Abstract The purpose of this study is to identify the relationships between the creep behavior of the 10% Cr martensitic steel with 0.008% B and 0.003% N and changes in microstructure and precipitations of secondary phases. Creep tests were carried out at 650 °C under an applied stress ranging from 180 to 120 MPa. The 10% Cr steel exhibits a linear stress vs. time to rupture dependence without creep strength breakdown up to approximately 40 000 h. The 100 000 h creep rupture strength at 650 °C is predicted to be 110 MPa. The high creep strength of the 10% Cr steel is attributed to high threshold stress of 111.5 MPa. Threshold stress is associated with the detachment stress, i.e. the stress required for detachment of dislocations from M23C6 carbides after finishing the climb, mainly. Analysis of the pinning pressures exerted from different precipitates shows that M23C6 carbides also play the main role in preventing the lath boundary migration and therefore, provide high stability of the tempered martensite lath structure under creep conditions. Coarsening of the lath structure under long-term creep conditions is associated with growth of Laves phase particles, mainly.
#1I. Fedorova(DTU: Technical University of Denmark)H-Index: 1
#2Fang Liu(Chalmers University of Technology)H-Index: 18
Last. John Hald(DTU: Technical University of Denmark)H-Index: 22
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A 10Cr creep resistant martensitic steel with 108 ppm B was normalized at 1100 °C for 1 h and air cooled. Fine (Cr,Fe)2B borides were observed on the majority of prior austenite grain boundaries, all of which were high angle boundaries, as revealed by EBSD-based reconstruction of parent austenite grains. Some high angle boundaries including twin boundaries were boride-free. Segregation of boron to austenite grain boundaries during slow cooling from 1100 °C led to boride nucleation and growth. Th...
Abstract The effect of temperature on the impact toughness and fracture behavior of a 10% Cr-2% W-0.7% Mo-3% Co-0.05% Nb-0.2% V-0.008% B-0.003% N (all in wt%) steel was studied. The ductile-brittle transition (DBT) occurs at 10 °C. At the DBT temperature (DBTT), the onset of unstable crack propagation occurs at the maximum load. The embrittlement is attributed to the onset of unstable crack propagation at stresses below the general yielding. A decrease in nitrogen content and an increase in boro...
Abstract The creep behavior of a 3%Co modified P92-type steel with high content of boron and low content of nitrogen was studied. The precipitation of Laves phase at lath boundaries provides a rapid decrease in the strain rate during transient creep. The finely dispersed (V,Nb)(C,N) carbonitrides uniformly distributed throughout and M23C6 carbides located at various boundaries/subboundaries result in extended steady-state creep. Gradual coarsening and an increase in the volume fraction of M23C6 ...
Abstract A low-nitrogen 10% Cr martensitic steel containing 3% Co and 0.008% B was shown to exhibit an extremely long creep rupture time of ∼4·104 h under an applied stress of 120 MPa at 650 °C. The creep behavior and evolution of lath martensite structure and precipitates during creep at these conditions were studied. The main feature of the microstructure under long-term creep is retention of the lath structure until rupture. The following microstructural factors affecting the superior creep r...
The effect of increasing tungsten content from 2 to 3 wt % on the creep rupture strength of a 3 wt % Co-modified P92-type steel was studied. Creep tests were carried out at a temperature of 650 °C under applied stresses ranging from 100 to 220 MPa with a step of 20 MPa. It was found that an increase in W content from 2 to 3 wt % resulted in a +15% and +14% increase in the creep rupture strength in the short-term region (up to 103 h) and long-term one (up to 104 h), respectively. On the other han...
Microstructure evolution under long-term aging and creep was studied in a 9wt%Cr–3wt%Co–3wt%W martensitic steel at a temperature of 650 °C and stress ranging from 100 to 220 MPa with a step of 20 MPa. This steel exhibited creep strength breakdown at an applied stress of 160 MPa and a rupture time of 1703 h. However, this creep strength breakdown did not coincide with the transition from short-term creep conditions to long-term creep, because deviation from the Monkman–Grant relationship occurs a...
Abstract The microstructural evolution and the dispersion of secondary phases were studied in a low-nitrogen 10%Cr martensitic steel with 3% Co and 0.008% B additives at 650 °C under an applied stress of 140 MPa. It was demonstrated that the superior creep strength of this steel can be attributed to the high resistance of M 23 C 6 -type carbides and Nb-rich MX carbonitrides against coarsening, resulting in a stable of the tempered martensite lath structure (TMLS) under short-term creep condition...
Abstract The effect of tempering temperature on microstructure and mechanical properties was studied in a low-nitrogen, high-boron, 9%Cr steel. After normalizing and low-temperature tempering, cementite platelets precipitated within the martensitic matrix. This phase transformation has no distinct effect on mechanical properties. After tempering at 500 °C, M23C6 carbides appeared in the form of layers and particles with irregular shapes along the high-angle boundaries. Approximately, 6% of the r...
AbstractThe interactions between dislocations and lath boundaries in Grade 91 steel were observed by an in situ transmission electron microscopy tensile test at 973 K. Dislocations glided slowly and bowed out in a martensite lath interior. The ends of the dislocation were connected to the lath boundaries. In a tempered specimen, the pinning stress caused by the lath boundary was estimated to be >70 MPa with a lath width of 0.4 μm. In crept specimens, lath coarsening reduced the pinning effect.
Abstract null null Understanding the evolution of microstructure and micro-region properties of weldments during cyclic loading is a challenge for the reliability assessment of high-temperature components. This work is devoted to quantitatively evaluating the variation of micro-region properties and corresponding responsible microstructural features of P92 steel weldments under interrupted fatigue tests and subsequent creep fracture. To achieve this target, high-resolution characterization techn...
Abstract The coarsening of Laves phase in a Re-containing 10% Cr-3% Co-3% W steel during both creep and ageing at 923 K was investigated. The depletion of W solutes from the ferrite matrix is accompanied with the precipitation of Laves phase, wherein creep strain accelerates both these processes. The equilibrium W content in the ferritic matrix of 1.24 wt% and the volume fraction of Laves phase of 1.6% is reached after 500 h of creep and 1000 h of ageing. This is related to lower activation ener...
#2Andreas Leineweber(Freiberg University of Mining and Technology)H-Index: 25
Laves phases with their comparably simple crystal structure are very common intermetallic phases and can be formed from element combinations all over the periodic table resulting in a huge number of known examples. Even though this type of phases is known for almost 100 years, and although a lot of information on stability, structure, and properties has accumulated especially during the last about 20 years, systematic evaluation and rationalization of this information in particular as a function...
Abstract The Z-phase (CrVN) precipitation in a 9% Cr–3% Co martensitic steel during creep at 923 K and 948 K has been investigated with aim to establish the effect of temperature on the nucleation mechanism of these particles and their coarsening behavior. Ostwald ripening of VX carbonitrides strongly affects these processes. An increase in creep temperature significantly accelerates the transformation of the nanoscale MX carbonitrides into the Z-phase particles causing the Z-phase nucleation in...
Abstract The nucleation of the Laves phase particles in a Re-containing 10% wt. Cr-3% Co-3% W steel with a low nitrogen and a high boron contents during creep is characterized by distinctive features. The precipitation process can be written as M23C6 carbide → M6C carbide → Laves phase. The nucleation of all phases in this precipitation sequence is heterogeneous. The M23C6 carbides precipitate on the boundaries of martensitic structure during tempering at temperature of 770 °C. The M6C (Fe3W3C) ...
The kinetics of the growth of M23C6 carbide particles in 9% Cr martensitic steel with a high boron content is studied under conditions of long-term aging and creep. It is shown that the grain-boundary diffusion is a mechanism that controls the coarsening of these carbides during the aging. Deformation accelerates the coarsening of particles during creep, which can be explained by additional diffusion along dislocation lines.