I think it is at forty below zero Centigrade (which happens to be same as forty below Fahrenheit), pure metallic tin becomes a powder!

As I recall, the pipes of the church organ in the great cathedral of St. Petersburg, being made of tin (as was the then-practice), collapsed completely during a cold snap.

Edit: "A cathedral in St. Petersburg (now Leningrad) installed a magnificant organ with tin pipes. Came a cold, cold winter and the pipes disintegrated--which is how chemists learned about white tin and gray tin. Ordinary metallic 'white tin' is stable only at relatively warm temperatures. In winter cold, there is a tendency for it to turn into a crumbly nonmetallic 'gray tin.'" Isaac Asimov's Book of Facts, p. 246)
http://www.joesabah.com/dseibert/021.htm; near the bottom