Ni系箔ろうでろう付したフェライト系ステンレス鋼重ね継手の塩酸溶液中の腐食挙動

抄録

Exhaust gas recirculation (EGR) coolers are standard accessory items to reduce internal combustion engine emissions and fuel consumption. These coolers are composed of stainless steel brazed with Ni-based brazing filler metals that can internally withstand high exhaust gas temperatures and corrosive environments. In this study, the corrosion behavior of the SUS444 joint brazed with MBF67 foil was examined by an anodic polarization measurement in hydrochloric acid and was compared with that of the SUS444 joint brazed with MBF20 foil. The result indicated that the SUS444 joint brazed with MBF67 showed corrosion with a much higher potential in the polarization curve than the SUS444 joint brazed with MBF20. The reason for the high potential was concluded that the Cr-depleted zone was not formed at the boundary layer between the SUS444 and MBF67 because of low B in MBF67, and the high phosphorus-containing (Ni, Cr)-P eutectic phase with high corrosion resistance remained at the brazed layer because of high P in MBF67.

Fig. 6　Comparison of optical micrographs between (a) before and (b) after polarization for SUS444 joint brazed with MBF67 foil in 0.025 mol/L HCl solution.