| 在Ae3-Ar3温度之间低碳钢形变诱导铁素体相变的实验研究 | |
| Alternative Title | Experimental investigation of deformation induced ferrite transformation at a temperature range between Ae3-Ar3 in a low carbon steel |
| 赵河山 | |
| Subtype | 硕士 |
| Thesis Advisor | 李依依 |
| 2007-06-08 | |
| Degree Grantor | 中国科学院金属研究所 |
| Place of Conferral | 金属研究所 |
| Degree Discipline | 材料加工工程 |
| Keyword | 形变诱导铁素体 应力-应变曲线 C原子扩散 热稳定性 亚动态相变 |
| Abstract | 对于结构材料，细化晶粒一直都是在不降低材料韧性的前提下提高材料强度的有效途径。通过超细晶粒钢的研究，人们逐渐发现形变诱导铁素体工艺是一种比控轧控冷工艺（TMCP）更有效的细化晶粒的途径，并对该工艺作了大量的研究。然而，到目前为止，形变诱导铁素体相变的转变机制仍然不十分明确。本文在前人的基础上，在Ae3-Ar3温度之间对低碳钢Q235的形变诱导铁素体相变作了更进一步的研究。 本文利用Gleeble3500热模拟实验机的强大模拟功能，在Ar3-Ae3温度之间针对Q235低碳钢进行形变诱导铁素体相变的模拟实验，对记录下来的各个变形参数绘制曲线进行分析，发现形变诱导铁素体相变过程中的应力-应变曲线上所表现出来的峰值是由于形变诱导相变在晶界或在晶内的发生而导致的软化效应所引起的。对应变-时间曲线和应力-时间曲线的分析表明，变形对诱导相变具有明显的推迟作用，所以形变诱导相变在形变接近结束之时才开始大量发生，导致相变的大部分时间发生在应变结束之后，因此，形变诱导铁素体相变具有亚动态相变的特征。严格意义上讲，形变诱导铁素体相变是一个动态形核的亚动态相变过程。 利用场发射扫描电镜观察试样微观组织，同时利用电子探针仪对组织内部的C浓度进行测量，并结合应力-时间曲线对诱导铁素体相的组织演变规律进行研究。分析表明诱导铁素体相中C含量远高于常规铁素体中的C含量，由于C含量的过饱和导致诱导铁素体是一种非稳定状态的过渡相。在变形处理之后对试样进行保温试验，结果显示，在保温过程中诱导铁素体相首先会发生铁素体晶粒的长大，但由于其热力学的不稳定性，随后会发生铁素体向奥氏体的逆转变。试样的回火试验显示，由于诱导铁素体相本质上是非稳定的过渡相，所以最终过饱和C原子的扩散逸出导致诱导铁素体相转变为稳态的常规铁素体相，利用维氏硬度计表征其力学性能，显示其硬度也随之降低。 |
| Other Abstract | For structural material, grain refinement is always the most effective way to improve the strength while not sacrificing the toughness. During the research on super-refined steel, deformation induced ferrite transformation (DIFT) was found as a more effective way than TMCP to refine steel grain, and thus plenty of efforts were put on this project, but there was no clear mechanism for DIFT yet. Based on the early research, this paper, therefore, has done a further work at a termperature range between Ae3-Ar3 in a low carbon steel aimed at studying DIFT. Based on the powerful simulation function, a series of general simulations of deformation induced ferrite transformation (DIFT) at a temperature range between Ae3~Ar3 in Q235 low carbon steel were conducted on Gleeble3500 which could precisely record all of the parameters during the deformation. Stduy on stree-strain cruves during DIFT shows that the peaks exhibited in the curves are involved with deformation induced transformation which happened in inner grain or grain boundary. According to the stress-time curve and strain-time curve, strain dramatically postponed the strain induced transformation which lead to the start of the transformation began right ahead of the finish of deformation. And thus, the majority of the ferrite transformation process mainly happened after the deformation. Strictly, deformation induced transformation was a metadynamic transformation process with dynamic nucleation. Obervations on microstructure by SEM and the measurement of carbon concentration by EPMA, the DIFT evolution was investigated combined with analysis on stress-time curve during the DIFT. The result indicates that the carbon concentration in DIF is far higher than that of conventional ferrite, deformation induced ferrite phase, therefore, is a quasi-stable transitional phase. A holding experiment after the deformation and a tempering treatment including a hardness measurement for the induced ferrite phase were conducted to study the deformation induced transformation and the thermal stability of the induced ferrite phase. Because of the thermal instability, an inverse transformation from DIF to austenite was found during the holding experiment after the deformation. What’s more, the super-saturated carbon would precipitate out from inner DIF, resulting in a transformation from DIF to conventional stable ferrite phase and a decrease in its Vickers-hardness during the process of tempering. |
| Pages | 69 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.imr.ac.cn/handle/321006/17103 |
| Collection | 中国科学院金属研究所 |
| Recommended Citation GB/T 7714 | 赵河山. 在Ae3-Ar3温度之间低碳钢形变诱导铁素体相变的实验研究[D]. 金属研究所. 中国科学院金属研究所,2007. |
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