Research of microstructure of spherical graphite iron by electropulsing annealing

This paper investigated the solid-state graphitization of spherical graphite iron by electropulsing annealing. The results indicated that the electropulsing annealing can accelerate the decomposition of cementite, improve the diffusion ability of carbon in the matrix and make more neonatal graphites in small size be formed. With the increase of electropulsing annealing temperature, the graphitization rate is accelerated. At the high temperature and the quick heating rate, the solid-state graphitization can be finished in a short time. Analysis shows that electropulsing annealing promotes the nucleation of graphite and the decomposition of cementite, consequently, the solid-state graphitization of spherical graphite iron is accelerated.     

脉中电场对渗碳体第一阶段石墨化过程的影响

通过试验研究了脉冲电场对球墨铸铁高温退火过程中渗碳体第一阶段石墨化的影响,结果表明,随脉冲频率的增加渗碳体分解加快,新生石墨数量增多.分析认为,脉冲电场通过增加奥氏体中石墨的数量,从而缩短渗碳体转变为石墨过程中碳原子的扩散距离来加速渗碳体的第一阶段石墨化过程.     

脉冲电流对铸铁固态石墨化中碳原子扩散的影响

分别在室温和高温条件下对球墨铸铁进行不同参数的脉冲电流处理,采用电子探针研究脉冲电流对球墨铸铁固态石墨化过程中碳原子分布的影响.结果表明,脉冲电流加速了渗碳体的石墨化过程,使渗碳体附近的奥氏体中碳原子分布更加均匀,增强了碳原子在奥氏体中的扩散能力.碳原子在奥氏体中扩散能力的增强源于脉冲电流提高了碳原子的扩散系数和缩短了碳原子的扩散距离.     

Electronic structure and magnetic properties of the α and γ phases of iron, their solutions with carbon, and cementite

The full-potential LMTO method was used to comparatively analyze the band structure, magnetic and cohesive characteristics, energies of formation of α and γ iron, their carbon solid solutions, and cementite. It has been found that the solid solution γ-Fe + C, similarly to γ-Fe, is characterized by an antiinvar transition and that cementite demonstrates invar behavior. The similarity of curves of the density of states, cohesive energies, and magnetic moments for the supersaturated solid solution of carbon in the fcc iron and cementite suggests the preferable formation of cementite in regions of concentration inhomogeneity of carbon distribution in the solid solution of γ iron.     

An experimental study of metastable graphitization of cast irons

It is known that the structure of cast irons and steels can contain both cementite and graphite. In unalloyed steels and cast irons cementite is a metastable phase and can be graphitized in the process of prolonged annealing, which is used in the production of malleable cast irons and graphitized steels. Alloying with carbide-forming elements (Cr, Mn, V, etc.) in various amounts can stabilize cementite, providing stably white or stably mottled cast irons. A recently discovered phenomenon connected with formation of metastable graphite in the structure of alloy cast irons and steels, which undergoes carbidization in prolonged annealing, has been called metastable graphitization and is much less known. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 25–28, March, 1998.     

超高碳钢石墨化的热力学分析及研究

对喷射态超高碳钢和普通铸造的母合金1．25C-3．0Si-1．5Cr进行了热轧试验，发现在渗碳体和奥氏体双相区热轧时有条状石墨生成。喷射态超高碳钢较母合金中的石墨数量少且石墨较细。从热力学角度分析了元素对石墨化的影响，得出变形可促进石墨的形成。通过控制化学成分，选择合理的热轧工艺减小碳的偏析，可有效抑制石墨的生成。     

脉冲电场处理对铁液凝固过程石墨化的影响

在未加任何孕育剂的情况下，铸铁铁液经过脉冲电场处理后，在凝固过程中发生了石墨化转变；在相同参数脉冲电场的作用下，处理时间长有利于石墨化转变的进行；原铁液中的硅有利于缩短处理时间，分析认为，脉冲电场的施加，引起了铁液中不同原子及原子团的电子施主/受主特性的改变，改变了铁液中碳的活度及原子团的尺度，从而引起铸铁铁液凝固过程中的石墨化转变。     

超高碳钢热加工时的瞬时石墨化

喷射成形超高碳钢在热加工过程中有可能在极短的时间内发生石墨化.这种石墨化是在添加过多的非碳化物形成元素而使碳的活度超过1的热力学条件下,在Acm以下一段温度内、在足够大的变形量下发生的.这种与热变形直接相关的瞬时石墨化之所以能够发生,是因为预存孔洞提供了有利形核点;大变形促使渗碳体迅速溶解;大变形引入的大量位错提供了碳原子聚集的快速通道.     

Iron layer formation during cementite decomposition in carburising atmospheres

In the following report cementite (Fe₃C) formation and subsequent decomposition is investigated on pure iron samples at 700 °C in CO-H₂-H₂O gas mixtures. The carbon activities of the atmospheres are a_C=15.9 and 20, values higher than the value of the equilibrium α-Fe+Fe₃C. During the carburisation process cementite forms at the surface. Graphite deposition at the surface initiates cementite decomposition. An iron layer of 1-3 μm thickness forms between cementite and graphite as a result of cementite decomposition. In previous studies of metal dusting on iron it was found that at lower temperatures T?650°C the decomposition product iron is found in the coke as small particles.     

Process of graphitization in gray cast iron under pressure

Conclusions  

Thermal expansion of cementite in hypereutectoid iron-carbon alloy

Iron forms a number of carbides, of which cementite Fe₃C has been studied best in steels. However, the nature of cementite has not been determined completely. It is known that carbon atoms can be arranged in two possible ways in the cementite lattice, namely, at the centers of trigonal prisms with iron atoms at the vertexes and at the centers of slightly deformed octahedrons (octahedral surroundings of iron atoms). The first variant is considered to be the most probable and is characterized by a lamellar structure that causes strong anisotropy of the physical properties of cementite. In the case of octahedral surroundings the structure should be quasi-isotropic with weak anisotropy of the cementite properties. In the present work the method of x-ray dilatometry is used to study the thermal expansion of cementite extracted from a hypereutectoid steel containing 1.72% C. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 1, pp. 6–9, January, 1997.     

渗碳体的结构和一次渗碳体形态的研究

对钢铁中的基本相渗碳体的晶格结构作了进一步的描述:一个碳原子位于由6个铁原子组成的三棱柱体中,每个铁原子为2个三棱柱体所共有;每个渗碳体晶胞含4个这种上下分层、反向、错位排列的三棱柱体,相应的化学计量比为12:4(即3:1)。应用计算机可以形象地揭示渗碳体的结构。根据成分过冷原理对从过共晶铸铁液相中结晶出树枝状一次渗碳体进行了分析。     

Electrochemical properties of iron silicocarbide and cementite in acidic and neutral environments

Voluminous specimens of individual Fe₅SiC iron silicocarbide and Fe₃C iron carbide phases were produced by mechanical alloying with subsequent pressing and considered as models of nonmetallic inclusions in carbon steels and siliceous cast irons. In an acidic sulfate solution, silicocarbide is highly active in hydrogen reduction and iron ionization in the active dissolution range. Therefore, the corrosion resistance of silicocarbide in acids is lower compared to iron and cementite, which is caused by the peculiarities of its crystal structure. In a neutral borate solution both on silicocarbide and cementite, two anodic peaks are observed that are caused by the dissolution of the corresponding phase and the additional oxidation of the passive film, which is characterized by the heightened defectiveness because of the carbon accumulation. Silicocarbide has lower dissolution currents compared to cementite and a higher resistance to the local activation and depassivation, which is caused by the presence of a superficial layer enriched in SiO₂.     

硅钡合金孕育处理KTH350—10的试验研究

用硅钡合金作孕育剂，并与相同条件下用铝孕育处理可锻铸铁进行比较，研究了钡对第一和第二阶段石墨化的影响。组织观察和性能测试结果表明：钡可促进第一和第二阶段石墨化过程，有利于获得铁素体基体；经硅钡孕育处理后铸铁组织中絮状石墨的外形趋于团球化，石墨的尺寸也有所减小，强度和塑性都有不同程度的提高。     

Cementite decomposition and coke gasification in He and H2-He gas mixtures

Cementite decomposition and coke gasification were investigated by first carburisation of iron samples at 700 °C in a 50%CO-49.81%H₂-0.19%H₂O gas mixture for 4 h and then further treatment in He and He-H₂ gas at the same temperature for different time periods. After carburisation cementite is formed at the iron surface covered by a coke layer. Scanning electron microscopy (SEM) shows carbon filaments and columnar layered bulk graphite in the carbon deposits. X-ray diffraction (XRD) and transmission electron microscopy (TEM) reveal only cementite as the iron-containing phase in the coke. Cementite in the iron specimen and cementite in the coke show a different decomposition behaviour during treatment in He and He-H₂ gases. In the iron specimen cementite decomposition proceeds fast and is comparable in both He and He-H₂ gases. However, cementite in the coke is much more stable than that at the sample surface especially in the case of only He gas. By using thermogravimetric analysis (TGA) no gasification is detected in He gas but very significant gasification in He-H₂ gas mixture until all the coke is removed. By adding some H₂O into the He-H₂ gas the gasification process is accelerated.     

750 ℃退火出炉温度对QT450-10球墨铸铁组织与性能的影响

利用光学显微镜、扫描电镜等方法研究了在750 ℃退火工艺下不同出炉温度对QT450-10球墨铸铁的珠光体含量、渗碳体形态、抗拉强度以及硬度的影响。结果表明,球墨铸铁试样在经过不同出炉温度下的微观组织均由铁素体、石墨球、石墨颗粒以及少量渗碳体组成。由于珠光体的分解、渗碳体残留以及石墨颗粒的形成导致在750 ℃出炉空冷时试样的抗拉强度下降7%左右、布氏硬度下降13%左右。随着出炉温度的降低,试样残留渗碳体的分解以及石墨颗粒的长大,导致抗拉强度、硬度均有所下降,当出炉温度为100 ℃时试样的抗拉强度下降10%左右、布氏硬度下降20%左右。     

球墨铸铁加热过程中渗碳体石墨化的原位观察

采用激光共聚焦扫描显微镜直接观察了球墨铸铁在加热过程中渗碳体的分解和石墨形态的演化。结果表明：球墨铸铁在加热过程中渗碳体逐渐溶解,加热速率越快,渗碳体的分解速率越快。加热过程中石墨形态的演变行为与加热速率有关。加热速率较慢,组织中出现了小石墨,原有石墨长大。加热速率较快,渗碳体周围的小石墨逐渐溶解变小。     

A THERMODYNAMIC STUDY OF THE Fe-C SYSTEM Ⅲ.THE METASTABLE IRON-CEMENTITE EQUILIBRIUM

在本文中,作者首先计算了铁、碳化铁的共晶平衡,得出共晶温度为1148°;这在以前因为缺乏液态铁碳合金内的活度数据是不可能计算的。其次作者综合分析了前人数据,主要根据1148°的介稳共晶温度及723°的介稳共析温度,算出碳化铁的热力学函数。根据这样算出的碳化铁热力学函数及有关热力学数据,作者(i)复核了碳化铁的共析温度及共析点成分;(ii)计算了碳化铁在奥氏体内的溶解度;(iii)计算了碳化铁在铁液内的溶解度及碳化铁液相线与石墨液相线的相交温度。最后,根据本文及稳定平衡部分的计算结果,作者将现行铁碳相图加以修正,俾合于热力学的要求。但关于碳化铁在铁液内溶解度的计算仅属于初步近似性质,有待将来研究。     

Effect of the size and shape of cementite particles on the structure and properties of deformed steel

Conclusions The shape of cementite particles has a considerable effect on the structure of deformed steel and its mechanical properties. The fine structure of ferrite resulting from plastic deformation of steel with globular cementite is similar to the structure of deformed carbon-free iron. Their dislocation structures are also similar. The shape, size, and internal structure of cementite crystals change little during plastic deformation (up to 50%). The strengthening of steel resulting from deformation is independent of the concentration of carbon and is the same as in carbon-free iron.Plate-like cementite, unlike globular cementite, favors the creation of a more dispersed ferrite substructure as the result of deformation. Also the cementite crystals become plastically deformed, and as a result a fine structure is created within the crystals. Most of the eutectoid grains are broken up during deformation, and as the result the plate-like structure is destroyed. In regions where the plate-like structure is preserved the cementite becomes finer and the distance between the platelets decreases. The finer the structure of the eutectoid before deformation the greater this effect. An increase of the dispersity of the eutectoid favors a more developed fine structure of ferrite and cementite as the result of deformation.Central Scientific Institute of Ferrous Metallurgy Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 2–8, February, 1964     

MICROSTRUCTURE EVOLUTION OF HYPEREUTECTOID STEELS DURING WARM DEFORMATION II. Cementite Spheroidization and Effects of Al

利用Gleeble 1500热模拟试验机进行单轴热压缩实验, 研究了合金元素Al的添加对过共析钢等温球化及温变形过程中渗碳体球化及所得超细(α+θ)复相组织的影响. 结果表明: 等温球化时, Al的添加使过共析钢获得较细小的渗碳体颗粒与较小铁素体晶粒的复相组织; 在温变形过程中, 合金元素Al能够阻碍Fe和C原子的扩散, 减缓片层渗碳体的熔断球化及渗碳体粒子的粗化, 抑制渗碳体粒子在铁素体内部的再析出, 获得超细(α+θ)复相组织.