Issue 37

D. Angelova et alii, Frattura ed Integrità Strutturale, 37 (2016) 265-271; DOI: 10.3221/IGF-ESIS.37.35 267 To adjust the parameters of the rolling mill for receiving quality products with desired properties by total thickness of 30 mm and 40 mm, there were developed and experimentally tested two speed-temperature-deformation regimes - Regime A and Regime B . Each profile size (30mm and 40mm) is obtained, performing deformation process in these two regimes; 10 pieces from each thickness are tested. Specific features of the different rolling regimes Regime A. Rolling process is carried out when the parameters of the rolling mill are set up as follows: large rolling forces (up to 75% of the maximum for the mill or up to 16,000 kN); high torque (running over to the equipment nominal value); large difference between the initial and the final thickness of the metal concerning each pass, H  [mm], respectively a high degree of deformation (reduction in thickness into each pass about 20%). Speed-temperature-deformation normalization rolling for Regime A is designed with 21 passes. Regime B . Normalization rolling process is performed with new setting of the parameters of the rolling stand, providing less stress (up to 68%), a low torque, small difference between the initial and the final thickness of the metal concerning all passes ( H  is between 13 and 16 mm) and decreased deformation, respectively to maximum 16-20%. All this leads to an increase in the number of passes to 25. Under these initial conditions and using an automatically applied optimization program, Regime B has been developed as a more efficient one. Testing After rolling, 40 specimens were machined for standard mechanical testing – 20 for Regime A and 20 for Regime B , of which 10 specimens for the final thickness of 30 mm and the same quantity for the thickness of 40 mm. Data obtained from testing concern mechanical (tensile strength, yield strength) and plastic (elongation) behaviour (of the final product), as well as impact energy providing information about impact strength. They (the data) are presented in Fig. 2. D ISCUSSION AND ANALYSES he data presented in Fig. 2 show that the final products obtained in Regime B have improved mechanical behaviour, corresponding to the standard EN 10025-2:2004, when the plates obtained by using Regime A cannot satisfy the requirements of this standard. This means that the rolling process of Regime A is unstable in comparison to the stable one under Regime B , wherein the rolling process is controlled, which leads to a sufficient improve of all mechanical properties and their steady reproduction. Usually mechanical testing results have the standard presentation as can be seen in Fig. 2, following by standard analysis. But these results can be presented in a new different way as it has been done in Fig. 3a and 3b. The Fig. 3 visualizes Energy-Stress Constructions-Spaces MNLQQ 1 M 1 N 1 L 1 for 30 mm and 40 mm plates/sheets (obtained under Regime B including automatic application of the mentioned above optimization procedure), which are built by using the final mechanical rolled-plate characteristics - yield strengths, R e , ultimate tensile strengths, R m , absorbed energies in impact tests, K. (Elongations after fracture are included in similar Constructions-Spaces in Fig. 5.) These Constructions-Spaces bring additional information about rolling technology and energy-mechanical properties of the finished/final products. The complicated three-dimensional Energy-Stress Surface MNLQ in Fig. 3a and 3b shows that although the minimum values of yield strength and tensile strength are above the minimum set by the standard, it is worth looking for further improvement of the speed-temperature-deformation regime of rolling that will make this surface smoother, meaning further (even higher) stabilization of technology and energy-mechanical properties of the finished/final product. At the moment Surface MNLQ looks smoother for 30 mm plates/sheets than that for 40 mm ones. In Fig. 4a and 4b complex pyramidal Spaces STUT 1 S 1 P have been built, each by: - the straight lines PU and S 1 T 1 of the average values of yield strengths and tensile strengths respectively, corresponding to the 10 tests for each thickness; and - the broken line ST, obtained from the average energy of impact tests and the stresses ( R m,av – R e,av )/2 (corresponding to the same 10 tests). It is easy to build a line corresponding to the average value of the stresses from the broken line ST. Thus the visualization of the pyramidal Spaces STUT 1 S 1 P makes it possible to predict dispersion of all stresses from the range between the yield strength and the tensile strength, enabling us to do some preliminary comparisons with the exploitation stress requirements.