Shigeki Azuma

Intergranular corrosion resistance of stainless steel diffusion‐bonded joints with B‐containing amorphous insert metal

Summary This paper describes an investigation of the intergranular corrosion resistance of austenitic stainless steel joints diffusion‐bonded with an amorphous insert metal containing 1.5 mass% boron, in order to clarify optimum bonding conditions for austenitic stainless steel pipes joined by a high‐speed diffusion bonding system. The sulphuric acid/copper sulphate test is conducted to evaluate the intergranular corrosion of bonded joints caused by a Cr depletion zone. Joints diffusion‐bonded with lower bonding pressure and shorter bonding time are more sensitive to intergranular corrosion. Under such bonding conditions, Cr boride and Cr carboboride precipitates causing selective corrosion are found in the bonding layer. Joints diffusion‐bonded under higher bonding pressure and with longer bonding time, however, show no intergranular corrosion and few precipitates in the bonding layer. With regard to the B‐containing amorphous insert metal used in the present investigation, the optimum bonding conditions...

Characterization of Al rich oxide layers on austenitic stainless steels by fluorescence spectroscopy

Abstract An Al rich oxide passivation technique has been developed to improve the corrosion resistance of the stainless steel to ozone added ultra-pure water. Fluorescence spectroscopy was applied to the study on the selective oxidation of aluminum containing austenitic stainless steel in low oxygen atmosphere at 1,353K. It was found that in the thermal oxidation under low oxygen pressure, the minor alloying constitution of Al resulted in the formation of thin oxide layers. The frequency shifts of fluorescence spectra show that the compressive stresses exist in the oxide layers as a result of the difference of the thermal expansion coefficients between substrate steels and α-Al2O3, and depends on the thickness of the oxide layers. It is confirmed that pure α-Al2O3 protective layers grown on the stainless steels, which remain stable and attached to the stainless steels in ozone added ultra-pure water. These act as a diffusion barrier and protect the stainless steels from the metal dissolution.