I have had 2 cracks on a steel 531 frame over a period of time . Had it repaired on both occasions { that is what I like about steel} and I am still using it for touring . Mind you I am a big chap and not a smooth pedaller and the it gets used for rough stuff as well .
Ps . I have had a titanium frame crack on a top tube as well .
Ps . I have had a titanium frame crack on a top tube as well .