abstract = "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 analysing
the influences of different steel making parameters is
presented. On the basis of the monitored data about the
casting-temperature changes, the total oxygen, the
number of added aluminium rods, the chemical analyses
before and after steel-making, 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 percent to 1.92 percent - by more
than 35 times.",