Understanding the differences in the common steel tubes used in tube chassis and roll cages is the key to building not only a fast car but that one that keeps you SAFE. In today’s chassis it is common to find Mild Steel ERW tubes, High Strength Steels (HSS) such as DOM and 4130 Chrome Moly (chromoly) and Advanced High Strength Steels (AHSS) like Docol® Tube R8. With DOM, 4130 and Docol® being the most common as many sanctioning bodies do not allow Mild Steel ERW. With all these tubes weighing the same dimension for dimension it is the production process and mechanicals that set them apart.
DOM, 4130 and Docol® are the most common steel used in racing as many sanctioning bodies do not allow Mild Steel ERW. All of these tubes weigh virtually the same per linear foot when comparing the same size (OD x wall), but the manufacturing processes and mechanical properties set them apart.
DOM - "Drawn Over Mandrel"
DOM refers to steel round tube that is “Drawn Over Mandrel” sometimes referred to as seamless tube, though it is not technically a “seamless tube.” Drawn Over Mandrel is a secondary process with the tube originally starting out as an EW tube is cold drawn to smaller dimension and wall thickness. This gives the tube a smoother surface finish, improved tolerances, high tensile strength and better alignment of the crystal lattice. A crystal lattice refers to the alignment of atoms in a crystal. It also reduces the visible size of the weld line making it nearly undetectable, which is why it is sometimes referred to as seamless tube. DOM comes in 1020 or 1026 steel. Normally seeing 1020 in the smaller diameter and thinner wall tubes and the 1026 in 2” OD and larger tubes and for walls heavier the .156”.
4130 Chrome Moly
4130 Chrome Moly tubing has been A.E.D.’s signature product since opening our doors in 1996. 4130 is a Cold Drawn and Seamless High Strength Low Alloy steel getting its informal name “Chrome Moly” from its two major alloying elements chromium and molybdenum. 4130 has been frequently used in the high performance industries since the 1940’s when it was predominantly used for aircraft frames. Today you still find 4130 in aircraft frames and motor mounts, in high-end bicycle frames and in all forms of Auto racing. It is a great material for all of these industries due to its high strength to weight ratio. Being a Cold Drawn Seamless tube 4130 has relatively smooth surface finish inside and out and has the ability to be used in a slip fit or telescoping application in certain sizes.
But not all 4130 Chrome Moly is made the same and it is very important to know where your steel is coming from. Over the years we have seen a number of mills producing 4130 specified tubes. Many of which we do not feel confident in selling their product. We have maintained over the years that we sell only the best tube from the most reputable mills – our mills of choice, Webco, Plymouth and Benteler. These are the mills that place the most care into the production of safety critical tubes for racing.
Docol® Tube R8
Docol® Tube R8, our newest major product introduction, is a Dual Phase steel that has a microstructure of one part ferrite and one part martensite. Ferrite gives Docol® its unique forming properties and martensite accounting for its strength. Docol® is a Quenched and Tempered product going through a special heat treatment in a continuous annealing line to give it its unique properties. Docol provides a stronger, safer and more consistent alternative to 4130 Cold Drawn Seamless tube.
Key Advantages of Docol®
- Stronger than 4130 by 10 to 15 percent.
- Heat Affected Zone (HAZ) in Docol® is much smaller in area, less brittle and retains better elongation than 4130 typically does.
- Docol® is much more tolerant to heavy fabrication. It does not warp and distort like 4130 and stays more relaxed in tooling and fixtures during fabrication.
- Greater resistance to fatigue.
- Docol® absorbs energy and presents a more consistent and controlled failure mode.
- Clean mill finish product – minimal, if any, surface prep required. Docol® does not have an oxide or decarb layer and looks like a high quality electric welded tube.
- Accurate and consistent dimensional and mechanical properties because this material is a rolled and welded strip
- Compatible with welding to 4130 and mild steel components.
- Suitable for TIG and MIG welding.
- Clean no scrap based material resulting in fewer inclusions.
Regardless of the material, you decide to use it is imperative to purchase it from a reputable source. This source should be able to provide full traceability of the material and provide the material test reports.