Improved Quality by Electro Slag Re-melting

by GÜnter Busch

Publisher - ALD Vacuum Technologies GmbH, Hanau, Germany.

Category - Engineering & IT

Electro Slag Re-Melting is a process performed after the primary melting steps in electro arc, induction or vacuum induction furnaces. Typical steels to be re-melted are tool steel with a share of 20%, stainless steels with 10% share and bearing steel with 5% share. To meet the higher service demands on these steels require increased use of re-melting technologies. The ingots from the previous melting process are used as self-consuming electrodes in the process of electro slag re-melting, which is performed under inert gas atmosphere to form a new refined ingot. The tip of the electrode is just immersed in the top of the slag bath surface and the liquid metal will be cleaned when droplets melt off and pass down through the slag layer on top of the formed ingot. The ingot shape can be round or rectangular in cross section. The main metallurgical tasks for the ESR process are:  Increase the ingot cleanliness by removal of non-metallic inclusions  Narrow range? Close control of reactive elements like Boron, rear earth elements and/or Titanium and minimum burn off  No Oxygen or Hydrogen pick up from the atmosphere  Higher material yield due to increased density and reduced top shrinkage cavity  Controlled directed solidification resulting in  No macro segregation and reduced micro segregation  Homogeneous distribution of the alloying elements The result will be steel with consistently higher and more uniform mechanical properties especially fatigue resistance and fracture toughness, which are important for many application especially in bearing, tool and die steels. For special steels and steels used in the aeronautical industry a triple melt will be necessary to achieve the required material properties. The final melt will be performed in a Vacuum Arc Re-melting (VAR) system. Experience in the automotive industry shows that it is possible to significantly increase tool lifeby using tool steels produced via re-melting technology, leading to reduced cycle (time?) and manufacturing costs.

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