Hyung Yong Ra

Microstructure and crystallographic texture of strip-cast 4.3wt%Si steel sheet

Since grain oriented silicon steel sheet was invented in 1935 by Goss, the material has been of considerable fundamental and technological interest to improve the sharpness of Goss orientation {l_brace}110{r_brace}{l_angle}100{r_angle} etc. In the present study, a Fe-4.3wt%Si strip was produced by the vertical type twin roll strip casting process and the microstructure and texture through the thickness direction were studied by optical metallography and quantitative X-ray texture analysis. The inhomogeneity of the texture and microstructure through the thickness direction were investigated.

Effect of Mn negative segregation through the thickness direction on graphitization characteristics of strip-cast white cast iron

Abstract A cast iron strip was produced using a twin roll strip caster, and the effect of Mn segregation on graphitization through the thickness was studied. Negative segregation of Mn was observed in the as-cast strip. It results from the negative segregation of Mn that the cementite is graphitized faster in the center layer than in the middle and surface layers.

Growth of α-alumina oxide film in high temperature oxidation of Fe-20Cr-5Al alloy thin strip

Fe-20Cr-5Al alloy system has been developed as an oxidation resistant alloy at high temperature and mainly used for high temperature heating element, fie grid, metal honeycomb for automobile exhaust gas system, etc. The oxidation resistance is mainly due to the formation of an {alpha}-Al{sub 2}O{sub 3} oxide film which has low volatility and good chemical stability. But the oxide film has weak interfacial adherence with the metal substrate and susceptibility to cyclic thermal history. It is thought that the adherence is influenced by growth behavior of oxide film. Experimental observation and mechanism on the growth step of the {alpha}-Al{sub 2}O{sub 3} oxide film have been rarely reported. The object of the present study is to study the growth behavior of {alpha}-Al{sub 2}O{sub 3} oxide films in high temperature oxidation of a thin strip Fe-20Cr-5Al alloy.

Spontaneous deformation during the high temperature oxidation of Fe-20Cr-5Al-(0, 0.06)La alloy thin strip

Growth stress and spontaneous deformation in Fe-20Cr-5Al-(0, 0.06)La alloy thin strip oxidized at high temperature have been studied. The spontaneous deformation of the metal substrate was considered as creep behavior. The activation energy for the creep was determined from the relationship between the strain rate and the reciprocal oxidation temperature. La free alloy thin strip showed an activation energy of 332 kJ/mol. A compressive stress of 652 MPa and tensile stress of 10 MPa have acted on α-alumina oxide film and metal substrate, respectively. These growth stresses were relaxed through not only the creep of the metal substrate but also the local detachment of α-alumina oxide film from the metal substrate. La added alloy showed an activation energy of 263 kJ/mol, which was lower than the activation energy in La free alloy. No cracking or fracture in α-alumina oxide films was found. The addition of La seemed to assist the progress of the stress relaxation through the creep of the metal substrate.

Dendritic growth of α(Fe,Si) ferrite in annealed Fe80Si8B12 metallic glass

Abstract Generally, experimental study on the dendritic growth has been confined to transparent organic materials. In this experiment, using the fact that, during the crystallization of Fe80Si8B12 metallic glass, dendritic growth of α(Fe,Si) ferrite occurs, we examined the growth direction, tip morphology, growth process, growth condition and initial secondary arm spacing of α(Fe,Si) dendrite. Experimental results revealed that the dendritic growth direction is , the dendrite tip morphology is a nearly exact paraboloid and the growth rate is controlled by the diffusion of boron into the amorphous matrix. Moreover, the dendritic growth condition of α(Fe,Si) does not satisfy the maximum velocity condition, but the marginal stability condition.

Formation mechanism of Fe80Si8B12 metallic glass

In order to gain an understanding of the glass-forming mechanism during the rapid quenching of a metallic alloy, the nucleation and growth process of the crystalline phase which competes with the metallic glass must be investigated. The microstructures of melt-spun Fe80Si8B12 alloy ribbons with different thicknesses were examined using optical and electron microscopy. The phase competing with the metallic glass isα-(Fe, Si) ferrite, nucleated by the homogeneous nucleation. The growth process ofα-(Fe, Si) dendrites was explained well by Liptonet al.s theory of dendritic growth in an undercooled alloy melt. It was concluded that the easy glass-forming ability during rapid quenching of the Fe80Si8B12 alloy is due to (i) the slow growth rate ofα-(Fe, Si) dendrite, and (ii) the wide gap between the temperatures of the maximum nucleation rate and the maximum growth velocity.