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Creep Resistance of VM12 Steel

Zieliński A., Golański G., Dobrzański J., Sroka M.

Archives of Metallurgy and Materials

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2016

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Vol. 61, iss. 3

1635--1640

EN

This article presents selected material characteristics of VM12 steel used for elements of boilers with super- and ultra-critical steam parameters. In particular, abridged and long-term creep tests with and without elongation measurement during testing and investigations of microstructural changes due to long-term impact of temperature and stress were carried out. The practical aspect of the use of creep test results in forecasting the durability of materials operating under creep conditions was presented. The characteristics of steels with regard to creep tests developed in this paper are used in assessment of changes in functional properties of the material of elements operating under creep conditions.

2

Mechanical Properties of VM12 Steel after 30 000 Hrs of Ageing at 600°C Temperature

Golański G., Zieliński A., Słania J., Jasak J.

Archives of Metallurgy and Materials

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2014

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Vol. 59, iss. 4

1351--1354

EN

The paper describes the influence of different times of ageing on mechanical properties and microstructure stability in hardened and tempered VM12 steel exposed to service temperature - 600°C. Detailed microstructural and microchemical analysis of secondary phases was carried out using scanning electron microscopy (SEM + EDX) and X-ray phase analysis of carbide isolates. Performed research has proved high stability of strength properties of the investigated steel, which is connected with the lath stability of the microstructure of tempered martensite. Slight changes in strength properties were accompanied by over 50% reduction in impact strength KV of the examined cast steel, from the level of 83 J in the as-received condition to 38 J after 30 000 hrs of ageing at the temperature of 600°C. Significant decrease in impact energy KV of VM12 steel results from the growth of the amount and size of precipitations on grain boundaries.

PL

W pracy przedstawiono wyniki badań zmian w mikrostrukturze i właściwościach mechanicznych stali VM12 po 30000 godzin starzenia w temperaturze 600°C. Przeprowadzone badania wykazały, że długotrwałe starzenie stali VM12 prowadzi do względnego wzrostu wydzieleń po granicach ziaren, głównie po granicach ziaren byłego austenitu oraz skutkuje zanikiem wydzieleń typu MX oraz wydzielaniem fazy Lavesa. Zmiany w mikrostrukturze w niewielkim stopniu wpłyneły na zmiany właściwości wytrzymałościowych (granicy plastyczności, wytrzymałości na rozciąganie) o ok. 7%, natomiast spowodowały ponad 50% redukcje udarności KV z poziomu 83 J w stanie wyjściowym do 38 J po 30 000 godzin starzenia. Ponadto starzenie stali VM12 skutkowało ok. 16% obniżeniem twardości HV10 co powiązano z zanikiem wydzieleń typu MX.

3

Quantitative characterisation of the microstructure high chromium steel with boron for advanced steam power plants

Zielińska-Lipiec A., Kozieł T., Czyrska-Filemonowicz A.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 43, nr 1

200-204

EN

Purpose: The purpose of the paper is to characterize the microstructure of high chromium steel with boron for advanced steam power plants. Design/methodology/approach: The microstructure of new 12% chromium steel developed for advanced power stations operated around 625-650 °C, has been characterized in order to correlate its structural parameters with steel creep properties. Microstructure of the as received condition has a significant influence on creep resistance of 9-12% Cr steels operating at elevated temperatures. Quantitative TEM analyses of steel microstructure were undertaken to determine the dislocation density within the sub-grain, the width of the martensite laths/sub-grains and the particle parameters (shape, size, distribution). Phase identification was performed using electron diffraction and X-ray spectrometry. The influence of the austenitisation temperature (1060 -1100 şC) on the microstructure of the VM12 steel with 145ppm boron was investigated. Findings: The results show that increase of the austenisation temperature caused slight increasing of a sub-grain size and decreasing of dislocation density within sub-grains in the steel tempered at 780 şC. The M23C6 and MX particle size was not significantly changed. Quantitative TEM analyses of the VM12 steel microstructure showed that favorable characteristics exhibit the steel which was austenised at 1060 °C. Research limitations/implications: The present study is focused on the influence of temperature of autenitisation on the microstructure of the VM12 steel with 145ppm boron. The quantitative parameters of the VM12 microstructure were determined. The VM12 steel is a high Cr martensitic steel developed for advanced coal-fired power station operating at temperature higher than 600 şC. Originality/value: Quantitative characterisation of the microstructure high chromium steel with boron for advanced steam power plants.