以U75V高速重轨钢为例，研究了加热保温处理对MnS夹杂的影响。采用高温共聚焦激光显微镜分别对铸坯和钢轨中MnS夹杂在连续升温过程中的行为进行了动态原位观察，结果表明MnS夹杂在600~870℃发生球化，在1180℃左右时， MnS夹杂开始发生固溶。根据原位观察结果，在电阻炉中进行了加热保温处理实验。试验结果表明，830℃保温后，MnS夹杂尺寸只是略有减少，长宽比降低。在1180℃保温后，大型MnS夹杂数量明显减少，小尺寸MnS数量增多，且随保温时间的延长，夹杂物数量减少，长宽比进一步降低。通过加热保温处理可以改善重轨钢中长条状大型MnS夹杂。

The influence of heat and insulation treatment on MnS inclusion was researched in U75V high rate heavy rail steel. The change process of MnS inclusions in casting slab and steel rail was in-situ observed by con-focal laser scanning microscope. The result shows the spheroidization of the MnS inclusions is found at heating temperature between 600 and 870℃ and MnS inclusions begin to dissolve the steel at about 1180℃. According to the results, another experiment of heat and insulation treatment was carried on in electrical resistance furnace. The result indicates that the size of MnS inclusions reduce very little and aspect ratio decreases after the insulation at 830℃, but after insulation at 1180℃ the number of large MnS inclusions reduce obviously and minor sized inclusions increase ,the inclusion number further reduces and the aspect ratio further decreases with the prolong of the time. The slender MnS can be controlled through heat and insulation treatment in rail steel.