Degradation of the Microstructure and Mechanical Properties of High-Chromium Steels Used in the Power Industry

Abstract

High-chromium martensitic steels are one of the basic creep-resisting construction materials used for the modernization of old and the construction of new power units. During the service under creep conditions, the metastable microstructure of martensitic steels undergoes gradual degradation. The rate of degradation mostly depends on the operating temperature, but it is also affected by stresses. The changes in the microstructure of martensitic steels have an influence on the decrease in their mechanical properties, including creep resistance. The knowledge and description of the changes in the microstructure of steels working under creep conditions allow extending the time of safe operation of the elements of power systems. The paper presents and describes the main mechanisms of degradation of 9-12%Cr martensitic steels on the basis of the independent studies and literature data.

The effect of inclusions on the high‐temperature low‐cycle fatigue performance of cast MarBN: Experimental characterisation and computational modelling

“…The precipitation hardening effect of boron‐enriched M 23 C 6 carbides along boundaries is considered to be the primary strengthening mechanism in modified 9Cr steels, and is further enhanced through the addition of W; however, Laves phase particles (Fe 2 W) are prone to coarsening during prolonged high‐temperature exposure . In P92 steel, these particles have been identified as significant contributors to precipitate strengthening, as particles reach a similar saturated size to M 23 C 6 carbides in less than 10 000 hours . This may be an indication as to why the cast MarBN examined here has equivalent cyclic performance and fatigue life, compared to a rolled P91 steel.…”

Microstructure and Mechanical Properties of Modern 11%Cr Heat-Resistant Steel Weld Joints

“…The electron microscopic examinations revealed that the microstructure of tempered martensite had subgrain structure with a low density of dislocation inside the subgrains and numerous M 23 C 6 and MX precipitates ( Figure 3 and Figure 4 ). In the steel in the initial condition, two types of precipitate are observed: M 23 C 6 carbides and MX (NbX, VX) precipitates were also observed for example in [ 1 , 23 , 24 ]. The M 23 C 6 particles are chromium-rich precipitates [ 1 , 24 , 25 ].…”

“…In the steel in the initial condition, two types of precipitate are observed: M 23 C 6 carbides and MX (NbX, VX) precipitates were also observed for example in [ 1 , 23 , 24 ]. The M 23 C 6 particles are chromium-rich precipitates [ 1 , 24 , 25 ]. Chromium-rich M 23 C 6 carbides are the predominant type of precipitates in this group of steels.…”

“…The construction of modern supercritical or ultra-supercritical boilers to reduce air emissions and fuel consumption required the use of modern creep-resistant materials, including but not limited to 9–12% Cr martensitic steels, for boiler pressure components. Martensitic steels are intended for, but not limited to, steam superheater components which are considered essential for a power unit [ 1 , 2 ]. However, the operating temperature of this group of materials is limited to 610–620 °C.…”

Experimental and computational characterization of the effect of manufacturing-induced defects on high temperature, low-cycle fatigue for MarBN

“…Using BSE, this has been attributed to tungsten rich Laves phase (Fe2W) formation [40], which are prone to rapid coarsening in-service [50]. In P92 steel, these particles have been identified as significant contributors to precipitate strengthening, as particles reach a similar saturated size to M23C6 carbides in less than 10,000 hours and contribute to precipitate strengthening along boundaries [51,52]. The saturated particle size of Fe2W in cast MarBN is a potentially interesting focus for future work on the long-term effect of Laves phase formation and growth under flexible loading.…”