Maui
Materials
- Mar 5, 2003
- 1,937
I have a customer who is manufacturing a turbine blade from 410 stainless steel. They are inspecting these parts using magnetic particle inspection (magnaflux testing). They have been complaining that they are picking up indications on approximately 30% of the parts, and are rejecting them as a result. They claim that the rejections are being caused by delta ferrite stringers. I obtained several of the rejected parts, and sent them to an outside lab for metallurgical analysis. The parts are in the process of being analyzed, but the testing so far has identified what appears to be very light chatter marks on the surface of one blade. I suspect that this is what has been causing the indications during magnaflux testing. After taking a photograph of the chatter mark, the lab polished the surface very lightly in stages to find out if there was any underlying metallurgical anomaly in the same area such as delta ferrite. None has been found. Other areas on the blades that were marked by the magnaflux inspector did not even reveal evidence of scratching. And polishing these areas did not reveal any delta ferrite or other identifiable cause for the testing indications. I suspect that the inspectors may have the equipment set up to be too sensitive, and are over inspecting these parts. By the way, the delta ferrite content of this steel is evaluated prior to shipment, and is well below the maximum 1% content that is allowed. My question is this: can anyone provide any evidence that delta ferrite stringers produce visible indications on 410 stainless steel during magnetic particle inspection? My suspicion is that this is extremely unlikely, but I would like to hear from those who are well versed in this testing procedure (since I am not). Thank you.
Maui
Maui