【作者】 李伟；

【导师】 汪凌云；

【作者基本信息】 重庆大学 ， 材料加工工程， 2007， 硕士

【摘要】 IF钢作为第三代冲压用钢有着广阔的应用前景。本文采用一次冷轧制度和增加了中间退火工艺的二次冷轧制度进行了Nb+Ti-IF钢冷轧工艺试验,完成了酸洗、一次冷轧、中间退火、精整、二次冷轧、再结晶退火等工序,制备出尺寸规格为200×1000×（0.325～2.16）mm的IF钢板带。通过单向拉伸实验对板料的基本深冲力学性能进行了测试和计算,结果表明,二次冷轧工艺能获得相对一次冷轧工艺更优的力学性能,在同等变形程度下,二次冷轧退火后获得的塑性应变比值最高达到3.08,比一次冷轧提高了18%,在此基础上综合基本深冲力学性能参数对模拟深冲力学性能之一的极限拉伸系数进行了预测。非线性参数拟合了三种硬化曲线数学模型,经判定得出了描述本试验用Nb+Ti-IF钢最优的加工硬化模型为:σ=Bε^{N/（1+C₁ε+C₂ε2）}用该模型揭示了不同冷轧工艺下板材的硬化能力:本试验中硬化能力相对较好的是首次冷轧60%,二次冷轧30%工艺对应的板料。通过金相和透射电子显微镜对IF钢的冷变形和退火组织进行了观察,随变形量的增加,变形愈趋均匀,再结晶后晶粒愈来愈细,二次冷轧工艺对应的退火组织总体更加均匀。在变形量大而且层错能较高的IF钢冷变形组织中,以刃位错为主的混合位错呈曲线分布在滑移带周围,并由于局域剪应力的存在,形成大量的排列很密的长条状的“剪切带”。通过X-射线衍射方法,测定了不同轧制工艺下板材主要织构分布。二次冷轧的形变织构的显著特征是<111>//ND织构相对中间退火得到了明显增强,增长最多的是{111} < 110>组分;α（{110}//RD）织构和γ（{111}//ND）织构的演变与第二次冷轧压下率之间没有简单的线性关系,但{001}织构几乎随着二次压下率的增加而增加。与一次冷轧后退火织构相比,二次冷轧退火织构有强度相对较低的{001}织构和较高的<111>//ND织构;在退火状态下,首次冷轧70%、二次冷轧20%的工艺对应的{111}与{001}面织构含量的比值最高,说明该工艺下退火态薄板测得的最高r值是准确的。更多还原

【Abstract】 As the third generation steel for stamping, the IF steel has the broad application prospect. In this paper, Nb+Ti-IF steel double cold rolling was carried on after intermediate annealing, which was after the single cold rolling, the procedure as acid pickling, cold rolling, intermediate annealing, the finishing, double cold rolling, the recrystallization annealing has been completed. Sheet size as 200mm （T）×1000mm （L）×（0.325 2.16 mm） was attained.The basic mechanical properties of stamping have been obtained by tensile test and computation, which result indicated that double cold rolling obtained superior mechanics performance than the single cold rolling technics under the same reduction, the plastic strain ratio after annealing obtained by double cold rolling technics reaches as high as 3.08, enhanced 18% compared to single cold rolling. Limit stretch coefficient as a stimulant mechanical property of stamping has been predicted by the data of the basic mechanical properties. Three kinds of hardened curves have fitted by the non-linear parameter fitting method, in which the optimum work hardening model describing the Nb+Ti-IF steel using in this experiment is:σ=Bε^{N/（1+C₁ε+C₂ε2）}The work hardening properties of sheets under different cold rolling technics have been studied by this model, the result indicated that the sheet under the cold reduction of 60% in first time and 30% in second time can obtain the best work hardening property. The cold rolling and annealing microstructures were observed by the transmission electron microscope and the metallographic microscope. Along with the cold reduction increase, the deformed microstructures turn uniform; grains after recrystallization turn symmetrical, even under the double cold rolling technics. In the IF steel microstructure of high degree cold deformed, the mix dislocation which primarily belong to edge-dislocation distribute around the slip-bands. As a result of the existence of shearing stress concentrated in some narrow region, massive and very dense“shear bands”as shapes of parallel sliver have form.The texture distributions under different cold rolling technics were measured by using XRD. The deformation textures under double cold rolling are remarkable character with the <111> //ND texture even the {111} < 110> component obtained obvious enhancement after intermediate annealing. The evolution ofα（{110} //RD） andγ（{111} //ND） textures is not being the simple linear relationships with the second cold reduction, along the increase of which the {001} texture grows. After double cold rolling and annealing, the recrystallization textures have lower intensity {001} texture the higher {111} //ND texture compared to single cold rolling; The recrystallization texture content ratio of {111} and {001} is highest after double cold rolling which reduction assignment is cold rolling 70% in first time and 20% in second time, the result indicated the highest r value of the sheet after this cold rolling condition is accurate.更多还原