The state of the art steel treatment in BOF converter uses bottom purging after main blowing to increase process accuracy, reproducibility and furthermore leads to better steel qualities. This process step shows significant effect on temperature and chemical composition of the elements carbon, oxygen and phosphorus. In this thesis the influence of bottom purging after main blowing on the resulting metallurgical target values are determined. Due to field tests at the new converters of voestalpine Stahl in Linz the principal relations between the purging time, intensity and temperature to the change in the chemical composition of the steel have been recorded and analyzed. Additionally experimental series have been carried out to clarify the effect of cooling slag and the influence regarding the sample time. The purging intensity shows no observable effect on the process target values. In fact the start value of the process parameter and the purging time after main blowing are the most crucial factors. The latter shows an improvement in the spreading of the results. Carbon and temperature decline linear after main blowing while phosphorus and oxygen reveal an exponential decrease. The influences of an off-center purging, the number of plugs in operation and the number of heats after the last reline reveal an impact on metallurgical results.