Influence of Precipitates Size and Distribution on Room Temperature Mechanical Properties and Accelerated Creep of X20CrMoV121

Abstract

The effect of microstructure on creep resistance of the low carbon chromium steel X20CrMoV121 after 100‐hours of static‐load test at a temperature of 580 °C and constant stress of 170 MPa was investigated. The specimens for the experiments were extracted from steam pipes of a steam power plant and heat treated. The effect of isothermal annealing on the microstructure and hardness as well as the kinetics of the precipitation of the carbide particles were determined.

Effect of Microstructure on the Accelerated Creep of 20CrMoV12‐1 and P 91 Steels

“…Accordingly, the hardness of the microstructure in Figure 1 was HB 253 and that of the microstructure in Figure 2 was HB 205. It was also established that the accelerated creep rate of the steel with the microstructure in Figure 2 was approximately four times greater than that of the steel from the same tube but with the microstructure in Figure 1 [6]. The basically different microstructures indicate that for the same tube the difference in the wall temperature on the flame and on the chimney side could achieve a level sufficient to induce internal recrystallisation in the martensite grains.…”

Change of M23C6 Particles Size and Spacing by Tempering a High‐Chromium Creep Resistant Steel at 800–550 °C

“…For example, for the growth of a particle with d c = 70 nm to d c = 80 nm, 10.8 particles with d s = 25 nm are dissolved. After 1334 h of tempering at 800 °C, the size of about 65% of particles was up to 25 nm . Thus, it is reasonable to conclude that by tempering and by creep tests, the particles spacing is increased by about 1 order of magnitude more rapidly by the dissolution of small particles to than of growth of average size of particles.…”

“…From the dependence cumulative frequency – particles size in ref ,. the apparent growth velocity g v = d p / t t with t – tempering time was deduced for particles with d p > 100 nm.…”

“…In this work, the changes of the total number of M 23 C 6 particles, the number of particles intercepting mobile dislocations at 800 °C, the particles dissolution velocity at 750–550 °C, as well as the changes of average particles size and spacing were calculated for the steel 0.18C11.5Cr1.08Mo0.29V . The steel was annealed for 30 min at 1050 °C to obtain the complete dissolution of carbide particles in austenite, oil cooled to martensite, tempered at 800 °C and afterwards tempered at 750–550 °C.…”

“…The steel was annealed for 30 min at 1050 °C to obtain the complete dissolution of carbide particles in austenite, oil cooled to martensite, tempered at 800 °C and afterwards tempered at 750–550 °C. The base of the analysis are the average size and cumulative frequency of particles after 100, 334, 1334, and 3335 h of tempering at 800 °C, 100 h of additional tempering at lower temperature and the coarsening equation of M 23 C 6 particles in refs …”