Although the recommended filler metal for welding 4130 is covered by ASM specifications 6457A (4130), a stainless steel filler metal is acceptable (312 preferrably because of the higher strength of a 309) if lower joint strength is acceptable. Lower strength filler metals can reduce cracking in some applications. In any case, low hydrogen filler metals must be used, and they must be kept dry to avoid hydrogen cracking. If you will check back through the archives of this Forum you will find that there have been much discussion and recommendations about welding 4130.

Chuck