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Assessment of Microstructure and Mechanical Properties of the Slag Ladle after Exploitation

Kalandyk Barbara, Zapała Renata, Sobula Sebastian, Tęcza Grzegorz, Piotrowski K.

Archives of Metallurgy and Materials

2021

Vol. 66, iss. 2

351--358

The results of tests and examinations of the microstructure and mechanical properties of cast steel used for large-size slag ladles are presented. Castings of this type (especially large-size ladles with a capacity of up to 16 m3) operate under very demanding conditions resulting from the repeated cycles of filling and emptying the ladle with liquid slag at a temperature exceeding even 1600°C. The changes in operating temperature cause faster degradation and wear of slag ladle castings, mainly due to thermal fatigue.The tests carried out on samples taken from different parts/areas of the ladle (flange, bottom and half-height) showed significant differences in the microstructure of the flange and bottom part as compared to the microstructure obtained at half-height of the ladle wall. The flange and bottom were characterized by a ferritic-pearlitic microstructure, while the microstructure at the ladle half-height consisted of a ferritic matrix, cementite and graphite precipitates. Changes in microstructure affected the mechanical properties. Based on the test results it was found that both the flange and the bottom of the ladle had higher mechanical properties, i.e. UTS, YS, hardness, and impact energy than the centre of the ladle wall. Fractography showed the mixed character of fractures with the predominance of brittle fracture. Microporosity and clusters of non-metallic inclusions were also found in the fractures of samples characterized by low properties.

Microstructural aspects of long-term ageing of martensitic 9% Cr steel with and without boron addition

Golański Grzegorz, Merda Agata, Klimaszewska Klaudia

Journal of Metallic Materials

2019

Vol. 71, no. 1

27--33

The study covered 9% Cr martensitic steels - X10CrMoVNb9-1 (P91) and X13CrMoCoVNbNB9-2-1 (PB2) after long-term ageing at the temperature of 620°C and soaking time up to 50,000 hours. The microstructural investigations of the tested steels were carried out using a TITAN 80-300 transmission electron microscope. The analysis of the changes in the microstructure included the identification of precipitates and computer image analysis: the measurement of dislocation density and mean diameter of the precipitates. The tests showed that the analysed steels still retained the lath martensitic microstructure, but also the processes of matrix softening were observed. The microstructure of the examined steels also showed numerous precipitates with various morphologies. The micro-addition of boron in the PB2 steel, compared with the P91 steel, influenced the retardation of the microstructure degradation processes through the limitation of the growth of M23C6 precipitates and Laves phase. This resulted in a slowdown in the processes of recovery and polygonisation of the matrix of the tested steel.

Badaniu poddano martenzytyczne stale typu 9% Cr - X10CrMoVNb9-1 (P91) oraz X13CrMoCoVNbNB9-2-1 (PB2) po długotrwałym starzeniu w temperaturze 620°C i czasie wygrzewania do 50 000 godzin. Badania mikrostrukturalne badanych stali przeprowadzono za pomocą transmisyjnego mikroskopu elektronowego TITAN 80–300. Analiza zmian w mikrostrukturze obejmowała identyfikację wydzieleń oraz komputerową analizę obrazu: pomiar gęstości dyslokacji i średniej średnicy wydzieleń. Przeprowadzone badania wykazały, że analizowane stale posiadały nadal zachowaną listwową mikrostrukturę martenzytyczną, ale także obserwowano procesy mięknięcia osnowy. W mikrostrukturze badanych stali widoczne były również liczne wydzielenia o różnej morfologii. Mikrododatek boru w stali PB2 w porównaniu do stali P91 wpłynął na spowolnienie procesów degradacji mikrostruktury poprzez ograniczenie wzrostu wydzieleń M23C6 i fazy Lavesa. Wpłynęło to na spowolnienie procesów zdrowienia i poligonizacji osnowy badanej stali.