铋在易切削钢中赋存状态及转化机制研究

本申请针对铋在易切削钢中的赋存状态及转化机制展开研究，在热力学分析基础上, 通过高温冶炼试验探究铋在易切削钢中的赋存形式，分析铋含量变化对易切削相组成的影响规律，寻找适宜的成分配比；通过枝晶生长热模拟实验、定向凝固仪实验，摸索易切削相在凝固降温过程的析出顺序，摸索凝固过程中易切削相竞争性析出的规律，归纳易切削相形态优化、成分均匀的控制条件；通过热处理实验、高温共聚焦原位观测实验，研究热履历对易切削相固溶、分解、相变、转化行为的影响规律，分析易切削相在化学冶金、物理冶金过程的赋存及转化规律；总结铋系易切削成分优化、组织均匀、形态优化的控制条件，为高品质易切削钢开发进行机理探索。

This application aims to conduct the investigation in the light of the occurrence state of Bi in free-cutting steel and its transformation mechanism. Based on the thermodynamic analyses, the high-temperature smelting experiments are carried out to determine the forms of Bi existing in the steel, and to analyze the laws of influence of various Bi contents in steel on the compositions of the free-cutting phases, and further to seek the proper proportions of the composition. Together with the experiments carried out by using a dendritic growth thermo-simulator and a horizontally directional solidification device, the precipitation sequences of the free-cutting phases during the solidification and temperature-drop are explored, the competitive precipitation laws of the free-cutting phases during the solidification are analyzed, and the control conditions for the morphology optimization and composition homogeneity of the free-cutting phases are sought. Combined with the experiments of heat treatment and in situ observation by a high-temperature laser confocal microscope, the laws of the effect of thermal history on the solid solution, decomposition, phase transformation, and conversion behaviors of the free-cutting phases are studied, the existence and conversion laws of the free-cutting phases in the process of the smelting-solidification -heating-rolling temperature-drop are analyzed, and the high-temperature physical parameters and critical variables of the free-cutting phases in the smelting-continuous casting-heating furnace-rolling are sought. Finally, the conditions for the composition optimization, microstructure uniformity and morphology optimization of Bi free-cutting series are concluded to lay the theoretical foundation for the development of the Bi-containing free-cutting steels