Materials technology Stainless grade copes with the performance of tool steel
Publisher: Eric Culp
Industeel, a division of steel giant Arcelor Mittal, has developed martensitic stainless steel for bar turning. The supplier explains how the metal properties and milling characteristics compare to the standard grade DIN X 33 CrS 16 (W 1.2085).
An injection mold is designed to contain the molten polymer in the mold, efficiently transfer heat from the hot polymer to the colder mold, and quickly eject the plastic part. In order to fulfill these main functions, some of the main requirements for the mold bases are high machinability to give toolmakers both high productivity and longer life (cost reduction), high mechanical strength and hardness. and constant, good thermal properties to facilitate heat removal through the mold structures and good corrosion resistance to ensure mold durability and reduce maintenance costs.
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Industeel stated that its Superplast stainless steel provides a corrosion resistant material for mold bases that combines excellent machinability with improved thermal conductivity.
Chemistry and microstructure
Standard mold base steels which have high carbon contents also have the disadvantage of being detrimental to machining operations. Superplast stainless steel has been designed with low carbon content, combined with 12% chromium content and the addition of alloying elements to achieve high mechanical strength and good corrosion resistance. The addition of sulfur associated with a specific treatment of sulphides aims to improve the machinability of the steel. The table compares the chemical compositions of standard tool steel and the new grade.
Micrographs of the stainless grade and the 1.2085 standard on delivery show that the new steel microstructure is composed of martensite and sulphides, with the absence of delta ferrite. On the micrograph of 1.2085, primary carbides are observed within a martensitic structure with sulphides. These primary carbides are linked to the high carbon content of this grade.