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Determination of microalloying elements in stainless steel matrix and inclusions

Determination of microalloying elements in stainless steel matrix and inclusions. Teija Sipola Doctoral student Process Metallurgy Research Group. The Content of presentation. “Sophisticated alloying practices” What is studied and why Electrolytic extraction method (EE) in general

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Determination of microalloying elements in stainless steel matrix and inclusions

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  1. Determination of microalloying elements in stainless steel matrix and inclusions Teija Sipola Doctoral student Process Metallurgy Research Group

  2. 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

  3. What? How? Why? • Inclusionshavebeenstudiedwidely and in detailusingthe EE method • Suitability of electrolytes to nitrides, oxides, sulphides and other1 • Someelectrolytesaremorecommonthanothers (10 % AA, 2 % TEA, 10 % HCl) • Is stillused in inclusionsstudies in 3D • What is dissolvedwiththesteelmatrixduring EE is lessstudied • Solublealloyingelements • Impurities • Someinclusions (depends on theelectrolyte) 1) Inoue R., Kiyokawa K., Tomodo K., Ueda S., Ariyama T., Three-dimensionalestimation of multi-componentinclusionparticle in steel, 2011

  4. What? How? Why? • Experimental design includesseveralsteps: • 1. Electrolyticextraction in a suitableelectrolyte (Avoidloss of inclusions); 2. Vacuumfiltration of theelectrolyte and inclusioncollection on a PC-filter; 3: Samplepreparation for solublealloyingelements; 3.1 Matrixexchange (notalwaysnecessary); 4. drying of thefilterwithinclusions; 5. Inclusiondissolution; 6. Samplepreparationfromdissolvedinclusions; 7: Measuring of alloyingelementcontents in steelmatrix and inclusions

  5. What? How? Why? • Step 5 alsoincludes: • Choosing a properdecompositionmethod for theextractedinclusions • Aquaregia, HNO3-HF, HNO3-H2O2… • Step 7 alsoincludes: • Calibration of choseninstrumentwithprimarystandards • Determination of precision • Trials (calculatingstandarddeviation) • Determination of accuracy • Measuringsampledilutions, controlsamples, spikedsamples • Blanksamples • Influence of spectralinterferences (ICP-OES)

  6. What? How? Why? • A way to useexistingmethod to producenewinformationaboutsteel • As a results, microalloyingelementcontent in steelmatrix and inclusions is obtained and it canbecompared to e.g. spark-OES data from a solidsampleor as an alternative/referencemethod to OES-PDA • Somesimilarities to a researchbyKinoshiro et al.2 • Limitations • Content < 0,001 w-% of anyelement is troublesome • Watersoluble, ”delicate” inclusionsarelost in anyelectrolyte • Contamination (Mg, Al, Ca) 2) Kinoshiro S., Ishida T., Inose M., Fujimoto, ISIJ International, Vol .54, 2014, No. 4, pp. 880-884

  7. Results so far… • For a stainlesssteelprocesssample results3indicated • ~50 % of alloyed Ti and Nbwereactually in theinclusions • 100 % of alloyedNi, Mn and Crwere in steelmatrix • In thisstudy 10 % HClelectrolytewasused, dissolvedmass ~1 g • Dissolvedmassis calculatedfromspark-OES data and themass of a dissolvedsample 3) Sipola T., Alatarvas T., Heikkinen E.-P., Fabritius T. Metallurgical and MaterialsTransactions B, 2015, available online

  8. Status in doctoral studies • There is a lot to studyregardingthestudy of solublealloyingelements and elementalanalysis of inclusions • Determination of boron (alsoothernonmetals?) • OtheralloyingelementsAl, Cu, V… • New stainlesssteelgrades • One referee articlepublished • “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 twootherpapers

  9. THANK YOU! • Questions?

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