Depending on what codes apply, you will probably have to develop a new welding procedure for this material as it has a unique chemistry.
Techanically, there is no such chemistry as AISI 8630HM. AISI 8630H has a specific chemistry and hardenability range, but the "M" on the end indicates "modified", which could mean just about anything. Typically, it indicates the chemistry is modified to slightly higher alloy content to increase hardenability, but it could also have other modifications with other objectives.
You will need to know the chemistry ranges and heat treatment and/or strength requirements of the original part to develop a qualified welding procedure.
It will require a seperate WPS under ASME IX, as it is an unassigned material. Let me save you some steps if this weld has to comply to NACE 01-75. We just spend about 6-7 months trying to develop a NACE compliant procedure for 8630M, with fruitless results. We finally did achieve a compliant hardness survey through manipulation of starting material heat treat, interpass temperature, and PWHT, but then yield and impacts were below minimums required. There might be a "sweet spot" where everything is in harmony, but it would require a full blown research effort to find it and the parameters would be so narrow, it would be very difficult to implement in production. OTOH, I do know a number of examples of successful cladding procedures (with hot wire tig) that are NACE compliant in this material, but for joining the material to itself, none could be located by either myself or the consulting metallugical engineer we retained.
