4130 chrome-moly can be welded with the TIG or MIG process. Preheat is generally not needed for thinner sections (0.120-in), but for tubing larger than 0.120 a 300F-400F preheat is needed to obtain acceptable results. A common filler metal choice for welding chrome-moly is ER80S-D2 .This filler metal is capable of producing welds that approximate the strength of the 4130. ER70S-2 is also an acceptable alternative to ER80S-D2, as well as 70S-6, although weld strength will be slightly lower.
4130 filler metal is typically used for applications where the weld will be heat treated. Due to its higher hardness and reduced elongation, it’s not recommended for sporting applications such as experimental airplanes, race cars frames, and roll cages. Some fabricators prefer using austenitic stainless steel filler metals to weld 4130 tubing. This is acceptable provided 310 or 312 stainless steel filler metals are used. Other stainless steel filler metals can cause cracking, and stainless steel filler metal is more expensive.
Rapid quenching of the base metal will create problems such as cracking. Always allow the weld to cool slowly.