Effect of structural factors on the creep properties of modified chromium steels

Abstract

The precipitation strengthening of modified chromium steels is effected predominantly by M 23Ce carbides. In molybdenum-modified 9% chromium steels, creep resistance depends on the dispersion of the M 23C 6 carbides and on the molybdenum content in the solid solution. There is no point in increasing molybdenum contents of molybdenum-modified steels above approximately 1 wt. %. In vanadium-modified steels precipitation strengthening is effected both by M 23C e carbides and by VCxN y carbonitrides.If the amount of nitrogen in solid solution is insufficient, this reduces the volume fraction of VCxN y in the structure and thus impairs the creep resistance of the steel. It is advisable to restrict the aluminium and titanium contents in the vanadium-modified chromium steels.ElnfluB der Mikrostruktur auf die Kriechelgenschaften von modifizlerten Chromstiihlen. An der Ausscberdunoshartunq von rnodifizierten Chromstahlen ist vor allem das Carbid M 23Ce beteiligt. In Mo-modifizierten 9%-Chromstahlen hangt die Zeitstandfestigkeit von der Dispersion des Carbids M 23C 6 und vom Mo-Gehalt in fester Losung abo Es gibt keinen Grund, den Mo-Gehalt in diesen Stahlen Ober die 1%-Grenze hinaus zu erhOhen. In V-modifizierten Stahlen beteiligen sich an der Ausscheidungshartung neben M23Ce-Carbiden auch die Carbonitride VCxN y. Wenn in der festen Losung keine ausreichende Stickstoffmenge vorhanden ist, verringert sich im GefDge der VCxNy-Volumenanteil, und dadurch verschlechtert sich die Warmfestigkeit des Stahls. In V-modifizierten chrometahten sollte deshalb der AI-und Ti-Gehalt, der den effektiven N-Gehalt in fester Losung verringert, beschrankt werden.

Influence of aluminium on creep strength of 9–12% Cr steels

“…Predicted rupture stresses at 600 • C compared to both NIMS data and Al containing steels from COST 538 denoted Bar 257 [16]. that is reported in literature will be evaluated in order to clarify the influence of aluminium [19][20][21]. Work on X20 CrMoV 12 1 steel has confirmed that the rupture strength decreases with aluminium additions [19].…”

“…that is reported in literature will be evaluated in order to clarify the influence of aluminium [19][20][21]. Work on X20 CrMoV 12 1 steel has confirmed that the rupture strength decreases with aluminium additions [19]. This decrease in rupture strength was up to 30% at 550 • C and 20% at 600 • C. The steel with highest aluminium content showed the presence of coarse AlN of 0.25-1.6 m in size, and it was concluded that these particles cannot contribute to particle strengthening.…”

Advances in Physical Metallurgy and Processing of Steels. Strengthening Mechanisms of Creep Resistant Tempered Martensitic Steel.

“…8,13) The rotor steel often contains fine M 2 X (mainly Cr 2 N) particles within subgrains. 5,6,8,14,15) HCM12A steel has Cu particles on sub-boundaries.…”

Strain Enhanced Growth of Precipitates during Creep of T91

“…It has densely populated dislocations while free dislocation density decreases gradually. [1][2][3][4][5][6][7] Since the deterioration of creep strength is accompanied by the loss of dislocation density and subgrain coarsening, the thermal stability of microstructure is of vital importance for heat resistant steels. [6][7][8][9] The microstructural stability of ferritic heat resistant steels is mainly controlled by the thermal stability of precipitates that are able to retard the growth rate of subgrains.…”