含La2O3奥氏体不锈钢堆焊合金层晶粒细化机制及对其耐腐蚀、磨损性能的影响

目的 通过在超低碳Cr19Ni10不锈钢堆焊合金中加入稀土氧化物La2O3，细化其微观组织，获得力学性能、耐腐蚀性能和耐磨性能等综合性能优良的堆焊合金层。方法 采用添加La2O3的超低碳Cr19Ni10不锈钢焊条制备了四种不锈钢堆焊合金。采用X射线荧光光谱、红外碳硫分析仪和X射线衍射分析仪，对堆焊合金层的元素组成和相组成进行了测定。采用金相显微镜和晶粒度统计软件，对堆焊合金层的微观组织形貌进行观察，并对晶粒度进行了统计分析。采用显微维氏硬度计和纳米压痕仪对堆焊合金层的硬度和杨氏模量进行了测定。采用电化学工作站和CSM摩擦磨损试验机对堆焊合金层的耐腐蚀性能和耐磨性能进行了评价，并且采用白光共聚焦显微镜对磨损后的磨痕形貌和尺寸进行了观察和测定。采用二维晶格错配度理论，对La2O3/γ-Fe界面间的晶格错配关系进行了计算。结果 在堆焊合金层中加入La2O3，随着La2O3加入量的增加，堆焊合金层奥氏体晶粒细化越明显。当La2O3的添加量由0%增加至1.5%时，奥氏体晶粒平均面积由400 μm²减少为210 μm²。堆焊合金层加入La2O3，可以明显提高其力学性能、耐腐蚀性能和耐磨损性能。当La2O3的添加量由0%增加至1.0%时，堆焊合金层的微观硬度由180HV增加到225HV，宏观硬度由125HBS增加到150HBS，杨氏模量由186 GPa左右增加到217 GPa，腐蚀电位由?0.4 V增加到?0.25 V，磨痕深度由50 μm减小到10 μm。La2O3(001)面和γ-Fe(110)面的二维晶格错配度为8.7%(<12%)，说明La2O3可以作为γ-Fe的中等有效异质形核基底，从而细化了堆焊合金层中的奥氏体晶粒。结论 La2O3可以有效地细化奥氏体晶粒，改善堆焊合金层的力学性能，提高其耐腐蚀和耐磨损性能。但是，La2O3加入量存在一个最佳值，当La2O3的加入量为1.0%时，堆焊合金层的综合性能最好。     

纳米孪晶强化贝氏体化涂层及其耐磨性

目的通过诱发纳米孪晶强化贝氏体化涂层强度及耐磨性。方法在250℃对中碳合金钢进行激光熔覆,并进行等温处理。通过残余应力测试、X射线衍射试验、扫描电子显微镜和透射电子显微镜观察、显微硬度和纳米压痕测试、往复磨损试验及磨损形貌表征,分别评价激光熔覆涂层的残余应力、物相、显微组织与结构、硬度梯度及微观硬度\耐磨性能。结果激光熔覆涂层平行和垂直激光移动方向的平均应力值分别为(209±20)MPa和(319±21)MPa。激光熔覆引入大量位错结构,使残余奥氏体尺寸降低至(37.5±2.5)nm。两组试样均为无碳化物贝氏体组织,其显微组织由针状的贝氏体铁素体以及残余奥氏体组成。在激光热作用及后续等温过程中,显微组织明显细化,并伴随生成大量塑性良好的纳米孪晶结构。激光熔覆涂层的平均显微硬度为650HV,较基体的平均硬度提升了约25%。相同磨损时间下,熔覆层的磨损体积为0.675 mm3,基体的磨损体积为1.142 mm3,纳米孪晶结构的形成大大提升了中碳合金钢的抗粘着磨损性能。结论在特定温度对中碳合金钢进行激光熔覆可以制备贝氏体化涂层,在热应力作用下,显微组织中形成的纳米孪晶结构能够对涂层增强增韧,同时提高其抗粘着磨损性能。     

Effect of rare earth oxides on the morphology of carbides in hardfacing metal of high chromium cast iron

The flux cored wires with different amounts of rare earth (RE) oxides additions for hardfacing (harden-face-welding) the workpieces of high chromium cast iron were studied in this work.The morphology of carbides in hardfacing metal was observed,and the type of the carbides was determined by optical microscopy,scanning electron microscopy (SEM),energy dispersive spectrometer (EDS) and X-ray diffraction (XRD).Based on the data of effect of RE on carbides morphology,the refined reason for carbide by RE oxide was discussed with the misfit theory.The results showed that,the microstructure of hardfacing metal was composed of martensite,residual austenite and M7C3 carbides.With the increasing amount of RE oxide additions,the volume fraction and roundness of the carbides were increased,however,the area and perimeter of carbides were decreased.It indicated that carbides in hardfacing metal could be refined and spheroidized by adding RE oxides in flux cored wires.     

含Nb元素堆焊层金属中碳化物的析出行为

以堆焊连铸辊为研究对象,研制三种不同合金元素Nb加入量的药芯焊丝,采用金相显微镜和扫描电镜对其显微组织、碳化物形貌进行了观察.采用X射线衍射仪对其相结构进行了测定.采用Thermo-Calc软件对含铌堆焊层金属中碳化物的析出行为进行分析.结果表明,堆焊层金属显微组织为铁素体、M23C6和MC.随着Nb元素含量增加,其显微组织得到细化,Nb C沿晶界析出.热力学计算结果表明,析出碳化物主要为MC,M23C6.随着Nb元素含量的增加,MC析出量增多,M23C6析出量减小.MC中主要是Nb元素,并溶解了一定量的Mo,V,Cr和Fe元素;M23C6中主要是Fe,Cr元素,即Nb元素含量变化主要影响MC型碳化物.     

纳米 Y2 O3 对过共晶 Fe-Cr-C 堆焊合金表面微观组织与耐磨性的影响

目的研制一种新型添加纳米Y2O3的过共晶Fe-Cr-C堆焊合金,改善堆焊合金粗大的初生M7C3碳化物,提高堆焊合金的耐磨性。方法采用明弧堆焊的方法制作堆焊合金,用金相电子显微镜对其表面微观组织进行观察,用洛氏硬度计对其表面硬度进行测量,用砂带摩擦磨损试验机对其表面耐磨性进行评价,用扫描电子显微镜对其磨损形貌进行观察。最后,利用错配度理论对M7C3的细化机理进行分析。结果过共晶Fe-Cr-C堆焊合金由初生M7C3和共晶组织(共晶M7C3、奥氏体及部分马氏体)组成。未添加Y2O3的堆焊合金初生M7C3比较粗大,其平均尺寸在22μm,硬度为55HRC,磨损量为0.85mg/mm2。经纳米Y2O3改性之后,堆焊合金的初生M7C3尺寸变小,其平均尺寸为16μm,硬度为57HRC,磨损量减少为0.59 mg/mm2,Y2O3的(001)面与正交M7C3的(100)面之间的二维错配度为8.59%。结论 Y2O3可以成为M7C3的非均质形核核心,从而细化了过共晶Fe-Cr-C堆焊合金的初生M7C3碳化物,提高了过共晶Fe-Cr-C堆焊合金表面耐磨性。     

304不锈钢热处理过程温度场和应力场数值模拟

以304不锈钢为研究对象,分别测量了304不锈钢试样经淬火和空冷后的残余应力场。建立有限元模型,模拟了上述试样的温度场和应力场,并将模拟的残余应力场和测量结果进行了比较,二者吻合较好,证明所建立的模型是有效的。在此基础上,分析了淬火和空冷过程中温度场和应力场的变化规律。     

高耐磨药芯焊丝堆焊组织及基体选择

制备了高铬铸铁型自保护药芯焊丝,并采用此焊丝分别在 Y-Ni4 铸铁、65Mn钢、40Cr 钢和灰口铸铁基体上进行堆焊.对不同堆焊试样进行硬度测试,对堆焊金属及其结合部位进行显微组织及断口形貌观察.结果表明,堆焊金属硬度在 60HRC 以上,断裂方式均为解理断裂.65Mn 钢堆焊试样熔合较好,且基本无裂纹,可在受冲击载荷较大的条件下使用;Y-Ni4 铸铁堆焊试样熔合良好,但在热影响区存在裂纹,应在冲击载荷较小或不受冲击载荷条件下使用;40Cr 和灰铸铁堆焊试样熔合不好,熔合区存在许多缺陷,不宜作为耐磨堆焊基体材料.

Abstract：

Four matrix materials, Y-Ni4 cast iron, 65Mn steel, 40Cr steel and grey cast iron, were hardfaced by the high chromium cast iron of self-shielded flux-cored wire separately. The hardness of different hardfacing specimens was measured, and the microstructures, fracture morphologies and the binding sites of different hardfacing specimens were observed. The results show that the hardness of the hardfacing metal is over 60 HRC and the fracture is of cleavage type. The fusion zones of 65Mn and Y-Ni4 hardfacing metal are good ones. However, the cracks can be observed in the heat-affected zone of Y-Ni4 hardfacing specimen. Therefore, the hardfacing metal of 65Mn steel is suitable for the condition of high stress wear and Y-Ni4 cast iron is suitable for the lower one. Besides, there are many defects in the fusion zone of 40Cr and grey cast iron hardfacing specimens, which are not suitable for the wear resistant matrix materials.     

热变形对中铬半钢热疲劳裂纹扩展动力学的影响

研究了热变形对中铬半钢热疲劳裂纹扩展动力学的影响。结果表明 :中铬半钢的热疲劳裂纹扩展符合 L =b Na(a<1)的关系。变形量小于 4 0 %时 ,随变形量的增加 ,裂纹扩展速率减小 ,其激活能随之增大。这些变化是由于碳化物形状的改变和粒状碳化物的析出所致。     

Measurement of Residual Stress Field of Hardfacing Metal with RE Oxide and Its Numerical Simulation

The temperature and residual stress fields of a medium-high carbon steel, welded by a cracking resistance electrode with rare earth (RE) oxide, were measured by thermo-vision analyzer and X-ray stress analyzer respectively. Meanwhile, the martensitic transformation temperatures of matrix, hard-face welding (hardfacing) metal welded by conventional hardfacing electrode and that welded by cracking resistance electrode with RE oxide were determined. According to the experimental data and the thermo-physical, mechanical parameters of materials, finite element method (FEM) of temperature and stress fields was established. In this FEM, the effect of martensitic transformation on residual stress of hardfacing metal of medium-high carbon steel was taken into account. The results show that, by adding RE oxide in the coat of hardfacing electrode, the martensitic transformation temperature can be decreased, so that the residual tensile stress on the dangerous position can be decreased. Therefore, the cracking resistance of hardfacing metal can be improved.     

稀土氧化物对中高碳钢堆焊金属中夹杂物的变质作用

采用电镜和金相等手段，对加稀土氧化物和不加稀土氧化物的堆焊金属中的夹杂物进行了研究，结果表明，稀土氧化物能细化堆焊金属中的夹杂物，减少了尺寸大的夹杂物数量，使其尺寸分布在8μm以下，同时，稀土氧化物能够改善夹杂物的形状，减少了形状系数大的长条状夹杂物数量，使形状系数接近为1的夹杂物较多。稀土氧化物还能变质堆焊金属中夹杂物的属性，可以形成铝、硅、镧的氧化物夹杂和铝、硅、镧的硫氧化物夹杂，并且减少了有害的硫化锰和铝、锰、钛复合夹杂物在堆焊金属中的存在。