• Analytical Science and Technology
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• v.5 no.2
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• pp.203-211
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• 1992

Fracture behavior and martensite substructure of Ni-36.5at.%Al alloy were investigated with the addition of vanadium which is known as scavenging element of grain boundary. The fracture surfaces were examined by scanning electron microscopy and the EDX spectrometer was applied for composition analysis of fracture surfaces. The substructure of martensite was studied by transmission electron microscopy. By addition of vanadium, fracture surfaces show mixed modes of intergranular and transgranular fracture and more Al content is found on the grain boundaries. For Ni-36.5at.%Al alloy, the planar faults observed in the martensite plates are the internal twins. By increasing the vanadium content, the modulated structure with stacking faults and dislocations dominates while the twinned martensite disappears. The stacking fault is determined to be extrinsic due to the substitution of V for Al. It is concluded that the segregation of sulfur on the high-energy state stacking fault area suppresses the intergranular fracture.

• Journal of the Korean Society for Heat Treatment
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• v.10 no.3
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• pp.188-197
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• 1997

Effect of martensite morphology on damping capacity and hardness of Fe-Ni-C martensitic alloys were studied. The morphologies of martensite such as lath, butterfly, lenticular and thin plate were prepared by adjusting nickel content and austenite grain size. The hardness increased in order of lath, lenticular, thin plate, butterfly. The damping capacities of the lath and butterfly martensites were higher than those of the other two morphologies, indicating that the dislocation substructure is more effective in the damping capacity than the twin substructure. Especially, the butterfly martensite showed the highest damping capacity among these morphologies because of presence of not tangled but free dislocations in there.

• Transactions on Electrical and Electronic Materials
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• v.15 no.1
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• pp.20-23
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• 2014

Dual phase steels have a microstructure comprising of a polygonal ferrite matrix together with dispersed islands of martensite. There are clear differences between the image quality (IQ) map of the dual phase and the corresponding ferritic/pearlitic structures, both in the as-heat treated and cold rolled conditions. Electron backscatter diffraction (EBSD) techniques were used to study the evolution substructure of steel due to plastic deformation. The martensite-ferrite and ferrite-pearlite interfaces were observed. The interface can be a source of mobile dislocations which the bands seem to originate from the martensite islands. In particular, the use of image quality is highlighted.

• Interaction and multiscale mechanics
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• v.1 no.4
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• pp.437-448
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• 2008

This paper examined the stability of high-dense dislocation substructures (HDDSs) associated with martensite laths in High Cr steels supposed to be used for FBR, based on a series of dislocation dynamics (DD) simulations. The DD simulations considered interactions of dislocations with impurity atoms and precipitates which substantially stabilize the structure. For simulating the dissociation processes, a point defect model is developed and implemented into a discrete DD code. Wall structure composed of high dense dislocations with and without small precipitates were artificially constructed in a simulation cell, and the stability/instability conditions of the walls were systematically investigated in the light of experimentally observed coarsening behavior of the precipitates, i.e., stress dependency of the coarsening rate and the effect of external stress. The effect of stress-dependent coarsening of the precipitates together with application of external stress on the subsequent behavior of initially stabilized dislocation structures was examined.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.2
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• pp.168-176
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• 2004

Interrupted creep tests were carried out on the Mod.9Cr-1Mo steel in order to investigate the structural degradation during creep. The ranges of creep stress and temperature were from 71 to 167MPa and 873 to 923k, respectively. The change of hardness and tempered martensitic lath width were measured in the grip and gauge parts of interrupted specimens. The lath structure was thermally stable in static conditions, but was not stable during creep, and the structural evolution was enhanced by creep strain. The relation between the change in lath width and strain was described in the from, $\delta$W= a ($W_s-W_o$)$cdot;varepsilon$, where $\varepsilon$ is the strain, $W_o$is the initial lath width, $W_s$ is the final lath width depending solely on stress, and a is the constant of the magnitude of 0.67 $\mu$m /strain. The change in Victors hardness was expressed by a one-valued function of creep life consumption ratio. Based on the empirical relation between strain and lath width, a model was proposed to explain the relation between change in hardness and creep life consumption ratio. The model revealed that about 65$%$ of dislocations in lath structures were eliminated by the migration of subboundaries.

• The Journal of Natural Sciences
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• v.7
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• pp.83-90
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• 1995

The microstructural and textural development during rolling is compared in two Hadifield's steels (high Mn steel), one having low carbon content (0.65 wt.%) and the other high carbon (1.35 wt.%).In low carbon Hadfield's steel (LCHS) mixed microstructures are formed which contain intrinsic stacking faults, deformation twins, and brass type shear bands. The deformation twins are thought to be formed by the stacking of intrinsic stacking faults. The similar development to 70-30 brass texture is observed in early deformation. However the abnormal texture is developed after 40 % deformation, which is thought to be due to the martensite phase transformation. In high carbon Hadfield's steel (HCHS) mixed substructures of dislocation tangles, deformation twins, and shear bands (both copper and brass type) are found to develop. The texture development is similar to that of 70-30 brass. This is consistant with no carbon segregation and no martensitic phase transformation in HCHS. In spite of the difference of substructure and texture development during rolling in two steels, the difference in stacking fault energy is measured to be small ($2 mJm^-2$). The carbon segregation is only occurred in LCHS. Thus it is thought that the carbon segregation influence the microstructure and texture development during rolling. This is related with martensite phase transformation in LCHS.