The selection of mold materials must meet three principles: Meeting working condition requirements, meeting process performance requirements, and meeting economic applicability requirements. Meeting working condition requirements includes wear resistance, toughness, fatigue fracture resistance, high-temperature performance, resistance to thermal fatigue, and corrosion resistance. Wear resistance is one of the most basic and important properties of a mold, with hardness being the main factor affecting it. Toughness requires the mold to have high strength and toughness to prevent brittle fracture. High-temperature performance requires the mold material to have high tempering stability to ensure high hardness and strength at operating temperatures. Resistance to thermal fatigue is a key performance characteristic of hot-working molds. Corrosion resistance is relevant for specific working conditions such as plastic molds.
Meeting process performance requirements means that the mold material should have good forgeability, machinability, hardenability, hardenability, and grindability, and should have low sensitivity to oxidation and decarburization and low tendency to quenching deformation and cracking. Meeting economic requirements means that, while meeting performance requirements, priority should be given to selecting lower-priced materials, using carbon steel instead of alloy steel whenever possible, and using domestic materials instead of imported materials whenever possible.
The most important factors for mold materials are thermal strength and thermal stability. Depending on the working temperature and forming material, commonly used mold materials include: copper-based alloy molds for working temperatures of 1000℃ (such as nickel alloys). Surface treatment technologies such as PVD, CVD coating, nitriding, and boronizing can significantly improve the surface hardness, wear resistance, and anti-galling performance of molds, extending their service life by several to tens of times. Ion plating in PVD can coat TiC and TiN on the mold surface [6]. Nitriding can form a hardened layer on the mold surface, improving surface hardness. To address specific challenges (such as adhesive wear in stainless steel forming), new mold materials such as KKm wear-resistant copper alloy, silicon nitride ceramics (Si₃N₄), and metal-ceramic composites have been applied. KKm wear-resistant copper alloy achieves anti-adhesion through chemical compatibility. Silicon nitride ceramics have the characteristics of high hardness, high temperature resistance, and zero adhesion. Metal-ceramic composites can achieve a combination of high surface hardness and high core toughness.
