In my 25+yrs of tig/mig welding I have yet to have a weld failure in either a mild steel or 4130 cage. Second pass is lower melting temp 309 and creates a good fillet to spread the load. So my first pass is concentrated but not huge. Critical joints single pass er70 with a larger weave pass of 309 on top. On off road cars with thicker tube in non critical areas single pass er70. Did a lot of formula v ? Cages which were 4130 purge welded single pass and post weld heat treatment. When I am tig welding a car if its a road car with thinner tubes I am usually single pass er70 that's 4130 or Dom. weld and joint design (which includes tube thickness choice) If you have joint failure it's usually it's usually two part. When welded properly 4130 can get you a stronger and lighter chassis without post weld treatment and still live a long time. When tig welding not enough coverage or too much penetration with out backside purge can lead to a weaker weld. 4130 is less forgiving when it comes to poor welds though.
To make a blanket statement that 4130 is more prone to HAZ cracks isn't really correct. As a welder you have to choose the right process for each joint and many times you can get the same result from two different processes. I have built cars using only 4130 or only 1020 and I have built cars that used both.
These threads about material and welding are always too funny.
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