Improvement of Hardenability and Static Mechanical Properties of P20 + 0.5Ni Mold Steel through Additions of Vanadium and Boron

• Published in: ISIJ International 2012, Vol.52(3), pp.424-433
• Main Authors: Beaudet, François, Blais, Carl, Lehuy, Hoang, Voyzelle, Benoît, L'espérance, Gilles, Masse, Jean-Philippe, Krishnadev, Madhavarao
• Format: Article
• Language: English
• Subjects: annealing; Applied sciences; boron; carbides formation; dilatometry; Exact sciences and technology; hardenability; mechanical properties; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; mold steel; vanadium
• ISSN: 0915-1559; 1347-5460
• DOI: 10.2355/isijinternational.52.424

Constant demand to optimize production of plastic components puts pressure on mold steels manufacturers to supply pre-hardened blocks with larger cross-sections. As the size of mold blocks increases, it becomes more difficult to maintain the same microstructure throughout their volume. Thus, the size of mold steel blocks is limited by the cooling rate reachable at their center. This situation has created the need for the development of new alloys with improved hardenability. Additions of vanadium up to 0.35 wt-% have been made to P20 + 0.5Ni mold steel. The addition of vanadium significantly increased hardenability, allowing the production of pre-hardened blocks with a cross section 88% larger than the same alloy without vanadium. Such additions of vanadium also increased the impact toughness by 120%, raised the yield strength by 17% and improved hardness after tempering by 24%. The effect of boron on the hardenability of the P20 + 0.5Ni steel was also investigated. It resulted in a significant increase in hardenability and, in theory, could permit the production of pre-hardened blocks with a cross-section 400% larger than the original material. Finally, our results show that 0.35 wt-% of Ni can be substituted by 0.15 wt-% of vanadium in a P20 + 0.5Ni steel and still maintain the same hardenability.