The Fluidity of Sodium and Strontium Modified Sand-cast Aluminium-Silicon Foundry Alloys

The fluidity of A319, A356 and A413 alloys has been measured using a sand-cast spiral in the 700°C to 750°C temperature range. Modification by either sodium or strontium has no detectable effect on the fluidity and does not change the temperature dependence of fluidity within this temperature range. Measurements at 745°C indicate that sodium levels up to 0.037 wt% or strontium levels up to 0.024 wt% have no effect on the fluidity of sand-cast A356 alloy.     

Water analogue validation of numerical model for fluid flow during slow shot phase in die casting process

Abstract

Air that becomes entrapped in the molten metal during the die casting process has a major effect on the formation of porosity in horizontal cold chamber die castings. In this study, a three-dimensional computational fluid dynamics model was developed to study the flow patterns of liquid metal in the injection chamber, in which the moving boundary conditions of the plunger movement was considered in detail. According to the principle of die casting machines, a water analogue system was designed and built to investigate the slow shot process. A colour high speed camera was used to record the fluid flow patterns under different plunger movement profiles. The numerical simulation results agreed well with the water analogue experimental results, which validated the numerical model of shot processing in the cold chamber of the die casting process.     

奥-贝球铁焊缝的组织与力学性能

用Ｘ射线衍射仪，光学显微镜和电子显微镜，系统地研究了球铁焊缝金属等温贝氏体转变过程，等温温度等温时间为焊缝组织与力学性能的影响。研究结果表明，球铁焊缝金属贝氏体相变快，等温时间在１５－２４０ｍｉｎ范围内焊缝基体组织主要为贝氏体铁素体和残工体且具有高的综合力学性能。     

奥－贝球铁焊缝的组织与力学性能

用Ｘ射线衍射仪、光学显微镜和电子显微镜，系统地研究了球铁焊缝金属等温贝氏体转变过程，等温温度及等温时间对焊缝组织与力学性能的影响。研究结果表明，球铁焊缝金属贝氏体相变快，等温时间在１５～２４０ｍｉｎ范围内焊缝基体组织主要为贝氏体铁素体和残余奥氏体且具有高的综合力学性能。随着等温温度从３１０℃增至４００℃，焊缝金属中残余奥氏体量增多，贝氏体铁素体条宽化，焊缝塑性提高，强度降低。     

等温淬火球铁(ADI)的微观组织与力学性能

ADI的显微组织由奥氏体加上针状铁素体的混合组织组成。其每一束针状铁素体由许多位相相同,厚度大约200 nm的薄铁素体片组成。其奥氏体有两种形态:一种是存在于针状铁素体之间的近似于等轴形的块状奥氏体;一种是存在于针状铁素体内的薄条形奥氏体。从晶粒尺寸数量级来说,针状铁素体的厚度约为200 nm,而铁素体内奥氏体的厚度仅为几到10 nm数量级。金属强化的几种主要方式,细晶强化、位错强化、晶界与亚结构强化、第二相强化、固溶强化等都在ADI得到了体现。正是由于ADI这种特有的微观组织使其具有了优越的力学性能。     

等温淬火球铁的微观组织与力学性能

等温淬火球铁的显微组织由奥氏体加针状铁素体的混合组织组成。其每一束针状铁素体由许多位相相同，厚度大约200纳米的薄铁素体片组成。其奥氏体有两种形态：一种是存在于针状铁素体之间的近似于等轴形的块状奥氏体：一种是存在于针状铁素体之内的薄片形奥氏体。从晶粒尺寸数量级来说，针状铁素体的厚度约为200纳米，而铁素体内奥氏体的厚度仅为几到10纳米数量级。金属强化的几种主要方式：细晶强化，位错强化，晶界与亚结构强化，第二相强化，固溶强化，细晶强化以及TRIP强化等都在等温淬火球铁中得到了体现。正是由于等温淬火球铁这种特有的微观组织使其具有了优黻的力学性能。     

铸态奥贝球铁组织与性能的研究

探讨了在砂型连续冷却条件下,向球铁中同时添加cu、Ni、Mo等合金元素,获得以奥氏体 贝氏体为主的多相复合组织球铁;考察了在冷却条件一定的情况下,添加合金总量对其力学性能的影响.结果表明:当添加合金总量(质量分数)大于3.60%时,铸态球铁ob可以稳定在900 MPa以上;当添加合金总量达到3.95%时,铸态球铁具有最佳的综合力学性能;继续增加合金添加量,冲击韧度和伸长率将下降.     

Microstructure and Mechanical As-Cast Alloyed Bainite Ductile Properties of a Wear-Resistant Iron

An as-cast bainite ductile iron with excellent mechanical properties and wear resistance was fabricated by alloying and centrifugal casting method, and the alloyed chemical composition was optimized by using the thermodynamic software Thermo-Calc. By using optical microscopy, transmission electron microscopy, scanning electron microscopy, and X-ray diffraction, the microstructure of the as-fabricated bainite ductile cast iron was characterized pertinent to the elements distribution in matrix and features of ferrite and retained austenite. The results of mechanical properties test show that the hardness and compressive strength of this alloyed ductile iron are 52 HRC and 2,200 MPa, respectively. The as- cast bainite ductile iron possesses highly abrasive wear resistance and the reason can be ascribed to the solid solution of the elements Si, Ni, Cu, and Mn in the austenite and the formation of carbides of elements Cr and Mo. The strength of bainite ductile iron is increased by the acicular bainitic ferrite in the matrix.     

Microstructure and Mechanical Properties of a Wear-Resistant As-Cast Alloyed Bainite Ductile Iron

An as-cast bainite ductile iron with excellent mechanical properties and wear resistance was fabricated by alloying and centrifugal casting method, and the alloyed chemical composition was optimized by using the thermodynamic software Thermo-Calc. By using optical microscopy, transmission electron microscopy, scanning electron microscopy, and X-ray diffraction, the microstructure of the as-fabricated bainite ductile cast iron was characterized pertinent to the elements distribution in matrix and features of ferrite and retained austenite. The results of mechanical properties test show that the hardness and compressive strength of this alloyed ductile iron are 52 HRC and 2,200 MPa, respectively. The ascast bainite ductile iron possesses highly abrasive wear resistance and the reason can be ascribed to the solid solution of the elements Si, Ni, Cu, and Mn in the austenite and the formation of carbides of elements Cr and Mo. The strength of bainite ductile iron is increased by the acicular bainitic ferrite in the matrix.     

等温淬火对低碳球铁组织与性能的影响

设计了低碳球铁的两组化学成分,通过金相、拉伸及硬度实验,分别研究了相同奥氏体化工艺(890℃×40 min)、不同等温淬火工艺对低碳球铁组织与力学性能的影响。实验发现,A组成分试样奥氏体化后,在340℃×60 min工艺下获得最好的力学性能(σb=1 103.98 MPa,δ=6.84%);B组成分试样在320℃×120 min工艺下获得最好的力学性能(σb=1 352.58MPa,δ=10.67%)。对比金相组织后发现,在最低温度等温淬火的B组成分试样组织最好。球化处理加二次孕育后,其球化级别及石墨球径级别提高、分布均匀。     

镍对低温高韧性球墨铸铁组织及性能的影响

试验采用了0-1.2%的镍对低温球墨铸铁进行合金化,并采用两阶段退火工艺进行热处理.结果表明,材料的微观组织由铁素体+石墨球+极少珠光体组成.加入质量分数0.71%Ni的球铁,经热处理后具有良好的冲击韧度,在-20℃、-40℃温度环境下,其冲击韧度分别达到16.6J和12.8J,可以满足球墨铸铁件在高寒地区的使用要求,并保证了在不降低低温冲击韧度的前提下,提高材料强度和硬度,从而弥补因硅量降低带来的强度不足的问题.     

垂直连铸球铁等温淬火后的组织与力学性能

采用垂直上引连续铸造技术对QT500-7进行铸铁管成型,对该铸件采用不同温度与时间的等温淬火,并进行微观组织与力学性能分析测试。结果表明,用该技术生产的铸件与普通砂型铸造的铸件相比较,不仅球化率高而且球化均匀,经过不同等温淬火后其抗拉强度和冲击韧度值明显升高,非常适合制作汽车发动机缸套和活塞环以及其他的铸铁空心零件。     

钼对铁素体球墨铸铁组织和力学性能的影响

通过在铁素体球墨铸铁中加入钼元素,研究了钼对其组织和力学性能的影响。结果表明,在730℃下保温4 h,可获得单一铁素体基体和细小石墨球颗粒的双相退火组织,石墨球分布均匀、圆整。钼的加入并不能细化石墨球组织,反而恶化石墨球形态。钼的加入使铁素体球墨铸铁的冲击韧度和伸长率显著降低,不利于高热应力工况下的反复使用。     

等温淬火时间对贝氏体球铁组织和性能的影响

将球墨铸铁铸件高温奥氏体化后于300℃等温淬火并保温不同时间,得到贝氏体球墨铸铁,研究了保温时间对贝氏体球铁的组织和力学性能的影响。结果表明,当保温时间较短时,奥氏体不稳定,冷却至室温或者经过机加工后会部分转变为马氏体,硬度值较高,但强度及塑韧性较差。适当延长保温时间,会得到稳定的奥氏体+贝氏体组织,具有较好的综合力学性能。保温时间继续延长时,会导致高碳稳定的奥氏体析出碳化物,使贝氏体球铁的强度和塑韧性下降。     

Effect of Cooling Rate on Microstructure and Mechanical Properties of Thin-Walled Ductile Iron Castings

This article addresses the effect of cooling rate on microstructure and mechanical properties as determined by changing molding media and section size. The research was conducted for thin-walled iron castings with 2-5-mm wall thickness and for the reference casting with 13-mm wall thickness, using different molding materials (silica sand and insulating sand “LDASC”) to achieve various cooling rates. Thermal analysis was performed to determine the real cooling rate at the beginning of the graphite eutectic solidification. In general, it was found that the predictions based on theoretical analysis of the solidification process of ductile iron are in good agreement with the experimental outcomes. Finally, the present study provides insights into the effect of cooling rate on the graphite nodule count, the ferrite fraction and mechanical properties of thin-walled ductile iron castings. The study shows that the cooling rate of thin-walled castings varies in a wide range (80-15 °C/s) when changing the wall thickness from 2 to 5 mm, accompanied by significantly changing the mechanical properties of ductile iron. The cooling rate can be effectively reduced by applying an insulating sand to obtain the desired properties of thin-walled castings practically in the whole range of ductile iron grades in accordance with the ASTM Standard.     

A Method of Magnesium Treatment for Producing Gravity-diecast Ductile Iron

Equipment for the in-stream treatment of ductile iron has been adapted for gravity-diecasting. The treatment unit consists of a pouring basin, reaction chamber, and a reservoir for holding treated iron. The device is highly mobile in so much that it can be transferred from furnace to successive dies and back again, allowing consecutive pouring. The authors have studied the effect of reaction chamber design and nodularising-alloy type on the microstructure of cast specimens, using three types of chamber design and three types of nodulariser at different temperatures. The results indicate that a carbide-free structure with a high nodule count of up to 1500 n/mm² within the as-cast structure of a diecast rod specimen of 30 mm dia. can be achieved using this treatment equipment, when employing suitable nodularising alloy and process chamber design.     

Heat transfer and solidification analysis in the mould region of a horizontal copper alloy billet continuous caster

Abstract

Mathematical modelling has been widely used as a powerful tool for process design and optimisation of the continuous casting process. A three-dimensional heat transfer model was developed to simulate heat transfer and solidification in a horizontal billet continuous casting system. In this model, the air gap formation and its effect on heat extraction from the billet was also modelled and considered. The developed model was run to simulate the heat transfer and solidification for an industrial billet casting machine. The predicted temperature distribution within the mould and billet was compared with those measured on an industrial caster and good agreement was obtained. Parametric studies were carried out to evaluate the effects of different parameters on the temperature distribution and solidification profile within the cast brass billet. Finally, the secondary dendrite arm spacing (SDAS) was determined experimentally and a semi-empirical correlation between measured SDAS and corresponding calculated cooling rate was proposed for continuously cast brass billet.     

马氏体球墨铸铁热浸镀铝层在重熔过程中的组织与性能变化

以球墨铸铁热浸镀铝为材料,对其进行氩弧重熔处理,研究处理前后的微观组织和性能变化。结果表明,氩弧重熔处理后,球墨铸铁热浸镀铝表面的富铝层和扩散层界线消失,微观组织过渡平缓。氩弧重熔处理后,试样的硬度明显提高,最大为900 HV。     

铁素体球墨铸铁凝固形貌及力学性能

结合铸造模拟仿真技术,研究了不同热模数铁素体球墨铸铁的凝固形貌和力学性能.结果表明:热模数较低(Mc=0.65 cm)时,奥氏体枝晶以大量球团状晕圈为主,石墨分布均匀、圆整度高,韧性较好;热模数增大到2.1 cm,离异树枝晶含量增多且晶粒粗大,石墨形态异化且珠光体含量较多,屈服强度和冲击韧性恶化.     

离心球墨铸铁管的组织及退火工艺研究

从大型离心球墨铸铁管上取样，用光学金相、电子金相法研究了铸造和不同退火状态下的离心球墨铸铁的组织，实行了低温退火新工艺。研究表明，采用低温退火，使片状珠光体转变为粒状珠光体，并且控制粒状珠光体量为15%-25%，其余为铁素体 石墨，具有良好的综合力学性能。