In the February 2001 edition of Playboy, along with lots of photographs of attractive young American women wearing hardly any clothes or nothing at all, was an interesting article about US astronauts who will be doing construction work in space.
On page 148 in the bottom right hand corner it says this: "Because normal steel turns brittle in the -200F to -250F of space, the tools are all made of beryllium copper."
What's so special about beryllium copper? And if normal steel is so brittle in cold, what about high tensile steel? When we eventually build really BIG space environments in the region of several billion tons in weight, like O'Neill Cylindrical Colonies about 10 miles across. and 30 + miles long, we will have to use iron/steel for the structure.