Next Article in Journal
Influence of β-Stabilizing Nb on Phase Stability and Phase Transformation in Ti-Zr Shape Memory Alloys: From the Viewpoint of the First-Principles Calculation
Previous Article in Journal
Center-Punching Mechanical Clinching Process for Aluminum Alloy and Ultra-High-Strength Steel Sheets
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Metals
Volume 14
Issue 10
10.3390/met14101191
metals-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Microstructural Evolution of P92 Steel with Different Creep Life Consumptions After Long-Term Service

by
Zhen Zhang
1,2,
Zheyi Yang
1,* and
Liying Tang
1
1
Xi’an Thermal Power Research Institute Co., Ltd., Xi’an 710054, China
2
School of Mechanical and Power Engineering, Nanjing Tech University, Nanjing 211816, China
*
Author to whom correspondence should be addressed.
Metals 2024, 14(10), 1191; https://doi.org/10.3390/met14101191
Submission received: 11 September 2024 / Revised: 13 October 2024 / Accepted: 17 October 2024 / Published: 20 October 2024
Browse Figures
Versions Notes

Abstract

P92 steel is widely used in ultra-supercritical units due to its excellent high-temperature performance. This paper studies the microstructure of P92 steel steam pipes in three conditions: as-supplied, after 80,000 h of service at 67.06 MPa stress, and after 100,000 h of service at 80.28 MPa stress. After prolonged service, the P92 steel retains its martensitic structure, but the lath width increases and the dislocation density decreases. In addition to M23C6, MX, and Laves phases, Z phase was also observed among the precipitates. The results indicate that the sizes of M23C6 and Laves phases increase with the progression of creep life consumption, with the coarsening rate of Laves phase being significantly higher than that of M23C6. However, the coarsening of MX phase is not evident. Compared to the Laves phase, the formation of the Z phase requires a longer period of time. The precipitation of the Z phase consumes MX carbonitrides, and it has been observed that the Z phase precipitates from the MX phase, with the two phases exhibiting a coexisting state.

1. Introduction

Ultra-supercritical power generation technology improves the efficiency of power generation by increasing steam pressure and temperature, making it more efficient, environmentally friendly, and energy-saving compared to traditional thermal power generation methods [1,2]. P92 steel is a novel variety of steel with 9% Cr that was developed in Japan during the 1990s. It is a high-temperature martensitic steel developed by increasing W content, reducing Mo content, and adding B based on P91 steel composition. P92 steel exhibits excellent high-temperature creep properties, which has led to its widespread application in the critical components of ultra-supercritical units, such as main steam pipelines, headers, and reheat steam pipelines [3,4]. It is a key material for improving the thermal efficiency of power plants.
The creep mechanisms of alloys are influenced by factors such as their microstructure, environmental conditions, and chemical composition. According to studies, diffusion creep [5,6] occurs under low stress and high temperature, relying on the diffusion movement of atoms. At high temperatures, grain boundary sliding [7] also becomes a significant creep mechanism, wherein grains slide against each other, leading to overall deformation. Superplastic creep [7] occurs in fine-grained materials under high-temperature conditions. The accumulation of microvoids usually appears during the creep fracture stage [8], caused by the growth of internal microdefects during the creep process. The primary creep mechanisms in martensitic steel are glide and climb [9,10]. The microstructure of martensitic steel contains a high density of dislocations and precipitated carbides, which act as obstacles to dislocation movement. During creep, dislocations bypass these obstacles through the climb mechanism, leading to plastic deformation.
The exceptional performance of P92 steel primarily depends on its substructure. Its martensitic microstructure is composed of martensitic laths, blocks, and packets, containing a high density of dislocations and finely dispersed carbonitride particles [11,12]. One of the most important strengthening mechanisms in P92 steel is based on the martensitic laths that prevent dislocation movement [13]. Additionally, P92 steel benefits from multiple strengthening mechanisms, including solid solution strengthening, precipitation strengthening, and dislocation strengthening [14]. After prolonged service under high-temperature conditions, the microstructure and mechanical properties of P92 steel undergo changes. The coarsening of MX carbonitrides and M23C6 carbides, the nucleation and growth of the Laves phase, and the recovery of the martensitic lath structure can all contribute to the failure of P92 steel, thus affecting its service life [15]. Although some researchers have been able to explain these microstructural changes through the evolution of damage model parameters, their work has also indicated that these changes relate to a reduction in creep performance [16]. To improve material performance, extend service life, and ensure the safe operation of equipment, it is essential to understand the relationship between microstructure evolution and creep performance.
Many researchers have focused on studying the changes in material microstructure and properties, primarily through creep testing or aging simulation. These studies considered the effects of temperature, stress, and aging time on the microstructure and mechanical properties, as well as the relationship between microstructure and service life. Shang et al. [17] studied the microstructural evolution of P92 steel under different stress conditions and its impact on creep behavior through uniaxial creep tests. Zieliński et al. [18] investigated the degradation of the microstructure of P92 steel at different temperatures and its effect on mechanical properties through aging treatment. However, creep tests often require the application of higher stresses to accelerate the testing process, with selected stress levels significantly exceeding service stresses. Similarly, aging tests frequently raise the test temperature to accelerate material aging, which accelerates microstructural evolution and performance changes. Some researchers have pointed out that using these accelerated conditions to predict material changes during actual service may not ensure accuracy [19,20]. There is limited research on the long-term microstructural evolution of P92 steel under actual service conditions, and there is a lack of real-world data on the aging of the microstructure and the deterioration of creep performance after prolonged service.
This study is based on the main steam pipes of the first ultra-supercritical units commissioned in China after long-term service. The microstructure of P92 steel under different service conditions was characterized using optical microscopy (OM) and transmission electron microscopy (TEM). The evolution of the microstructure and its relationship with creep life loss are discussed.

2. Experimental Details

2.1. Experiment Material

The experimental materials used in this study were sourced from two sections of a main steam pipeline made of P92 steel, belonging to a 1000 MW ultra-supercritical unit in China’s first 1000 MW ultra-supercritical power plant, Huaneng Yuhuan Power Plant. Due to the overhaul of two units, we obtained samples of the main steam pipeline in two different service conditions. The pipeline samples were taken from the straight section of the main steam pipeline, which is subjected to radial pressure due to the action of steam. The service time and stress levels of the two pipelines differed. The first section of the main steam pipeline had an inner diameter of 349 mm and a wall thickness of 72 mm, and had been in service for 82,000 h (damage state 1). The macroscopic image of the sampling pipe is shown in Figure 1b. The second section of the main steam pipeline had an inner diameter of 559 mm and a wall thickness of 95 mm, and had been in service for 100,000 h (damage state 2). The macroscopic image of the sampling pipe is shown in Figure 1c. Both sections of the pipeline operated under an internal pressure of 27.46 MPa and a temperature of 605 °C. The manufacturer of the pipeline was PCC (formerly Wyman-Gordon) from Worcester, MA, USA. The internal pressures of the two steam pipelines, converted to equivalent stresses, were 67.06 MPa and 80.28 MPa, respectively. The chemical composition of the P92 steel in the two conditions is shown in Table 1. In addition, P92 steel from the same manufacturer, in its as-supplied state, was also selected as experimental material. The as-supplied steel was normalized at 1050 °C for 4 h, then air cooled, followed by tempering at 760 °C for 6 h.

2.2. Experiment Procedure

The required material for specimen preparation was removed from the pipe samples using sawing and wire cutting methods. During sampling, areas within 100 mm from both ends of the pipe samples and areas near the burst opening were avoided to prevent the influence of end restraint and excessive deformation on the material’s creep damage. Both metallographic and TEM samples were taken from longitudinal sections in the middle of the wall thickness direction of the pipe parent material. The metallographic samples were mechanically ground and polished, then etched in a solution of 50 mL hydrochloric acid, 100 mL water, and 5 g ferric chloride. The microstructure was then observed using a ZEISS LSM700 optical manufactured in Oberkochen, Germany. The samples for TEM observation were prepared by cutting metal plates to a thickness of approximately 5 mm using wire cutting methods. These plates were then ground with sandpaper to a thickness of about 5 µm. The thinning process combined electrolytic double-jet thinning and ion thinning techniques. Electrolytic double-jet thinning was performed using a FISCHIONE magnetic-driven double-jet electro-thinner (manufactured in Export, PA, USA) with a solution of 5% perchloric acid in anhydrous ethanol, operating at a voltage of 31–40 V and a temperature below −20 °C. The ion thinning was carried out using a GATAN 691 model instrument from Pleasanton, CA, USA. The martensitic lath width, subgrain size, and the size of various precipitates were all measured using TEM (JEOL Ltd., Tokyo, Japan). In addition, TEM is a commonly used method for directly observing the dislocation structure of a material’s microstructure. High-resolution images of dislocations within the material were obtained through TEM, and dislocation density was calculated based on these images.

3. Results

3.1. The Microstructure Observed Under the OM

Figure 2 shows the OM images of P92 steel under different creep life consumptions. Figure 2a depicts the as-supplied state of P92 steel, where the typical tempered martensitic lath structure is uniformly distributed throughout the matrix, which is one of the key microstructural features of P92 steel. The laths are densely packed, with no obvious blocky ferrite or banded δ-ferrite phases present. Figure 1c and Figure 2b represent P92 steel under damage state 1 and damage state 2, respectively. The microstructure remains a martensitic lath structure, with precipitates dispersed throughout the material. No significant martensite lath degradation was observed, and no creep voids appeared, reflecting the stability of the martensitic organization of P92 steel in the long-term high-temperature service condition. However, the width of the martensitic laths and the specific distribution of carbides are difficult to discern using optical metallography alone. Therefore, assessing the material’s aging state based solely on optical images presents certain challenges.

3.2. The Microstructure Observed Under the TEM

Figure 3 presents TEM images of P92 steel in the as-supplied state. Figure 3a,b display the microstructure of P92 steel with no life depletion. At this stage, the martensitic laths are clearly defined with an average width of 486 nm. M23C6 carbides with an average size of 134 nm are observed at the prior austenite grain boundaries and martensitic lath boundaries. Fine MX carbonitrides, averaging 77 nm in size, are found within the martensitic laths, at dislocation sites, and along subgrain boundaries. Both M23C6 and MX serve a pinning function, with their pinning effects delaying the motion of dislocations as well as the migration of laths and subgrain boundaries. This pinning mechanism plays a critical role in enhancing the long-term creep strength of martensite steel. At this stage, the dislocation density is high, approximately 1 × 1010 cm−2, with a significant amount of dislocation entanglement present. The selected area electron diffraction (SAED) patterns for M23C6 and MX are shown in Figure 3b.
Figure 4a,b show the microstructure of P92 steel under damage state 1. Compared to the as-supplied condition, although most of the lath structures in the P92 steel after service maintain their regular shape, some martensitic laths have started to recover, with areas showing polygonal shapes. At this stage, the average martensitic lath width slightly increases to 510 nm. The dislocation density decreases to 5 × 109 cm−2, with localized formation of dislocation networks. The size of M23C6 carbides significantly increases compared to the as-supplied state, reaching 342 nm, while the MX phase shows minimal changes, with its average size increasing slightly to 109 nm. Additionally, Laves phase particles appear. These Laves phases are primarily located at lath boundaries and near M23C6 carbides, with an average size of 339 nm. It is evident that Laves phase forms after M23C6 carbides in the steel, and since the size of the two phases is similar at this stage, the growth rate of Laves phase must be higher than that of M23C6 carbides. Figure 4b shows the SAED patterns of Laves, M23C6, and MX phases under damage state 1.
Figure 5 shows the microstructure of P92 steel under damage state 2. Due to the recovery of dislocations in the martensitic structure during high-temperature creep, the dislocation density decreases, ultimately leading to the formation of a polygonized grain structure. In this process, the originally dense martensitic lath structure is gradually replaced by more stable equiaxed grains, with large areas transforming into a polygonized structure. At this stage, the average width of the martensitic laths increases to 594 nm. The dislocation density further decreases to 3.5 × 109 cm−2, with dislocation entanglement eliminated and dislocations becoming more regularly arranged, forming dislocation walls. The M23C6 phase shows no significant change, with an average size of 339 nm. The Laves phase continues to grow, with a slight increase in size to 386 nm.
The average size of the MX phase is 113 nm with no significant change, but its quantity has decreased. This may be due to the fact that, after long-term service at high temperatures, some carbides and nitrides in the MX phase gradually dissolve back into the matrix, leading to a reduction in the amount of precipitates. Figure 6a shows the MX phase under damage state 2. In addition, Z phase precipitates were observed in the microstructure under this condition, as shown in Figure 7a. Clearly, the formation of the Z phase requires a longer time compared to the Laves phase. We observed that Z phase precipitates from the MX phase, and in the images, the Z phase is still surrounded by the MX phase. The growth of the Z phase is accompanied by the consumption of the MX phase, which is also a significant reason for the reduction in the amount of MX phase. At this stage, the Z phase and MX phase coexist, with the Z phase gradually precipitating while the MX phase has not yet fully transformed into the Z phase. Figure 7c,d show the SAED patterns of the MX and Z phases, respectively.

4. Discussion

We observed martensitic laths in P92 steel under different conditions. From the results above, it can be observed that with increased creep life consumption, although OM results indicate that the martensitic laths exhibit a certain degree of stability, TEM results show a gradual coarsening of the martensitic laths. The size changes are illustrated in Figure 8a. The lath strengthening, based on the martensitic lath structure, effectively impedes dislocation movement, and smaller lath sizes provide improved strengthening effects, making this one of the key strengthening mechanisms for P92 steel [13,21]. Martensitic lath widening currently occurs through two mechanisms [22,23,24]: “Y”-type lath boundary migration and the merging of parallel lath boundaries. The “Y”-type lath boundary migration mechanism refers to the movement of “Y”-type interfaces of martensitic laths under the influence of temperature and stress, leading to lath widening. The parallel lath boundary merging mechanism involves mobile dislocations within parallel laths moving to the lath boundaries, where they cancel out opposite-sign dislocations at the interfaces. This causes the interfaces between parallel laths to disappear gradually, resulting in lath widening. The increase in lath width, accompanied by recovery, leads to a decrease in the strengthening effect of the laths.
The microscopic structure of creep deformation originates from the migration of dislocations and subgrain boundaries [25,26]. Dislocations are a critical microstructural feature in high-chromium heat-resistant steels. The movement and recovery of dislocations are closely related to creep strength. At high temperatures, the lattice resistance to dislocation slip and energy consumption decrease, facilitating dislocation movement and grain boundary migration, thereby promoting grain coarsening [27]. During the creep process of P92 steel, dislocations continuously slip and are absorbed by the boundaries, leading to a reduction in dislocation density, as shown in Figure 8b. In as-supplied P92 steel, the dislocation density is 1 × 1010 cm−2. This density rapidly decreases to 5 × 109 cm−2 in damage state 1 and further reduces to 3.5 × 109 cm−2 in damage state 2.
Subgrain boundaries are typically formed by low-energy dislocation networks. Subgrains obstruct dislocation movement, affecting dislocation density. As shown in Figure 3, a large number of free dislocations with high density are present within the subgrains in the as-supplied state and they are entangled with each other, creating significant resistance to dislocation movement. The dislocation network at subgrain boundaries has low energy, making dislocation movement difficult [28]. Subgrain boundaries reduce internal stress by accumulating dislocations. As creep life degradation increases, subgrain boundaries gradually migrate and reorganize, leading to an increase in subgrain size. The subgrain sizes under different creep life consumptions are shown in Figure 8c.
The M23C6 phase is an important precipitate in P92 steel, primarily composed of Cr and C, and has a complex cubic crystal structure. They tend to precipitate and grow more readily at high temperatures. M23C6 carbonitrides act as pinning agents at boundaries, impeding dislocation slip and recovery, and play a crucial role in controlling grain boundary coarsening [29]. With increasing creep life consumption, M23C6 carbonitrides coarsen due to the Ostwald ripening mechanism, with smaller particles gradually dissolving while larger particles continue to grow [30], as demonstrated by the size changes in Figure 9. This coarsening reduces the pinning effect of M23C6 phases on dislocations, accelerating the broadening of laths or blocky structures and their evolution into subgrains, leading to a loss of subgrain boundary hardening [15].
As shown in Figure 3, no Laves phases were observed in the as-supplied P92 steel. After a period of service, the Laves phase gradually precipitates. In damage state 1, the size of the Laves phases approaches that of the M23C6 phases. By damage state 2, the size of the Laves phases exceeds that of the M23C6 phases, as shown in Figure 9. Clearly, the growth rate of the Laves phases is significantly faster than that of the M23C6 phases. The likely reason for this is that the growth of Laves phases primarily occurs via grain boundary diffusion mechanisms [31]. Compared to within the crystal lattice, the activation energy required for atoms to diffuse along grain boundaries is lower. As creep progresses, smaller Laves phase particles are more easily dissolved, leading to the accumulation of alloying elements at grain boundaries or other interfaces, which promotes the growth of Laves phase particles. In contrast, the growth of M23C6 phases relies mainly on volume diffusion mechanisms. The activation energy for volume diffusion is much higher than that for grain boundary diffusion, making the diffusion of alloying elements within the crystal lattice more difficult [30,32].
The Laves phase has two growth mechanisms [33,34]: one is independent nucleation, which does not rely on M23C6 carbides; the other is dependent nucleation, where the Laves phase nucleates near M23C6 carbides and directly consumes adjacent M23C6 carbides. The consumption process preferentially occurs along the M23C6 carbide or ferrite interfaces and then gradually extends toward the center of the M23C6 carbide, because the Si and P elements present on the surface of the M23C6 carbides or ferrite promote the formation of the Laves phase. In P92 steel, the Laves phase typically exists in the form of Fe2W and Fe2Mo, where W and Mo, as the primary alloying elements, diffuse at high temperatures and combine with iron to form the Laves phase. As the Laves phase precipitates and grows, W elements gradually accumulate from the matrix to the grain boundaries and form Laves phases. This process leads to a decrease in the concentration of W elements in the matrix, thereby weakening the precipitation strengthening effect of W elements on the matrix [35]. Small Laves phase particles produce significant precipitation strengthening effects in the early stages of precipitation, while larger Laves phases that precipitate at grain boundaries can cause grain boundary embrittlement, affecting ductility, toughness, and creep resistance, which adversely impacts material performance. Under external forces, strain concentration occurs in the matrix near large Laves particles, serving as nucleation sites for voids, ultimately leading to a decrease in creep performance. Grain coarsening of Laves phases is a key factor in the cracking of P92 steel, with microcracks often initiating near Laves particles and subsequently propagating into the matrix, eventually forming macrocracks [36].
MX carbonitrides are among the most stable precipitates in P92 steel, and their size changes under different damage states are shown in Figure 9. They are primarily composed of V and Nb, precipitating in the form of fine, small particles with very high resistance to coarsening and a slow coarsening rate at high temperatures [37]. Although some coarsening of MX phases occurs during long-term service, their thermal stability allows them to maintain significant strengthening effects during high-temperature applications. These fine MX precipitates along the lath boundaries hinder the migration of grain boundaries and dislocations during prolonged creep. With increasing creep life consumption, MX phase transforms into Z phase and is consumed.
In damage state 2, Z phase, which is a relatively stable nitride, precipitates. MX carbonitrides are preferred nucleation sites for Z phase because they have a semi-coherent interface, which reduces the interfacial energy [15]. The Z phase nucleates on existing MX particles by the diffusion of Cr from the matrix into MX [38]. Once Z phase particles nucleate, they can grow rapidly by consuming adjacent MX carbonitrides. During the transformation from MX to Z phase, the MX phase gradually disappears, followed by the formation of a new phase with an irregular M2N lattice structure, due to the entry of Fe and Cr into the VX phase, and finally, the MX phase evolves into the Z phase with a regular M2N lattice structure [39]. Cr is a very important element influencing the precipitation of the Z phase. In 9% Cr steel, Z phase appears only after prolonged service due to its lower Cr content. For steels with a Cr content of 11–12%, Z phase precipitation and complete dissolution of MX can occur within a few thousand hours at 650 °C. In 9% Cr steel, Z phase precipitation begins only after 30,000–40,000 h at 650 °C [26]. After the Z phase precipitates, it grows rapidly and consumes the MX phase, which reduces the dispersion strengthening effect of MX but does not promote precipitation strengthening. Therefore, the precipitation of Z phase may be detrimental to the creep performance of P92 steel [40].
Based on the above results and discussion, glide and climb remain the primary creep mechanisms in the in-service P92 steel, and the evolution of the microstructure affects the material’s creep performance. This is consistent with the mechanisms primarily observed in the experimental studies mentioned at the beginning.

5. Conclusions

In summary, this study investigated the microstructural evolution of P92 steel in three states: as-supplied; after 80,000 h of service at 605 °C and 67.06 MPa; and after 100,000 h of service at 605 °C and 80.28 MPa. The impact of microstructure on creep behavior was also discussed. The main conclusions are summarized as follows:
(1)
P92 steel retains a martensitic lath structure even after extended service, but with increasing creep life consumption, the width of the martensitic laths and the subgrain size gradually increase and the dislocation density decreases.
(2)
In the as-supplied state, P92 steel precipitates mainly consist of M23C6 and MX phases. With increased creep life consumption, Laves and Z phases precipitate sequentially. The size of M23C6 and Laves phases gradually increases, while the MX phase shows little change.
(3)
At 605 °C and 80.28 MPa, after 100,000 h of service, P92 steel exhibits precipitation of the Z phase. The precipitation of the Z phase consumes the MX phase, and at this stage, the Z phase is relatively small and coexists with the MX phase.

Author Contributions

Conceptualization, Z.Z. and Z.Y.; methodology, Z.Z.; validation, L.T.; resources, Z.Y.; data curation, L.T.; writing—original draft preparation, Z.Z.; writing—review and editing, Z.Y.; funding acquisition, Z.Y. All authors have read and agreed to the published version of the manuscript.

Funding

The authors gratefully acknowledge the financial support of the National Natural Science Foundation of China (No. 52101001).

Data Availability Statement

The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.

Conflicts of Interest

Author Zheyi Yang and Liying Tang were employed by the company Xi’an Thermal Power Research Institute Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

  1. Fan, H.; Zhang, Z.; Dong, J.; Xu, W. China’s R&D of Advanced Ultra-Supercritical Coal-Fired Power Generation for Addressing Climate Change. Therm. Sci. Eng. Prog. 2018, 5, 364–371. [Google Scholar] [CrossRef]
  2. Masuyama, F. Advances in Physical Metallurgy and Processing of Steels. History of Power Plants and Progress in Heat Resistant Steels. ISIJ Int. 2001, 41, 612–625. [Google Scholar] [CrossRef]
  3. Zhang, Z.; Wang, X.; Li, Z.; Xia, X.; Chen, Y.; Zhang, T.; Zhang, H.; Yang, Z.; Zhang, X.; Gong, J. Machine Learning-Assisted Probabilistic Creep Life Assessment for High-Temperature Superheater Outlet Header Considering Material Uncertainty. Int. J. Press. Vessels Pip. 2024, 209, 105211. [Google Scholar] [CrossRef]
  4. Li, Y.; Hu, L.; Yan, J.; Ji, X.; Wang, W. Effect of Structural Induced Stress on Creep of P92 Steel Pipe to Elbow Welds. Metals 2022, 12, 1792. [Google Scholar] [CrossRef]
  5. Langdon, T.G. Identifiying Creep Mechanisms at Low Stresses. Mater. Sci. Eng. A 2000, 283, 266–273. [Google Scholar] [CrossRef]
  6. Ashby, M.F. Boundary Defects, and Atomistic Aspects of Boundary Sliding and Diffusional Creep. Surf. Sci. 1972, 31, 498–542. [Google Scholar] [CrossRef]
  7. Gifkins, R.C. Grain-Boundary Sliding and Its Accommodation during Creep and Superplasticity. Metall. Trans. A 1976, 7, 1225–1232. [Google Scholar] [CrossRef]
  8. Cocks, A.C.F.; Ashby, M.F. On Creep Fracture by Void Growth. Prog. Mater. Sci. 1982, 27, 189–244. [Google Scholar] [CrossRef]
  9. Zhao, J.; Gong, J.; Saboo, A.; Dunand, D.C.; Olson, G.B. Dislocation-Based Modeling of Long-Term Creep Behaviors of Grade 91 Steels. Acta Mater. 2018, 149, 19–28. [Google Scholar] [CrossRef]
  10. Xiao, B.; Xu, L.; Zhao, L.; Jing, H.; Han, Y. Deformation-Mechanism-Based Creep Model and Damage Mechanism of G115 Steel over a Wide Stress Range. Mater. Sci. Eng. A 2019, 743, 280–293. [Google Scholar] [CrossRef]
  11. Abe, F. Precipitate Design for Creep Strengthening of 9% Cr Tempered Martensitic Steel for Ultra-Supercritical Power Plants. Sci. Technol. Adv. Mater. 2008, 9, 013002. [Google Scholar] [CrossRef] [PubMed]
  12. Hald, J.; Korcakova, L. Precipitate Stability in Creep Resistant Ferritic Steels-Experimental Investigations and Modelling. ISIJ Int. 2003, 43, 420–427. [Google Scholar] [CrossRef]
  13. Jin, X.; Zhu, B.; Li, Y.; Zhao, Y.; Xue, F.; Zhang, G. Effect of the Microstructure Evolution on the High-Temperature Strength of P92 Heat-Resistant Steel for Different Service Times. Int. J. Press. Vessels Pip. 2020, 186, 104131. [Google Scholar] [CrossRef]
  14. Maruyama, K.; Sawada, K.; Koike, J. Advances in Physical Metallurgy and Processing of Steels. Strengthening Mechanisms of Creep Resistant Tempered Martensitic Steel. ISIJ Int. 2001, 41, 641–653. [Google Scholar] [CrossRef]
  15. Zeng, Y.; Jia, J.; Cai, W.; Dong, S.; Wang, Z. Effect of Long-Term Service on the Precipitates in P92 Steel. Int. J. Miner. Metall. Mater. 2018, 25, 913–921. [Google Scholar] [CrossRef]
  16. Lombardi, P.; Cipolla, L.; Folgarait, P.; Bonora, N.; Esposito, L. New Time-Independent Formulation for Creep Damage in Polycrystalline Metals and Its Specialisation to High Alloy Steel for High-Temperature Applications. Mater. Sci. Eng. A 2009, 510–511, 214–218. [Google Scholar] [CrossRef]
  17. Shang, C.G.; Wang, M.L.; Zhou, Z.C.; Yagi, K.; Lu, Y.H. The Microstructure Evolution and Its Effect on Creep Behaviors in P92 Steel under Different Stresses. Mater. Charact. 2023, 198, 112744. [Google Scholar] [CrossRef]
  18. Zieliński, A.; Golański, G.; Sroka, M. Assessment of Microstructure Stability and Mechanical Properties of X10CrWMoVNb9-2 (P92) Steel after Long-Term Thermal Ageing for High-Temperature Applications. Met. Mater. 2016, 54, 61–70. [Google Scholar] [CrossRef]
  19. Yong, L.; Jiaqing, W.; Junjian, L.; Yue, W.; Wen, F. Microstructure and Mechanical Property Changes of P92 Steel for Main Steam Pipe in Ultra-Supercritical Power Plant After Long-Term Service at High Temperature. J. Mater. Eng. Perform. 2024, 33, 4911–4919. [Google Scholar] [CrossRef]
  20. Liu, C.; Peng, Z.F.; Peng, F.F.; Chen, F.; Liu, S. Phase Parameter Changes of Specific Positions of P92 Steel Specimens during Creep Rupture Test at 625 °C. J. Mater. Eng. 2020, 48, 98–104. [Google Scholar]
  21. Yang, M.; Long, S.; Liang, Y. Study on the Key Role of Hierarchical Microstructure for Strength and Plasticity in a Lath Martensitic Steel. IOP Conf. Ser. Mater. Sci. Eng. 2018, 324, 012043. [Google Scholar] [CrossRef]
  22. Zhang, Y.; He, H.; Wang, H.; Chen, G.; An, X.; Wang, Y. Evolution of Microstructure and Mechanical Properties of 9Cr Ferrite/Martensite Steels with Different Si Content after Long-Term Aging at 550 °C. J. Alloys Compd. 2021, 873, 159817. [Google Scholar] [CrossRef]
  23. Xu, Y.; Nie, Y.; Wang, M.; Li, W.; Jin, X. The Effect of Microstructure Evolution on the Mechanical Properties of Martensite Ferritic Steel during Long-Term Aging. Acta Mater. 2017, 131, 110–122. [Google Scholar] [CrossRef]
  24. Morsdorf, L.; Jeannin, O.; Barbier, D.; Mitsuhara, M.; Raabe, D.; Tasan, C.C. Multiple Mechanisms of Lath Martensite Plasticity. Acta Mater. 2016, 121, 202–214. [Google Scholar] [CrossRef]
  25. Polcik, P. Modellierung Des Verformungsverhaltens Der Warmfesten 9–12%-Chromstähle Im Temperaturbereich von 550–650 °C.; Shaker: Nordrhein-Westfalen, Germany, 1999. [Google Scholar]
  26. Hald, J. Microstructure and Long-Term Creep Properties of 9–12% Cr Steels. Int. J. Press. Vessels Pip. 2008, 85, 30–37. [Google Scholar] [CrossRef]
  27. Zhao, Y.; Liu, K.; Zhang, H.; Tian, X.; Jiang, Q.; Murugadoss, V.; Hou, H. Dislocation Motion in Plastic Deformation of Nano Polycrystalline Metal Materials: A Phase Field Crystal Method Study. Adv. Compos. Hybrid Mater. 2022, 5, 2546–2556. [Google Scholar] [CrossRef]
  28. Ghassemi-Armaki, H.; Chen, R.P.; Maruyama, K.; Yoshizawa, M.; Igarashi, M. Static Recovery of Tempered Lath Martensite Microstructures during Long-Term Aging in 9–12% Cr Heat Resistant Steels. Mater. Lett. 2009, 63, 2423–2425. [Google Scholar] [CrossRef]
  29. Wang, X.; Xu, Q.; Yu, S.; Hu, L.; Liu, H.; Ren, Y. Laves-Phase Evolution during Aging in 9Cr-1.8W-0.5Mo-VNb Steel for USC Power Plants. Mater. Chem. Phys. 2015, 163, 219–228. [Google Scholar] [CrossRef]
  30. Xinmei, L.; Zhang, Z.; Zou, Y.; Baoshuai, D.; Wei, Y.; Yin, Z. Microstructure of P92 Steel for Main Steam Pipeline of Ultra Supercritical Units after 50,000 h Service. IOP Conf. Ser. Earth Environ. Sci. 2019, 358, 042021. [Google Scholar] [CrossRef]
  31. Jin, X.; Zhou, L.; Xi, Y.; Fu, Y.; Zhu, B.; Li, Y.; Zhao, Y.; Xia, X. Comparative Study on Microstructure and Properties of P92 Steel After Long-term Service. Proc. CSEE 2023, 43, 8378–8388. [Google Scholar] [CrossRef]
  32. Jin, X.; Zhu, B.Y.; Xia, X.X.; Li, Y.F.; Liu, X.B.; Zhang, Y.W.; Xu, C.L.; Yin, J.; Jia, W.Q. Study on the Microstructure Evolution and Effect on Mechanical Properties of P92 Steel during Long Term Service. Materialia 2024, 35, 102124. [Google Scholar] [CrossRef]
  33. Yin, S.; Yang, L.; Liu, Y.; Yang, R.; Wang, Y.; Zhao, F. Stabilities of the Precipitates in CLAM Steel during 30,000 h Thermal Aging. J. Nucl. Mater. 2022, 567, 153805. [Google Scholar] [CrossRef]
  34. Prat, O.; Garcia, J.; Rojas, D.; Sauthoff, G.; Inden, G. The Role of Laves Phase on Microstructure Evolution and Creep Strength of Novel 9%Cr Heat Resistant Steels. Intermetallics 2013, 32, 362–372. [Google Scholar] [CrossRef]
  35. Xinjun, J.; Zhiqiang, S.; Chunpo, T.; Yao, X.; Long, Z.; Shaohua, Y.; Zhongbing, C. Analysis on the Microstructure and Properties of P92 Steel after Long-Term Service at High Temperature. J. Phys. Conf. Ser. 2020, 1653, 012009. [Google Scholar] [CrossRef]
  36. Komazaki, S.; Kishi, S.; Shoji, T.; Chiba, H.; Suzuki, K. Thermal Aging Embrittlement of Tungsten-Alloyed 9%Cr Ferritic Steels and Electrochemical Evaluation. J. Soc. Mater. Sci. Jpn. 2003, 52, 42–49. [Google Scholar] [CrossRef]
  37. Guo, X.; Gong, J.; Jiang, Y.; Rong, D. The Influence of Long-Term Aging on Microstructures and Static Mechanical Properties of P92 Steel at Room Temperature. Mater. Sci. Eng. A 2013, 564, 199–205. [Google Scholar] [CrossRef]
  38. Cipolla, L.; Danielsen, H.K.; Venditti, D.; Di Nunzio, P.E.; Hald, J.; Somers, M.A.J. Conversion of MX Nitrides to Z-Phase in a Martensitic 12% Cr Steel. Acta Mater. 2010, 58, 669–679. [Google Scholar] [CrossRef]
  39. Yoshizawa, M.; Igarashi, M.; Moriguchi, K.; Iseda, A.; Armaki, H.G.; Maruyama, K. Effect of Precipitates on Long-Term Creep Deformation Properties of P92 and P122 Type Advanced Ferritic Steels for USC Power Plants. Mater. Sci. Eng. A 2009, 510–511, 162–168. [Google Scholar] [CrossRef]
  40. Sawada, K.; Kushima, H.; Kimura, K. Z-Phase Formation during Creep and Aging in 9–12% Cr Heat Resistant Steels. ISIJ Int. 2006, 46, 769–775. [Google Scholar] [CrossRef]
Metals 14 01191 g001
Figure 1. (a) Pipe sampling site; (b) pipe sample in damage condition 1; (c) pipe sample in damage condition 2.
Figure 1. (a) Pipe sampling site; (b) pipe sample in damage condition 1; (c) pipe sample in damage condition 2.
Metals 14 01191 g001
Metals 14 01191 g002
Figure 2. OM images of P92 steel under different conditions: (a) as-supplied state; (b) damage state 1; (c) damage state 2.
Figure 2. OM images of P92 steel under different conditions: (a) as-supplied state; (b) damage state 1; (c) damage state 2.
Metals 14 01191 g002
Metals 14 01191 g003
Figure 3. (a,b) The microstructural morphology of as-supplied P92 steel.
Figure 3. (a,b) The microstructural morphology of as-supplied P92 steel.
Metals 14 01191 g003
Metals 14 01191 g004
Figure 4. (a,b) The microstructural morphology of P92 steel under damage state 1.
Figure 4. (a,b) The microstructural morphology of P92 steel under damage state 1.
Metals 14 01191 g004
Metals 14 01191 g005
Figure 5. The microstructural morphology of P92 steel under damage state 2: (a) TEM image; (b) SAED pattern of the Laves phase; (c) SAED pattern of the M23C6 phase.
Figure 5. The microstructural morphology of P92 steel under damage state 2: (a) TEM image; (b) SAED pattern of the Laves phase; (c) SAED pattern of the M23C6 phase.
Metals 14 01191 g005
Metals 14 01191 g006
Figure 6. (a) The MX phase under damage state 2; (b) the SAED pattern of the MX phase.
Figure 6. (a) The MX phase under damage state 2; (b) the SAED pattern of the MX phase.
Metals 14 01191 g006
Metals 14 01191 g007
Figure 7. The microstructural morphology under damage state 2: (a,b) Z phase precipitating from the MX phase; (c) SAED pattern of the MX phase; (d) SAED pattern of the Z phase.
Figure 7. The microstructural morphology under damage state 2: (a,b) Z phase precipitating from the MX phase; (c) SAED pattern of the MX phase; (d) SAED pattern of the Z phase.
Metals 14 01191 g007
Metals 14 01191 g008
Figure 8. Microstructural changes with different life consumptions: (a) martensite lath width; (b) dislocation density; (c) subgrain size.
Figure 8. Microstructural changes with different life consumptions: (a) martensite lath width; (b) dislocation density; (c) subgrain size.
Metals 14 01191 g008
Metals 14 01191 g009
Figure 9. Variation in precipitate size with different creep life consumptions.
Figure 9. Variation in precipitate size with different creep life consumptions.
Metals 14 01191 g009
Table 1. Chemical composition of the P92 steel.
Table 1. Chemical composition of the P92 steel.
ElementCSiMnPSCrNiMoCuVTiNbAlBWZrN
State 10.0960.420.470.0110.0018.690.250.370.160.21<0.0050.0580.030.00251.77<0.010.039
State 20.0950.290.470.0130.0148.880.370.380.160.18<0.0050.0570.00530.00551.68<0.0050.048
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Zhang, Z.; Yang, Z.; Tang, L. Microstructural Evolution of P92 Steel with Different Creep Life Consumptions After Long-Term Service. Metals 2024, 14, 1191. https://doi.org/10.3390/met14101191

AMA Style

Zhang Z, Yang Z, Tang L. Microstructural Evolution of P92 Steel with Different Creep Life Consumptions After Long-Term Service. Metals. 2024; 14(10):1191. https://doi.org/10.3390/met14101191

Chicago/Turabian Style

Zhang, Zhen, Zheyi Yang, and Liying Tang. 2024. "Microstructural Evolution of P92 Steel with Different Creep Life Consumptions After Long-Term Service" Metals 14, no. 10: 1191. https://doi.org/10.3390/met14101191

APA Style

Zhang, Z., Yang, Z., & Tang, L. (2024). Microstructural Evolution of P92 Steel with Different Creep Life Consumptions After Long-Term Service. Metals, 14(10), 1191. https://doi.org/10.3390/met14101191

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop