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New steel alloy offers better advantages for molds |
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Pre hardened 400 series stainless steel (DIN 1.2316) is generally used for calibration tools and mold inserts for the plastic processing industry. The consumption of plastics has influenced the tool steel market, with a demand for more specialized type of tool steels. Increasing ingot sizes can lead to microstructural inhomogenities, such as carbide segregation and the appearance of d-ferrite - which have a negative influence on the properties of the typical pre hardened stainless steel. Microstructural inhomogenities have a detrimental effect on properties such as the machinability, polishability and corrosion resistance along with a negative influence on the mechanical properties of the material. To prevent these negative effects, an alloy - Bohler M303 Extra has been developed with a more homogeneous microstructure, and with better mechanical properties as well as better polishability and machinability.
It has been found that at $16 by weight of chromium, a delta ferrite phase occurs at forging temperatures up to 1200�C. This effect could be increased by chromium segregation. To reduce the effect of delta ferrite, nitrogen is one of the alloying elements that can be added. The partial substitution of carbon by nitrogen reduces the amount of chromium rich M23C6-carbides. As a consequence, the chromium content of the alloy can be reduced without lowering the chromium content of the matrix at typical hardening temperatures. This reduces the carbide segregation. The new alloy uniquely fills the demands that many mold makers have that are not being addressed offering benefits such as:
• Good polish finish
• Lower heat treatment costs
• Steel ready for machining
• Saving of time & money
• Better corrosion resistance
• Consistent results of molds
Application is generally in moulds for chemically aggressive plastics, moulds for household appliances, extrusion tools and moulds for fittings.
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