热处理过程中界面固相反应控制锰硅类氧化物变性的机理研究

Mechanism on Modification of MnO-SiO_2-Type Oxide by Interfacial Solid-State Reaction During Heat Treatment

采用扩散偶的方法,利用高温共聚焦激光显微镜和高温感应炉研究了1473K热处理过程中Fe-Mn-Si合金与MnO-SiO_2-FeO氧化物的固相反应及其对二者成分及物相的影响规律,并分析了凝固过程中合金与氧化物平衡成分变化情况,揭示了高温界面固相反应控制MnO-SiO_2-FeO氧化物变性的内在机理。结果表明,热处理过程中合金与氧化物发生的界面固相反应造成合金内Mn、Si元素的损耗,靠近界面处合金内会形成大量MnO-SiO_2颗粒,而氧化物中由于FeO成分的分解,产生了单质Fe颗粒,随热处理时间的延长,MnO和FeO含量分别呈上升和下降的趋势。

In order to control physicochemical characteristics of inclusions in steel through appropri- ate heat treatment process, solid-state interface reaction between solid alloy deoxidized by Mn and Si and MnO-SiO2-FeO oxide during heat treatment was studied. Using confocal scanning laser microscope （CSLM） and high temperature induction furnace, the reaction between the Fe-Mn-Si alloy and MnO-SiO2- FeO oxide during heat treatment at 1473 K and its influence on the compositions and phases in the alloy and oxide were investigated by diffusion couple method. A suitable method for pre-melting oxide and pro- ducing diffusion couple of Fe-Mn-Si alloy and MnO-SiO2-FeO oxide was proposed to obtain good contact between them. After that, the diffusion couple sample with 17 foil for reducing oxygen partial pressure and bulk alloy containing the same compositions was sealed in a quartz tube for carrying out subsequent heat treatment experiment. In addition, equilibrium compositions and phases of the oxide and alloy dur- ing solidification and the solid-state reaction mechanism between them were analyzed and discussed. Quantitative analysis of each element in alloy and oxide was calibrated by standard sample before analy- sis. Results showed that solid-state interface reaction and element diffusion between the Fe-Mn-Si alloy and MnO-SiO2-FeO oxide were observed which indicated that the alloy and oxide in the diffusion couple was not equilibrated at 1473 K, even though the liquid phases of them were equilibrated at 1873 K. The activity of FeO in MnO-SiO2-FeO oxide decreased with the decrease of temperature and excess oxygen diffused from oxide to alloy. Mn and Si contents in the alloy were consumed by the chemical reaction and some MnO-SiO2 particles in the alloy near the interface generated. As the heat treatment time increased from 10 h to 50 h, the widths of particle precipitation zone （PPZ） and manganese depleted zone （MDZ） in- creased from 79 and 120 μm to 138 and 120 μm, respectively. During the heat treatment, the width of MDZ was always greater than that of PPZ. Moreover, due to the separation of the FeO, pure Fe particles formed in the oxide. The MnO and FeO contents in the oxide increased and decreased respectively with the increase of the heat treatment time.