Reynolds 531 is a brand name, registered to Reynolds Cycle Technology

Reynolds Cycle Technology

Reynolds Cycle Technology is a manufacturer of tubing for bicycle frames and other bicycle components based in Birmingham, England established in 1898.-History:...

 of Birmingham

Birmingham

Birmingham is a city and metropolitan borough in the West Midlands of England. It is the most populous British city outside the capital London, with a population of 1,036,900 , and lies at the heart of the West Midlands conurbation, the second most populous urban area in the United Kingdom with a...

 in the United Kingdom

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

, for a manganese-molybdenum, medium carbon steel bicycle

Bicycle

A bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....

 tubing.

Introduced in 1935 and for many years at the forefront of alloy steel tubing technology, 531 tubing has been superseded by more complex alloys and heat-treatment/cold work cycles as Reynolds continues to compete with other manufacturers of steel for the bicycle industry.

The approximate alloying composition of 531 tubing is 1.5% Mn

Manganese

Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...

, 0.25% Mo

Molybdenum

Molybdenum , is a Group 6 chemical element with the symbol Mo and atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek , meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages, since its ores were confused with lead ores...

, 0.35% C

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

, and is similar to the old British BS970 En 16/18 steel (EN 16 is similar to grade BS970

Steel grades

Steel grades to classify various steels by their composition and physical properties have been developed by a number of standards organizations.*SAE steel grades*British Standards*International Organization for Standardization ISO/TS 4949:2003...

 605M36). Its mechanical properties and response to heat treatment are broadly similar to the AISI 4130

AISI steel grades

The Society of Automotive Engineers designates SAE steel grades. These are four digit numbers which represent chemical composition standards for steel specifications. The American Iron and Steel Institute originally started a very similar system...

 standard alloy steel, also used for bicycle frames, among other applications. This material was used to form the front subframes on the Jaguar E-Type

Jaguar E-type

The Jaguar E-Type or XK-E is a British automobile, manufactured by Jaguar between 1961 and 1975. Its combination of good looks, high performance, and competitive pricing established the marque as an icon of 1960s motoring...

of the 1960s.

Reynolds 531 is now only available to special order, but "was the standard of excellence for many decades" among bicycle frame building materials.

Nearest Available Stock material is BS4t45 to Bs4T100 (T45)