Preheating is not required. PWHT depends on if you are welding CA6NM class A or Class B. For class A, PHWT between 1050 and 1150F, and for class B, intermediate PWHT at 1225-1275, then cool to below 200F and re-PWHT at 1050-1150F. This is all per ASTM A487. Typical maximum interpass temperature is 400F. Use 410NiMo filler metal. It is available for the FCAW, SAW, SMAW, GTAW, and GMAW processes