Evolution of phases during tempering of P91 steel at 760℃ for varying tempering time and their effect on microstructure and mechanical properties

Abstract

In the present investigation, a systematic study has been undertaken with regard to the effects of tempering time on room temperature mechanical properties of P91 (X10CrMoVNNB9-1) steel. Samples cut from P91 (X10CrMoVNNB9-1) industrial pipe were normalized at 1040 C for 40 min and then tempered at 760 C for different tempering times starting from 2 h to 8 h. Detailed analysis of microstructure, particle size, inter-particle spacing, and secondary phase carbide particles of the tempered samples was conducted by secondary electron microscopy technique. Optical microscopy was also utilized to characterize the tempered samples and for the measurement of grain size. In order to reveal the various phases formed during tempering of P91 (X10CrMoVNNB9-1) steel, X-ray diffraction was carried out. To study the fracture surface morphology of tensile tested and impact tested specimen field-emission scanning electron microscopy was carried out. The effect of tempering time on the microstructural parameters revealed an increase in grain size up to 4 h of tempering and then decreased because of recrystallization. The coarsening of secondary phase carbide particles M 23 C 6 was revealed with an increase in tempering time. As a consequence, yield strength, hardness, and ultimate tensile strength were observed to decrease with increase in the tempering time. However, a drastic change was observed in the yield strength, ultimate tensile strength, and toughness after tempering for 6 h. From the present study, it was concluded that optimum combination of yield stress, ultimate tensile strength, hardness, and toughness obtained after tempering at 760 C for 6 h.

Structural and electronic properties of chromium carbides and Fe-substituted chromium carbides

“…The calculated cell parameters of all the Cr-C compounds are shown in table 1. The experimental values of the lattice parameters [27][28][29][30][31] shown in parenthesis are in good agreement with our calculated values. The average deviation of our results from the experimental lattice parameters are less than 1%.…”

“…N=Number of atoms within the crystal lattice used for calculation. Experimental values of lattice parameters in parenthesis, i-v [27][28][29][30][31].…”

Optimization of PWHT of Simulated HAZ Subzones in P91 Steel with Respect to Hardness and Impact Toughness

“…However, predominantly optical microscopy was done considering that the microstructures of the base metal P91 and all HAZ-subzones were already thoroughly investigated [7,14,49,59,[65][66][67], such that this work was focused on the optimization of PWHT with respect to mechanical properties, and considering the findings of Li et al [62], who found that if the hardness of P91 was above 189 HV, operation was safe and there was no need to inspect the microstructure. Optical micrographs only enable observation of the grain size of prior austenitic grains and of the coarsest carbide particles.…”

“…The reports in the literature confirm our observations. The major portion of precipitates are M 23 C 6 carbides, where M is predominantly Cr, followed by Fe and Mo [14,49,[65][66][67]. They are mostly coarser than other carbides and prevail on the former austenite boundaries.…”

Study on warm forming effects of the axial-pushed incremental rolling process of spline shaft with 42CrMo steel

“…Forming temperature has a great influence on the microstructural evolution of materials. 32 Figure 4 shows the initial microstructure of the hot-rolled 42CrMo steel and the microstructures after compression process at different forming temperatures (strain rate: 0.1 s −1 , deformation degree: 55%). The initial microstructure of the hot-rolled 42CrMo steel was composed of the equiaxed ferrite and lamellar pearlite, as shown in Figure 4(a).…”