Effect of alloying Copper on the Corrosion Resistance of Stainless Steels in Chloride Media

Ujiro, T.,Satoh, S.,Staehle, R. W.,Smyrl, W. H. 한국부식방식학회 2003 Corrosion Science and Technology Vol.2 No.3

In order to explain the effect of alloying Cu on the corrosion resistance of stainless steels in chloride mediaIbr both ferritic and austenitic stainless steels, the corrosion behavior of Cu-hearing stainless steels was investigated. Alloying Cu showed heneticial effect in an active potential range and harmful effect in a noble potential range. The beneticial effect of alloying Cu was explained by the stability of deposited Cu on an anodic surface. Difference in the effect of alloying Cu between the ferritic and austenitic steels was ascribed by the differences in their corrosion potentials and thc morphology of the deposited Cu.

Corrosion Resistance of Cr-bearing Rebar in Simulated Concrete Pore Solutions

Tae, Sung-Ho,Ujiro, Takumi Iron and Steel Institute of Japan 2007 ISIJ international Vol.47 No.9

<P>As a fundamental study on the Cr-bearing rebar with the necessary corrosion resistance for use in steel reinforced concrete structures under corrosive environments This study was investigated to corrosion resistance of Cr-bearing rebars in simulated concrete pore solutions with content of chloride ion. The rebars were made from steels containing Cr from 0 to 16%. SUS304 stainless steel and SD345 carbon steel were also used. Simulated concrete pore solutions were saturated with Ca(OH)<SUB>2</SUB>, containing 0.27%, 1.07% and 21.4% NaCl. The pH value of the solutions was adjusted to 12.5, 11, 10 and 9 by HCl. Pitting potential and impedance, corrosion morphology of the steels in the solutions were investigated.The results of the study showed that the corrosion resistance increased as the Cr content increased regardless of the content of chloride ions, and that the Cr-bearing rebars with a Cr content of 5C% and 9% showed good corrosion resistance in 1.07% NaCl solutions at pH 12.5 and pH 10, respectively. Cr-bearing rebar with a Cr content of 16% showed as good corrosion resistance as SUS304 steel even in 21.4% NaCl solutions at pH 10.</P>

Effect of Imposing Temperature Gradient in Stretch Forming Process for Ferritic Stainless Steel Sheets

Takaaki IGUCHI,Takumi UJIRO 한국소성가공학회 2010 기타자료 Vol.2010 No.6

A new stamping method developed by the authors, in which a temperature gradient is imposed on the workpiece during stamping, is capable of improving stretch formability in stamping of ferritic stainless steel sheets. Unlike the conventional warm stamping method, the temperature gradient is utilized in order to diffuse the strain distribution induced in the material. Basically, the portions of the sheets which are in contact with the top of the punch and die face are heated, while simultaneously, the portions in contact with the punch corners and die corners are intensively cooled The authors developed a finite element simulation model of stamping which analyzes mechanical and thermal behaviors simultaneously utilizing LS-DYNA3D. The numerical analysis, combined with a numerical model which evaluates the ductile fracture limit of the material in the high temperature region, confirmed that the new stamping method improves stretch formability and the optimal temperature gradient is given. In order to verify the numerical analysis, an experimental apparatus was constructed, comprising a set of stamping tools containing heaters and cooling circuits. The experiments demonstrated the correctness of the numerical analysis and the effectiveness of the new stamping method.

Corrosion Resistance of Cr-bearing Rebar in Macrocell Corrosion Environments Due to Different Concentrations of Chloride Ions

Tae, Sung-Ho,Noguchi, Takafumi,Ujiro, Takumi Iron and Steel Institute of Japan 2006 ISIJ international Vol.46 No.10

<P>Reinforced concrete specimens were prepared by embedding 10 types of Cr-bearing reinforcing bars having different Cr contents and supplying saltwater from the upper surfaces to allow chloride ions to penetrate into concrete, thereby forming macrocells, with the aim of developing Cr-bearing rebars having corrosion-preventing properties required under macrocell-corrosion conditions due to differences in the chloride concentrations. The time-related changes in the macrocell corrosion current density, soluble chloride ion content of concrete, and half-cell potential were then measured during corrosion-accelerating test up to eight months. Also, the corrosion area and corrosion loss of anodic and cathodic bars were measured at the end of the 8-month corrosion-accelerating test to investigate the corrosion-inhibiting property of Cr-bearing rebars in macrocell corrosion environments due to chloride ion concentration in concrete.As a result, the Cr content required for corrosion inhibition was found to be more than 7% in macrocell corrosion environments with a difference in soluble chloride ion concentrations of not more than 2.4 kg/m<SUP>3</SUP>.</P>

Service Life Estimation of Reinforced Concrete Structures Made Using Cr-bearing Rebars in Microcell Corrosion Environments

Tae, Sung-Ho,Kyung, Je-Woon,Ujiro, Takumi,Shin, Sung-Woo Iron and Steel Institute of Japan 2007 ISIJ international Vol.47 No.9

<P>Reinforced concrete structures made using Cr-bearing rebars subject to microcell corrosion were assumed with the aim of developing Cr-bearing rebars having the required corrosion resistance in microcell corrosion environments. Their service lives were then estimated for each type of corrosion environment based on a microcell corrosion rate model, and requirements for Cr-bearing rebars to achieve a service life of over 100 years were calculated. As a result, the service lives of concrete structures reinforced with Cr-bearing rebars were found to increase as the Cr content increased in all types of corrosion environments. Also, Cr-bearing rebars with Cr contents of not less than 11% and not less than 7% ensured service lives of over 100 years in harsh and moderate chloride attack zones, respectively. In carbonation zones, a Cr content of not less than 3% was proven to provide corrosion resistance for over 100 years.</P>

Corrosion Resistance of Cr-bearing Rebar in Concrete with Chloride Ion Content

Tae, Sung-Ho,Lee, Han-Seung,Noguchi, Takafumi,Ujiro, Takumi,Shin, Sung-Woo The Iron and Steel Institute of Japan 2006 ISIJ international Vol.46 No.7

<P>As a fundamental study on the performance of Cr-bearing rebars in steel reinforced concrete structures exposed to corrosive environments, The test specimens were made by installing 8 types of rebars in concretes with a chloride ion content of 0.3, 0.6, 1.2, 2.4 and 24 kg/m<SUP>3</SUP>. Corrosion accelerated curing were then conducted with them. The corrosion resistance of Cr-bearing rebars was examined by measuring crack widths, half-cell potential, corrosion area and weight loss after 155 cycles of corrosion- accelerating curing.The results of the study showed that the corrosion resistance increased as the Cr content increased regardless of the content of chloride ions, and that the Cr-bearing rebars with a Cr content of 5% and 9% showed high corrosion resistance in concretes with a chloride ion content of 1.2 and 2.4 kg/m<SUP>3</SUP>, respectively.</P>

Corrosion Resistance of Cr-bearing Rebar to Macrocell Corrosion Caused by Concrete Cover Crack

Tae, Sung-Ho,Lee, Han-Seung,Noguchi, Takafumi,Ujiro, Takumi,Shin, Sung-Woo The Iron and Steel Institute of Japan 2006 ISIJ international Vol.46 No.7

<P>Artificial cracks were made in the cover concrete of specimens embedding ten types of steel rebars having different Cr contents with the aim of developing Cr-bearing steel rebars resistant to macrocell corrosion environments induced by cracking in cover concrete. The cracks were subjected to intensive penetration of carbon dioxide (carbonation specimens) and chloride ions (chloride attack specimens) to form macrocells. Both groups of specimens were then subjected to accelerated corrosion curing, during which the macrocell corrosion current density was measured. The corrosion area and corrosion loss were also measured at the end of 105 cycles of this accelerated curing. In a macrocell corrosion environment induced by localized carbonation, the minimum Cr content of rebars required for corrosion resistance was 7%. Rebars with a Cr content of 11% were proven corrosion-resistant in a chloride ion concentration macrocell with a concentration difference of not more than 3 kg/m<SUP>3</SUP>.</P>