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.

Residual Stress and Microstructure Characterization of 34CrMo4 Steel Modified by Shot Peening

34CrMo4 steel is widely used for drill stem in oil exploration, because of its excellent properties, such as favorable hardenability, shock absorption, less tendency of temper brittleness, and eminent wear resistance. In this study, the main works are residual stress test and microstructure characterization of 34CrMo4 steel upon various shot peening treatments. The residual stress distribution with effect depth was studied upon the shot peening. Face-to-face paste sample preparation method is required for continuous observation for microstructure evolution of shot-peened specimen from the treat surface to matrix. Grain refinement, lath structure, and precipitates are clearly observed in the gradient deformation layer.

Structural Characterization of Low Carbon Foil by Asymmetrical Rolling

At room temperature, the low carbon steel were cold rolled from 0.5 mm to 1 μm without intermediate annealing by asymmetrical rolling (ASR) process. the microstructure were investigate by Electron Backscatter Diffraction (EBSD) and transmission electron microscopy (TEM). Lath structure (~300 nm) and local nanograins (~60nm) were obtained through ASR with extensibility up to 50,000%. The high angle boundaries were predominant. The results indicated that inhomogeneous deformation and combination deformation mechanism of dislocation slip and grain boundary slip in the foil ASR process.

Effect of Silicide on Dynamic Recrystallization in Near Alpha Titanium Alloy

Dynamic recrystallization in Ti-1100 was investigated. Ti-1100 is one of near α titanium alloys and contains Si for improving high temperature mechanical properties. Ti-1100 exhibits martensitic transformation by quenching into iced brine after solid solution treatment. Hereafter specimens subjected to quenching into iced brine and to cooling in air after solid solution treatment are called IBQ specimen and AC specimen, respectively. After tensile test at high temperature, IBQ specimen exhibits morphological change from lath structure to equiaxed structure, but AC specimen does not. It is indicated that dynamic recrystallization occurs during the tensile test of IBQ specimen. Effect of silicide on the dynamic recrystallization was investigated using two specimens: one included more silicide precipitates and the other less. The former specimen shows smaller recrystallized grains than the latter. It is indicated that the specimen including more silicides exhibits smaller recrystallized grains.

Microstructural Evolution in a 9%Cr-3%Co-3%W-VNb Steel during Creep

Microstructural evolution in a 9Cr-3Co-3W-0.2V-0.06Nb-0.05N-0.005B steel crept at T=650°C under an applied stress of 140 MPa up to strains of 1, 3, 5.75 and 12%, which represent primary, secondary and tertiary creep stages and rupture, respectively, was studied. The steel was initially normalized from 1050°C, and finally tempered at 750°C for 3h. After tempering the boundaries of tempered martensite lath structure (TMLS) were decorated by M23C6 carbides, M6C carbides and Laves phase particles. The 3% W additives provide the narrow size distribution of the boundary particles excepting M6C carbides. The depletion of thermodynamically none-equilibrium content of W from the solid solution during creep leads to following events. (i) Continuous precipitation of small Laves phase particles occurs during all creep stages and results in the formation of bimodal size distribution. As a result, the average size of Laves phase particles remains unchanged during creep. (ii) Coarsening of M23C6 carbides starts to occur only at the transition to tertiary creep. (iii) Transformation of laths to subgrains followed by their growth is observed during all stages of creep. The density of particle located at lath/subgrain boundaries decreases from 5.6 to 2.6 μm-1 during creep up to rupture. However, no full transformation of TMLS into subgrain structure has been revealed.

Effect of Tempering on Microstructure and Creep Properties of P911 Steel

The microstructure and creep properties of a P911-type steel normalized at 1060°C and then subjected to one-step tempering at 760°C for 3 h or two-step tempering at 300°C for 3 h + 760°C for 3 h were examined. The transmission electron microscope (TEM) observations showed that the tempered martensite lath structure (TMLS) with a lath thickness of 340 nm evolved after both tempering regimes. High dislocation densities of 3×1014 or 5×1014 m-2 retained after one-and two-step tempering respectively. M23C6 carbides with a mean size of 120 nm and V-rich MX carbonitrides having a “wing” shape with an average length of about 40 nm precipitated on high-and low-angle boundaries and within ferritic matrix, respectively. A number of Nb-rich M(C,N) carbonitrides with a mean size of 20 nm precipitated on dislocations during low temperature tempering. The creep tests were carried out under constant load condition at 650°С at applied stresses of 100 and 118 MPa. Analysis of creep rate versus time curves showed that the use of two-step tempering decreases the minimum creep rate providing an increase in the creep strength in long-term conditions.