Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
The control of non-metallic inclusions is very important for the improvement of
performance during the application of tool steel. This present study was performed to
see the effect of changing of some process parameters during the vacuum degassing of
the melt and how these changing parameters affects the characteristics of inclusions in
tool steel. The main parameters that were changed during the vacuum degassing were
the change of induction stirring, argon flow rate from both the plug 1 and 2 and
different ladle ages for different heat. Electrolytic extraction method was used to
observe the morphology and characteristics of inclusions as a 3 dimensional view in
tool steel. Four lollipop samples from four different heats were used for the
experiment and all the samples were after vacuum (AV) degassing. In this study four
different types of inclusions were found and they are classified as type 1, 2, 3 and 4.
Of them type 1 inclusion was the major one with mostly spherical shaped. This study
shows that among the three parameters, induction stirring has the biggest effect for the
total number of inclusions per volume in the sample than the other two parameters
Heat 4A showed the lowest number of inclusions per volume comparing with the other
heats. The main reason behind this can be said that the induction stirring was the
lowest comparing with the other heats with moderate argon flow and ladle age of 12.
Extreme value analysis was used in this study to predict the probability of getting
largest size inclusions in a certain volume of the metal. For the prediction of the
largest inclusion size, both the electrolytic extraction (3D) and cross-sectional (2D)
method was used. Later in this study comparison was done to determine the accuracy
of both the methods and it is concluded that for the type 1 inclusions electrolytic
extraction method shows almost similar trend with cross-sectional method and
electrolytic extraction method shows better accuracy for the prediction of largest size
inclusions than the cross-sectional method. Electrolytic Extraction method is also
applicable for the prediction of largest size inclusions for multiple types of inclusions.
2010. , 48 p.
Tool Steel, Electrolytic Extraction, Vacuum degassing, Non-metallic inclusions, Induction stirring, Argon flow rate, Ladle age, Extreme value analysis.