The hard stuff – a quick guide to tubular steels in motorsport

Aerospace BS4T45 to BS5T100, in accordance with BS6S100 condition tubing (T45)

This high tensile carbon manganese cold drawn seamless steel has been used on the Spitfire and Hawker range of aircraft, which is perhaps part of the reason why it’s so popular in Britain. But the main reason is that it has a superb strength-to-weight ratio, is ductile and is also weldable without pre- or post-heat treatment. It can also be brazed.

It is an aerospace-grade steel with high tensile strength (900N/mm2 maximum, 700N/mm2 minimum) and a minimum yield of 620N/mm2

4130

Popular in the US, 4130 has an excellent strength-to-weight ratio and is a chromoly steel (aka CrMo or Cr-Moly), which means it contains chromium and molybdenum. Experts say this material is not as easy to weld as others, such as T45, because it needs both pre- and post-welding heat treatment to combat cold cracking. Incidentally, this is why you often see unpainted spaceframes and ’cages in racecars, so it’s easier to spot cracks. Typical figures are: minimum tensile strength, 620N/mm2; minimum yield strength, 517N/mm2 and minimum elongation, 10 per cent. Note: the carbon content is 0.33, however the FIA / MSA UK regulations Section K state 0.3 per cent max so this can fail the requirement for ROPS

25CrMo4

This is a very similar steel to 4130 and is widely used in continental Europe. It has lower quantities of manganese than T45, but higher levels of chromeso will require a stress relieving process.

Note: there are many heat treated conditions, which must be stated at time of purchasing as 25CrMo4 is only the material, not the actual finish.

15CDV6

Used at the highest levels of motorsport, 15CDV6 is a micro-structured chromium-molybdenum-vanadium structural steel that is very well suited for welding and bending, but is also expensive to produce. Depending on the spec, this can have a minimum tensile strength of 1000N/mm2 with a minimum yield of 790N/mm2 and an elongation of 12+ per cent (these numbers are for GT1000 material). Note: while15CDV6 is said to be easy to work with and ideal for complex applications, it is not suitable for home builders.

ROPT510

Where this differs from other high-spec motorsport steels is in it not being an aerospace standard material, which means it costs less. It does, however, easily meet the FIA, SFI and Motorsport UK standards.

Pro Formance Metals, alongside its manufacturing partners, developed this steel as an off-the-shelf material for motorsport use and it has been in worldwide use for over a decade.

Its minimum tensile strength is 510N/mm2; minimum yield is 370N/mm2 and elongation is a minimum 25per cent.

Cds

This is a generic term and while ‘Cold Drawn Seamless’ applies to all of the steels described here, these have particular chemical compositions and heat treatments that set them apart as high-spec materials.