【作者】 郭艳辉；

【导师】 王国栋； 王昭东；

【作者基本信息】 东北大学 ， 材料加工工程， 2009， 博士

【摘要】 IF钢板广泛应用的最主要原因在于它极其优良的深冲性能。IF钢板优良的性能与钢板中晶体的织构密切相关。板材中的γ纤维织构(＜111＞//ND,ND为轧面法线方向)越强,其深冲性能越好。铁素体区热轧工艺,即温轧工艺能够有效提高IF钢中的γ纤维织构,这一点已经得到了公认。众多的科研工作者已经对IF钢温轧工艺进行了大量的研究,但是对其后续的冷轧和退火过程织构的研究尚少。本文通过X-ray分析和EBSD分析对Ti-IF钢板温轧,冷轧及再结晶过程中织构的演变规律和形成机制进行了系统实验研究。论文主要工作和结果如下：1)热轧织构对冷轧和退火织构起着决定性作用,本文选取了具有不同热轧织构的Ti-IF钢板,对其进行冷轧和退火,通过X-ray分析对不同的热轧织构在随后的冷轧和退火过程中的演变过程进行了综合性研究。结果表明：只有当冷轧板中γ纤维织构上各组分分布均匀并且取向密度较高时,最终的退火板中才能形成理想的分布均匀的γ再结晶纤维织构。这就要求热轧板中形成以γ纤维织构为主的织构类型,这种热轧织构可以通过温轧后高温卷取或者温轧后直接退火获得。2)应用EBSD技术研究了温轧后直接退火时再结晶初期温轧Ti-IF钢板的微观组织结构形貌、再结晶晶核的取向和形成位置及晶核的长大规律。结果表明,温轧后退火过程中Ti-IF钢板的再结晶机制以定向形核机制起主要作用。在温轧Ti-IF钢板再结晶初期,γ取向的再结晶晶核优先形成于γ取向的变形带内部和γ取向与α取向变形带的晶界上。γ取向的再结晶晶核形成后,首先吞并其周围相邻的γ取向的变形基体；再结晶后期,吞并κ取向的变形基体,形成再结晶γ纤维织构。3)通过选择多种冷轧压下率,对温轧高温卷取和低温卷取的Ti-IF钢板进行冷轧实验,以及X-ray分析,得到了冷轧过程温轧Ti-IF钢板中取向变化的路径为：{110}<001>-{554}<225>-{111}<112>-{111}<110>-{223}<110>-{112}<110>-{113}<110>-{114}<110>-{001}<110>。并从冷轧织构入手解释了再结晶织构的特点,结合退火后钢板的性能分析,确定了获得最佳退火织构和深冲性能的冷轧压下率为75%。4)对冷轧后退火过程中温轧Ti-IF钢板的织构变化及机理进行了系统研究,确定了最佳退火温度范围为710-750℃。研究表明：退火温度为710℃和750℃时,得到了单一的强烈均匀分布的再结晶γ纤维织构；退火温度为600℃时,减弱的α纤维织构并没有完全被丫取向晶粒吞并,有部分转变成了{554}<225>-{332}<113>组分。退火温度不同,再结晶初期形成的晶核取向不同,对600℃退火保温较短时间的Ti-IF钢板进行EBSD分析发现,冷轧后的退火过程中,温轧Ti-IF钢板的再结晶机制仍以定向形核为主,但再结晶初期形成的晶核的主要取向除γ取向外还有{332}<113>取向。5)通过在冷轧和退火过程中,对温轧和常规热轧的高强Ti-IF钢板的织构演变及性能对比分析表明,尽管织构类型基本一致,但是温轧Ti-IF钢板的织构比常规热轧的Ti-IF钢板的织构强烈很多,由于织构的遗传性,冷轧退火后,温轧Ti-IF钢板的再结晶织构也强烈得多。因此,温轧的Ti-IF钢板具有较高的r值和n值。证实了在不改变化学成分的前提下,温轧工艺是提高高强IF钢深冲性能的有效手段。更多还原

【Abstract】 IF steel is widely used to due to its excellent deep drawability. It is well known that the drawability of IF steel is closely related to the texture formed during recrystallization and that a high volume fraction of near{111} components is essential for good drawability. Ferritic rolling, namely, warm rolling has been generally accepted as an effective method to improve {111} components in IF steel. Many researches have been conducted on the warm rolling process, however researches on the subsequent cold rolling and annealing process are quite scarce. In this paper, texture evolution during warm rolling, cold rolling and annealing of the Ti-IF steel is systematically investigated by means of the micro structure observation, X-Ray diffraction and EBSD analysis. The main work and the results are as follows:1) The hot rolled texture has decisive effect on the cold rolled and annealed texture due to the heredity of texture. The texture evolution during cold rollng and annealing process has comprehensively studied by XRD analysis with different initial texture hot bands. The results show that an ideal y fiber beneficial for improving deep drawability can be formed after annealing only when a well-proportioned y fiber dominates in the cold rolled texture. This requires the formation of strong y fiber in the hot band, which can be obtained by high temperature coiling or direct annealing after warm rolling.2) The microstructure, the orientation of the nuclei, the nucleation site at the early stage of recrystallization and the growth mechanism of the nuclei have been studied by EBSD analysis in Ti-IF steel during direct annealing after warm rolling. It is concluded that the formation of the recrystallization texture is dominated by the oriented nucleation mechanism. The recrystallized nuclei with y-orientation emerged preferentially at the beginning of recrystallization and preferred to form in the deformed bands withγ-orientation and on the boundaries betweenγandα-orientation. The recrystallized grains first consumed their neighboring y-oriented matrix, and then consumed the a-oriented deformed bands at the late stage of recrystallization, leading to strong y-fiber.3) The texture evolution during cold rolling with various reductions has been investigated in warm rolled and subsequent high and low temperature coiled Ti-IF steels. The orientation rotates along the following path:{111}<112>-{111}<110>-{223}<110>-{112} <110>-{113}<110>-{114}<110>-{001}<110>. The characteristic of the recrystallization texture has been analyzed from the point of cold rolled texture and the best cold rolling reduction is 75% which is determined by analyzing the properties and the recrystallization texture.4) The texture evolution during annealing after cold rolling of warm rolled Ti-IF steel has been systematically studied in this thesis. It is found that 710-750℃is the optimal annealing temperature range. When the annealing temperature is 710℃and 750℃, a strong and well-proportioned y fiber is obtained.When the annealing temperature is 600℃, the reduced a fiber transforms to{554}<225>-{332}<113> components as well asγfiber at the late stage of recrystallization. The EBSD analysis shows that orientated-nucleation dominates during recrystallization, but the orientation of the nuclei includes{332}<113> component besides y orientation.5) The texture evolution and the properties of the austenite rolled and the warm rolled high strength Ti-IF steels have been compared. Aithough the texture types have no differences, the intensity of the texture in the warm rolled one is much higher which leads to higher mechanical properties in the warm rolled, cold rolled and annealed high strength Ti-IF steel. It is proved that warm rolling is an effective method to improve the drawability of high strength Ti-IF steel.更多还原