Hardened Tooling Steel Selection and Injection Shrinkage Tolerances
Verify tool steel composition and heat treatment phase stability independently to ensure injection shrinkage predictions match finished part tolerances.
NAK80
Meaning
Pre-hardened plastic mold steel containing nickel, aluminum, and copper undergoes an age-hardening process to deliver uniform hardness through its entire block thickness without additional heat treatment by the toolmaker. Within precision tooling shops, nak80 behaves as a time-saving material choice for small to medium inserts that require excellent polishability and consistent machining characteristics. The alloy delivers a hardness of roughly forty Rockwell C directly from the mill, which eliminates the risks of quenching cracks or dimensional growth that occur during conventional hardening.
Manufacturers specify nak80 for clear plastic products like dashboard covers and camera lenses due to its extremely uniform grain structure. Precise control over chemical precipitation ensures that the steel offers a mirror finish that remains free from the micro-pinholes found in lower grades. The usage limits of this grade suggest it is not ideal for large heavy-duty dies that require extreme surface pressure or long-term high velocity glass-fiber injection.
Practitioners in China rely on nak80 when delivery speed is a priority and consistent performance is expected across multiple identical mold cavities.
Metallurgical Mechanism
Formation of copper and aluminum precipitates during the age-hardening stage at the steel mill creates the foundational hardness of the metal matrix. During the slow cooling of nak80 after refining, these elements form small dispersed phases that lock the crystalline structure against slippage. This metallurgical property makes the steel consistently hard from the skin to the center of a large block, unlike shallow hardening steels.
Uniformity of internal tension allows the toolmaker to remove massive amounts of material via EDM or milling without the piece warping. If the steel were traditionally hardened, the toolmaker would have to allow for significant extra material that would then be ground away after tempering. The low sulfur content inside nak80 minimizes the risk of sulfide inclusions that would cause streaks during mirror polishing.
Finishing Application
Adoption of specific polishing protocols allows this grade to reach a high gloss that stays clear after many thousands of injection cycles. When a worker applies diamond abrasive paste to nak80, the material responds with a predictably high sheen because its hard precipitates support the metallic matrix during the rubbing action. If the steel has been stored in poor conditions, it must be cleaned deeply to prevent localized oxidation from ruining the polish.
The age-hardened nature of the steel makes it slightly more abrasive than standard P20 during the machining phase, requiring high quality inserts. Because it provides good EDM characteristics, complex shapes can be sparked into the cavities without leaving deep recast layers. Once the surface is ready, it provides a stable interface that resists the buildup of plastic residues and gases during high speed production.
Operational Guideline
Thermal stability of the tool is maintained as long as the surface temperature during the molding process does not exceed the aging temperature of the steel. Because nak80 is already hardened, exposing it to temperatures above five hundred degrees for an extended period would cause a permanent loss of strength. When welding repairs are necessary, matching filler rods must be used carefully with precisely controlled preheating to prevent a soft spot at the interface.
The alloy has a higher price per kilogram than common mould steels, which restricts its use to critical inserts rather than the entire massive frame. Small, detailed parts for mobile phones or medical instruments represent the ideal application for the stability it offers. Its resistance to atmospheric corrosion is better than standard tool steels but falls below that of martensitic stainless grades like S136.