Some problems in the production of ductile irons by investment casting

Because of the excellent performance of ductile irons and the unique superiority of investment casting, the preparation of complicated and thin-wall ductile iron castings by investment casting shows a good development prospect. In this present work, combined with the actual product experiments, the characteristics of shell making, spheroidization, inoculation and defect prevention are presented, and some suggestions are given for investment casting of ductile iron.     

湿型球墨铸铁件收缩特性的试验研究

采用正交试验的方法，浇注一系列铸件，测量铸件的冷却曲线；解剖铸件，测定铸件质量、铸件及缩孔体积。研究了碳当量、孕育、铸件模数以及铸型条件对湿型球铁件收缩特性及缩孔缩松的影响。为开展数值模拟预测球铁件缩孔、缩松的工作打下了基础。     

Influence of cooling rate and antimony addition content on graphite morphology and mechanical properties of a ductile iron

Cooling rate and inoculation practice can greatly affect the graphite morphology of ductile irons.In the present research,the effects of the cooling rate and antimony addition on the graphite morpholog...     

HT300高强度缸体缸盖材料熔炼技术研究

分析了熔炼工艺、碳硅成分、锰硫成分、合金化及孕育处理对高强度灰铸铁铁液质量的影响,认为大量使用生铁使铁液收缩倾向增大且使铸件性能降低;增碳剂的选用是全废钢熔炼的关键;在较高碳硅含量条件下生产高强度灰铸铁件,必须设法在熔炼过程中增加石墨晶核,并增硫防止石墨长成粗大片状;适当的合金化和孕育处理,可以使铁液的收缩倾向得到明显改善。指出可以通过延迟开箱时间使铸件在砂箱中缓慢冷却以消除铸造应力,为生产优质铸件提供最后保证。     

HT300高强度缸体缸盖材料熔炼技术研究

分析了熔炼工艺、碳硅成分、锰硫成分、合金化及孕育处理对高强度灰铸铁铁液质量的影响,认为大量使用生铁使铁液收缩倾向增大且使铸件性能降低;增碳剂的选用是全废钢熔炼的关键;在较高碳硅含量条件下生产高强度灰铸铁件,必须设法在熔炼过程中增加石墨晶核,并增硫防止石墨长成粗大片状;适当的合金化和孕育处理,可以使铁液的收缩倾向得到明显改善。指出可以通过延迟开箱时间使铸件在砂箱中缓慢冷却以消除铸造应力,为生产优质铸件提供最后保证。     

Phase transformation and fatigue properties of austempered ductile irons

A series of studies were carried out regarding ausferrite transformation, the growth of ferrite from austenite, during isothermal holding. The mechanical properties associated with microstructures of alloyed and unalloyed austempered ductile irons (ADIs) were also investigated. Heat released from ausferrite transformation has been quantitatively measured in a previous study. The effect of alloying elements on the heat evolution rate and on the morphology of ausferrite has also been discussed. Mechanical property testing was carried out on specimens of ductile iron austempered at 593 K and 633 K for 2 hrs. Tensile properties and high-cycle fatigue life tests were also made. In addition, phase transformation of ADIs during ultrasonic vibration treatment was also investigated. SEM micrographs of deformed samples indicate and confirm the occurrence of stress-induced transformation of ADIs. The alloyed ADIs isothermally-held at 633 K develop an optimum tensile strength, elongation and superior impact toughness and good high-cycle fatigue strength. These properties are attributed mostly to a large amount of dispersed blocky austenite. This retained austenite may become work hardened during deformation.     

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。     

Occurrence and effect of casting skin in compacted graphite iron

Most iron castings retain their as cast surfaces because of their geometric complexity and to minimise the machining costs. However, the mechanical properties that are documented in standards (i.e. ASTM) are tested on fully machined test bars. Therefore, the effect of the as cast surface and subsurface features (commonly referred as ‘casting skin’) on mechanical properties should be evaluated. Preliminary works have shown the negative effect of the casting skin on mechanical properties of grey and ductile irons. This paper reviews the recent works on the casting skin effect on tensile and fatigue properties in compacted graphite and ductile irons. It was found that the tensile and fatigue strength were reduced by 9 and 40% respectively because of the presence of the casting skin. In addition, the correlations between processing parameters (e.g. nodularity and section thickness) and the casting skin features were presented. The experimental results suggest that the Mg depletion because of metal–mould and metal–air interactions was the main reason for the formation of the casting skin.     

钇基重稀土镁复合球化剂在铸态高韧性厚壁球铁件上的应用

应用钇基重稀土镁复合球化剂，铸造厚大断面高韧性球铁冷却壁，成功地获得了铸件中心部位铸态高性能。超过了用户要求和美国ＡＣ公司的标准。铸件中心部位铸态延伸率≥１７％，接近了铸件外层或附铸试块的水平。     

三片式阀体缩孔（松）缺陷的解决

针对三片式阀体铸件结构特点,分析了缩孔缩松缺陷产生的原因,即铸件结构不合理,内浇道不能进行有效的补缩。通过增加工艺补贴,加大内浇道等工艺措施,有效的解决了该铸件的缩孔缩松问题。     

大断面重型球墨铸铁件电弧炉熔炼的生产实践

介绍了采用电弧炉生产大断面球墨铸铁件的铸造工艺及生产过程,通过铸造过程数值模拟软件预测分析了凝固时间和铸造缺陷,确定了冷铁尺寸及布置。结果表明,采用高纯生铁、废钢等优质纯净的原材料、严格控制铁液温度和化学成分、合理的球化处理和强化孕育等技术措施,获得组织和性能符合要求的大断面球墨铸铁铸件。     

Effects of forced cooling on mechanical properties and fracture behavior of heavy section ductile iron

To develop materials suitable for spent-nuclear-fuel containers, the effect of forced cooling on mechanical properties and fracture toughness of heavy section ductile iron was investigated. Two cubic castings with different cooling processes were prepared: casting A was prepared in a totally sand mold, and casting B was prepared in a sand mold with two chilling blocks placed on the left and right sides of the mold. Three positions in each casting with different solidification cooling rates were chosen. In-situ SEM tensile experiment was used to observe the dynamic tensile process. Fracture analysis was conducted to study the influence of vermicular and slightly irregular spheroidal graphite on the fracture behavior of heavy section ductile iron. Results show that the tensile strength, elongation, impact toughness and fracture toughness at different positions of the two castings all decrease with decreasing cooling rate. With the increase of solidification time, the fracture mechanism of conventional casting A changes from ductile fracture to brittle fracture, and that of casting B with forced cooling changes from ductile fracture to a mixture of ductile-brittle fracture.     

消除碳素钢精密铸件表面渣、气孔的措施

精密铸造生产中,碳素钢精密铸件因含碳量高,浇注过程中吸气、氧化严重,铸件表面容易出现渣、气孔,主要集中在组树方案中铸件的上表面,影响铸件的外观及质量.在常规方法不能完全解决的情况下,引入砂模铸造工艺设计方法,通过外加直浇道,钢水从外加直浇道中注入型壳,使钢水在型壳内平稳上升,产生的气及渣随同钢水通过内浇道顺利浮出铸件,避免组树方案中铸件上表面产生渣气孔,改善铸件表面质量,减少铸件后期的修补成本.     

为铸造厂生产优质铸造生铁已刻不容缓

论述了优质铸铁件,特别是球铁、等温淬火球铁（ADI）和蠕铁件的市场需求及生产这些铸件必需的优质铸造生铁（包括高纯生铁）成分要求;指出优质铸造生铁大都是小高炉生产的,由于国家有关部门下令关闭200 m3以下的高炉,造成优质铸铁件必需的原材料缺乏危机;建议国家有关部门均衡考虑制造业中各行业的发展,有计划地落实铸造生铁,特别是优质铸造生铁和高纯生铁的生产和供应问题.     

耐低温冲击风电球铁铸件生产工艺要点

简述了风电类耐低温冲击球铁件的发展趋势。以生产QT350-22AL轴承座为例,介绍耐低温冲击球铁件的工艺要点,包括:(1)生产中必须选择高纯生铁,原材料中Si、Mn、S、P含量越少越好;(2)球化剂选用REMgSiFe合金,孕育剂必须具有较强的抗衰退能力,并进行2次孕育;(3)采取适当的措施降低铸件冷却速度,加强球化率在线检测;(4)通过热处理保证基体为全铁素体,以满足低温冲击韧性的要求。     

低钙钡的硅钡孕育剂

介绍一种低钙钡的硅钡孕育剂，其Si、Ba、Ca、Al组元配比合理，既具有强的石墨化作用，又具有良好的脱氧性能，因此能延缓孕育衰退时间，防止铸件局部白口，使铸件硬度均匀。用于铸态球铁，可以获得足量的铁素体；用于灰铸铁，可以稳定获得A型石墨，石墨长度达4～6级，力学性能提高。     

A Study of the Microstructure,Mechanical Properties and Weldability of Low-carbon Ductile Iron

Abstract

Low-carbon cast iron (1.7–1.8% C, 1.7–2.2% Si) test bars and castings were prepared in a production foundry for evaluation of their microstructures and mechanical properties. The experimental variables were (a) inoculant types and (b) heat treatment cycles. Results indicate that low-carbon ductile cast irons with graphite present in spheroidal/compacted form may be satisfactorily produced on an industrial scale, after appropriate inoculation. However, a short normalising cum tempering heat treatment is necessary for the development of optimum mechanical properties. Low carbon irons can be satisfactorily welded to similar grades of cast irons as well as to steel.     

铸态QT850-3球墨铸铁曲轴的生产

介绍铸态QT850-3曲轴的生产工艺.采用低磷、硫炉料,感应炉熔炼,加入（质量分数）0.3%铜和0.02%锑进行合金化,并采用随流孕育强化孕育效果.为提高铸件致密度和尺寸精度,采用覆砂铁型铸造工艺.从曲轴不同部位取样测试性能结果,抗拉强度和伸长率分别都超过850 MPa和3%.曲轴样品已通过运转试验,情况良好.     

Effects of silicon,magnesium and strontium content on the qualities of Al-Si-Mg alloys

According to the specification of AA standard, the magnesium content of 356.1 alloy ranges from 0.25 to 0.45%. In producing Al-Si-Mg alloy the strontium content for the modified 356 (Al-7%Mg) alloy might range from 0.005 to 0.02%. Therefore, 356 alloys might be produced with different percentages of Mg and/or Sr. The effects of changes in Si content (from 6.6% to 10.8% in gravity casting and 6.5% to 10.3% in squeeze casting), Mg content (from 0.36% to 0.48% in gravity casting and 0.3% to 0.44% in squeeze casting), and Sr content (from 0.0007% to 0.0158% in gravity casting and 0.0015% to 0.04% in squeeze casting) on the microstructures, density, mechanical properties and strength of different Al-Si-Mg alloys were fully investigated and discussed. Different melts were poured in the ASTM B108 permanent mould and dies in a vertical squeeze machine to produce bar castings. These bar castings were then machined and the mechanical properties tested. Experimental results showed that if a high strength and a high elongation were desired in a squeeze casting after T6 treatment, an increase in Si and Sr content to 9.9% and 0.019% (Mg at 0.3%) would lead to 280 MPa strength, 12% elongation and Weibull modulus of 34 in reliability of strength. If both strength and reliability were desired in a squeeze casting after T6 treatment, an increase in Si content to 10.3% (Sr at 0.0015% and Mg at 0.3%) would result in 294 MPa strength, 8.7% elongation and a great Weibull modulus of 67. In gravity casting, after T6 treatment, increasing Si content to 10.4–10.55% and Sr content in the range of 0.0007–0.0208% and 0.35% Mg could develop 282–284 MPa strength at about 6.6% elongation with Weibull modulus of around 31. In Al-7Si-Mg alloy, increasing Mg content from 0.26% to 0.48% decreased the tested elongations of both as-cast and heat treated squeeze castings and gravity castings.     

煤矿运输机上联接板铸件的工艺设计

针对煤矿运输机上联接板的结构特点及其技术要求,设计了铸件分型面、浇注系统、胃口及冷铁和熔炼参数.对铸件的浇注结果进行了分析,根据披缝厚度重新计算了浇注系统,采用断面渐变的浇道控制内浇口铁水流速,使铸件夹渣缺陷明显减少.试制的上联接板铸件通过顾客水压和加工验证,可批量稳定生产.