發(fā)布時間：2018-06-27 00:02

  本文選題：微觀組織 + 層錯能　； 參考：《中北大學》2015年碩士論文

【摘要】：通過總結(jié)分析國內(nèi)外的研究發(fā)現(xiàn)，TWIP鋼的研究正在朝著探討詳細微觀形貌對其組織性能變化的影響方向發(fā)展。而材料的微觀組織形貌實際上是變形機制的具體表現(xiàn)，那么，通過分析TWIP鋼在塑性變形時微觀組織形貌，來研究變形機制相互競爭規(guī)律，是當前急需弄清的問題。 首先本文主要對TWIP鋼在室溫靜態(tài)壓縮和拉伸變形下的變形機制競爭規(guī)律進行研究，觀察不同變形量下的TWIP鋼的微觀組織，分析其組織演變過程；其次分析不同熱連軋溫度范圍對TWIP鋼力學性能的影響，結(jié)合汽車用鋼對鋼材的性能要求，確定出最佳的熱連軋溫度范圍，得出了以下結(jié)論： (1)在室溫靜態(tài)壓縮條件下，位錯運動貫穿整個變形過程，在變形初期，位錯反應促使層錯形成與長大，從而完成形變孿晶的形核。隨著變形的繼續(xù)，層錯逐漸消失，取而代之的是大量的形變孿晶。在晶粒內(nèi)，由于孿晶之間的相互交割，所以晶粒被分割成許多細小的格紋狀晶粒，并且隨著變形量增加，晶粒產(chǎn)生扭曲現(xiàn)象。在變形后期，由于晶粒被分割得足夠小，抑制形變孿晶的產(chǎn)生，所以削弱了TWIP效應。TWIP鋼在壓縮變形后的微觀組織中的形變孿晶形成過程不同于拉伸變形下單個孿晶系優(yōu)先形成的情況。孿晶形成速度明顯比靜態(tài)拉伸下要快，這可能與形變孿晶的形成機制有關(guān)。 (2)在室溫靜態(tài)拉伸變形條件下，在TWIP鋼的變形初期，變形機制以位錯的相互作用以及位錯與相界、亞晶界相互作用為主；隨著變形量的進一步增大，，晶體內(nèi)的形變孿晶在晶界處形成，孿生機制被激活。TWIP鋼的變形機制是以TWIP效應為主，而以位錯滑移作用為輔；在變形后期，主要變形機制是位錯滑移逐漸消弱了TWIP效應，從而誘發(fā)了去孿生機制。層狀組織出現(xiàn)，孿晶特征減弱，從而導致樣品的局部變形和失效。 (3)隨著熱連軋溫度降低，TWIP鋼的屈服強度、拉伸強度和屈強比升高，而延伸率、應變硬化指數(shù)和強塑積隨熱連軋溫度的降低而降低。在變形后期過程中，熱連軋溫度較高，有利于產(chǎn)生持續(xù)的加工硬化現(xiàn)象，從而提高材料的均勻變形能力。依據(jù)TWIP鋼在汽車車身上的實際用途，以及汽車零件對鋼板的使用要求，得出最佳的熱連軋溫度范圍為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

本文編號：2071910