多相高强度低合金钢的力学行为研究

发布时间：2018-04-22 14:27

本文选题：大变形管线钢 + 多相钢　；参考：《北京科技大学》2016年博士论文

【摘要】：油气输送管道在通过冻土层、海底、地震带以及塌陷和滑坡等地区时常承受一定塑性变形,从而发生弯折、扭曲和断裂等破坏,引发失效事故。开发能承受大变形而不发生失效的大变形管线钢已成为高性能管线钢发展的一个重要方向。大变形管线钢的形变能力与多相组织应变硬化行为和失效行为密切相关。多相钢中“软-硬”相的合理搭配是实现高塑性的重要技术路线。本文通过对多相钢的力学行为进行实验研究和数值模拟计算分析,揭示了多相钢组织选择和体积分数调控对应变硬化能力／行为、应力比及塑性损伤行为的影响,可为大变形管线钢的工程化应用提供实验和理论依据。组织特征及其本构关系影响着铁素体／贝氏体(F/B)多相钢的应变硬化能力,控制成分和相变可以获得不同强度及应变硬化能力的组织。提高F/B多相钢中组织之间强度差可降低屈强比。F/B多相钢的应变硬化行为呈现出与贝氏体体积分数相关的特性。通过修正C-J分析方法对多相钢的应变硬化过程进行分段以及对各阶段应变硬化能力表征,合理地解释了应力比、屈强比、应变硬化指数及均匀伸长率随贝氏体体积分数变化的规律。并分析了应力比、应变硬化指数、屈强比及均匀伸长率之间的关系及适用条件。相关结论得到了工业化大生产和实验数据的验证,具有较高可靠性。F/B多相钢中组织分数和组织形态(形貌和分布)对其强度和塑性损伤有明显的影响。鉴于这种影响通常很难通过实验测量,本文通过微观力学数值方法计算并分析了体积分数和组织形态对多相钢强度和塑性损伤的影响。结果表明,组织体积分数对多相钢强度和塑性损伤的影响显著,其损伤机制与形变机制密切相关,均呈现出与组织分数相关的特性。而组织形态对强度影响不明显,但对塑性损伤有较大的影响。最后,论文结合一种F/B多相钢,对其拉伸过程中的微观应变分布进行了数值模拟分析和预测,并对形变组织和损伤进行了实验观察,其结果与实验吻合。
[Abstract]:Oil and gas pipelines are often subjected to plastic deformation in frozen soil, seabed, seismic zone, collapse and landslide, which results in bending, twisting, fracture and so on, which lead to failure accidents. The development of large deformation pipeline steel which can withstand large deformation without failure has become an important direction in the development of high performance pipeline steel. The deformation capacity of large deformation pipeline steel is closely related to the strain hardening behavior and failure behavior of multiphase microstructure. The reasonable collocation of "soft-hard" phases in multiphase steels is an important technical route to achieve high plasticity. Based on the experimental study and numerical simulation analysis of the mechanical behavior of multiphase steel, the effects of structure selection and volume fraction control on strain hardening capacity / behavior, stress ratio and plastic damage behavior of multiphase steel are revealed in this paper. It can provide experimental and theoretical basis for engineering application of large deformation pipeline steel. The microstructure and its constitutive relation affect the strain-hardening ability of ferrite / bainitic F / B multiphase steel. The microstructure with different strength and strain-hardening ability can be obtained by controlling the composition and transformation. The strain hardening behavior of F / B multiphase steel can be reduced by increasing the strength difference between the microstructure of F / B multiphase steel. The strain-hardening behavior of F / B multiphase steel is related to the volume fraction of bainite. The strain hardening process of multiphase steel is segmented by modified C-J analysis method, and the strain hardening ability of each stage is characterized. The stress ratio and the yield strength ratio are explained reasonably. The variation of strain hardening index and uniform elongation with the volume fraction of bainite. The relationships among stress ratio, strain hardening index, flexural strength ratio and uniform elongation are analyzed. The results are verified by industrial production and experimental data. The microstructure fraction and microstructure morphology (morphology and distribution) of F- / B multiphase steel have obvious influence on the strength and plastic damage. In view of the fact that this effect is usually difficult to be measured experimentally, the effects of volume fraction and microstructure on the strength and plastic damage of multiphase steel are calculated and analyzed by means of micromechanics numerical method. The results show that the microstructure volume fraction has a significant effect on the strength and plastic damage of multiphase steel, and the damage mechanism is closely related to the deformation mechanism. However, the effect of microstructure on strength is not obvious, but it has great influence on plastic damage. Finally, the microscopic strain distribution in the tensile process of a kind of F / B multiphase steel is numerically simulated and predicted, and the microstructure and damage of the steel are observed experimentally. The results are in good agreement with the experimental results.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG142.33

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