Recommended hot runner materials for resisting grain growth

Microalloyed steels including Ti, Nb and V and naturally fine grained steels are proposed. The precipitated phases in these materials act as pinning sites for grain boundaries and efficiently prevent aberrant grain growth at high temperatures, making them appropriate for hot runner systems in long-term high temperature service settings.

 

1. Ti-containing steel (titanium carbide-reinforced kind)

Representative grades : H13+Ti, 4Cr5MoSiV1-Ti

Suppression mechanism: Ti produces very stable TiC (titanium carbide) which is hard to dissolve at high temperatures and pins the grain boundaries for a long time, offering the strongest resistance to grain growth.

High temperature core areas Nozzle, manifold, applicable scenes: Especially ideal for long-term continuous production.

Advantages TiC has poor solubility up to 1200°C and so has a stable pinning effect on grain boundaries.

 

2. Niobium Carbide Reinforced Steel

Typical grades: H13+Nb, 3Cr2W8V-Nb

Suppression Mechanism: NbC precipitation during austenitization successfully prevents grain engulfment, especially in the setting with considerable temperature swings.

Applicable Scenarios: Hot runner sections with rapid temperature swings or moulds needing numerous heat treatment for repair.

Features: NbC has modest solubility and can dynamically precipitate during recrystallisation, enabling "self-healing" pinning.

 

3. Vanadium Carbide Reinforced Steel

Typical Grades H13+V, 5CrNiMo-V

Suppression Mechanism: VC particles are stable at medium-high temperature range (600-900°C) and exhibit good pinning force.

Scenarios: Medium temperature range or auxiliary runner components; reasonably low cost.

Note: VC is very soluble at extremely high temperature; not suited for harsh situations above 1000°C.

 

4. Steel, Fine-Grained (Deoxidised with Aluminium)

Typical Grades: Al-Killed H13, Fine Grained H13

Inhibition mechanism: Al deoxidation makes AlN spread to inhibit grain coarsening after heating.

Application areas It is recommended for the production of new moulds, with fine and consistent original microstructure (grain size 5-8).

Protection Principle: AlN already acts from the first heating step and prevents excessive formation of austenite grains.