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The influence of boron on the microstructure of martensitic chromium steels for power plants

Bryła K., Spiradek-Hahn K., Zielińska-Lipiec A., Firganek H., Ennis P.J., Czyrska-Filemonowicz A.

Inżynieria Materiałowa

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2004

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R. XXV, nr 3

702-705

EN

Two 9% Cr martensitic steels with 30 and 100 ppm B, were investigated by means of LM and TEM in the as received condition and after long-term creep deformation at 600°C. The aim of the study was to show the boron distribution and identify the influence of boron in the investigated steels. By means of trace autoradiography method, the incorporation of boron into the M23C6 precipitates in these steels was detected. In the steel doped with 100 ppm B, boron was densely distributed on prior austenite grain- and lath boundaries as well as within martensite laths contributing to the stabilization of M23(C,B)6. It significantly improves creep rupture strength of this steel.

PL

Za pomocą mikroskopu świetlnego i transmisyjnego mikroskopu elektronowego przeprowadzono badania mikrostruktury dwóch stali martenzytycznych chromowych zawierających 30 i 100 ppm B w stanie dostawy i po długotrwałym pełzaniu w temperaturze 600°C. Celem pracy było ujawnienie rozkładu boru i określenie jego wpływu na mikrostrukturę badanych stali. Za pomocą metody autoradiografii śladowej ujawniono zawartość boru w wydzieleniach M23C6 i w osnowie w obu stalach. W stali z dodatkiem 100 ppm B, ślady wskazujące na obecność boru były gęsto rozłożo na granicach ziarn austenitu pierwotnego, granicach listew martenzytycznych, jak również wewnątrz listew martenzytu. Bor, poprzez wpływ na stabilizację węglikoborków M23(C,B)6, znacząco poprawia czasową wytrzymałość na pełzanie tej stali.

2

New 9-12% chromium steels for advanced power generation: microstructure, properties and application limits.

Ennis P.J., Czyrska-Filemonowicz A.

Inżynieria Materiałowa

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2001

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R. XXII, nr 4

311-318

EN

The thermal efficiency of steam power plant can be significantly increased by raising the temperature and the pressure of the steam entering the turbine. The development of the modified 9% chromium steels P91, P92 and E911 has provided the constructional materials for components capable of operation at temperatures up to and perhaps beyond 600 degrees centigrade. The emphasis in the development has been placed on improving the long-term creep rupture strength; this has been achieved by alloying the basic 9% Cr 1% Mo steel with V, Nb, and N to provide fine, stable precipitates. The strengthening mechanisms are transformation hardening which provides a high initial dislocation density; precipitation hardening by carbides at the martensite lath boundaries which eventually form the sub-grains; fine carbide, nitride and carbonitride precipitates within the sub-grains. Solid solution strengthening has also been enhanced by additions of W. Steam oxidation tests have shown that Cr contents above 11% are neccessary for the formation of protective oxide scales in steam-containing environments at 600-650 degrees centigrade; in air 9% Cr is sufficient. The temperature limits imposed by steam oxidation of the steels depend on the component wall thickness and on the maximum acceptable oxidation rate in terms of spalled oxide and reduction of load-bearing cross-section. The potential for further development of the high Cr martensitic steels towards a steel which combines in a single composition the strength of the 9% Cr steels with the steam oxidation resistance of the 12% Cr steels is discussed.

3

Quantitative TEM microstructural investigations of high temperature deformed ODS alloy incoloy MA956.

Dubiel B., Wasilkowska A., Ennis P.J., Czyrska-Filemonowicz A.

Inżynieria Materiałowa

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1998

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R. XIX, nr 3

552-555

EN

In the present study quantitative transmission electron microscopy (TEM) analyses of high temperature tensile and creep deformed INCOLOY MA956 have been carried out to evaluate the microstructural parameters affecting the deformation mechanisms. The results obtained enabled modelling of high temperature deformation behaviour of the alloy investigated.

4

Correlation between microstructure and long-term creep behaviour of 9% Cr steel P92 for advanced power plants.

Zielinska-Lipiec A., Ennis P.J., Czyrska-Filemonowicz A.

Inżynieria Materiałowa

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1998

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R. XIX, nr 3

229-232

EN

The microstructure and creep properties of the 9% Cr-0,5Mo-1,8W-V-Nb steel P92, a Japanese steel developed for advanced coal-fired power stations with operating steam temperatures around 600 degrees centigrade have been investigated. The study showed that the microstructural changes responsible for the decreasing creep rupture strength at temperatures 600 and 650 degrees centigrade were a marked decrease in dislocation density, an increase in subgrain size with continuous polygonization of the dislocation structure, and slight coarsening of the M23C6 and MX precipitates.