Properties Of Steel:
In recent years we have seen major advances in Steel tubing. Custom Built Steel frames can now be built almost as light as the lightest carbon frame.
Steel is made mostly from iron and adding or subtracting ingredients when molten forms different types of steel.
4130 is an alloy steel known as Chromoly and contains with iron, carbon, manganese, cromium and molybdenum. It is formable, strong, tough and ductile i.e can be deformed considerably before reaching its fracture point.
Cheaper steel frames are generally formed from 1020 carbon steel which is significantly lower in strength than 4130.
Stiffness is a strong point in using steel. The modules of elasticity for steel is approximately 30million psi. The Titanium alloy Ti3Al-2v is in comparison only 15.5 million psi and 6061 Aluminium 10million psi.
The ratios 3:2:1 are almost identical to the density ratios between the 3 differing materials meaning the stiffness:weight ratios are about the same. This is true only when concentrating on the material’s behaviour in terms of tension or compression.
If you compare a 1” length tube and a 2” length tube of equal wall thickness, the bigger tube will be 8 times as stiff as the smaller tube whereas the weight will only double
Elongation is and indicator of ductility and is usually expressed as a percentage. The steels used in bike tubing have typical elongations of 9% to 15%, as elongation decreases the risk of brittle frame fracture increases.
Stress on a bicycle frame concentrates at the joints. When the joints are at corners the stress is intensified and when joints are welded there is further stress at the edge of the heat affected zones. There are 3 types of stress being Joint, Corner and Heat and all 3 come together at the edge of a weld.
Tensile Strength varies considerably across different steel alloys and also brands.
In the ever evolving world of Bicycle Frame Material – A Custom Lugged Steel Frame is becoming an exotic sought after item.
Steel has a lot going for it. No other frame material can make all these claims:
• Tensile strengths of steel bicycle tubing have doubled in the last few years, leading to lighter and livelier, and most importantly, more comfortable frames.
• Aesthetically and technically superior brazed lug construction can only be used for steel frames. Steel lugs reinforce the joints allowing lighter gauge tubing. This leads to longer lived frames and a more responsive ride.
• Steel has a higher density than other frame materials so it provides a more lively ride and better feedback when riding at close to the limit of traction.