] on all four modes (Fig. 1.a). Recent the between standing cooling does not have time for fully recrystallizing of austenite grain and growth is difficult (Fig. 1.b). The share of the recrystallized volume and average grain size of austenite. Fig. 1 shows the entry point for the front end of the strip in the deformation and at the end of the pyrometer for the temperature of the end of rolling. Application cooling (regime 3) reduces the average grain size of austenite at the exit of the stands and thus improve the mechanical properties of the metal. In regime 2 on the average grain size in the central layers of the band decreases from 18.1 to 16.9 mcm for the front end (Fig.1c) and from 15.9 mcm to 15.3 for the rear end (Fig.1.d) than with number 1. Reducing the size of the austenite grain from the front to the rear end of the strip associated with the use of acceleration in the finishing train (breaks are reduced in the process of rolling) and a constant temperature by the end of the rolling length of the bar in the presence of a temperature “wedge” at the entrance to the finishing group. Application cooling mode at number 3 lowers the temperature of the metal in the last gap, which leads to a decrease in the average grain size at the exit of the mill. As opposed to the regime number 3, in the last three cooling intervals (mode number 4) gives the average grain size of austenite grain size is close to rolling without cooling (mode number 1) at the same speed mode.