Process Design Of Super-low-carbon Stainless Steel Lower Ring In Runner

The structural characteristics of the Lower Ring in the Runner for the Right Bank of Three Gorge Power Station are introduced in this paper. Particular attention is shown to the cause of elliptical deformation. Through this analysis, process control parameters are established in order to minimize the volume of the elliptical deformation. The result is the production of consistent castings able to meet both the machining requirements, and the quality specified in the technical standard. On the technological design side, after statistically analyzing the dimensions of previously produced lower ring castings reasonable technological parameters, such as casting yield and machining allowance are summarized. In order to assist the directional solidification, a step gating system and insulated feeders are used, and simulation is made by Huazhu CAE. This simulation showed the internal quality met the detection requirement after examining the liquid-phase solidification and shrinkage and dispersed shrinkage. On the melting side, duplex melting with arc furnace and ladle refining, decreases the content of carbon, sulphur and nitrogen This results in a chemistry that meets the standard requirement. In addition, by monitoring the process over the series of castings, the melting times were able to be shortened. On the heat treatment side , blue annealing+ normalization+ secondary temper was used. A normalizing temperature of 1050℃, primary drawing temperature of 650℃, and secondary drawing temperature of 600℃were used. The resulting microstructure was a mix of stable martensite and definite numbers of inverse austenite This resulted in the mechanical properties meeting the standard requirement with an optimal balance between strength and plasticity.