some of the modern motorcycles still for sale at dealerships new and rolling out of factories are the same as whats used in bicycles... its usually not the steel itself, but the joins. or any heat affected areas. i have had a haro frame do a strange sort of spiral crack down the top tube, starting a few inches from the headtube...
on that note, ive seen lengths of 19mm bar get turned into drifts, only to find the bar had a crack running the entire length, that was only revealed when heated up redhot for the final stage, hardening the points. hi quality heat treating bar from a reputable supplier. it does happen.