I just pasted this from wikipedia- didn't know it was from the home town
Reynolds 531 is a brand name, registered to Reynolds Cycle Technology of Birmingham in the United Kingdom, for a manganese-molybdenum medium carbon steel bicycle tubing.
Introduced in 1935, and for many years at the forefront of alloy steel tubing technology, it has been replaced and superseded by ever more complex alloy mixtures and heat-treatment/cold work cycles as Reynolds has continued to compete with other manufacturers of steel for the bicycle industry.
The approximate alloying composition for 531 is 1.5% Mn, 0.25% Mo, 0.35% C, and is similar to the old British BS970 En 16/18 steel. Its mechanical properties and response to heat-treatment are broadly similar to the AISI 4130 standard alloy steel, also used for bicycle frames, amongst other applications. This material was used to form the front subframes on the famous Jaguar E-Type of the 1960s.
Reynolds 531 is now only available to special order. But in the past was use by "Raleigh Bicycle Company" of Nottingham, England for their racing cycles, with other Reynolds tube used for the professional models.
