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.     

On the Roughening of Grey and Nodular-graphite Cast Irons during Surface Melting

The gas tungsten arc (GTA) welding process has been used to melt the surface on a series of grey and nodular-graphite iron castings. The topography of the fusion zone was foum to be markedly different for the two types of cast iron: for grey cast iron the resolidified surface was very rough, with surface perturbations leading to localised height differences of up to 0.4 mm, while for nodul-graphite iron a macroscopically smooth surface was obtained. A model has been developed to account for the observed phenomena based upon the influence of sulphur on the interfacial tensions responsible for the spreading of the liquid phase on the surface of the underlying unmelted region. It is hypothesised that surface-active sulphur is available in grey cast irons to exert a depressive influence on the interfacial tensions, but that in nodular-graphite irons the sulphur is rendered immobile through its combination with magnesium. The results have implications for other directed energy surface melting processes such as laser anc electron-beam melting of cast irons.     

利用大量回炉料和废钢生产高牌号灰铸铁

介绍了铸铁冶金质量指标及其影响因素,分析了利用大量回炉料加废钢生产的灰铸铁力学性能、切削加工性能和铸造性能比普通灰铸铁优良的原因.生产实践表明,生产此类灰铸铁的要点是增碳、高温熔炼和控制ω(C)、ω(Si)量;此类灰铸铁的三角试块断口组织致密、呈银灰色、白口宽度不大,抗拉强度为290 MPa,石墨由90％的A型石墨和10％的B型石墨组成,基体组织为5％铁素体+95％珠光体.在焦炭质量及供风条件一定的情况下,温度越高,增碳率越高,废钢用量比例可以越大.     

Nb对高CE灰铸铁耐磨性能的影响

研究了Nb对高CE灰铸铁耐磨性能的影响,结果表明：（1）Nb可以提高灰铸铁的耐磨性,加入0.25%的Nb时,铸铁的相对耐磨性可提高55%;（2）Nb在基体组织中的固溶强化作用提高了基体的显微硬度,当w（Nb）量为0.46%时,基体显微硬度提高40%;（3）灰铸铁耐磨性能的提高应该归因于基体中的富Nb相,因为富Nb相在基体中的分布及形态对提高铸铁的耐磨性起着明显的作用。     

合金铸铁和铸造不锈钢在海水中耐蚀性

报告了21种合金铸铁、铸造不锈钢在海水中的暴露试验结果:高Ni铸铁在海水中有较好的耐蚀性;Cr-Sb-Cu铸铁在海水中的耐蚀性好于灰口铸铁;添加Ni、Ni-Cr、Ni-Cr-Mo、Ni-Cr-Cu、Cu-Sn-Re或Cu-Cr的低合金铸铁在海水中的耐蚀性比灰口铸铁没有提高;加入Ni、Ni-Cr、Ni-Cr-Mo或Ni-Cr-Cu的低合金铸铁在潮汐区的耐蚀性与灰口铸铁相同;高Cr、Mo铸造不锈钢在海水中有好的耐蚀性.     

合成铸铁在轮类铸件生产中的应用

采用中频感应电炉熔炼和合成铸铁工艺生产HT200和HT250牌号灰铸铁,并对其力学性能和金相组织进行了统计。与传统灰铸铁生产工艺相比,合成铸铁工艺不仅降低了生产成本,而且可以改善灰铸铁的力学性能。     

铌在铸铁中的应用及其作用情况介绍

介绍了铌合金在灰铸铁、球墨铸铁、不完全激冷（indefinite chill）铸铁和镍抗可焊接（weldable Ni-Resist）铸铁中的应用情况;分析了铌合金在铸铁中的作用机理,认为NbC能为共晶团提供核心是加Nb细化共晶团的原因,而且NbC的弥散分布可以提高铸铁耐磨性、硬度和强度;综述了铌合金化技术原理,指出铸铁加铌合金化主要有与固体废铁料一起加入大块料和出铁时加入细颗粒两种较为经济的方法。     

Evaluating vibroabsorption properties of cast iron by a composite parameter

Gray cast irons occupy a special place among structural materials with a well-defined heterogeneous structure that possess a high damping capacity. Gray cast irons are used for the production of a wide range of parts that experience static and cyclic sign-variable loads. They are used as structural materials with a high damping capacity due to their high adaptability to manufacture and the possibility of quite wide control over their properties by introducing various modifiers into the melt. The present work is devoted to evaluation of the quality of gray cast irons with various shapes, amounts, and distributions of graphite inclusions and various structures of the metallic base using the Sugimoto composite parameter and specific characteristics of strength and rigidity. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 33–36, April, 1998.     

干扰元素对铸铁组织和性能的影响

介绍了来源于铸造生铁中的S、P、Pb和废钢中的Mn、Cr、Ni、Mo等元素在铸铁中形成碳化物,影响球化,增大缩孔缩松倾向,降低灰铸铁强度的情况。提出了消除其有害影响的主要措施:(1)严格管理炉料、控制铁液的化学成分;(2)加入抗干扰元素;(3)采用高纯铸造生铁。认为使用高纯生铁是解决原材料困扰的重要途径之一。     

Microstructure and wear properties of low-alloy phosphoric gray cast irons

The effects of various alloying elements on the microstructure and wear properties of phosphoric gray cast irons were examined. The wear properties of gray cast irons were examined with wear tests in the lubricated condition at various final loads and sliding speeds. It is found that the microstructure and the morphology and size of flaky graphite do not change much with a small addition of alloying elements such as V, Nb, Mo and Cr. However, the wear resistance of phosphoric gray cast iron is found to increase significantly with an increasing amount of alloying element. For a given amount of alloying element, it is found that V and Nb are very effective, whereas Mo and Cr are less effective in increasing the wear resistance of phosphoric gray cast iron. The increase in the hardness of steadite caused by the segregation of carbide-forming elements is found to be responsible for the excellent wear resistance of low-alloy phosphoric gray cast irons.     

高强度灰铸铁熔炼技术发展趋势及最新研究成果

回顾了灰铸铁熔炼技术的发展历史,认为提高熔炼过程中石墨的形核能力是提高熔炼技术的重要途径。通过冲天炉与感应炉双联熔炼和感应炉增碳熔炼HT250材料的对比试验数据,说明采用感应炉增碳工艺可以有效地减轻铁液的收缩和白口倾向,减少灰铸铁的断面敏感性,改善石墨形态,提高材料性能。指出随着熔炼工艺水平的提高和铁液炉前处理技术的创新,HT300材料已产业化应用,HT350及更高牌号的灰铸铁材料也已经能够达到。     

镍奥氏体铸铁的生产

镍奥氏体铸铁是具有良好的吸震性的耐蚀铸铁，通过加入镍的严格成分控制，以及采用合理的熔炼工艺，能稳定地获得铸态奥氏体基体，有效地降低铸铁组织中的阳极区阴极区极区的活性，达到改善耐蚀性能的目的。镍奥氏体球墨铸铁的基体得到强化不仅使其耐蚀性能稳定，而且综合性能也得到提高。     

On the damping capacity of cast irons

The treatment of experimental data on the amplitude-dependent internal friction (ADIF) in terms of various theoretical models has revealed a staged character and the main mechanisms of the processes of energy dissipation in graphite with increasing amplitude of vibrations upon cyclic loading. It is shown that the level of the damping capacity of lamellar cast iron depends on the relationship between the elastic and strength characteristics of graphite and the matrix phase. In cast irons with a rigid matrix structure (pearlite, martensite), the energy dissipation is determined by the volume fraction and morphology of the initial graphite phase. In cast irons with a softer metallic phase (ferrite), the contact interaction of graphite inclusions with the matrix and the properties of the matrix introduce additional sources of high damping.     

金属型对灰铸铁和球铁力学性能的影响研究

采用铜合金金属型和铸铁金属型浇注灰铸铁和球铁Y形试块，加入不同量的Mn、Ti、Cu和Sn，研究金属型材料和添加合金对灰铸铁和球铁抗拉强度和疲劳强度的影响。结果发现：与采用铸铁金属型浇注相比，未加合金、采用铜合金金属型浇注的灰铸铁和球铁的力学性能略高。采用铜合金铸型浇注时，由于冷速较快，使石墨和基体组织细化的作用较强，添加合金元素改善力学性能的作用较为明显，而且反复浇注时，铜合金金属型的热应力较小。因此，灰铸铁和球铁采用铜合金金属型铸造比采用铸铁金属型有利。     

Effect of microstructure and mechanical properties on cutting force of different cast irons with similar tensile strength

Flake graphite iron,compacted graphite iron and spheroidal graphite iron with various tensile strengths were cast. They were selected and grouped according to roughly the same tensile strength,and then the main cutting force in each group was measured and compared. The microstructures of different cast irons were characterized. The relationship between the cutting force and microstructure was established. Results show that the graphite morphology in cast irons determines the strength. In order to obtain the same strength of the cast iron with sharply edged graphite,more or finer pearlite in the matrix is needed. Graphitic cast irons with high pearlite content and smaller pearlite interlamellar spacing have higher hardness. For the cast irons with different graphite morphologies,but almost the same tensile strength,the main cutting force is obviously different,along with the hardness. Harder cast irons have a greater cutting force,but the difference in cutting force is not proportional to hardness.     

现代灰铸铁熔炼技术

严格控制冶金因素提高灰铸铁性能，从炉料选材到熔炼操作，结合生产经验和认识做了论述。对铸铁质量提出应在结晶过程做深入研究，从而进一步提高性能。     

高强度D型石墨铸铁的研究进展

综述了灰铸铁中产生D型石墨的原因，D型石墨对灰铸铁性能的影响以及D型石墨灰铸铁的应用。国内外的研究表明：深过冷，在灰铸铁中加入提高过冷度的合金元素（钛，铝，锑，碲，稀土元素等）或者二者的结合都会促进生成D型石墨；D型石墨灰铸铁具有较高的强度，较好的抗氧化性，抗生长性，抗热疲劳性和耐磨性；D型石墨灰铸铁已经广泛用于生产玻璃模具，压缩机缸体，压缩机曲轴等铸件。笔者还介绍了采用钒钛生铁生产的D型石墨合金铸铁凸轮轴的性能特点及其应用情况。     

Structure and fracture toughness of high-strength perlite-cementite cast iron after plasma treatment

Treatment of cast iron is a promising application of surface strengthening by highly concentrated energy sources. As a structural material, cast iron in widely used in many branches of industry. The conventional methods of bulk heat treatment and surface strengthening (for example, by high-frequency currents) do not make it possible to realize completely the potentially high operating properties of cast iron. At present, considerable experience has been accumulated in plasma and laser strengthening of various grades of cast iron. However, the literature contains little data on the interrelation of the structure, phase composition, hardness, and wear resistance with the crack resistance of cast irons. At the same time, analysis of operational damage in cast iron parts shows that brittle fracture and breaking are an important cause of failure in such parts. The present work is devoted to investigation of the structure, the nature of disruption, and the criteria of short-term crack resistance of cast irons in surface strengthening by a highly concentrated plasma jet.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 2 – 6, April, 1996. UDC 669.15-196:620.178.7     

Effect of Tin on the Phase Transformations of Cast Irons

Copper, manganese and essentially tin are used as alloying elements for obtaining cast irons with a fully pearlitic matrix in the as-cast state. Addition of tin, at a level of about 0.10-0.15 mass%, seems to be the only practical way for avoiding growth of ferrite in the stable eutectoid reaction and to fully transform the matrix of the material to pearlite in the metastable eutectoid system. While the role of copper and manganese has been previously rationalized, the way tin affects the eutectoid transformation in cast irons is still a matter of debate. The present work makes use of an assessment of the Fe-Sn system and of experimental data in the Fe-C-Sn system to evaluate the effect of tin on phase equilibria in this latter system. One ternary parameter is estimated and the resulting modification is applied to literature data on Fe-C-Si-Sn equilibria. Finally, solid-state phase transformation temperatures are calculated and used to discuss experimental information dealing with pearlitic cast irons. It is proposed that pearlite formation in Sn-bearing cast irons is associated to the transient formation of a Fe₃SnC compound which has an ordered FCC structure.     

Studying elastic deformation behaviour of cast irons by acoustic emission

Abstract

The deformation of metallic materials includes both an elastic and a plastic deformation. In the case of cast irons, the elastic region becomes less pronounced as the graphite changes from spheroidal to flake shaped, as observed in nodular and grey cast iron, respectively. The present study aims to correlate the shape of the graphite phase with the deformation behaviour, where the plastic deformation and other strain accommodating events are quantified by measurements of the acoustic emission events occurring in the interior of the material at loading. It also aims to explain how the appearance of cast iron stress–strain curves depends on the graphite morphology where, for instance, spheroidal graphite cast irons exhibit a seemingly linear elastic behaviour in contrast to flake graphite cast irons. The present study includes a series of pearlitic cast iron material grades with differences in nodularity and carbon equivalent, respectively. It is shown that as the roundness of the graphite phase increases, the ability to absorb energy increases. The measured acoustic emission indicates that plastic deformation occurs in the seemingly linear elastic region regardless of the cast iron grade, i.e. no cast iron grade exhibits perfect linear elasticity. The plastic deformation rate in the elastic region increases as the roundness of the graphite decreases and as the carbon equivalent increases. It is shown that the plastic deformation governs the resulting modulus of elasticity in all kind of cast irons, i.e. the modulus of elasticity decreases as the yielding of the material increases. The present study improves the understanding of the deformation behaviour in the elastic region of different cast irons. The survey shows that acoustic emission testing is a useful method when studying the deformation behaviour of cast irons.