Why does my Stainless Steel Knife Corrode?

My metallurgist colleague was very disappointed in this knife because she believed that stainless steel wouldn’t corrode. Unfortunately if left in still water oxidation pitting will occur in all stainless steels. My colleague was very surprised to get corrosion in this knife because it is usually hand washed and then just left with a little water on it, similar to other utensils, but after six months it had started to rust. The corrosion may be the result of the relatively high carbon content in the knife, which means it is likely to form carbide particles which act to sensitise the steel.

X50CrMoV15 is a German standard with around 0.5 wt% carbon (percentage by weight) and total around 15 wt% chromium, molybdenum and vanadium. This is regarded as being highly stain resistant. Usually a steel is regarded as stainless it is possible to maintain a chromium level above 12 wt% at the surface, since this has been found to form a stable oxide layer.

C Si Mn P S Cr Mo V
0.45 – 0.55 max 1 max 1 max 0.04 max 0.015 14 – 15 0.5 – 0.8 0.1 – 0.2

Z-knives have previously found that rusting occurred on X50CrMoV15 as a result of using dishwasher on otherwise unused knife.

P1050432

P1050433

P1050436

P1050439

`Japanese' Cooks Knife

`Japanese’ Cooks Knife

New York Times announcement regarding the discovery of stainless steel.

New York Times announcement regarding the discovery of stainless steel.

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