【作者】 张琦；

【导师】 黄海波； 涂益友；

【作者基本信息】 东南大学 ， 材料科学与工程， 2018， 硕士

【摘要】 高强度钢丝被广泛应用于桥梁缆索、轮胎钢帘线和切割钢丝等,是现代工业极为重要的产品。微合金化高碳热轧盘条是高强度钢丝制品的生产原料,其珠光体微观组织特征决定了盘条的拉拔变形能力和钢丝最终性能。本文以高碳钢热轧盘条为研究对象,探究了奥氏体化条件以及合金元素Mn、Si对盘条共析转变过程及转变组织的影响规律,为高性能热轧盘条的成分设计和热处理工艺改进提供一定的理论支撑。在本文的实验条件取得如下主要结果:奥氏体化温度越高,奥氏体保温时间越长,珠光体团的尺寸越大。相同奥氏体化温度条件下,奥氏体化保温时间延长,对高Si钢TTT曲线鼻尖温度和珠光体转变始末时间影响较小,珠光体片层间距基本一致。与之相反,奥氏体化保温时间延长,可使低Si钢TTT曲线明显右移,导致转变实际过冷度增大,珠光体片间距减小。而奥氏体化温度升高,会使珠光体转变TTT曲线右移,珠光体片间距减小。900℃奥氏体化/580℃盐浴淬火,高Si钢和低Si钢都能在32s内发生完全的珠光体转变,高Si钢转变速度比低Si钢略快,其中高硅钢的生长速率达到2.96×10^-7m/s高于低硅钢的生长速率(8.98×10^-8m/s)。快速转变过程中,在γ/α/M₃C三相界面附近Mn未能及时扩散,难以达到局部平衡的稳态生长浓度分布条件,其生长过程并不完全符合（α+M₃C）两相区的稳态生长,表现出珠光体片间距随转变过程逐步增大的非稳态生长特征。Si强烈倾向富集于铁素体中,且其扩散速度快,在反应早期既能完成分配过程,铁素体中的Si富集可以促进Mn向渗碳体中的分配。当盐浴温度升高时,Si扩散足够快,渗碳体中脱离的Si原子可以快速扩散至铁素体片层内部,界面附近铁素体中Si富集的现象消失。元素再分配过程中大量的Mn元素被从铁素体相推向渗碳体相,由于Mn的扩散速度远低于Si,进入渗碳体的Mn元素来不及扩散至渗碳体心部,而呈现出了界面附近Mn堆积的现象。更多还原

【Abstract】 As a very important product in modern industry,high strength steel wire is widely used in bridge cables,tire cord and cutting steel wire.High carbon hot rolled rod is the raw material of high strength steel wire products.The microstructure of the pearlite determines the mechanical properties and the ultimate performance of steel wires.In this paper,high carbon hot rolled rod is studied to explore the effect of austenitizing conditions as well as alloy elements Mn and Si on eutectoid-transformation process and the microstructure of wire rod,which provide certain theoretical support for component design and heat treatment process of high-performance hot rolled wire rod.The following main results are obtained in this experiment:The higher the austenitizing temperature and the longer the holding time were,the larger the pearlite colony size was.With the same austenitizing temperature,the longer the holding time was,the smaller the effect on the nasal tip temperature of the TTT curve and the starting and ending time of the pearlite transition of the high Si steels were,while the interlamellar spacing of the pearlite was basically the same.In contrast,if austenitizing time is prolonged,the TTT curve of low Si steel will be significantly shifted to the right,leading to the increase of the actual undercooling and the decrease of interlamellar spacing of the pearlite.Also the increase of austenitizing temperature will cause the right shift of TTT curve and the decrease of interlamellar spacing.When austenitized at 900℃and isothermal transformed at 580℃,both high and low Si steels could completely accomplish the pearlite transformation within 32s,the high Si steel growth rate reached 2.96 x 10^-7 m/s which is higher than that（8.98 x 10^-8m/s）of low Si steel.During rapid transformation process,the conditions of steady-state growth of local equilibrium were difficult to meet on account of the belated diffusion of Mn near theγ/α/M₃C three-phase interface,The growth process is not completely in line with the steady-state growth of two phase area which showed the non-steady-state growth feature like the increasing pearlite interlamellar spacing.The diffusion velocity of Si was fast and it strongly accumulated to ferrite.In the early stage of reaction,the distribution process can be completed,and Si atoms in bccα-Fe structure tend to accelerate Mn atoms diffuse into cementite phase.When the salt bath temperature rises,Si diffusion is so fast that the Si atoms separated from the cementite can rapidly diffuse into the ferrite core,and the Si enrichment phenomenon in the ferrite near the interface disappeared.due to the diffusion rate of Mn is far lower than Si which resulted that Mn cannot diffused to the cementite core and the Mn accumulation phenomenon near the interface was presented.更多还原