Injection Mold Qualification Protocol and Tooling Steel Selection Criteria
Tool steel selection and scientific qualification protocols dictate mold life, cycle efficiency, and dimensional capability under continuous production.
420 Stainless Steel
Meaning
High-chromium martensitic steel provides a combination of moderate corrosion resistance and high wear resistance when hardened by heat treatment. Hardened 420 stainless steel contains at least twelve percent chromium, which is sufficient to form a passive oxide surface layer that prevents oxidation in mild atmospheric environments. Lower carbon grades lack the ability to achieve the high hardness values needed for cutting tools and mold inserts.
Alloy Composition
A balanced mixture of iron and chromium forms the basis of this grade, with a carbon fraction of about fifteen hundredths to forty hundredths of a percent that facilitates thermal hardening. This formulation provides sufficient hardenability without creating excessive grain boundary carbides. Higher concentrations of carbon would compromise the toughness of the metal.
Hardening Response
Extreme thermal cycles optimize the mechanical properties of the material. Heating the metal dissolves carbides before a rapid quench in oil transforms the microstructure. Tempering must follow immediately to relieve internal stresses.
Corrosion Resistance
The passive chromium oxide film achieves its maximum development when the material is fully hardened and polished. Rough surfaces or retained carbide particles can disrupt this protective barrier, leading to localized pitting. Aggressive chemical mixtures lie beyond the protective capability of this grade.
The alloy retains its integrity when exposed to fresh water and mild organic acids.