Ti-V-Mo复合微合金化高强度钢组织调控与强化机理研究

发布时间：2018-07-29 18:52

【摘要】：随着资源、能源和环境压力的日益增大,高强度钢的开发越来越受到世界各国的极大重视,并已发展成为应用范围很广的一类钢种。在钢铁材料的各种强化机制中,晶粒尺寸细化到2～3 μm时,进一步细化晶粒尺寸难度很大,细晶强化效果很难继续提高；置换固溶强化提高强度的效率比较低；位错强化、相变强化尽管提高强度明显,但对钢材塑韧性损害较大；沉淀强化是除细晶强化以外对塑性损害最小的强化方式,也是高强钢提高强度的重要研究方向,且一直并没有被充分利用,并且,传统高强度钢中沉淀强化增量一般在200 MPa以下,因此,增大沉淀强化增量是提高钢材综合力学性能的最佳强化方式。合适的复合微合金化,一方面能够提高析出相的体积分数,另一方面可以细化析出相的尺寸,因而是提高沉淀强化增量的最为简单有效的方法。因此,采用合理的多元复合微合金化,结合优化的热机械控制工艺,研制具有大沉淀强化增量的热轧高强度钢具有重要的理论意义和工业应用价值。本文采用Ti-V-Mo复合微合金化,结合优化的热机械控制工艺,通过控制奥氏体和铁素体中MC相的合理析出,以期制备出具有大沉淀强化增量的热轧高强度钢。利用透射电镜(TEM)、扫描电镜(SEM)、电子背散射技术(EBSD)和物理化学相分析(Physics-chemical phase analysis)等实验手段对Ti-V-MO钢的组织进行了表征,其主要的研究内容和成果如下：建立了(M1,M2,M3)X型四元复合析出相在铁基体中的热力学模型,并在Ti-V-Mo复合微合金化钢中得到成功应用。对Ti钢、V钢、Ti-V钢、Ti-Mo钢和Ti-V-Mo钢中MC相在铁基体中的热力学、动力学、低温粗化动力学等进行了计算与对比。结果表明：Ti-V-Mo复合微合金化在不增加全固溶温度的前提下,减少了MC相在奥氏体中的潜在析出量、增大了MC相在铁素体中的析出量,降低了MC在奥氏体中的最快析出温度,低温铁素体中MC相具有很强的抗粗化能力,Ti.V-Mo复合微合金化是实现大沉淀强化增量的最佳微合金体系。计算得到了MoC与奥氏体和铁素体之间的半共格比界面能随温度变化的关系式,为含Mo复合析出相的热力学计算提供了基础数据。研究了形变储能对高Ti-V-Mo钢中奥氏体中(Ti,V,Mo)C相析出动力学的影响及奥氏体相变诱导析出量对铁素体中(Ti,V,Mo)C相析出动力学的影响。结果表明：增加奥氏体的形变储能,促进高温下(Ti,V,Mo)C的析出,阻止奥氏体晶粒的长大；适当增加奥氏体中MC相的形变诱导析出量,使得铁素体中(Ti,V,Mo)C沉淀析出的最大形核率温度降低,形核率增大,有利于获得析出密度更大的纳米级析出相,使沉淀强化增量趋于更大。估算接近实际生产条件下,(Ti,V,Mo)C在铁素体中的最大形核率温度在630～650℃,最快析出温度在720-740℃,为获得细小的铁素体晶粒和较大的沉淀强化增量提供了理论指导。探讨了终轧温度、冷却速度、卷取温度等工艺参数对Ti-V-Mo钢组织及性能的影响规律,得到了在实验室条件下高Ti-V-Mo钢获得最佳力学性能的具体工艺参数。系统研究了不同阶段(Ti,V,Mo)C粒子成分的变化规律。结果表明：终轧温度在800～850℃,冷却速度大于20℃/s,卷取温度在600～625℃时,高Ti-V-Mo钢的综合力学性能最为优异；在600℃和650℃较高温度卷取时,析出相以含V为主,Ti含量低；在500℃和550℃卷取时,析出相以含Ti为主,V含量低。通过优化的热机械控制工艺,实验室研制出了抗拉强度和屈服强度分别为1134 MPa和1080 MPa,断后延伸率和均匀延伸率分别为13.2%和6.8%的热轧高强度薄板钢,沉淀强化增量高达444～487 MPa,突破了传统高强度铁素体钢的沉淀强化增量极限。对不同卷取温度下高Ti-V-Mo复合微合金化热轧高强钢的强化增量进行了估算和分析,讨论了卷取温度对屈服强度和MC相粒子对均匀塑性的影响规律。
[Abstract]:With the increasing pressure of resources, energy and environment, the development of high strength steel has been paid more and more attention from all over the world, and has been developed into a kind of steel with a wide range of applications. In the various strengthening mechanisms of steel materials, the grain size is very difficult to refine the grain size and the strengthening effect of fine grain when the grain size is refined to 2~3 m. It is difficult to continue to improve, the efficiency of the replacement of solid solution strengthening to improve the strength is relatively low; dislocation strengthening and phase transformation intensification, although increasing the strength obviously, have great damage to the plastic toughness of steel, and precipitation strengthening is a strengthening method of minimum plastic damage except fine crystal strengthening, which is also an important research direction of high strength steel. It is fully utilized, and the precipitation strengthening increment in the traditional high strength steel is generally below 200 MPa. Therefore, increasing the precipitation enhancement increment is the best strengthening method to improve the mechanical properties of the steel. It is the most simple and effective method to improve the increment of precipitation enhancement. Therefore, it is of great theoretical significance and industrial application value to develop a hot rolling high strength steel with a large precipitation enhancement increment with reasonable multicomponent composite microalloying and optimized thermal mechanical control technology. The Ti-V-Mo composite microalloying is used in this paper, and the optimized heat is combined. The mechanical control process, by controlling the rational precipitation of MC phase in austenite and ferrite, is expected to produce hot rolled high strength steel with large precipitation enhancement. Using transmission electron microscopy (TEM), scanning electron microscopy (SEM), electron backscattering (EBSD) and physical and chemical phase analysis (Physics-chemical phase analysis), and other experimental means of Ti-V-MO steel The main research contents and results are as follows: the thermodynamic model of the (M1, M2, M3) X type four element composite precipitates in the iron matrix was established, and it was successfully applied in the Ti-V-Mo composite microalloyed steel. The thermodynamics, kinetics and low temperature coarsening of MC phase in Ti steel, V steel, Ti-V steel, Ti-Mo steel and Ti-V-Mo steel were in the iron matrix. The results show that the Ti-V-Mo composite microalloying reduces the potential precipitation of the MC phase in austenite without increasing the total solid solution temperature, increases the precipitation of the MC phase in the ferrite and reduces the fastest precipitation temperature of the MC in the austenite, and the MC phase in the low-temperature ferrite has a strong resistance to coarse. The Ti.V-Mo composite microalloying is the best microalloying system for the enhancement of the precipitation enhancement. The relationship between the MoC and the austenite and ferrite interface between the austenite and the ferrite is calculated, and the basis for the thermodynamic calculation of the precipitated phase containing Mo is provided. The influence of the precipitation kinetics on the C phase in the body (Ti, V, Mo) and the precipitation kinetics induced by the austenite phase transition induced precipitation on the ferrite (Ti, V, Mo) C phase. The results show that the deformation of austenite can be increased by increasing the deformation energy storage of austenite, promoting the precipitation of the Ti, V, Mo), preventing the growth of the austenite grain, and increasing the precipitation in the austenite. The maximum nucleation rate and nucleation rate precipitated in the ferrite (Ti, V, Mo) C precipitated and the nucleation rate increased, which was beneficial to obtain the nanoscale precipitates with larger precipitation density, and the precipitation enhancement increment tended to be greater. The maximum nucleation temperature of (Ti, V, Mo) C in the ferrite was estimated at 630~650, and the fastest precipitation temperature was 720 under the actual production conditions. -740 C provides theoretical guidance for obtaining fine ferrite grain and larger precipitation enhancement increment. The influence of finishing rolling temperature, cooling rate and coiling temperature on the microstructure and properties of Ti-V-Mo steel is discussed. The specific process parameters of the best mechanical properties of the high Ti-V-Mo steel under the laboratory conditions are obtained. The variation of the composition of C particles at different stages (Ti, V, Mo) was investigated. The results showed that the final rolling temperature was 800~850 C, the cooling rate was higher than 20 C, and the overall mechanical properties of high Ti-V-Mo steel were the best when the coiling temperature was 600~625 degrees C. The precipitation phase was mainly V and Ti content was low at 600 and 650 C, at 500 and 550. When coiling, the precipitated phase is mainly Ti, and the content of V is low. Through the optimized thermal mechanical control technology, the tensile strength and yield strength are 1134 MPa and 1080 MPa respectively. The post fracture elongation rate and the uniform elongation rate are 13.2% and 6.8% respectively, and the precipitation enhancement increment is up to 444~487 MPa, which breaks through the tradition. The increment limit of precipitation intensification for high strength ferrite steel is calculated and the strengthening increment of high Ti-V-Mo composite microalloyed hot rolled high strength steel at different coiling temperatures is estimated and analyzed. The influence of coiling temperature on yield strength and MC phase particles on uniform plasticity is discussed.
【学位授予单位】：昆明理工大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG142.1

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