Characterization of segregation degree for large size metal component and application on high-speed train wheel.

Elements segregation has a significant impact on the performance of steel products and becomes more serious with the increase of products size. Many studies have been carried out on segregation in solidification. None of the studies on the quantitative analysis of segregation evaluation for the full surface of large-size metal components. In this paper the elements segregation degree (Ds) is used for large size metal component analysis for the first time corresponds to the specification of permissible variations for the final product composition. The permissible variations are able to constrain the upper limit of the segregation degree. Based on the data of non-alloy steel and low alloy steel, alloy steel, stainless steel and heat-resistant steel in ASTM (American Society for Testing and Materials) A29/A29 M and GB/T 222, the correlation between upper and lower permission variation to element content was established and the regression formula was obtained respectively. Each element content was corresponding to a specified permission limit. The segregation degree of steel products was easily evaluated by the formula precisely. The 95% prediction interval was utilized as the upper and lower variation line to evaluate the segregation degree of large-size sample. The method was successfully applied in the full-scale mapping of longitudinal section of the high-speed train wheel by Original Position Analysis for Large Samples (OPA-LS) technique. The negative and positive Ds of Al in high-speed train wheel were over DS(MAX) and the limit specified by GB/T 222, which indicated the Al segregation should be controlled.