Standard methods of analysis are being continuously developed by national (SSI) and international (IS01 committees t o produce methods with the precision and accuracy t o enable materials t o be analysed t o more demanding criteria. Following development, they undergo inter-laboratory tests to evaluate performance. An IS0 Standard (ISO) 5725, "Precision of Test Methods-Determination of Repeatability and Reproducibility for a Standard Test Method by Inter-laboratory Tests," has been prepared as a guide t o such trials.This paper introduces and explains the significance of terms defined in the Standard and discusses the objectives of inter-laboratory tests. It also interprets these by reference t o the trials undertaken t o test standard methods developed for the analysis of iron, steel and iron ores. In particular, the relationship between these data and the concept of K-factors suggested by Johnson and others t o relate precision and accuracy with concentration is discussed. The significance of K-factors in day-to-day laboratory operation is also considered.
A general scheme relating the chemical and instrumental methods available for isolation and identification of microconstituents in steel is presented. Several techniques are discussed in more detail. These include electrolytic solution, selective centrifuging, and use of the petrological microscope. High-silica values were obtained when thiocyanate and citrate were used as electrolytes in electrolyses of the Klinger and Koch type. The anomalous values were traced to oxidation of silica in the steel to silicic acid. Washing the residue with sodium carbonate eliminated this problem. The authors describe use of a potentiostat for selective solution of complex austenitic 15Cr-25Ni steels containing additions of other metals. Use of the threshold centrifuge to separate residues by weight and size for X-ray diffraction analysis is discussed. An example of identification of spinels in a globular silicate inclusion by the petrological microscope is also presented. Throughout the paper the complementary nature of the various methods and the use of methods in combination are stressed.
Recent developments in metallurgical analysis, which have potential for use in industry, are described. The paper concentrates on three techniques : firstly the use of pulse distribution analysis in spark-source optical emission spectroscopy to determine soluble aluminium in steel separately from the aluminium that is present as inclusions in the steel matrix; secondly, glow discharge spectroiiietry for the determination of alloying elements in steel, a technique which has potential for both bulk and surface analysis of steel, and lastly, inductively coupled plasma spectrometry. Data are presented, together with reproducibility measurements, which give the optimum conditions for niultielenient analysis of stccl using this technique.
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