Böhler Edelstahl Steely resolve for cleaner metal
Additional requirements for hardened, tempered steels have been driving material developments.
To meet the rising demands on mould steels, Böhler Edelstahl offers its M268 VMR grade based on the standard material 1.2738.
The steel is a pre-hardened and tempered material with very high cleanliness, fit for the highest degree of polishability, the supplier explained. It further noted that an Ni content of 1.1% provides good through-strength after hardening and tempering, even for large cross-sections.
Böhler said high cleanliness can be achieved with the vacuum-melting and remelting (VMR procedure). Unlike commonly used steels, such as 1.2738 (M238), these steels excel in extremely high cleanliness and thus are best suited for a high-gloss polish. The vacuum-melting and remelting technology facilitates the manufacture of steels with the lowest content of gases and trace elements and the lowest possible micro- and macro-segregations. This good polishability has positive effects on large surfaces and complex geometries, the company added.
Besides M268 VMR with a usual strength after hardening and tempering of 1,000-1,100 N/mm2, the company also sells the grade with a strength of 1,150-1,300 N/mm2. This provides both increased polishability and higher compressive strength.
Consequently, the grade suits higher-performance plastic moulds, Böhler said. It explained that other tool steels, such as hot-work steels, have been used in these applications. They are delivered as soft-annealed steels and need heat treatment prior to use. M268 VMR moulds need no such treatment and can be used immediately after delivery, the company said. Moreover, the risk of producing rejects due to distortion and cracking during heat treatment is thus eliminated. | ec