Jong Pil Won

Characteristics of Inconel 718 Filler Metal Affecting to Welding Metal Zones of Cast Steel for Piston Crown Material

Since the oil price has been significantly jumped for recent some years, the diesel engine of the merchant ship has been mainly used the heavy oil of low quality. Thus, it has been often exposed to severely corrosive environment more and more because temperature of the exhaust gas of a combustion chamber is getting higher and higher with increasing of using the heavy oil of low quality. As a result, wear and corrosion of the most parts surrounded with combustion chamber is more serious compared to the other parts of the engine. Therefore, an optimum repair welding for these parts is very important to prolong their lifetime in a economical point of view. In this study, Inconel 718 filler metal was welded with GTAW method in the cast steel which would be generally used with piston crown material. And the corrosion properties of weld metal zone, heat affected zone and base metal zone were investigated using electrochemical methods such as measurement of corrosion potential, anodic polarization curves, cyclic voltammogram and impedance etc. in 35% H2SO4 solution. The weld metal and base metal zones exhibited the highest and lowest values of hardness respectively. Furthermore, the corrosion current density of the weld metal zone indicated the lowest value, having the highest value of hardness. The corrosive products with red color was more or less observed in the base metal zone, while the weld metal zone exhibited the general corrosion without corrosive products of red color. The microstructure of the pearlite with black color was predominantly observed in the base metal zone, however, the microstructure of ferrite with white color increased increasingly in the heat affected zone, and the microstructure of ferrite with white color was significantly observed in the weld metal zone. In particular, the polarization characteristics such as impedance, polarization curve and cyclic voltammogran associated with corrosion resistance property were well in good agreement with each other. Keywords : Repair welding, Inconel 718 filler metal, GTAW, Weld metal zone, Electrochemical method, Corrosion current density, Hardness. Microstructure

Evaluation of Welding Metal Zones in the Case Welded with 0.5 Mo Filler Metal to Forged Steel for Piston Crown Material

Since the oil price has been significantly jumped for recent some years, the diesel engine of the merchant ship has been mainly used the heavy oil of low quality. Thus, it has been often exposed to severely corrosive environment more and more because temperature of the exhaust gas of a combustion chamber is getting higher and higher with increasing of using the heavy oil of low quality. As a result, wear and corrosion of the most parts surrounded with combustion chamber is more serious compared to the other parts of the engine. Therefore, an optimum repair welding for these parts is very important to prolong their lifetime in a economical point of view. In this study, 0.5Mo filler metal was welded with SMAW method in the forged steel which would be generally used with piston crown material. And the corrosion properties of weld metal zone, heat affected zone and base metal zone were investigated using electrochemical methods such as measurement of corrosion potential, anodic polarization curves, cyclic voltammogram and impedance etc. in 35% H2SO4 solution. The heat affected and base metal zones exhibited the highest and lowest values of hardness respectively. And, the corrosion current density of the heat affected zone indicated the lowest value, having the highest value of hardness. It appeared that the corrosive products with red color was wholly covered on the surface of the base metal zone, while its products was not observed in the heat affected zone. The microstructure of the pearlite with black color was more or less observed in the base metal zone with patterns such as crystal and needle, in particular, the crystal pattern of ferrite microstructure with white color was considerably included in the base metal and heat affected zone, and the ferrite microstructure was significantly observed in the weld metal zone. In particular, the polarization characteristics such as impedance, polarization curve associated with corrosion resistance property were well in good agreement with each other. Keywords: Forged steel, Microstructure, 0.5Mo filler metal, SMAW, Weld metal zone, Electrochemical method, Corrosion current density, Hardness.

Passing Aged Years to Polarization Characteristics of the Steel Bar Embedded in Mortar Specimen (W/C:0.4)

The structures of reinforced concrete has been extensively increased with rapid development of industrial society. Furthermore, these reinforced concretes are often exposed to severely corrosive environments such as sea water, contaminated water, acid rain and seashore etc.. Thus, the corrosion problem of a steel bar embedded in the concrete is very important in terms of the safety and economic points of view. In this study, a multiple mortar test specimen (W/C:0.4) that had six types of cover thickness was prepared and immerged in flowing seawater for five years. And the effects of cover thickness and immersion years on the corrosion properties of the steel bars were investigated using electrochemical methods such as measuring corrosion potential, anodic polarization curve, and impedance. At the beginning of immersion (0 year), corrosion potentials exhibited increasingly nobler value with increasing the cover thickness. However, after being immersed for 5 years, the corrosion potentials conversely shifted in the positive direction with decreasing the cover thickness. As a result, the relationships between corrosion potential and cover thickness were not in good agreement with each other after 5 years. In addition, after 5 years, the thinner cover thickness, the higher value of impedance at 0.01Hz. It is considered that corrosive products deposited on the surface of the steel bar embedded in mortar specimen in the case of thinner cover thickness played the role as a resistance polarization which resulted in decreasing the corrosion current density. Consequently, it seemed to be somewhat problem that evaluation on the corrosion property in reinforced steel would be estimated by only the corrosion potential measurement. Therefore, it is suggested that we should take into account various parameters such as cover thickness, corrosion potential, and immersed years etc. for its accurate assessment. Keywords : Cover thickness, Corrosion potential, Anodic polarization curve, Impedance, Resistance polarization

Evaluation of Thermal Conductivity and Heat Flux by Insulation Analysis of Double-Wall for Cryogenic Storage Tank

The double-walled steel vessel filled with insulation powder in the space between two walls was used to minimize heat transfer by radiation and conduction in cryogenic storage tank. And, evaluation of the insulation effect by the thermal conductivity of perlite powder and the effect of heat flux by welding conditions were carried out with insulation analysis of double-wall. The solid supports were also used to bear the weight of the inner container. Furthermore, thermal and structural analysis of the tank was performed to study the effect of vacuum and weldment geometry of the internal supports. If the degree of vacuum were low, the thermal conductivity of perlite increases rapidly and the heat flux should be increased in proportion to the thermal conductivity. Two types of solid supports did not show significant differences in the aspect of working stress or heat flux. Therefore, it is considered that the heat flux is less sensitive against the weldment geometry.

The Effect of Cover Thickness to Corrosion Characteristics of Reinforced Steel Bar Emedded in Mortar Specimen (W/C:0.6) Aged 5 Years in Seawater

Reinforced concrete structures have been increasingly widely used through numerous industrial fields. These structures are often exposed to severely corrosive environments such as sea water, contaminated water, acid rain, and the seashore. Thus, corrosion problems of the steel bars embedded in concrete are very important from a safety and economic point of view. In this study, the effects of cover thickness on the corrosion properties of reinforced steel bar embedded in mortar specimen (W/C:0.6) were investigated using electrochemical methods such as corrosion potentials, polarization curves, cyclic voltammograms, galvanostat and potentiostat. Corrosion potentials shifted to the noble direction, and the value of AC impedance also exhibited a higher value with increasing cover thickness, furthermore, polarization resistance also increased with increasing cover thickness. This is probably that the thinner cover thickness, seawater solution is easy to arrive at embedded steel compared to other thicker cover thickness, so, its steel bar may be easily corroded due to chloride ion, which is resulted in shifting corrosion potential to negative direction, decreasing polarization resistance. Consequently, it is considered that the relation between corrosion resistance of reinforced steel and cover thickness is nearly matched with each other. However, its corrosion resistance estimated by measurement of corrosion potential was not well in agreement with value obtained by polarization curves.

Corrosion Characteristics of Reinforced Steel Bar Emedded in Mortar Specimen(W/C:0.4) Aged 5 Years in Seawater

Reinforced concrete structures have been increasingly widely used in numerous industrial fields. These structures are often exposed to severely corrosive environments such as sea water, contaminated water, acid rain, and the seashore. Thus, corrosion problems of the steel bars embedded in concrete are very important from a safety and economic point of view. In this study, the effects of cover thickness on the corrosion properties of reinforced steel bar embedded in mortar specimen were investigated using electrochemical methods such as corrosion potentials, polarization curves, cyclic voltammograms, galvanostat and potentiostat. Corrosion potentials shifted in the noble direction, and the value of AC impedance also exhibited a higher value with decreasing cover thickness, furthermore, polarization resistance also increased with decreasing cover thickness. This is probably that the thinner cover thickness, it is easy for the dissolved oxygen and chloride ion to intrude and diffuse to the steel bar, thereby making it easier to corrode on the steel surface compared to thicker cover thickness, which is resulted in forming the corrosive products on the steel surface. Therefore, it is considered that the corrosive products plays a role to provide nobler value of corrosion potential and higher value of impedance. Consequently, it seems that the corrosion resistance of inner steel bar may depend on mainly not cover thickness but the resistance polarization due to corrosive products in the case of immerged for 5 years in this experiment.

Characteristics Evaluation of Weld Metal Zone Welded with Various Repair Welding Filler Metals

Recently, the fuel oil of diesel engine of marine ships has been changed with heavy oil of low quality as the oil price is getting higher and higher. Therefore, the wear and corrosion against all parts of the engine, such as cylinder liner, piston crown, and spindle and seat ring of exhaust valves has predominantly increased due to its consumption. Thus, the repair welding of the piston crown is a unique method to prolong its life in a economical point of view. In this case, filler metals having a better corrosion and wear resistance are mainly being used for repair welding. However, the piston crown on the ship’s job site is often actually being welded with mild filler metals. Therefore, in this study, the mild filler metals, such as E5016, E1216, and E2316, were welded to the SS401 steel as the base metal, and the corrosion properties of their weld metal zones with and without post weld heat treatment were investigated with some electrochemical methods in 0.1% H2SO4 solution. The weld metal zone welded with E1216 filler metal exhibited the best corrosion resistance among the filler metals with irrespective of heat treatment, however, its corrosion resistance was somewhat decreased due to the post weld heat treatment(annealing:625oC, 2hr). In particular, the weld metal of E2316 exhibited relatively a good corrosion resistances by the post weld heat treatment.

Evaluation of Effect of Welding Methods to Corrosion and Hardness Characteristics of Welded Zone

Recently a fuel oil of the diesel engine in the merchant ship has been changed with heavy oil of low quality as the oil price is getting higher and higher .Therefore, the wear and corrosion against all parts of the engine are significantly increased with using of heavy oil of low quality. In particular, the degree of wear and corrosion in between spindle and seat ring of exhaust valve are more serious compared to the other parts of the engine due to severe environment such as the high temperature of exhaust gas and repeating impact. Thus, repair welding is a unique method to prolong their lifetime in an economical point of view. In this study, an effect of welding methods to corrosion and mechanical properties of both weld and base metal zone was investigated with some electrochemical methods such as measurement of corrosion potential, cathodic and anodic polarization curves, cyclic voltammogram and AC impedance etc. in. The hardness of the weld metal zones exhibited comparatively higher values than that of the base metal zone. And their corrosion resistances were also increased compared to the base metal. The weld metal zone of P1F( plasma welding with 1 pass) showed a relatively good corrosion resistance as well as the hardness compared to the other welding methods. Consequently, it is considered that plasma welding method is a desirable method compared to other welding methods for both better corrosion and hardness properties.

Evaluation on the Plate Laminated Method Using 3D CAD/CAM/CAE System for Construction of Canoe Hull

Generally canoes are the most popular boat in leisure activity on the water. Recently, its demand has been continuously increased, furthermore, the recent users hope that those canoes are high degree of quality, mass production and cheap cost etc.. For solving this problems, the wooden canoe manufactured by the strip construction method has been commonly used for leisure activity of various field. However, this method mentioned above is not suitable for mass production which needs a effective operation, managements as well as cheap product cost. In this paper, the new construction method, called the piling-up laminated construction method which is composed with new both 3D design system and manufacturing technology to satisfy all the canoe shape accepting previous users various needs and the need of mass production is studied with using the laminated wooden plates. The manufacturing technology of the laminated plate kit type could be applied flexibly in both the mass production and small production by users order. Furthermore, the laminated plate kit type compared to the strip construction method could be decreased to about 1/3 the time required for production, manpower and cost. Consequently, it could be verified that the laminated plate kit type was able to make a major contribution to improve the reliability of product.

The Effect of Thiourea Additive to Elimination of the Iron Dissolved in Flux Solution of Hot Dip Galvanizing Process

Hot dip galvanizing is being widely used to the numerous constructional steels such as a guard rail of high way, various types of structural steel for manufacturing ship and for some other fields etc.. Recently, the cost of zinc is getting higher and higher, thus, a proper manufacturing process should be developed possibly to reduce the cost of production. one of hot dip galvanizing process, that is, flux solution immersion process is very important to control more effective coating. However, flux solution is deteriorated with increasing its using time because dissolved iron from structural steel due to continuous flux treatment was increasingly increased, which is resulted in coating badness and increment of dross. In this study, the effect of additives to elimination of iron dissolved in flux solution was investigated with four types of inner solution, that is, solution of inner barrel was filled with seawater, NaOH, NH4Cl, including parameters of amounts of thiourea(0.2,0.4 ,0.6 and 0.8g) and electrolysis experiment was carried out with applied current density at 20mA/cm2. The best effect for elimination of iron from flux solution is considered that inner barrel with separator should be filled with solution different from original flux solution which contained in iron ion, that is, its inner solution should be composed with seawater added with additives such as thiourea(0.4g), NaOH(0.2 g) and NH4Cl(10g). In particular, we can see that the optimum amount of thiourea to extract effectively iron from flux solution is 0.4g.