We banged up our a arm in the last race, and I thought it might be helpful for some to see the process of how to properly repair a damaged weldment. Note that the arms are 4130 boxed style, but also have a mild steel tubular sub-frame for extra durability. It is this frame that held the arm together after the impact that caused the damage. The damage occured in the final miles of the San Felipe 250, and would have sidelined us, or at least cost us our first win, if not for the sub-structure. The inner tubing that ties the inside edge of the weld bung directly to the outside uniball receiver was our saving grace. I used mild steel on this tube for malleability purposes. 4130 may have cracked at the weld whereas the mild steel, with its high yield to tensile gap, allowed the joint to flexx without sacrificing weld integrity. Notice how I added the back up plates to support the butt-welds. After welding, the end of the arm was stress relieved using a rosebud end on an oxy-acetylene torch until the welded area reached 1100 degrees F. The heat range for properly stress relieving 4130 is 1075-1150 deg. I do this process in the evening, with the lights out, so I can accurately see the proper dull cherry red glow of the metal indicating the desired temp range has been achieved. I know this color red from testing and practicing heating metal using digital pyrometers and Tempilsticks to confirm the intensity of the glowing material. If you build using chro-moly (4130 normalized) and don't stress relieve your weldments, then you are merely wasting expensive materials, and sacrificing weld integrity. In that case, you are better off using 1020 mild steel. It is nearly as strong as 4130 (tensile strength), but allows the welded joint much more elasticity before failing. Virtually making it as tough as chro-moly, but without the strict welding protocol requirements.
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