Materials technology Stainless grade faces off with tool steel performance
Industeel, a division of steel giant Arcelor Mittal, has developed a free-machining martensitic stainless steel. The supplier talks about how the metal’s properties and milling characteristics stack up against standard grade DIN X 33 CrS 16 (W 1.2085).
An injection mould is designed to contain the polymer melt within the mould, efficiently transfer heat from the hot polymer to the cooler mould and quickly eject the plastic part. In order to fulfil these primary functions, some of the main requirements for mould bases are high machinability to give toolmakers both high productivity and longer tool life (cost reduction), high and consistent mechanical strength and hardness, good thermal properties to facilitate the removal of heat through the mould structures and good corrosion resistance to ensure mould durability and reduce maintenance costs.
Industeel said its Superplast stainless steel offers a corrosion-resistant material for mould bases that combines excellent machinability with improved thermal conductivity.
Chemistry and microstructure
Standard mould base steels that have high carbon contents also come with the disadvantage of being detrimental to machining operations. Superplast stainless has been designed with a low carbon content, combined with a 12% chromium content and the addition of alloying elements to achieve high mechanical strength and good corrosion resistance. The addition of sulphur combined with a specific treatment for sulphides aims at improving 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 standard 1.2085 in as-delivered condition 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 related to this grade’s high carbon content.