Tool Steel Grade Selection and Cavity Shrinkage Tolerances
Selecting tool steel grades for precision cavities requires balancing grain direction, heat treatment distortion, and alloy verification to hold tight part tolerances.
Electroslag Remelting S136
Meaning
Metallurgical refinement processes utilize a secondary melting technique under highly controlled slag chemistry to eliminate impurities and minimize micro-segregation in high-performance tool steel. The use of electroslag remelting S136 ensures that the stainless steel used for mold cavities achieved maximum purity and isotropic mechanical properties. This premium grade of steel is preferred for optical-grade injection molds that require a mirror finish.
Steel Quality
The refining process operates by melting a consumable electrode through a pool of molten slag that removes sulfur and non-metallic inclusions. As the purified droplets solidify in a water-cooled mold, a highly uniform crystalline structure forms. This controlled solidification reduces the size of carbides and distributes them evenly throughout the matrix.
It prevents the formation of hard spots that cause polishing defects.
Application Value
Plastic lenses and medical components demand flawless surface finishes that can only be achieved with highly polished cavities. Normal grade steel contains tiny gas pockets or inclusions that pit when polished to a mirror finish. Using the refined grade ensures that the surface remains free of microscopic voids during the polishing process.
This choice extends the production life of the mold.
Supply Compliance
Purchasing departments verifying tool steel origin must demand steel mill certificates that confirm the secondary refining method used. In China, standard S136 is widely available, but only the refined grade provides the fracture toughness needed for high-pressure molding of abrasive resins. Quality auditors use optical microscopy and hardness testing to verify that the steel delivered matches the specified electroslag grade.
Using cheaper, non-refined alternatives results in premature mold cracking and costly surface deterioration during production. Therefore, the specification of the remelted grade must be explicitly included in the tooling agreement. This requirement prevents suppliers from substituting lower-grade steel to cut costs.