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. For many years the forefront of alloy steel tubing technology, it has been replaced and superseded by ever more complex alloy mixtures and heat-treatment/cold work cycles as Reynolds has continued to compete with other manufacturers of steel for the bicycle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.
Following on from the success of 853, Reynolds have added 631 to the range of AIR HARDENING STEEL tube sets. This seamless cold drawn steel tube will allow the benefits of this new steel to be used in the manufacture of a wide range of frames and is now considered a worthy successor to our legendary 531 tubing. Like 853 it is suitable for TIG welding and brazing and in the heat affected joint areas will gain strength, to ultimate tensile strengths in excess of heat treated chrome molybdenum. The strength to weight ratio of 631 is equal to that of many aluminium frames, and it has an excellent fatigue life whilst providing a supple ride quality suitable for long distance events.