Corrosion resistant materials protect them selves from oxidizing (corroding) by forming a thin protective layer of ceramic. When this layer forms we say the material is now passivated.
When stainless steel parts such as nuts and bolts are forced together, the passivated layer can be scraped off causing the parts to weld together. When disassembled, the welded material shows evidence of pitting and damage
This welding together and damage is called galling.
Galling can be best avoided by the use of dissimilar materials, e.g. bronze to stainless steel, or even different types of stainless steels (martensitic against austenitic, etc.), when metal-to-metal wear is a concern.
Nitronic alloys (trademark of Armco, Inc.) reduce the tendency to gall through selective alloying with manganese and nitrogen.
Nickel also contributes to passivation, as do other less commonly used ingredients such as molybdenum and vanadium.
- On February 15, 2018