There are essentially three classes of steel that are used to make bicycles:
High Tensile Steel: The alloying elements are mixed together to form a low carbon steel easy to work with. The strength is usually on the lower side of the other two types of steel described below. They are cheap, easily available and do the job but are heavier because they are used in straight gauge form meaning they are of the same thickness throughout the tube. And depending on the mill strength, frame engineering and position they tend to be harsher in ride quality.
ChroMoly Steel: By adding chromium and molybdenum to the alloy mix, this steel is made stronger. And lighter by the process of butting. Since they are stronger, material is usually drawn out from the center part of the tubes in the butting process. This also changes the natural frequency of the bike and improves the ride quality by damping a certain amount of road buzz.
Super Steel: These are a class of proprietary steel mixes developed by the pioneers of bicycle tube manufacturers. The likes of Reynolds, Columbus etc. They are allowed to go through proprietary heat treatment methods and/or alloyed with special elements like Vanadium to achieve exceptional tensile strengths. Hence, some of them can be made to thicknesses as low as 0.38 mm. This leads to ultra light builds or builds with superior control over ride quality.
At Scolarian, all our stock frames are made completely of seamless CroMoly Steel. And we offer custom frames to be made from either our special CroMoly steel or any of the super steel ranges from our partners at Reynolds & Columbus.