It depends on what it is being used for and how thick it is. If it is being used as a motor shaft, pump shaft, engine crankshaft or structural member, you need to find out why it cracked. If I recall correctly, ESAB produces a E4130 or similar electrode for SMAW. SMAW will have a slower cooling rate than GMAW (aka wire welder) and be less likely to crack when welding. You will need to preheat also and possibly stress relieve depending on the end use.
Marty
As the other post stated, alot depends on the thickness and the application of the weldment. Chromium-Molybdenum steels are covered under ANSI/AWS D 10.8-86. Thin gauge material can often be welded with ER70S-6 following low hydrogen techniques. This is just speculation though since we do not know the exact application. I hope this helps.
Mike Sherman
Shermans Welding