双电极焊条TE4303单弧焊接分析

从焊接效率与节能、微观组织、力学性能、断口形貌等方面对钛钙型双电极焊条(TE4303)单弧焊进行了研究.结果表明,与传统单芯焊条(E4303)电弧焊相比,当采用相同的焊接电流时,TE4303单弧焊熔化系数和熔敷系数可提高1倍,熔化单位重量焊条金属节省电能约20%～30%;TE4303单弧焊对母材热输入小,接头熔合比小,...     

Vacuum Brazing of WC-8Co Cemented Carbides to Carbon Steel Using Pure Cu and Ag-28Cu as Filler Metal

The wetting and spreading behavior of commercial pure Cu and Ag-28Cu alloy on WC-8Co cemented carbide were investigated by the sessile drop technique. The contact angle of both systems obviously decreases with moderately increasing the wetting temperature. Vacuum brazing of the WC-8Co cemented carbide to SAE1045 steel using the pure Cu or Ag-28Cu as filler metal was further carried out based on the wetting results. The interfacial interactions and joint mechanical behavior involving microhardness, shear strength and fracture were analyzed and discussed. An obvious Fe-Cu-Co transition layer is detected at the WC-8Co/Cu interface, while no obvious reaction layer is observed at the whole WC-8Co/Ag-28Cu/SAE1045 brazing seam. The microhardness values of the two interlayers and the steel substrate near the two interlayers increase more or less, while those of WC-8Co cemented carbide substrates adjacent to the two interlayers decrease. The WC-8Co/SAE1045 joints using pure Cu and Ag-28Cu alloy as filler metals obtain average shear strength values of about 172 and 136 MPa, and both of the joint fractures occur in the interlayers.     

Surface hardening of Fe-based alloy powders by Nd：YAG laser cladding followed by electrospark deposition with WC-Co cemented carbide

This paper presents the results of a study concerned with the surface hardening of Fe-based alloys and WC-8Co cemented carbide by integrating laser cladding and the electrospark deposition processes. Specimens of low carbon steel were processed firstly by laser cladding with Fe-based alloy powders and then by electrospark deposition with WC-8Co cemented carbide. It is shown that, for these two treatments, the electrospark coating possesses finer microstructure than the laser coating, and the thickness and surface hardness of the electrospark coating can be substantially increased.     

Microstructure and bend strength of WC–Co and steel joints

Abstract

Tungsten inert gas arc welding of WC–30 wt-%Co cemented carbide and steel was carried out using a variety of filler alloys. Precipitation of Fe₃W₃C occurred at the joint interface and this reduced the bend strength and toughness of the welded joint. The problem could be alleviated by adjusting the carbon concentration of the filler metal.     

Cr_3C_2对WC-6.5％Co硬质合金组织和性能的影响

通过向WC-6.5%Co硬质合金中添加0%～2.0%的晶粒长大抑制剂Cr_3C_2,研究了其对硬质合金组织和力学性能的影响。研究结果表明,Cr_3C_2的添加细化了WC晶粒,但不能完全抑制WC晶粒的异常长大。Cr_3C_2使合金的硬度提高,但是却降低了合金的致密度和抗弯强度。Cr_3C_2添加量为0.5%时,合金的综合性能最好。     

Visualization of gas metal arc welding on globular to spray transition current

The transfer modes in gas metal arc welding have important effects on welding quality. However, present study of metal transfer modes is not yet fully understood. In this study, welding arcs was visualised using the optical emission spectroscopy technique. The carbon steel wire electrode was used for welding with 80% Ar?+?20% CO₂ shielding gas. The results showed that the globular to spray transition current was 330–350?A. During globular to spray transition, argon,CO₂ and Fe plasma tended to gradually change from localising near the arc axis to a two-layer structure having 11,000?K in high-temperature region away from the arc axis and around 7000?K in low-temperature region near the arc axis.     

Ni3Al添加量对WC-Co硬质合金中WC晶粒形状的影响

采用粉末冶金制备技术,以粗WC粉末、Co粉和WC＋Ni3Al预合金粉末为原料制备出WC-40vol％（Co—Ni,Al）硬质合金。利用扫描电镜和透射电镜研究了不同NbAl含量对WC-40vol％（Co—Ni3Al）硬质合金中WC晶粒形状的影响规律。结果表明：W在Co粘结相中的固溶度接近25．4wt％,而W在Ni,Al粘结相中的固溶度接近9．5wt％,随着NbAl含量的增加,粘结相对W的固溶度减小,合金中的WC晶粒圆钝和细小;WC晶粒表面上出现明显的台阶。相应的,延长烧结时间,WC—Co—Ni3Al硬质合金具有与WC—Co硬质合金相同的WC生长行为,WC-40vol％（Co—Ni3Al）硬质合金中的WC晶粒表面上的台阶处出现明显的刻面。     

放电等离子烧结温度对纳米硬质合金性能的影响

采用放电等离子烧结(SPS)这种新的烧结技术制取92WC-8Co纳米硬质合金。主要就放电等离子烧结92WC-8Co硬质合金的烧结温度进行研究探索,对不同的烧结温度进行对比实验,以找出最佳的硬质合金SPS烧结温度。最终发现:1150℃为放电等离子烧结纳米92WC-8Co硬质合金的最佳烧结温度,在该温度下,硬质合金制品可达到14.88g/cm3的致密度,硬度可达到94.2HRA。     

Synthesis of WC-Co composite powders with two-step carbonization and sintering performance study

In this study, WC-Co composite powder was synthesized by two-step carbonization method using W, Co and C as raw materials. X-ray diffraction (XRD) showed that the η phase (Co₆W₆C) was kept at 1100 °C for 1 h under vacuum, and it could be completely carbonized into WC-Co composite powders. The surface morphology of WC-Co composite powders was analyzed by scanning electron microscope (SEM). The effects of η phase and second phase (W phase) on WC morphology and Co phase distribution were investigated. Electron backscattered diffraction (EBSD) was used to analyze WC-10 wt% Co cemented carbide particle distribution. Comparison of transverse rupture strength, hardness and fracture toughness of two kinds of WC-10 wt% Co cemented carbides synthesized by WC-Co composite powders + WC and WC + Co respectively, the cemented carbide of composite powders + WC increases the fracture toughness from 11.4 ± 0.3 MPa·m^1/2 to 12.4 ± 0.3 MPa·m^1/2.     

高Ni钎料-WC硬质合金颗粒复合堆焊焊条的探讨

以SiC材质成型舟皿作为模具,尺寸为2～5 mm的YG8型WC硬质合金颗粒为耐磨相,CuZnNi合金为胎体金属,加入NiCrBSi合金粉末以提高胎体金属的Ni含量与Cr含量,采用钼丝氢气炉烧结制备高Ni钎料-WC硬质合金颗粒复合堆焊焊条,并对成型后焊条的断面形貌及胎体金属成分进行分析.结果 表明,硬质合金颗粒在焊条内呈...     

碳量及B类孔隙对WC-8%Co硬质合金抗弯强度的影响

采用粉末冶金方法制备了WC-8%Co硬质合金试样,经氢气烧结后,利用钴磁测试仪、强度测试仪、电子显微镜和金相显微镜分别对试样的钴磁和抗弯强度进行测定、对试样断口和金相缺陷进行观察。研究了WC-8%Co硬质合金抗弯强度与碳量(相对磁饱和)、金相缺陷(B类孔隙)之间的关系。结果表明:将试样碳含量及孔隙度控制在一定的范围内,可以使试样抗弯强度保持在较高的水平,当试样相对磁饱和为88%~92%,B类孔隙为B00时,合金显微组织中WC晶粒较为均匀,无异常长大情况,WC-8%Co硬质合金抗弯强度可达3 286 N/mm2;同时,抗弯强度值的大小随孔隙度的增多而下降。另外,氢气烧结后经HIP处理可以有效消除WC-8%Co硬质合金中的孔隙缺陷,从而提高合金抗弯强度,经HIP处理的试样的强度比正常样的强度高出2.3%。     

低碳钢芯奥氏体不锈钢代用焊条的研究

采用半固态流变压铸成形工艺，研究了高剪切速率双螺杆机械搅拌制浆机中剪切速率对半固态镁合金浆料质量的影响规律。试验表明，在其它工艺参数相同的条件下，随着螺杆剪切速率的增大，半固态浆料的固相率降低，初生α-Mg相晶粒平均尺寸减少，剪切速率高于2730s^-1时，晶粒的圆整度变化不大；剪切速率低于1365s^-1时，组织形态明显恶化。     

钎料对YG8合金与低碳钢焊接性能的影响

采用两种铜基钎料HL841(CuZnMnSnNiCo合金)和HL105(CuZnMn合金)对YG8硬质合金和低碳钢进行真空钎焊,并对比研究了焊缝的微观组织、元素扩散情况及接头抗拉强度。研究表明:两种钎料与硬质合金结合处形成互溶区,HL105形成的互溶区宽度大概为1μm,而HL841形成的互溶区宽度约为3μm;HL841钎料中的Co、Ni等元素有利于形成Fe-Co-Ni单相固溶体,同时钎焊过程中钎料中的Co还能缓解硬质合金中粘结相Co的扩散流失。这些原因使得采用HL841焊接的试样的接头力学性能优于HL105。     

Effect of VC and NbC additions on microstructure and properties of ultrafine WC-10Co cemented carbides

The nanocomposite WC-Co powders were prepared through planetary ball milling method. Effects of grain growth inhibitor addition and the vacuum sintering parameters on the microstructure and properties of ultrafine WC-10Co cemented carbides were investigated using X-ray diffractometer, scanning electron microscope and mechanical property tester. The results show that VC and NbC additions can refine the WC grains, decrease the volume fraction of Co₃W₃C phase in ultrafine WC-10Co cemented carbides, and increase the hardness and fracture toughness of the base alloys. After sintering for 60 min at 1400 °C, the average grain size and hardness of ultrafine-grained WC-10Co-1VC cemented carbide are 470 nm and HRA 91.5, respectively. The fracture toughness of cemented carbide WC-10Co-1NbC alloy is over 7 MN·m^?3/2.     

铸钢轧辊亚微米WC-4Co电火花沉积涂层高温性能

用新型电火花沉积设备,把WC-4Co陶瓷硬质合金材料沉积在铸钢轧辊材料上,制备了电火花沉积合金涂层,用SEM和XRD等技术研究了沉积层在300 ℃的高温耐磨性和800 ℃高温氧化100 h后氧化膜形貌、组织结构和高温抗氧化性能.结果表明,沉积层厚度为20～30 μm,沉积层由Fe3W3C,Co3W3C,Si2W和W2C等物相组成.300 ℃高温条件下沉积层的耐磨性比基体提高了3.4倍,300 ℃高温条件下沉积层的磨损机理主要是粘着磨损、疲劳磨损、氧化磨损和磨粒磨损的综合作用.800 ℃高温条件下沉积层氧化100 h后的氧化膜的厚度约为10～20 μm;氧化膜主要由Fe3O4,Fe2O3,W20O58和Si物相组成;800 ℃高温下沉积层抗氧化性能比基体的抗氧化性能提高了2.6倍.细小弥散分布的硬质相提高了沉积层的抗高温磨损性能和抗高温氧化性能.     

Role of Co Content on Densification and Microstructure of WC–Co Cemented Carbides Prepared by Selective Laser Melting

WC–Co cemented carbides, well-known as the conventional tooling materials, have not been successfully produced by one step additive manufacturing processes such as selective laser melting(SLM) yet. The microstructure evolution as well as WC grain growth behavior has rarely been investigated in detail during SLM process. In this study, the WC–Co cemented carbides with different Co contents(12–32 wt%) were prepared by optimized SLM processes for comparative investigation of densification behavior, microstructure characterization and mechanical property. The increase in Co content in feedstock carbide granules can improve the densification behavior during SLM process. The SLM processed WC-12 Co shows larger average WC grain size and higher percentage of coarser WC grains as compared with both WC-20 Co and WC-32 Co. The microstructure characterization, combined with finite element simulation, shows the WC grain growth mechanisms include agglomeration and dissolution-deposition of WC during SLM process and agglomeration of WC is an important mechanism especially for WC–Co cemented carbides with Co content as low as 12 wt%. The comparison between horizontal(perpendicular to the SLM laser beam) and vertical(parallel to the SLM laser beam) cross sections of carbides shows that SLM process introduces a certain degree of microstructure and mechanical behavior anisotropy for WC-12 Co, WC-20 Co, and WC-32 Co.     

The influence of welding condition on the microstructure of WC hardfacing coating on carbon steel substrate

Tungsten carbide (WC) hardfacing coating technique is widely used to improve the performance of carbon steel blade exposed to acidic and abrasive conditions during production. This paper deals with the influence of welding parameters on the microstructure and carbide distribution of WC. WC hardfacing was deposited onto carbon steel by shielded metal arc welding (SMAW). Welding parameters such as welding current, number of weld layers, electrode drying and base material preheat were the focus of this work. Coating hardness, microstructure and elemental composition were analysed in detail. The effects of the welding parameters on WC hardfacing coating microstructure and hardness value were characterized by scanning electron microscope (SEM) and micro-Vickers hardness tester respectively. The larger carbide growth in overall coating region is mainly dictated by high current (200 A), increased number of weld layers (3 layers) and presence of base material preheat due to sufficient heat energy initiating carbide growth. The investigation also revealed that high current affected the growth of smaller carbide particles in matrix region significantly. Meanwhile, number of weld layers and base material preheat influences were seen during hardfacing with lower welding current. The absence of electrode drying led to uniform smaller carbide distribution in matrix region. It was found that increased number of large carbides and uniformly distributed smaller carbides in WC hardfacing deposit increased the hardness value of the coating.     

低碳钢搅拌摩擦焊用摩擦头的失效研究

选用YG8硬质合金作为摩擦头材料进行低碳钢的搅拌摩擦焊试验。采用游标卡尺测量工具、X射线衍射仪和能谱仪等分析摩擦头在焊接过程中的主要失效形式。结果表明,YG8硬质合金摩擦头在低碳钢的搅拌摩擦焊过程中的主要失效形式为机械磨损、氧化剥落、搅拌针脆性断裂和轴肩变形失效等。引起失效的主要原因是摩擦头长时间的高温高压摩擦,导致粘结相Co分布不均匀或部分扩散流失,严重破坏了硬质合金的骨架模型;失效后摩擦头组织中出现了游离碳和硬脆相Co6W6C,减弱粘结相Co对基体相碳化钨的固溶强化作用,最终导致摩擦头的硬度、强度和耐磨性等下降。     

硬质合金真空钎烽的研究

为了提高盾构隧道掘进机硬质合金刀头和钢基体的连接强度及使用寿命,选用801钎料,对42CrMo钢与WC-8％C0硬质合金进行真空钎焊试验,研究钎焊温度和钎焊压力对钎焊接头性能的影响,并用剪切试验确定最佳工艺参数。通过使用扫描电镜观察显微组织及能谱分析钎料中各元素在母材中的扩散情况,探讨了该钎料与母材的结合性能。结果表明,采用60kPa的压力在980℃下钎焊,钎料形成的中间,层与母材结合较好,无裂纹等缺陷,连接层厚约40-50mm;剪切强度达到415MPa,Zn与Mn发生了向硬质合金中的明显扩散,Co偏聚于连接层与钢的界面;压力的适当增加有利于提高界面结合强度,但压力过高导致连接层变薄,不利于缓解接头热应力。     

电铁塔用细晶高强钢焊接接头组织与性能研究

采用焊条电孤焊、CO2气体保护焊焊接了控扎控冷制备输电铁塔用细晶Q420低合金高强钢.研究焊接接头显微组织和力学性能,并对比分析热轧制备Q420钢焊接接头的冲击韧性.研究结果表明,选择E5515焊条、ER55-G焊丝焊接所得细晶Q420高强钢焊接接头焊缝金属主要由铁素体和少量珠光体构成,ER55-G焊丝由于添加Ti元素...