Mechanical properties of compacted graphite cast iron with different microstructures

Tensile strength, fracture toughness and impact properties were evaluated in compacted graphite (CG) cast iron with ferritic, pearlitic and ausferritic microstructures. Ultimate tensile strengths for the ferritic and pearlitic samples were 337 and 632 MPa respectively. The austempered samples showed a significant increment in the strength and recording values between 675 and 943 MPa. The fracture toughness test revealed that the stress–intensity factor K_IC was 34·0 MPa m^1/2 for the ferritic CG iron, 39·7 MPa m^1/2 for the pearlitic and between 51·0 and 58·0 MPa m^1/2 for the austempered irons. On the other hand, CG iron with ferritic matrix exhibited the best impact properties with absorbed energy of 33·3 J. The absorbed energy of the pearlitic CG iron was the lowest, 14·3 J, while the austempered samples showed values between 17·2 and 28·4 J. Complementing these results, the critical crack size was also analysed.     

Grey cast iron cast in shell and sand moulds: relationship between tensile and wedge strengths

The tensile strength S_t of grey cast iron can be calculated from measurement of wedge strength S_c by using a linear relation between both variables: S_t = AS_c-B. The coefficients A and B depend on the casting process, the geometry of wedge penetration tool and specimen, and also on the device used to perform the wedge penetration test. Low alloyed grey cast irons of FL15, FL20, FL25 and FL30 basic materials have been cast in shell and sand moulds, at two different pouring temperatures and with and without inoculation. These changes in the process produce large variations in the structure and mechanical strength of the materials. Although these variations are important, the relationship between tensile and wedge strengths can be well described by an equation of the above mentioned type with a unique pair of values for coefficients A and B. IJCMR/453     

High temperature response of selected microstructures in Fe-Mn-Cr-Cu corrosion resistant alloy cast irons

High temperature response was determined by thermo-gravimetric method for the microstructures in the (1) as-cast, (2) 950 °C, 10 h, air cooled, and (3) 1050 °C, 10 h, air cooled conditions for four newly designed cast irons designated as B1 (6Mn-5Cr-1.5Cu), B2 (7.5Mn-5Cr-1.5Cu), B3 (6Mn-5Cr-3.0Cu), and B4 (7.5Mn-5Cr-3.0Cu) and intended to resist aqueous corrosion under marine conditions. The current study was undertaken as corrosion resistant compositions may have potential applications as high temperature materials. It was observed that while the as-cast microstructure was useful only up to 600 °C, the above mentioned heat treatments raised the useful temperature limit of application to ∼800 °C. The relative performance of the alloys was a function of the austenite volume fraction and its stability, morphology, and stability of the second phase and the proneness of the alloys to carbide transformation. The data thus obtained is of considerable interest for alloy design in the future as it lays down guidelines for developing modified compositions exhibiting excellent high temperature response.     

实现绿色集约化铸铁熔炼的新方法

由新型环保、多功能冲天炉、集中点控可燃流体预热装置和HTM(High Turbulence Mixer)"三炉一体"组成绿色集约化铸铁熔炼,不仅明显提高了铁液的冶金质量,而且极大地改善了铸铁熔炼的作业环境,可为全面实现绿色集约化铸铁生产打下了重要的基础.     

Microstructure and fatigue properties of plasma transferred arc alloying TiC-W-Cr on gray cast iron

In this paper, TiC-W-Cr powders were alloyed on grey cast iron by plasma transferred arc (PTA). The alloying samples were characterized the microstructure, microhardness, fatigue life and fatigue crack growth. From the results, it is indicated that two distinguishing region: alloying zone, heat affected zone are formed on the surface after PTA alloying. The alloying zone mainly consists of primary austenite, martensite, a eutectic of (Fe,Cr)₇C₃ carbide and austenite as well as the uniformly distributed un-melted TiC particles. PTA alloying TiC-W-Cr eliminates the stress concentration at the edge of graphite and produced hard carbide, resulting in frequent crack deflection. As a result, the Weibull distribution of fatigue life demonstrates that PTA alloying TiC-W-Cr exhibits longer lives compared to matrix and PTA hardening without reinforcement, but more scattered. In addition, on the basis of the careful observation of fatigue crack growth, it is shown that the fatigue crack growth rate could be retarded by PTA alloying TiC-W-Cr at low stress intensity.     

Heat treatment in high Cr white cast iron Nb alloy

Wear resistance of high Cr white cast irons can be improved by means of heat treatment. This type of cast iron alloy may present a microstructure with retained austenite. The amount of retained austenite changes with the applied heat treatment, which will have an influence on wear properties. The purpose of this work was to study the influence of several parameters such as quenching and tempering temperatures and subzero treatment in the wear performance of the high Cr white cast iron Nb alloy. In this way, the performance was evaluated using pin-on-disc abrasion test. The worn surface was examined by scanning electron microscopy, and the main wear mechanisms were identified. The microstructural characterization was also performed with carbide identification. This Fe alloy has proven to be good for applications in mining and alcohol-sugar industries.     

Study of rare earth element effect on microstructures and mechanical properties of an Al-Cu-Mg-Si cast alloy

The improvements of microstructures and properties of a high strength aluminum cast alloy were studied.The effects of rare earth elements on the microstructures and mechanical properties of the high strength cast alloy Al-Cu-Mg-Si were investigated.The result shows that the addition of rare earth elements can change the microstructures in refining the grain size of the alloy and making the needle-like and laminar eutectic Si to a granular Si.With the increase of the rare earth, the tensile strength and elongation of the alloy increase first and then fall down.The mechanical properties of the alloy will reach the highest value when the content of rare earth elements is about 0.7%.     

Carburiser properties transfer into the structure of melted cast iron

Heredity in the microstructure of cast iron produced solely from scrap (synthetic cast iron) was considered experimentally. The carbon deficiencies were adjusted using anthracite, synthetic graphite and petroleum coke as carburisers. The small flakes of anthracite resulted in smaller graphite flakes in the final microstructure, proving that heredity is affected by the carburiser as much as by the particular “pig iron-steel scrap-cast iron” combination.     

Effect of iron on microstructure and mechanical properties of primary AlSi7Mg0.3 alloy

Effect of Fe on microstructure and mechanical properties of the primary AlSi7Mg0.3 alloy and the potential of Mn addition to counteract any adverse effects was investigated in the present work. The primary AlSi7Mg0.3 is a better alloy than its counterpart with twice as much Fe. β platelets grow twice as big when the Fe concentration is doubled. This, in turn, increases shrinkage porosity and leads to a 3-fold decrease in the tensile elongation values. Adding an equal amount of Mn helps to modify the β platelets into more compact α particles and also reduces shrinkage porosity. While these structural changes are reflected by a modest improvement in the mechanical properties, Mn addition fails to offer a full recovery in the ductility of the AlSi7Mg0.3 alloy. Hence, limiting the Fe content of the primary AlSi7Mg0.3 alloy to 0.12 wt% is worthwhile and pays off with superior microstructural features and mechanical properties.     

QPQ技术中渗氮时间对合金铸铁组织及摩擦性能的影响

采用OM、SEM、硬度测试、摩擦磨损试验等方法研究了QPQ技术中渗氮时间对合金铸铁组织与摩擦性能的影响。结果表明,QPQ处理后,合金铸铁表面形成的渗层物相主要由Fe_2-3N、Fe₂O₃和FeO组成。渗层厚度的平方与渗氮时间存在线性关系,在580 ℃渗氮盐浴条件下,氮元素在合金铸铁中的扩散激活能为70.07 kJ/mol。在90~150 min渗氮时间内,随着渗氮时间延长,渗层的表面硬度值由522 HV0.05降低至441 HV0.05,当渗氮时间延长至180 min,表面硬度值回升至455 HV0.05。与未处理试样相比,QPQ处理的试样具有更小的摩擦因数,并且QPQ处理后试样表面的犁沟显著变浅,表面的金属剥落也得到明显改善,且随着渗氮时间的增加,渗层厚度增加且稳定材料。经180 min渗氮处理的QPQ试样具有最优综合性能,表面硬度值为455 HV0.05,摩擦因数为0.32。     

QT-500球墨铸铁表面激光熔覆镍基合金的组织与性能

利用DL-T5000型二氧化碳激光器在QT-500球墨铸铁表面熔覆镍基合金,分析了激光熔覆层的显微组织,测试了其显微硬度及磨损性能。结果表明:所制得熔覆层组织致密、无裂纹,与基体形成了良好的冶金结合。从熔覆层表面到基体热影响区,组织依次为大量的树枝晶、等轴晶、树枝晶。熔覆层的硬度较基体提高了5倍,熔覆层的总磨损率大约为基体的1/6。熔覆层耐磨性能增强的主要原因是镍基合金与涂层元素镍、铬等固溶强化和碳化物等析出相的强化作用。     

细化变质处理对铸造Al-7.5Si-4Cu合金力学性能和组织的影响(英文)

研究了单一和复合Al-5Ti-B、RE和Al-10Sr细化变质剂对砂型铸造Al-7.5Si-4Cu合金力学性能、显微组织、细化变质效果及其金属间化合物变化的影响。结果表明:与单一细化变质处理以及铸态相比,经过添加质量分数为0.8%的Al-5Ti-B、0.1%的RE和0.1%的Al-10Sr细化变质剂复合细化变质处理后铸造Al-7.5Si-4Cu合金的力学性能和显微组织都得到了显著改善。对于单一细化变质处理,加入0.8%的Al-5Ti-B中间合金后,合金的抗拉强度和布氏硬度得到大幅度提高,并且细化了α(Al)相。加入0.1%的RE中间合金后,合金的伸长率得到了最大程度的提高。这是因为RE的加入使铝合金熔液而得到净化,同时改变了金属间化合物的形状。而加入0.1%的Al-10Sr变质剂后,合金的屈服强度得到改善,但其他性能的改善有限。Al-10Sr变质剂对共晶硅具有较强的变质作用,但使得铝合金熔体含气量增加并形成严重的柱状晶组织。利用硅相的平均面积和长宽比描述细化变质效果得到的结论与力学性能和组织分析的结果相同。     

Thermal fatigue characteristics of plasma duplex treated nodular cast irons

The correlation between the thermal fatigue resistance and microstructure of untreated and plasma surface engineered nodular cast irons was investigated. Both the ferrite and pearlite matrix nodular cast irons were evaluated. During the tests, 60 mm long cylinders with 20 mm diameter were subjected to 1000 high frequency induction heating and water cooling cycles, lasting 7 and 5 s, respectively. The thermal fatigue damage was evaluated by analyzing the crack dimensions and distributions. The results showed that the plasma surface treatment increased thermal fatigue resistance. When thermal cracking occurred, the cracks always nucleated at the surface of the specimen. In addition, the nodular cast iron with a pearlite matrix had a better resistance to thermal fatigue than that of the ferrite matrix.     

Effect of variable heat treatment modes on microstructures of Fe-Cr-B cast iron alloy

The effect of heat treatment mode on the microstructure of Fe-Cr-B cast iron alloys was investigated in this paper by comparing the difference of precipitation patterns of secondary particles after thermal cycling treatment （TCT） with those after normal heat treatment （NHT）. No obvious differences were found in precipitation patterns of secondary particles between TCT and NHT when experimental temperature was below Ar1. However, when temperature was over Ar1, there were significant differences, with secondary particles prominently segregated at the grain boundaries under TCT, while the particles evenly distributed in the matrix under NHT. The reason for the microstructure differences could be associated with the development of non-equilibrium segregation of boron during TCT.     

TiC_P/3Cr13复合材料的显微组织和力学性能研究

用熔铸工艺过程中的原位反应合成方法制备了TiCP 颗粒增强 3Cr1 3钢基复合材料。试验结果表明 ,该工艺制备的复合材料工艺性能优良 ,易于加工成形。当TiCP 颗粒的体积分数小于 8%时 ,显微组织中TiCP 颗粒分布均匀 ,没有出现颗粒的团聚及由于TiCP 颗粒引入而形成的组织缺陷。TiCP 颗粒的加入能有效地提高材料的常温及高温强度 ,但在一定程度上降低了材料的塑性和冲击韧性     

Dynamical coarsening processes of microstructures in non-dendritic AlSi7Mg alloy remelted in semi-solid state

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热处理对TiCp/Fe复合材料基体组织与力学性能的影响

通过不同的热处理工艺改变原位TiCp／Fe复合材料的基体组织，探讨了原位TiCp／Fe复合材料不同基体组织与性能的关系。试验结果表明：在热处理过程中基体组织明显改变，TiC增强相不发生变化。退火处理降低材料的硬度，提高材料的韧性。淬火 低温回火处理使材料的强度和硬度提高，而韧性没有明显的下降。采用等温淬火工艺，可使TiCp／Fe复合材料具有最好的综合力学性能。     

固溶处理对铸造Al-Si-Cu-Mg合金组织与性能的影响

对固溶处理过程中铸造Al-Si-Cu-Mg合金析出相溶解过程进行了研究。结果表明:在固溶处理初期,组织中θ相的数量逐渐减少,但在(FeMn)3SiAl12相中还有一定的Cu含量;而固溶后期,富铁相中的Cu含量也明显降低,且难溶的Al3Ti针状相也发生钝化,但部分Q相尚存在;随着固溶时间的延长,合金基体中Cu和Mg的含量逐渐增多,且富Mn和富Ti相也在合金基体中略有溶解;合金的固溶强化作用主要来源于富Cu相的溶解。在Al-Si-Cu-Mg固溶处理过程中,合金力学性能的提高主要来源于共晶硅相形貌的改善、析出相溶解引起的固溶强化及组织的均匀化。     

铸造Mg-Zr-Er-Zn合金的力学性能和阻尼行为

通过电子显微镜、阻尼性能和力学性能测试等研究Mg-0.6Zr-0.6Er-1Zn合金力学性能和阻尼行为.结果表明:加入0.6%Er 1%Zn后,在晶界附近存在含Er和Zn的质点减缓了枝晶生长,起到细化Mg-0.6Zr合金组织的作用,使得其晶粒尺寸减小至60 μm左右,抗拉强度、屈服强度和伸长率分别达到198.8MPa、83.0MPa和24.5%,较Mg-0.6Zr合金均有不同程度的提高,且比阻尼为48.1%,仍具有较高的阻尼性能.     

汽车用铸造镁合金的组织与力学性能

研究了Sr含量和振动凝固振幅对铸造AM50-Y镁合金组织与力学性能的影响。结果表明,随着振幅的增加,铸态镁合金的晶粒尺寸不断减小,组织中的块状或者条状相逐渐演变为点状弥散分布,合金的抗拉强度、屈服强度和伸长率逐渐上升,振幅为2.5 mm时达到极大值。随Sr含量增加,振幅为2.5 mm合金的晶粒尺寸比未振动合金要小,抗拉强度、屈服强度和伸长率增大。