静态变形下TWIP钢的变形机制竞争规律研究

发布时间：2018-06-27 00:02

  本文选题：微观组织 + 层错能　； 参考：《中北大学》2015年硕士论文

【摘要】：通过总结分析国内外的研究发现，TWIP钢的研究正在朝着探讨详细微观形貌对其组织性能变化的影响方向发展。而材料的微观组织形貌实际上是变形机制的具体表现，那么，通过分析TWIP钢在塑性变形时微观组织形貌，来研究变形机制相互竞争规律，是当前急需弄清的问题。 首先本文主要对TWIP钢在室温静态压缩和拉伸变形下的变形机制竞争规律进行研究，观察不同变形量下的TWIP钢的微观组织，分析其组织演变过程；其次分析不同热连轧温度范围对TWIP钢力学性能的影响，结合汽车用钢对钢材的性能要求，确定出最佳的热连轧温度范围，得出了以下结论： (1)在室温静态压缩条件下，位错运动贯穿整个变形过程，在变形初期，位错反应促使层错形成与长大，从而完成形变孪晶的形核。随着变形的继续，层错逐渐消失，取而代之的是大量的形变孪晶。在晶粒内，由于孪晶之间的相互交割，所以晶粒被分割成许多细小的格纹状晶粒，并且随着变形量增加，晶粒产生扭曲现象。在变形后期，由于晶粒被分割得足够小，抑制形变孪晶的产生，所以削弱了TWIP效应。TWIP钢在压缩变形后的微观组织中的形变孪晶形成过程不同于拉伸变形下单个孪晶系优先形成的情况。孪晶形成速度明显比静态拉伸下要快，这可能与形变孪晶的形成机制有关。 (2)在室温静态拉伸变形条件下，在TWIP钢的变形初期，变形机制以位错的相互作用以及位错与相界、亚晶界相互作用为主；随着变形量的进一步增大，，晶体内的形变孪晶在晶界处形成，孪生机制被激活。TWIP钢的变形机制是以TWIP效应为主，而以位错滑移作用为辅；在变形后期，主要变形机制是位错滑移逐渐消弱了TWIP效应，从而诱发了去孪生机制。层状组织出现，孪晶特征减弱，从而导致样品的局部变形和失效。 (3)随着热连轧温度降低，TWIP钢的屈服强度、拉伸强度和屈强比升高，而延伸率、应变硬化指数和强塑积随热连轧温度的降低而降低。在变形后期过程中，热连轧温度较高，有利于产生持续的加工硬化现象，从而提高材料的均匀变形能力。依据TWIP钢在汽车车身上的实际用途，以及汽车零件对钢板的使用要求，得出最佳的热连轧温度范围为1100℃～900℃。
[Abstract]:It is found that the research of TWIP steel is developing towards the direction of discussing the influence of detailed micromorphology on the microstructure and properties of TWIP steel by summing up and analyzing the domestic and foreign researches. The microstructure of the material is actually the concrete manifestation of the deformation mechanism, so it is urgent to study the law of the mutual competition of the deformation mechanism by analyzing the microstructure of TWIP steel during plastic deformation. In this paper, the mechanism competition of TWIP steel under static compression and tensile deformation at room temperature is studied, the microstructure of TWIP steel under different deformation is observed and the evolution process of TWIP steel is analyzed. Secondly, the influence of different hot rolling temperature ranges on the mechanical properties of TWIP steel is analyzed. According to the performance requirements of automotive steels, the optimum temperature range of hot strip rolling is determined. The following conclusions are obtained: (1) under static compression at room temperature, the dislocation movement runs through the whole deformation process, and in the early deformation stage, the dislocation reaction promotes the formation and growth of the stacking faults, thus accomplishing the nucleation of the deformation twins. As the deformation continues, the stacking faults gradually disappear, instead of a large number of deformation twins. Due to the intersecting of twins within the grains, the grains are divided into many fine lattice grains, and with the increase of the deformation amount, the distortion of the grains occurs. In the later stage of deformation, because the grain is separated into small enough, the formation of deformation twin is restrained. Therefore, the TWIP effect is weakened. The deformation twin formation process in the microstructure of TWIP steel after compression deformation is different from that in tensile deformation. The formation rate of twinning is obviously faster than that under static tension, which may be related to the formation mechanism of deformation twins. (2) in the initial deformation of TWIP steel under static tensile deformation at room temperature, The deformation mechanism is mainly dislocation interaction, dislocation interaction with phase boundary and sub-grain boundary, and with the further increase of deformation amount, the deformation twin in crystal forms at grain boundary. TWIP effect is the main deformation mechanism of TWIP steel, while dislocation slip is the main deformation mechanism in the later stage of deformation, and dislocation slip weakens TWIP effect gradually, which induces the twinning mechanism. With the appearance of layered structure, the twinning character weakens, which leads to the local deformation and failure of the samples. (3) with the decrease of hot rolling temperature, the yield strength, tensile strength and flexural strength ratio of TWIP steel increase, while the elongation of TWIP steel increases. The strain hardening index and the strong plastic product decrease with the decrease of the hot rolling temperature. In the later stage of deformation, the hot strip rolling temperature is higher, which is conducive to the production of continuous work hardening phenomenon, thus improving the uniform deformation ability of the material. According to the practical application of TWIP steel in automobile body and the application requirement of automobile parts to steel plate, the optimum temperature range of hot strip rolling is 1100 鈩

本文编号：2071910