Changes in size- and spatial distribution of precipitates and their effect on stationary creep rate of two grades of creep-resistant 9-12% Cr steels, X20 and P91, as a function of ageing at two ...different conditions were investigated. Ageing of both steels was performed at 650°C lasting up to 2 years and at 750°C lasting up to 6 months. Prior to the ageing, simulation of two weld heat-affected zone HAZ regions, i.e., coarsegrained microstructure (γ), and grain-refined microstructure (α+γ) was performed. Accelerated creep tests at 580°C and 170 MPa, lasting up to 100 hours were performed on the above microstructures prior to- and after the ageing. In addition, optical and SEM imaging were performed on metallographic specimens, followed by image analysis. Deterioration of the creep performance show a proportional behaviour with the precipitate coarsening, which is more pronounced after the ageing at 750°C. Comparatively, the increase of the stationary creep rate after the ageing at 650°C was more pronounced in the steel X20 than in the P91. In both steels and both tempering temperatures, the most troublesome region with respect to the creep behaviour was observed to be the simulated intercritical (α+γ) HAZ microstructure.
Thermo-graphic investigations were carried out on niobium microalloyed steel. During tensile testing temperature changes of samples, due to elastic and plastic deformation, were measured using ...infrared camera. The results of temperature measurements indicate that the specimen’s temperature is lowered during the elastic deformation. This temperature drop is in other studies associated with so-called thermo-elastic effect which occurs in the metals during elastic deformation. Parallel with the infrared camera, surface of samples was recorded with digital imaging camera. Analysis of recorded images was analyzed using digital image correlation method. This is used to determine the deformation that occurs during stretching. The results show that during elastic deformation of samples the volume of samples is slightly increased. The volume change of samples and temperature drop, due to thermo-elastic effect, are compared for all samples. The analysis of experimental results explains that the thermo-elastic effect is directly related to the change of specimen volume during the elastic deformation of steel.
The evolution of the chemical and phase composition of carbide precipitates in X20CrMoV12.1 steel after longterm service of 56 000 θ (470 – 530 °C at up to 18MPa) and after heat treatment (650 and ...800 °C) was investigated using transmission electron microscopy and Auger electron spectroscopy. The precipitates found were mostly of M
type, the S- and v-phase and traces of M
C. In service loaded state the presence of M
precipitates was also established. The evolution sequence is obviously M
C → M
!M
The difference of the experimental and the calculated creep rates of the steel grade X20CrMoV121 with M23C6 particles in temperature range 763–913 K was examined in terms of temperature, iron ...self‐diffusion rate, glide stress, and number of ferrite lattice vacancies. The Ashby‐Hornbogen creep equation is modified by adding a parameter that represents the effect of number of lattice vacancies; consequently, the difference of the experimental and the calculated creep rates is diminish to the level of average particles size assessment accuracy.
The effect of vacancies content and mobility, as well as of glide stress on creep rate of steel X20 is examined in range of creep tests 550–640 °C. It is found that the effect of increase of vacancies content prevails. With inclusion of the corresponding parameter, the difference of calculated and experimental creep rate is diminshed to the accuracy of assessment of carbide particles.
Sixty years have passed since the foundation and the first publishing of the Metalurgija Journal. On the occasion of this Anniversary, the goal of the Article is give List of Boards and Co-workes ...which dedicated eff ort have managed to over come many technical and organizational problems by regularity publishing.
The difference of the experimental and the calculated creep rates of the steel grade X20CrMoV121 with M23C6 particles in temperature range 763-913K was examined in terms of temperature, iron ...self-diffusion rate, glide stress, and number of ferrite lattice vacancies. The Ashby-Hornbogen creep equation is modified by adding a parameter that represents the effect of number of lattice vacancies; consequently, the difference of the experimental and the calculated creep rates is diminish to the level of average particles size assessment accuracy.
The change of the number of M sub(23)C sub(6) particles intercepting mobile dislocations by creep of high-chromium creep resistant steel is deduced. With tempering at 800 degree C, the number of ...intercept particles decreases slower than the total number of particles. The dissolution velocity of particles is greater by smaller particles. By tempering at 550 degree C and higher, the dissolution of small particles increases the intercept particles spacing and the creep rate for about 1 order of magnitude stronger than the increase of average particles size. M sub(23)C sub(6) particles size, number and dissolution velocity were deduced for tempering of a X20 steel at 800 to 550 degree C. The dissolution of small particles increases the particle spacing for above one order of magnitude more than particles coarsening. By creep tests above 550 degree C, particles spacing and creep rate are increased significantly by dissolution of small particles.
The change of the number of M 23 C 6 particles intercepting mobile dislocations by creep of high‐chromium creep resistant steel is deduced. With tempering at 800 °C, the number of intercept particles ...decreases slower than the total number of particles. The dissolution velocity of particles is greater by smaller particles. By tempering at 550 °C and higher, the dissolution of small particles increases the intercept particles spacing and the creep rate for about 1 order of magnitude stronger than the increase of average particles size.
The change of the number of M23C6 particles intercepting mobile dislocations by creep of high‐chromium creep resistant steel is deduced. With tempering at 800 °C, the number of intercept particles ...decreases slower than the total number of particles. The dissolution velocity of particles is greater by smaller particles. By tempering at 550 °C and higher, the dissolution of small particles increases the intercept particles spacing and the creep rate for about 1 order of magnitude stronger than the increase of average particles size.
M23C6 particles size, number and dissolution velocity were deduced for tempering of a X20 steel at 800 to 550 °C. The dissolution of small particles increases the particle spacing for above one order of magnitude more than particles coarsening. By creep tests above 550 °C, particles spacing and creep rate are increased significantly by dissolution of small particles.
Creep stress transfers matrix‐particle in conjunction and disjunction particle matrix are examined. The effect of angles creep stress, dislocation glide, and stress transfer particle face on ...dislocation glide, and climb components of creep stress are calculated. The glide force and gliding velocity in particles disjunction matrix are deduced.
The interaction acting stress (σa) – polyhedral particles is examined by a model based on linear mechanics. The glide component (σg) of acting stress decreases to σg = 0.023 σa, governing gliding velocity and creep rate. The gliding velocity gv = 558 nm s−1 and ferrite lattice glide resistance Rg = 3.16 × 10−13 N are calculated.
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