CUTTING FORCES IN HIGH SPEED TAPPING CAST IRON BY TUNGSTEN CARBIDE TAPS

The engineblock production lines need high speed tapping with tungsten carbide taps. In the tapping process, the machining precision and the tool life of taps are directly influenced by tapping forces. And the parameter optimization of tap structures is also correlated with the variation of tapping forces. Therefore, the study of tapping forces is necessary in developing new style taps. Several experiments about some novel carbide taps are performed on a vertical machining center by a Kistler dynamometer system in blind tapping both gray cast iron and ductile cast iron. And the variations of tapping forces are analyzed in tapping-in and tapping-out periods. It indicates that cutting forces hardly vary with the tap wear in tapping cast iron. Contrarily, tapping forces are closely correlated with the holding method. Besides, it also depends on the helix angle, the flute numbers and the plasticity of the work material to some extent.

Interaction between alloying and hardening of cast iron surface

To improve wear resistance of surface will increase the service life of gray cast iron directly. This paper presents that gray cast iron surface coated with alloy powder is locally remelted by TIG arc to increase the wear resistance. The influences of arc current and scanning rate etc on surface properties are found. Under different conditions, the microstructure, hardness and wear resistance of remelted layer are analyzed and measured. The results indicate that the gray cast iron surface can be strengthened by TIG arc local remelting treatment. Especially, surface alloying hardening effect is best and surface properties are improved remarkably.

Structures and Properties of Iron Matrix Composites with Tungsten Carbide Particle by EPC-V Process

In this paper the Expendable Pattern Casting with dry sand Vacuum(EPC-V) process is used to manufacture iron matrix composites with tungsten carbide particle.Microstructures of the composites layers were analyzed.The abrasive wear resistance of the composites layers were tested and compared with that of high chromium cast iron.The results show that the iron matrix composites with tungsten carbide particle have high hardness.The abrasive wear resistance of composites with tungsten carbide particle is higher than that of high chromium cast iron.The properties of the matrix materials have been improved remarkably.

Study on in-situ WC particles/tungsten wire reinforced iron matrix composites under electromagnetic field

By applying electromagnetic field to a system consisting of tungsten wires and grey cast iron melt,the grey cast iron matrix composite reinforced by either in-situ WC particles or the combination ofin-situ WC particles and the residual tungsten wire was obtained.By means of differential thermal analysis(DTA),the pouring temperature ofiron melt was determined at 1,573 K.The microstructures of the composites were analyzed by using of X-ray diffraction(XRD),scanning electron microscopy(SEM) equipped with an energy dispersive spectrum(EDS) and pin-on-disc abrasive wear test.The obtained results indicated that,with the enhancing frequency of electromagnetic field,the amount ofin-situ WC particles gradually increases,leading to continuous decrease of the residual tungsten wires.When the electromagnetic field frequency was up to 4 kHz,tungsten wires reacted completely with carbon atoms in grey cast iron melt,forming WC particals.The electromagnetic field appeared to accelerate the elemental diffusion in the melt,to help relatively quick formation of a series of small FeW-C ternary zones and to improve the kinetic condition ofin-situ WC fabrication.As compared with the composite prepared without the electromagnetic field,the composite fabricated at 4 kHz presented good wear resistance.

Sliding Wear Behavior of a Grey Cast Iron Surface Remelted by TIG

The sliding wear behavior of a grey cast iron surface remelted by tungsten inert gas （TIG） was studied and compared with the unremelted one in the current work. To evaluate the wear behavior a Pin-on-Disk wear test machine was used. Pins which were prepared from the samples with the remelted layers of different thicknesses of 1.2, 1.8, 2.5 and 3 turn were worn on an AISID3 steel counterface having a hardness of 63HRC under the applied loads of 54, 76 and gg N at a constant sliding velocity of 0.45 m/s. Scanning electron microscopy （SEM） equipped with energy dispersive X-ray analysis （EDS） and X-ray diffraction （XRD） techniques were used to characterize worn surface and subsurface and also wear debris obtained from the wear tests under different test conditions. Results showed that surface remelted grey cast iron have better wear properties for all applied normal loads in comparison with unremelted ones. Microscopic studies on the worn surfaces and subsurfaces of samples revealed that dominant wear mechanism for surface remelted samples was mild oxidative, while it was severe for unremelted samples. Increasing remelted layer thickness and then forming grosser microstructure lead to a decline of wear properties, whereas lower thickness of remelted layer with finer microstructure due to having higher cooling rate through remelting process can withstand better against wear.

钨极氩弧焊焊接粉末冶金高铬铸铁/低碳钢的焊接性能及组织演变

以粉末冶金高铬铸铁和低碳钢为原材料,采用多道次手工钨极氩弧焊,研究了焊接电流对焊缝组织演变和力学性能的影响,提出了焊接接头组织演化模型,并探讨了其断裂机理。结果表明,焊接接头的抗拉强度在焊接电流为140 A时达到538.1MPa,分别是烧结高铬铸铁和低碳钢抗拉强度的95.3%和97.4%。由于二次回火和合金元素扩散/偏析的作用,焊接接头的显微硬度在水平方向上由高铬铸铁一侧向低碳钢一侧逐渐降低,而在垂直方向则呈M形分布。当焊接电流为140 A时,焊缝的熔合区主要由奥氏体和回火马氏体组成,在熔合区与低碳钢母材之间存在一个单一奥氏体柱状晶区;在熔合区与烧结高铬铸铁母材之间,存在一个柱状高铬铸铁区域,该区域的碳化物为粗糙树枝状,沿基体晶界分布。

Effect of alloying elements W,Ti,Sn on microstructure and mechanical properties of gray iron 220

Experiments were carried out to observe the variation in microstructure and mechanical properties of gray cast iron by adding pearlite promoting alloying elements such as Ti,Sn and W.Results show that adding Sn,Ti,and W with different concentrations improve the microstructure,Brinell hardness and tensile strength of gray cast iron.With the increase of alloying element concentration,the average graphite length and graphite content increase linearly.At the same time,average cell size and the maximum graphite length also decrease linearly.Brinell hardness and tensile strength of gray cast iron also increase with an increase in alloying elements contents,and attain the maximum when Ti=0.561%,Sn=0.561%and W=0.945%.However,at higher concentrations of Ti=0.810%,Sn=0.631%and W=1.351%,the tensile strength decreases from 333 MPa to 297 MPa and the Brinell hardness decreases from 248 HB to 225 HB.The decrease in tensile strength and Brinell hardness at the higher concentration level is attributed to the formation of coarse and thick graphite flakes.

热处理对含钨高铬铸铁组织及性能的影响

采用金相显微镜、扫描电镜观察微观组织，X射线衍射仪分析相组成，并测定洛氏硬度、冲击韧性及耐磨性，研究了热处理对含钨高铬铸铁组织及性能的影响。结果表明，钨在高铬铸铁基体和碳化物中均匀分布，热处理对钨的分布影响不大，钨能显著提高高铬铸铁的性能。含钨高铬铸铁合理热处理工艺是1050℃奥氏体化淬火，250～350℃回火，在该热处理条件下的组织为马氏体＋碳化物＋少量残留奥氏体，铬的碳化物类型为Cr7C3、Cr23C6，钨的碳化物有WC1-x、W6C2.54、W3C，硬度为62～63HRC，冲击韧度为7～8J／cm^2，耐磨性比不含钨高铬铸铁显著提高。

钨对Cr24高铬铸铁组织及性能的影响

研究了钨元素对Cr24高铬铸铁组织及性能的影响。试验结果表明,钨元素在碳化物和基体中均匀分布,钨的碳化物以WC1-x、W6C2.54、CW3形式存在,铬的碳化物类型以M7C3、M23C6为主。铸态下,组织为马氏体+奥氏体+碳化物。含钨量为1.0%时,硬度HRC为58～59,冲击韧度为11～12J/cm2,钨含量达到3%时,冲击韧度明显下降,含钨3%的磨损失重最少;经1050℃淬火250℃回火,含钨量为1.0%的硬度HRC为60～61,冲击韧度为8～9J/cm2,磨损失重最少。

碳化钨增强钢铁基耐磨复合材料的研究和应用

评述了制备复合材料的铸渗法、粉末烧结法、堆焊法、电渣熔铸法等工艺方法,以及碳化钨和钢铁基体的选择、界面反应和强度、复合材料的性能和应用现状。重点介绍了粘结剂、其他添加剂、碳化钨颗粒形状、粒度及其分布、浇注温度等对铸渗工艺及其表面复合材料的影响。阐明铸渗法是一种有前途的制备工艺,自蔓延工艺和铸造工艺的组合有可能取得新的成效。指出复合层厚度在10mm以上的铸渗工艺,工程化和产业化关键技术以及复合工艺的稳定化是今后的研发重点,表面耐磨复合材料较适用于零部件的局部磨损和低角度的冲蚀磨损,应据磨损工况来选择制备工艺及其复合材料。

含钨量对铸态290Cr26MoW耐磨铸铁组织和硬度的影响

铸态合金耐磨铸铁适用于大型或复杂结构耐磨件。通过金相组织观察、X射线衍射相结构分析、图像分析仪定量金相测试和力学性能检测,研究了含钨量对铸态290Cr26MoW耐磨铸铁组织、结构和硬度的影响规律。结果表明,在含0～2.79%W的范围内,随着含W量的增加,铸态290Cr26MoW耐磨白口铸铁的初生基体数量减少,共晶团数量增加,共晶碳化物数量增加;铸态290Cr26MoW耐磨白口铸铁的碳化物结构类型没有改变,M7C3型碳化物为共晶碳化物;铸态290Cr26MoW耐磨白口铸铁基体的奥氏体比例增加,马氏体减少。马氏体多位于共晶团,即共晶碳化物周围。铸态290Cr26MoW耐磨白口铸铁的硬度由共晶碳化物数量和硬度以及基体中奥氏体和马氏体数量比共同决定。

铸铁局部重熔强化的实验研究

通过实验，对铸铁局部钨极氩弧重熔强化原理进行了探讨，找出了电弧电流、熔化速度等工艺参数对金相组织和性能的影响规律，并分析了合金元素的强化作用．通过与铸造激冷和ＷＣ堆焊件的对比实验，表明重熔强化处理是一项发挥铸铁潜在能力的表面改性新技术．

凸轮轴的钨极氩弧重熔淬火工艺

概述高密度能量束如激光束、等离子束或电弧束用于铸铁重熔淬火的优、缺点。介绍凸轮轴钨极氩弧重熔淬火工艺过程、局部重熔淬火的原理、3个机械变速运动、电流强度变化、生产现场质量监控。分析凸轮轴重熔淬火中主要质量缺陷产生的原因,得出提高硬化处理合格率的现场措施。

等离子弧堆焊WC增强型高铬铸铁的组织和性能

采用等离子弧粉末堆焊技术在Q235钢表面分别堆焊高铬铸铁和WC增强型高铬铸铁,通过对各堆焊层的显微组织、化学成分、显微硬度、耐磨性和耐蚀性进行对比分析,揭示WC颗粒对高铬铸铁堆焊层的影响。结果表明,高铬铸铁堆焊层显微组织由初生(Fe,Cr)7C3和共晶组织组成,WC增强型高铬铸铁堆焊层由初生碳化物、WC颗粒和共晶组织组成。与高铬铸铁相比,WC增强型高铬铸铁由于WC的加入,初生碳化物面积分数非常高,共晶组织数量相应减少;WC增强型高铬铸铁的硬度,耐电解腐蚀性和耐热腐蚀性均优于高铬铸铁。两种堆焊层熔合线处的硬度陡降,结合线扫描结果说明,WC的加入不影响WC增强型高铬铸铁堆焊层与基体界面处的冶金结合和堆焊质量。

硬质合金堆焊层经热处理后的耐磨性研究

对B、C、N共渗层、碳化钨型硬质合金(D707)堆焊层、高碳高铬铸铁型硬质合金(D618)堆焊层等几种不同表面处理工艺,经相应热处理后的腐蚀磨损性能进行了研究。结果表明,两种硬质合金堆焊层经850 ℃空冷、850±5 ℃油淬+400 ℃回火后,均具有较高的硬度和优异的耐腐蚀磨损性能,且简化了表面处理工艺。

钨对Cr20高铬铸铁组织及性能的影响

研究了钨元素对Cr20高铬铸铁组织及性能的影响.试验结果表明,钨元素在碳化物和基体中均匀分布,钨的碳化物以WC1-x、W6C2.54、CW3形式存在.铸态组织为马氏体+奥氏体+碳化物.含钨量质量分数为1%时,硬度为56~59 HRC,冲击韧度为10~12 J/cm2,耐磨性是不含钨时的2倍,含钨量达到3%时,冲击韧度明显下降,但耐磨性是不含钨的2.3倍;含钨量为1.0%的试样经1 050℃淬火250℃回火,组织为马氏体+碳化物+少量残余奥氏体,硬度为60~61 HRC,冲击韧度为8~9 J/cm2,其耐磨性是不含钨的3.0倍.

合金对铸铁局部重熔强化的影响

针对提高铸铁耐磨性的问题，介绍了用 TIG电弧对涂敷合金元素的灰铸铁表面进行局部重熔处理时，合金种类及合金加入量对试样表面性能的影响 .并在不同条件下，对重熔层的相结构、元素分布、显微组织、硬度和耐磨性进行了测试和分析 .结果表明，合金化可显著提高 TIG重熔处理产生的灰铸铁表面强化效果，使表面性能有很大提高 .

变质处理钨合金白口铸铁的研究

以廉价钨渣铁合金为主要合金原料制造钨合金白口铸铁衬板,研究了稀土变质处理提高其使用寿命的可能性。研究结果表明,钨合金铸铁经适量稀土变质处理后,共晶碳化物由网状分布变成断网状分布,冲击韧性和耐磨性显著提高。变质钨合金铸铁用于制作球磨机衬板,使用安全、可靠,使用寿命比高锰钢衬板提高100%～150%,与高铬铸铁衬板相当,生产成本接近高锰钢,比高铬铸铁降低30%～40%。

钨合金白口铸铁共晶碳化物团球化研究

钨白口铸铁成本低,但共晶碳化物呈连续网状分布,脆性大,在承受冲击载荷的工况下使用易断裂,使用范围受到严格限制。研究了Ce、K、Na复合变质处理对其组织和性能的影响,还提出了评价碳化物变质效果的圆度概念。变质处理后,钨合金白口铸铁的共晶碳化物形态发生了显著变化,在常规热处理条件下,共晶碳化物变成了团球状,使之冲击韧性提高了72.2%、耐磨性提高了49.9%。对共晶碳化物团球化机理进行了深入分析,并讨论了共晶碳化物团球化对力学性能和耐磨性能的影响。变质处理的钨合金白口铸铁轧辊使用寿命比高铬铸铁轧辊提高20%以上,生产成本降低30%以上,推广应用变质钨合金白口铸铁具有较好的经济效益。

Cr25Mo2W3耐磨铸铁硬度和抗冲刷腐蚀性能

高铬钼钨耐磨铸铁以高硬度著称。通过金相组织观察、X射线衍射相结构分析、图像分析仪定量金相测试、电子探针微区成分分析、力学性能检测和盐水砂浆中的低角度冲刷腐蚀试验,研究了含碳量和含钼量对高铬钼钨耐磨铸铁组织、结构、硬度、冲击韧性和抗冲刷腐蚀性能的影响规律。结果表明,淬回火的280Cr25Mo2W3铸铁是以马氏体和残余奥氏体为基体,以(Cr、Fe、W、Mo)7C3和(Fe、Cr、W、Mo)23C6为增强相的复合材料。在含碳量2.03%～2.79%的范围内,随着含碳量的增加,淬回火的Cr25Mo2W3耐磨铸铁的硬度逐渐提高,冲击韧度先升后降。随着含钼量的增加,280Cr25W3铸铁硬度提高,冲击韧度下降。M7C3和M23C6数量的增加以及M7C3显微硬度的提高,是提高铸铁硬度和降低韧性的主要原因。高硬度280Cr25Mo2W3耐磨铸铁的M7C3横剖面(择优生长方向的垂直面)硬度HV1645,纵剖面硬度HV1383,经淬回火热处理该铸铁的硬度达HRC65,具有优异的抗低角度冲刷腐蚀性能。