MODELING OF OCCURRENCE OF SURFACE DEFECTS OF C45 STEEL WITH GENETIC PROGRAMMING

Carbon steel C45 with an increased content of carbon is used for tempering in the automotive industry for highly stressed parts (axles, shafts), machine parts, screws, drills for wood, axes, knives, hammers and similar. In the present work an attempt of analyzing the influences of different steelmaking parameters is presented. On the basis of the monitored data about the casting-temperature changes, the total oxygen, the number of added aluminum rods, the chemical analyses before and after steelmaking, the added lime, the aluminum-cored wire, the calcium-silicon-cored wire, the sulphur-cored wire, the rolling dimensions, the casting speed, the opening of the ladle nozzle with oxygen and surface defects (scrap fraction) on rolled bars, a mathematical model was obtained with the help of the genetic programming method. The results show that the most influential parameters for the surface-defect occurrence on the C45 steel are the opening of the ladle nozzle with oxygen and aluminum. On the basis of the results, the steelmaking technology was changed. Instead of the aluminium-killed steelmaking technology the aluminium-calcium-free (ACF) steelmaking technology was used. The batches from an aluminium-calcium-free steelmaking period statistically have a significantly lower level of surface defects (scrap fraction). The scrap fraction was reduced from the average of 68.45 % to 1.92 % - by more than 35 times.