渗碳体的形态和分布对珠光体钢丝拉拔形变及性能的影响

发布时间：2018-04-29 06:41

本文选题：珠光体钢丝 + 拉拔形变　；参考：《东南大学》2015年硕士论文

【摘要】：为研究适合拉拔形变的珠光体组织,以珠光体钢丝为原材料,经退火处理得到球状珠光体组织,经淬火+高温回火处理得到不同尺寸的球状渗碳体+基体铁素体组织,以这四种组织的拉拔形变过程为研究对象,采用扫描电镜(SEM)、透射电镜(TEM)和电子背散射衍射(EBSD)等手段,研究了渗碳体的形貌、分布、尺寸对钢丝冷拉拔形变的影响,并探讨了其形变强化机制,得出以下结论：比较研究了片状珠光体钢丝(片状渗碳体+铁素体)与球状珠光体钢丝(球状渗碳体+铁素体)的冷拉形变过程,结果表明：1)片状渗碳体在形变中表现出一定的变形能力,处于有利取向的层片细化、间距减少,不利取向的层片则发生了弯曲、扭转,甚至断裂、碎化；硬的球状渗碳体在钢丝形变时不发生塑性变形,而会随着铁素体的塑性变形逐渐转向于平行拉拔的方向,应变量为1.6左右时已基本平行于拉拔方向,同时形变组织中的碳化物周围出现了较多的微观缺陷。2)片状珠光体钢丝强度远高于球状珠光体钢丝,且片状珠光体钢丝在应变量ε1.6左右时,加工硬化率明显增加。3)片状珠光体组织的110织构强度随应变量的增加不断增强,与球状珠光体组织相比,片状珠光体组织的织构强度更高。对球状珠光体钢丝和淬火+高温回火态钢丝(球状渗碳体+铁素体)的冷拉形变过程进行对比研究,结果表明：1)当组织中存在较多的大尺寸碳化物,且碳化物弥散分布时,容易在形变时产生缺陷。2)渗碳体粒子平均粒径越小,粒子分布越弥散,强度越高,因此淬火+高温回火态(小尺寸Fe3C球)钢丝强度高于淬火+高温回火态(大尺寸Fe3C球)钢丝,球状珠光体钢丝强度最低。3)根据加工硬化率可将形变过程分为三阶段：较小形变(ε0.4)时球状珠光体组织的加工硬化率较大：中等形变阶段(0.4ε1.6)三种组织的加工硬化率相当；较大形变阶段(ε1.6),碳化物弥散分布的组织加工硬化作用更明显。球状渗碳体+铁素体双相材料的形变强化研究结果表明：1)材料形变后,在晶粒内形成了多处高密度位错缠结区,在碳化物周围形成了位错环、位错缠结,以此阻碍后续位错的运动,使材料加工硬化。2)位错在大颗碳化物周围更容易形成位错缠结,周围应力更集中,因此更易形成缺陷。3)渗碳体为球状时,形变过程中碳化物不变形,其周围形成了严重的位错塞积和应力集中,因此组织中易出现缺陷；渗碳体为片状时,渗碳体在钢丝拉拔过程中能与基体协调变形,组织中不易产生缺陷,因此片状珠光体的可拉拔性能更佳。
[Abstract]:In order to study the pearlite microstructure suitable for drawing deformation, the spherical pearlite structure was obtained by annealing with pearlite wire as raw material, and the ferrite structure of spherical cementite matrix was obtained by quenching and tempering at high temperature. The effects of morphology, distribution and size of cementite on cold drawing deformation of steel wire were studied by means of scanning electron microscope (SEM), transmission electron microscope (TEM) and electron backscatter diffraction (EBSD). The mechanism of deformation strengthening is also discussed. The following conclusions are drawn: the cold tensile deformation process of sheet pearlite steel wire (lamellar cementite ferrite) and spherical pearlite steel wire (spherical cementite ferrite) is studied. The results show that the plate-like cementite shows a certain deformation ability during deformation. The layers in favorable orientation are thinned and the spacing is reduced, while the unfavorable orientation of the lamellae is bending, torsion, even fracture and fragmentation. The hard spherical cementite does not produce plastic deformation when the steel wire is deformed, but gradually turns to the direction of parallel drawing with the plastic deformation of the ferrite. When the strain is about 1.6, it is basically parallel to the drawing direction. At the same time, there are many microdefects around carbide in deformed microstructure. 2) the strength of lamellar pearlite steel wire is much higher than that of spherical pearlite steel wire, and the lamellar pearlite steel wire is about 1.6 when the strain is about 1.6. The strength of 110 texture of lamellar pearlite increases with the increase of strain, and the texture strength of lamellar pearlite is higher than that of spherical pearlite. The cold tensile deformation process of spherical pearlite steel wire and quenched high temperature tempered steel wire (spherical cementite ferrite) is studied. The results show that: 1) when there are more large size carbides in the microstructure and the carbides are dispersed, The smaller the average particle size of cementite particle is, the more dispersed the particle distribution is and the higher the strength is. Therefore, the strength of quenched high-temperature tempered steel wire (small size Fe3C ball) is higher than that of quenched high-temperature tempered steel wire (large size Fe3C ball). According to the work hardening rate, the deformation process can be divided into three stages: when the deformation is smaller (蔚 0.4), the working hardening rate of the spherical pearlite is higher than that in the middle deformation stage (0.4 蔚 1.6). In the larger deformation stage (蔚 1.6), the effect of microstructure hardening on the distribution of carbide dispersion is more obvious. The results of deformation strengthening of spherical cementite ferrite biphasic materials show that after deformation, there are many high density dislocation entanglement regions in the grains, dislocation rings and dislocation entanglement around the carbides. In this way, the movement of subsequent dislocations is obstructed, and the working-hardening. 2) dislocations of materials are easier to form dislocation entanglement around large carbides, and the stress around them is more concentrated, so it is easier to form defects. 3) when the cementite is spherical, the carbides do not deform during deformation. Because of the serious dislocation accumulation and stress concentration around the cementite, defects are easy to occur in the microstructure. When the cementite is flake, the cementite can deform harmoniously with the matrix during the drawing process of the steel wire, but it is not easy to produce the defect in the microstructure. Therefore, the pullability of lamellar pearlite is better.
【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG356.46;TG162.85

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