Investigation on Thermal-stress Coupling Effect and Transformation of the Layer Covered on Graphite Nodules in the Parts Made by ADI with Ultrafine Structure
Author of the article:XU Yang;GE Liling;YAN Fuxue;LUO Qiwen;JIANG Bailing;LIU Baojian;YAN Guojun
Author's Workplace：School of Materials Science and Engineering,Xi'an University of Technology,Xi'an 71004& China
Key Words：ADI the thermal-stress coupling effect continuous casting propagated dislocations
Abstract：
Our preliminary observation and analysis had shown that a hybrid transition layer covered on the graphite nodules would be formed due to a great quantity of latent heat coming from the solidification of graphite and austenite in the process of producing hollow nodular cast iron profiles by the upwards continuous casting. The layer can purify the metallic matrix in the casts because a great deal of impurities and compounds, which were formerly distributed in the metallic matrix, were collected in the layer. The nodular cast iron profiles produced by the process can be quenched into ADI with an ultrafine structure by an isothermal quenching. When the parts made from the quenched profiles were in their course of working and suffered from an elastic deformation with a high frequency and low amplitude in, an obvious thermal-stress coupling effect would happen in them, that is, the quenched structure of metallic matrix around the graphite nodules were transformed into a "strain aging and thermal aging" complex structure. The hardness of the complex structure was slightly smaller than that of quenched structure, but the complex structure can inhibited obviously the initiation of cracks. These changes in the matrix may come from automatic elimination of propagated dislocations, which were activated by micro-regions temperature fields centered at graphite nodules.
