【作者】 张治民；

【导师】 李硕本； 郑炀曾；

【作者基本信息】 燕山大学 ， 材料加工工程， 2003， 博士

【摘要】 本文在于寻求一种制造直齿圆柱齿轮的新原理、新方法，以达到提高产品性能和生产率、降 低生产成本和能耗、减少环境污染的目的。首先系统研究了齿轮用钢20CrMnTi温变形力学行为和微观组织响应。发现该材料在650～850 ℃具有良好的塑性；在770℃形变诱导铁素体不仅可使晶粒超细化，而且使流变应力大幅度 下降，接近于850℃变形的流变应力，这种超细化的效果，在随后的热处理中，能够保留下 来。研究提出的“逐次控制变形”原理和实现该原理的“径向分流，轴向导流”、“开放式充填 ”方法，解决了直齿圆柱齿轮成形的关键问题。应用以上原理和方法制定的工艺和设计制造 的工装，并经小批量实验证明：成形力小、齿型充填好、产品精度高，表面粗糙度小，且便 于脱模。所成形的齿轮经检测达到用户的要求，并在工程上得到应用，说明了该原理是可行 的，方法是合理的。同时为齿轮“渗碳-温挤压”成形奠定了基础。为研究渗碳梯度材料的力学行为，本文提出使用圆环试样渗碳后获得不同的碳含量，并应用 渗碳-脱碳方法,得到了0.22%、0.44%、0.62%、0.81%和1.12% 5个不同碳含量的试样，达到 了离散化的目的。所有圆环试样选自同一根20CrMnTi棒料，因此渗碳后的样品除碳含量外， 其余成分完全一致，使试验结果 “突出”了碳浓度变化对材料宏、微观响应的影响,为非均 匀材料的特性研究提供了一种实验新方法。借助于计算机数值模拟技术，首次研究了圆环试 样压缩变形时，试样高度对变形均匀性的影响，结果表明：增加试样的相对高度和减少变形 时的摩擦，能够提高试样的变形均匀性。首次系统地研究了渗碳20CrMnTi钢的力学行为和微观组织响应。实验发现：流变应力随碳含 量的变化具有3个基本特征，即高温（850℃）变形时流变应力随碳含量的增加而下降；较低 温度（690℃）变形时流变应力随碳含量的增加而上升，介于两者之间变形时由于相组成的 变化使流变应力呈现出复杂的变化规律，在所有3种流变应力变化中0.62%的碳含量成为“突 变点”。同时还建立了渗碳20CrMnTi钢的力学模型，并给出了流变方程。微观组织研究结果表明：流变应力的变化是微观组织变化的宏观响应，其中较高温度变形流 变应力单调下降与碳含量增加动态再结晶率提高有关，尤其是碳含量达到0.62%时动态再结 晶明显加快，因此成为流变应力的“突变点”；较低温度变形流变应力单调上升，是因为微 观组织由低碳的铁素体和奥氏体复相组织变化到高碳的奥氏体和渗碳体复相组织。温变形的 渗碳20CrMnTi钢晶<WP=5>粒细化机制与热变形明显不同，温变形细化作用更为显著，在应变率0.1s-1，770～810℃变 形时，“项链式”动态再结晶成为细化晶粒的主要机制，可将未变形16??m～20??m晶粒细化 到2?m～3??m； 降低温度（690～730℃）、增加应变率使渗碳样品变形初期形成孪晶，条片 形孪晶借助于晶界滑动和局部变形，最终演变成貌似“糖葫芦串”的细晶粒，但细化率不高 ，不能覆盖整个基体组织。为提高齿轮的性能，提出直齿圆柱齿轮“先渗后挤”的渗碳层非均匀分布的制造技术，建立 了渗碳层合理分布模型。应用齿轮精密成形研究成果，对圆柱直齿轮进行了“先渗后挤”工 艺试验。结果表明：通过控制成形温度和模具参数，得到了渗碳层分布较为合理、晶粒显著 细化的齿轮，达到了预期的目的。更多还原

【Abstract】 This paper presents a new method and principle for manufacturing straight cylind rical gear in order to improve production performance and productivity, reduce p roduction cost and energy consuming, and decrease environment pollution.The mechanical behavior and microstructure response during warm deformation of t he gear using 20CrMnTi steel have been studied firstly. We find that the materia l has better plasticity in the temperature range from 650℃ to 850℃; The deform ation inducing ferrite not only makes grain super refining, but also reduces flo w stress greatly at the temperature of 770℃. The effect of super refining can b e kept down in the heat treatment afterwords.The principle of "successive control deformation" and the method to realize "rad ial shunt, axial diversion and open filling" of the principle have solved the ke y problem of deforming for straight cylindrical gear. Proved by small lot produc tion, the set technology and the designed equipments using the above principle a nd method have many advantages such as small forming force, better filling for g ear teeth, high production precision, low surface roughness, and convenient patt erns drawing. The produced gears can satisfy the consumers demands and have been used in engineering, which show that the principle is feasible and the method i s reasonable, and lay the basis for "carburization- warmextrusion" forming techn ology of straight cylindrical gear. In order to study the mechanical behavior of carburized gradient materials, the annulus specimens with different carbon cont ents were obtained after carburization. By using the method of carburization- de carbonization, five specimens with different carbon content of 0.22%, 0.44%, 0.6 2%, 0.81% and 1.12% were acquired, so the purpose of dispersion was reached.With the help of computer simulation technology, how the specimens height affect the deformation homogeneous has been studied firstly by means of the annulus sp ecimens compression and results show that deformation homogeneous can be improve d by increasing relative height of the specimens and reducing friction. All the annulus specimens were chosen from the same 20CrMnTi bar, so the rest component are the same other than the carbon content after carburization. Therefore, the e xperimental results highlighted the effects of the carbon content on the macro a nd micro response of the materials and a new experimental method was provided fo r characteristic study of the nonuniform materials.The mechanical behavior and microstructure response of the carburized 20CrMnTi<WP=7>steel have been studied firstly. Experiments show that the flow stress has 3 bas ic characters with the change of the carbon content, i.e., the flow stress will fall at the temperature of 850℃, rise at the temperature of 690℃ and present t he complicated changing law at the temperature between 650℃ and 850℃ with the increase of the carbon content. 0.62% carbon content becomes a break point among the 3 kinds of the flow stress. The research of the microstructure shows that the change of the flow stress is t he macro response to the change of the microstructure. The monotonic decrease in the flow stress at higher temperature has a close relationship with the improve ment of the dynamic recrystallization rate caused by the increase of the carbon content. The rate of the dynamic recrystallization is obviously quickened when t he carbon content is up to 0.62% which is the break point of the flow stress, wh ile the monotone increase of the flow stress at lower temperature is the result of the micro structure changing from the heterogeneous structure of ferrite and austenite with low carbon to the heterogeneous structure of austenite and cement ite with high carbon. The grain fining mechanism of warm deformation, whose fini ng effect is more marked, is obviously different from that of hot deformation fo r the grain of the carburization 20CrMnTi.. The "necklace" dynamic recrystal, wh ich can fine grains from 16(m~20(m into (m~3(m, becomes the main更多还原