The Effect of Substrate Temperature on Properties of RPA Deposited Maraging 250 for Tooling Repair

Abstract

During cladding, the heat input from a new overlay can induce metallurgical changes in the previously deposited layers and change their mechanical properties. This effect is encountered during cladding repair of tooling with robotic pulsed arc (RPA) and was the target of this study. The alloy used for cladding was Maraging 250 steel, an age hardenable 18% nickel alloy. A parametric study was undertaken to correlate between cladding with and without cooling of the substrate and the resulting mechanical properties. Twenty layers of Maraging 250 were deposited (a) with forced air cooling to below 250°F (b) with thirty seconds hold time between layer w/o temp control (c) with water-spray cooling to below 250°F, resulting in an average hardness of 42.2HRC, 51.8HRC and 39.1HRC respectively. A fourth block was deposited cold by forced cooling between passes to below 250°F and was subsequently aged at 900°F for three hours and air cooled. The hardness of this specimen ended at 49.5HRC, as anticipated. For die repair with Maraging 250, temperature control during deposition is therefore desirable, to target a hardness range of 42–44HRC. This hardness range provides a satisfactory combination of elongation strength and toughness for tooling application.