Why Surface Hardening?

Industrial moulds operate under constant pressure, friction, thermal shock and the effect of abrasive raw materials. While the mould core must retain its toughness, the working surface must exhibit high hardness. Surface hardening techniques are the solution that meets this dual requirement.

Nitriding

Nitriding is a hard compound layer formed by the diffusion of nitrogen atoms into the steel surface. Because it is applied at low temperatures (480–580 °C), dimensional change in the mould geometry is minimal. Hardness values can reach up to 1000–1200 HV.

  • Gas nitriding: low cost, long process time
  • Plasma (ion) nitriding: precise control, short cycle time
  • Salt bath nitriding: high efficiency, requires specialised facilities

Carburising (Case Hardening)

By holding low-carbon steels in a carbon-rich atmosphere at high temperatures (900–950 °C), the surface carbon content is increased and then hardened by quenching. This produces a deep, hard case (0.5–2 mm). It is preferred for press moulds that require high impact resistance.

PVD and CVD Coatings

Physical vapour deposition (PVD) and chemical vapour deposition (CVD) methods enable very hard ceramic films such as TiN, TiAlN and CrN to be applied to the mould surface. The coating thickness is on the order of microns; however, hardness reaches 2500–3500 HV.

Hardness is not the only criterion when selecting a coating; the coefficient of friction, adhesion behaviour and operating temperature must be evaluated together.

Induction Hardening

Using electromagnetic induction, the surface is rapidly heated locally and then quenched. This makes it possible to harden only the working areas of large and complex moulds. Its operational cost is low.

Comparative Selection Guide

  1. For moulds with tight tolerances: nitriding or PVD
  2. Under high impact loads: carburising
  3. For localised area hardening: induction
  4. For wear protection and anti-galling: TiAlN / CrN coating

The right hardening method can double mould service life and significantly reduce maintenance costs. The Alba Pigment engineering team provides consultancy on surface treatment selection throughout the mould supply process.