Effect of the heat treatment on the mechanical properties of a precipitation hardening steel for large plastic mold

Continuously growing activity in the area of the engineering plastics led to the necessity of developing new low-cost, high-performance plastic mold steels. In fact, when it is necessary to fabricate large plastic components, such as bumpers and dashboards for motor vehicles, the traditionally adopted ISO 1.2738 plastic mold steel exhibits low fracture toughness and highly inhomogeneous microstructures (continuously varying from surface to core), as obtained from the pre-hardening (quenching and tempering) of large blooms. New alloys and alternative manufacturing routes may allow to obtain plastic injection molds with good mechanical, wear and weldability properties. Precipitation hardening tool steels are being proposed for such an application, yielding improved mechanical properties and lower overall costs and lead-time. A precipitation hardenable steel, developed for injection molding of large engineering polymer components, was investigated. The microstructures and the mechanical properties of the precipitation hardenable steel bloom were investigated after the steelwork heat treatment. Moreover, the strengthening mechanism by means of aging heat treatments was examined on samples subjected either to the steelwork heat treatment only, or also to a successive laboratory heat treatment. To the purpose, X-rays diffraction and EDS analyses were carried out in order to indentify second phases electrochemically extracted from aged and not aged samples.