• Applied Microscopy
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• v.47 no.1
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• pp.43-49
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• 2017

A new method was introduced to distinguish the ferrite, bainite and martensite in transformation induced plasticity (TRIP) steel by using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). EBSD is a very powerful microstructure analysis technique at the length scales ranging from tens of nanometers to millimeters. However, iron BCC phases such as ferrite, bainite and martensite cannot be easily distinguished by EBSD due to their similar surface morphology and crystallographic structure. Among the various EBSD-based methodology, image quality (IQ) values, which present the perfection of a crystal lattice, was used to distinguish the iron BCC phases. IQ values are very useful tools to discern the iron BCC phases because of their different density of crystal defect and lattice distortion. However, there are still remaining problems that make the separation of bainite and martensite difficult. For instance, these phases have very similar IQ values in many cases, especially in deformed region; therefore, even though the IQ value was used, it has been difficult to distinguish the bainite and martensite. For more precise separation of bainite and martensite, IQ threshold values were determined by a correlative TEM analysis. By determining the threshold values, iron BCC phases were successfully separated.

• Journal of Magnetics
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• v.12 no.2
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• pp.68-71
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• 2007

Even a pure bulk Fe has a complicated magnetic phase and its magnetism is still needed to be clarified. In this study we investigated the magnetism of bcc and fcc bulk Fe with total energy calculations as functions of atomic volume. The full-potential linearized augmented plane wave method was adopted within a generalized gradient approximation. The ground state of bulk Fe is confirmed to be of ferromagnetic (FM) bcc. For fcc structured Fe an antiferromagnetic (AFM) state is more stable compared to FM states which exist as low spin and high spin states. The stable AFM states were found to accompany a tetragonal distortion, while the FM states remained in a cubic symmetry. At an expanded lattice constant a high spin FM state was calculated to be able to be stabilized with significant enhanced magnetic moment compared to the value of the ground state, bcc FM.

• Korean Journal of Materials Research
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• v.15 no.9
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• pp.566-576
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• 2005

This paper describes an ab Initio study on interface energies, misfit strain energies, and electron structures at coherent interfaces Fe(bcc structure)/MCs(NaCl structure M=Ti, Zr, Hf). The interface energies at relaxed interfaces Fe/TiC, Fe/ZrC and Fe/HfC were 0.263, 0.153 and $0.271 J/m^2$, respectively. It was understood that the dependence of interface energy on the type of carbide was closely related to changes of the binding energies between Fe, M and C atoms before and after formation of the interfaces Fe/MCs with the help of the DLP/NNBB (Discrete Lattice Plane/ Nearest Neighbour Broken Bond) model and data of the electron structures. The misfit strain energies in Fe/TiC, Fe/ZrC and Fe/HfC systems were 0.390, 1.692 and 1.408 eV per 16 atoms(Fe: 8 atoms and MC; 8 atoms). More misfit energy was generated as difference of lattice parameters between the bulk Fe and the bulk MCs increased.

• Korean Journal of Materials Research
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• v.16 no.8
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• pp.473-478
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• 2006

The coherent interface energies and misfit strain energies of Fe/XN (X=Ti, Zr, Hf) systems were calculated by first principles method. The interface energies in Fe/TiN, Fe/ZrN and Fe/HfN systems were 0.343, 0.114, and 0.030 $J/m^2$, respectively. Influence of bond energy was estimated using the discrete lattice plane/nearest neighbor broken bond(DLP/NNBB) model. It was found that the dependence of interface energy on the type of nitride was closely related to changes of the bond energies between Fe, X and N atoms before and after formation of the Fe/XN interfaces. The misfit strain energies in Fe/TiN, Fe/ZrN, and Fe/HfN systems were 0.239, 1.229, and 0.955 eV per 16 atoms(Fe; 8 atoms and XN; 8 atoms). More misfit strain energy was generated as the difference of lattice parameters between the bulk Fe and the bulk XNs increased.

• Journal of Magnetics
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• v.4 no.1
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• pp.1-4
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• 1999

The microstructure and magnetic properties of$ Fe_{87}Zr_7Si_4B_2$ nanocrystalline alloys were studied by magnetization measurements and M ssbauer spectrometry over a wide temperature range. Three well resolved spectral components have been found and attributed to bcc-Fe grains (with almost pure iron structure), residual amorphous matrix enriched with solute elements and interfaces formed at the grain-matrix boundaries. It has been shown that, contrary to the expectation, during crystallization the atomic segregation occurs leading to the formation of primary bcc-Fe grains and the partition of Si atoms into the residual amorphous matrix.

• Nuclear Engineering and Technology
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• v.53 no.5
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• pp.1619-1625
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• 2021

This paper demonstrates the possible nondestructive analysis of iron artifacts' metallurgical characteristics using neutron imaging. Ancient kingdoms of the Korean Peninsula used a direct smelting process for ore smelting and iron bloom production; however, the use of iron blooms was difficult because of their low strength and purity. For reinforcement, iron ingots were produced through refining and forge welding, which then underwent various processes to create different iron goods. To demonstrate the potential analysis using neutron imaging, while ensuring artifacts' safety, a sand iron ingot (SI-I) produced using ancient traditional iron making techniques and a sand iron knife (SI-K) made of SI-I were selected. SI-I was cut into 9 cm², whereas the entirety of SI-K was preserved for analysis. SI-I was found to have an average grain size of 3 ㎛, with observed α-Fe (ferrite) and pearlite with a body-centered cubic (BCC) lattice structure. SI-K had a grain size of 1-3 ㎛, α-Ferrite on its backside, and martensite with a body-centered tetragonal (BCT) structure on its blade. Results show that the sample's metallurgical characteristics can be identified through neutron imaging only, without losing any part of the valuable artifacts, indicating applicability to cultural artifacts requiring complete preservation.

• Proceedings of the Korean Magnestics Society Conference
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• 2008.12a
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• pp.275.1-275.1
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• 2008

• Transactions of Materials Processing
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• v.21 no.6
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• pp.366-371
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• 2012

Atomistic simulations have become useful tools for exploring new insights in materials science, but the length and time scale that can be handled with atomistic simulations are seriously limiting their practical applications. In order to make meaningful quantitative predictions, atomistic simulations are necessarily combined with higher-scale modeling. The present research is thus concerned with the development of a multi-scale model and its application to the prediction of the mechanical properties of body-centered cubic(BCC) iron with an emphasis on the coupling of atomistic molecular dynamics with meso-scale discrete dislocation dynamics modeling. In order to achieve predictive multi-scale simulations, it is necessary to properly incorporate atomistic details into the meso-scale approach. This challenge is handled with the proposed hierarchical information passing strategy from atomistic to meso-scale by obtaining material properties and dislocation mobility. Finally, this fundamental and physics-based meso-scale approach is employed for quantitative predictions of the mechanical response of single crystal iron.

• Electrical & Electronic Materials
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• v.7 no.5
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• pp.397-402
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• 1994

기계적 합금화방법을 이용 실온에서 철분말의 질화물을 얻을 수 있다. 이때 얻어진 준안정 철질화물은 질소농도가 14.9[at. %N]이하에서는 bcc 구조의 과포화 고용체가, 그리고 19.4[at. %N]이상에서는 고온상인 hcp 구조임을 확인할 수 있었다. 또한 bcc상의 Fe원자당 Volume은 문헌에 보고된 N-martensite의 것보다 작은 값을 나타내었다. 제조된 철질화물의 실온 포화 자화값은 질소농도가 증가함에 따라 감소하였으며, 이 결과는 bct 구조의 철질화물에서 질소농도가 증가함에 따라 자화값이 증가하는 것과 대조적이었다.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1333-1335
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• 1994

The nitrification of pure iron powders is found to occur even at room temperature by high energy ball milling in $NH_3$ gas atmosphere. The powders of metastable iron nitrides ($0<at.%N{\le}23.3$) thus produced are identified as the super-saturated bee structure for the N content below 14.9 at.%N and the high temperature phase of the hcp structure above 19.4 at.%N. The atomic volume of Fe in the bcc phase is found to be smaller than that of the N-martensite reported in the literature. Magnetization at room temperature gradually decreases with increasing the N concentration in contrast to the enhancement reported for the bet nitrides. Neutron diffraction experiment also provide detailed information about the local structure surrounding the nitrogen atom. The coordination number of Fe atom around a nitrogen atom for the iron nitride containing 9.5 at.%N turns out to be 3.9 atoms.