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Eur. Phys. J. AP 6 , 243–250 (1999) T HE E UROPEAN P HYSICAL J OURNAL APPLIED PHYSICS c ± EDP Sciences 1999 Advanced microscopy techniques resolving complex precipitates in steels ? W. Saikaly 1 ,R .Soto 1 ,X .Bano 2 , C. Issartel 2 ,G .R igaut 2 , and A. Chara¨ ı 1 , a 1 Laboratoire de M´ etallurgie, EDIFIS b , case 511, Facult´ e des Sciences et Techniques de St. J´ erˆome, 13397 Marseille Cedex 20, France 2 CRPC – SOLLAC, bˆatiment DB26, 13776 Fos-sur-Mer Cedex, France Received: 3 July 1998 / Revised: 29 September 1998 and 25 January 1999 / Accepted: 16 March 1999 Abstract. Scanning electron microscopy as well as analytical transmission electron microscopy techniques such as high resolution, electron diffraction, energy dispersive X-ray spectrometry (EDX), parallel electron energy loss spectroscopy (PEELS) and elemental mapping via a Gatan Imaging Filter (GIF) have been used to study complex precipitation in commercial dual phase steels microalloyed with titanium. Titanium nitrides, titanium carbosulfides, titanium carbonitrides and titanium carbides were characterized in this study. Both carbon extraction replicas and thin foils were used as sample preparation techniques. On both the microscopic and nanometric scales, it was found that a large amount of precipitation occurred heterogeneously on already existing inclusions/precipitates. CaS inclusions (1 to 2 μ m), already present in liquid steel, acted as nucleation sites for TiN precipitating upon the steel’s solidification. In addition, TiC nucleated on existing smaller TiN (around 30 to 50 nm). Despite the complexity of such alloys, the statistical analysis conducted on the non-equilibrium samples were found to be in rather good agreement with the theoretical equilibrium calculations. Heterogeneous precipitation must have played a role in bringing these results closer together. PACS. 61.16.Bg Transmission, reflection and scanning electron microscopy (including EBIC) – 81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging 1 Introduction The steel industry has been interested in developing a product that meets demand for higher strength with ex- cellent formability. Dual phase steels (ferrite matrix with islands of martensite) are a new type of steel that have excellent formability and good strength [1]. One way to increase the strength of these dual phase steels is by ad- dition of a dispersoid forming element such as titanium. Titanium forms different types of precipitates which, de- pending on their size and density per unit volume, will af- fect the steel’s mechanical properties. Electron microscopy has previously been used to identify similar precipitates. However, the nature of precipitates changes with compo- sition and thermomechanical treatment and, hence, pre- cipitates found in our steels had to be characterized.
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