• Journal of the Korean Society for Heat Treatment
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• v.14 no.2
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• pp.81-88
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• 2001

The effects of post-oxidation and sulfnitriding treatments on the phase transformation in the nitrided case of tool steels have been studied. Dense and compact $Fe_3O_4$ layer was formed at the outer surface of nitride compound layer by post-oxidation treatment and multi layer of iron sulfide(FeS) was formed in the compound layer by sulfnitriding treatment. The surface hardness decreased because of formation of the soft oxide or sulfide at the nitride surface. Diffusion layer of nitride case was not affected by post-oxidation treatment or sulfnitriding treatment of nitrided alloy tool steels.

• Journal of the Korean Society for Nondestructive Testing
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• v.8 no.1
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• pp.38-43
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• 1988

Microstructure and mechanical properties of most steels change by heat treat treatment. Such variation of stucture and properties of steel cause an impedance change on electromagnetic induction coil. The objective of this study is, by searching the relationship between the mechanical property or microstructural changes and impedance value of induction coil, to examine the applicablity of a monitoring the heat treated condition of products nondestructively.

• Journal of Ocean Engineering and Technology
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• v.16 no.3
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• pp.59-64
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• 2002

In the present study, we examined the influence of prestrain on creep strength of Class M alloy(STS310S) and Class A(STS310J1TB) alloys containing precipitates. Prestrain was given by prior creep at a higher stress than the following creep stresses. Creep behaviour before and after stress change and creep rate of pre-strained specimens were compared with that of virgin specimens. Pre-straining produced the strain region where the strain rate was lower than that of a virgin specimen both for STS310J1TB and STS310S steels. The reason for this phenomenon was ascribable to the viscous motion of dislocations, the interaction between dislocations and precipitates in a STS310J1TB steel, and the interaction of dislocations with sub-boundaries in a STS310S steen which has the higher dislocation density and smaller subgrain size resulted from pre-straining at higher stress.

• Journal of the Korean Society for Heat Treatment
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• v.17 no.2
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• pp.78-86
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• 2004

Effects of the annealing parameters on the formation of ferrites transformed at low temperatures were studied in cold-rolled ultra low carbon steels with niobium and/or chromium. Niobium and chromium were found to be effective in the formation of the low temperature transformation ferrites. The low temperature transformation ferrites more easily formed when both higher annealing temperature and longer annealing time, allowing substitutional alloying elements to distribute between phases, are in combination with faster cooling rate. It was found from EBSD study that the additions of niobium or chromium resulted in the increase in the numbers of high angle grain boundaries and the decrease in those of the low angle grain boundaries in the microstructures. Both granular bainitic ferrite and bainitic ferrite were characterized by the not clearly etched grain boundaries in light microscopy because of the low angle grain boundaries.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.129-130
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• 2010

Lap splice of longitudinal reinforcing steels was located in the plastic hinge region of most bridge piers that had been designed and constructed before the adoption of the 1992 seismic design provision of Korea Highway Design Specification. This research aims at improving the seismic performance of reinforced concrete bridge piers with lap-spliced longitudinal steels, of which the plastic hinge region was wrapped by the shape memory alloy (SMA) wires. Quasi-static test was used to investigate the seismic behaviours of RC test specimens.

• International Journal of Korean Welding Society
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• v.2 no.1
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• pp.52-56
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• 2002

This report was prepared to give informations on a proper way to develop new consumables for the steels with improved weldability. Traditionally, hydrogen control has been pursued mainly for suppressing the HICC in HAZ but it also has contributed to HICC in weld metal. Facing the limitations in reducing the hydrogen content, it is now important to consider the microstructural control approach in order to improve the HICC resistance of weld metal . It has been shown that changes in alloy design, and hence composition and microstructure, was quite effective in producing high strength weld metal with improved resistance to cold cracking. Besides the economic test methods for evaluating susceptibility of multipass weld metal is essential to promote the development of welding consumables.

• Journal of Welding and Joining
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• v.15 no.5
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• pp.46-55
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• 1997

This study has evaluated the liquation cracking behavior in the heat affected zone of several Ni base superalloys (Incoloy 825, Inconel 718 and Inconel 600). 304 and 310S austenitic stainless steels were also included for comparison. In addition, the mechanism of liquation cracking in the HAZ was postulated based on the extensive microstructural examinations with SEM, EDAX and TEM. The liquation cracking resistance of Ni base alloys was found to be far inferior to that of austenitic stainless steels. The liquation cracking of Incoloy 825 and Inconel 718 was believed to be closely related with the Laves-austenite(Ti rich in 825 and Nb rich in 718) and MC-austenitic eutectic phases formed along the grain boundaries by constitutional liquation and incipient melting under rapid welding thermal contraction. Further, liquation cracking resistance of the HAZ was dependent not only upon the type and amount of low melting phases but also on the grain size.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.931-932
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• 2006

The microstructures of Ni-containing P/M steels produced by admixed powders or diffusion alloyed powders are usually heterogeneous. To improve the microstructure homogeneity, the effects of Mo and Cr additions in the prealloyed powder form were examined. The results showed that the microstructural homogeneity was improved and superior mechanical properties were achieved with increases in the alloy content, particularly for the Cr. Such a beneficial effect was attained due to the reduction of the repelling effect between Ni and C, as was demonstrated through thermodynamic analysis using the Thermo-Calc software.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1004-1005
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• 2006

The effect of tempering temperature and microstructure on dry sliding wear behavior of quenched and tempered PM with 0.3% graphite and 1-2% Ni steels was investigated. The sintered specimens were quenched from $890^{\circ}C$ and then tempered at $200^{\circ}C$ and $600^{\circ}C$ for 1 hr. Wear tests were carried out on the quenched$\neq$tempered specimens under dry sliding wear conditions using a pin-on-disk type machine at constant load and speed. The experimental results showed that the wear coefficient effectively increased with increasing tempering temperature and decreased with increasing Ni content.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.405-406
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• 2006

Raw materials from different sources, produced by a given process and having equal chemical composition, are supposed to be equivalent. The differences in sintering behavior have been investigated on P/M steels obtained from four diffusion-bonded powders (Fe + Ni + Cu + Mo) on atomized iron base, at the same alloy contents. Two levels of carbon and two sintering conditions have been investigated. Dimensional changes, C content, hardness, microhardness pattern, universal hardness, fractal analysis, pore features, microstructure features, and rupture strength have been compared to characterize different raw materials. The results show that the claimed equivalence is not confirmed by experimental data.