Desulphurization of VIM 690 Ni-base alloy

The reduction of sulphur during the VIM of Ni-base alloy was studied by using prefabricating MgO and CaO crucibles.The former was added with La rare earth element,and has no effective desul-phurization when the sulphur content was less than 0.0030(wt%) in raw materials.The latter was added with Al,it can make the sulphur content in the ingot reduced to 0.0004(wt%).Desulphurization mechanism is that CaO crucible with Al addtion induced to form 3CaO·Al₂O₃ low melting point slag,whereafter desulphurization reaction will conduct on the interface of between 3CaO·Al₂O₃ slag and liquid metal.The working plasticity of the alloy is increased,and the welding cracking is avoided as well.