• Journal of Welding and Joining
• /
• v.16 no.6
• /
• pp.59-68
• /
• 1998

In this study, effects of solidification modes (primary $\delta$-ferrite, primary ${\gamma}$-austenite) on the pit initiation and propagation in the 304L and 316L austenitic stainless steel weld metals were investigated. The solidification mode of weld metal was controlled by the addition of nitrogen to Ar shielding gas. Through the electrochemical experiments (potentiodynamic anodic polarization and potentiostatic time-current transient test) and metallographic examination (microstructure and elemental distribution), the following results were obtained. The more the volume content of nitrogen in the shielding gas were, the lower critical current density for passivity was observed. In comparison with weldments solidified through the primary $\delta$-ferrite solidification mode and the primary ${\gamma}$-solidification mode, the former showed higher critical pitting potential and a longer incubation time for stable pit initiation than the latter. However, in the pit propagation stage the former exhibited a faster dissolution rate than the latter. These results were believed to ee related to the distribution of alloying elements such as Cr, Mo, Ni and S.

• Corrosion Science and Technology
• /
• v.2 no.5
• /
• pp.247-251
• /
• 2003

The corrosion forms of automotive body panels are various. One of the representations is a corrosion pitting and its propagation on the lapped portion by galvanic corrosion. But it has been difficult in correlation analysis about the corrosion propagation rate and mechanism of pitting and the actual automotive body in field. This present study interprets experimentally the rust pitting occurrence mechanism on the lapped panels through experimental methods. And field car investigation was executed for correlation analysis with experimental results. This paper compares corrosion propagation rate by pitting on hot-dip galvannealed steel sheets with corrosion forms in the automotive field condition. The research fundamentals which make it possible to predict the pitting occurrence and propagation on the lapped panels in the actual vehicles are given.

• Proceedings of the KSME Conference
• /
• 2004.11a
• /
• pp.319-324
• /
• 2004

In this study, the high strength and superior toughness spring steels as the suspension material, used for automobile and railroad industries were utilized to carry out the following investigations. Corrosion times were controlled in 7, 14, 30 and 60days to examine the relation between corrosion pit and compressive residual stress in the static corrosion environment after shot peened. And then corrosion current and corrosion potential were measured for every 24 hours to investigate the corrosion mechanism. Shot peened material shows the low or rate of corrosion current as compared with unpeened material. In case of peened material which has the highest residual stress, it has a low corrosion current density.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.13 no.3
• /
• pp.17-23
• /
• 2005

In this study, the high strength and superior toughness spring steels as the suspension material, used for automobile and railroad industries were utilized to carry out the following investigations. Corrosion times were controlled in 7, 14,30 and 60days to examine the relation between corrosion pit and compressive residual stress in the static corrosion environment after shot peened. And then corrosion current and corrosion potential were measured for every 24 hours to investigate the corrosion mechanism. Shot peened material shows the low or rate of corrosion current as compared with unpeened material. In case of hot peened material which has the highest residual stress, it has a low corrosion current density.

• Journal of Ocean Engineering and Technology
• /
• v.6 no.1
• /
• pp.140-147
• /
• 1992

Corrsion fatigue test was performed under rotated bending in 3.5% NaCl aqueous solution having a temperature from 278.deg.K in order to investigate the effects of aqueous solution remperature on the corrosion fatigue fracture of raw material steel(SS41) and dual phase steel that was produced from SS41 by a series of heat treatment. Corrosion fatigue life decreases remarkably with increase in solution temperature or with decrease in stress level. The corrosion fatigue life and the crack propagation rate at 303.deg.K show the similar behaviors with those at 318.deg.K, which is assumed to be caused by concentration polarization phenamena. The number and the lengths of microcracks increase with increase in solution temperature, so they lead to the decrease in corrosion fatigue life.

• Journal of Advanced Marine Engineering and Technology
• /
• v.19 no.3
• /
• pp.62-69
• /
• 1995

In order to investigate the effect of TiN coating on corrosion fatigue behavior of metal, the rotary bending corrosion fatigue tests were carried out in 3% NaCl solution by using the round bar specimens of high-speed steel, SKH-9, coated with TiN by PVD method. From the experimental results, fatigue strength of TiN coating steel in air was obvious improvement as compared with that of the substrate because of the restriction of dislocation movement in near surface of the substrate by hard thin film. In 3% NaCl solution, corrosion fatigue life of TiN coating specimen in high stress level was improvement same as in air. But in low stress level, corrosion fatigue life of TiN coating one was equivalent to that without coating, due to much crack initiated from corrosion pits formed at the substrate by failure of coating layer.

• Corrosion Science and Technology
• /
• v.10 no.1
• /
• pp.37-42
• /
• 2011

Aluminum was electrochemically etched in acid solution and the surface area was magnified by the formation of etch pits. Etched aluminum was covered with a compact and dense dielectric oxide film by anodization and applied to the aluminum electrolytic capacitor electrode. Capacitance of aluminum electrolytic capacitor is closely related with surface area, which depends on size and number of etch pits. Size of etch pits need to be controlled because inside of the pits can be buried by the formation of dielectric oxide film. In this work, the effect of ultrasound pretreatment on the aluminum etch pit formation and capacitance were investigated. Additionally, the relationship between the second etching effect on pit size and capacitance was studied.

• Journal of Industrial Technology
• /
• v.17
• /
• pp.291-295
• /
• 1997

The tests of stress corrosion cracking in structural carbon steel were carried out under the conditions of acid fog and general water. As the result of measurement SCC rupture time under acid fog was observed to be much shorter than that of general water at the same stress level. Therefore, acid fog drops the SCC strength in structural carbon steel due to strong corrosion. In the SCC process by acid fog, crack initiation was caused by pit corrosion and local stress concentration, and distinctive feature of crack growth shows branching since crack grows to the corrosion direction. Moreover, corrosion products were observed by clevage corrosion on the crack surfaces.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.7 no.5
• /
• pp.89-95
• /
• 1999

In this study, the corrosion resistance of the aluminum casting commercial materials used in the automotive engine parts with respect to the anti-freeze coolant environment has been tested by the potentio dynamic method. especially, the effect of borax additive in engine coolant on the corrosion resistance of the aluminum casting materials has been evaluated. It was found that the borax in commercial engine coolant, used to prevent the corrosion in cast iron engine, causes a pit corrosion of aluminum casting materials at high temperature. During the engine endurance test with the coolant containing borax, the aluminum cylinder head was failed by the pitting corrosion near the exhaust port. Conclusively, it was suggested that the use of borax in the anti-freeze coolant be restricted for the automotive with aluminum cylinder head.

• Journal of the Korean institute of surface engineering
• /
• v.31 no.5
• /
• pp.251-260
• /
• 1998

Stainless Steel is being used widely for various purposes due to its good corrosion resistance. There have been many researches to produce colored stainless steel by several methods such as anodizing and ion-plating. In this experiment, we $Ti_XN$(C,O) on the films SUS304, aluminium, and glass substrates with DC magentron sputterinng system made by Leybold Hereus, and strdied the structur, corrsion and pit characture of the TiXN observed by TeM image was black and whink and white columnar hed a very fine(200$\AA$) dense sturcture,and the diffraction resistance at the $3{\times}10_6A/\textrm{cm}^2$ and $10_{10}\times{cm}^2$current density were obtained in the under-stoichiometry $Ti_xN$ compound of Ar/$N_2$(Ar:$N_2$=100:6, titanium-rich compound) and the over-stoichiometry compound of Ar/$N_2$((Ar:$N_2$=60:15) respectively. When the thiness was over 1.64$\mu\textrm{m}$, good pit resistance could be obtained and its improvement was especially affected by perfect surfaceface. Typical TiN anodic polarzation curves of very unstable corrosion were observed by $Ti_xN$ film on the glass and perfect film of 3.28$\mu\textrm{m}$ thickness.