• Applied Microscopy
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• v.4 no.1
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• pp.5-10
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• 1974

In this work the effect of pre-rolling on the homogenization and on the mechanical properties of 4.6% Mg-0.5% Mn-0.18% Cr-Al alloy has been studied. At room temperature tensile strength and elongation have been found to increase in the pre- rolled homogenized sample compared to those of the as cast sample. At $400^{\circ}C$ this pre-rolled homogenized sample has shown a little lower tensile strength and a remarkably higher elongation than the samples as casted or homogenized without pre-rolling. Metallurgical microstructure of the pre-rolled homogenized sample has shown conspicuously less secondary phase such as ${\beta}$-phase at the grain boundaries than the other samples. The difference of magnesium content between grain boundaries and within the grains has been also checked by EPMA. The test results show enhanced homogenizing effect by the pre-rolling before homogenizing heat treatment.

• Journal of the Korean Society for Heat Treatment
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• v.18 no.1
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• pp.18-23
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• 2005

Effect of cold rolling on microstructural changes has been investigated for a Zn-15%Al alloy to elucidate the reason for its work softening behavior. Fully annealed microstructure of the Zn-15%Al alloy is characterized by ${\eta}$ grains and (${\eta}+{\alpha}$) lamellar colonies, where ${\eta}$ and ${\alpha}$ are Zn-rich HCP and Al-rich FCC phases, respectively. The hardness decreases continuously with increasing cold rolling degree, exhibiting work softening behavior. It is revealed that during the cold rolling, (${\eta}+{\alpha}$) lamellar colonies gradually change into equiaxed ${\eta}$ and ${\alpha}$ grains due to dynamic recrystallization at room temperature, while pre-existing ${\eta}$ grains are only deformed without recrystallization. Furthermore, cold rolling causes the precipitation of dissolved Al solutes in ${\eta}$ grains. In view of these results, change of (${\eta}+{\alpha}$) phases from lamellar to equiaxed morphology, which results in structural softness and increase in equiaxed ${\eta}/{\alpha}$ grain boundaries with higher mobility, and deterioration of solution hardening by precipitation of Al solutes from ${\eta}$ grains, are thought to contribute to the work softening of Zn-15%Al alloy.

• Korean Journal of Materials Research
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• v.9 no.7
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• pp.740-747
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• 1999

Grain refinement is the only strengthening mechanism that improves both strength and toughness. Controlled rolling and accelerated cooling techniques have been known to be effective method to improve the mechanical properties by controlling the recrystallization and/or grain coarsening during processing. Repeat phase transformation $(\gamma/\alpha)$ by repeat heat treating is another way of grain refinement. In this study, a combined effect of controlled rolling and repeat heat treating was investigated. To study the effects of Mo addition and process parameters, Mo alloyed low carbon steels were prepared and thermomechanical controlled processes were simulated in the Gleeble system. The Mo addition resulted in an increasement of the grain coarsening temperature and suppress austenite recrystallization. The optimum condition for the refinement of austenite was obtained when the controlled rolling was performed twice with the same heat treatment condition, and reduction ratio of second pass was higher than that of first pass.

• Korean Journal of Materials Research
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• v.25 no.1
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• pp.32-36
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• 2015

Hot rolling of Mg-6Zn-0.6Zr-0.4Ag-0.2Ca-(0, 8 wt%)Li powder was conducted at the temperature of $300^{\circ}C$ by putting the powder into the Cu pipe. The microstructure and mechanical properties of the samples were observed. Mg-6Zn-0.6Zr-0.4Ag-0.2Ca without Li element was consisted of ${\alpha}$ phase and precipitates. The microstructure of the 8 wt%Li containing alloy consisted of two phases (${\alpha}$-Mg phase and ${\beta}$-Li phase). In addition, $Mg_2Zn_3Li$ was formed in 8%Li added Mg-6Zn-0.6Zr-0.4Ag-0.2Ca alloy. By addition of the Li element, the non-basal planes were expanded to the rolling direction, which was different from the based Mg alloy without Li. The tensile strength was gradually decreased from 357.1 MPa to 264 MPa with increasing Li addition from 0% to 8%Li. However, the elongation of the alloys was remarkably increased from 10 % to 21% by addition of the Li element to 8%. It is clearly considered that the non-basal texture and ${\beta}$ phase contribute to the increase of elongation and formability.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.132-135
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• 2003

Asymmetric rolling, in which the ratio of the rotation rates of the upper and lower rolls was 2, has been used to introduce an intense plastic shear strain for the purpose of grain refinement and developing shear deformation textures through the sheet thickness to improve the strength and plastic strain ratio of AA1050 aluminum alloy sheets. The alloy sheets were rolled at room temperature without lubrication. The textures and microstructures of the sheets were investigated by x-ray diffraction and electron back-scattered diffraction (EBSD) analyses with emphasis on effects of combinations of rot ling directions.

• Transactions of Materials Processing
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• v.17 no.7
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• pp.507-510
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• 2008

Effect of V addition on the precipitation behavior and strength of Fe-36Ni based high strength Invar alloy for power transmission wire was investigated. Fe-36Ni Invar alloy plates were fabricated using conventional ingot casting followed by hot rolling. High strength can be obtained through precipitation hardening and strain hardening by cold rolling. Simulation using FactSage$^{(R)}$ revealed that equilibrium phases which can be formed are two kinds of MC-type precipitates, $Mo_{2}C$ and $M_{23}C_6$ carbide. The latter stoichiometric carbide was expected to be formed at relatively lower temperature of $800^{\circ}C$.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.136-138
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• 2003

Strain states of clad sheets consisted of AL3003 and SUS430 were studied by FEM simulation. Main simulation parameters include roll size, reduction, material properties, material temperature, and friction between roll and material (or friction between materials). To investigate the effect of friction on the evolution of strain states, the friction coefficient between roll and material (or fraction coefficients between materials) was varied. Components of strain rate, strain were compared according to the variation of friction coefficients. And strain states during cladding were compared with those induced by simple rolling process.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.527-530
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• 2002

A lot of efforts have been focused on the optimization of PIT parameters for Bi-2223/Ag wire. In this paper, initial annealing of Bi-2223/Ag wire to transform Bi-2212 orthorhombic from Bi-2212 tetragonal Precursor was investigated. This initial annealing step at low oxygen partial pressure were to transform Bi-2212 orthorhombic structure and to reduce the formation of second phases at superconducting wire. However Bi-2223 Phases were appeared at higher annealing temperature. Critical currents(Je) of Bi-2223/Ag tapes were sintered at low oxygen Partial pressure were higher than that of the wires sintered at atmosphere condition. In order to investigate the effect of rolling reduction ratio, Bi-2223/Ag HTS tapes were rolled with different reduction ratio. There were no clear difference of Je and filaments shape with various rolling reduction ratio.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.535-538
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• 2002

Cube-textured Ni substrates for YBCO coated conductors were fabricated by cold-rolling and annealing of Ni powder compacts. To establish the optimum sintering temperature, tensile test was performed for the Ni rod sintered at various temperatures. The Ni rods prepared at above 100$0^{\circ}C$ showed good mechanical properties due to the complete densification of the Ni rods. The Ni rods were rolled to final thickness of 100 ${\mu}{\textrm}{m}$ and then annealed at 100$0^{\circ}C$ for various annealing time for texture development. The texture analysis made by 2 $\theta$ scan and pole-figure showed that the cube texture was developed in a short time of a few munitues. The FWHM of in-plane and out of plane texture of the prepared Ni tapes was 8-10$^{\circ}$. The AEM surface roughness of the Ni tapes was as smooth as 3 nm.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.08a
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• pp.145-152
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• 2004

The flow stress value was calculated by comparing predicted and measured roll force. Using basic on-line roll force model and logged mill data the flow stress equation of high strength steel for automobile was derived. The flow stress equation consists of the flow stress equation of carbon steel and flow stress factor calculated by neural network with input parameters not only carbon contents, strip temperature, strain, and strain rate, but also compositions such as Mn, p, Ti, Nb, and Mo. Using the flow stress equation and basic roll force model, precision roll force model of high strength steel for automobile was derived. Using test set of logged mill data the flow stress equation was verified.