We did a test to induce corrosion on stainless steel type DIN 1.4528. We placed test parts in different Si-emulsions and stored them at 60°C for 48hours. After that some parts showed pitting corrosion on places where on beforehand the surface was flattened (the parts were cylinders). Other samples turned completely black. After wiping the loose (black) particles off, the surface was still smooth but it had changed colour. It seemed to me that this was no corrosion. Can someone help me with this ? Is it possible that carbon can migrate towards the surface of the part ? What are good tests to find out if a product induces corrosion more/faster than others ?