OES-PDA tool

OUR TOOL 1: NEW OES-PDA ANALYSIS TOOL FOR FAST DETERMINATION OF STEEL CLEANLINESS, TOTAL OXYGEN CONTENT AND STATUS OF INCLUSIONS

Figure OES-PDA. New online modelling tools for OES-PDA analysis systems have been developed for more accurate and robust control of steel cleanness and states of inclusions in continuous casting including the ladle operations before casting

The development of the OES-PDA new system has been carried out by Casim Consulting in close cooperation with SSAB Raahe, University of Oulu, Finland, but also with active international cooperation with two European steel plants. Fully automatic, online determination of different micro cleanness parameters of production samples in steel plant was the final target.

Typical micro cleanness parameters are:

•       Amounts of inclusion, types, sizes

•       Total oxygen content (TOC)

•   Composition of main inclusion types

The main developments:

1.  Improved prehandling. Incorrect data needs to be detected and removed or handled correctly. Incorrect data can originate from various factors:

•   Entry of the top slag during sampling

•   Reoxidation during sampling with air inside the sampler

•   Sample surface contamination

•   Porosity or holes in the sample

•   PDA single sparks may ignite incorrectly, etc.

2.  The sample needs to be representative. Indicators have been developed to detect if the sample is not representative, i.e. taken too early after ladle treatments where alloying elements are added as FeSi or CaSi or too early after vacuum treatment.

3.      Special treatments for Ca and Mg inclusions and separation of CaS from CaO and in general sulfides from oxides. Practically all Ca and Mg are bound to inclusions in the cooled samples, so special treatment is needed for these elements.

4.  Many other developments have been carried out such as separation of the endogenous inclusions from the exogenous ones and calculating total oxygen separately for these different oxide groups. In clean steel, the exogenous oxygen should be close to zero and the endogenous oxygen low. Inclusion sizes are calculated using the ablated mass of the spark and concentrations of the elements in this mass.

5.  The developed model takes into account many elements, as Al, Ca, Mg, Si, Mn, Ti, Cr, etc., their inclusions and precipitates.

6.      The validation of the new tool and system has been carried out mainly with comparing the calculated total oxygen contents (TOC) with Leco measurements. Good agreements have been obtained (figure below). We also noticed the importance of the good prehandling procedures as well as the procedure to separate the exogenous inclusions from the endogenous. With these procedures, even dirty samples can be saved and aplied and so the system is very robust and accurate.

7.  The tool has now been in fully automatic use in the SSAB steel plant for several years. The results are

Impacts:

•   Preventive actions possible

•   Cleanness and state of inclusions can be controlled better

•   Many kinds of quality and practical problems can be solved

•   Different production paths can be compared and tested

•   Saving the output datasets in a databank system for longer term statistical analysis of quality and effect of changes made in the processes on the quality

•       Even dirty samples can be saved and used

Reference: S. Louhenkilpi, T. Antola, T. Fabritius, A. Jokilaakso, ’OES-PDA method for fast on-line analysis of the state of inclusions and cleanliness in liquid steel’, Clean Steel conference, Budapest, Hungary, 18-20 September 2018

Contact: seppo.louhenkilpi@casimconsulting.com

Figure OES-PDA. New online modelling tools for OES-PDA analysis systems have been developed for more accurate and robust control of steel cleanness and states of inclusions in continuous casting including the ladle operations before casting.