【作者】 马超；

【导师】 李爱农；

【作者基本信息】 武汉理工大学 ， 材料加工工程， 2009， 硕士

【摘要】 模具生产技术水平的高低不仅是衡量一个国家产品制造水平高低的重要标志,而且在很大程度上决定着这个国家产品质量、效益及新产品开发能力。随着我国工业的不断发展,对模具性能要求越来越苛刻,寿命问题日益突出。表面强化技术作为提高模具使用性能和使用寿命的一种重要手段,在模具工业中占有十分重要的地位,得到了国内外的广泛关注。金属粉型药芯焊丝是近年来国际发展的新趋势,被称为“代替实芯焊丝的焊接材料”。该焊丝除了具有金属粉型药芯焊丝焊接质量好、无渣、高效率和合金成分可方便调节等固有的优点外,合理的设计粉芯中的合金成分,按通常工序制造与修复轧辊等设备,充分利用必需的消除应力工序的高温回火,堆焊层金属在奥氏体转变为回火马氏体的同时更主要是通过二次硬化析出了大量碳化物导致硬度增加,使得该焊丝还具有焊态硬度低、机加工性能好和时效态硬度高、耐磨性能好等优点,解决了某些高合金实芯焊丝轧制困难的问题,同时克服了现行堆焊材料硬度高、加工性能差或者硬度低、加工性能好、耐磨性差的矛盾,并能克服焊道之间的软化现象,使堆焊表面硬度较为均匀,对耐磨件的堆焊具有重要意义。本文选择两种不同药芯焊丝进行自动埋弧堆焊,并对堆焊层合金的组织与硬度进行系统的研究分析。利用光学显微镜、扫描电镜和X-射线衍射对堆焊合金的组织进行了初步分析和探讨,结果表明堆焊合金组织为马氏体+残余奥氏体+碳化物。在消除应力处理时,在回火过程中残余奥氏体发生了相变,增加了马氏体的含量而提高了硬度,同时合金碳化物的析出形成了较多的硬质相,产生了所谓“二次硬化”现象,使得回火后的硬度更加稳定。同时初生碳化物,共晶碳化物与基体结合的更好更牢固,增强相互之间的作用,并相应提高合金的韧性。总结出这种堆焊层组织即马氏体+残余奥氏体+碳化物,既具有高的耐磨性,又具有较高的韧性,通过反复加热和冷却过程的耐热疲劳性实验,分析了不同冷却过程萌生裂纹概率的大小,并分析了在此过程中裂纹产生的机制。采用这种“少量多元”的合金体系,即加入少量,多种强碳化物形成元素在堆焊层金属中形成优质,多元和复合的合金强碳化物,利用不同的合金碳化物在不同的温度范围内所具有的良好强化作用,保证了堆焊合金在高温下具有良好的抗回火软化性能和较好的耐磨性能,降低了合金元素的消耗成本。更多还原

【Abstract】 Mould technique is not only a important symbol of national product manufacture level,but also decide the country’s product quality,the benefit and the ability of developing new product to some extent.As the development of the industry,the requirement of the performance of moulds becomes higher and higher,the life question is prominent day by day.Surface strengthening technique plays a very important role in the mould industry,and draws extensive attentions.Metal powder-cored wire is the new tendency of the international development in recent years,being considered a welding material instead of solid wire.This welding wire not only has the inherent properties of metal powder-cored wire such as with better welding quality,no-slag,highly efficiency and conveniently adjusting the alloying elements etc.,but also has the advantage of low hardness in as-welded good machinability,high hardness in as-aged and better wear resistance with customary working procedure on making or repairing equipments such as rollers when reasonable designing the alloys content.The author adequately makes use of the high-tempering in the required stress relieving working procedure.During this working procedure,the hardness of overlaying metal increases by the reason of austenite changing into tempered martensite and more chiefly the simultaneous precipitation of a lot of carbide by secondary hardening.This wire can solve the hard rolled problems of some solid wires with higher alloys while it can get over the conflicts of existing overlaying materials what are always possesed high hardness with poor machinability or low hardness,good machinability with poor wear resistance.Further,it also can overcome the interacting phenomena between welding beads and make the external hardness of overlaying metal homogenepus.Be sure it could be found the important significance in the overlaying of wear-resistant equipments.In this paper,two different flux-cored wires were selected to automatically hidden arc overlay weld,and the microstructure and hardness of overlaying alloy were analyzed systematically.Optical microscope,SEM and XRD were used to study the microstructure of overlaying alloy.The result shows that the microstructures include martensite,retained austenite and carbide.When dealing with stress relief, there is a phase transition from retained austenite in the tempering process,increase the content of martensite with the hardness increment.At the same time,much more hard phases have been obtained with the precipitation of alloy carbide,which is so-called "secondary hardening" phenomenon,stabilizing the hardness after tempering.Meanwhile,primary carbides and eutectic carbide combine with substrate more firmly,increasing the toughness of alloy accordingly.Results show that this kind of overlaying microstructures has good wear resistance,but also has high toughness.By the thermal fatigue resistance experiments of repeatedly heating and cooling,the probability of initial cracks in different cooling process was analyzed, and the mechanism for cracks initiating in this process was also analyzed.Using small amounts and muti-component alloy system,which is adding small amount,various-strong carbide formation elements to form high quality, muti-component and compound alloy strong carbides in overlaying metal.According to different alloy carbides having different effects in different range of temperatures, the adding of such alloy dements ensure overlaying alloy has good anti-temper softening property and good wear resistance,reducing the cost of alloy dements.更多还原