【作者】 徐晋勇；

【导师】 徐重； 高原；

【作者基本信息】 太原理工大学 ， 材料加工工程， 2007， 博士

【摘要】 模具是制造业的重要基础工艺装备。用模具生产制件所达到的高精度、高复杂程度、高一致性、高生产率和低耗能、低耗材，使模具工业在制造业中的地位越来越重要。模具在汽车、能源、机械、信息、航空航天、国防工业和日常生活用品的生产中被广泛应用。据统计，75％的粗加工工业产品零件、50％的精加工零件由模具成形；家用电器行业的80％零件、机电行业的70％以上零件也都要靠模具加工。模具钢是模具工业的基础，也是最重要、消耗量最大的一类模具材料。据测算，模具所用钢材在模具工业总产值中占近20％，按2004年国内模具工业530亿元产值计算约106亿元，数量在88万t左右，其中模具钢占大部分。目前我国常用的冷作模具钢仍是低合金工具钢如CrWMn和高碳高铬工具钢Cr12MoV及Cr12等这些老的钢种。CrWMn钢有适当的淬透性和耐磨性，热处理变形小，但CrWMn钢锻后需较严格地控制冷速，否则易形成网状碳化物，导致模具在使用中的崩刃和开裂。高铬钢中因含铬、碳量较高，使共析及共晶点左移，共晶碳化物较多，又称之为莱氏体钢。其中铬大部分集中在M₇C₃型共晶碳化物中，是促成碳化物不均匀分布的主要元素。高铬钢铸态时存在鱼骨状共晶碳化物，这种状态随着钢锭凝固速度减慢和锭型尺寸增大而加剧，这种鱼骨状共晶碳化物用热处理无法消除，只有靠锻造的方法将共晶莱氏体击碎。高碳高铬工具钢属高合金钢，合金含量较高。合金元素钨、钼、铬是合金钢的主加元素。我国是钨资源大国，其储量、产量和出口量均居世界首位，储量占世界钨总储量的40％以上；我国钼储量居世界第二位，但据资料统计表明合金钢的主要合金元素钨、钼资源在世界范围内勘测，其可靠的储存量仅够40～60年使用，加上潜在的储量，也仅够使用100年。铬是一种重要的战略物资，是合金钢的重要原料之一。但我国是一个铬铁矿资源严重短缺的国家，国内生产十分有限，长期以来主要依靠进口解决国内供应问题。因此节约合金元素，既具有重要的战略意义，又可节约钢材成本。从资源与价格的角度考虑，世界各国极为重视低合金钢的发展。磨损是常见的一种失效方式，世界摩擦学会统计表明，摩擦损失了世界性一次能源的1／3～1／2，据有关资料介绍，磨损给工业国家带来的损失可达国民生产总值的2％～8％。我国仅就冶金矿山、农机、煤炭、电力和建材5个工业部门不完全的统计，每年仅由于磨损而需要补充的备件就达100万t钢材，相当于15～20亿人民币。机械工业每年所用的钢材，约有一半是消耗在备件的生产上，而备件中的大部分是由于磨损寿命不高而失效的。由于磨损失效开始于材料表面，因而本研究形成的高合金层与整体冶炼高碳高合金冷作模具钢相比，只需少量的合金元素，具有节约合金元素，降低生产成本的特点。本研究对于我国坚持节约合金元素资源，走可持续发展道路无疑具有重要的科学意义和实用价值。利用表面技术提高材料表面性能，是近十几年来提高钢铁材料耐磨性能的新型工艺技术。双层辉光离子渗金属技术是一种表面处理技术，是等离子表面冶金领域中的核心技术。其目的是通过双层辉光离子渗金属技术提高材料表面的合金元素含量，经后续处理提高材料表面的性能。等离子表面冶金高速钢就是利用双层辉光离子渗金属技术，在低碳钢或低合金钢表面，首先渗入合金元素钨、钼、铬，然后进行固溶和渗碳处理，使表面形成近似高速钢成分的高碳高合金层。通过后续的高温淬火和高温回火，表面性能接近冶金高速钢。当工件使用条件在需要具有高温硬度和红硬性的时候，使用等离子W-Mo共渗+渗碳+高温淬火+高温多次回火的工艺技术能够很好的解决这一问题。但在许多的实际生产过程中，零件的使用状况是处于室温条件下，不需要高温硬度或红硬性。此时若仍采用W-Mo共渗工艺技术，将造成能源的浪费，合金化原理也不够理想。本研究课题双层辉光离子Cr-Mo共渗形成高耐磨LD冷作模具钢的研究，就是继双层辉光离子W-Mo共渗形成表面高速钢工艺技术后，探索和研制一种在低碳钢或低合金钢表面Cr-Mo共渗及离子渗碳后，经980℃～1050℃淬火+低温（高温）回火，提高材料表面耐磨性和满足一般红硬性要求的表面梯度结构新材料及新工艺方法，性能达到一般的红硬性要求。是一种在实际生产中，针对高耐磨要求而研制的表面材料。该技术的研制和开发，拓宽了双层辉光离子渗金属技术的应用领域和范围。本研究课题是利用双层辉光离子渗金属技术在低碳钢表面进行Cr-Mo共渗，表面合金成分达到高耐磨冷作模具钢的要求，之后进行超饱和离子渗C，经后续处理，表面形成高耐磨强化层。本研究课题对Cr-Mo共渗的影响因素，渗Cr-Mo后不同含C量的淬火温度、深冷处理时间对耐磨性能的影响，渗Cr-Mo后进行离子渗N、N-C共渗对耐磨性能的影响等进行了深入研究。本研究课题还针对双层辉光等离子体特性进行了实验研究。研究了此类等离子体中的阴极壳层的特点，等离子体中的电子温度，电子密度及其随放电参数的变化，并对这种等离子体的一些物理特征及动力学过程进行了初步的探索和研究。本研究获得了以下结果：1．利用双层辉光离子渗金属技术，在低碳钢表面进行Cr-Mo共渗，表面形成高合金层，合金成分达到高耐磨冷作模具钢的要求，之后进行超饱和离子渗碳，表面含碳量超过平衡碳计算值，再经淬火、回火处理，形成的碳化物呈粒状或短棒状，碳化物细小、弥散、均匀，尺寸一般≤1μm，彻底消除了冶金高碳高合金耐磨冷作模具钢中碳化物不均匀和轧制加工复杂的问题。2．低碳钢表面经双层辉光Cr-Mo共渗及复合工艺强化处理后，碳化物主要类型为Cr₂₃C₆、Cr₇C₃、Mo₂C、Mo₆C。3．采用丝状源极进行双层辉光离子Cr-Mo共渗，渗层厚度随Mo含量的增加而增加，Mo的加入促进了渗层厚度的增加。4．在低碳钢表面双层辉光离子Cr-Mo共渗形成高合金层后，在后续处理工艺中，即可以进行渗C处理，也可以进行离子渗N、N-C共渗处理，提高表面耐磨性能，与W-Mo共渗形成表面高速钢工艺相比，增加了后续强化处理工艺的方法，可以满足对耐磨强化层的不同要求。而且，N元素的渗入，具有减摩作用，N-C共渗处理试样的摩擦因数较低碳Q235钢基体经离子渗C+淬火+低温回火试样的摩擦因数的降低54.6％；渗氮处理试样的摩擦因数较低碳Q235钢基体经离子渗C+淬火+低温回火试样的摩擦因数的降低58.9％。5．低碳钢表面双层辉光离子Cr-Mo共渗形成高合金层经离子渗C+980℃淬火+低温回火处理，摩擦因数较低碳Q235钢基体经离子渗C+淬火+低温回火试样的摩擦因数的降低11.6％，相对耐磨性较低碳Q235钢基体经离子渗C+淬火+低温回火试样提高1.6倍，较T10钢淬火+低温回火试样提高9.3倍。6．低碳钢表面双层辉光离子Cr-Mo共渗形成高合金层经离子渗C+1050℃淬火+高温回火处理，相对耐磨性较低碳Q235钢基体经离子渗C+淬火+低温回火试样提高0.5倍，较T10钢淬火+低温回火试样提高5倍；抗回火软化性与M2钢相当，高于高耐磨冷作模具LD钢。7．耐磨性能试验表明：低碳钢经双层辉光离子Cr-Mo共渗及后续处理工艺复合强化试样的相对耐磨性高于未渗金属+离子渗C+淬火+低温回火试样；低碳钢表面双层辉光离子Cr-Mo共渗形成高合金层经离子渗C+980℃淬火+低温回火处理试样的相对耐磨性高于经离子渗C+1050℃淬火+高温回火处理试样；深冷处理试样的相对耐磨性高于未经深冷处理试样；随着深冷时间的延长，试样的相对耐磨性提高，摩擦因数降低。8．在等电位辉光放电等离子体中，当辉光放电电压为500～1000V、P=30～100P_a时，电子温度在1～10eV范围内变化，其值高于高气压异常辉光放电一个数量级；而其电子密度在10²¹m^-3数量级，其值在工业典型等离子体密度范围内(10¹²-10²⁵)m^-3，且高于典型辉光放电的电子密度范围(10¹⁴-10¹⁸)m^-3。等电位辉光放电状态为异常辉光放电状态，促使更多自由电子在阴极产生；封闭辅助阴极减少了自由电子向边界扩散，但保温效果增强，其总的效果就是增加电子密度，超过了一般辉光放电中的电子密度。这是等电位辉光放电效应的两个特色。9．在不等电位辉光放电等离子体中，源极电压的变化对电子温度的影响不明显，而工件电压的变化对电子温度的影响较大；在源极电压较低时，工作气压的升高对电子温度的影响较大；随着源极电压的升高，对其影响逐渐减弱。更多还原

【Abstract】 Die arrangement industry is the basic processing equipment of manufacturing industry. It is die arrangement that it could be arrived high precision, complexity, consistence, productivity, and low energy consumption, material consumption. Die arrangement industry is more and more important in the manufacturing industry. Die arrangement is used widely in the automobile, energy, machine, information, aviation aerospace, defensive industry and daily life. It is reported that die arrangement could be used to process 75% of roughing operations, 50% of precision works, 80% of parts in household appliances industry, and 70% of mechanical and electrical products. Die steel is the base of die arrangement industry. It is one of the most important material. The consume quantity of die steel is the most. It is estimated that the value of steel material used in die arrangement is near to 20% of total value of die arrangement industry. The value of die arrangement industry is 530 hundred million yuan and die steel is 106 hundred million yuan in 2004. The mount of steel consumed is about 88 ten thousand tons in die arrangement industry. Among them, most of it is die steel.Low alloy tool steel and high carbon high chromium steel, such as CrWMn, Crl2MoV and Cr12, are still classical steels in our country. The characteristic of the CrWMn steel is as follow. Quenching degree and wear resistance are determinate. Deformation is a little in the heat treatment process. Cooling speed of forged CrWMn steel has to be confined. Others, net carbides could be formed and break would be produced in the used of the die arrangement. The Content of chromium and carbon is higher. Eutectoid and eutectic point are moved to the left in the phase diagram. The amount of eutectic carbides is higher in the high chromium steel. High chromium steel is one of ledeburitic steels. Most of chromium are found in the compound of M₇C₃ in the steel. It is the main element produced asymmetry of the carbides. Fish bone eutectic carbides is found in the cast structure of high chromium steel. It would be turn worse with the slowed freezing rate and the aggrandized size of cast steel. The Fish bone eutectic carbides are not erase by heat treatment. It is the only way to break up the eutectic ledeburites by the forging operation.High carbon high chromium tool steel is one of high alloy steels. The content of alloy is higher in the steel. The elements of tungsten, molybdenum, and chromium are main alloying elements in alloy steel. The resource amount of tungsten of China is the most in the world. It is about 40% of the amount of existed in the world. The reservation of molybdenum of China is the second in the world. The statistical information indicated that the main alloying elements （W, Mo） of alloy steel, observed and used in the world, could only be used for 40～60 years. Included the prospective reserves, it also could only be used for 100 years at most. The chromium, one of main elements in alloy steel, is one of strategic materials. Chrome ironstone is serious short in the China. So saving alloying elements not only has significant strategic meanings, but also reducing the cost of steels. Considered the resources and price, low allow steels are paid attention to development in the world.Abrasion is one of main destroying forms of mechanical parts. The statistic showed by the World Friction Institute that 1/3～1/2 of the world primary energy sources was lost by abrasion. It was introduced that the cost of abrasion was about 2%～8% of GDP of the industrial country. It was imperfect stated, By five industrial departments such as metallurgy mine, farm equipment, coal, electric force, and building material, that spare parts required supplement was more than 1 million tons steels , which was about 15～20 hundred million RMB. About a half of steels was used for the production of spare parts every year in the mechanical industry. However, most of the spare parts were invalid owing to its low abrasive life. Abrasion invalidation initiated the surface of material. Compared with the smelted cold work die steel of high carbon high alloy steel, the content of the alloying elements is lower in the high alloy layer by the double glow plasma surface alloying technique. It could be saved the amount of the alloying elements and reduced the cost of the process. The study has scientific sense and practical significance for saved alloying elements and developed endurably of our country.Improved material surface property is an important method by surface modifying technique. It is a new way to improve wear resistance of surface of ferrous material in recent years. Double glow plasma surface alloying technique is one of surface modifying techniques. It is one of important way in the field of surface metallurgy technique. It is to increase the content of alloying elements in material surface and then improved the surface property by treatment followed.It is called plasma surface metallurgy HSS （high speed steel） formed surface HSS on the surface of low carbon and low alloy steel by double glow plasma surface alloying technique. It is alloy elements, such as tungsten and molybdenum, is infiltrated into the substrate and then solution and carburizing treatment is followed. High carbon high alloy layer is built up on the surface. The content of component is about up to HSS. The surface property of the substrate is approximate to property of HSS after high temperature quenching and tempering. It could satisfy the request on high temperature hardness and red hardness treated by plasma surface infiltration of W-Mo, carbonization, high quenching, and repeated high tempering. When the work pieces are used at ambient temperature, it is not need for high temperature hardness and red hardness. It would result in the waste of the energy in the condition used the W-Mo infiltrated and the alloying principle is not satisfied.Behind formed low-alloy HSS by double glow plasma surface W-Mo-infiltrated, it is researched to built Cr-Mo surface high wear resistant cold die LD steel by the technique in this paper. By the process of double glow plasma Cr-Mo infiltrated, plasma carburization, quenching between 980°C～1050°C, and lower or higher temperature tempering, it is to find a new way to build up a kind of gradient material and improve the property of wear resistance and red-hardness on low carbon or low alloy steel surface. It would meet the need for high wear resistance material in practical application. The study could develop the application field of the double glow plasma surface metallurgy technique.In this paper, It is research on Cr-Mo strengthened layer by double glow plasma surface metallurgy technique and treatment subsequently. In the study, they are researched deeply on influence of Cr-Mo infiltrated process, quenching temperature at different carbon content, wear resistance by cryogenic treatment, ion nitride, and N-C infiltrated.The characteristic is researched in this paper on double glow plasma surface metallurgy technique. They are been analysis on the plasma which are the feature of the cathode layer, affected electronic temperature and density. The preliminary search and study are made about physical characteristic and dynamic process of the plasma.In the paper, the results have been achieved:1. The high alloy layer of Cr-Mo could be obtained on the surface of low carbon steel by used double glow plasma surface infiltration of Cr-Mo technique. The content of constituent elements of the layer is about up to that of the high wear resistance cold work die steel. Subsequently ultra-saturated plasma carbonization is made, the carbon content of the surface is more than the calculated value of available carbon. Strengthened layer on low carbon steels is built up after the substrates are treated by quenching and low tempering. The shape of the carbides is granular and chunky structure. Compared with nonuniform distribution of carbides and complicated rolled process of high carbon high alloy wear resistance cold work die steel, the carbides of the alloyed layer are compact, uniform and disperse. The dimension of carbides in the surface layer is less than 1μm.2. After it is infiltrated of Cr-Mo and post-processing on low carbon steel, the main carbide styles of Cr-Mo strengthened layer are Cr₂₃C₆, Cr₇C₃, Mo₂C, and Mo₆C. 3. The depth of layer is built up with the increasing of the content of molybdenum of source cathode in the process of double glow plasma surface infiltration of Cr-Mo with acicular source cathode. With the infiltrated of molybdenum, the layer thickness increases.4. To improve the surface wear resistance, it could be treated by carburized, ion nitride, and N-C-infiltrated in the post-processing of Cr-Mo-infiltrated substrates. Compared with the process of formed low alloy HSS by double glow plasma surface W-Mo-infiltrated, it is more processes to meet the need of different request for wear resistance strengthened layer. It make friction coefficient reduce by the infiltration of the nitrogen element. Compared with friction coefficient of Q235 steel ion carburized, quenching and low tempering, that of the N-C-infiltrated substrate of Cr-Mo-infiltrated is reduced by 54.6%, that of the ion nitride substrate of Cr-Mo-infiltrated is reduced by 58.9%.5. The substrate, processed by Cr-Mo-infiltrated, ion carburized, quenching at 980°C and low tempering, is compared with that of Q235 steel ion carburized, quenching and low tempering. The friction coefficient is reduced by 11.6% and the average relative wear resistance is 2.6 times. The average relative wear resistance is 10.3 times in comparison with that of the T10 steel processed by quenching and low tempering.6. The substrate, processed by Cr-Mo-infiltrated, ion carburized, quenching at 1050°C and low tempering, is compared with that of Q235 steel ion carburized, quenching and low tempering. The average relative wear resistance is 1.5 times. The average relative wear resistance is 6 times in comparison with that of the T10 steel processed by quenching and low tempering. Resistance to tempering of the strengthened layer is similar to that of metallurgical M2, and it is higher than that of the high wear resistant cold work die LD steel.7. The substrate, post-processing strengthened treatment of Cr-Mo-infiltrated, is compared with that of Q235 steel ion carburized, quenching and low tempering. The substrate, processed by Cr-Mo-infiltrated, ion carburized, quenching at 980°C and low tempering, is compared with that of processed by Cr-Mo-infiltrated, ion carburized, quenching at 1050°C and high tempering. The substrate by cryogenic treatment is compared with that of non-cryogenic treatment. The abrasion experimental results show that the relative wear resistance of the former is higher than that of the later. Along with increased of cryogenic time, the relative wear resistance of the substrate is improved and the friction coefficient is reduced.8. In the equal potential glow discharge, when the voltage is 500-1000V and the working pressure is 30～100P_a, the electronic temperature is about 1～10eV and the electronic density is 10²¹m^-3. The electronic temperature of the equal potential glow discharge is higher than one order of magnitude that of abnormal glow discharge at high pressure. The electronic density of the equal potential glow discharge is in the range of that of type of industry plasma (10¹²-10²⁵m^-3) and higher than that of the type of glow discharge (10¹⁴-10¹⁸ m^-3). The equal potential glow discharge is one of abnormal glow discharge. It could produce more free electron on the surface of cathode. At the same time, it could not only inhibit free electron to move towards boundary, used closed assistant cathode, but also to enhance the temperature. As a result, the electronic density is increased in the equal potential glow discharge plasma. This is the two type of the equal potential glow discharge.9. In the non-equal potential glow discharge, the electronic temperature is not prominent affected by the source voltage and prominent affected by the piece voltage. When the source voltage is lower, the electronic temperature is affected distinctly by the work pressure. When the source voltage is higher, the influence is weakened gradually on the electronic temperature.更多还原