Determination of microalloying elements in stainless steel matrix and

inclusions

Teija SipolaDoctoral student

Process Metallurgy Research Group

Teija SipolaResearch group of Process Metallurgy

The Content of presentation

• “Sophisticated alloying practices”– What is studied and why– Electrolytic extraction method (EE) in general

• Experimental design – Some additional information about the measurement

techniques– Limitations

• Some results from the first published article

• A part of mandatory doctoral studies: Doctoral training plan and seminar, 4 credits

What? How? Why?

• Inclusions have been studied widelyand in detail using the EE method

– Suitability of electrolytes to nitrides, oxides, sulphides and other1

– Some electrolytes are more common than others (10 % AA, 2 % TEA, 10 % HCl)

– Is still used in inclusions studies in 3D

• What is dissolved with the steel matrix during EE is less studied

– Soluble alloying elements– Impurities– Some inclusions (depends on the

electrolyte)

1) Inoue R., Kiyokawa K., Tomodo K., Ueda S., Ariyama T., Three-dimensional estimation of multi-component inclusion particle in steel, 2011

Teija SipolaResearch group of Process Metallurgy

What? How? Why?

• Experimental design includes several steps:

• 1. Electrolytic extraction in a suitable electrolyte (Avoid loss of inclusions); 2. Vacuum filtration of the electrolyte and inclusion collection on a PC-filter; 3: Sample preparation for soluble alloying elements; 3.1 Matrix exchange (not always necessary); 4. drying of the filter with inclusions; 5. Inclusion dissolution; 6. Sample preparation from dissolved inclusions; 7: Measuring of alloying element contents in steel matrix and inclusions

Teija SipolaResearch group of Process Metallurgy

What? How? Why?

• Step 5 also includes:– Choosing a proper decomposition method for the

extracted inclusions• Aqua regia, HNO3-HF, HNO3-H2O2…

• Step 7 also includes:– Calibration of chosen instrument with primary standards– Determination of precision

• Trials (calculating standard deviation)

– Determination of accuracy• Measuring sample dilutions, control samples, spiked

samples• Blank samples

– Influence of spectral interferences (ICP-OES)

Teija SipolaResearch group of Process Metallurgy

What? How? Why?

• A way to use existing method to produce new information about steel– As a results, microalloying element content in steel

matrix and inclusions is obtained and it can be compared to e.g. spark-OES data from a solid sample or as an alternative/reference method to OES-PDA

– Some similarities to a research by Kinoshiro et al.2

• Limitations– Content < 0,001 w-% of any element is troublesome– Watersoluble, ”delicate” inclusions are lost in any

electrolyte– Contamination (Mg, Al, Ca)

2) Kinoshiro S., Ishida T., Inose M., Fujimoto, ISIJ International, Vol .54, 2014, No. 4, pp. 880-884Teija SipolaResearch group of Process Metallurgy

Results so far…• For a stainless steel process sample results3 indicated

• ~50 % of alloyed Ti and Nb were actually in the inclusions• 100 % of alloyed Ni, Mn and Cr were in steel matrix • In this study 10 % HCl electrolyte was used, dissolved mass ~1 g

• Dissolved mass is calculated from spark-OES data and the mass of a dissolved sample

3) Sipola T., Alatarvas T., Heikkinen E.-P., Fabritius T. Metallurgical and Materials Transactions B, 2015, available online

Teija SipolaResearch group of Process Metallurgy

Status in doctoral studies

• There is a lot to study regarding the study of soluble alloying elements and elemental analysis of inclusions

• Determination of boron (also other nonmetals?)• Other alloying elements Al, Cu, V…• New stainless steel grades

• One referee article published– “Determination of alloying elements Ti, Nb, Mn, Ni and Cr in double stabilized

ferritic stainless steel process sample using an electrolytic extraction method and separate analysis of inclusions” Metallurgical and Materials Transaction B, 2015 (online)

• Working on two other papers

Teija SipolaResearch group of Process Metallurgy

THANK YOU!

• Questions?

Teija SipolaResearch group of Process Metallurgy