ASTM A487-93 is a standard specification for steel castings suitable for pressure service. Class 4B designates a nickel-chromium-molybdenum cast steel, 105ksi tensile, 85ksi yield.
I am not permitted to attach the spec as it is copyrighted, I strongly recommend contacting ASTM to get the full text in electronic form, as there are numerous other items regarding welding and heat treat to be noted.
Re ASTM A487/A487M-93(2003), 'Standard Specification for Steel Castings Suitable for Pressure Service'
Review its Scope & Referenced documents & purchase it if desired at