• Korean Journal of Materials Research
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• v.14 no.6
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• pp.379-388
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• 2004

To investigate the effect of D-ferrite on the hot workability and surface defect of STS 304 billets containing 3 wt. % Cu, microstructure observations and high temperature mechanical properties test were carried out for the specimens extracted mainly from raw or oxidized billets. It was found that the total $\delta$-ferrite content has little influence on the hot workability, even though the fracture cracks due to high temperature tension or compression test were initiated and propagated mostly along $\delta$/${\gamma}$ boundary in the specimens. On the other hand, it was supposed that the direct causes of surface defects in the wire rolled from the as-continuously cast billet were the grain boundary embrittlement arose from the deep diffusion of oxygen into the grain boundary, and the oxidation of $\delta$-ferrite connected by a grain boundary to the surface during the billet reheating process as well.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11a
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• pp.284-287
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• 2001

Multi-pole anisotropic Sr-fertile sintered magnets has been studied by powder injection molding under applied magnetic field. The orientation of anisotropic Sr-ferrite powders higher than 80% during injection molding is achieved at the following conditions; apparent viscosity lower then 2500 poise in 1000 sec$\^$-1/ shear rate and applied magnetic field higher then 4 kOe. For the high fluidity and strength of injection molded compact, and the effective binder removal without defects during solvent extraction and thermal debinding, the optimum multi-binder composition is paraffin wax(PW)/carnauba wax(CW)/HDPE = 50/25/25 wt%. The rate of binder removal is proportional to the mean particle size of Sr-ferrite powders whereas it is inversely proportional to the content of Sr-ferrite powders and the sample thickness. The high magnetic properties of Sr-ferrite sintered magnets are; 3.8 kG of remanent flux density, 3.4 kOe of intrinsic coercivity, and 1.2 kG of surface flux density (1-mm-thick) in the direction of applied magnetic field.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.229-234
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• 2002

The variation of HAZ toughness with nitrogen content and weld cooling rate was investigated and interpreted in terms of both microstructure and the amount of free nitrogen. The presence of free nitrogen in HAZ was investigated by internal friction measurement and its amount was measured by hydrogen hot extraction analysis. Both nitrogen content and weld cooling rate influenced HAZ microstructure and high toughness was obtained at a mixed microstructure of acicular ferrite, feffite sideplate and polygonal ferrite. If nitrogen content is too low or cooling rate is too fast, bainitic microstructure is obtained and toughness is low. On the other hand, if nitrogen content is too high or cooling rate is too slow, coarse polygonal ferritic microstructure is obtained and toughness is deteriorated again. ill addition to the microstructural change, high nitrogen content also resulted in a large amount of free nitrogen. Therefore, nitrogen content should be kept as low as possible even if the mixed micostructure is obtained. In this experimental condition, the maximum toughness was obtained at 0.006% nitrogen content when weld cooling time ($\Delta$t$_{8}$5/)) is 60s.TEX>5/)) is 60s.

• Corrosion Science and Technology
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• v.6 no.4
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• pp.164-169
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• 2007

Hydrogen induced cracking (HIC) was studied phenomenologically and the effect of microstructure on HIC was discussed for the steels having two different levels of nonmetallic inclusions. Steels having different microstructures were produced by thermomechanically controlled processes (TMCP) from two different heats which had the different level of nonmetallic inclusions. Ferrite/pearlite (F/P), ferrite/acicular ferrite (F/AF), ferrite/bainite (F/B) were three representative microstructures for all tested steels. For the steels with higher level of inclusions, permissible inclusion level for HIC not to develop was different according to steelmicrostructure. On the contrary, HIC occurred also at the martensite/austenite (M/A) constituents regardless of steel microstructure when they accumulated to a certain degree. It was proved that M/A constituents were easily embrittled by hydrogen atoms. Steels having F/AF is resistant to HIC at a given actual service condition since they covers a wide range of diffusible hydrogen content without developing HIC.

• Journal of the Korean Ceramic Society
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• v.29 no.7
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• pp.505-510
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• 1992

The influence of excess iron content (x) and reaction atmosphere on permittivity, permeability and microwave absorbing properties has been investigated in composite specimens embeded with (Ni0.4Zn0.6O)1-x(Fe2O3)1+x powders. A nitrogen atmosphere used for the reaction of the ferrite with excess iron composition (x>0) enhances spinel formation, and thereby increases both the magnetic and the dielectric loss of the ferrite composite. We also investigated the relation between the electromagnetic constants and the absorbing properites using impedance-matching solution maps for zero reflection. It is suggested that a superior microwave absorber can be fabricated through atmosphere and excess iron control during the powder process.

• Nuclear Engineering and Technology
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• v.34 no.6
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• pp.574-585
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• 2002

The microstructural characteristics and its related mechanical properties of RPV cladding have been investigated using small punch (SP) tests. SA508 Cl.3 RPV steel plates were overlay cladded with the type ER309L welding consumables by submerged arc welding process. Although the RPV clad material had a small portion of 5 ferrite phase, it still showed the ductile to brittle transition behavior The transition temperature was determined by the SP test and it depended on the content of $\sigma$ phase, specimen size, and determination methods. The fracture appearance of SP specimen was changed from circumferential to radial cracking as test temperature became low, and below the transition temperature region, ER309L cladding usually fractured along the 6 ferrite by the low temperature failure of ferrite phase.

• Journal of the Korean Ceramic Society
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• v.43 no.11 s.294
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• pp.703-709
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• 2006

We report on the synthesis of highly uniform, single phase zinc and cobalt thin films prepared by the Liquid Phase Deposition (LPD) method. X-Ray diffraction, TGA and EDX measurements support the assumption that the as deposited films are constituted by a mixture of crystallized FeOOH and amorphous M(OH)$_2$ (M=Co, Zn) which is converted upon heat treatment in air at 600?C into the corresponding zinc ferrites. The films with adjustable chemical compositions are identified with a crystal structure as spinel-type and present a spherical or rod-like microstructure, depending on the both the nature and concentration of the divalent transition metal ions. Zinc ferrite thin films present a superparamagnetic behavior above blocking temperatures which decrease with increasing the Zn content and are ferromagnetic at 5 K with coercivities ranging between 797.8 and 948.5 Oe, whereas the cobalt ferrite films are ferromagnetic at room temperature with magnetic characteristics strongly dependent on the chemical composition.

• Journal of Welding and Joining
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• v.33 no.4
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• pp.37-43
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• 2015

Characteristics of dissimilar metal welds between STS 316L and carbon steel ASTM A516 Gr.70 made with GTAW have been evaluated in terms of microstructure, ferrite content, chemical analysis, hardness and corrosion resistance. Three heat inputs of 9.00, 11.25, 13.00kJ/cm were employed to make joints of dissimilar metals with ER309 wire. Based on microstructural examination, the amount of vermicular type of ${\delta}$-ferrite was increased with increasing heat input due to the increase of Creq/Nieq in the second layer of welds. Based on the EDX analysis of weld metals, Cr and Ni content in the 2nd layer increased while those content in the first layer of welds decreased with heat inputs. Cellular solidification mode in the 1st layer and dendritic solidification mode in the 2nd layer due to different cooling rates were prevailed, respectively. Heat affected zone which formed hard microstructure showed higher hardness than the weld metal. The salt spray test of dissimilar metals weld joints showed that the carbon steel surfaces only corroded. The weight loss rate due to corrosion increased up to 100hours but it decreased above 100 hours. There was little difference in the weight loss caused by corrosion regardless of heat inputs.

• Korean Journal of Materials Research
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• v.29 no.6
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• pp.349-355
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• 2019

This study deals with the microstructure and tensile properties of 600 MPa-grade seismic reinforced steel bars fabricated by a pilot plant. The steel bar specimens are composed of a fully ferrite-pearlite structure because they were air-cooled after hot-rolling. The volume fraction and interlamellar spacing of the pearlite and the ferrite grain size decrease from the center region to the surface region because the surface region is more rapidly cooled than the center region. The A steel bar specimenwith a relatively high carbon content generally has a higher pearlite volume fraction and interlamellar spacing of pearlite and a finer ferrite grain size because increasing the carbon content promotes the formation of pearlite. As a result, the A steel bar specimen has a higher hardness than the B steel bar in all the regions. The hardness shows a tendency to decrease from the center region to the surface region due to the decreased pearlite volume fraction. On the other hand, the tensile-to-yield strength ratio and the tensile strength of the A steel bar specimen are higher than those of the B steel bar with a relatively low carbon content because a higher pearlite volume fraction enhances work hardening. In addition, the B steel bar specimen has higher uniform and total elongations because a lower pearlite volume fraction facilitates plastic deformation caused by dislocation slip.

• Journal of the Korean Society for Heat Treatment
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• v.9 no.1
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• pp.34-44
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• 1996

Austenite stainless steel was produced by arc welding with current 650A, voltage 50V and welding speed 10cm/min. It was post-welded and then heat treated at $1,050^{\circ}C$ for 120min. And then it was immersed in water or in air. The microstructural changes, ferrite contents, mechanical properties, and stress corrosion cracking(SCC) were investigated. The SCC was studied in 42wt% boiling $MgCl_2$($140^{\circ}C$) under the constant stress using SCC elongation curve. The results showed that; 1. The as-welded spedimen seemed to increase ${\delta}$-ferrite content largely, and revealed continuous network of lathy and vermicular type. The post-welded heat treatment changed the morphologies of ferrite from continuous type to island type. 2. The as-welded, air and water quenched specimens had the ${\delta}$-ferrite content 9.7%, 3.2% and 2.1% respectively. We also showed that ${\delta}$-ferrite was Cr-rich and Ni-poor by EPMA. 3. The time of failure on the SCC was measured and it was used for corrosion elongation curve. The condition of SCC was investigated under $35kgf/mm^2$ load and the results were as follows; 4. The intergranullar cracking by stress corrosion was most distinct in weld metal while the transgranular cracking occurred in the air cooled specimen.