Meaning
High-chromium martensitic alloys provide the corrosion resistance and high polishability required for plastic injection molds. The use of aisi 420 stainless steel extends to high-precision tooling for medical devices where surface finish and dimensional stability are paramount. Constant exposure to condensation or corrosive breakdown products during molding necessitates a material that prevents pitting and oxidation of cavity surfaces.
The alloy contains specific carbon and chromium balances to ensure it achieves both high hardness and excellent rust resistance after heat treatment.
Alloy Chemistry
Chromium concentrations between twelve and fourteen percent by weight establish the baseline corrosion performance of these steels. Carbon content in aisi 420 stainless steel is sufficient to allow hardening through heat treatment. Molybdenum and silicon additions optimize the microstructure during cooling, preventing coarse grain formation in large blocks.
Heat Treatment
Hardening processes involve heating the steel to high austenitizing temperatures followed by quenching in gas or oil. For molds made of aisi 420 stainless steel, double tempering is executed to relieve internal stresses and stabilize the crystalline structure. Achieving a hardness of fifty to fifty-two Rockwell C ensures the tool resists deformation under high injection pressures.
Tooling Wear
Abrasive action from fiberglass reinforcement or mineral fillers eventually erodes mold cavity details over long production runs. Tooling fashioned from aisi 420 stainless steel resists abrasive wear better than softer pre-hardened steels, but is more brittle. Correct cooling lines prevent thermal fatigue and micro-cracking during fast cycles.
