【作者】 涂益友；

【导师】 蒋建清；

【作者基本信息】 东南大学 ， 材料加工工程， 2006， 博士

【摘要】 现代化工业应用的背景下,对钢丝制品高性能低成本化要求越来越高。而钢丝生产技术的快速发展,通过增大拉丝变形应变量的方法实现了钢丝的高强度化,并且随着钢丝拉拔技术的进步,拉丝速度越来越快,生产效率也日益升高。因此,现代钢丝生产主要是一个高速大应变的塑性变形问题。由于对这一客观的问题缺乏深度的理解与系统研究,故长期以来我国钢丝制品业的技术进步主要靠经验的摸索,缺乏有力的理论支撑。鉴于此,本文较为系统地研究了高速大应变工业生产条件下高碳（珠光体钢）钢丝拉拔形变过程,通过大量的形貌分析、微观分析、力学分析、统计分析和综合分析,发现了大应变量变形条件下高碳钢丝高强度的组织源泉,并根据这一认识开发制定了高强度中碳钢丝生产工艺。主要创新成果如下:研究了高碳钢（SWRH72A）从Φ5.5mm冷拉拔至Φ1.5mm左右的变形过程,综合分析了钢丝的组织和力学性能的变化情况。结果表明,形变后的钢丝,横截面上晶粒显著细化,而在纵截面上晶粒逐渐被拉长呈纤维状;其抗拉强度则随着形变量的增加而不断增加;形变前的珠光体团为随机取向,Fe3C片很平直;随着形变量的增加,Fe₃C片逐渐转到与拉丝轴平行的方向上,基本与拉丝轴方向一致。珠光体片层间距随着拉丝应变量的增大而减小,应变量较大时（>1.5）,珠光体片层间距变化正比于exp （-ε/2）。SWRH72A钢丝强度随拉拔变形应变量增大而增大,并且应变量较大时,强度增长速度明显快于应变量较小阶段。初步分析珠光体钢丝强化机制得知,变形初期由于珠光体片层间距较大,其加工硬化符合Hall-Petch关系;应变量增大,珠光体片层间距随之减小,片层基本沿丝轴方向排列,铁素体片层厚度<100nm,类似于细片层叠层材料,其强化机制符合奥罗万（Orowan）机制,加工硬化率明显比变形初期高。珠光体钢（SWRH72A）大应变量拉拔变形形成的珠光体片层定向排列（沿丝轴）,片层间距极为细小（<100nm）的叠层结构,在塑性变形过程中表现极高的加工硬化率,为珠光体钢丝实现高强度化提供了组织保证。研究了经大应变量拉拔变形后SWRH72A钢丝的微观结构特点,在本文的实验条件下X射线光电子能谱（XPS）、磁学性能（VSM）、X-射线衍射分析（XRD）、差热扫描分析（DSC）的结果协同说明了SWRH72A钢丝经ε=2.60冷拉拔变形后约有20%的渗碳体分解了,并有部分碳原子进入于铁素体中形成过饱和铁素体。大应变量变形后钢丝在300℃以下回火30min,其高强度保持稳定。但回火温度进一步升高,钢丝叠层组织结构被破坏,钢丝强度迅速下降,这进一步说明珠光体钢单向薄片叠层结构是其获得高强度的组织保证。更多还原

【Abstract】 As applied to the modern industry, high performance steel wire with a low cost were demanded. Along with the fast development manufacture technique, severe cold drawing was used for high strength, simultaneity the drawing speed was faster. So the manufacture of steel wire was mostly a high speed severe plastic deformation. Because of lacking systemic investigation of this problem, technique advancement in steel wire industry was almost experiential.Therefore, the process of drawing pearlite steel was investigated in detail in this thesis. The reason that caused high strength of high carbon steel wire was studied with the methods of morphological analysis, mechanics analysis, statistical analysis and synthetic analysis. And the production technics of high strength medium carbon steel wire was established on this theory. The main research results were as following:The evolvement of microstructure and mechanics performance of SWRH72A steel wire had been studied,which was drawn fromΦ5.5mm toΦ1.5mm. Grains were refined in transverse section and fibrous shaped in longitudinal section after eight steps drawing. The tensile strength of wire was increased rapidly. With the increasing of drawing strain, cement lamellae that initially have random orientation became progressively aligned along the drawing axis. Interlamellar spacing of pearlite decreased progressively during the cold drawing process, and it was proportional with exp (-ε/2) when total strain was over 1.5. Tensile strength increases with increasing drawing strain. In the initial stages of drawing, the strengthen of peatlite steel was accorded with Hall-Petch relationship. There was a deviation from the Hall–Petch behaviour when the interlamellar spacing of pearlite decreased to less than 100nm.The microstructure characteristic of severe cold drawn SWRH72A steel wire were analysed by XPS, VSM, XRD. It was found that 20 percent cementite dissoluted after drawn. And ferrite became supersaturation because partial carbon atom came into it. Severe cold drawn steel wire held high strength as the aging temperature was below 300℃. When the temperature rised over 300℃, the fine-scale multilayer structure was destroyed and the strength of steel wire droped remarkablely.A model accounting for the cementite dissolution is proposed. It relies on the Gibbs-Thomson effect and diffusion-controlled dissolution. The increase in the cementite molar free energy, as an indirect consequence of the thinning of the cementite lamellae, appears to be the driving force and更多还原