【作者】 谢英杰；

【导师】 刘相华； 赵德文；

【作者基本信息】 东北大学 ， 材料加工工程， 2008， 博士

【摘要】 本文结合国家高技术研究发展计划(十五863)课题“500MPa碳素钢先进工业化制造技术”和国家自然科学基金项目“成形功率泛函积分线性化及在金属加工中应用研究”,对普通C-Mn成分开发HRBF500盘圆钢在控轧控冷工艺过程中组织演变规律和力学性能的变化进行了研究,并据此进行了工业试验。论文的主要内容包括：(1)盘圆钢轧后各冷却区温度演变及返红现象的研究以盘圆钢的实际轧后冷却过程为计算条件,考虑了辐射、强制对流、自然对流等热损失过程,利用ANYSYS软件建立了盘圆钢断面的瞬态温度场模型,研究了从精轧机组出口到斯太尔摩强制风冷区的整个控冷区盘圆钢横断面温度、返红现象随时间的变化规律,为定性分析轧后控制冷却过程的显微组织演变及力学性能的变化奠定基础。(2)精轧机组轧件的变形及温升研究为了计算高速线材精轧过程的非均匀变形,分析了等效矩形法的基本原理,据此提出了一种不需要进行等效矩形转换而直接求解椭圆—圆孔型系统等效应变的新方法,称其为相交面积法(Overlapping Area method),简称OA法。根据相交面积和孔型入口面积的比值,确定了高速线材精轧机组椭圆—圆孔型系统的宽展类型、等效应变的范围；为检验OA的有效性,利用OA法求解了精轧机组的温升。计算温升与实测结果符合较好,相对误差小于10%。利用温升计算结果分析了精轧入口温度、出口速度对整个机组累积总温升的影响,结果表明：总温升随出口速度降低而降低,但当降速10%轧制时,这种降低效果并不显著；总温升随入口温度降低而近似线性地升高。(3)试验钢室温拉伸性能及变形特性对于几种试验钢单轴拉伸下的变形特性进行了对比和分析。结果表明,在均匀变形阶段,不同屈服形式试验钢具有相似的加工硬化特性；而在低应变区,不同屈服形式试验钢的加工硬化性质差异很显著。从屈服现象的物理本质出发,对于试验钢出现无明显屈服同时变形特性与双相钢相类似的现象,综合运用多晶增殖模型、位错增殖理论、残余应力理论等给出了较全面地解释。根据理论分析结果,提出了消除试验钢无明显屈服点现象的措施。(4) HRBF500试验钢的工艺模拟与设备校核以普通C-Mn为研究对象,采用单道次压缩实验辅以显微组织观察,模拟分析了轧后冷却工艺过程,研究了Mn含量和冷却速度对相变过程、组织形貌等的影响。利用成形功率泛函线性化方法对控温轧制时粗轧机组的设备能力进行了校核。结果表明,3#粗轧机轧辊强度及电机负荷均处于安全范围内。(5)开发HRBF500盘圆钢的工业试验基于热模拟实验和温度场的模拟结果,通过对化学成分、轧制温度、冷却参数等的调整,确定了TMCP工艺中各参数的范围。对20MnSi成分采取提C降Mn调整后,生产出满足国标要求的HRBF500盘圆钢。更多还原

【Abstract】 The work of this dissertation was carried out integrating with the 863 project of ’The Advanced Industrial Manufacture Technology of 500MPa Carbon Steel’ and the ’Research on Functional Linearization of Deformation Power and Its Application in Metal Forming’which sponsored by National Natural Science Foundation of China. The microstructure evolution and mechanical properties of plain C-Mn tested steel during controlled rolling and controlled cooling were investigated. In addition, industrial trials to develop HRBF500 wire rod were carried out. The main works are shown as following:(1) Temperature evolution and reheating behavior of hot rolled wire rod in the controlled cooling zonesThe transient temperature field model of hot rolled wire rod was developed by ANSYS software to calculate temperature distribution inside the workpiece from exit of the finishing mill to Stelmor fans cooling zone. The effects taken into account were radiation, forced convection and natural cooling. The temperature field and reheating behavior of the workpiece with time during controlled cooling were analyzed, which provided the foundation for the qualitative prediction of the microstructure evolution and mechanical properties.(2) Deformation and temperature jump of the workpiece in the finishing millIn order to calculate the inhomogeneous deformation of hot rolled wire rod, a new analytic method called OA (Overlapping Area) method to solve the effective strain without using rectangular sections conversion is therefore proposed on basis of the principle of the equivalent rectangular approximation method. The spread types and the range of effective strain in oval-round passes were determined by a parameter which is the ratio of overlapping area to the entry area for a given pass. To validate the OA method, it was used to calculate the temperature jump during finish rolling ofΦ6.5mm wire. The results show that the calculated values of accumulative temperature jump is in good agreement with the measured ones as the maximum relative error is no more than 10%. The effect of the entry temperatureθand finishing exit speed v on the total temperature jumpΔθwas analyzed. The results show thatΔθslightly decreases with lowering the speed by 10%, but it almost increases linearly with decreasingθ.(3) Room tensile properties and deformation behaviour of tested steelThe mechanical behaviors of several tested steels in uniaxial tension were compared including the relationship between work-hardening coefficient, work-hardening index, work-hardening rate and true strain. The results reveal that in uniform deformation stage the different yield style tested steels possess the similar strain hardening characteristics, and their characteristics have an obvious difference in small strain stage. From physical essence of yield phenomenon, the reason of no yield point with abnormal mechanical properties similar to dual phase steel for tested steel was analyzed with the colligation of several theories including dislocation multiplying, residual stress theory, the multiplication yield model of polycrystalline metal, and so on. Then, the corresponding countermeasures were put forward.(4) Process simulation and capacity of rolling mill checkThe microstructure evolution for plain C-Mn steel in controlled cooling process was investigated using single pass compression test and metallographic analysis. Moreover effect rule of cooling rate and Mn content on microstructure was obtained. The capacity of roughing mill was checked during controlled rolling by the functional linearization of deformation power method. The results show the roll strength and electric engine load of No.3 roughing mill are within the permissive range.(5) Industrial trials to develop the HRBF500 wire rodIndustrial trials were carried out on high speed wire mill based on the results of thermal-mechanical simulation and temperature field analysis. The process routine was determined by adjusting chemical composition, rolling temperature and cooling parameter in order to improve mechanical properties. After decreasing Mn content and increasing C content, HRBF500 wire rod was successfully produced.更多还原