frequently asked questions
Q. Are the tubes seamless?
Yes, the tubes are seamless.
Q. What kind of heat treatment has been done on the tubes?
The tubes have undergone Stress Relieved Annealing. We can only tell you the temperature at which the tubes are annealed that is 865 Deg Celsius. It is then cut, pickled and lubricated in the acid pool, cold worked to get the final dimension and then layered with anti rust oil. We cannot disclose you the exact time for the cooling period or the temperature hold up period as that makes the steel's strength vary from company to company and is a trade secret of ours.
Q. Why are the tubes dark/black in colour?
You will find some of the delivered tubes of darker shade than the ones previously ordered if any or a mixture of both. We have used anaerobic method of heat treatment for some batches. Hence, the colour. The layer can be removed by using a sandpaper.
Q. Do we need to do post-weld heat treatment?
No, you don't have to do post weld heat treatment if you use these tubes. First of all tubes with wall thickness less than 3mm typically do not need heat treatment as the core also gets cooled at a similar rate as the outer surface. When you use AISI 1010/1020 or commercial grade 4130 whose yield strength are around 350MPa and 450MPa respectively, after welding the strength of the tubes at the heat affected zone (HAZ) reduces to less than half of the yield strength to about 150MPa. Now since our tubes have a yield strength of 650Mpa after welding it drops to 500Mpa. You can calculate for yourself from the welding test reports. The load at break of the weld point is way more than your car will ever face in any situation.
Heat treatment done to relieve the residual stresses and to change the micro structure to bring the strength back to normal. Since, the drop in strength with these tubes is not that significant, you don't need post weld heat treatment.
There is a risk of Cold Cracking and Hydrogen Embrittlement lead fractures when you weld but that is mostly applicable for martensitic steels or very low carbon steel (usually<0.12% C). During welding of these tubes, hydrogen can still seep in at elevated temperatures leading to cracking of the welds. So make sure you take proper precautions. Make sure the inert gas pressure settings are optimal to create a very good envelope during welding and also refrain from continuous welding rather go for segmented approach. Arc welding is a strict No. The filler rods have a coating which could lead to deposition of moisture and a subsequent introduction of hydrogen. Whatever the case, the cracks if they develop because of release of gases trapped in the weld will show up after 24 hours. Make sure you do a thorough check up of the welds.
Just a few knocks by a good old ball peen hammer would relieve the stresses, post weld cooling. The chromoly used in NASCAR is a commercial grade 4130 and does need heat treatment at times depending on the wall thickness, the welding setup etc.
Q. Do we need to take any special care during bending?
Yes, it is very important you mention the strength of the tubes to your tube bending guy so that he uses the proper force and uses the proper fixtures. Also, ideally they would heat the bent radius to allow for a smooth bend and avoid tearing at the bent radius.
Q. What kind of filler material do we need to use?
For TIG welding you could use ER70S-2 filler and the same in the spool form for MIG welding. The wire diameter(0.8mm/1.2mm/1.65mm) can be chosen according to the comfort of the welder and the chosen joint. ER80S-D2 could be used at critical joints such as control arms to achieve stronger weld joints.
Q. What is the difference between tube and pipe?
Pipes are primarily used for transferring fluids whereas tubes are used as structural material. Most importantly, pipes are classified by their Internal Diameter as the volumetric capacity is of relevance. Whereas, tubes are classified by their Outer Diameter as the structural strength (bending stiffness and strength) is of importance. Following is an illustration of the dimensional difference.
Q. Why does one or more edges of the flat bars have a fillet?
All our flat bar extrusions have a 5mm radius fillet in the direction of cross section of the extrusion. Hence, depending on your cut dimensions, one or more edges may include the outer edge of the extrusion bar and hence the fillet. As is evident, the maximum number of fillet edges will be four.