Meaning
Metallurgical regions adjacent to a weld undergo structural changes due to intense heat exposure without reaching the melting point of the base metal. This heat affected zone represents a vulnerability in mould repair where the original tempering of the tool steel is compromised. Hardness levels in this area often fluctuate, leading to potential cracking or uneven wear during the production run.
The zone ends where the temperature remained below the critical transformation point of the alloy.
Hardness Gradient
Localized heating creates a transition in the crystalline structure of the steel from the weld nugget to the unaffected base material. In the heat affected zone, the steel may become excessively hard and brittle or soft and prone to deformation. These variations depend on the cooling rate and the initial heat treatment of the mould.
Residual Tension
Internal forces accumulate within the metal as it expands and contracts during the welding cycle. If the heat affected zone is not managed through pre-heating, the resulting tension can cause immediate stress cracks.
Repair Constraint
Successful tool restoration requires minimizing the width of this zone to preserve the mechanical properties of the cavity. Precise control of the welding parameters prevents the heat affected zone from extending into critical shut-off surfaces.
