Study On The Influences Of Alloying Elements And Rolling Process On The Organizational Performance Of20CrMnTi Steel Bars

20CrMnTi steel is one of the most commonly used medium strength carburizedgear steel which has high hardenability and centre hardness. It is constantly used toproduce the important wear-resistant parts of machines such as gear, shaft and thepiston pin of the automobile and agricultural machinery. There are several cut andturning processes in the gear fabrication procedure, therefore, the machining quality ofthe gear would be intensively influence by the microstructure, alloying elements, andthe hardness of the20CrMnTi steel bars is required to be less than217HBW. Alloyingelement segregation and cooling rate after rolling were discussed to improve the barhardness in order to reach the user requirements. The distribution of alloying elementswas analyzed by original position statistic distribution analysis technique (OPA) in thecontinuous casting slab to determine the electromagnetic stirring technological. Theinfluence of the finishing rolling temperature and cooling rate to the microstructureand properties of bars was studied by hot compression experiments. The variation ofstress, strain and temperature field during rolling was discussed by finite elementsimulation, the principal element caused hardness volatile of bars were researched toprovide a theoretical basis for improving the production process. The main results areas follows:(1) The distribution of alloying elements was analyzed by OPA in the continuouscasting slab produced with different process. The distribution of C、Mn and Cr wasmore uniform as the electromagnetic stirring current increases, the distribution of Tiwas inversed. The results showed that when the electromagnetic stirring current was400A, carbon and other alloying elements were the most evenly distributed.(2) Continuous cooling transformation curve of20CrMnTi steel was obtained bythe hot compression tests. The morphologies of the products of austenite duringcontinuous cooling were studied. The hot compression results also showed that20CrMnTi steel obtained better microstructure and mechanical properties when thefinishing rolling temperature was950~1000℃, the cooling rate of0.2~0.3℃/s.Degenerate perlite formed and caused the increase of the hardness of the bars whenthe cooling rate was0.5℃/s.(3) The variation of stress, strain and temperature field during rolling wasdiscussed by finite element simulation; the change of the temperature field andcooling rate was analyzed.The change of the temperature field and cooling rate of two sizes of rods in the cooling process was compared, the results indicated that thetemperature distribution of Φ80mm bar was more uniform after rolling, while itscooling rate was faster, make the hardness higher than Φ150mm bars.(4) Industrial trials found that when using400A,2.5Hz electromagnetic stirringcurrent, controlling the final rolling temperature and reducing the cooling rate of thebars, the hardness of the gear steel rods was reduced, the difference of hardness ofdifferent specifications of bars was decreased.