【作者】 汪云辉；

【导师】 丁桦； 田学锋；

【作者基本信息】 东北大学 ， 材料加工工程， 2008， 硕士

【摘要】 为了满足汽车工业对安全性、经济性、环保以及表面质量的要求,钢铁工业正在不断的改进创新。在21世纪,大多数汽车钢的研究主要集中在开发新型UHSS来满足超轻钢汽车车身(ULSAB)计划。这些钢种包括双相钢、相变诱发塑性(TRIP)钢、孪晶诱导塑性(TWIP)钢和硼钢。TRIP(Transformation Induced Plasticity)钢又称相变诱发塑性钢,TRIP钢板具有高的强度、延展性和冲压成形能力,用作汽车钢板可减轻车重、降低油耗,同时有较强的能量吸收能力,能够抵御撞击时的塑性变形,显著地提高了汽车的安全等级,具有明显的优越性。TWIP(Twins Induced Plasticity)钢是通常是指锰含量为15%-30%的高锰钢,TWIP效应又称孪生诱发塑性效应,是指超高锰钢中因为机械孪晶的形成而具有的不寻常的塑性。TWIP钢由于具有高的加工硬化率、高的延展性、高的强度等一系列优良的机械性能,因此在未来的汽车工业生产中具有广阔的发展和应用前景。本文以锰含量为18.8%和23.8%的两种高锰奥氏体钢作为研究对象,研究了不同锰含量的高锰钢在不同变形量时的组织和变形机制,以及热轧高锰钢的组织和力学性能,并分析了两种钢的拉伸应变硬化行为。为大规模工业生产、应用提供了理论基础与实验依据。本文的实验内容包括：(1)通过光学显微镜、透射电镜以及X射线衍射分析了18.8Mn和23.8Mn实验钢在室温下,应变速率为1×10-3／s时不同变形量的显微组织和变形机制。18.8Mn实验钢塑性变形初期为位错滑移和TRIP效应；变形中期主要以TWIP效应为主；变形后期主要发生TRIP效应,在整个变形过程中都伴随着TRIP效应发生。23.8Mn实验钢变形机制主要是TWIP效应。(2)通过对两种实验钢的真应力真应变曲线分析,微观组织的观察以及X射线衍射对不同变形量时相组成的测定,探讨了拉伸硬化阶段曲线所遵循的规律。对18.8Mn钢的变形分为四个阶段：1)弹性变形阶段；2)塑性变形的线性阶段；3)塑性变形的非线性阶段；4)马氏体开始屈服阶段。对23.8Mn钢变形分为三个阶段：1)弹性变形阶段；2)塑性变形的线性阶段；3)塑性变形的非线性阶段。(3)研究了锰含量为18.8%的热轧实验钢的力学性能与组织组成,其抗拉强度达930MPa以上,延伸率达41%以上,强塑积达36GPa%以上。同时对锰在奥氏体钢中的强化机制进行了分析。锰元素的固溶强化并不是高锰奥氏体钢最主要的强化机制,应力诱发的相变强化及TWIP效应才是关键的强化机制。更多还原

【Abstract】 To meet the needs of vehicles such as safety, efficiency, environmental, responsibility and good surface quality, the steel industry is constantly make progress. By the 21st century, most projects of automobile steels have been focused on developing new kinds of UHSS and new style steels to meet the needs of the plan of ultra light steel auto body (ULSAB). These steels include dual-phase steel, (TRIP) steel, transformation induced plasticity (TWIP) steel and Boron steel.Transformation Induced Plasticity (TRIP) steels exhibit a superior combination of strength and ductility compared to precipitation hardened steels and solution hardened steels. TRIP steels meet these requirements that the weight decrease for fuel efficiency as well as the safety is continuing to be major concerns in automobile manufacturing. The large scale production of TRIP steel sheets has become a fact with production technology improvement and development, and the application prospect will be wider.TWIP steel is mainly manganese steel with Mn mass contents of 15%～30%, TWIP is twinning induced plasticity effect, and it can induce unusal plasticity because of the mechanical twinning in ultra high manganese austenitic steel. TWIP steels exhibit some special mechanical properties, such as high work-hardening, large elongation and high tensile strength. The improvement and application will be wider in the vehicle industry in the future.In this article, two different content high manganese austenite steels(18.8Mn and 23.8Mn) are studied. The relation between Mn contents and deformation microstructure and mechanical properties of samples have been studied, the microstructure and mechanical properties of the hot rolling steel and the tensile strain hardening behaviours of the steel have been studied. These are many conclusions can offer gist of theory and experiment for commercial run.The contents of this article include following items: (1) By the optical microscope, transmission electron microscopy (TEM) and X ray diffraction, the steel of the relationship between deforming amount and microstructure have been studied of the steel that take tensile strain experiment of room-temperature with the strain rate of 10-3/s. The microstructures of the samples at different deforming amount were analyzed, the result indicates that when there exist both TRIP effect and TWIP effect in steel during tensile strain experiment, the dislocation and TRIP happens earlier;the TWIP happens in the medium-term;the TRIP happens in the last. The 23.8 Mn experimental steel exist both TRIP effect. And TWIP effect, but the TWIP effect becomes the main deformation mechanism of the steel.(2) The induration stage of the tensile strain curve have been studied by the true stress and true strain curves.of the two kinds of steels and the optical microscope, transmission electron microscopy (TEM) and X ray analysis discussed, and analysis what law have followed. The 18.8Mn experimental steel deformation could be divided into four different stages:1) elastic deformation phase;2) the linear plastic deformation stage;3) the nonlinear of deformation of the plasticity stage.4) the beginning of the martensite yield stage. And the 23.8% deformation could be divided into three different stages:1) elastic deformation phase;2) the linear plastic deformation stage;3) the nonlinear of deformation of the plasticity stage.(3) The hot rolling process of the 18.8Mn experimental steel, and the microstructures and the mechanical property of the samples have been studied. the ultimate tensile strength is 930MPa, the elongation of the steels is 41%.And the strengthening effect of the Mn among the austenitic steel have been studied. The studied indicated that the solution strengthening is not the main mechanism in the high Mn austenitic steel, and the twinning induced plasticity effect is the important mechanism.更多还原