Milton,
please allow me to attach some addenda with regard to your topic.
Yesterday I had a discussion with a colleague who has experiences in steel materials comparing with what you have stated. From him I have received a printed version of a company's leaflet (Edelstahl Witten Krefeld), please see also:
http://dew.edelstahl-e.com/dew/produktbroschueren.jspThere I have found the mentioned brochure also as an english language pdf, see also the attached ultrafort6355_english.pdf.
It deals with a steel for ballistic protection based on a Ni - Co - Mo alloy system and contains some particular information in regard to how this material has to be processed etc.
Due to they are recommending therein a welding filler material coming from FONTARGEN (A 770 M) in Germany and FONTARGEN again is a subsidiary of BOEHLER UDDEHOLM in Austria, I made a quick search and found some more interesting information regarding those materials (technical data, welding, mechanical processing,...).
Therefore please see also the attached Maraging_Steel.pdf.
Just as an additional information... :-)
Best regards,
Stephan