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Microstructure and microhardness of annealed austenitic cast steel

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Microhardness of a material reflects the elastic-plastic properties around the point of measurement. It is also a very sensitive indicator of changes in both the microstructure and properties due to a heat treatment or mechanical treatment, and the process of aging that occurs in materials during operation [1?€6]. Microhardness measurement taken under the conditions of low testing loads allows making a number of indentations in selected areas of the sample. For example, in the material with a multiphase structure, like the creepresistant austenitic cast steel, the size of the indentation (depending also on the amount of load applied) represents, in most cases, the average microhardness of a matrix with the precipitates of different origin (Fig. 1). Microstructure of this material is characterised by a relatively small volume content of large and hard precipitates, and a soft matrix with fine secondary precipitates [4]. When the random microhardness measurements are taken at different points on the sample cross-section, a map of the microhardness values can be created in the form of a microhardness distribution density function reflecting local microstructure of the examined material. This means that to various peaks in this distribution one can assign the presence of different structural components, such as a relatively homogeneous matrix, matrix with increased number of fine precipitates, and matrix with large precipitates [3?€6]. The aim of this study was to use the results of the random HV0.01 microhardness measurements to describe changes in the microstructure of 0.3C-18Cr-30Ni cast steel with an addition of titanium, where the said changes have occurred as a result of annealing at a temperature of 800?‹C. EXPERIMENT Studies were conducted on the creep-resistant austenitic cast steel (Tab. 1) melted in an open induction furnace with acid lining [5]. Test ingots were annealed in air at 800?‹C for 10,[...]

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