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Production of ultra-pure steel intended for forged elements

Michaliszyn A., Wcisło Z., Rydarowicz M

Journal of Achievements in Materials and Manufacturing Engineering

2012

Vol. 55, nr 2

742--747

Purpose: The purpose of this research is to analyse the technology of making ultra-pure steel intended for casting forging ingots. Forging ingots, whose mass amounts to 8 Mg, are cast using the bottom pouring method after vacuum steel degassing in the ladle. Design/methodology/approach: Data from 24 melts were analysed. Researchers studied not only the final content of oxygen, sulphur and hydrogen after vacuum steel refinement but also the quantitative amount of non-metallic inclusions in forgings made of ingots. A simulation was also conducted. Its purpose was to assess the optimal share of bauxite in the production of refining slag. The simulation was performed using thermodynamic software called FactSage 5.5. Findings: Analysing the final concentration of oxygen dissolved in liquid steel led to a conclusion that approx. 90% of analysed types of steel can be categorized as ultra-pure. The simulation results concerning refining slag formation show that the use of bauxite as a slag forming additive lead to an increase in the liquid phase, and what follows, a decrease in the share of solid precipitations - including the precipitations of lime. Research limitations/implications: It was concluded that all stages of ultra-pure steel production must be conducted conscientiously and meticulously. It is also necessary to improve the conditions of vacuum steel refining process by equipping steelworks with a new vacuum device, e.g. of VOD type. Practical implications: If all stages of steel making are conducted conscientiously and meticulously and the steelworks are equipped with a device for vacuum steel refinement, then the produced steel (from the point of view of quality) can be competitive in the market of the ultra-pure steel intended for forged products. Originality/value: The simulation results concerning the production of refining slag show that the use of bauxite as a slag forming material leads to an increase in the share of liquid phase. Refining steel under a heating layer contributes to the improvement of steel purity - which is measured by analysing the share of surface non-metallic inclusions. Refining steel under refining slag with a basic character and physical properties adapted to the temperature close to the liquidus temperature of steel contributes to a decrease in the amount of non-metallic inclusions, a decrease in their size. It can aslo affect the shape of inclusions - making them almost spherical in shape. This method should be optimised and further research should be conducted into improving the purity of steel intended for forged shafts for the power industry.

Rozwój metod ilościowej analizy wtrąceń niemetalicznych z zastosowaniem do ultraczystych stali wysokostopowych

Pawlak S. J., Maciosowski A., Gazdowicz J.

Prace Instytutu Metalurgii Żelaza

2008

T. 60, nr 4

58-60

W oparciu o posiadane oprogramowanie do ilościowej analizy obrazu nowoczesnych mikroskopów świetlnych i skaningowych skorygowano metodyki ilościowej analizy wtrąceń niemetalicznych w zastosowaniu do ultraczystych stali wysokostopowych. Wykorzystano nowo pozyskane moduły oprogramowania do zautomatyzowanych pomiarów, przydatnych do analiz bardzo małej ilości cząstek z uwzględnieniem podziału na rodzaj cząstek (azotki, siarczki). Zaproponowano korekty do znormalizowanych metod ocen ilościowych wtrąceń stosowanych do wymienionych materiałów.

Based on possessed software for quantitative analysis of the image from modern light and scanning microscopes, the methodologies for quantitative analysis of non-metallic inclusions used for ultra-pure high-alloy steels were corrected. T7ie newly acquired software modules for automated measurements, useful for analyses of very small amounts of particles taking into consideration the division into particle types (nitrides, sulphides), were used. Corrections to standardised methods for quantitative assessments of inclusions used for the above-mentioned materials were proposed.