b'TECH TIP - WELDING Tech Tip 67: Since the beginning of tube chassis race cars, there have been different opinions & debates on tubing materials & welding procedures. One common debate is on should we use DOM, Docal or 4130 Chromoly tubing. It is fact that 4130 is significantly stronger.About 1/3 more. In fact, we can use the same diameter 4130 & DOMand use 1/3 thinner wall thickness on the 4130it will be 1/3 lighterand still be slightly stronger than the DOM.So why the debate?Many racers & bench racers think 4130 chromoly is more brittle when welded. Theyre not right or wrong. It depends on how hot the welding process was. Welding 4130 steel at excessively high temperatures can lead to problems, primarily related to the material\'s microstructure, impacting its mechanical properties. Overheating can cause the steel to become brittle, reducing its strength and making it prone to cracking under stress. Additionally, excessive heat can alter the grain structure in the heat-affected welding zone leading to a weaker weld that is more susceptible to failure. This happens with DOM & Docal also. But to a lesser degree.DOM & Docal are more forgiving, but heavier & not as strong.A key concern when welding up a roll cage or tube chassis is having the weld too cold or too hot. This applies to ALL steel, including DOM & Docal. Too cold is a formula for instant failure.Too hot will make the metal too brittle & fail over time. Getting the weld temperature just right is an art of very experienced & knowledgeable welders. Not every good welder can get the welds the perfect temperature everytime.Uh-oh!Now what?The fail safe strategy is to weld a little too hotthen come back later & "normalize" the weld areas.You do this with a rosebud torch & 400 temperature crayons from any welding store.Crayon mark 4 sides of the weld in every location.Using a rosebud tip on your torch, slowly bring the temp up until the crayon changes color. Then let it cool down slowly.Do NOT quench the weld with water or oil.That will harden it.This works better in a warm shop, versus in the cold air. Do not confuse this with annealing. Annealing would require much higher temperature & make the metal dead soft.Another way to do this . if you have a chassis without the body on it . is to put the entire chassis in a large commercial powder coat oven at 400 for 30 minutes.Obviously your local powder coat shop will charge you for this, but this method normalizes ALL the welds on chassis at one time.We strongly urge this with all frame clips & full tube chassis, plus all welded suspension components. Now you have the best of all worlds.Light, strong & durable.MIG versus TIG welding. Always TIG weld 4130 & stainless. They can be MIG welded, but it is not as strong. Mild steel & DOM can be MIG or TIG welded & be 100% structurally sound, if welded correctly. Drag race car builders & some others always TIG & look down on MIG because it is not as pretty.But NASCAR race cars have been MIG welded for decades & still are. If you want yours to be pretty, pay more & have it TIG welded. But it wont be stronger. 27 0'