• Proceedings of the KWS Conference
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• 2005.06a
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• pp.273-275
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• 2005

Variation of hardness and corrosion potential of welding zone was investigated when cold arc welding of cast iron was carried out with a parameter of Ni electrode. Hardness of HAZ was the highest compared to other welding zone. And corrosion potential of HAZ was also more negative value than other welding zone. However there was not a proportional relation between hardness and corrosion potential. Local corrosion of HAZ was clearly appeared than other welding zone by small anode and large cathode in seal water solution.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.325-328
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• 2008

In recent years, developments of light weight vehicle are one of the most important issues in automotive industry. It is important to know the variations of the mechanical properties in the hydro forming process for the safe and durable design purposes. Generally, tube hydroforming process consists of three main processes such as bending, preforming, and hydroforming. It means that the strain hardening histories of final products are nonlinear. In this study, strain hardening behavior during hydroforming has been investigated by hydroforming of engine cradle as a model process. The variation of mechanical properties such as local hardness and strength were used as an index of strain hardening during respective processes. The correlationship between strength and hardness obtained from tensile test has been equivalently converted into correlation between hardness and measured strain.

• Journal of Welding and Joining
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• v.22 no.1
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• pp.43-49
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• 2004

Contact tip is located so near to welding arc that it is heated to high temperature during long time welding. In such a situation, tip changes in its microstructure and in turn its mechanical properties. This study was intended to investigate those changes by using simulated heat treatment. As a result of this study, it was confirmed that tip of Cu-P alloy hardened with severe cold deformation lose its initial hardness to a large extent within 60 min due to the occurrence of rapid recrystallization while that of Cu-Cr composition hardened by proper aging treatment can preserve its intial hardness for about 1,000 min or longer. Based on these results, suggested was a guideline that can classify contact tips into two different grades: deformation-hardened type and precipitation-hardened type. Following a guideline, a tip with Cu-Cr composition can be classified into the deformation-hardened type if it is in the over-aged condition. Such a guideline is well described.

• 한국해양학회지
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• v.3 no.2
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• pp.47-54
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• 1968

Monthly mean values for EDTA hardness in the Han River water were determined for March 1966 through May 1967. The hardness was retained a range of 22-59 mg/L the maximum value of 59 mg/L was approached in the months of mid-winter, indicating a seasonal variation. The annual ranges of Ca and Mg were 3.7-9.1 mg/L, 1.5-10.4 mg/L, respectively. The annual range of Mg:Ca ratio was 0.18-2.60. And the hardness correlated closely with Mg volume. In Korea, fortunately, most river waters are not yet suffering from damaging pollution. We must try to establish our water quality criteria based on scientific data, and make research recommendations for the following water uses; public water supplies, aquatic life and wildlife, industry, recreation and aesthetics.

• Korean Journal of Environment and Ecology
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• v.25 no.3
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• pp.295-301
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• 2011

In order to investigate the geographical variation of Glycine max distributed in southern area of Korean peninsula, 19 local strains(Goseng, Pyeongchang, Ganghwa, Pocheon, Geumsan, Seocheon, Jincheon, Danyang, Tongyeong, Sancheong, Gumneung, Wolseong, Woolneung, Wando, Naju, Gochang, Jangsu, Jeju, Bukjeju), which located from $33^{\circ}15'N$ to $38^{\circ}11'N$, were selected according to their latitudes and geographical distances. The seeds of these strains were collected and their contents of mannose and galactose were investigated. Mannose contents in the seeds were variable in the range between the highest 12.207mg/g(Gochang) and the lowest 6.648mg/g(Geumsan). The contents of galactose were represented remarkable differences from 9.967mg/g(Danyang) to 16.949mg/g(Bukjeju) also. The local strains were classified into 4 variation types such as the inland type I(Wolseong, Jangsu, Danyang), the coastal type I(Gochang, Naju, Jeju, Goseng, Woolneung, Bukjeju, Ganghwa, Seocheon, Tongyeong), the inland type II(Geumsan, Pocheon, Pyeongchang) and the coastal type II(Wando, Jincheon) and 2 strange strains(Gumneung, Sancheong) according to the geographical climatic type and the ratio of mannose/galactose, which indicate the hardness of seeds in Leguminosae, ranged from 0.63 to 0.78. The variation types are very significant genecologically as an evidence for microevolution related to speciation in cultivated plants.

• Journal of the Korean Society for Heat Treatment
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• v.13 no.4
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• pp.246-252
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• 2000

Stellite 12 alloy-powder was overlaid on 410 stainless steel valve seat using plasma transferred arc(PTA) process. Variation of characteristic of microstructure and hardness of deposit with current(90~150 A) and preheat temperature(R.T.~$400^{\circ}C$) was investigated. Important conclusion obtained are as follows; All welding conditions used produced a sound deposit layer with no defect in single pass welding. The maximum deposit had 4.0~4.8 mm in thickness and its bead width was increased with increase of current and preheat temperature. The deposit showed hypoeutectic microstruture, which was consisting of primary cobalt dendrite and networked $M_7C_3$ type eutectic carbides. The amount of eutectic carbides was decreased and its dendritic secondary arm spacing was increased with increase of current. Hardness of the deposit was decreased with increase of current. Preheat temperature up to $400^{\circ}C$, however, showed little influence on the hardness and microstructure. The hardness was also influenced by diluted Fe content near the interface in addition to microstructure and dendritic secondary arm spacing. Hot hardness at $500^{\circ}C$ showed higher than 300 HV.

• Journal of Technologic Dentistry
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• v.18 no.1
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• pp.15-25
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• 1996

This study is to measure and compare the hardness and tensile strength of each time after we recast seven times continually only with and metal alloy Chromium-Cobalt alloy used in the production of partial denture frame work. The result of the experiment were as follow; 1) The result of the hardness measurement The result of the first casting was $490.48{\pm}38.38$ and that of the second recasting was $455.18{\pm}35.61$ and form the third recasting. the result were $518.38{\pm}37.68$ and over. The change of the hardness difference between each recasting was as follow; The hardness difference between the first casting and the second recasting was $35.25{\pm}31.93$ and that between the second recasting and the third recasting was $63.20{\pm}54.02$. There was a statistically significant difference(P<0.01) in the above hardness, however, there was little difference on the whole. And after the third recasting, the hardness grew high a little bit. That is why low-melting metals such as Cr, Mn, Cu of alloy ingredient was evaporated or there was an effect of changes in metal crystal structure, I suppose. 2) The result of the tensile strength measurement. There was a statistically significant difference(P<0.01) between the first casting and the second, the fourth recasting, however. there was little difference in general.

• Corrosion Science and Technology
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• v.7 no.2
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• pp.134-137
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• 2008

Cold arc welding of cast iron has been widely used with repair welding of metal structures. However its welding is often resulted in the galvanic corrosion between weld metal zone and heat affected zone(HAZ) due to increasing of hardness. In this study, corrosion properties such as hardness, corrosion potential, surface microstructures, and variation of corrosion current density of welding zone with parameters of used electrodes for cast iron welding were investigated with an electrochemical evaluation. Hardness of HAZ showed the highest value compared to other welding zone regardless of kinds of used electrodes for cast iron welding. And its corrosion potential was also shifted to more negative direction than other welding zone. In addition, corrosion current density of WM in polarization curves was qualitatively smaller than that of HAZ. Therefore galvanic corrosion may be apparently observed at HAZ. However galvanic corrosion may be somewhat controlled by using an optimum welding electrode.

• Journal of the Korean Society for Heat Treatment
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• v.3 no.4
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• pp.10-22
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• 1990

A study has been investigated on the effect of mechanical properties (tension strength, rotary bending fatigue strength, wear resistance, hardness) according to the carbide particle size variation by the treatment of 1) quenching tempering, and 2) quenching, subzero treatment and tempering. The material used in this investigation was a typical bearing steel, high C high Cr, AISI E 52100. The result obtained in this study were as follows : (1) Finer the carbide particle size increasing the hardness and retained austenite in same quenching condition. (2) Finer the carbide particle size reduced the tension and rotary bending fatigue which were resulted from austenite grain growth and carbide precipitation on grain boundry that induced by carbide refine heat treatment. (3) Finer the carbide particel size increasing the wear resistance which were resulted by uniform distribution of carbide and increased hardness induced by microstructural uniform hardenability of matrix. (4) When the carbide particles were refinded, subzero treatment is effective only wear resistance and hardness.

• Journal of Advanced Marine Engineering and Technology
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• v.26 no.1
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• pp.68-75
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• 2002

Stellite 12 alloy-powders were overlaid on 410 stainless steel valve seat by plasma transferred arc(PTA)process. Variation of microstructure and hardness of overlaid deposit with aging time at $750^{\circ}C$ was investigated. The deposit showed hypoeutectic microstructure, which was consisting of primary cobalt dendrite and networked $M_{7}C_{3}$type eutectic carbides. After aging new M_{23}C_{6}$ carbide was formed by the partial decomposition of $M_7C_3$ type eutectic carbides and finely dispersed $M_{23}C_6$ type carbides were also precipitated in the matrix. Hardness of the deposit was increased with increase of aging time at $750^{\circ}C$ and showed maximum value at 35hours. After showing maximum value, it was fallen down again at 70hours because of overaging. The increase of hardness in aging is ascribed to the formation of new stable $M_{23}C_6$ type carbide by the partial decomposition of $M_7C_3$ type eutectic carbides and also precipitation of finely dispersed $M_{23}C_6$ carbides in matrix.