电脉冲连续退火对AZ91镁合金带材组织和性能的影响

研究了电脉冲连续退火对冷轧时效态AZ91镁合金带材显微组织和力学性能的影响。结果表明:电脉冲退火在较低的温度下快速完成了α-Mg基体的再结晶,可显著细化晶粒。当退火温度为210℃时,α-Mg基体发生完全再结晶,其平均晶粒尺寸由冷轧态的约30μm减小为约7μm,带材的抗拉强度由冷轧态的410 MPa减小至334 MPa,断后伸长率由冷轧态的3.7%增大至23%。电脉冲退火后带材的拉伸断裂方式由冷轧态的脆性沿晶断裂转变为韧性穿晶断裂。电脉冲在其热效应和非热效应的共同作用下快速完成再结晶过程以及β-Mg17Al12相阻碍α-Mg基体晶粒长大,是电脉冲退火细化晶粒的主要原因。     

Modelling of compacted graphite cast iron solidification-Discussion of microstructure parameters

A melt maintained for hours in a press pour unit allowed the following changes over time from spheroidal graphite to compacted graphite iron by casting thermal cups at regular time intervals.This provided extensive experimental information for checking the possibility of simulating solidification of compacted graphite irons by means of a microstructure modelling approach.During solidification,compacted graphite develops very much as lamellar graphite but with much less branching.On this basis,a simulation of the thermal analysis records was developed which considers solidification proceeding in a pseudo binary Fe-C system.The simulated curves were compared with the experimental ones obtained from three representative alloys that cover the whole microstructure change during the holding of the melt.The most relevant result is that the parameter describing branching capability of graphite is the most important for reproducing the minimum eutectic temperature and the recalescence which are so characteristic of the solidification of compacted graphite cast irons.     

Study on numerical simulation of nodular graphite iron microstructure formation

In this paper, the mathematical and physical model was developed based on thermodynamics and solidification theory before the eutectoid transformation of nodular graphite iron occurred. The Local Element Substitute and Magnification Method was brought forward and 3-dimensional numerical simulation program based on the model and the new assistant algorithm was developed and used to calculate the samples. Results of calculation have good agreement with experimental data. To display the microstructure formation during solidification of nodular graphite iron, a 2-dimensional numerical simulation program combined with the result of the 3-dimensional numerical simulation of experimental samples was compiled.     

球墨铸铁QT450-10、QT500-7的退火工艺优化与组织分析

本文以球墨铸铁QT450-10、QT500-7为研究对象,根据铸件原热处理生产工艺中存在的组织形态粗大及分布不均匀等问题,提出了退火工艺的优化方案,研究了不同退火工艺条件下球墨铸铁的组织形态和铁素体、珠光体及石墨的含量,并对台车式退火炉的炉温不均匀问题提出了改进意见.实验结果表明,采用合理的退火工艺,并在生产条件下保证...     

电脉冲处理对低碳钢显微组织的影响

将15钢淬火-冷轧处理得到薄饼晶层状结构,在不同条件下对试样进行电脉冲处理,用TEM对组织结构进行对比观察,研究不同电脉冲处理条件对显微组织的影响.结果表明:电容量增加使温度升高达到再结晶温度是材料发生再结晶的主要因素,脉冲次数增加能促进材料再结晶;其它参数一定时,电容放电时间越短,组织细化效果越明显.     

Modelling of microstructure and property distribution within industrial nodular graphite iron casting

A kinetic model that uses the internal state variable approach has been developed and implemented as a user-subroutine in a finite element model (FEM) program in order to relate the heat flow calculations to the micro-structure evolution within a complex shaped industrial nodular graphite iron casting. The model initially requires the input of the chemical composition and from there it is coupled with the heat flow calculations from which the evolution of the constituent phases are calculated utilising the constraint conditions imposed by the phase diagram and the kinetic equations. A further sophistication of the model involves the use of a separate set of response equations to relate the microstructure and the composition to the macro-mechanical properties, such as hardness, yield and tensile strength. In a calibrated form, the process model is capable of describing the microstructure evolution during primary and eutectic solidification as well as the subsequent solid-state transformations. IJCMR/368     

Numerical simulation of microstructure evolution on near eutectic spheroidal graphite cast iron

A multiphase cellular automaton model was developed to simulate microstructure evolution of near eutectic spheroidal graphite cast iron (SGI) during its solidification process, and both dendritic austenite and spheroidal graphite growth models were adopted. To deduce the mesh anisotropy of cellular automaton method, the composition averaging and geometrical parameter were introduced to simulate the spheroidal graphite growth. Solute balance method and decentered square algorithms were employed to simulate austenite dendrites growth with different crystallographic orientations. The simulated results indicate that the graphite nodule grows in a spherical morphology when the surrounding environment of a single graphite nodule is same. However, for two adjacent graphite nodules, the environment is different. The higher the carbon concentration, the faster the growth of graphite. By comparison with experimental results, it is found that the microstructure evolution of near eutectic spheroidal graphite cast iron during solidification process can be reproduced quantitatively by numerical simulation with this model.     

The influence of copper on microstructure and mechanical properties of compacted graphite iron

Abstract

The influence of copper content (0·26 to 1·31 wt-%) on microstructure formation and mechanical properties of compacted graphite iron (CGI) has been evaluated through standard metallographic analysis, colour etching techniques and tensile testing of machined test bars. The properties investigated are yield strength, tensile strength and elongation. The castings were made in an industrial environment from a combination of CGI returns, pig iron, cast iron- and steel scrap. A total of four heats were cast in specially designed sampling cups (3 different cooling rates), chill wedges as well as tensile test bars machined from sand moulded cylinders (20, 45 and 85 mm in diameter). The results clearly illustrate the combined effect of copper and cooling rate on nodularity, chilling tendency as well as pearlite content. A discussion concerning the effect of graphite morphology on the ferrite growth is also included.     

Modeling the effect of the microstructure of compacted graphite iron on chip formation

The unique mechanical and physical properties of compacted graphite iron (CGI) have awarded the material such desirable and increasing demands in both automotive and locomotive industries. The graphite round edges combined with irregular graphite boundaries highly enhance crack arrest resistance within the matrix and participate into the good adhesion of graphite–matrix interface, compared to gray cast iron. However, the praised mechanical performance of compacted graphite iron (CGI) compared to gray iron, and its superior thermal properties compared to nodular iron (ductile iron) have come with CGI's relative poor machinability. Finite element simulation of the microstructure of CGI will provide better understanding of the behavior of the metal during machining and will establish a good foundation of CGI machining optimization.Modeling of the microstructure of CGI chip considering the three main constituents of the metal; graphite, pearlite, and ferrite, was possible using the accumulated plastic strain fracture criterion. Although there is no distinctive boundary line between adiabatic shearing and surface crack initiation chip formation principles in real metal cutting, chip formation simulation showed that it was predominantly due to crack initiation and propagation. Cracks initiated at either the graphite particles or the graphite–matrix interface promoted by the fracture of surface graphite particles then progressed through the matrix. The characteristic segmental chip produced in CGI machining was mainly driven by the presence of graphite embedded in the matrix. Chip segments formation initiated at the graphite particles (or graphite–matrix interface) then progressed towards the chip-tool tip. Modeling of the graphite/matrix interface was based on the utilization of cohesive zone elements. Comparison between the modeled CGI microstructure and graphite-free modified microstructure highlights the significant role of graphite on chip characteristics. Comparison between the simulated segmental chip and real CGI chip validated the proposed simulation and proposes it as a valid foundation for further CGI machining optimization.     

退火处理对金属型铸态奥-贝球铁组织和性能的影响

对金属型铸态生产的奥-贝球铁进行退火处理以改善力学性能,通过正交试验研究退火工艺对其组织和性能的影响.试验结果表明:退火处理对石墨形态无明显影响,但会改变基体中贝氏体的类型;低温退火可在硬度变化不大的情况下有效地提高金属型铸态奥-贝球铁的强度和塑性、韧性,抗拉强度可达到1080MPa.这表明了金属型铸造和退火处理相结合的方法可获得高性能铸态奥-贝球铁.     

Fabrication of SiC particle dispersed spheroidal graphite cast iron composite by vacuum assisted casting and its microstructure

Abstract

SiC particle preforms were infiltrated with spheroidal graphite cast iron melt by vacuum assisted casting in the sand mould, and spheroidal graphite cast iron composites in which the particles were dispersed in the surface region were fabricated. Although the melt infiltration was not accomplished when the melt was poured under atmospheric pressure, the infiltration was accomplished by the vacuum assisted casting when the SiC particle volume fraction and preform thickness were optimised. When the Si content of the cast iron was 2˙5 mass%, the phase consisting of mainly Fe₃Si was formed at the particle/matrix interface due to the reaction between the cast iron melt and the particles during the infiltration. The matrix of the composite consisted of fine spheroidal graphite particles, ferrite, pearite and chill crystal. Although the increase in the Si content suppressed the reaction and chill, no infiltrated area was observed in the composite.     

Effect of microstructure on resonant vibration fatigue fracture of ferritic spheroidal graphite cast iron

The effect of graphite nodule size, counts and eutectic cell wall inclusions on the fatigue fracture behaviour under resonant vibration of spheroidal graphite (SG) cast iron was investigated in this study. Experimental results indicated that the variations of graphite nodule size and counts slightly influence resonant frequency. The D-N curves (deflection amplitude vs. number of vibration cycles) of all test materials show similar manner. The deflection amplitude maintains a constant value for a certain period of vibration cycles (region I) and then decreases significantly with increasing the vibration cycles (region II). The feature of fatigue fracture behaviour under resonant vibration of ferritic SG cast iron can be concisely divided into four steps, namely (1) crack initiation, (2) crack linking, (3) the major cracks formation, and (4) deepening of the major cracks in the through-thickness direction. The initial three steps correspond to the region I period of the D-N curves, and the fourth step occurs in the region II period. Increasing the graphite nodule counts and refining the microstructure increase the region I period, and improve the resonant vibration fatigue life. During fatigue fracture process under resonant vibration, cracks mainly initiate from graphite nodules and some from eutectic cell walls. The eutectic cell wall inclusions are more crowded in SF specimen than that in PF specimen. So, the crack path of SF specimen is more tortuosity. The feature of fracture surface is mostly the brittle fracture.     

Investigation of the growth of cavities for graphite inclusions during the annealing of white cast iron

IPL, Academy of Sciences of the Ukrainian SSR. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 42–43, April, 1991     

脉冲电流轧制对AZ31镁合金微观组织与力学性能的影响

对比研究脉冲电流轧制工艺与温轧工艺对AZ31镁合金板材的力学性能、织构、微观组织与沉淀相等方面的影响。结果表明：脉冲电流具有促进冷轧AZ31镁合金低温再结晶能力的作用。脉冲电流轧制后的镁合金板材组织由细小的等轴再结晶粒与析出相构成,没有发现孪晶组织,并且完全再结晶,原始晶粒均被细小的再结晶晶粒取代,再结晶晶粒内的位错密度低。而温轧镁合金组织则由稍拉长变形孪晶、粗大的再结晶晶粒和析出相构成,再结晶的晶粒内位错密度高。两种轧制方式下的镁合金析出相均为Mg17Al12。脉冲电流轧制后镁合金的织构具有典型基面织构的特征,而脉冲电流轧制镁合金的织构则出现横向偏转;脉冲电流轧制后镁合金的屈服强度与伸长率均比温轧镁合金的大,但抗拉强度正好相反。     

Formation of the microstructure and properties in deformation heat treatment of high-strength cast iron with globular graphite

Conclusions  

拉拔变形量和退火工艺对铜包纯铁线材组织与性能的影响

采用拉伸复合法制备了铜包纯铁线材,研究了拉拔变形量、退火温度和时间对铜包纯铁线材组织与性能的影响。结果表明：随着拉拔变形量的增加,铜包纯铁线材铜、铁晶粒越来越小,铜晶粒呈现不规则形状,铁晶粒呈现典型的流变形特征,线材抗拉强度逐渐升高,电导率、伸长率逐渐降低;随着退火温度的升高和退火时间的延长,铜和铁的晶粒逐渐长大;随退火温度的升高,铜-铁界面铜、铁原子发生扩散,形成一定厚度的扩散层,线材的抗拉强度降低、伸长率提高,电导率先升高后降低;随着退火时间延长,复合线材的电导率和伸长率逐渐升高,抗拉强度降低。     

电脉冲孕育处理对Zr基块体非晶热稳定性及退火晶化的影响

通过先对Zr55Ni5Al10Cu30合金熔体施加脉冲电流处理,再利用非真空吸铸法制备出Zr55Ni5Al10Cu30块体非晶合金的方式,研究了电脉冲孕育处理对非晶热稳定性及退火晶化的影响。差分扫描量热(DSC)及X射线衍射(XRD)分析结果表明:经电脉冲孕育处理后Zr55Ni5Al10Cu30块体非晶合金的玻璃转变温度上升,晶化温度降低,过冷液相区变窄,同时玻璃转变激活能和晶化激活能有所减少。电脉冲孕育处理没有改变Zr55Ni5Al10Cu30块体非晶合金退火晶化相演变过程,但提高了非晶退火晶化率。电脉冲孕育处理对Zr55Ni5Al10Cu30块体非晶合金的晶化起到了促进作用。     

In-Situ observation of the carburization of solid iron by graphite

The carburization of solid iron by graphite was investigated by using confocal laser scanning microscopy to understand the initial carburization reaction mechanism of solid iron by solid carbon at high temperatures. As the carburization was initiated, a liquid layer was formed at the interface and grew parallel to the interface after an incubating period for the liquid phase formation. This required incubation time decreased with an increasing temperature due to the decrease in the solubility limit of carbon in ??-Fe. A moving interface model was used to interpret the carburization and melting behavior of solid iron by solid carbon with consideration for the diffusion of carbon in both solid and liquid phases. Using the moving interface model, the diffusion coefficient of carbon in the liquid Fe-C alloys was obtained. $D_L (m^2 /s) = 5.1 \times 10^{ - 7} \exp \left( { - \frac{{53.9 \times 10^3 }} {{RT}}} \right)\{ 1458 - 1623K\} $ The rate of carburization in the solid and liquid phases was evaluated. As the liquid phase was formed, the contribution of solid phase in the carburization decreased from 9.5% at 1.3 s to 5.4% by 20 s.     

脉冲电流对ZK60镁合金板组织与性能的影响

利用光学显微镜(OM)、电子背散射衍射(EBSD)和扫描电子显微镜(SEM)对ZK60镁合金板组织与性能进行分析。利用高密度脉冲电流对轧制变形ZK60镁合金板进行处理,使变形组织在较短时间内发生完全再结晶。再结晶晶粒的平均晶粒尺寸达到3μm,抗拉强度可达310 MPa,伸长率达30.7%。然而,经过同样时间的等效热处理,变形ZK60板并未发生完全再结晶。脉冲电流提高了轧制变形ZK60镁合金再结晶形核速率,加速了再结晶转变过程。脉冲处理优化了ZK60镁合金组织,使其获得了较高的综合力学性能。     

电脉冲处理对冷拔铜丝组织与性能的影响

采用电脉冲处理方式,控制冷拔铜丝再结晶过程,研究了电脉冲作用下材料的微观组织及力学性能变化。结果表明：与常规管式炉退火相比,电脉冲作用下冷拔铜丝的再结晶时间缩短90％以上,再结晶温度降低50％;抗拉强度提高8％;延伸率提高20．3％。电脉冲处理条件下,材料再结晶是由热效应和非热效应共同作用引起的。