This Wikipedia article describes the phenomena quite well.
http://en.wikipedia.org/wiki/Stress_corrosion_cracking
The stainless steel mentioned there, 18/8, commonly used in Cutlery (watch out messers Giles and Foodie) is particularly prone to Stress Crack Corrosion. However, you do need some sort of stress to initiate it, which you won't find on your watch case or cutlery.
I remember my university mess hall's fine example of SCC well. In those days the salt and pepper sellers were made from stainless steel. They were shaped like bell jars, with a black plastic base that could be removed for refilling. The pepper seller had 3 holes in and the salt seller 5 (or vice versa, I can't remember). The way these bell jar shapes were formed was obviously by pushing a disc of stainless steel over a bell jar shape in some sort of die. This meant that the shape was highly stressed. Only the salt sellers cracked, not the pepper pots. The cracks started at the base and propagated upwards towards the less stressed section. It was quite obvious how the pepper pots never cracked.
Valuable lessons are learnt from small observations and some enquiry.
