Inhomogenity in microstructures

Abstract: The purpose of the present thesis is to quantitativelycharacterise structural features which contribute to thematerial anisotropy and to relate developed parameters to thematerial properties. Various forms of structural inhomogeneitywere quantified with the help of comuterised image analysisusing quantitative metallography and statistical analysismethods.New parameters were related to the material properties.The following materials and inhomogeneities related to theirstructures were investigated. Ferritic-pearlitic and duplexstainless steels in various states of deformation and heattreatment,showed banded structures with a range of bandingintensity. The variation of intensity of pearlite banding inthe ferritic-pearlitic steels was represented by the Feretslope ratio parameter, which was shown to be related to thevariation in the hydrogen induced cracking behaviour. Chordslope ratio parameter represented the intensity of banding inthe duplex stainless steel caused by the deformation during hotworking. The welding simulated ferritic austenitic stainlesssteel structures had various ferrite and austenite contentswith no specific orientation. The amount and distribution ofthe austenite phase was the main factor controlling the impactenergy of weldment, since this factor is related to the nitridefraction which in turn controlles the impact energy. Aninhomogeneous distribution of short (-alumina fibres within amatrix of Al alloy with 3% Cu caused a reduction of creeprupture strength of the composite material. The number and typeof cracks in thermo-mechanical fatigue tested specimens of anoxide dispersion strengthened alloy, were related to thestrain. The wear resistance and the impact energy of cold-worktool steels were controlled by the content of carbides, by thecarbide type and by the carbide size range. Macrosegregation incontinuously cast steel slabs was characterised using the newparameters: segregation factor M, width of a segregation bandW0,5 , centreline segregation intensity C and the heterogeneitvindex H. Measured values well corresponded to the qualitativecharacterization of the macrostructural heterogeneity.Keywords:Image analysis, two-phase structure banding,macrosegregation, carbon steel, duplex stainless steel, metalmatrix composite, nickel-base alloy, cold-work tool steel,austenitic stainless steel.