Corrosion Behavior of Ferritic Stainless Steel Joint Brazed with Ni-Based Brazing Foil in Hydrochloric Acid Solution

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.