The carbon planing area of stainless steel is gray
Thread Content
Recently, it was discovered that 22Cr dual-phase cast steel was re-shot blasted, pickled and passivated due to defects. Flaky gray spots were found in the original repair area (see picture). These gray spots can be easily polished off with sandpaper (like the carbon layer attached to the workpiece). After being polished off, they will still appear after being shot-blasted, pickled and passivated. This is still the case after repeated repetitions (the depth of polishing is 1-2mm). Carbon planing will indeed add carbon, but it won't be that much or deep, right? Currently, because there is no nitric acid, only hydrofluoric acid is used for passivation. Is it caused by too much hydrofluoric acid? Can anyone analyze it, thank you
For 22Cr dual-phase cast steel, carbon planing will increase the carbon content and lead to Cr depletion, and pickling will cause corrosion. If the carbon is sanded off after planing, there will be no gray appearance without pickling. But there is no longer corrosion resistance ；
Also, what is the abrasive used for shot blasting?