P92 Heat-resistant Steel Research Articles

Cooling Rate Dependency of Retained δ-Ferrite in the Coarse-Grained Heat-Affected Zone of P92 Heat-Resistant Steel

Cooling Rate Dependency of Retained δ-Ferrite in the Coarse-Grained Heat-Affected Zone of P92 Heat-Resistant Steel

Study on the microstructure evolution and effect on mechanical properties of P92 steel during long term service

P92 heat-resistant steel is widely utilized in ultra-supercritical units due to its exceptional properties. This study examines the microstructure evolution and mechanical properties change of P92 during service spanning 0 to 93,000 h, while also exploring the correlation between microstructure changes and property variations. The results indicate that the matrix of P92 steel retains its characteristic tempered martensite structure, and the large-angle and small-angle grain boundaries in the steel remain nearly unchanged throughout extended service periods. However, the deterioration of P92 steel properties can mainly be attributed to alterations in precipitate size and martensitic lath width. The size of M23C6 and Laves particles increased from their initial dimensions of 150 nm and 0 nm to 260 nm and 370 nm, respectively. Moreover, the width of the martensitic lath increased from 350 nm to 700 nm. The martensitic lath contributes over 60 % of the theoretical tensile strength, playing a pivotal role in the exceptional strength of P92 steel during service. The presence of coarse Laves particles at the interface leads to a rapid reduction in impact energy, decreasing from approximately 130 J to 50 J, negatively affecting the impact energy of P92 steel.

δ-Ferrite Retention in the Weld Metal of P92 Heat-Resistant Steel Treated by CaF2–Cr2O3 Fluxes

δ-Ferrite Retention in the Weld Metal of P92 Heat-Resistant Steel Treated by CaF2–Cr2O3 Fluxes

Effect of Post-weld Heat Treatment on Microstructure and Mechanical Properties of P91 Heat-Resistant Steel Coating on Mild Steel

Effect of Post-weld Heat Treatment on Microstructure and Mechanical Properties of P91 Heat-Resistant Steel Coating on Mild Steel

Investigation of Grain Misorientation on Creep Void Nucleation in P91 Heat-Resistant Steel by Experimentation and Crystal Plasticity Simulation

Investigation of Grain Misorientation on Creep Void Nucleation in P91 Heat-Resistant Steel by Experimentation and Crystal Plasticity Simulation

Exploring Cr and O Transfer Mechanisms in the Weld Metal of P92 Heat-Resistant Steel Processed by CaF2-Cr2O3 Fluxes

Exploring Cr and O Transfer Mechanisms in the Weld Metal of P92 Heat-Resistant Steel Processed by CaF2-Cr2O3 Fluxes

Cascading phase transformations in situ for the simulated coarse-grained heat-affected zone of P92 heat-resistant steel

Cascading phase transformations in situ for the simulated coarse-grained heat-affected zone of P92 heat-resistant steel

Creep behavior and life prediction of P91 heat-resistant steel using modified Wilshire model

The reliable prediction of long-term creep life is of great importance in order to ensure the service safety of high-temperature components. In this work, the novel Wilshire-Cano-Stewart (WCS) relationships were introduced to model the creep behavior and predict the long-term creep life of P91 steel based on the short-term creep data. The accelerated creep experiments were firstly carried out at the temperature range of 580–620 °C, while the stresses varied from 135 to 200 MPa. According to the analyses of normalized-mean-squared error (NMSE) and mean logarithmic error (MLE), it demonstrated that the WCS model can express all the obtained creep data very well due to the average relative errors lower than 10%. Meanwhile, these values are much lower than those of traditional Time-Temperature-Parameter (TTP) models. In addition, the WCS model can provide the reasonable estimates of 200,000 h creep life with accelerated creep measurements lasting up to only 2000 h.

Effect of Annealing Time on Microstructure and Properties of P91 Heat Resistant Steel SMAW Joint

The microstructure and properties of shielded metal arc welding (SMAW) joint of P91 heat-resistant steel annealed at different holding time were observed and analyzed. The results show that the martensite and residual austenite structures in the weld zone and coarse grain heat affected zone (CGHAZ) were transformed with the extension of holding time. After 760°C+4h annealing, a large number of white rod-shaped precipitates appeared in the weld zone. The main components of precipitates were Fe, Cr, Mn, V, Si, and a small amount of oxides appeared. After 760°C+5h annealing treatment, relatively fine white granular precipitation appeared in the weld zone, and a large number of oxides and some precipitates have been dissolved. After 760°C+6h annealing treatment, the precipitated phases were composed of Fe-Cr, Fe3Si, Ni-Cr-Fe, Fe2MnAl. Compared with the annealing treatment for 5h, the microstructure of the precipitated phase is fine and uniform, dispersion distribution of second phase particles, and the material mechanics is relatively stable.

Simulation of crystal plasticity of P92 heat resistant steel considering martensitic lath structure

Based on the theory of crystal plasticity, coupled with dislocation and lath hardening models, this paper establishes a crystal plasticity finite element model describing the high temperature creep of P92 steel. Open source software was used to generate lath models with an average size of 350nm, 650nm and 950nm to explore the effect of lath coarsening on the high-temperature creep behavior of P92 steel. The results show that the roughening of the slats increases the rate of creep deformation, resulting in a decrease in the service life of the material. Observing the slat model, it can be seen that the roughening of the slats enlarges the numerical gradient of stress and strain, and aggravates the overall plastic strain of the model. The coarsening of the slats accelerates the movement of dislocations, causing the density of movable dislocations to increase, and at the same time the shear strain amplitude of the slip system increases, thereby reducing the hardening behavior of the material.

Research Situation of Welding Performance for P92 Heat Resistant Steel

In this paper, the welding performance of P92 ferritic heat resistant steel in recent years was introduced. P92 steel was a ferritic/martensitic steel, which had been brought to commercial maturity during the last decade due to its excellent high temperature performances. However, the welding related problems of P92 steel was gradually exposed with the wide application, causing a serious impact on the production and operation of boiler unit. Therefore, Strengthening research and development of suitable welding process and post weld heat treatment process that can lead P92 heat-resistant steel to being better serve in the power industry for our country will be the focus of metal workers in the next step.

Microstructural evolution of P92 steel in IN740H/P92 dissimilar weld joints during creep deformation

In this study, we report the microstructural development of heat-affected zone in P92 heat-resistant steel during creep deformation in cross-weld specimens with dissimilar weld joints between IN740H/P92 materials. Different specimens were prepared via the interruption of creep testing at 50, 70, and 90% of the measured creep-rupture life and were carefully examined and compared. To explain the deformation behavior, finite element analysis was performed in conjunction with softening behavior measured by electron back-scattered diffraction and hardness mapping. The FGHAZ II region defined in this study could be related to the generally known inter-critical heat-affected zone, which showed major changes in microstructure during creep deformation due to the accelerated softening by dynamic recrystallization as well as to the development of a triaxial stress state. As a result, cavity formation and growth was observed only in the FGHAZ II region, which ultimately led to fracture.

Microstructure analysis of P91 heat resistant steel in service for 3 years

P91 heat resistant steel is an important material for supercritical units. In this paper, a P91 heat resistant steel pipe which has been used for about 3 years is analyzed by means of hot tensile test, metallography and scanning electron microscope. The results show that the microstructure is martensite and a large number of Cr-rich precipitates are distributed at the grain boundary. There are pores and cracks in the fracture of high temperature tensile specimen.

Influence of thermal ageing on creep rupture mechanism and creep life of P92 ferritic steel

In order to analyze the effect of thermal ageing on creep rupture mechanism and establish a method for predicting the creep rupture life of P92 heat-resistant steel under thermal ageing, creep tests were performed on P92 steel specimens, aged at 650 °C for different times under different applied stresses. Optical microscopy and scanning electron microscopy were utilized to observe the microstructure after thermal ageing and creep rupture. Voids and cracks were distributed in the grains of P92 steel before thermal ageing, whereas the voids were clearly distributed around M23C6 precipitates and Laves phase along sub-grain boundaries after thermal ageing. The creep damage tolerance factor of the unaged and short-time aged samples ranged from 2.5 to 5, and the creep rupture was caused by dislocation movement. After high-temperature thermal ageing for 3000 h, the damage tolerance factor increased to > 5 and creep rupture was caused by precipitate coarsening. A theoretical method was established to predict the creep rupture life of heat-resistant P92 steel under thermal ageing, providing consistent results with the American Society of Mechanical Engineers (ASME) long-term test and trend.

Effect of the microstructure evolution on the high-temperature strength of P92 heat-resistant steel for different service times

Grade 92 heat-resistant steel is an important material for ultra-supercritical units. The degradation of the P92 properties affects the safety of structural components during long-term service. In this paper, the microstructural evolution of P92 depending on different service times was quantitatively studied using scanning electron microscopy and transmission electron microscopy. The effect of each strengthening mechanism on the strength of P92 is discussed. The results show that the dimensions of M23C6 and Laves phases increase with increasing service time, but the growth rate of the Laves phase is higher than that of M23C6 and the size of MX carbonitrides remains almost unchanged. The width of the martensite lath increases from the initial 350 nm–750 nm after 70,000 h of service. The dislocation density significantly decreases and then stabilizes with increasing service time. The high- and room temperature tensile properties worsen and then stabilize during long-term service. The thermal yield stress of P92 during service was calculated. The results show that the high-temperature strength of P92 steel is mainly affected by lath and dislocation hardening during the initial service time; as the service time increases, the strengthening mechanism transforms into lath and precipitate hardening.

In Situ Observation of Phase Transformations in the Coarse-Grained Heat-Affected Zone of P91 Heat-Resistant Steel During Simulated Welding Process

The solid-state phase transformation in the coarse-grained heat-affected zone of P91 steel under simulated welding thermal cycle has been investigated in situ by confocal scanning laser microscope. It is found that γ-austenite initiates from the triple point of δ-ferrite grain boundaries (GBs), then at ordinary δ-GBs, and eventually from grain interiors. Upon further cooling, martensite laths are observed to nucleate and growth instantaneously, with the growth rate being estimated ranging from 175 to 454 μm/s.

Influence of long-term thermal ageing (＞10,000h) on low stress creep deformation of P92 heat-resistant steels

ABSTRACTMicrostructure evolution of P92 heat-resistant steel during long-term service has high influence on the creep property. In this paper, P92 heat-resistant steel samples were aged at 898 K for 10,000 h, 15,000 h and 25,000 h. The effect of thermal ageing on microstructure was analysed through optical microscopy and scanning electron microscopy. The creep behaviour at specific shear stresses (14.7 MPa, 20 MPa, 25.6 MPa, 41 MPa) was investigated through helicoid-spring creep testing. The relationship between microstructure evolution and creep properties was discussed. The results demonstrated that the basic morphology of P92 heat-resistant steel samples following long-term thermal ageing was martensite strip structure, while the precipitated phases were MX, Laves and M23C6. The coarsening of M23C6 carbide was slower than Laves phase during thermal ageing of 15,000 ~ 25,000 h. Precipitation strengthening for the grain interior was corresponding to the Orowan mechanism. In the regions of high shear stresses (14.7 MPa, 20 MPa), the Laves phases played an important role in dislocation motion inhibition at grain boundaries, while in the regions of low shear stresses (25.6 MPa, 41 MPa), the M23C6 phases played a significant role in dislocation motion inhibition at grain boundaries. Moreover, the main precipitate which affected the creep of P92 heat-resistant steels under the lower shear stresses of 14.7 MPa and 20 MPa was Laves phase and the higher shear stresses of 25.6 MPa and 41 MPa was mainly M23C6 phase.

Effects of Precipitates Evolution on Low Stress Creep Properties in P92 Heat-resistant Steel

The evolution of precipitates in P92 heat-resistant steel sustained under thermal aging at 923 K for different times were analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), while the effects of precipitates evolution on the low stress creep properties were experimentally analyzed through uniaxial creep testing and multiaxial “helicoid spring creep testing”. The results demonstrate that the coarsening of M23C6 carbide is significantly slower than the Laves phase in the thermal aging of 0~8000 h. The creep resistance of the P92 heat-resistant steel is enhanced at 923 K aging for 3000 h, and the strengthening effect is significantly apparent under the lower stresses. Moreover, the microstructure degradation factor of the P92 heat-resistant steel in the low stress region at 923 K is different that under the lower stresses of 20 MPa and 35 MPa is mainly Laves phase and the higher stresses of 65 MPa and 75 MPa is mainly M23C6 carbide.

Shortening the Long Creep Strength Evaluation Period with the Assistant of Stress Relaxation Behavior

P92 heat-resistant steel was used to demonstrate that creep rupture life evaluation period could be shorted by the assistant of the creep data from short-period stress relaxation test without reducing the prediction precision. Research showed that the minimum creep rate and the relaxation creep rate were exchangeable, and the stress exponent and the apparent activation energy analysis of the constant strain creep and the constant stress creep showed a similar deformation mechanism at the condition of T and . The creep rupture life predicted through the combination of these two kinds of creep data was closer to the real creep data than that evaluated by the traditional method based on the time to rupture only, and the precision of the evaluated creep strength increased at last 14.5 %.

Influence of holding time of annealing treatment on microstructure and properties of TIG welded joint for P91 heat-resistant steel tube

Influence of holding time of annealing treatment on microstructure and properties of TIG welded joint for P91 heat-resistant steel tube